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STRUCTURE & DEVELOPMENT
OF
PLANT GROUPS
BY
H. MUKHERJ1, M, Sc.
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PREFACE
The want of a text-hook (kuling with the life-hiRlnrics of
diiTerelll plant groups was very keenly felt by the t-:tudcnts
and teachers alike for a considerable length of time, The
present volume, it is hoped, will remove that difficulty as it
Coven the entire syllahus for B,A, & B.Se, Pass course in
Botany of all Indian Universities,
Authorities dilfer in rq!,ard 10 the classilicationg of plant
gnlllps, specially of the lower plants. but it would he out of
place to c1isClU,S them here. I have simply endeavoured to
arrange the materials under Thallophyta (Algtc, Fungi,
Bactcria and Lichens), Bryophyta (Liverworts. Anthocerotes
and Mosses), Ptel'idophyta (Lycopods. Equisct ums and Fcrns)
llnci Spermatophyta (Gymnosperms an d Angiosperms). and
the life-historics of these groups and the progress from the
lower to highcr forms form the pdndpal feat urc~ of this
\'olumC', The familks of Angiosperms, however, have heen
treated separately ill the Vol.
of lhis hook.
n
1 have freely consulted the hoob of StraShllJ'gel', Small,
Smith, Holman & Robbins, Hill, Ovcrholts & Popp, Smith,
Gilbert. Evam cl aI, Couller, Barnes & Cowles. Ch,uuhcl'lain,
ConltC'1' & Chamherlain. Pearson. Hcnd)C, Camptx'U. Bower,
Eames. Buller, Gwynne-Vaughan & Barnes, Bessey a11(1 others,
to all of whom T OWl' my <leep Hens(' of gratiluc1e,
T am al~() indchLCd to 11\y ('!;teemed friend and old
C'olleagut' Sri S, N. BflllCl'ji o[ the University College of Science
& Technology, C. D" for his invaluable help and guidance
in tl1(> prcparation of thi~ hook Lastly, it is my pleasant
iv
duty to owe acknowledgmcnt to Sri .A.. K. Ganguly, once my
pupil and now my collcague, for his COIlHtant help in tlH.:
preparation of the manllscript, for proof-reading and vaillahle
suggestions.
Any criticism or 8LIggcstion for imprnvcml'u t will be
·thankfully received.
City College,
23 rd Septcmber, I949.
I-I. M.
To
My Beloved .friend
S. N, Banerji Esq" M. Sc,
Lcctlll't!f, Calcutill Universitv.
CONTENTS
Pagc
CHAP fER
I.
r.
Thallophyta
Alga::
2
A. Myxophycea! (Cyallophyccre)
Gleocapsa
Oscillatoria
Nostoc.
H. ChlorophyccR'
Chlamydomonas .
Volvox.
Ulothrix.
Prntococcus
Oedogonium.
Spirogyra .
Zygucma
Cosmarillm
Caulel'pa
Vallchcl'ia.
GHlata.
C. Ph,~ophyceH:
Ec tocarp \I:; •
7
5)
10
12
16
33
FUCllH'
D. Bacillariophycea.'
E. Rboduphycea:
BatrachospcnnulU
Polysiphonia.
If, Fungi
A. Phycomycetes
Phytophthora
Mucor
B, Ascomycetes
1:;+
88
VIll
Page
Saccharomyces
Elll'otium
Pcziza
C. Basidiomycetes
Ustilago
Puccinia
Agaricm
SchizOluyce
tes (Bacteria)
11 I.
IV. Lichens
CHAPTER
CH.\l'TER
CHAPTER
Index
II.
III.
IV.
Bryophyta
Riccia
11archantia
Anthoceros
Polytrichul11_
pteridophyta
Lycopodium
Selaginella
Iscetes
Equisctum
Polypodium
Marsilea
Gymnosperms
Cycas
Pinlls
Gnetum
I 12
I 17
121
5
12 7
12
135
145
IS°
153
ISS
159
16+
Ifl
177
18 5
IS7
196
20 3
'0:
20 9
21 7
227
23S
23 6
24 6
260
273
CHAPTER J
THALLOPHYTA
The thallophytes rcpn:~cnt the oldest and the Il1(J~t primitive
Types of plants characterised by the simplicity of struc1 me of
their n:l:!,c'tative hoclics and of reproductive method, In size.
the thallophytes range from microscopic forms to mac.roscopic
(lnes, often attainin,f!; a length of about 25-30 llictres. Thallophytes arc fllrther characterised bv thc la(k of differentiation of
plant -hodv into roots, stems and ]ea\'cs: such an llll(liifl'1'entiatcd
plant-body is called a thallus. The thallus in the simplest case
consists of a single cdl, whereas the more cDlnplcx fm-ms arc
l1111lLicellular. whIch arc either all alike or may show considerable differentiation of tissues. Some thallophytes develop stnnlike. leaf-lil,e and root-likc orl!;ans, btlt their structures arc very
simple as compared to those in hi~hcr plants_ Other charae leI'S
whi(_h separate thallophytc8 from their allied groups arc: (I)
unicellular scx-ore,ans in the maioritv of cases. but when multi<..dlular, all the celI~ for111 the gnl1letc~. i_c" there is no jacket of
slcrile ceUs slUToundin~ the gametes as in the case of Bryophytes
and Pteridophytes; (2) one-celled sporangia, hut these are not
so in the case of higher plants; and (3) the zygote nevL'}' forms
a multicellular C'mbryo while still enclosed within the female
sex-organ.
The thallophytes Teprocluce in a variety of ways. The uni·
cellular forms lISually reproduce by the method of cell-division,
giving rise to two daughter cells, each of Wl1ich is complete in
itself and represents a dIstinct individual. When m1l1tic!211ular,
specialised cells arc often delimited for the p1ll'pose of reproduction. These spe(_ialised cells arc in general known as spores,
each of which is capable of giving rise to a new plant. The
spores are produced within sacs to which the general term spor(lI1giu is applied. But these methods of reproduction arc asexual
in 11 <lturc. They also rcproduce sex)lIally. The sexual repro(lnctive units arc 'known as gametes, which arc naked prntoplasts
formed within specialised cells known as g{/metttl1g·ia, ,\Vhen
~'lRUCTURE
AND DEVELOP:\Ib:'-;T OF P1.,\:\,1 GRuUP:"
tbe gametes fw,e. they give rise to hodies known as zy!:!,olcs
whic.h develop into nt.:w plants. The gmm:lic union may be an
union of two gametes of equal size (i.lugaIllY). or ~)y the unioll
of two motile gamete, of unequaL size (allisogamy). or by the union
of a ::.mall 1ll()lilt· and ciliated male gaillcte (anthcrozoid or
~permatozoicl) with a large. non-ciliated. passive female gamete
(nosphcre or ovum) ((JoglllIlY). When th(; reproduction is oogamOll". the gametangia are difleren.tiated illto tlIltheridiulIl (male)
producing the <lnthernzoids and oogonium (female) giving rise
to nus ph ere or ()\ um. The pIH:I10ml'I10Il of 'alternation of
generati()IlS' has heen definitely estahlished in the thallophytes.
rhllLl,!.:h not well-marked in all cases.
The !l10 main groups of thallophytes which stand out prominently ,I1'e: the Algal amI the Fungi, wl1Dse characters will
he cli"llls~ed ill tht.: foll()wing pages.
Difierences r-ei,ween alga,e and fungi.
(II Alga.: possess the green colouring matter known as
clzlornphyll; Fungi. on the other hand. m:ver POSS(;hS chlorophyll.
(2) Alga: arc <lulophyll'S i.e .• they (all prepare their own food
from simple inorganic materials with the help of chlorophyll:
Fungi are lu:tcrophytes i.e. tht.:y cannot prepare their own fnod.
hence they must secure their fooel either directly or indirectly
frolll other organisms and as snch lin:, as parasite'S 0)' saprophyte!:'. (3) Alga: cannot live in clarkncss as light is absolutely
necessary for the preparation of their food; Fungi can live in
light as well as in darknens. (4) The vegetative body of Alg<c
is composed of parenchyma tissue; whereas the body of Fungi
is composed of plectenchyma made up of fungal tissue. (5) The
cell-walls of AIgx are mainly composed of cellulose; hut those
of Fungi mostly of chitin or fungus cellulose.
I.
Algae
The alg<c constitute an impm'tant group of thallophyles.
Thev all possess chlorophyll, and are, therefore, c.apable of manufacturing their ciWll food. The chlorophylL, though invariably
present. is not always pure green in colour, because the green
colour is sometimes masked by the presence of other pigments
TIIALLOPHi'TA-.\LG~
3
~L1d1 as blw", golden brown, red, etc., and on this Ullom depends
the classification of the group. The habitat~ of the alg,e an·
vcry diverse: some live in fre~h water, some in br<1lki,h w:Iter.
~Otnc arc nlarin~, sOine of them )!;lIWi \)n YI)Lk" <\ntt wa\\". 1l1" on
barks of trees, while ()thers liyc a~ eJltiophVles within illC tih~uc~
of certain higher plants. In a few (a5c.- a~ in L~d1ellS, the al/2:'{'
live in symbiotic associatioIl with fungi. The \ egclali\ e lJDdy
may be a COtuocyte, or a single uninucleate cd], ur it may he
composed of numerous uni-, bi-, 01' !lmlti-nuclcatc cells, gi\ ing
rise to a compact thallus, with certain amount of tissue-c1illerentiation in some very highly organised multicellular form!';, as in
hl'l)\\ 11 fmd red al)!;a~. The c(;l\-wa11 i>o usuallv compo,ed of
((:llulosl', and the resene fooel malel'iab arc '~ranh, oil and
vari'lus other hubstallces.
• Thc alga: may reprodule sexllaily as '~ell as ;lhc)..ually. The
asexual modes of reproduction arc a>;sutia ted with great simplicity
of structure amon~ tbe lowlY l\lrms, while ITlOl\: ,tcl\ ,mced f~)rm~
arc marked by the increasing complexity of the vcg(·tativl' hlldi(~
and ,well-deyelopecl sexual repr~l(luction.
The alg:.e arc usually divided into fi,·c main sub-clivi,ioI1S ,:i:::."
l\~:yxophycere
(or Cyanophycere) or blue-green alg:.e, the
ChJ.orophyceoo or grass-green algre, the Phaeophycere or brown
alga', the Bacillariophycere or diatoms, and the RhodoFhycere
or reel alg:.e. This classification must not he considered as complete or exhaustive since a few slltall forms havc not becn
included.
the
A. Myxophyceae
OJ'
Cyanophyceae
General characters.
This group of blue-green aigre consists of a small assemblage
of primitive thallophytic plants not apparently closely related to •
other sub-divisions of algre. They arc inhabitants of clamp
terrcstrial places or entirely aquatic in nature. Among aqua tic
for111s a great majority arc fresh water species as free-floating
organisms (plan71ton). Some species are marine and may occur
as epiphytes on other marine alg~ or found within their tissues
as cndophytes.
S1RULTURE .~~D DEVELOl':\IENT OF P1.A]\'T GROUPS
Thc chief, characteristics of ]\ryx()phycea~ are-(r) a primitin:
and simple type of cell-structure, (2) the presence of a bluc
pigment called plzycoc)'allill and a red pigment* in addition to
the Ilsual photo,ynthetic pigmentg (chlorophyll a. chlorophyll h,
carotin ami XlllZtlzojJlz)'llJ and these arc not localisecl ill the_chloro-
plasts but arc clistrilmtecl ill the peripheral portion of the protoplast known as chrollwplasm and (3) the presellce of a primitive
type of nuclells called "central lweiy," which lacks a nucleolus
and a nuclear membrane.
Other prominent features which arc
not restricted to t11elll alone arc (r) the presence of an (Juter
gelatinous cell-wall surrounding the protoplast, (2) production of
photosynthetic reserYes mainly in the form of glycogen
IJLll
not
,tarch and (3) total absence of sexual reproduction by gamC'lic
Ull10n
and
the
formation
of
other
flagellated asexual re-
productive units.
The thallus is either strictly unicellular or in great majority
of species the daughter cells. following cell-divisions. rcmain
united forming either a filamentous or non-filamentous colony.
Non-filamentous colonies show a great variety of forms: cubical,
hollow and spherical, plate-like or irregular in outline.
In unicellular forms the cell-wall surrounding each protoplast consists _of two conccntric portioIls: (a) an inner thin and
firm layer, chiefly made up of cellulose, and Cb) an outer gelatinous
portion. often callee! the sheath.
This sheath may be thick or
thin. hyaline or coloured, anc! may often he stratified in appear<tnce.
On the other hand, in filamentous colonies this gc!atinous
layer is restricted only to the free and outer faces of the ccll.
The
protoplast
of
l\Iyxophyce<e
interesting but difficult problem.
.----------_.-
presents
an
cxtremdy
All investigators rccognise that
.._-- -- - -------
~".--------------~- ~--
• _" Thi~ 1'~(1 pi~mellt, is known as ,ol'lli:ojllll/('I'lfll pli//"()('I !ltlilill HOlllt'wlmt
,mllla!' to the red pl~ItlPllt llli.'l"lIeltlijJlin of RhodlipityC'C'w.
Tlr,ILLOPII1TA-ALG/E
tht: protoplast consists of an ollter pigmented portioll called
clzrnmojJ!aslil which surrounds a clear central portion, the ,~()­
called "ce/ltral b()dy,"
These parts ha\'c been \'arinusly inter-
preted from time to time. Thl: majority of tht: invt:stigators hold
the central hody as the nudem and the olller portion as the
cytoplasm containing pigments in the form of minute granulcs.
the cell lacking chloroplast.
Recent inyestigatiol1S show that the
central IJocly Illay be regarded as the primitive or 'incipient'
nuclells, but consists of a network of colourless material ill
t.he meshes of. which are emhedded granules of chromatin. This
primitive typc of nuclcll8 illustrates a step in the process hy which
nucki of higher plallts have evolved. Tbe peripheral portion has
Chromoplasm
Central-body
Fig. 1.
t:l"l'RUCTTlRE AND IlIVlHIONS OF THE (;ELL~ IN N[YXOl'lIyn:.·jo;
been recognised to be the cytoplasm corresponcling to the cvtoplasm of higher plants.
S0111e filamentous species of Myxophycex have thc ability to
move spontaneously.
The locomotion may be clue to the forwnrcl
or the hackward gliding of the filament, spiral progression or retrogression. or a slow waving of the terminal portion of the
fIlament.
Reproduction.
The methods of reproduction arc extremely simple and are
entirely asexual in nature.
These arc as follows;
STRUCTURE ,\ND DEVELOP.MENT OF PLANT Gl\OUPS
1.
Cell-division. In unicellular types multiplication takes
place by cell-di\'ision and the two daughter cells. thus formed,
remain united hv a common gelatinous sheath.
Hcpeatccl ccll-
didsions, in this way, may givc rise to a non-filamentous colony,
Hut in caR' of multicellular forms this process of cell-division he('tImeR a method of growth and not a means of multiplication.
2. Fragmentation.
Til filamentolls forms, thalli capable: of
indefinite growth, usually break up under certain conditions into
smaller portions, consistinp; of
go lies.
2,
3 or more cells. callcel h01"1Jw-
Each hormogonc by cell division, gives rise to a new fila-
lllentolis colony and possesses great capacity for locomotion. This
hreaking up of the filamcnt is either clue to animal-bring. or
death of certain cells of the filament, or weaker union hetwCl'll
certain cells of the filament.
3.
Spore-formation. In
most
filamentous
forms
certain
"cgetative cells of the filament for111 a kind of resting cells
called allinctcs.
During the formation of an akinete a vegetative
cell enlarges, accumulates reserve food within it and the entire
protoplast becomcs invested hy appreciably thickened original cellwall forming the spore-coat, which is often differentiated into an
outer exospore and an inner endospore.
The spores remain either
singly or in groups and may either occur anywhere in the filament or have a fixed position (next to the heterocyst). They are
resistive to unfavourahle external conditions, can tide over unfavourable periods and germinate during the rainy season giving
rise to new individuals.
In game marine forms the protoplast of certain vegel<llive
cells may divide to form a number of small, spherical or angular
spores, called cndospores, filling thc original. cell-cavity.
Reterocysts.
All filamcntous M yxophyce<e, excepting the
l11elllbers of the Family Oscillatoriacex, form spore·like hodies
TH,ILLOl'IIYTA-ALGiE
i
which ditTcr structurally from ordinary vegetative cell,. and spores.
They occur singly or in
l'air~,
and arc eitil(:r t<:nllinal or inter-
calary in positioll. During cicyclopmellt a vcry young vegetative
cell expands, its protop]a,m becomes transparent, hornngcJ1CJlIs
and viscous and a wall, internal to the (Jri,e;inal cell-wall, is seen'ted
round the protoplast. If the
heteroly~t ()ccllpie~
portion of the 111a111ent, there is a pore
OIl
tile terminal
its walls through \\hich
cytoplasmic connections between it and its adjacent vegetative
cell can ht: observed.
On the othrr hanel, if it be intercalary,
there an~ two sHch pores and these pores arc closed at maturity
hy huttoll-like thickenings called polar nodules.
Heterocyst~
art:
generally fnnction less, hut they mav germinate ill exceptional
cases.
Gleocap!la.
(Family Chro()c()ccacex).
Gl('()c(/ jlSa
Sll b-aerial
is a gel1 us of unicellular forms chiefly found in
rather than aquatic habitats.
They arc \'Cry common
in green houses and sometimes fonnd on flower
constantly kept moist.
nu rocks
~)r
i)()(S
which are
They often form a gelatinous coating
on moist stone walls forming olive-coloured, purplish-
brown, reddish
Of
violet-coloul'{'cl planr masses.
Vegetative body.
The thallus is unicellular, but frequently two to several
daughter cells remain aggregated together within the sheath of
the parent cell formine; a more or less persistent gelatinolls colony
of no definite shape. In such cases the cell-walls of individual
cells are quite distinct fr0111 one another but are more or less
confluent forming the colony.
Each cell is more or less spherical
in shape at maturity and its protoplast being surrounded by a
thick homogeneous or stratified, hyaline or coloured gelatinous
c'
o
STRUCTURE AND DEVELOPMENT OF PLANT GROUPS
cell-wall
(sheath)
enclosing an mller firm cellulose layer.
The
protoplast has much the same structure and range of colour as
arc [nund among other j\l yxophycece.
Reproduction.
G1e()CajJ!;(l
di\-ision,
repnJduCt:s asexually only by the process of
During the process a
cell wmewhat elongates,
B
('(~1l­
its
c
A
Fig, 2.
A-D,
VARIOUS
HT.\GllH
OP
Ulr!()('(/j)8(l.
f.'ELL-D1VlSIO~.
THB
DAU(m:t'l!:ll
1,~IBEDjlEll IN THE (fELA:t'1NOUS MATRIX l'RODlJCED
l'I~LLH
llEI~n
BY THElH WALLS.
'central body' divides into two masses and cytokinesis takes place
by the process of constriction, Each daughter protoplast then
secretes its own gelatinous sheath.
THALLOPH'iTA-ALG.·E
9
Oscillatoria.
(Family OsciliatoriClcca?).
The majority of the ~peck~ o[ [his IJ1uc-\.in:l:11 alga an:
inhabitants of fresh water. while other.; arc marin!::. Thev' llla\'
occur singly, or llltcnvoven with one another. forming ex~cnsi\'~
sheets llsually on tern:strial Sll bstrata. They arc found in all
possible habitats, ·vi;:;., moist rocky clilTs. damp soil, muddy hanb
uf streams and ponds: they may often grow luxurielltly in pools
of stagnant water and are fUlwd as a free-floating (Jrgani~\tl inter·
mingled with other alga:.
Vegetative body.
The thallus i~ all un branched, cylindrical, narrow or broad filament, entirely
Wilhollt or with barely percl'[Jtihle w<ltl:ry.
hyaline and mucilaginous sheath.
Each
filament consists of it sinl!;le row of cells in
the [01'111 of short cylinders, which may even
be shorter than thev are wide. The tenni'
nal cell is usually convex or rounded at its
free encl, but in ROl11<: casc:s it may taper to
a point. In some species these free out<:l'
wall of the apical cdl may be thickened to·
form a definit<: qllyptra. The cell-SlfUcture*
is morc or less similar to th()~(' of other
M yxopb yce~e.
R e:oroduction,
Oscillatoritl reproduces only by the \'eg-e'
method. Reproduction by the formation of zoospores or by gametes is unknown.
Each filament does not grow indefinitely in
length but regularly breaks Ul) into short
fragments, called lwrmogmzes, each con- Fi)!. 3. ()"l'il{(//(J};a.
raining 2, 3 or several cells. Bdorc scparaA PORTION OF
.
1
1 l' . l '111 t11<:
THf: FILAMENT.
tlOll, t 1e hOl'l1logones are (e ll1utec
Ii.lament by the formation of double: concave disks (separation
tatin~
, Ful' llrtaiiK-Vide p;ellerai characters.
',IIW( fURL
1,)
disl~s)
.\~J)
Dl:n:r.op"rr:NT
OF PI. \l\T GROUPS
of gelatinous consistency between the hormogoncs.
Each
hormogonC' may develop into a new filament by division.
The most (harac.teri~tic feature of Oscillatori" is the fan
that the filamcnts, particularly the honuogones, are ~apahle of
,,\\ayin?; or oscillating l1lm"cments to which the plant OWl"~
iN
name.
NOf,1toc.
(Family N ostocacex)
IYostoc occur!'
in nature as a fn.'e-floatin~.J?l1f.~~"t;~l}. {dga
forming lump of jelly-like J~laSSes (colonies) in which
filamenb are em bedded.
nUmtTO\l,
'Vhen young these arc of microscopic
,ize, more or less spherical in shape and solid.
As the colony
increases and becomes macroscopically visible in ~ize it remains
!,olid
01'
may become
w!1voluterl surface.
expanded
~hects
hollo~\'
and
ha~
<t
smooth or somewhat
The hollow coluny may rupturc anel form
with irregular margins.
They live either immt'l"O-
ccl in water bllt sometimes prefer moist terrestrial habitats beingattached to the sul)stratum.
Some species occurs as cndophytes
in other plants, such as .1nthoceros, Cycas, J,cmn{l, etc.
species are edible and arc used as food in the. yarious
Some
part~
of
the world.
Vegehtive body.
The thallus is an unbranched, contorted filament with a
definite gelatinous sheath. USllal1v several filaments o CCliI'
111
densely interwoven masses and always remain emhedded withi.n
a film of gelatinous envelope.
Each cell of the filament is sphe-
rical, barrel-shaped, or more or less cylindrical in shape. The
cells of the filament increase in number hy cell-division in parallel
planes. DlIl'ing division they nearly
~eparate,
round off and
becomc tangent to one another giving rise to a filament resembling a string of heads.
The cen-structure is mo]'c or less similar
TIIALLOI'HYTA-ALG,E
to those of other lVIyxophyce,c. if
II
The characteristic feature of
each filament is the presence of heterocysts, * [lsHally intercalary
hut may he terminal in position.
Polar nodule
Fig. 4.
Frr,A~fEN'l'OUS COLONIE~ WI'l'IUN
IIETlmOCY~TS
N08/0r..
THE GET,A'l'INOllA MATRIX,; l\EVERAL
5lTOWN, llIVIDIN(J 1'HE FILAMllNTfl IN'I'O HOI\\WGONIA.
Reproduction
Nostoc reproduces asexually either hy fragmentation, or by the
formation of akinctes. A filament seems
to
the heterocyst, forming short filaments
* For details-Vid e "clleral dHlracters.
break off easily, next
called
to
hormogones, ~
S'IRUCTURE AND DEVl::LOl'lI.IEN1' OF PLi\:'\T GROUl'S
I:
showing characteristic
mm·emellts.
Each
bormogone may grow
in to
it
long JIlamen t
by repeated cell-clivi-
sions. N umel'OllS
ho1'-
l110gulles are formed.
in this wav. "ithill
the origi nal colonial
cm dope.
B
With the
ael \'en t of the period
(If
danger
certain
(next
to
the
!lcterocysts)
of
the
cells
filamcnt form thickwalled, spheric al
e1lipsl)idal,
01',
l 11
d
II
akineteE
r ('
cold
can
c
A
resting
cclls. called akilldes::'
These
Heterocyst
Fig. 5.
lYm·drw.
GER:-llNA'PlON OF AN AlnNETlS; 0, ~'OR:l;rNrlOlI
Of' AN AR1NETE NEXT 'fO }n;'I·JlIW'TS1'~.
A-B,
or
draught and uncler favourablc cunclitinlls can give nse to new
filamen ts.
B.
Chlorophyceae
General characters.
The Chlorophyce;e, or green alga\ are generally recogniscd
by their green or yellowish-green colour and arc characteriBccl
by the presence of chloroplasts possessing the same photosynthetic
pigmcnts-chlorophyll ll, chlorophyll b, carotin and xrmtlwj)hyllas in the vascular plants and in the same proportions. Thcy differ
from the l\'Iyxophycc<c (I) in having a more definite a~lcl well.' Fur details-\Tj,le general charactel's.
TH.\LLOPIIYT,\-ALGi};
advanced cell-structure \\ith protoplast thoroughly differentiated
inro cytoplasm, chloroplasts ancl a definite nuclells: (::q by the
possession of simple to highly advanced plant bodies which arc
mostly multicellular structures showing great achances over th:),c
of lVlyxo1_)hyce;e, the ll1embers of which are not advanced bC\,()jd
the colonial forms: (3) by the production of motile, ciliated.
reproductive cells at some stage in the life-cycle of the maim-ity
of the green alg~e: and ('t') in having definite asexual and sexual
modes of reproduction in contrast to the simple method of reproduction by fragmentation among the J\Iyxophycea". In most (If
them starch is the visihle proc1uCL of photosynrhesis. Asexual
reproduction takes place hy zoosp())"es, aplanosporcs or akillctcs.
The motile reproductive cells bave their flagella, two or four in
Dumber, at the anterior end and arc: equal ill length. The e;amett's
may be isogametes, anisog;amctes or heteroe,ametes, being alwav~
produced within unicellular sex organs, and the sexwil reproduction. therefore, ranges from isol!amy to oogamv.
The members of this group arc found hoth in fresh and
salt waters. The maiority of tlwm occlir as submere;ed. frcohwater a(luatic plants being attached to submerged rocks, wood
pieces and similar other ohjects. hut may also float on tbe surfacc
of stagnant water forll1in~ green scums. Ouite a large number
of species grow on moist soil, rocks and cliffs, clamp wood work.
harks of trees and even on snow and ice. A few species arc
internal parasites on land plants, or may occur as epiphytes upon
land animals.
In general, the members of Chlorophycere show great variatioIl
form and strnctllre of their vegetative hody, ran).!;ing from
simple unicellular types to typical multicellular filaments through
intermediate colonial forms. 'When multicellular, the number of
cells may ,be definite or indefinite. But when indefinite, the cens
of the thallus may he arranl!;ec1 in irrel!;ular masses, in filaments,
in sheets, or in solid or hollow cylinders. The unicellular forms
may he non-motile or motile by cilia. Typically, the plant body
is filamentous which occ\lpies a prominent place amon)?; most of
the 'orders o[ the green alg~.
111
'With the exception of a few primitive unicellular genera. the
protoplast of Chlorophyce~ is sUl'l'onncled by a distinct cell-waH
which often becomes considerably thick. The cell-wall comists
q
SIRU<:IURE .'ND ilh\,ELOPMENT OF PLANT GROUPS
(It at kabt two concentric portions: (a) an inner hOltlogellolls or
concentrically stratificc1layer, mo~tly or wholly made up of cellulose
amI (b) an outer pectose layer which in some genera may be
chirinised or impregnated with lime.
The pl'Otopll1st is well-ditferentiated into cytoplasm, nuclei
and chloroplasts. It mostly occurs as primordial utricle surroundill~' a c(ln~picuous central vacuole. But, in some cases, several
vacuoles may be present instead. vVhen the cells are ciliated,
as in unicellular and some colonial forms, there arc usually two
small cuntractile vacuoles ncar the base of the flagella. They
wlltract alte:rnately and arc regarded as excretory organs. In
wille cases, the sap of the vacuole IJecomes coloured due to
anthocyanin. There may be one or 1110re nudei in each pmt(lplast and thesc arc found cither in the primordial utricle or arc
suspended in a mass o[ cytoplasm. in the c<:ntre o( the vacuole
hy mean!' of cytoplasmic threads. The nucleus p()~sess a distinct
nuclear I11c111heran(', one or more nuclei and a characteristic
chromatin reticulum. The nuclear division is mitotic. The chloroplasts are most characteristic and arc of variolls forms. They
may he cup-shaped, laminate, entire or perforate, disciform and
arc peripheral in position and arc mostly with one or more
pyrenoicls. Each pyrenoid has a central proteinaceous portion
which is surrounded by plates of starch. The food reserves are
usually in the form of starch, hut fats and oils are found in some
cases.
The motile ve:getative and reproductive: cdls arc provided with
flaF:t:lla inserteel 'I t the anterior end of the cclI. They are usually
two in numher, but may be four, eight or many and arc llsllally
of equal length. Located near the insertion of the flagella there
i~ an orange-red to reddish brown circular Of oval spot, called
the eyespot or stigma. which is regarded as a photo-receptive
mgandlc and is supposed to control the direcLive movement of
the flagella.
Reproduction.
The methods of reproduction in green alg<e arc well-advanced
and show great variation. All the thrce principal methods of
reprotluction arc found in this group as detailed helow:
THALLOl'Hl TA-ALG.£
15
(I) Vegetative. Thi~ take~ plact by the pnlLe,",s of fragmelltation. Among tilamentous forms, fragmentation i~, either dlle til
atcidental breaking of a filament or (.ertain (.dls of the filamcllt
lIlay produce sp()r('~ or gawctes bO r 118 t short bCCli()n~ uf the
filament become ultimately separated from one: another rc!-ulting
in the inerea~e of the nUlllbcr of filameIlt',. The colonial genera
I'cprm!uce vegetatively by al ciclt:ntal fra';l11entatiou of the colony.
Among unic.ellular form, \ egetativc reproduction ah\ ay~ take:;
plau: by cell-division, \\ hich in multicellular forms hecollll ~ ~l
method for the growth of the thallm.
{2} Asexual. Asexual reprodu(.tion usually take,., plaLl~ by the
production of spores within metamorphfJ::.ed vegetatiH: cells. Thl'
spores may vary in number. lrOlll Ol1e to many. in each cell aud
may be eitlll:r naked and motile (Jr provided \\ilit cli~tal walk
The motile spores arc known ;l'i ::;(J(Js/J(lrcs which arc provicll:d
'with two, four or more cilia of equal IC'ngth at the anterior end.
The liberation of zoospores usually takcs place hy the formatioll
of a pore in the wall of the mOlhl:J' cd! or by the hreaLing or
gclatinisatioll of the sporangial wall. The non-motile ~p()res are
known as ajJianosj)()res ,~hose walb arc (Iuite c1istincl from the
wall of the mother cell. These art' in l'eality mudified ZO(l~porcs
which have secreted walls around them prior to the liberation
from the mother cells. The aplannspores are liheralccl hv the
rupture or decay of the wall of the mother cell. The mother cdl
producing these spores is t~rmed a sporangium, which in most
cases is not morphologically' different from the vegetative cells.
Sometimes the walls of the aplanospores hecome greatly thickencd
Akinete
.,/
Fig. 6.
FORMATION OF A1UNETE
IN (' HLOl\Ol' IIYf'EAE.
to form hypnospores. Asexual reproduction also takes place by
the formation of akinetes. III such ca8CS a single non-motile
spore is formed within the sporangium whose wall is not distinct
from that of the spore. But, the vegetative cells often become
vcry much thick-walled containing abundant food reserve to form
16
S-IRUCTURT: _\KLJ DEVl:LOP:\II:NT OF PLANT GROUPS
akinetC'-like structures for tiding the alga on:r unfa vOlLl'ahlt:
periods.
(3\ Sexual. The sex-nal reproduction in ChlorophYlc.!:: rang;e:s
in complexity from the SiUlplcsl to the 1110st complc:x sex structures and the methods of gamctic union may be "arranged in an
(-\ olutionary scnes and are noticeable from the most primiti\-e to
[he most highly advanced forms with specialised and differentiated
,ex ~ trllCtllres.
In the simplest case, se"Xllal union is hy iSOK{[IllY, i.e., gametic:
union takeR place he tween morphologically identical ciliated or
non-ciliated gametes. as in thc U[othrix, Spirog'l'1'(/. ctc. In som('
caseR the plaut reproduces by anisogamy, in which gamelic unioll
is effected between two ciliated gall1etes of unequal size. as in
the Caulerpa. The mll~t ael\'ancec! method of reproduction is
()oga11lY. In this case, gametic IInion rakeR place betwcen a small
ciliated, motile, activc male ~amete (antherozoicl or spermatozoid)
and a large non-ciliated, non-motile, passive female gamete:
(oospherc or ovum). as in the Fallcherill, Ocdogonium, etc. The
male gametangillm producing the antherozoiels is known as rhe
tll1tlzeridilllll and is usuallv a distinct structure easily recognisable
frolll the vcgetative cells. Each antheridi1l11l produces OIlt' 0)'
more anthcrozoicl~, In 1110st cases the oDsphere or egg is produced
singly within the female p:ametangiu111 knOWil as the ooe:ol1iu17l
which differs morphologicallv from the vegetative cells. The
zygote former! as a result of sexual union uSllally, after a period
nf rest, '!ives rise to one or more new plants.
(.t) Parthenogenesis, There <lre variollS instances in which
/vll'tliellos(,orl's are forilled directly from tlw g-all1C'tes in the ahsence
of ~exLlal union.
Ch1amy 3IJmonas
IFI/ mil_'.' Ch la I1lV do I1l(J1Uldacl'tr)
ClLltllllyrlrJ1/WI7I1S is a wielely clislribulerl free-swimming. _green
a1'!_<1 which inhahits stagnanL \\-ater or damp soils.
Vegetative body
The plant-hody is unicellnlar and the cells arc either spherical.
ellipsoidal or pyriform (pear-shaped) in shape. TIle' protoplast
is 'iUITOllll(lcd hv a definite lav('r of cl'1lulos(' cell-wall and in Some
THALLOPHYTA-ALG.tF.
some cases an additional exterIlal gelatinous sheath may he
present. Each cell is provided with twO flagella which arc inserted
at its anterior end and are very close to each other. In some
cases the cell-wall is pl"Ovided with a distinct papilla at the
anterior encl. The major portion of the protoplast is usually
occupied by a single, l1lassive, cup-shaped chloroplast. There is
a single nucleus which is, in most cases, embedded in a colourless
cytoplasm filling the cup. Sometimes the chloroplast may be
star-shaped or laminated in form. Usually a single pyrenoid is
cytoplasm
Fig. 7. (!MrIJII.'It/(lJI'oIllIr.<.
A YEGE'l"A'l'IVI~ n:Lf.
present in each chloroplast, but in some cases two or more
pyrenoids may be present or they may be totally absent.
Typically, there arc two contractile vacuoles at the anterior eneI
of the protoplast occupying the bases of the flagella, but the
number and position of these vacuoles may vary in different
species. There is a photo-receptive organ, the 'eye-spa,t'. which
lies at the anterior end and is supposed to be corg:ernecl in
directing the movement of the flagella.
':
2
IS
<,IRULIURL
\,D DLVIIOP\lL"Il 01
PI \l'.r (,ROUP"
ReproductlOn
(_ hl(/ill') do 1I1()IW I
Iqllocluu,",
buth ,("Lxu,llly ,md "L,<ually
(1) Asexual. Dmmg d,exu,ll LLpwduttIOll tbe plOtopLIl>L vI
(,teh \ LgC [,ltI\ L (dl cllHclc, longttudllld.llv lUto two plotoplasts,
\\lnth .lg.llll dnlciL <WelIC dnlelc fnullIng 4 01 8 daughtci protopl.!"t, £,Ilh daugbtcl plOtoptlbt then btcrltt~ a wall ,Hound It
,mel dc\ clops a pan of flagella ttt It~ antcllOl end The ccll w,tll
of the pttlE.nt cclll upturcs 01 undo gOt, gdatllll~'ltlOn ,mel therehy
the claughtu cen... are hbelatcel
l,nciv th(. plotoplast of ,1 Vtgd,ltl\(. (.cll c.ollt1<1Ctb,
up and fOl m~ <Ill aplmlOlpO) ( "ftu q(.ulung tt '" all ot
VO)
IOllllLl,
It, own
(. hlaJnydoJl101lt1s whln gJ()'" 11 on d,IIllP ,011 tht (]'WghtLl
(.dl, fmmc.d by the qU(((.qql\l clnlblon, ot thL plotopl,l"t do not
clu dop then fldgella but Hmam embetlrlt cl 111 .l lO!l1!l10n gLl,ttln
otl, rpatux fOl I11lc] bv the !!;danl1h,tnnll of thL U ll-w,\ll of the
A
B
rIb
.\
}1)]{\fAlION
or
8
('/dwlI!JdllIliOIIlI'
[,A1LCll, \\I1HLN fHi] r IHI Nt (I Lt ,
1 AI \[J LI \ ~T\GI
n
p,UC.llt lell Thl~ I, u~llallv follow(d by dlVl'lOll dnd le-dlv1~lon
of the claught<.i <.dls and. by ~ub ..equent gela1.1111QallOn of then
walh fOl m WlOlllL' lOIl<,lqnng of hllnch(.cl~ of l( ll, t mhlcldlcl III
a common matrix. This is known as the ., PlllJll('l!a .stage
n:sc:mhling the gcnm Pa/melIa, a green alga forming <lmOrphllm
lo\onilR. If these colonies be flooded Wilh water, ealh dau~htc:r
Lell may develop its Hagella and may ,~im away [rol11 .the colony.
Sometimes these daughter cell~ lIlay develop into n:sting "pOrt·,
ulllc:d ahillt'tes. .
(2) Sexual. :'.[ost spccie;, of ChlllmycZoll!(lllllS reproduce
sexually by conjugation. The method of formation of the
gamete, is similar to the formation of the daughter lells [rom
a \"c?;Native protoplast as already stated. But in this ca~w the
lltlJllhlr of claughter cells may be S, r6, or 32 and they are usually
Il<l kul hiflagcllated protoplast;;, when walled, the protoplast of
eae b gamete leaves its original wall before union. Union may
take place lwnv(en the gametes c1eriv'ccl from the same Len
(110 111 othallic), or between gametcs derived from different cells
(hetcrothallic). The fuging gametes may lw morpbologically alike
(i.WJgaIII t'les) , or rarely one may he larger than the other (all isogamett's). Durine; fusion both the gametes arc usually active.
J'llt ill some cases one may be pas,ive. After union of the gamete,
the flagella either disappear or may persist for the time being
so that the resulting quadrifiagellate zygote rcmain!; motile for
i:>ometime. Finally it comes to rest and secretes a wall around
it. The wall of the zygote is thick and shows surface-reticulations.
Dr may hear spiny projections. Before germination tpe diploid
Iluclells of rhe zygote undergoes reduction division, typically
forming four haploid nuclei, of which three may degenerate. By
c1evHgc process uninucleate protoplasts arc formed following rcduction division and each protoplast is metamorphosed into a
hitlagelJatecl daughter cell. These lells arc finally libnated bv
the rupture of the zygote-wall.
;>
Volvox
(Family Volv()cacea:)
I' a/v()x is a fresh-water green alga which occurs abundantly
tanks, pools, etc.
The plant body is found in the form of a colony where there
are often a few thousand cells which arc arranged in the form
of a hollow sphere, one cell-layer in thickness. Each cell of
the colony is surrounded by a cornparativcly thick gelatinous
111
20
STRUCTURE ,IND DEVEI.Ol'l\IENT OF 1'1.,INT GHOIJI'S
sheath. It is more or less ()vnl in shape, JUtH a single nuclells
i! ig. D.
A
r 011",,1\
)fA'l'IJUE CDUINY WITH YOlINU ('<lI,nNlEs INHllH:.
and a cup"shaped chloroplasts with two l.·qunl cilia horne tllw:mls
the surface of the colony. It is elm.: to the 11l()"t:IlWnl
1111',1,.:
cilia of all the cclh that the colony moves in 'V<Iter.
or
Repl'oduction.
(1) Vegetative. As the colony attains malll1"ity a few (II' iI'S
cells, generally 4"10 in l1l1lnlJCr, become many limes large·], t hall
the ordinary cells and lose their Hagella. Each of Ihes(' cillarg('rl
cells, by repeated divisiolJ, givC's rise to a spherical grllllp Ill'
cells and fOTm a daughter colony which swims al)()llt in t1w
cavity or the parent colony. The daughter cnlonies aH' 11lLim:tldy
libcratccl due to rupture 01' decay of the motIle!: ml()llY:
(2) Sexual. The bcxual reproduct.ion is (Jop;amolls (111(' to
fertilization of it motile anthcrozoid with a llol1-molill' l'gg.
THALLOPIIYTA-ALGiE
:!I
Though the gametes may bl: fOl'llll:cl in any amI every edl of
the colony, the gamete-formation i~ IllHially IT~trictl'l1 to certain
culls onl y,
Fig, 10, ['(If "(la',
["OIt\fl'l'HlN Ill' llAlIllll'J'Lfl ('or.nNY fN 'rill; ItL\I [Jlo' M.II [TTlI'. ('I)LtlNY WllH'T1
II IH I))~'I' IT" ('jLlA ANIl S'I'AIL'I INn '1'0 I,'nftAf A NlJW ('m,ONY,
t:C'1l
Durin).!; the development of male gametes or <lntllC'l'OzlIlcb; a
l'lllargc~ and l[)~l's its Jlagclla, It then undergoes rcpeated
Fig, 11.
_I
l'oZI'(/,r,
Nl,;Anr.Y MA'fnm: AN'I'wmrnWM .1'1' '1'1ll] ltmll'I'; AT nm I.E!'!' A
%nnH[>n1U~ WlIIC'!l !lAH LOH'l' I'l'~ r)[],IA ANn IS K'l'AltTIN(l
'rn f'OUM AN ANTIIEnIllIn~t
di visi(}n~ and f(}rms a platl', 01' it hollow.sphere of small. spi ndk8h"pc(1, hillagcllalv celll'., llw (/11 I I!eroz,oids, Dl:vdolll11t'lll of
[~ig, 12,
1',,1 "0,1',
,\ I' I II I. 1.1.1"1', A lIO()HI'Ofm WffI('ll liAR L()~'I' l'1'H ('((,1,1 IK 1'-('AJl.'('INtl '1'0 1'()Jt~1
\\; }';(;n; NI':X'!' '1'1) '('ITAT IS AN TWO ,irrS'L' m:I,'OIlE Ffm1'l!.l7.\'1 ION;
1\'(' 'f'fm IllIlJ1 'I', ~IA'I'tJlli', ZYllDTf:S Alll. ~f~("N,
2C!
hTRUCTURE AND ])EVELOPi\IENT OF PLANT (;JHHJI'S
female gametes or eggs Lakes place chll' to the enlargcllll'llt o[
other cdls of the same (m()lloxious) or of a tlilIen:nt (dio:ci()w,)
colony which lose their !lagella. Such a cdl, however. doc:; 110t
clivide but grows 10 many times irs orig-inal size. n:lllaill~ llOIlflagellate and forms the egg.
The mature antherozoicls escape {rom the colollY, either as
frec-swimmillg individuah. or as a fr~e-~\Vill1mill).!; (,'0101\:' that
dissociates into individual male gameles later Oil. Tlil' «n(I1<'I"O'
zoids. attracted bv an egg, make their way through 111l' gelatinous
envelope which surrollnds the egg, but only 011(' of them finally
unites wirh the egg aud forms the zygote ((los/)(Ire).
The zygote develops it thick wall and i~ retained within Ill\'
colony until its decay. Thcll it falls to th(' ]JollOl11 of till' poo1
and undergoes a period of ]"cst. Finally, the wall of tIll' Zygotl'
breaks and the protoplast comcs out. It c1i\'icll'~ ancl SOOll forllls
a free-swim11linp; colony of the Volvox plant.
Ulothrix
(Fa mily Ulotrichaccre)
The majority of the species of tll i~ gn'('11
alKa arc inhabitants of {n'sh water. II'hile
the l'cmaiuinp; OlWS aH' mnrilll'.
Chloroplast
J-.>o;."':::::::W-
Vegelativ&
Cell
Fi;;-, 13,
i:/nt/lli.I',
HCl)'PI·.IS'l' AND 'I'Ilg "Ft:I,.
rA'I'IVI~
(,!:f,r.
Vegetative body
The vegl't:ltivc body to a thallus whh 11
unbranched filamL'llt oj' ilHklinitl'
lcn,e;th, consisting of a single I'OW of short,
cylindrical eells joined cud OIl l'IH1. The
JiJall1cnt is c1ifferentiated illlo hnsl' alld
apex, since its hasal ccli is mlnnrl(·ss,
elongated and grad ually n:lrrm\'l'd 10 forlll
a hold/asl which I]('lps in its iltlnd1l1H'llt
to the sllhslratlllll . Each cdl (>():is('SRI'S
either a thick HI' a thin ('('II-wall. whil'h
oftel1 hl'mn)('~ stratifiecl.
Thl' Pl'o(opla!'l
of each ccli is always llnilluci('atl' and
('ontains a sill~le girdll'-shaped l'hlol'(Iplasl.
which partially to (,Ol1lJllet<.:ly, l'ncil'dl's it.
The chloroplast colltains Oll(, to sn'l'l' a I
pyrl'1l oid s.
IS
an
,,
1 IIM.LOPlIn A--AU;k
-,)
Reproduction.
Ulothrix n·produteo in a variety ot ways 1llentiolled h<.:!ow:
(I) Vegetative. Thio type' ot reproduLtion takeo piau' w,nally
by t1](' accidental breaking of tl1l' filament into many fragll1ent~
witb a few cello in each,
(2) Asexual. l\sexual reprodlJ( tion takl!~ place I)y the
formation o[ z()()sj)(m's, which develop from the protoplaots of
ordinary
vegetative
cello
excepting
hold fast,
According to ~pl'('ics, the
the
l1l1111-
.
1tr'""1'Ii""~~'1
I)('r of zoospores proc]uCl'c] from ell( h protllplabl Illay be [, 2,
..j.,
H, '0 or ,p.
cw,e, during the formation
In any
of zoospores
the1"e is slight l"Olltra( lion o[ the protoplast
followed hv
lIU(
lear divisioll anel ouhoc-
IIlll'nt cleavage of the cytoplasm formingtwo daug-h leI' dlloroplas lS and this prot CbS
may contilllH' IIlltil J2 daughter protoplasN
an' formed,
Em h daughter protoplast is
metamorphoscd into it qlladl'ij/tlgel/alt'
z()n~p(J)"(',
Whell a sin!!;1c Z()OSP0l"(' i~
formed the prot()pla~l of till' entire vege"
tative cell b dircctly mctal1l()rph()~ccl inw
it. Each z()OSpOrl' i~ pyriform ill shape:
'
1
1 Fi!-(14. (i/oIIIl/L
allC1 cOlltains a prollllllen 1 eye-sl)()1 ocate( A [,OM'ION m' 1/11: 1'1l.~
towards tilt' flagl'lla.
Tht' z()()~pOreH art' MI:N1' ,1lOWINU 1'[[1,
.
) IIltMA"I'IIlN OF /, ,O"'OIll '-.
liberated tilrolH!,h a pOI'~' in tlte lat('ral wall
of the parcnt cd!.. '1'11('Y bwiHl ~Ktivl'ly ill watel' fmlll olle to
~t'\'('ral days, hur ultimall'lv CC'aSl' their lIWV('I1WUt and attach
themselves to hOl11l' objt'cts in water at the flagellated ('w1.
Finally, the f1al!,ella di~appl'ar, a wall is bl'( I't'ted around each
anc! hy elongatioll or tht' ('(,11 awl Hllh..,l'ljlll'1\t divisiolls Ill'W plants
an' fornlt'd,
tlH'll
\VIH'1l Z()Ohp()re~ art' not liberated from tht' pareIl t ('ells, c'Hch
of them Recretes It ('ell·wall arouncl it and forllls a thin-walled
a/)/(lIl()I'j)()J'I"
TIll' "plauospoJ't's lllay gl'l'I11inatl' even hcCore
liheratioll from the pan'Jll (·dl. III MJl1]{.! (';lS('S, the prowpla1lf
21)
"lnU(TURe A,\D [ll.\'!'[OP:\ILXl or Pilii'd (.ROUP::'
Vegetative body
The vegetative body may Ill' unicellnlar" or in gj'~Jlljl~ of ,1.
3, -t or rarely more cell~, Each cell is ,pherJcal to ,dhpsOlrlal 111
form, with a quite thilk wall. devoid of any gclalll~OllS ,sl:v.'tth.
The multicellular condition arises only due to succe~SlVc dl\ l~l()ll~
of the solitary cell. \Vhen grol'<illg unLler conditions of txcn.sive
moi,ture, cell-divisions mav continue to form lolonies of 50 or
A
o
c
B
Fig, ] 6,
A,
A YEGE'rAl'IY~J "loLL;
PI ntorO('Cll,<,
B-l1, VIlGI;rATIYF
FORM~'IION
HEPHOIl['( '1'JON ,\:-111
(W n~U(lII'I".R r'ELL~,
more cells and there may be a developmellt of a profusdy and
irregularly hranched condition (Pseudo '/lleHrOC()CCLlS stage), The
protoplast of each cell contains a definite nuclear membrane. and
a large parietal, laminate and marginally lobed chloroplast. uollally
without pyrenoicl",
Reproduction
Pr()toc()cct/s reproduces only vegl'tatively hv mcall~
divi~i()n,
or
The two or more c1aughtl'1' lells, thus formed,
ll'llllleLV
remain attached with one another for sometime. or thl'Y mav
ultimately separare ane! a<;~ume a spherical ~hap(.',
Oedcgonium
(Fllmily OedOp,IJllil/cew)
OL'do[!,(Jl1illll1 i~
a frl'!-oh-wmcr, wbmeq.;ccl. filamentull~. ~l'l:eJ1
It occurs in permanent or semi-permanent pools or jllll1ck
• \.II species, at the beginning, arc ,e~"ik i,e,. attachl'd tn >Ol1ll'
Sll b~tratum, Some remain ill this conditio]] rhrough:llll theit
c::ntire length of life. \\bile in others, filamcnts get detadled hom
rhe ,uhstratum ami flual Oil the 'Hlrfale of water forming cll'n'iciv
interwoven ma,se~, Some are epiphytic and grow on stems aneT
lr:aves of Slllm1Cl'gecl aquatic "ase lllar plants or 011 larger gn'('n
alga:',
alga.
III \Ll OI'IIYf.\-\LG.L
Vegetative body.
The thallus i~ an unbranched filament comlstll1g uf a ,inglL:
row uf cylindrical cdis joined end to encl. Thc filamellt ~hl)\\:,
distinction into Ilase and apc),..
The bas.:ll (cll b('tomes modified
and forms a holdfast by mcans
"".',
of which the thallus fixes itself
it""1---i-~'fI'
caps
to the substratum. The apical
cell is usually convex, hut may
Chloroplast
be pointed.
( reticulate )
The c("l1-wall, though appears to he homogenolls, consists
of thr~e conccnt1 ic portions: Nucleus
(I) an innermost cellulose layer
lying in contact with the protoPyrenold
plast, (2) a median pectose layer
and (3) an outermost layel
chiefly made up of chiLin. In
the basal cell thls outcrmo,t
chitinolls layer is absent.
The
transveme wall of each cell towards the distal end is provided
Fig. 17. Oerlogoliilllll.
with transvcrsc striations which
A YEGE'I'.<I.TIvn CELT,.
lOnstitute the " apical cap".
Thus, the intercalary cells also show distinction into base and
apex.
The pr()to1~la.;t,
an adult cell, lies next to the tell-wall
Ulntaining- <t sin~lc nucleus. Th(' nucleus is large, bi~(\lit-shapL'c1.
with one or more prominent nucleoli and a distinct nuclcat
reticulum. It lies midway between the two polefl of a cclI and
is located in the peripheraJ layer of cytoplasm. The chlQropla~t
is verv characteristlc. It is in the fonn of a hollow (ylinclrical
net extending from pole to pole and is lodged in the peripheral
layer of cytoplasm, external to the llucleus. There are numerous
pyrenoids at the crossings of the reticulum, each being surrounded
by a plate of starch. The starch grains, as they are formed,
may move away from the pyrenoicls and accumulate in the
connecting t-otrands of the' thloropb~t. thereby finally obRcming
the nature of it. This is known as 'stroma' starch.
in
:;:8
S'lRUC1URE A;:';D Dk:VELOPi\IENT OF l'L\l\T GRUUpS
Reproduction.
OcdogoJlilll1l reproduces by vegetative. ascxuat aml sexual
Illnh ods.
(,I) Vegetative. \Vhcn reproducti()u takes place vegetatively it
is lhiefiy hy the (LcLiciclllaJ brcaking of the filaments and in
"ubmerged aCluatic ;,pecies it is by the process of fragmentation.
(2) Asexual. l\lo~t spccics or Ocdog(ll1illlll reprodllccs asc:-..ually by the procluttitlll ()f 11lultitlageJ1atc zoospores formcd
with:n z:IlJsp()rangia. .\I1Y iutcrcaJar:- n'gelativ(~ cciI, rich in
aCClFllllJated uil-reserve, may he(om(' a zDusporangiul1l and form
a Zf,I)'pon:. During it;, formation tl1l' nuclcm ;,Iightly recedes
Vesicle
Zoospore
3
F'j!,!. 13.
1-3. FnrL\[.\TIfJN AND
(h Ilr>{/f)1I1 lllJi.
LlJlJ:n~'I'ION OF ZOO~I'(JlIr.;
4.
A
ZfH)~['flIt);,
iB\\arcls and a hyaline rcgi()n appears in the cytoplasm
bct\\cen the ceU-\~all and the nuclells. Around thc margin
of this hyaline region numerous granules (lJ/ejJlwrojJlasts)
TH.ILLOl'JIYTA-AU;.l,
appear, each of which prohably ghes n~e to it flagellum.
After the formation of the flagdIa the cell-wall bnak ...
transH:rsc!y at the regioll of the apical cap and tJH'; Illctall1orphoserl multi flagellate protopJabt c~capl.'s as it Z{J("P;l]"c
heing enclosed by a hyaline vesicle. The \ e~idc ,gradually
increases in size and finally disappears lilJt~rating th<: zumporc
in the surrounding water. The zoospore with its crown of flagella
an;uncl the base of the hyaline encl. swims for sometinl<:. cumes.
to rest OIl some substratum with the anterior end dowl1\\ artls.
The flagella arc finally withdrawn an(l the protoplast ~ligh tly
dongales, develops a holclfast and finally ,ecreteh a wall anlllne{
it. This one-celled plant then elongates and by rqll'<1tl'cl eelldi vision gives rise to a new fila men t.
Sometimes OcdogeJllilllll may form ahindt's, in (hain' n[
IO-{O,
\\ithil1 the vcgetative lelk The akin('T{Cf, c{)lltain
~Llfficiellt amount of reservl'
~tarch
and ted-colourcd (Jil.
Undcl' fa\'ourahlc ulll~litjnn~
an akinete germinates into a
new plant.
(.:;) Sexual. Sexual reproduction in Oedogoui1l1ll is of
an ,o~)g,am~u~ type in which
p:ametic nnion takes place bv
the fugion of a small motile
spermatozoid with a larp;e.
non-motile egg.
Thc' sexual
organs, antheridia and (Jogonia, lUay be produced on the
filaments of normal size (IWICrm/drolls species), or the oogomil are borne on
normal
filament, the anthcridia heing
produced on special d~Mrf
male filaments or l1{tnn(lndri11111
(nannandro/ls
species)
consisting of a few celk
Fig, 19, Or d"!lrmi1l7l!.
C1CHMlNA'l'ION OF ZOOSPORTI \ND
rOnM\'['ION OF A YOUNG PLANT.
~o
:-.TRU('l URE .\:\11 m:VI:LOP:\lENT OF I'L\:\T t;ROUPS
:\ lacrandrom !>pccies may be l11oncccious (homotlzallic) or
dio.:cious (hcterotllllllic).
Any n:getativc cell, excepting the baH:;1
one lllay act as an antheridial
mother-cell.
The position of
the antheridium lllay be terminal or intercalary.
The
:lIlthericlialll1other-cdl divides
Antherozoid
into
two daughter cells of
unequal size, the shorr termiVesicle
/l.ntherJdLUn1
.... r' ,1.
bcing
nal
cell
into
an
IOWLl·
much longer sister ccll
may.
III
thericliai
transformed
antheridium.
The
turn, act as an anmother-cell
divide repeatedly in a
and
S1l11l-
lar n1anner forming a row of
Fig. 20.
FOR~[ATION
(lrdo!l0niulII.
OF
r.Im;n,\TWN
OF
AN'l'HERID[A
ASH
.\NTHEl\OZOJn~.
H--fo antheridia.
The proto-
plast of each antherirlium is
metamorphosed into a single
spermatozoid, or it divides into two daughter protoplasrs ami
forms two spcnnatozoicls.
The
sperl11atoz()icl~
look like zoospores,
but much smaller in size al!CI with fewer flagella.
liberation of the
~,pennatozoids
The mode of
is similar to that of the zoospores
and there is usual form<tti:m of vesicle at the time of liherati()n.
Similarly, the terminal or any in tercalary vegetative cell
mav act as an oogonial mother-cell.
The oogonium may he
terminal or intercalary in position. The oogonial mother-cell,
as before, divides into two daughter cells of unequal Hize, the
shorter cell at the distal end forms the oogoniulll and is alwaVl;
provided . . \ith one or more caps at the upper end. The lower
larger si8ter cell is called suffultory cell. This cell either remains
as ~llch or acts as an oogonial mother-cell, which divides and
'1 IlALLUl'lIl
IA-,\L(,~1.
31
re-eli, ide~ forming HI () or Ilwre in tCl'cal;uy oogonia in a chain. The
ooglluililll swells and becomes more or le~~ ,pherical with a cliamet(:1' greater than that of any vegetative cell. The prot()pla~t
(If the oogonium gradually metamorpho"es into an uninuclcated
ousphcn· or ovum. As the oogonium approachc~ maturity - a
"mall pore or transverse crack 1:0. formed in its \\al1 toward:, the
u
Antherozoid
Oogonium
Ovum
3
Fi~.
J .•\N
21
()(lr,ONI\ OF A '{\OHANTHtOU,., !':;PI ('I,LL.. 01
nO(lONIU.lI HCADY rOH FER I ILlZA1'lON ..
')F Fr:n:m JlA'f10N,.
3,
Z. rnr.
(n r/()(/ONUlIlf,
SA:IlE .lU~ L ,1.'1 1 HE 'flME,
AN LlOUONll'M \yHH A 1.\'0011: (OO~l'I)UC),
upper em!. JU~l before fertilization the !ludeu:, of rIll' 0\ Ull1
migrates from the centre towards the pore where the ovum
,lightly contracts from the oogonial ",all and forms a hyaline
receptive spot just outside the nucleus.
Nrl}1!llmdrous speLics arc diceci()UB (heterothallic).
The
structure and mode of development of the oo)?:onia arc similar
to those in macranclrous species
Androsporangl '
and these are borne on filaments
of normal size, The dwarf male
filaments
bearing anthericlia arc
11l'oclucccl as a result of germinaOF O('dOillJniIlJII.
ciOll of a special type of zoospores
called androspores formed within androsporangia. TIle mode of
formation of anclrosporangia i~ similar to that of the anthericlia,
Fli{.
22.
ANDTIOSI'OIUNUIA
P
'-,1 RUCTURI
\,n
flIV1IOP'H.Nf
Of
The plotoplast of an ,lllClt O~pOl anglllm
onlv one ancho~pOll
The
PI \"1 CROUPe,
l~
andlo~pOlL<',
111e tamO! pho,ed mto
<;mula!
\,1th the "pel matozOld, ate hlx rated In the
"ptllll,ltoZ()Jd."
clch bung ,ulllJunckcl h,
\Vhen thl
hhtl,l[er]
IL<,lcll
fleely in watel and comes
an OogOlllal mothel cdl
01
III
111
<;'lnlt
ctppldl lIlel:
\,av a, the
,I le,Jdl \Ihen
dlo,ctppLdl, thL ancbo,p HL
the nughbmuho{]ci of
In the
[0l1l1L1
tll,r
"\lIn'
111 OOglllllUI11
e"o,l the <lmh lJ'opor e
It"elf
with
hVdhne end d(nln-
cltt,llhc<;
It,
11,11 (I <;, to thL o()gomal
\v,tll 01 to the "all ot
the <;ufiultOl V ((.]] an'l
£OIm, thl (hhll f m,tll
fi1.11mnl thele
In thL
Llttu, I' hen It affi"\(,
ito,df tn the. \1<111 of thl
oogOlll,tl l1101h(] -(.('11 If
found [0
the d \\ ,ll f nulL
fil,II11Lll t all\ ,w" on the
<"ufful t01 y C( 1I aftel th(.
dlVl'>lOn ,mel fOJ matlon
of oogonium
When
heen
ha,
f0lll1
an
aneho<;pol"e
affi::-..e<;
i t,elf to the wall, It
l)~
Z3 ()Ulflf!fHlllliJI
develop" a holdfd<;t,
"'1\.1'<\1 HI:PnllDlrl[ON 0) \ "IAN~\"
nl 01 ~ '01'[( II,
"Ull aund q Itself \\lth a
delicate wall and 101 m q an one called plant (gelllZllllf.!;) TIm cell
ac.t~ a<, an dllthu Ic[wl 1110lhl.l lcll dlld Cllt', oft OJ1( (ll mUI e alllhe-
Iuh" at
t\~o
Into
It,
ctpL X
and fOJ 1'1,
ThL plOtJpLI~t of eeleh anthellclllllll dn ((Irs
l\I,) spo matozcllC!"
JVml1lanclrOll\ "pecles of Oedogonlltln may bem hath (Jog-onra
and anchO"pOlangia on the ,ame filanlC'J1t (gvn{{lldr()~porom), or
they
die
bOll1e on clJffuel1t fil,ll11Ulb ui 110l111cl1 ,lEt. (U!W(//l(Z,lllll)
33
In both macrandrous and nal1l~androus species fertilizatioll
of the ovum takc's place by the entry of a spermatozoid through
the pore at the hyaline receptive spot. The zygote (oospore)
slightly retracts from the oogonial wall and soon forms a wall
of two or three concentric layers around it. The middle layer
lllay often show pit, or reticulatiom. At maturity, the oospore
becomes reddish-brown in colour clue to the a(cul11ulation of oil.
Finally, tlle oogonial wall disintegrateq, the oospore falls to the
bottom of the pool where it undergot:s a peliod of rest for a
year or more. Prior to g(·rmination the diploid nucleus of the
protoplast under~oes reduction division forming + haploid nuclei.
Subsequent division of the protoplast £01 JUS four zoospores around
the [our nuclei. At
the rime of germination the wall of the
Zoospore
OOSpOlC
hUl'bt<; and
zomporeq ("cape being
~U11011nded by vesicle.
Finallv, the ye<;icle
disappears, the Z008Fig. 24 0, '/"'/11/1111111.
pores swim freely in
GDR~rrNATING ('O~P()Hli.
water.
Subsequent
development of zoospore and the formation of the vegetative filament arc similar to the zoospore produced by a vegetati\'e cell.
(3) Parthenogenesis. Some ~pecics may rcgulmly form ptll'(ah()o~p()res) i.e., developed from unfertilised eggs.
The parthenospOles completely fill up the entire cavity of the
oogonium and possess walls like zygotes.
thcn()~pol'es
Spirogyra
(Family ZygnemataceaJ)
Spira,e,yra represents one of the commonest fresh-water g-rcen
alga which is usually found as a free-floating inhabitant of the
stagnant water of ponds, tanks, ditches, etc., as a green slippery
mass. Occasionally, it is found in currents of running streams
and spring-s, where it attaches itself to rocks or other objects by
means of holdf(l~l~ or lwptera. These develop as much-branched,
outgrowths of the lateral walls of the vegetative cells.
3
3-f
",IHUCl'PRL \ND m:VLI OPi\lLNI or PLiI]';1 CROUPt:,
Vegetative body,
The vegetative hody of the plant consists of an unbranched
filament, a numher of \vhlCh arc intermingled with one another
imo a mass, Wlll!l1011ly called as the pond-scum. A filament
i~ composed of <l single row of cylindrical cells joined end on
end, usually in the Lase of free-floating spccieb, without any
di&tinction into base and apex. The filament in('lcases in length
by ordinary Lell-division and by subsequent growth of individual
cell~, each of which is equally (apable of further division. The
Conjugating cells
\
,/
Cell-wall
Chloroplast
'''~'''_A~'''''- Pyre no ids
Nucleus
Cytoplasm
Zygospore
A
B
FIg. 25
A
8p!10U!IHI.
l'OltTION or tHI: rILA\ILNI' ~lIOWINL: VeGLl'AI'IVI. ('lLlh ,
Sl:(( LR~lVr: ~lAGr:" TN ,(,ALAHH-OHM (ON"JUGA lION.
n,
lateral walls of the celIb are three-layered, the inner two of
cellulosc and the oulell110st one of pectose of vmiable thickness,
35
The middle lamella (cross \\ all) is macl(; up of pectose with a
layer of ccllulo~c on <:ither bide It is ,imple in dwarf and shorter
filaments, but replicate (annular ingrowth of cellulose layers) in
slender and Ilarrm\'(.T ones. The protoplasm is granulated.
vacuolated and in the form of primordial utricle. The nucleus.
containing a distinct nucleolus. lie~ in it sheath of cytoplasm at
the centre and i~ susp.:nded in the vacuole by means of conspicuous cytoplasmic strands, extending from the p<:riphery of the
protoplasm. The mor.t remarkable clements in a cell arc a
varying Ilumber (1-7) o£ ribhon-shaped chloroplasts, peripheral
in location and running mually spirally throughout the length
(If the cclI. Each chloroplast has Sll100th or serrated lateral
margins and a varying number of dense, highly refractive.
(olourlC:~5 proteinaceom hocIies, the pyrciloids (in regular axile
series or scattered). which form the seats 01: deposition of starch
grains as reserve food.
Reproduction.
Spil'ogyra reproduces bv the vegetative and
~exual
methods
only.
(1) Vegetative. The vl'get"tive multiplicatio.l takes place by
the breaking down of th(; filament either due to the wftening
of the middk lamella between two adjacellt cells or by an accidental bn>aking o[ the filament. The fragments, thm formed.
may be unicellular or multicellular and each such fragment, by
repeated cell-division. gives rise to a new plant.
(2) Sexual. In sprin):!; the plant reproduces sexually by
conjugatiuIl, i,e., by the union o[ two similar or morphologically
identical gametes. which are formed hy the protoplasts of ordinary
vegetatiye cells. Each of these vegetative cells is called a gametangium, and its undifferentiated, nninucleated protoplast is called
a gamete'.
In dicecious species. conjugation takes place hetween the cells
of two different filaments. At first the two filaments lie in close
approximation with each other throughout their entire lengths
and there is a secretion of a common gelatinous envelope around
the two fil?-ments. \Vhen the two filaments are thus in contact,
short papillre are developed from the cell-walls of ordinary cells
of the adjoining filaments. These papillre come in contact by
36
STRUCTURE AND DEVELOPMENT OF PLANT GROUPS
corresponding pairs and grow in opposite directions. Thus, the
original filaments are pushed apart. Finally, the end-wall~ of
these outgrowths are dissolved away and the cells are thus
connected by an open tube· (conjugation tube). By this time the
protoplasts (gametes) of the two conjugating cells have begun to
contract and after the formation of the conjugation tube, the
protoplast (male gamete), which began its contraction earlier,
migrates through the conjugation tube and unites with the other
protoplast (female gamete) there, fonning the zygote, called
zygospore, which secretes a wall around it. The wall formed
around the zygospore is a three-layered resistant structure, of
which the middle layer is coloured and. shows ornamentation.
In exceptional cases the chloroplasts contributed hy the male
gamete disintegrates. This type of conjugation is known as
scaLarij()l'I11 conjugation.
In mUllcccions species conjugation takes place between the
adjoining cells of the same filamenl. This is termed lat1'l'al
Rep'i~ate septum
Gamete
Conjugating cells
Conjugation tube
Zygospore
B
A
A-B,
I<'ig. 26.
8phor/llla.
flTAGES IN LATERAL (JON.j[JUA'1I0N
conjugation. The zy.gospore may he globular, ellipsoidal, or
cylindrical with obtuse ends, rarely flattened and dislOicl
in shape.
37
TIT \LLOPIll TA-ALG.E
Though the galllete~ are morphologically identic.al, thl;
migration of one of them into the other gametangium proves
111<.:m to be physIOlogically or biologictlll.v difterenuatccL ih the zygOS})OlC attains matlllity
there i, reduction di> i~ion of i[~ fu"ion-nuc.lell"
forming fOUl haploitl nuclei, of \\hic.h thl ce
ulldergo clibintegratioll. Aftel a (onsiderablc
period of rest the zygm,pOl e germinates, ib two
olltennost wall-layers 1 upture and its innermo5t
\\ all-layer surrounding the protOplast emerges in
the form of a tulmlar outglOwth. By the formatiun of a transverse septum a (ell is formed at
rhe di,tal end and this cell, by successi.e ce11Zygolpore
eli, isiul1s, give, ribe to a Spirngyra filament.
It
.
.
FIg. 27 '''jJllfI'I!lJfl
ha~ been ObbCI \ ecl that dUllllg '>calanform A
ULl\MINAlIl-I(,
uJI1jugatirm ueually all the u:lb of one filament ZH,ospom:
lllay produce gametes of one sex so that aftel
C(lnju~ati(Jn there is migration of all the gametes of one
Fig. 28.
P HO lG.\!ICI1.0ClltAPll
lW SrrnOGYIlA SHOWING S[ALUU·
fORM CONJUGATION
filament (may he regmdecl as the male) to the cells of other
filament (female) forming zygotes there.
But, it may so
38
STRUCTGRE J\ND DEVELOPMENT UF PLANT GROUPS
happen that each filament may contain both male and female
gametes so that cross-conjugation may occm forming zygotes in
both the filaments. It should he noted that all the cells of 'a
filament may be fertile, or there may be regular alternation of
fertile and sterile ones.
(3) Parthenogenesis. ·When conjugation fails, the gametes
surrounds itself with a thick wall and forms a parllu:nospure or
azygostJOre ; each after a period of n:st germinates into a !lew
gal1letoph)~tic plant.
THALLOPHYT A-:\LG.~':
39
Zygnema-
(Family Zygnematacc:l')
Zyg/leJija is another widcly-distrilmn:d, fresh-water, green alga
which occurs ill mllch the same type of habitats as cln~s Spirogyra.
Vegetative body.
The th allus. likl: S /)irngyra,
is an umbranchcd filament without any distinction into hase
and apex. A filament consists
(J f a single row of similar cylindrical cells Llsually having
lengths slightly greater than
breadths, occasionally the cell
may he 2-5 times as long as
broad. Holdfasts or haptera
Stellate
arc rarely fonned. The wallChloroplast
structure is mLlch the same a~
that in Spirogvra. but the outerNucleus
most pectose layer rarely becomes thick. The transverse
Cell wall
walls are never replicated. The
Cytoplasm
protoplast is uninucleate and the
nucleus is embedded in a broad
strand of cytoplasm cOllllcctine;
two chloroplasts on either side
and this band occupies the
longitudinal axis of the cell.
Each chloroplast is stellate or
star-shaped with a prominent
pyrenoid at its centre and it may
have numerous delicate strands
extending toward~ the periphery
of the cytoplasm. The filament
increases in length by cell-division and suhsequent growth of
Fip:, cO. ZY!lllCIJLo.
the individual cells. Prior to
P AliT (l Ii' A FILAlIIEN'r.
the cen-division the nucleus
divides mitotically into two, so thac after cytokinesis, each
STRUCTlTRC AND DEVELOP,\ILNT OF PLANT (,ROOpS
daughter (ell receives one
daughter nuclcu~ and a
chloroplast ol the parent
c.ell, the former lying lateral
to the latter. Suhsequent1v, the ch 10roplast with
i~s pyrenoirl divides into
tWil and thc nucleus migrates and ()(_(.upie~ a pmition midway hetween the
two daughter chloropla:>t8.
Reproduction.
COlljUil'llti01l. _ _ _~II
or gametes
ZYgllClll!1 reproclulC'o
ve~etativu
anc[
bv
sexual
mcrhods.
Zygote9
( Din erent.
stages 01
maturation)
(1) Vegetative.
Zygnema reproduces by the
vegetative method.
This
usually takes place hy the
accidental bl'eal<ing of the
filament and never clue to
the softening of the crosswalls of the adjac.ent cells.
(2) Sexual. 1\ bst Spl'Lie, of ZY{!JlfIlUi reprodlile
sexually, in the spring, 1ly
the process of wnjugatioll.
Conjugation 1',
llsually
scalariform, hut
latcral
ClJ1ljugation i~ not of rarc
OCC111'e11ec. The process of
Fl~. 31. 2//(///('//111.
scalariform
c.onjugation
Sut( Ls"rvc :o.l'AGLb IN (ON.HJ[,HIOJ" AND
ron~rATlON 01' l:):[WSPORCS.
i" much the same as
that in Spirogyra, hut in
some ~peeies Goth the gametes becomes amceooid, migrate
towards each other, {use in the conjngation tuhe and £orm a
zygospore there. In other cases, like Spirogvra, the gametes of
one filament (m<tle) become active, ama:boid and migrate through
IHALLOl'Hl L\ -.\Ll.. L
the conjugation tube~ to the gall1ete~ ut the other filament
(female). unite and form zygospore~.
After gametic unioll there is a development of a wall around
the zygute and this wall at maturity bec.Dllles three-layered (a thin
inner layer of cellulme, a median layer of ccllul()~c which is often
chitinisecl, and a thin outer layer of Lellulose or pectose). The
colouration and ornamentation are restrictecl to the middll" layer,
a~ in SjJil·ogyra. The protoplastb o[ the zygote, after fusion, U)l1tains a diploid nuclem and four chloropla~ts, bm later on the
two chloroplasts contributed by the male gamete eventually disintegrate. The zygotes, at maturity, arc finally liberated by the
disintegration of the gametangial wall or of the wall of the conjugation tube and usually undergoes a period of rest to)' several
c
B
A
FJp; 32.
A-(',
Z!I!lnllllll.
~TAGL~ IN I Ill: (.blDl1"AllON 1'1' I IlL 1.IcGOIt..
months. With the advent of the following spring the zygote
germinates and !Jrior to this germination there is a reduction
division of the zygote-nucleus forming four haploid nuclei, of
whic h three disintegrate. Dudlig germination the two outer walb
of the zygote rupture and the protoplast being still enclosed hy
the inncrmost wall-layer may partially or wholly escape frnm thc
ruptured walls. This protoplast hy repeated division gives rise to
a new filament.
(3) Parthenogenesis. When conjugation fails a gamete may
form {{zygospore or parthenosporc. But these arc not produced
in abundance in the genlls.
Cosmarium.
(Family Desmidiacex)
Cosmarium and other members of the Family Desmicliaceac
arc commonly known as "Desmicls',' They are all inhabitants of
42
STRUCTURE AND DEVELOPl\IENT OF PLANT GROUPS
fre~h water and are found sparingly intermingled with other freefloating alga': everywhere.
Vegetative body.
CosmariZlI1l is an unicellular genus which may be easily
recognised in having ;:mall compressed cells, each being divided
by a conspicuous median consttiction (silws) into two distinct
symmetrical halves (semi-cells) united together by a comparatively
B
A
c
D
Fip;, 33,
_1, A
E
CQ8Iflrrriu'll/.
n,
VEOE1'ATlVI: (JELL IN flEl'l'WN;
VJAGRAlII}.[Al'IG UEPREHENT.tTJON
OF 'I'HE VEGETA'I'IVE CELL / C-E,~'nONT, SIDE AND VERTIC'AL vmw>'
OF THE VElm'!'A'I'IV~: r:ELL (Din~/rrrml/l([ti,,),
narrow connecting zone (isthmus), Its species are c1istinguislllxI
partly from such characters as cell-shape, ornamentation of the
THALLOPITYTA-ALGiE
43
wall, etc. Each cell should be examined in front, side and yertic:al
views. In front view the semi-cells may he circular, elliptical,
reniform or sub-cjuadrangular in shape, whereas in vertical view
they are usually elliptical in outline. In side view the semi-cells.
in most cases, appear more or less circular in outline.
The cell-wall in Coslnarium is never spiny and it
three concentric layers:
consist~
of
(1) an innermost thin cellulose layer,
(2) a sOl11ewhat thicker median layer consisting of cellulose and
pectic compounds and (3) an outer thick or thin layer of gelatinous
sheath made up of pectose. Excepting the isthmus-region the
inner two layers arc perforated by vertical pores, being usually
arranged in a definite pattern and are distributed all over the
semi-cells, or may be localised. The outer wall is usually smooth,
but may sometimes appear somewhat granular.
The protoplast contains a single nucleus which always lies at
the isthmus and is sometimes connected with the string-like
projections of the chloroplast. Each nucleus contains a conspicuous nucleolus and a well-defined nuclear reticulum.
Usually there is only one chloroplast ill each semi-cell, but
sometimes twO or four chloroplasts may be present. Each chloroplast contains a single pyrenoid and is provided with four to
several radiating plate-like extensions.
The cells of Cos1n(lrium exhibit movement which consists in
a series of jerks. This is due to the secretion of gelatinous
material through the vertical pores.
Reproduction.
Cosmarium reprodnces both by vegetative and sexual methods.
(1) Vegetative. The vegetative method of reproduction takes
place
by
the
method
of cell-division
and
two
daughter
cells are formed from .the parent cell. During the process the
+1-
STRUCTURE AND DEVELOPlvlENT OF PLANT GROUPS
nucleus first divides into two daughter nudei and the istlHllus
slightly elongates. A transveyse wall is formed across the isthmus
A
B
c
Fi!!:. 34.
A, A
Un'<Ulfuiu'lll
VEGE'l'A'rrVE ('I,LL; ll-D, VgUETA'J'II'E IlEI'RODUC'I'ION SJlOWJNI:
FOil MATroN ,OF JlAlJlaT~'lm CELLS.
in sLlch a way that each scmi-cell receives Olle daughter nudclls.
The portion of the isthmus attached to each semi-cell now
elllarges and forms a new semi-cell and in this way two daughter
cells are formed. The daughter cells remain attached to each
other for sometime but finally separate. Thus, it is evident that
of the two semi-cells, one semi-cell is younger than the other
which belongs to the parent cell. The newly formed semi-cell
receives a chloroplast with a pyrenoicl by the division of the
l)re-existing one of the other semi-cell. Sometimes pyrcnoicl may
be formed de no't'o in the newly formed chloroplasts.
THALLOPHYTA-ALG)E
45'
(2) Sexual. Sexual reproduction is isogamous and consi~ts
in the union of two identical gametes produced usually by tWf)
mature individuals. Conjugation may also take place between
two newly formed sister cells. During conjugation usually two
mature cells come to lie in contact with each other and become
surrounded by a common gelatinous sheath secreted for the
Fig. 35. ('o"lJIlIl'hlln
STAGES IN SEXUAL UEPRDTlUC"rION, FOR~[ATION
OF THE ZYGO~['E.
(S)
AND GER)UNATION
purpose. The protoplast of each cell functions as a gamete.
Each cell then breaks at the isthmus and the gamete
escapes. The two gametes, thereupon, fuse outside and after
secreting a thick wall around it form a somewhat globose Or
angular zygospore. Its wall may be smooth, papillate or spiny.
The zygospore, after a considerable period of rest, germinates.
46
STRUCTURE ANIl DEVELOP;\IENT OF PLANT GROUPS
Th(; fusion nucleus undergoes a reduction division forming four
haploid nuclei, of which two degenerate and the remaining two
are functional.
halye~,
The
protopla~l1l
th(;ll divides into two equal
each r(;cc:iving one functional nucleus and a chloroplast.
Each daughter protoplast finally devciops into vegetative cdl
which is liberated by the rupture of the zygote-wall.
(3) Parthenogenesis.
parlhellosporcs
may
be
When conjugation fails ({zygospores or
fOl"I11(;d.
The
parthcnospor(;,
during
germination, contains three degcnerating nuclei and one functional nucleus which by division becomes the nuclei of the two
resulting vegetative cell.
Caulerpa
(Family Caulerpacerc)
Ctllllerpll is
it
green alga, the species of which are mostly
Jistributt:d in the tropical seas.
They OCCUf generally in shallow
and calm waters being usually rooted in sand or mud.
Quite a
large number of species, however, grow attached to rocks or coral
reds and may sometimes also occur as epiphytes
()11
mo\s o£
mangrove plants.
Vegetative body.
The thallus is one-celled and shows higher morphological
difft'fcntiation. It is ditIeremiated into a prostrate, more or kss
branched, cylindrical, rhizome-likt: portion which b(;ars on its
underside root-like rhizoids and erect cylindrical branches or the
"leafy shoots" on its upper side.
Thus, die external form is
comparable to that of a vascular plant with creeping rhizome.
The upright branches bear lateral outgrowth or assimilators which
-arc usually flattened, hut the forms of the shoots may vary from
species to species often resembling cacti, the mosses or the lycopods.
The entire unicellular body is a branched Coc!locyte without tfan8-
l'H.\LLOPHYTA-ALG.'E
47
vtrse septa, The cytoplasm is continuous lying imtl'llal to the
cell-wall and contains numerous nucld and disciform chloroplasts
tt
Rhizome.like portion
Leafy shoots"
Rhizoid,like portion
D
Fig, 36,
('(111/"1'1'(1,
A~J), P(1ItTlONS DE' TJlE YEGE'l'A'l'lVlJ nODmH OF IHFFEHlcN'r INDIAN SPEC'lES
OF 'IHE SAME
without pyrenoids, Thefe is a single central vacauo!e which runs
throughout the entire length of the plant,
48
STRUCTURE AND DEVELOPJ:\IENT OF PLANT GROUPS
The cell-wall is comparatively thick and is provided with
numerous transvei'se and longitudinal skeletal strands or trabecuix
traversing the central cavity of the thallus. These trabecula; are
most strongly developed in the rhizomatous portion, hut becoming
few..:r and fewer in the assimilators and may be poorly developed
Fig. 37.
~
1Il
RAIlECllL:l',
C'mtil'1:JJO.
TN RHIZQ)[ATOIIS PORTION
the thizoids or altogether absent.
As the thallus gradually
becomes older due to the deposition of successive strata of wallmaterials, the lateral wall as well as the t.rabecula; become distinctly stratified in appearance.
The wall is composed of callose,
pectin, pectic acids and pentose, cellulose being entirely absent.
The rigidity of the plant is maintained clue to the turgidity of the
thallus and thickness of the cell-walL
Reproduction
(I} Vegetative. Cmtlerpa reproduces vegetatively in which
older parts of the rhizome gradually· die away, thereby separating
49
THALLOPHYTA-ALGA':
the crect shoots. These detached shoots are dispersed by the
waves and possess the remarkable power of producing new plants ,
when affixed to any suitable substratum. In this way rapid multiplication of the plant is effected.
(2) Asexual. Seyeral species
of Caulerpa reproduce asexually
by the production of zoospores,
but the details of the zoosporeformation
and their behaviour
are very little known. Zoospores
may be produced from any portion of the leafy shoots or rarely
from the rhizome.
After their
formation, the zoospores appear
to
remaIn
111
reticulate masses
within the cell and numerous
papillate outgrowths are developed on the surface of the thallus.
These papilhe are known as "ex-
trusion papilhe" through which
zoospores are liberated in a mass
of mucilagenous matter in such
Fig-. 38.
Ouu/el']Ja.
TUADI1CllL:r.:.
enormous quantity that the water surrounding the thallus appear
green for the tilne being. Each zoospore is biflagellate, pyriform
in shape and possesses a single ~urved chloroplast without pyrenoid
arid a conspicuous eye-spot. According to
SOll1c*
the entire thallus
in many species dis organises after the liberation of zoospores.
• Dostal 1929. Erllst 1931.
4
50
STRUCTURE AND DEVELOPMENT OF PLANT GROUPS
(3) Sexual. Sexual reproduction by the union of gametes has
been reported in several oriental species.* 1n one of them, Calt/erpa
,
Fig. 39. ('lIlll,'rjJ(/.
FORMATION AND LIDEllATION OF ZOOSr'Ol\ES 'l'H[WUtaI E)('l'ItUHldN
PAPII,L.l·l ON THE ~URFACE cW UlAn: SHOOTS; C, DEVELOI'~IENT
OF EX'l'ItU!-\ION PA1'ILL.l·:.
A-B,
clavi/era., reproduction has been shown to he anisogamolLs and the
plant, hetel'othallic.
Vaucheria
Vaucheria is 'Ill inhabitant of .f~esh water, though a few marihe
species are not uncommon. Some are terrestrial and may grow on
bare moist soil or in plaughccl fields forming extensive interwoven
felty sheets.
------------* Iyengar 1933.
TiIALLOl'IIYTA-Ai.G.E
Vegetative body
The thallus consists of sparingly brdllched tubular, comncytic
filament having no
They
are
cr()s~
attached
walls excepting at the reproductive region::;.
to
the
sub-
stratum bv means of rhizoid-like
branches.
The growth of the thallus is
restricted
to
branches.
The
the
apices
of the
cCl:nocytic
thallus,
when injmed, may develop transverse
septa blocking
ponion.
the injured
The cell-wall is thin :uid
consists ()f all inner layer of cellulose and a pectose layer external
to
it. Just within the cell-\yall there
15
a thill layer of c)'wplasm sur-
rounding. a large central vacuole
which runs, without interruption,
throughout the entire length of the
thallus,
pheral
Enibeclded in the perilayer
of
c)'toplasl1l
al'L~
numerous nuclei and chloroplasts,
the former lying towards the inner
face and the latter towards the
outer face of the cytoplasm,
The
Rhizoid·like branche.
chloroplasts are without pyrenoids
anel arc either circular or elliptical
in outline. Food reserves are stored
li'ip;.
AN
40.
'V (llll'l, pr;a
EN'l'raE PLANT.
as oil under natural condition, but
when continuollsly illuminated star!==h may be formed instead.
~L\~~\"
52
STRUCTURE AND DEVELOPlIIENT OF' PLANT GROUPS:
Reproduction
Vallcheria reproduces both asexually and sexually.
(r). Asexual. There are various methods of asexual reproduction. Typically, the method is hY' means of large multiHagcllatc zoospor.es, such being formed singly within a club~shaped
zoosporangium developed' at the apex of a branch. Dunng the
development of a sporangium. the distal end of a l)raneh forms R
Zoosporangium
2
Germinating zoospore
Fig-. 41.
_loP.X1.TAL REPItODUCHON SIIOWING FORMA'l'lON
AND LlDEHATION OP ":OO~POREH (1-3\; 4,
A GEl\,\[ANATING ZOOSl'OItE.
club-shaped swelling and a portion of the protoplast is cut otT hy
its transverse division just a little behind the branch-apex. This
portion of the protoplast is' finally separared by it transverse septum
and forms the zoosporangium containing a multinucleate protoplast. This protoplast then slightly contracts, the nuclei and
chloroplasts change their positions, a pair of flagella develops external to each nucleus and a multifiagellate zoospore is formed.
At maturity, the apex of the Zoospol'angium softens forming it
small pore through which the zoospore squeezes its way and filjally
swims freely but slowly in water. After it short period of
activity, the zoospore comes to rest, withdraws its flagella and
THALLOPHYTA-ALGA::
53
secretes it wall around it. Germination starts illllllediately by the
formation of one or more tubular outgrowths which finally develop
into a new thallus .
. In species of ~r{/ll~'hcritl growing on damp soil in green-houses
thl: entire protoplast of the sporangium instead of producing a
zoospore may develop into a thin-walled aplrmospore or a thinwalled alzilZetc. This aplanospore is liberated by the rupture of the
sporangial wall and on germination gives rise to a thallus. The
akinete becomes separated from the thallus or germinates in situ.
Sometimes due to scarcity of water, the entire protoplast of
Villtcheria undergoes transverse divisions into short segments,
.around each of which a thick wall is secreted. These arc thickwallcd aplanosporcs (hypnospores) which either germinate direcrly
or protoplast of :~ach divides into a number of thin-walled 'c:ysts'.
At maturity the protoplast of each cyst escapes in an amccboid
fashion and eventually comes to rest, rounds up, secretes a wall
around it and germinates into a new thallus.
(2) Sexual. All species of Vauclzcria reproduce sexually and
are oog:.unous. They arc mostly hOlllotlw1liu, i.e., they bear both
male and female sex organs on the same thallus. A few marine
species arc heterothallic, i.e., the male and female sex organs arc
borne on different thalli. .
In homothalltc species both alltheridia and oogonia develop,
either side by side on the same filament, or on a common lateral
branch, or OIl dillerent branches of the. same thallus lying quite
close to each other. They develop either simultaneously or antheridia may develop earlier.
The antheridium, which is usually an elongated, hook-shaped
structure, develops at the apex of a short lateral branch. During
its development the apical portion of the lateral branch becomes
densely filled with multinucleate protoplasm with a few chloroplasts. This demer portion is separated from the rest of the
protoplasm by a transverse cleavage and is soon followed by the
formation of a septum. The cell, thus cut off, is an antheridium.
Its protoplast is eventually divided into several uninucleate segments, each of which is finally metamorphosed into a spennatozoic! with two terIilinal flagella of equal length. At maturity, the
spermatozoicls are, in most cases, liberated in the surrounding
STRUCTURE AND DEVELOPivlENT OF PLANT GROUPS
54
water through an apical pore formed by the gelatinis<ttion of the
apex of the anth~ridiull1.
Usually, simultaneous with the formation of the anthericliul1l
oogonial development begins and there is' an accumulation of
colourless multinucleate mass (If cytopla~l1l (called U'twderjJ!aslIl)
in the rnain filament ncar ahout the ha~e of the antheridial
branch. This is followed by the formation of a later;il bulge into
( biFlagellate)
4
5
Fi~.
1-5.
42.
['(1111,11 "I'ill.
lJEVEL{)J'~IENT OF SEX OlLGANR AN'D PJtrl(,ES~
m' SI,;XlTAL
IlEl'llODU(_,'l'ION
which the wanderplasl1l migrates. A~ the hulge increases in ~IZl:
numerous nuclei and chloroj)lasts also accumulate within it and
eventually forms the oogonium, which is Cut oIT from the main
, THALLOPIIYTA-,\LGA:
S5
filament lw the formation of a seiJtulll, when the oogonium is
~ituated at
the apex of a branch, it start~ its development a~ an
apical swelling which is finally cut. otT f1'0111 the rest of the brand!
by the formation of a transverse septum. .A mature o(1f!,'l!niullJ
There is great diversity (If opinion
contains an Unilll.IClealc egg.
as to the formation of the uninuclcall' qq.;.
According
to)
some
the uninucleate conditioIl is obtained by the degeneration of all
the nuclei exc<.:pting the one,
other~
hole! that all the nuclei hut
one, migrate out of the oogonium before the formation of the
transverse septum, There arc still others who hold that the
differentiation of the ovum and fertilization take place prior to
the formation of the transverse walL
At maturity a 'beak'
IS
formed at the end of the oogonium and it undergoes gdatinisation forming an <1pical pore through which a droplet of gelatinPllS
material exudes.
The spenllatozoids, liberated from tlIt.: neighb?uring antheridia, swim towarclR the oogonium ,lnd accumulate r()und the
droIjlet.
Usually
several
spermatozoids
enter
through
the.
apical pore of the oogonium but only one fertilizes the ovum.
The nuclei of the two gametes, following union, soon after fuse
near about the apical pore, but the fusion-nucleus finally migrate
towards the centfe of the' zygote. Following fertilization the
zygote secretes a thick wall, often consisting of 3-7 layers, around
itself and its protoplasm hecomes rich in oil-reserves. This zygote,
after a neriod 'of rest for several mOllths, germinates into. a neW
filament,
It has been held hy the aJgologists that the division ~f
'the'zygote-nucleu3 prior to its germination is probably reductional.
Ohara
(Family CharojJhyccre)
. Cham or stonewort is a
s\ibmcr~cd
green alga which usually
grows in fresb-water ponds and lakes ·heing attached
to
a muddy
56
STRUCTURE AND DEVELOPl'vlENT OF PLANT UIWUPS
or Randv bottom, often forming an extensive ~uh-aqllatic vegetation bel~w the surface of water. Several species hecome incrllstated
with calcium carbonate.
Vegetative body
The thallus
oJ an erect
COIlSISts
branched axis being attached to 1he
substratum by
Ill.eans
of
rbizoids.
The rhizoicls arc branched tilamcll ts
whiCh mayor" may not have nodes
and internodes.
The erect
axis
is
distinctly differentiated into nodes and
internodes,
At each node there is
[l
whorl uf branches of limited growth
thc "leaves ",
usually
or
The so-called leaf
POSSCSSI:S
more
3-8 internodes.
branches
(l~
One
llltlitnitcd
growth may abo dl'vel()t> in the axils
these
of
lca\'(~s.
In" HOlTle
each internode consists of
elongated cell which
i~
species
11
sing'le
1I\all \'
1 ill1t'~
longer than its breadtb, hut ill most
cases the il1tl:rnodal cdl is corlit:(/Iud
i.e., sur)'oulUlccl hy a Hingle layer Ill'
much
gmaller, vertically
clollgall:ll
cells.
The cells in the terminal P()l'~
tion of a branch "are always
Fig. 45.
A
l'OHTInN OF 'l'B!,:
llOny.
('//11/'11.
V1WB'l'ATTVj,
nucleate
and
rnincnt
vacuoles.
mature
always
regions
witholll
But
a
vacuole is" always present.
latter case the cytoplasm is in the form of primordial
prothe
lI1
lar~('
"lIlli.
C:Cll tral
III the
It trick
""ith
THALLOPHYTA--ALGJE
57
innumerable slllall ellipsoidal chloroplasts and
It
few comparatively
Th(~ nuclei arc more or less irregular in shape and
large nuclei.
increase in 11lll1lher by amitosis.
The disposition of chloroplasts
in the cytoplasm is vertically parallel and they appear to be ill
spirally twisted files.
The cytoplaSlll shows streaminp; movemcnt
.and. movcs in longitudinal direction so that there is an ascending
stream on one siele and descending on thc other.
Reproduction
Cham reproduces hy vegetative and sexual methods. Zoospores arc entire] y lacking in them.
(I)
vegetative. This type of reproduction IS quite common
~lJl(l may be elIec:1ecl by the formation" (If special vegetative repro-
ductive bodies snch as '(a) ftllZyltlsc stars, which are star-shaped
aggregates of cells demcly filled with starch graills and clevdopccl
in the lower internodcs, (h) 111l1b£ls formed nil the rhizoicl~ and
(e)1 protoncma-llke olltgrowt-hs developed from the nodes.
(2) Sexual. Chara reproduces sexually by (Jog-amy. Tlll:
male reproductive structlll'C is call<:d a glo/11I1c and the female
,'one, a nucltlc, though they are sornctillles loosely calleel antheriThc~e
dium and oogolllUm respectively.
are always produced at
the nocles of the so-called leaves and occupy die sicks facing the
main axis.
IVInst of the species are hOl11othallic, though hete1"O-
thallie species arc
110t:
uncommon.
definite orientatioll with respect
to
The nuclIk ane! glohuk have
each other, the former heing
plact~d ahove .the latter and they may cie\'l'lop either simultaneomly
fIl'
the globule dt:vclops earlier.
A superftcial nodal ce1l of the so-called leaf filcing towarcl1;
th(~ main axis forms an apical cell that cuts oil: two ("clls, the upper
ollt' dongates and forms the internodal cell that acts as the'
pedicel oJ the future globule and the lower cell divides and
divided to f01'111 a node.
1'('-
The apical cclI enlarges, becomes spheri-
SR
oTRUCTURE AND DEVELOPl\IENT OF PLANT GROUP::;
cal :mcL cl}vides by two vertical pl<:111e8 w [orm four cells which
re-llividc transversely to form an ociant.
Each
of
these
octHllts
divides into two cells by a wall parallel to the surfacl' (p('ric1iual.
division) forming two daugh tel' cells, of which th('
.l"ig. 46.
.A
(JUe
nl"U·fl .
l'On'l'TON 010' A " LI':AF''' BEAJUNn
ANIl
Oll reI:
N()I'(q,g
(a.ORnr.l~.
divides again in a similar manner so that a row of threl' cells i!>
formed. 'Of these, the outer cdl is a shield-cdl, the middle one
~s
a handle-cell or manulif'illm and the innermost. one is n prim/lry
capitulum. The shield-cells,
a~ they
attain maturity, elllar~c
:tlHl
expand laterally so that a cavity gra(lually develops within I"Iw
THALLOPHYTA-ALGA;;
59'
globule. With the gradual developmcllt of .the cavity, the handle:
cell~ or .the manubria also elimgate radially and there is an
Primary capitulum
Manubrium.
T!'ig. 55,
0111lfll.
SIW'J'lON 'I'!!HOIJ(HT A ULDllUr,J'; KllnWJNn JlJFl'f)lU~N'I'
PAl\'L'H,
ingrowth of the pediCel-cell within the cavity, the primary capi"
tuin remaining in closc contact with OIlC another. The outer
wall of a mature shield-cell dcvc]ops radial inward projcctiol1p
STRUCTURE i\ND DEVELOI'MENT OF PI,ANT GROUl'S
60
(anticlinal walls), thus incompletely dividing the cell iuto several
compartments. Each primary capitulum divides and forms six
secondary capitula which mayor may not divide any further.
The secondary capitula cut orr cells which fol'm branchccl or unbranched filaments. These filaments may also he produced fro111
the primary or tertiary capitula. Each antheridial filament may
l~jl\1 \1 \m\;1!llr
D
B
Fig. 48.
("111m.
TIm PEDICEL wInr AN:[']umIDIAL ~~If,AMJo:N'rH ON {:AI']'{'lll,i\: B-1,;, PArt'!'
OF
AN'VHEItIIHAL ~'ILAMBN1~' BHIlWINr: ~'{'Am,!-l IN 'L'lIE ]l{WNr.nT'MI':N'I'
A,
nm
OF AN'I'HEIWZOIDH; ]1',
lITA'rrrRJol
AN'I'Hlmo:t.OJJ)R.
contain about 5-150 cells, each of which when :fully clevclopcci heCOlues an anther'idi1t1J1 whose protoplast is metamorphosed into a
biflagellate. spirally coiled antherozoid. At maturity the globuk
appears bright yellow or red in colour and the shield-cells Sepal'ale
from one another, thus expose the mature lInthcridial fil:uuc.:nts
THALLOPIIYTA-ALG}E
61
which are attached to the capitula on the halldle-c<.:lls or manubria. The liberation of anthcrozoid in the surrounding water
then takes place in the morning through a small pore in the
antheridial wall.
A cell of th<:: basal node of the globule facing towards the
main axis divides to form a row of three cells. The lowermost
cell docs not divide at all but simply enlarges and becomes the
Fig. 59,
(.'//(/1'11,
VETtTII:AI. SW::TION 'l'IlHOIJ(lH A MA'l'lJllE NU(,llLI'"
jJcd£cal-cell snppol'ting the developing Ducule,
The uppermost
cell acts as the mother cell of the oogonium, This cell elOl:gates
and divides unequally by it transverse wall into a shQrt basal celt
or stalll call and an upper elongated oogonium. TJle protoplast of:
62
STRUCTURE AND DEVlo:LOl'lI,ll;NT UF PLANT lawup:,;
the oogonium is gradually llletanlOrpbosec: into ,all uninucleate
oosphere or uvum) which becomes dl:llS<:Jy hlll:cl wuh largl: suirch
'. --Primary Pl'otoncmn
A,
Fig, 50, Uhill'll,
t;NTRY OE' ANTmaWZOIDK '!'HlUlUCllI ',rtm ANUULNn:
TilE COIIONA," B-g, tlKIlMJNNrINCl Zy(l(]'I'I~H AN])
OF YOIINIJ PLAN~r,
RI.l't'~ ,I\I~'I'
m'\l,(\\\'
J)gVJ.;r.OI',~tF;N'I'
grains prior tv fertilization, Durin!!; ("he developtnt:llt' of tbe
oogonial mother-cell thl: I1lcdi,lll cdl of the original axial row
TIIALLOI'HYTA-ALGA;
divides aml re-divides by vertical walls into five lateral ('I: !I s
surrounding a central one. These lateral cells then grow upwarcb
forming a protective covering or sheath of the oogonial mothercell. Each of theRe· cells then divides transversely so that two
ticn of five- cells each arc formed, The ccUs of the lower tier,
calleel the tube-cells, elongate spirally several times sllrrcHmding
the enlarging oogonium and bear the upper ticl' of jive cells which
mature into corona at the top of the lltH:lllc. A t maturity the cells.
of the sheath slightly separate just below the corona forming Jive
Hngular op'enings.
Fertilization l'lleD. follows in which the· free-swimming anth<:fOzoicls <:nter the nucul<: through the angular openings, one ultimately penetrates the oogonium through its gelatinif;cd wall and
finally unites with, the oVUln there. The fertilized OVllm then
HeCtetcs a thick wall and forms an oO~P()l'(:. As the oospore
matures the inner tangential walls of the tuhe-cells also thicken
forming' an additional protective' covering round it while the
unthickenccl portions of the ;;hcath become disorganised. This
oospore, SUlTOlllltlccl hy the thickened sheath, falls to the hnttom
of the pool and after a resting period of st'vLTai wl!('ks germinatl's,
During germination the zygote-llllcleliS [ravels tr}wards the
apex of the zygote and divides by reduction division into four
dill]oid nuclei. This is followed by the division oJ the zygote into
two asymmetrical cells, of which the distal one is llninuc1.eate and
the hasal, trinucleate. The distal cell is then exposed hy the nlpture of the zygot<;-wall and undergoes divisioll into two cells h)'
a vertical wall. Of these two CCUR, one hecomes the -rhizoidal illitial-cell and the other, pr()toncmal 'initial-cdl. The nuclei of tlie
hasal cell eventually clisintcgrat(', The rhizoidal-initial cell forms
a colourless rhizoid with nocks and iuternodes. From its nodes
sccolldill'Y l'hizoids may aisel develop. The protol1cl'l.lrtl initial-cell
also elongaLes and forn~s a green filamentous j)rimlfl'}, jJro[ollema
difTerentiatecl into nodes and internodes. The lower"J1lost node
of the this ptin1ary protollema lUay hear rhiz()idtll or secondary
j)l'otrmemal apjwndages. The next upper node also hears a whorl
of appendages of ,~hich all but: one arc ~il11plc g-reen filaments.
The remaining one clong-,Hcs into a typical axis of th<: new Cli.~lra
~~
.
64
STRUCTURE AND DEVELOPMENT OF PLANT GIWDl'S
In the life history of Cham the plant body represents only thegametophytic generation and the nucleus of the zygote represents
the diploid cell in the entire life cycle.
C.
PEIAEOPHYOEAE
The Phreophycere, or the brown alga::, rcpn:~('llts a group (If
marine algre having wide range of distribution and includes forms.
varying from plants of microscopic size and simple slructul"l!
to the largest alld most hig'hly dill'c]'clHiatcd bodies of macroscopic forms among the thallophytes.
Its members are characterised in having: (I) cells with dl'finite nuclei and plastids with all the photosyn thctic pigments
(chlorophyll (/, chlorophyll b, carotin and xanthophyll) and an
accessory golden hrown pigment, called !uco-xanl.ltin, which
usually masks entirely the green COlOlll' of the chlorophyll;
(2) thalli which are always multicellular and ill 111()~t cases
possessing a definite macroscopic form; and (~) ciliatt'd reproductive cells, zoospores or gametes, which are pyriform in shape
with two laterally inserted cilia of unequal length. The two
latter characters separate this group from hoth the green and
red algre.
.
\Vith the exception of two or three fresh-wilt(~l' species.
nearly all the brown algx arc marine and these fOl'Im a!Lain
their greatest development in the cool ocean waters of the
temperate and fri~id (arctic and antarctic) zones Ihan those which
are inhabitants of warm ti·opical seas (e.g. Sar,/!;assu/II, ]}ictyo til ,
etc.). Most of the marine species grow attached to rocks or
similar other objects along the shores upto a' (Jt.:pth of 50 feet
uncler the water. Some of the giant' kt:lps' (c.p; .. [,mnillaria .:tnd
and others) grow dong the Pacific coasts of America on rocks
at a depth, even beyond 60 feet, helow 1'11(' sl1l'face of water.
Others may grow as epiphytc's in associatiol1' with other algn.'
or within thcir ti~;sues as enclophytcs.
The Phreophycea: show great diversity in form and su'uclure
()f the plant body among its various fw:m])Cl's and in a great
majority of case;; possessing regular al ternation of p;el1eratiol1S
between free living multicelllllar gametophytc ancl sporophyte.
Both the generatiOlis may he identical in form and stl'tlcture,
or the sporophyte is lm:ger than the gamctophYle, or vice v('J'sa .
TlIAI.LOPI-lYTA-AU;,E
Both these gelwrations may be annual or perennial, or the
gametophyte is anllual and the sporophyte perennial. The range
of thalli varies frlm1 genus to genus, all the way beginning from
single, few-celled gametophytcs or sporophytes of microscopic
size to definite macroscopic: forms attaining a length of SO-JOO
[cct or more, withotiL having any relationship between the size
and longevity of: the plants concerned. The gallletophytc or the
sporophyte of a plant, possessing a ddinite form, is differentiated into a holclfast supporting an upright simple or branched
portion which is either solid or hollow and tubular but may
abo he spherical or compressed. Creat complexity in form is
ellcountered among the 'kdps' where the thallus is differentiated into a root·like holdfast, 11 :iilllple OJ' branched stelll
(stille) and one or more leaf-like blades.
The cell of brown alga: has a distinct cell-wall which is
differentiated ill to an innc~' firm cdlulose portion ai1d an outer
gelatinous portion made up of a pectic- compound known as
, a[g.·in '. The p]"owplas[ is vaclIolated and gCJlerally contains
a sing-lc Duch·us of normal form and slrllcture. The division of
protoplast takes place hy mitosis.
During the division,
cel1troSOl1les become evident ncar the poles and these appear
to he a constant feature in tbe dividing cells o:E the vHrioUR
memhers of the Plueophycea:. There is usually 1110re than one
plastitlH in each cdl and arc always without pyrenoicls. They
a]"(: usually flattc1led or discoid in shap'e and. may have irregular
outline. 'l'he plnsticlH, in additioll
the four photosynthetic
pigments, cOlltain. a golden brown carotinoid pigment, jllco;'((mtllin, which is supposed to he it mixture of two pigments,
fuco-x{ln{ hin a amI 11lco-xalll hin b. Food re~erves are in the
form of carhohYllrates which are found in a disHOlvecl state in
the vacuoles anel ill the cytoplasm. Of these, sugar is prest'nt
in small quantity. A dextrin-like carbohydrate (polysaccharide)
known as 'laminari?! J is always present. Another widely distri·
lJlltcd· carhohydrate is ·//lIIlll2ito/. Fat's and oils are also foune! .in
some species.
t;)
Reproduction
The llwthods o[ reproduction .in Plw~nphycere arc VC1'Y diverse
and a brief summary of the princ:ipal methods 11a8 been given
below.'
S
66
STRUCTUHE AND DEVELOPMENT 01" PLANT GROUl'S
(I) Vegetative. Many brown alga.: reproduce hy thi!; method
by the process of fragmentatioll of the youn~ or adult thallm.
Fragments of the thallus. thlls produced, may hecome detached
from the parent plant and Hoat away to form new individuals
or they remain united with one another forming an aggregarioll
of individuals. being attachecl to the su hstratlll11 by the C'OllH110U
holdfast. In some cases special reproductive branches (jJropa{!;u/a)
are formed and these arc separated from the parellt plant, ultimately developing into new individllals.
(2) Asexual. All brown alga.:, excepting the FIlCliS and a few
allied genera, reproduce asexually by the productioJl of Z()(J,\'!JCJrcs
or aplanospores. The zoospores are produced within both unilocidar (or unicellular) and plurilocular (or mlllticcllular) sporHngia
and arc always borne on the dijJloid thallus (sporophyte}. Unilocular sporangium is a true sporangium, hccallse n:dllctioll
division of the 11l1inll~lcate protoplast takes place prior to the
formation of the haploid zoospores. The llucleus ()-f the protoplast first divideR reciuctionally inro two nuclei, which suhRecillently divides and re-clivides mitotically into 32. 04 OJ' 128
nuclei. This is followed by the cleavage of the jlrotoplast forming' uninucleate masses, each of which is finally ll1t'l<llllOrp!wsed
into a biflagellate zoospore. Each !If these Z()()RJlOl'l'S, aft(,r
liberation, produces a haploid thallus (gamctophyte). Tht' ZOOS-.
pores producecl by the plurilocular spmallgiulll is diploid, each
of whicl1 on germi~ultiol1 gives rise to a diploicl thallus similar
to the thallus from which it is (lerived. These Z005Jl0\'('S arc.
thcrefore, termed neutral z()()sj)()res and the sporangium, '/I(!utral
sporangium. During the formation of neutral zoospon~~ the
uninucleate protoplast of each cdl of the pll1l'iloculm' sporangium
(lielltl',ll sporangium), without undergoing recluctioll division. iH
directly metamorphosed into a nentral zoospore with two. flagella,
Thus, hy the nelltral zoospores the ~amc generation is rc-dllpUcated, Sometimes the unilocular sporangium, instead of proclucing the zoospores, may produce 4-8 large, non-flagellated aplanosporeH.
(3) Sexual. Sexual leproduction in the brown alg<c may be
a case of (i) isqgamy i.e" by the union of two motile morphologically identical gametes, (ii) anisogamy, i.e,. hy the union of two
motile gametes of unequal size and (iii) ()ogmny, i.e. ,hy the union
THALLOPHYTA-ALGA!:
or
a motile, ciliated spermatozoid with a non-motile, non-ciliated,
passivc oospherc or ovum. Thc isn- and aniso-gametes arc
produced within multicellular gametangia which are similar in
appe1!rancc with the nentred sporangia but these are tt!rcwys producal on the gametophyte which is either homothallic or heterothallic. The zygotes, thus produced, develop into new sporoph ytes. Several members of the Pha;ophyce<e arc oogamous and
heterothallic. The male sex organ, the antheTidiunl, may be
unicellular or mtdticcllular and the cntire protoplast of each cell
is directly ll1ctamorphosecl. into a singlc antherozoid with two
flagella. The female sex organ, the oogonium, is always unicellular containing within it a single oosphere or ovum. In some
cases the ovum is extruded from the oogonium or even discharged fro111 it so that fertilization takes place outside the body
of the oogonium.
(.f) Parthenogenesis. When sexual uniOll fails- the: gametes
either degenerate or the llllSlll'Cessful gametes or (Jospheres may
devdop into pllYlhcllosjJurcs.
Ectocarpus
(Family Ectocarp(lcex)
ECIOC{lTPUS i~ a brown alga, all Hpecies of which are marine
and wielely clistnhute([ in the world. It has a life cycle in which
there is an alternation of a free-living multicellular spowphytk
generation with a free-living multicellular gametophyric generation which are identical 111 vegetative structure.
Vegetative body.
The thallus is differentiated into a prostrate, irregularly and
more or less profusely-branched portion by means of which it
remaiJ~s atttchecl to the substratum and an erect portion made
up of tufts of hr'lllchecl Hlam~~nts whose cells arc joined end. to .
end in a single series like Ulot1wix and are generally narrowed
towards the apices of the branches. In Some species the older
portions of the" main branches arc corticated by the develop"
mt;nt of a sheath. formed by the descending rhizoidal b'ranGhes.
68
STRUCTURE AND DEV1;Ull'MENT OF l'I.I\NT GHOlll':-\
The protoplast of each cell is unilludeate anlI L'lllllnins
l~ilher
Ncutrul sporangium
~Fig,
A,
51.
EMoCIUZillN,
I>. PORTION OF 'l'lIE Tnl>.LLUS 'Vl'rH UNII,OCUJ,I>.R Hl'OHANGIA; 13, '1'IlE NA.III·;
W[TU NI,UTl1i\L SPORANGIA; C, 'rIm flAME Wl'l:Ir \lO'I'n 'IlNII,O\illLAII
AND NEU'I'nAL ,~I'ORANG1A; :0, lINILOnULAR SI'OHANOIlli\[ RIlO\\'INn
DIVISION OF rl'S JoI\()TOPLAHTS .. E, A 7.nn,~I'OH.I';,
1l1~my disc-shaped chloroplasts or a few band-shaped
irregular margins.
OIlL'S
wi tIl
THALLOPlI'iTA-AT.GAC
Reproduction
EClocarpus reproduces both asexually and sexually.
(I) Asexual. The asexual reproduction takes place by the
formation of hiHagellatc zoospores formed within unilocular or
multilocular zoosporangium borne by the sporophytic plant,
usually terminally and singly on lateral branchlets.
The terminal cell of a branchlet enlarges considerably,
becomes more or less ellip80iclal in shape and forms an unilocular
sporangium. As it increases in size the number of chloropla~ts
abo increases comiclerably. The nucleus ~rst divides by reductioll division and is suhsccluently :Eollowed by several mitosis into
32-64 daughter nuclei. Then, there follows a progressive cleavage
of the (:ntirc protoplast forming several uninucleate daughter
protoplasts, each with a single chloroplast. Each daughter protoplast is finally metamorphosed into it zoospore with two laterally
inserted flagella of unequal length. The whole lllass of zoospores,
thus formed. arc extruded through a small opening at thl: apex
of the Zoospol'angiUln and begin to swim freely in water in all
directions. Each z()ospon:, after a period of activity, comes to
rest and develops into a new gametophytic plant.
The development of multicellular sporangium also takes
place from the terminal cell of a lateral branchlet. This cdl,
by repeated trall$vcrse and vertical divisions, for111s hundreds of
small cubical cells, arranged in 20-40 transverse tier~. The
protoplast: of each cell is t11(:n metamorphosed directly into .l
Hingle biflagcll:nc zoospore. These zoospores arc liberated
through a small pore, either terminal or lateral, on the wall.
Each zoospore, aher a period of activity, comes to rest and
giv(:~ rise to a sporophytic plant, i.e .., a plant of the Rame generation from which it has developed.
It is
he noted t11M the nnilocnlar sporangia are sporangial
to the formation of haploid zoospores and these are horne on the spofophytic
plaut (diploid). The lllLlltilocular sporangia hOI'll(: by the sporophyte are also diploid. The zoospores produced by these strllctun~s are diploid since there is JlO reductioll division prececding
their fOl'mation. Tn oreIer to differentiate the multilocular
sporangia from the multilocular gametangia, which are 111orphoto
in llatlll't: in wbich redllction division takes place prior
STRUCTURE AND llEVEI.Ol'MEN'l' OF PLANT (;){OUl>,R
70
logically alike hut aJ:e borne Oll the gallletophytic plant, Ihl:~t:
have been designated as ncutral sl'ow'II,!!,'ia and thl: zoo~p()n:",
Nelltl'al ZOOspores
D
Neutral S'porangium
Fig, 61.
A-F,
SUGCESSIVJ,: R'I'AGES IN 'I'lm
G, LlBEI~A'rtON
OF
]~l'Iorll1'])u",
J)EVEL()]'~n:N1'
Nlm~rRAr.
G
(H' N1W'I'IiM, HI'OllAN(:IA j
ZI1\l;;I'Ollf:";.
nCHtral zoospores, as they give rise to the ~all1c gellcratioll
(sporophyte) inste,1cl of the alternate generation (gamctophyl'c), '
THALl ,01'1 1YTA-ALG./E
(2) Sexual. Sexual reproduction takes place hy the fusion of
physiologically dilferent isogame,tes produced within multilocular
gametangia horne by the gametophytes.
.
The structun: and mOlic of development of these gametangia
arc similar to those of the neutral sporailgia borne by th\;
sporophytic: plant. Each protoplast of a g:unewngium develops
Fif!;, 53.
A, .\
g{:I(lell)'JlII.~.
r:A~IE'L'AN(lflr:\r r.IIIJo:IIA'l'INU nAMwrr-:s; B-T), HTA(IEK IN :I'HE
[iNION OF (}A~n:Tl';1; " l~, A 7.\:HO'I,'m,
into a hiflagellate gamctt:. The gametes are similar to ZO\ISpOrCs
and fusion DeemS only between the gametes from separate
gametophytic plants (hcterothallic) which are often interpreted
as sexually distinct. The diploid zygote, thus formed l1S a result'
of union of gametc~, germinates and fOl'I11R the sporophytic plant
(eUploid).
7'2
STRUCTURE AND DEVELOPMENT OF PLANT GROUl'S
Recent investigations, however, have shown that in the life
cycle of an Ectocarpus there is an alternation of a disincL haploid
generation of sexual plants bearing male and female gametes
respectively and a generation of diploid asexual plant producing
the zoospores.
(3) .Parthenogenesis. Sometimes the gametes may develop
parthcnospores which give rise to new gameropbytes.
Fucus
(Family FLtcacca:}
FuclIs, the best known brown alga, is wieldy distrihuted and
is an inhRbitant of salt w~ter along the coasts of the oceans of
the temperate ancl colder zones. J\lost of the species grow permanently attached to rocks between the high and low tick It:veh
and are often torn loose by storms and carried IUll1drt:d of miles
away into the sea.
Vegetative body.
The thallm, which is a spc;rophyte, shows the greatest complexity of form with an external differentiation comparahk til
that of a vascular plant. It has a disc-like holdfrlsl from which
arises a stem-like stipe that bears a broad leaf-like flattelled
portion, the frond. The plant as a whole is I - Z ft. long and
the leafy portion of the thallm sh()ws regular dichotnnwus
branching. As the plant grows the fronds may fork repcatl'dly.
The thalli of some species of Fuel/s (e.g. Fuclts vI'sicu/o.\·us)
contain, a little hehind the apices of the branches, air-bladdcrs
which arc formcd dill' to the accumulation of gas in large illtercellular spaces and these help the plants to keep crect when they
arc submerged under watt:['.
A cross section of' the thallllS showR that it is intcrnal1y
differentiated into two distinct tissues: (I) the central medulla
composed of loose mass of colourless dongatecl cells ancl (z) the
slllTOl)ncling cortex forming- a compact dark brown outer rq;ion
made up of more or less isorliametric cells which contain chromatophores towards the periphery. The p1'otop1ast* of vegetative
cell is vacuolated and usually contains a single nucleus having a
THALLOPHYTA-ALG,lc
nuclear membrane. nucleolus and chromarin netwurk. There
usually more than one chromatophore without pYl'elloicl,
I"i~.
,\
54,
'" /.{.I'1I8
73
.1S
'1'1',,;('''/118118,
ltA'I'{llU, '1'III1LI.IIS '''I'1'1l RWOI.LEN Jmll~ (IF Tllg IIltANI'rmg CON'l'.IlNINIl
CflNf'I';P'I'Ai'LE, TN WHWH H)'X·{)I!Il.,NS AB.E 1'I'Ill;llgl>,
Reproduction
FuclIs always reproclllces by the sexual method and the
gametic union is of an {)ogamolls type. Thoug-h a sporophyte,
it bears g-amct:ang-ia, anthericlia and oogonia, within spherical
chambers called cOllceptaclcs. At maturity the tips of the
branches become swollen in which these COllccptacies arc embedded and thes(; apIH.:al' as warty clevatiom on tlw surface even
when 'viewed without a lens, A mature ccollceptacic is globose
which' opens at the But'facc hy a small pore, the o.l'tio/e, Nu;ncrous
slender nmlticdlulnr unbranched hai1'$, called paraphyses, grow
i.J.
Sl'RUCTTJRE AND
DEVELOp~rENT
OF PLANT GROUl'S
out from the inner, surface of the cnnceptftcle and these arc
usually directed towards the ostio\c and in some species grow
out through it forming cottony tufts.
The common eastern species, FUCHS vesic'll!oslIs, is cliu:cious
(hercrothallic) since sOllle plants have cOllceptaclcs containing
only antheridia while other plants contain only oogonia. Hilt
in sOllle species the antheridia and oogonia may be produced
with ill the same conceptacle.
I"ip;. 56.
1'11"118
'I'f'N"il'ldlJ,<ll8.
PAwr OF CROSS SECTION (W THE TllALLm; 'fllltoU(al A
CON'fAININ(l ANTIIl~!mHA.
:MALl~ CONfnWJ:M'I.l~
The anthericlia, at the beginning, are ovoid cells which arc.
produced on much·branched hairs -and arc associated with the
paraphyses within the antheridial or mixed conceritacles. Each
of these ovoid cells, which is destined to develop into an :tnthl'l'i-
THALLOPHYTA-ALGA,
75
cliu1l1, is uninucleate and this nucleus divides and re-divides
until 64 nuclei are produced, the fir~t nuclear division being reductional. >I< Ultimately each nucleus, with some amount of
cytoplasm, becomes more or less pear-shaped sjJcnlw/()zoid with
Ii'ig-. 57. fl'llellH ·",,~,'i~/ll{m/l,"
PAlt'r OF I:IWHS HI',C'l'ION OF 'I'liE 'l'HALLUH '['IIIWUCH A FIlM,ILg
r:ON(,I';l'TA()Lr~ CI1N'!'AININC': onr:ONIA.
two laterally attadTl'd cilia of unequal lcnp;th and an eye spot.
At maturity the wall of the anthcridiu1l1 ruptures and the whole
mass of spennarr.zoicls with ill it escapes and arc lodged in a
cOllsiclcrahle amount of mucilage secreted hy the paraphyses for
the PllI])()Se. Th~~ FucHs plant. when cxpostd to air during low
tide, lllldcrgocs :,;hrinkagc as a result the mass of gametes. em·K· It.
is to he lIoted that Uw u(lvelopment of thu Hpel'm:ttozoid~ iR
Himill1l' to the cleveiofllnent of ZOtlSpm'llR from 1Illilo('.uial' SpoJ':lllgia Pl'O[lll('ed
nIl the Rporophytc of N~tlJr(lI''1JI{,~ and thnt in this CURll the spores jJl'ot.)lH.'Pll
lIy tllll l1I1iloenlal' ~plll'fLl1f.(ia fl1net.iol1 a.~ l(~lIlejcH.
STRuc:rURE AND DEVELOPMENT OF PLANT GROUPS
bedded in the mucilage, are extruded through the ostiole. At
high tide these arc washed off and the spcl'matozoicls arc set: free
for fertilization.
B
Paraphysis
Antbero:l!oia
Fig. 58.
A,
Fuc/I".
AN AN'l'HmRIDIAL "RANCH WITI{ AN'l'IlERIDIA; H, I,lllmtA'l'lON tn'
ANTHIlROZOIDS; C, "'lIE OOGONIUM; D, oonONIUM ~'nOM WnW'll
GROUP OF BHlHT OOHPHEltE:, Rnl,L ENcr,OHI'J) WITHIN 'l'lTg INNKI~
OOGONIAL WALl,S IS BSC!Al'TNG; E, LA'l'Im ~:rA(mH; F, OOHl'llOl:n:
(Iwn) SORROIINln:n BY NUMlmous AN'I'lnmm:Ofl)H,
THALLOPHYTA-ALGA!:
71
The oogonia arc also produced among the paraphyses within
the oogonial or mixed conceptacles. During the development of
an oogonium a short outgrowth develops from the layer of cells
forming the wall of the conceptade. This outgrowth divides
transversely into two cells, the clistal one becomes the oogoniuDl
while the basal olle iH called the sllllll cell. The oogonial cell,
densely filled with cytoplasm, iH uninucleate and as it enlarges
the nucleus divides by three successive divisions forming eight
daughter nuclei, the first division being always reductional. This
A
:Fig. 59.
A-n,
Pll"lI.~.
])IWgr.op~mN'l' OF Y()1TNlI l'f"IN'l' ["ltQM A GEItMIN1TINCl ZYGO'rl~.
is followed hy the division of the cytoplasm into eight uninuclt!(lte
masses, eaeh of which becomes rounded and forms an egg. The
oogonial wall hecomes differentiated into two relatively finn layers
Hep:ll':ltecl from each other hy a softer gelatinous layer, when the
eggs heCOll1C mature the ollter wall ruptures and the eight eggs
78
STRucrURE lIND DEVELOl'lIIENT OF PLANT CROUN;
e:;cape from the outer wall of the oogoniul11 being still en dosed
by the two inner walls, and are pushed towards ,intI lina11y
tl~rough the oSliole. These two inner layers also rupture in
succession and the eggs arc finally extruded into the sea where
fertilizatioll takes place.
The fertilization of the eggs outside the hody of the plant
is made possib~e by reason of the great Humber and motility
of the spennatozoids and alw due to characteristic smell of a
substance secreted by the egg by which the spennlltozoicls are
attracted. Each fertilised ovum then secretes a thill cellulose
\\'all around it forming a zygote and this docs not he come a
resting spore. It soon gerlllinates and grows into a new plant.
The life history. of FllCUS cloes not repres<CJ1t regular alter"
nation of generatihl1s. The plant is the sporophyte having the
douhle l1umher of chromosomes (diploid or 212). The haploid
number (i.e. '12) is found ill the gametes (spennatozoicls and ova)
and this is established during the first division of tIll: nuclei of
antheridial and oogonial cells as a result of recluction division.
The return to the diploid phase is soon acomplishecl by the ullioll
of the gametes and with the formation of zygote. which develops
into the sporophytic plant.
D.
BACILLARIOPHYCEAE
The Bacillariophyce<c, popularly known as Diatoms, constitute
a very large assemblage of unicellnlar alg1c. Owing to the colour
of their chrOlnatophores they appear to he hrown algae hut they
are usually considered as a separate and distinct group. They
arc read~ly distinguished from other alga: by the following
salicnt features: (a) the vegetative body is usually unicellular
anel alway~ non-llagellateel. being made up of a silicified wall
consisting of two overlapping halves; (Ii) the photosynthetic
reserve materials are fats and volutin 1mt never starch; (c} the
photosynthetic pigments of the chro11latophol"cs arc masked hy
the presence of a golden brown pigment known as difltomin;
(en special typc of large rejuvenescent cells (aux(Jspores) arc
formed, either directly from the vegetative protoplast or as a
result of sexual union, a feature not found in other groups of
algre.
79
THALLOlHYTA-ALGili
Occurrence and
dis~ribution
Diatoms are jnhabitanr~ of hoth I'resh and salt water, being
usually associated together in great ahundance. S()lll\; diatoms
Girdle.view
Valv~·view
o
B
Fili. 60.
A-E,
Di(lt(!1i!~.
DIWBItllWr l':lI'ElI 01' Dlol.T0:MS.
are either strictly marine or strictly fresh watcr. Both fresh.
watcr and marine diatoms may be sessile in habit or free-floating
80
STRUCTURE AND DEVELOPJ\TENT OF PLANT GROUPS
(plankton), when sessile they are ~;ltachcd 10 otber types of alg[l:
or affixed to rocks or othcl' solid inanimate ohjl'cts und.er watel'.
After the death of individual cells, the siliciJiecl wall of it
diatom remains unaltered and great numbers of these walls are
depo~ited at the bottom erE ponds, lakes or any other hoely of
water in which diatoms thrive. If the conditions are favourab]c
depositioll goes 011 unimpeded as a reslI] t aCCllllllllation may
attain conslclerable thickness. Deposits of such fossil diatoms
arc known as tiialoJHaccol!s earth which are [ound distTilmted aU
oyer the world. The industrial lIses of this diatolllaceous l'arth
arc very variee! VIZ., as a filtl'rill,l!; material, as a Stl bstallce lls(~cl
in insulation of boilers, blast furllaces., etc., as a cementing
material, ail a mild abrassivc ill metal polislH's aud toothpa~t:('s
and as an ahsorhent for Ji<juid ni1l"oglycerilw, lIlt! (·xplosive
m.aterial of the dvnamite.
Diatoms are usually unicellular and display a great divcrsity
of forms but: sometimes cells arc Huire(l t())!;l~thcr to form simple
filamentous or hrandwd colonies. Each cell of a living diatom
or its wall alone is called a fmslule, which consists oj' two over·
lapping halves or valves that fit together like a petri dish. The
outer valve is called ejJithectI and the inncr, hYj)()lheca. Each
frustule thus presents two different views, namely girdle view
and valve vicw, according to the position in which it is observed,
Both the valves of a fmstule, with their ouier walls strollgly
slicifiecl, are made up of an organic matrix chieHy consisting of
pectin, there being 110 microchemical reaction for cellulose. The
siliceolls deposit on a valVl' is not uniform but in the form of
numerous line transverse markings Of ribs amI also as slllall
protuberances anel areolx. The are()la~ lllay consist of minute
vertical pores as .incomplete canals which do not perforate the
wall completely. They are sddom perforated by minute porc~
through which l11ucilagel1cous secretion comes out. The ornnmentation is either radially symmetrical with reference 10 a
central point (Centric diatoms), or hilaterally symmetrical or
asymmetrical with respect to a long axis (Pell'l/(//I? diato'llls).
Lying internal to the cell·wall there is a thick layer of'
cytoplasm as primordial utricle surrounding a conspicuous central
vacuole and containing one or more chromat:()pIJOres, with or
'J'IIALLOPHYTA-ALGA:
.8r
withOlll nne to several pyrcl10ick There is only one spherical
to ovoid nucle1Js of the normal type embedded in the Ijcripheral
layer of cytoplasm or it is SuspL'lldecl in a mass of cytoplasm at
the ('entre of the vanwIe and is connected to the peripheral layer
hy means of broad cytoplasmic strands.,
The chromatophores arc mostly rich golden brown in colour
and vary in shape anri number from species to species. This
golden brown colour of the chromatophores is due to the presencc of a special pigmcnt: Immvn as diatomin, which masks the
pllOtosynthetic pigments, chlorophyll and the associated carotillOi(ls. Food reserves are· in the :form of fatty oil accumulated
(\s droplets of vHl'iahlt size in the cytoplasm or in the chromatophore~.
MallY planktonic lInicellular diatoms exhibit spontaneolls
l110vt:ment, either as a series of jerks directed along the long axis
of the cell or as forward and hackward progression and retrogression and these art al~(J seen in some of the colonial forms,
Reproduction
Diatoms reproduce vegetatively by cell-division, During the
process the protoplast of the mother-cell first increases in bulk
and as a result of this inCl'eas~ the two valves of the frustule
arc slightly pushed apart, This is first followed hy nuclear divi·
sion and subsequently by longitudinal cleavage of the cytoplasm
in such a manner as to form two daughter protoplasts, each
being retained wir,hin a valve. Each daughter protoplast forms
a new cell-wall on its naked side jnst fitting into the old valve.
Thus, the two valves of the frustnle arc of clifIel'cnt ages. The
daughter cells after their formation usually separate hut may
remain attached in some species. Of the two daughter cells,. thus
formed, one is obviously larger than the other and if this proGess
be repeated the daughter cells become gradually smaller and
smaller until it reaches a definite minimum sizc, when no further
cell-division occurs and the plant takes rccourse to other method
of reproduction by which the size of the original plant is regained.
This transformation of size fro111 small to large is due to th~
formation ()f a special rejuvenescent cell, called auxos,pore.
Among "Centric c1i,ltoms" auxospores are formed singly
within. ,a .vegetative cell. During the process the two halves. of a
6
8:::
STRUCTURE AND DEVELOPMENT 01' l'I,ANT GROUPS
frustule are pushed apart, the exposed protoplast swells lhrice
its original size, becomes roullded and is finally enclosed by two
new silicified halves secreted for the purpose. '1 he auxusllorcs,
thus furmed, rel1lain attachec! tu the nall uf the parent ccli for
sometime and subsequently each germinates by transVl:rse division of its protoplast forming two cells which Llsnally ltividc and
n.:-clivide in the same plane. The cells, thus formed, arc larger
than the original vegetative cell.
Among .. Pennate diaroms" <lUxospol'es are forllled as
follows:
During conjugation two gallletes produeed frolll l!ach yt'hCtar.ivc cells fuse in pail'S and form two zygot.cs (allxospores), or
a single gamete is prochlcecl from each vegetative ccll and two
such gametes fuse 10 form a zygote (<LUXll!4pore), or the two
gametes produced by a single vegetative cdl unite with each
orhe!' to form a single zygote (auxospore), Ol' the nuclells of
I'cgeralin: cdl divides to form two gallll:te nuclei which l'c-unite
to for111 a zygote (auxospol'c). or the aux[)spore may clevdop
parthcnogenetically from a single gamete.
An aux()spo)'(;, no matter how it is formcd, divid('s IOllg'jl11dinaHy to form two vegetative c<;lls.
E.
Rhodophyceae
The RhodophyceLC, or the reel alga:, are readily distingnislwcl
from other alg~c by the following salicnl characters: (a) pres('nee
of chromatophores with a red pigmcllt, jlll)'cocrythri'll, in addition
to usual photosynthetic pigments and rarely with a hlue pigment,
j)hyt'ocyallin ,; ··the· presence of phycoerythrin ill larg(' quantity
'often gh-cs the plant a distillctive red colo 111' though grecn, olive
grceh and golelen hrown reel aig,c are not uncommon; (h) total
lack of nOll-flagellated asexual spores, as in the case of Myx()phycere; (c) traI18portation of non-flagellateel male gamete to the
female sexual organ, the carj)()g;ollium, and deposition against it at
the tim'l: of sexllal reproduction: (c) indirect formation of spores
llH)Stly' takes place fro111 the zygote, but in some Gll1l'S thc zygntl:
direct! y eli vides to form spores.
Great majority of reel algre arc strictly marine hilt freshwater' species arc not UIlcornmOIl. The latter arc found in
all oceans including the arctic and antarctic oceans where the
THALLOPIIYTA-ALG~E
num:JxT of species is very few. They usually occupy the intertidal or littoral zones, but there are ROme which grow at levels
never exposed by tides. These latter species usually grow in
a~oociation with Chlotophycc,c and Ph[eophyce~e. The greatest
depth at which ,Rhodophyce~ occur has been reported to he
zoo metres. lVlajority of the marinc Rhoclophycea:~ arc normally
I'Icssile and grow upon rocks or some other inanimate Btl bstratum.
some species grow upou other Chlorophycea~, Ph;:cophycere and
Hhodophycere, either as epiphytes or as true parasites, being
lllOStly restricted to a single host. The sessile species when
become detached and free-floating soon die.
In great majority of cases there is a large single vacuole in
each (;ell and the protoplasm usually forms a thin lining layer
just internal to the cell-wall. The cell-wall is made up of cellulose anel variollS other pecrie compounds. In mObt cases a porelike opening is found ill the .wall between adjacent cells tbl'ough
which broad. cytoplasmic strands connect the twO protoplasts.
The vegetative cells are mostly uninucleate, but in some multinucleate oncs the Humber of nuclei may be upto three to four thousands in each cell. Each resting llucleus posbesses a well-dclined
nuclear membrane, a cOllspicuous llucleolus ,mel an intervening
hyaline zone. In each of the vegetative cell of primitive red
algx there is single, celltrally located, star-shaped chromatophore with a central pyrenoid without any starch sheath characteristic of the Chlorophyce~c. In more advanced spede~ they are
'disciform withour pyrenoid and usually more than one in each
cell. Carbohydrare food reHt'rvt'1' are found ill the f01'111 of small
grainB, knowll as jZoridctln st(/rch, distributed in the general
nH1HS of cytoplasm outside the chrol1'lHtophores.
The tloridean
:;tarch is an intermediate pro(luct hetwecn starch and dext.rin
ilnd when treated with indine sollition becomes light browll or
wine-reel in colout'. Uesicles a soluble sligar, /l()Tid(lside, ofwn
accumulates.
The chrol11<ltophol'es of red alg,e c011tain the same photosynthetic pigments (chlorophyll a, chlorophyll 11, carotin Hnd
.''Cuntlwphyll) but the relative proportion is' different hom that
in the higher plants. In [(cldition to these 11 water-soluble red
pigment. j>hycocrytll1'in, is always present. Besides, in some
species a blue pigment is also present and this pigment resem-
84
STRUCTURE AND DEVELOPMENT OF Pl.ANT GROTTl'R
bles the phycocyanin of Myxophycc[c. The great: diversity IrE
shapes and colours in Rhoclophycca~ is nhviollSly duc to the
variation in the component ratio of thcse pigments.
With the cxception of two genera, the thallUR of Hhodophycere is multicellular. This multicellular thallus may hc simple
branched filament made up of a row of cells or it may asslIme
a complex body ot definite macroscopic f01'111. The complex tyPt'H
usually attain a height of IO c.m. hllt may he more than it
metre in a fcw cases.
Reproduction.
(1) Vegetative. Rcd algre seldol1l reproduce vegetatively.
Vegetative rcprodnction takes place hy the fragmentation of the
thallus.
(2) Asexual. Asexual reproduction takes place hy one or
,more typcs of non-flagellated asexual spores as followfl:
(a) Neutral s/101"es.
giul11. The protoplast
phosed into a neutral
forming daughter cclls
neutl;al spores.
These spores are formed within it SPOr<lllof a vegetativc cell is directly metamorspore or it undergoes repeated division
which arc directly metamorphosed into
(b) lvlollospnres. These· are formed singly within sporangia
borne upon gal11etophytic gcneration. Sometimes these sporangia
hecoplc detached from the gametophytcH, float away and theilwalls eventually rupturc liberating the naked sporcs.
Batrachospermum
(Family Batr(lchospel'macca:)
Batrachospermum, a simpler red alga, grows gencrally in
temperate and tropical climatcs in rapidly flowing streams or in
cold springs being attached to the stoncs, pchbles 01' wood work
during spring and summcr. Sometimes it also OCCllI'S in lakes
upto a depth of SO mctres.
Vegetative body
The plant is characterised by having a thallus body of
delicate, freely-branched, filiform filamcnts varying in size from
it fcw to several inches in length,
The branches usually appcal-
THAI,LOPHYTA--ALG,E
85
as moniliform and have a gelatin()llS cOllsistency. Its colour varies
£1'0111 bluish green to olive green, but may be of violet or reddish
tint when it grows in deep water under shady places, The older
portions of the thallus are made up of large cells arranged ill <Ill
axial row bearing numerous vertical branches, which arc either
simple or divided in a forked manner, and the lateral branches <Ire
B
Fig. 68.
.A, A
Blltrad,081wrnwlTI .
l'OR~I'ION
n,
010' 'l'llB 'l'HALLUll KHOWING 'rIlE OENllltAL HAlll'L';
TIImm WHom,s ,m' nIB THALLUS ENLAucmn.
alHO repeatedly forked, The lateral branches usually occur Ul
the form of globose dUSH:rs at the nodes imparting to the plant
its characteristic beirdcd appearance ancl these may lie quite
close 01' a little distance apart from one another., Fl'()111 the
basal cell of the lateral branches threads also grow downwards
covering the external surface of the large axial r~w of cells
ultimately forming a complete cortex like a sheath. The proto-
86
STRUCTOlU'. AND DEVELilPl\U:I\:T OF PLANT (atOUI'S
pbst: of each cell is lIninudcaled ancl {,()IHains ~everal discoid
dongated Chl'Oln<ltophores, each with a pyrl'twid.*
Ill'
ReproductiOl1.
Batrac/z()Sj)('I'1I1I11I1 reprodl1ces both as('xually and sexually.
(1) Asexual. Asexual reprodllction always takt~ placl' ill the
young gametophytes by the production of lIIotlosj)()rcs proclllu:d
singly within sporangia. called lJ101ws/lorttllgi(/. Btl1: in some
species they may also develop terminally on short lateral hraudwR
of the adult plant". The t1l<:llIosporangilllll is a glo]Jose stTurture
which differs in shape from the ve~et:at:ive cell. The mOlHlf;pO]'C
is discharged from the 1ll()n()spnral1l~il1m <lS <l naked tllll{J,_·]Joid
protoplast which finally comes to rest, sec']'(!t"es a wall around it,
and directly g'ives rise to a new plant.
.(:3) Sexual. The plants arc e;a11letophVles which may 1l(,
either homothallic or hetcrothallic. The CtlJ"j)()WJ11illl1l. or lhe
female sex organ, develops terminally on a fl'w-(:elkcl short
secondary lateral hranch, called the carpo,!!:onial filament. the
cells of which have demer prornplasts and arc Wi1"llOllt chromatophores. When ready for fertilization it- has <t swollen hast'
with a prominent nucleus and it Cnl1SpiclloUR]Y prolongccl distal
portioll. the tricho,e:Ylle. The male sex organ is ("1I11ed the silcrmatangiwn which develops usually terminally on specialised ("('11.
the spermatogonial mother-cell. produced on special hrallches as
a terminal memher. Each spcrmatangiull1 is uninucleate and at
maturity it becomes j:!;lohose to somewhat clol1f.!;:ttcrl in appearance. Its protoplast, called the SjJCJ"1IUltill1H. is mually colourless
hut luay someti.mes contain a chromatnphore .. The ~pc1'1nHtillm
ultimately escapes by the rllpturc of the spcrmatangial wall.
being still enveloped hy another delicate wall whose morphological nature is doubtful.
The spcrmatia, after liheration, are carried away hv the
currents of water and arc flnallv lodged on the wall of the trichogyne. At the point of contact the imcrvelling wall~ clissolve
and the nucleus of the spermatilll11 migrates into the trichogvne
and fineTs its way into the hase of the c<1rpogoni1ll1l where fusion
takes place between it and the carpogonial 11lldcus. III some:
". For cletailR-Vide gelleral c·llfLl'arLeI'R.
THALLOPIIYTA-AL<;A,;
cases it has been ()bserved lhat the spennatial nucleus may
divide intb two nuclei during its passage iIlW the trichogyne
and of which ol1e fuses with the carpogollial nuclcils. After
fusion the basal portion (1£ t.he carpngoniwll hecomes sL'parated
from the trichogyne hy the formation of a cross wall. This is
followed hy an immediate rcrlucrion division of the zygote
Fig'. C9.
A,
JI(II ['(/(.'],0"/1(''1U//('I/I.
rHtnUp OF ANTlmltIllIA; B. ~{A'I'Ultg (.'AIU'nl\l1NrIJ~'[: EHILY
.\Nfl I.A'I'lm (1;~) H'I'A<H:S tW nONIMt)]lLAH'I'-lllwl,:r.flI'Ml·;N'I·;
MA'I'lTlm (lON1MOIILAH'I' WI'I'I1 CAlII'OBPOnANrlWM.
(C-Ilj
F.
nllckus and tWO daughter nuclei are formed, of which one
mip;rates into it lateral protrusion of the wall of the old zygote
and is ultimately ellt ofT hv the formation of a wall. The re-
88
STRUCTURE AND nEVEI.Or~l\"IENT OF PLANT (;RQUPS
maining llw:leus may divide again and repeal: the ~aml! process.
Frolll these cells a mass of filaments (gonim()blllst fila7llents) is
produced. At the distal end of each filament a spore, called
GlirpOSpore, is formed. This mass of lilaments with the termin;d
carpospol"es and the relllaim of the earpogoniul1l is callee! a
cystocarp. The nudei of the cells of these filaments and those
of the carpospores are, therefore, all haploid structures. Whell
the em-pospore matures the cell-wall hur~ts, tlll:. protoplast nnats
away, comes to rest, secretes a wall around it and germinates into
a simple filamentous plant (Chtllltransill stage) from whose
branches ultimarely adult gametophytic planrs arc ded\'ecl. It
is to be !loted that in the entin; life history the zygote only
represents the diploid f,tructurc.
Polysiphonia
(Family. IVwdomclaccn:)
Poly.I'iplumilt, the most thoroughly sntdicd red alga, is well
known and the details of its life history illustrate certain principal [eature~ of j{hoclopltyceac: i.n general. It chidly occurs in
shallow water along the coasts of the Atlantic and Pndlic oceans ;
some species lUay also gr0w as epiphytes on certain members
of the Family Fucace::c.
In the life history of Polysij)honia thel;e are plants of three
kinds: (r) maZe plant bearing spel'mat<lngia, (2) feuutle' plant
hearing carpogonia and ultimately forming cystocarp as it result
of fertilization and (3) tctras/)()ric plaut developed from carpospore
and producing' spores in groups of four caned tetraspores. Half
of the tetraspores Oil germination produce the male plallt~ and
the other half, the female plants. Thus in the lift' cyd6, the
male and female plants represent the sexual or gamctophytic
generation, while the tetrasporic plam which never produces
gametes but alw:1Ys produces tetraspores represents the asexlial
or sporophytic gcneration. These sexual and asexual plantH not
only ditler in their flluctions hut they reproduce each other in
succession showing alternation of generations.
Vegetative body
The thalli in general are small being a few to several inch('~;
in length. Each thallus is made up of several united tllanwnt~
THALLOPHYTA--ALG~E
or siphons for WhICh the narne 'Polysi/Jlumia' i~ derived. It bears
at its basal end an dongated l.I11Septatc rhizoid whose apical portion
lrig. 70.
A
IJ ol!/siplwl1ia,
l'OJ:l,'rroN O{o' nm 'l'HAf,t,UK HHOWINCl ~I'rnl GENT~ltM, HABIT.
expands to form an irregularly lobed holclfast.
Secondary
rhizoitb may also develop from the lower portion of the thallus
90
STRUCTUlU: AND DEVELOPMENT OF PLANT GROUI'S
fo]' additional anchorage of the plant.' The thallm. as it grows
in length, produces along its length in a spiral successi()ll d idlCltolllously-hranched. gradually tapering multicellular Iilalllents. tIlt:
trichoblasts, made up of a single row of cells (ulliscriate). [n
some !;pecies the older portion of the 'polysiphOllOllS' thallus may
hecome ensheathed (corticatecl) hy the formatioll of a peripheral
laver of small cells. The characteristic protoplasmic (.'onncniollS
at:c evident between the vegetative cells* of the thallus. The
uninucleate protoplast of a trichohlast-cell is usually colollrkss
or it may contain a faintly coloured chromatophore.
Repl'odtlCtion.
Sexual. Most species of Polysi/JhO'lria an' hCll·rothal1ic.
The ll~ale sex orga;1s, the spermatmrg;ia. arc produced frolll
superficial sjJcrrIUltall{!:ial 'l1wl!zcr-ccll in very dense c1nSlel'S 11 pon
the hranches of 1"he fertile lTichohlasrs situated neal' the groWill~
apex of the male thallus. A spcrmatangial mother-cell prndu('('R
2-4 spcrmatangia. each of which is a silupk. sillgle cell-SlntClln'c
producing spenllatium. At maturity th<: wall of the sperll1i1tangium I'Ilpt1Il"CS and the spermatilllll escapes as a single, walled
cell leavin).!; the I'll1pty wall of the spel'matangium attached to
the filament. It Roats in water and is finally eanicd to lhe
carpogonium.
The female ~ex organ. the c{{r,{logoni'llln, is produced upon
a greatly reduced fertile trichohlast of a female gametophyte.
The branch. bearing the' carpogonium is called the carpogonial
branch, which is a cnrved 4-ccllecl filament whose terminal n'lI
is metamorphosed into a carpogonium. Some of the adjacell1'
Ceng arc known ,IS auxilliary cr:lls. The carpogonilllll cOllHist~ of
an enlarged uninucleate basal portion and an elongated upper
portion, callcd tlw lr'iclwgvnc, with its ephemeral lluclells.
At the timc of fertilization the spermatiull1 attadlCH itself'
to the trichogyne, the intervening walls dissolve and its nucleus
migrates into the trichogync and then in to the carpogonial base
where it fuscs with the nucleus of the carpogoniul11. With the
fusion the diploid num her is established in the resulting zygIJtcnuclcus. Afler fertilizatioll, the zvgote-nuclclls migrates into rlw
auxilliary cell and divides mitotically several times so that tllet'('
arc several diploid nuclei mixed with several haploid mlclei
THALLOPHYTA--Al,GA':
')1
owing to the fusion of the adjacent uuxilliary cells.
Thesl' arc
emhedded in the cytoplasm with suf11cient amount of rescnc
materials enclosed within the comlllon wall of the carpogonial
base. Froll1 this structure numerous short multicellular filaments
(goninwbTast filaments) begin to develop into which the diploid
nuclei migrate, At the distal end of each l11a111ent a spore, called
the ["(/rj)().\·j)()rc, is formed within an IInicl'llu\ar carp()sporan~ilLm,
The carposporc evidently cOJ)tains a llucleus with dOllble !lumher
.In).!;, 71..
A,
l'()/.'I8iplwllill,
l'On'l'JON OL' 'rg'l'ltASl'OnAN(lI,\L llltANCHr,WI' ~1l0I\"iN!l
'['g'rJtASl'OItAN!lIA;
1.1, !'lMAI,I, POlt'I'ION OF IlltAN(·.l1L),;'1'
SHOWING
Sl'Ji:ltMA'j'ANOIAL
cl,ll~'mlt
AND
BIlANCJllc]l
HAr.n.R; C, ~MAI.!, POIt'l'ION 01" nH~N('ll WI'I'H YOU1Hi
pmU('AfII'; D, A!-"l'JoiJt ]o'I':lt'l'ILIZA'I'I()N ANn FOILl!A·
HMA[,L
1'fON <W AIlXIl,LIAllY CELL.
of chromosomes, Along- with the development of the carpospores, certain cells of the hapioicl filaments also grow up and
covel' the "mass of filaments heaL;ing the carpospores, This resulting enveloping ~tructure is haploid and urn-shiped containing
within it the diploid carpospores and the whole structure JR
called. the cystocar{l, When the carpospol'es attain maturity they
arc liheratecl from the cystocarp and each on germination produceR the asexual or sporophytk plant (tetrasporic plant or tetra~porophyt('). The plant, thus prodll'~'l~d .from the diploid carposporc, is therefore a diploi(l struc:turc.
. These plants arc· strictly asexual in miture and produce
sporangia on short stalk-cells derived from the central region of
the axis of the plant in COllr~e of development, Each sparan-
9::
STRUCTURE ANI) DEVELOPMENT tW I'LANT {;R(JUPC;
giUl1l is a terrasporangiuIn since its nucleus during developmellt
undergoes reductioll division forming four hnptoid nuclei arDund
which a group of fum spures, called tctm,lj>ores, is formed during
the maturation period. The tctraspores, at maturity, arc lihenw:d
by rupture of the sporangial wall. Half of the tctraspores 011
germination pruduce the male gaIllctophytcs, the nlher h:llf, the
female ga1l1etoph ytes.
II.
FUNGI
This great group of thallophywH is readily diHtingllishcd
fmm other groups by the total lack of the photosynthetic pig.
ment, ch/oro j>hyll.• resulth~g in the di~ability of m,llltlfacturing
their own food. Hence, they arc compelled to jive either as
parasites, or as ~aprophytes. But sometimes they livt: in close
association with alga~, as in the case of lichellH: sllch a mode
of life is known as sy In b'ios'is in which the assoda les dcri Vl'
Ilmtual benefit tram each other. They also live in dose association with the "oots of certain higher plants. particularly forest
trees. This combination of the fungus alld the host is knowll as
mycorrhiza. This symhiotic physiological relationship docs not
seem to be distinctly harmful to the tree. yet it is often thought
to be a mild form of parasitism. The habitats ot' fllngi are
extremely diverse. They not only occur as parasites and sapropltytes bilt are often found as epiphytes and may even he
subterranean.
"NIost fungi have a life history which consists of two phases:
(a) t1egetative phase, in which the fungns grows through the host:
or substratum and constructs its vegetative hody and (h) rejiroductive phase, in which the fungus produces spores or other
reproductive structures hy means of which it perpetuates
itself.
The vegetative body. with the exception of the unicellular
.. forms, consists of a more or less extensive, BlUch-branched, fila.
mcntous, colourless or coloured structure called the mycelium
in which is a single filament'll branch called a hyjJha (plural.
hyphx). This mycelium originates as a result of germination of
a spore, which in the simplest case is unicellular and uninucleate
and mayor may not be motile, A spore germinates, by pllshingout from any point or from a thin plac(' (germ IJore) in it~ wall,
THALLOI>IIYTA- ·FUNG!
93
in a tube-like or a filament-like process, called the germ-lube.
Rapid elongation and hranching follow and a mycelium is
formed, the growth of the hypha being restricted at the tip.
The mycelium may he He,ptate or aseptate. 'When aseptate.
the protoplasm is continuolls throughout and contains llulllerow;
minute nuclei and vacuoles within it: such a mycelium is known
as cwnocyte. The septate mycelium contains many hyphal cells,
and each cell contains uninucleate, binucleate or multinucleate
protoplast.
Among higher fungi the life cycle consbts of two
phasc~:
(a) monocaryon jlhase, in which the mycelium consists of hyphaI
cells which are regularly uninuckatc anel (b) dicaryon phase,
with binucleate cellg. In 80111e cases the nucleus of uninucleat\?
and binucleate cells divide several times so that the hyphal cells
becOlue multinucleate.
The fungal pn'toplast consists of a granular or reticulated
cytoplasm, which in older'region leaves 11 vacuole in the middle
of the cclI. The nuclells lTIay show it delicate nuclear reticulum
with one or more nuclei, its contents contracted into a dense
thl'omatin body €ulToundcd by a hyaline area. The division of
the nucleus is usually mitotic.
In some cases the cell-wall is made up of pure cellulose hut
in others little cellulose is present, the greater part of the wall
'heing a fatty acid complex with a chitin base.
Owing to the absence of the photosynthetic pigments fungi
accmllulate carbohydrate reserves as sugars and glycogen instead
of as starch. Oils and proteins are also foimd as resetvc
materials. The fungal protoplast also seCl'eteH various types of
enzymes during jts activity and these not only hdp the fungu~
to deal with reserve materials but also assist the parasitic fungi
to enter or break down the tissues of the host.
In many cases the hyph::c of the fungal mycelium grow together, inter.twine, adhere and form a thick tissue ealled plccten.
'chyma. It is of two types: (a) jJ-roso-plectenchyma or i l 1'Osenchyma, when in a tissue the single hyphal elements are l'ccognis.'
able and (b) para-plectenchyrna or pseudo-parenchyma, in which,
the hypha! individuality is entirely lost so that they appeal' more
or less isodiametric in section rescmbling a parenchyma.
9-1
STRUCTURE AND DEVI~LOI'MENT OF PLANT (';!WlII'S
\VhCll the plcctenchyma beconll'~ t1Iheriform ill appearance
with a pseudo-parenchymatic outer rind and a pmsl'llchymatic
central core, it is called sc/ero t ill 111. A sclerotium i~ a resting
boely, with abundant food reserves, which ca1'l'i('!'s the fungus over
unfavourable conditions of growrh and OIl thc return of norma]
conditions either directly clcvclops into a mycelium or givcs rise
to a fructificatioll.
Sometimes plcclcl1chyma is formed chiefly
from parallel hyph<c forming root-like strands, called rhizollUJrldls,
which under suit'lble conditions give rise to the mycclilJll1,
Reproduction
l\iost fungi rcproduce hy
methods.
\'egetalivl~,
asexual anel sexual
(I) Asexual. Asexual reprmluClioll takes place by the production of 011C or more types of asexual reproductivc bodics calkd
sp()1'es. Some of these types arc formed by the sporophyte al a
specific timc in rhe life cycles of' higher fungi (Ascolllycetes and
Ha~icliomycctes) immcdiately fllllowing reduction diviRioll of the
spore mother-cells. When formed within (endogenous) the mother
cells, they are calleel ascosp()re.l· and the mother cell, ascus
(plural, ascI); when the mother-cell produces sport's l'xteJ'nally (cxogenous), the spores are termed basidio.l'P01'c.\· and
the mother-ccli, a basidium (plural, /)(/,I'idia). Thciil' two
types of "pores actually correspond to the iipores of vascular
plants. Other types of sporcs are also formed for {[CC(,SS01'y
methods of multiplication and elo not possess allY rcbtion to a sexual proccss and do not take part in the alternation of generations, They arc purely \'egetative ill nature and
produce mycelia, idcntical Wilb, those producing them. They
arc dcvices for rapid lllcrcasc and disseminatioll of the
organisms and arc either procluced hy the sporophyte
(e.g. Rusts and a few other Hasidiolllycctes) OJ' by the gallll' tophyte (e.g. most of the Phycomycetes and Ascomycetes). S()I11(~
of the principal types of thesc accessory spores arc: (I)
chlmnydosp()res, formed by thc direct transformation of hyphal
cells Or segments of mycelium which become enlarged, thickwalled, filled with food amI act as resting spores; (2)
spol'{I11giospores, formed within cnlarged unicellular sacs, ('aIled
'I'HALLOPHYTA-F UNGf
95
splJrangia, due
to the successive cleavage of their protoplasts;
thest: spores may be either naked and amoeboid, or are provided
with cilia forming free-swimming cells Clllcl are known as Z()osjJon:s,
~illd the 8porangia. z()()spomngia. \Vhen the spores, thm formed,
hecol1le distinctly walled and non-lllotile, they are H:rmed
IljJ/mIOSj!OTt'S or 8imply sporl's; and (3) umiditl, when cut ()n' exter.
nally from the tip of a hypha, fall oil and arc disseminated by
the wind.
(2) Vegetative. Besides tbil' 111ethod of multiplicati()l1 the
fungi may reproduce vegetatively by the fragmentation of the
whole thallus or of considerable portions of it. Vegewtive
cells of some yeasts and also the ascospores aml the hasidiosporcs in s0111e higher fungi may give rise to lateral outgrowth~ ~hich cm off huds and thi~ process of cell-multiplication is known as hudding.
(3) Sexual. Sexual reproductioll in fungi is extremely
diverse when con~id('rec1 in details, hut when taken as a whole
it shows some evolutionary s('quellec.. Among lower P11ycomyn:tcs -isogalllY is represented hy the union of two Z()(}sj}()1"Clike 1ll0J'phologically identical cells. called gml1c/es, which fuse
11l pairs to form a Illotile zygot.e. l\. somewhat advanced
(ollllitioll is also noticed among Phycomycctl's where r]ll.'n'
is a Hnioll of two flagellated gall1~tes of unequal size
({llJisugamy), of which the larg(:r one is regarded as the
female cell.
The next higher step in the sexllal process,
when t:0l1sidered in t'volutionary sequl'nce, is ()()K(/my. In this
case the female gamete (o()sjJ/wre or O'lmm) is a large, nonciliarcd, nOll-motile and pa~sivc cell· and the mall' gamete
(s/JlTmatozoid or (III thcrozoid) is a small, ciliat~:d, motile and
active cdl as in a fl:W phyc()rnycew~, Besides thelie normal processes therc arc cases where variation occur. For instance, in
SOl1le AscOlnycetes the 111ale gamete is freed as naked or very
thin-walled, non-motile sperm which becomes attached to the
wall of the oogonium or a tllhc-likl: extension of the oogonium.
called tric/togyllc. Among higher Phycomycetes distilJct sperm
cc.:lb arc not produced hut only male nuclei arc introduced into
the oogonium. Sometimes fusion takes place between two
gametangia, distinguishable or nnclistinguisliablc,. whereby the
nmltinudeate protoplasts of the two eventually unite. Among
96
Sl'RUC'l'UR8 AND DEVELOl'l\IENT OF I'L,\NT GIWUPS
HasrcliomycGtes, with the exception of Rmt fungi, sex organ~ are
entirely absent but the mycelium may exist in two or IllOJ'C
sexually differentiated strains. In sllch cases, allY cdl of a pI ant
of one sexual phase may unite with any cell Ill' the plant of the
opposite sexual phase, as it result of \\'hkil a sporophylic 111'
diploid (dicaryon) mycelium is produced.
The product of union of gametes is it zyg()te, zygospore or
oospore, depending on the nature of the uniting gametes. Such
spores are known as sCil;'ual sjiores which are diploid and they aliin
take part in the ;\lternation of generations.
Clas,sification of Fungi
The fnngi arc more or less universally divided in the rour
classes as follows:
A.
Tlln
b"d,v is nSlIaIly :\'
lllycdinlll which may SIlIlIl1·
Vei-(diCt.in
f'IPII(J~ytic
1) 11 !I"fillI ill.'I~ tll8
tho/'o, J/l(.I'Or,
timr.s he "D,nnt OJ' J'ncliHl(mtnl'Y
B.
A
well-d"velolled N"1)tll/"
is always
(0,
p;"
I~tn,)
'111.111'1'7;'11'/11
)H'CRent:
(Il) Chnl'ueLcrisLic 1lllexna) Mlml'eA, thH
((.'n(J'~J!/)I'I",q,
ure f01'DlOr] "lIilo!lell(lll,q11l
wit.hiu Hp(~daliHer1 ~P01'I\
mother-erlls ('ailed
A~Cfl/ll!lMI(~,q
(lRni
1'(unYI'C,Q,
(h) Chal'acLel'istic. asexual
b(l8idio8JiO?'r~.
KI'Ol'CH,
(o.p;.
8(/1''''/1(-
RW'(J/.ill'1n, P~zi,z(l (11:",)
tlw
forme,1 ":I"!YP1lflilSly
on speein,lise(1 HIJOl'"
mother-coils knowll ilK lJ((s!'tUa .. ,
arB
H(lRitZi()1I/1I(~l'ff'8
(0.1-(,
rr,9ii·ll1(/(),
l'lI"rini((, .. j {1(ItinI/S, otc,} . '
((') Dolll aSCl)SpOrl~8 nnd lHlbil)io;<po}'OH
are not produced lmt t.ho fungi
reproduce mORt)y b~· means of
conidia,
[)//I)('I'/<>l>li (e,g.
riuIJI, IlAhm'nlll()81)(l'l'iu?Il,
PlII1Y!
A.
If''lI,~{l.
pte,)
Phycomycetes
The class Phycomycctc~ (alga-like fungi) is so called became
it resembles certain. green alg.e as regards the structure of their
filamentous veget<ltive hody and their modes of reproc!uctkm. Jt
TIIALLOPlIYTA-FUNGI
97
jnclllclL'~ ~t1('h common fungi ~s bread lUottle! (RhizojJlls), water
mould (Saj11"o/l·glli!I). "white I'Ust" of mUotards (illburgo) and the
downy
mildews
(Pcrollosj,ora).
The
lower
l110~rly
are
fOl'mt{
aquatic and may liv~~ either as paraHirl'~ 011 plants and animalH or
~;apr0l'h ytl'S OJl Sli hllwrgcd
para~it:e5
of them arc
ul')!;anic lil<ltlTials.
A great majori I y
()ll terrestrial phanerngHlllil'
phlllt~
or th(·y
live as saprophytcs on variol\S <ll'composcd Ol'gallic materials .
.Ol:hel's are ilmphihipus, occurring as parasites Oll liviug Ol'ganibllls
or as saprophvtt:s in clamp soil. Tbe vegetative body, when present, is a much-branched ClellocYlic ll1yc.·cliUIl1 hut its older portioris
may
snmerimt:s
become
ZO{)SP()J'c~
spores,
both
within
ullcdlulal'
and.
sacs
~Cpiatl~.
Asexual
sJl()rangi()~p()rcs,
known as
reproductivt:
arc
produced
sj)()rangia which arc cut
off [1'Om the tips of hyphx: Some of them may product:
conidia and gonidiospores.
gamous,
aniso!!;amous
01'
Sexual reproduction may he isouogamolls.
Besides.
among
some
higher forms union between gametangia takes place whcrehy
their undifferelltial:~~d llmltfnudeate protoplasts unite to form
a
zygote.
The
zygote,
proc!uce(:l
as
a
result
of ·scxua]
union, Tonns a thick wall and passes through a period of
rest prior to germination.
The Phycomycetes have heen hroadly divided into three main
suhdivisions. These are:
((I) Archimycetes: Characterised in having rounded or lobed
nOll-mycelial thallll8 formed ~lue 'to the enlargement of zoosporcs,
sometimes posRes~~ing rhizoicls; higher forms .may develop a
rUdimentary' myceliul11,
Exal1lplcs-Synchitrium, OljJidium, crc.
(b) Oomycetes: Characterised in having a well-developed
ccenocytic mycelium, often become sept-ate
j
characteristic mode
of sexlIal reprOdl,lctiou is oog-amy and the zygote is always an
oosjJore; accessory spores m'e mostly motile zoo~pores· formed in
7
98
STRUCTURE AND DEVELOl'!\·lENT OF PLANT GROUPS
lllOst of them.
Examples-Sapro!egn£a, PhytoplilllO},(/, PyLhilWtJ
Pcronospora, etc,
(c) Zygomycetes:
Characteri~ed
in having a wdl-dcvdopcd
l1lycelium, oft(;n becoming septate; characteristic mode of ~cx\lal
reproduction is by conjugation of two gaml'tangia whert: undifferentiated contcnts fuse to form a zygote know1\ as zygospore;
a.ccessory spores flte nOll-motile aplallOSpOI'CS, known as sjl()ran-
giospores, forlllcd
within
unicellular
~ac
called
SJ)(lfllll,pJIUH.
Examplcs--RhizojJllS, ltducor, etc.
Phytophthol'a
(Family P_l'lhillcc:r:)
The species of Phyl()jJhtlw1'a usually (lC<:lll' as parasil(~s on
lcl'rcstrial fluwering plants, Inll also live as sapl'Ophytl'S,
,
l"ip;, 72.' l'hytolJlilho1'(l injl!sl(lll.,.
LEAVI~~, OF rOTATO ::;UOW-NC} 'l'BI\MINAI, AND
MAI\GINAL INFEOTIONS OF ". LA'l'B IlLl(lll'l' ",
Of
THALLOPHYTA-FUNGI
these 8pecies, P.
and
znjest{/HS
99
causes a disease known as
Jate
blight
of the potato, the most seriolls of all potato diseases.
Tot
The aerial parts of plants, particularly the leaves, are attacked
and as a result these arc gradually killed and dried up causing
a blight, but sometimes rhe tuhers ilre alRo invaded making soft
or dry rots.
Vegetative body.
The vegetative body or the mycelium of P. infestans is a
co.!nocyre which lives tl1 the intercellular spac?s of the host-tissue.
B
.A
.l<'ig. 73.
;\-B,
It
clnlWR
Pit !/lojlhllwl'a iUjl'"IIIIIS.
oH"J'H)NH ')'IlIlOIJUH )'f)'I'A'I'D 'l'IJlIJWH A Ji'J,'ji! ''J'E!I
C I IJA'rg
BJ~lnH'L' I' RO'!'.
nourishmcnt
£1'0111
Wi'I'lJ
the adjacent living cclls by short
specialised hyphal branches. known as 11(lusto6a, which penetrate
them,
Bepl'Odllction
P. 'injestans rej)l'(l(luces both asexually and sexually.
(a) Asexual.
aerial septate
fron~
At the tilm: of asexual reproduction. slenclcr
hyplut~
come ollt through the gtomata. in gr_0ups
the intel'lull mycelium.
TheRe arc: knowll as coniclioj)hores.
The conidiophore is :ympodially hranched
and bears conidia at
the tips of its brancheR.. Each conidium is ovoid·
shaped anel. thick-walled, and has
it
or
lemon-
thin-waUed hyaline apical
100
STRUCTURE AND DEVELOPl\IENT OF PLANT GROUl'S
papi1lao It C(ll1ta]'118 rnultiuudeated and gTU, lluJated protoplasm
with several vacuoles and oil tll'0l)S aB food-reserves, At l1liltll rity
lrig, 74,
Ph ,l/lopldlwra illj,'xl(lll",
j. 'l'J!I\EE-lll~MgN,qHlNAL TlIMlRA~[ OF A PART (){' AN INFECTED U;Al!' lH'
POTATO sHowINCl 'l'UE FUNGUS 'EMgUGING THItOUrm THE H'l'OMA'I'A
AND SUCOESRIVg STA(mR IN 'j'l-m DEVgLOI'MgN'r OF CONIl>IOPHOllES
AND OONIDIA,
the conidium germinates in two ways and the type of germinatiou'
is influenced by the conditions of temperature, moisture and
substratum.
THAL;:~OPln'TA-FUNGI
WI
When the temperature condition is comparatively high and
there is less of moisture, the conidium germinates directly by.
plltting forth one or more germ-tubes which penetrate the h05t-
tiss\les through the stomat~· of the leaves or stems, or by breaking
throngh the epidermis. But, when there is exce~sivc moisture
Fig. 75. l'n.lItoplLt1wtrl.
A-C.
DIFFBItENT TYI'i;S 010' (:ONIlHA; D-E, fL, 1i~:AGWl IN 1'HB (IF.I!,MJNA'l'ION
010' A CONIIJIlTM; I<'__!.G, CONIDIA llNlt'M1NA'1'ING ANT> 'l'llmHlnJNG
HNunNDAIlY CONIDIA IN ARTH'ICIAL (ml}!'Um;.
and .the temperatUre' ~ondition is low, the collidiu,m behaves like
it Z()osj)ora'ltgium.
Its multinucleate protoplast by cleavage prt)-
cess forms biciliate zo()sjmres. At maturity the apical papilla nf
t:l~c
Zoospol'allgiul11 dissolves and the zoo~pores come out through
I()Z
STRUC'l'UHE AN» DEVEI.OPi\lENT OF PLANT l~ROUl'::-;
the terminal pore. Each zoospore aft('\' a period of aCt:lVlty
settles clown, lOlll1ds up and puts funIt a gertn-lllb,' which hrillgs
Zoosporangium
Fig. 76.
l'hlltvlJtIWrtt:.
A-E,
S'rAnES IN :emjJ GEIl]\UNA'l'LON OF' A ZOOSl?o.UANGIUM ANll
liORMNL'WN Oli ZOOBPOREA; F. A ZOOSPORE; G-,J. (llm]\[)NA'l'T()!;
OF A ZO()SPOllE 'l'0 FORM 11'WW:J'WN 'l'um:A[)S.
about infection. of the host plant as stated before. The infection
of the tubers probably takes place directly tlll'ough the lenticels.
When this fungus is grown artificially on culture media, the
THALLOl'IIY'j'A-FUNG!
mycelium often forms thick-walled chlmnytlosjH!fcs. Each chlamydospore is more or less spberical, terminal or intercalary, with
numerous oil drops as foocl-resl:rVes. On germination a chlamydospore either produces an extensive mycelium, or one or more
simple or branchc<l hyph,e on which conidia or z(lOspnrangia
an: borne.
A
I"ig. 77.
A-D,
J'llytolJ/ill,m(l,
,\ nlmMINA'l'INfl
](lNDH OF CHI,AMl'DOHPI1IU:R; E.-F,
L'ItOlIIH'INO ,\ HF(!nNllAItY cnNlIll!I~1
('HLAJ\1YnO~pf))m
HI ATtTIFlr'IAJ. {'UIJI'll.ltf:,
(b) Sexual. P. in/est'tlls is ()oganlOlls. Normally sex ()rgH~ls
do n{)t: appear to form in the host, hut: they have bccn obtain'ccI
III allUl1dance in artificial [ultU1'l'.
The sexnal 'lrgans, (/Iltheriel/llm and oogonium, are borne
at the tips of specialised hyphal hranches wh ieh when very young
10.1
STHUCTURE AND DEVELOPMENT OF .PLANT GROUl'S
callnot be readily distinguishe~l from each other.
However, the
two branches grow towards each other and the tip of the female
hranch penetrates the apex of the male branch.· The apical portion of the 111111e branch, with its densely accumulated protoplasm,
is' cut off hv the formation of one or two tl'an~verse septa forming
an antheridiulll. Meanwhile, the tip of the oogonial branch
grows through the anthericlium and comes out on its other side
forming a rounded swellillg. This is the young oogonium which
B
Fig. 78.
J'hi/lojihtl/llrtl.
"\-C,
;\'I'Al:El:\ iN !'HE DEVF.L01'Mi'NT OF AN'I'mmnHUl\1 ANn nOfH1NlllM ANIl
FOnll'[A'l'lON (lIo' ()()~l'OltE; A, OOflONIAL lNCEPT I'mnc:ICS TilE AN'l'HlmIIJIAI.
RItANC'I! ; B, BMERGl,;NC8 Of 'l'H1~ OOGONIAl, lNCBI"r AND F()JtMATION' 0.'
A YOUNG O()(;(1NHlil1; (:, A ItIl'l'~ OO:-\POHl, WI~'HIN TUB ()(I(iON!11M
Wl'l'H ~'HP; gil[l~rY AN'l'IIF,ltlTIIU,\l A'I'1'AC'lmD TO ITS llAKf"
contains gtanulawd cytoplasm anel many nuclei. The base of the'
()ogOl~illln is fUl1lH.::I-shapecl and it lies within the an theridiu m.
This type of antheri~1ium is known as mnphigYllrms. The
oogoniulll is separated from the rest of the hypha by the formation or all irregular plug at its base,
Mosi: of the nuclei of the oogonium degenerate and the
. remaining ones divide, undergo further disiutegration with the
exception of one nucleus around which cytoplasm collects and
an oosphere ts formed. A peripheral layer of cytoplasm surround·
ing the oospore is also recognisable alld is known as the pcril'laslIl.
Similarly, the aJ~thericlial nudei also divide and then all but one
disintegrate. Soon there follows the formation of' a conjugatioll
tube through which the male nucleus anel some cytopJaRl1l al:e
delivered to the oosphere. Fertilisation follows, the male and
the female nuclei fusc to form an oDSjJOrr. The oOHpore aftlT' a
IDS
THAl.LOPIIYTA--FUN(;r·
period of rest germinates and gives ri~e to a short h~rpha]. Hvstem
Oll
.wl1ich sporang:ia are horne.
Control of the disease.
The disease caused by Phytophtlwra can be dfectivdy con·
trolled by spraying or dusting with a fungicide.
A fungicide is a
-chemical substance l.'1hich is toxic to the fungi and possessing
killing or inbibiting c1Iect on the parasite without injuting or
disfiguring the host plant.
(c(~.Jlper
The sprayings of Bordeaux mixtures
sulphate. lime and. water in varying prnportions), or
dusting with
copper-lime
dust
(dehydrated copper
sulphate,
hydrated lime and calcium arsenate) have givei1 increased yields,
better control of fungi and insects and lessene(~ the physiological
defects.
Besides these, there arc other methods, such as, selection
(If healthy seeds at the time of sowing, or hy storing the tuhers
at low tcmperatureH (at or below 40" F.) which can prevent the
spread of the discaHe.
~
Mucor
(Family Mucoracc[e)
Mucor, commonly known as mould,
IS
frccillently found
as a saprophyte Oil decayed and rotten organic matter, particularly if the medium is rich in starch and sligars.
white cottony growth of mould on hOl'seclung.
It forms a
presl~l'vecl
fruits,
cheese, 1110ist leather, etc., usually clming the rainy semmn.
Vegetative body.
The vegetative hody of thc' fungus. which is a filamentous
and much-hranchcd thallus, is known as the mycelium and the
filaments of which the mycelium is ·maclc lip arc called the
hyphm. Some of these hyphtc penetrate the substratum,' serve
as
anChOl'R
therefrom.
for the superficial mycelIum and draws nourishment
The mycelium is normally non-sqnate. Hnd contains
106
:-;TRUCTURE AND .DEVEI.OPi\lENT OF PLANT GROUPS
$
alllludant granular cytoplasm, numcrous minute nuclei and small
vacuoles and is thcrefore a CIL'I![Jc),le. \Vhilc non-septate condition
is characteristic of the young, in vigorously growing myceliUlll cross
walls arc freqnently found in th~ older hyph[C and the reproductive parts arc gencrally scparat(.'d from the \'('~('tati\'c ones hy
septa.
Sporangiophore
Fig. 79.
HYCELIUM
,\Nll
illlll·ol'.
SPOHANlllOl'HOlmH llEAHINf:
HI'OnANOlI.
Reproduction.
Mucor reproduces hoth asexually and scxually,
r. Asexual. \Vhcn conditions are favourable the plant: reproduces asexually hy thc formation of s/J()rcs (or gOllidia).
During the process some aerial hyphit: hear at: 'their tips some
spherical sjJurangia (or gOl1idang'ia) and. each simple aerial branch
bearing a sporangium i~ callcel a sjJol'G11{!:io/Jhore (or gOllidangilJphol'e). The formatioll of sporangium takc~ place in the following
way:
An aerial hypha gradually elongates and after it has elongated
to a certain height, its tip hegins to enlarge into a sporangium and
into this enlargelllent a cenain amount of cytoplasm Wit'll many
THALLOPHYTA-FUNGI
nuclei and a considerable amount of reserve food flows from
the adjoining region. Then a dome-shaped area of vlKlInk" appear
within the cytoplasm tow~rds the base of the sporangial wall. This
region . of cytoplasm is knowll as the colu1flclla-jJlasm whic1-1
is surrounded by'(1 peripheral layer of micleatccl cytoplH~lll known
as spore-jJlasm. '1 he vacuoles then flatten, fuse end to end into
OnG continuous cavity around. which gradually a wall is laid dowll
~orming the so-called columeULl. Then there follows a progressive
cleavage of the sporaugial cytoplasm £roni the periphery to the
Sporeph;rsri'l
Columelloplasrn
Spore!
li'i#', ilfucol',
A-D,
HUC:CNHSIVN H'j'AWGH IN" 'j'HlD Ilb;VllI.OI'MIGN'l' 0", Sl'OllANGIUM,
COLlfMm.l.A ANll Hl'OlWH (Ml SEEN IN ,,,r.nNI1I'['UD1NAl' SEr:l'IONS),
centre and vice Vf!rsa, with the result that the cytoplasm hccoll1('s
gradually cut off into smaller and smaller polyhedral blocks eventually resulting into small mnl tinuceate or rarely uninucleate units.
These ultimate units take Oll a clefinite wall and become the spores
without any further nuclear division, "When mature the spores
arc' thin-walled and ovate in shape, hyaline or dully coloured in
mass, The wall breaks up and ultimately disappears on coming in
lOR
STRUCTURE AND DEVELOPMENT OF PLANT GROUPS
contact with water. In some species. where t:h(~ sporangia] wall is
thin, this process is rapid and if the sporangium remains untouched
in moist air it forms a conspicuous 'sjJorangial dtoj1" holding tIll:
spores in suspension. Tl~e sporallgioph(/fc o~~ los.jug turgidity then
collapses, usually brings the drop ag:/inst <j. solid surface, and it
spreads. out rapidly owing to sur£ac~ tension. Ultimately on
drying, the spore-masses remain firmly' aclhel'cnt together with
mucilage, ,which however is readily dissolved and the spot'es ~n
later
separated in water. Each spore under favourable concli-'
dons puts forth one or 1110rc germ-tubes which ultimately ramifying develops into a ilew l11ycc1h.un.
0;1
2.
Sexual: Under certain conditions, espedally when the
food supply of 'the mycdium is exhausted, the plant reproduces
sexu,tlly and the organs of sexual reproductioll arG formed. The
reproduction is isogamous which consists in the conjugatioll of
two alike gametes. Durint~ the process two dub-shaped hyphre
(progamctllngia) of different scxcs* (plus and mi11us sirains)
approach~ cOl'ue in contact end on cntl with each other and a
conjugate cell is (Jut off at the apex of each progametangiul1l by
thl' formation of a transverse wall. The two conjugating cells are
two gmnetllngia' and ,their undifferentiated protoplasmic' contents
form the gametes. The remainder of the special bl':andt hearing
'a gametangium is known 'as saspensor. The d<ii.1ble wall hei:we(~n
the gametangia is generally broken down, the two multinttdeat.ed
gametes thereupon coalesce, cytoplas'l11 with cytoplasI11 but the
nuclei fuse in pairs and a zygospore is formed. Those llucld
which do not fuse ultimately degellt.:rnte. The resulting zygospore
increases in size and forms a heavy, dark and oflcn Spilly or
otherwise roughened \Vall. After a considerable period of 1'('st the
zygospore increases in ~ize and then germinates, its outer wall
(exospore) hursts .'lnd the inner waH (endosjlore) puts forth a .long
germ-tube known as prolllYL'tJliu1n which ultimately becomes tCl'minilted by a ge1'1l1-sj)(Jmngi1l1l1. Eaeh of the spores contained.
therein, OIl being set free germinates under suitable c(;nclitiol1s,
puts forth a germ-tube which ultimately ramifying produces a
'Ill 1904 Blal{8s1ee dCBlollstru,tell tIll' pn!Sl!llC:l' of t.WfJ Hoxlildly
different Htralns in ill 11('0[' whieh he termed ,bR (+) OJ' fll)nnie and (~) 01'
lllnl~.
ZygusjlOl'e.fDl'JlUttinn is ollly possiblo lly tho uniol1 of thoHe ~W()
Koxlnlly rlil'forelli. ~I"ri).lns' of lllyceiin. Although i.hc IllYl.'oiia am llllll'l'hoiogieaily ,imilal', the ],1118 alld miilll.' sh'aills a1'O phYHiologi"ltlly diffol'ont.
THALl,OPHYTA-FUNGI
new mycelium. Jt is to bc uotcel that reduction division uf the
diploid nuclei only occur~ ill the gcrrn:sporangilll1l anc! SlllCl'
A~
"to,.,
:'):
. t~;\
(~
....}:..
.
.
"1":'
,,
,
Germ-sporangium .
A
H
Fig. 81.
Aluco)'
"il!'/lI(di.~.
A.,...H,
CON'fAL"I' In' (+) ANn ( - ) .MYClJ:LIA ANll ~'OlU{i\'l'ION 01,' PltOGAME'l'AN1HA i:
C, l'R() (l AM E'l'AN(lIA , llIV!mlTl 'ro h'ORM GA~{E'J'ANOIA AND S[JRI'I'NllORB;
0, (.'()NJUllAl'lON; g-G. FOltMA'l'WN ANn lJI,VF1L()l'MNNT OF ZYGOS"ORB; II, (:EIl~IINA'rWN 011' .zYOOf.!l'nItl~ AND F01UIA'1'LON
()I.' mmM-BI'OHANGIUM.
lvIllcor is hcterothallk, the separation of the two sexes (+ and -)
occurs probably in the fomation of sporangia, that is, the spon:s
arc all of one sex in one sproran.gilllll, ~ithel' aU + or all -.
110
,Sl'RUCTURE AND DEVELOPMENT OF l'Lt\NT GROUl'S
'"
"
.. (\"
'~
,
~.
[<'i;!; 32,
PU!lTOMICROOTlAl'Il SHOW INU
Ol!' ZYGORPOUE IN 11[111'01',
'
'
Fl)llMA'['lON
3· Parthenogen'esis: The gametes may develop without COI1jugation into a kind of spore known as (Izygosp(Jrc or parthcuosporc.
Torula state or yeast condition of Mucor.
If a portion of the mycelium of Mucur be placed in a sugar
solutioll it becomes divided hy Uilwwerst' walls into thin-walled
cells known as oidia. These cells go 01.1 huckling like the 'yeast
and can excite alcoholic fermentation in the sugar solutioJ1 producing [llcohol and carbon dioxide,
B.
Ascomycetes.
The class Ascomycetes, commonly known as "sac fungi", iuclude snch forms as the 'brewer's yeasts' (SaccJwromyces), the
black mould (A >pcrgillus niger), the blue moulds of orange:.;
(Pcl1icillillln ex-pansllln), the powdery mildews of cultivated crops
(Erysiphe), the LUp fungi ,(Pcziza), . the common edible morel
(Morchella), the ;'rgot (Claviceps) and other fungi of considerable
economic importance. A great .number of them are parasites 011
higher plants but most of the species arc saprophytes.
The Asocomycetes are characterised by the production oC
specialised asexwl! reproductive cells, knowll as ascospore,\', produced, usually eight in number, within a mother cell called an
THALLOPlIYTA-FmWI
I II
(spon: sac) which are typically club-shaped or cylindricaJ, hilt
lllay also be ,globose or pyriform in shape. The asci arc oftcn
arranged sick by side in a definite layer forming a hymeniu/Il,
hut l>l.lluetill1cs they occur singly or arc arranged irregularly so
that llO definite hymeniulll is formed. Intermingled with the
asci of a well-developed hymenium there also oCCllr sterile haploid
bninches, m;u ally· slightly extending the asci in length, known as
paraphyses. An ascus develops as (~ dicaryoJl cell in which
the nuclei fusc tlnd then divide reductionally into eight
lluclei which with some adjacellt cytoplasm arc cut off by walls
(free cell-formation) forming ascosjJores. Among the simpler
ascOInycetes, as the yeasts, the entire vegetative body (a cell) is
directly transformed into an ascus. In addition to ascospores
multiplication may also take place by means of conidia and
chlamydospores.
asclls
In most Ascomycetes the asci usually arise in groups and Jlrotected hy a common wall of hyphal tissue knowll ;u; peridi1l1n and
a definite structure thus formed is a fruqification called ascocllrj,l.
\Vhe.l1 young the a~(.;()earp is somewhat glohose in form and
remaim completely closeel. At maturity, it: dtIll:r remains as
sllch and opens ouly hy the de<.:a y or irregular splitting of the
peridiul11, or becomes flask-shaped in outline opening only hy a.
terminal pore callcel ostioZc. In some cases it opem out to form
a cup-shaped or saucer-ohapcd structure in the concavity of wh1<.:h
the asci are arranged in a hymcnium. This latter type of fructification is known as apotheciu:m. The other two forms arc
termed i>crithecittm.
The vegetative hody of Ascomy('ctc~, with the exception of
unicelllllar yeasts, consists of a mycelium which is tllU<.:h-branchc<l
and septate, and cDllt'aim unillucleate Of multilluCleate cells. The
11Iycelium usually develops within the substratum but in a few
qlse~ part .oI it may he superficial. In saprophytic forms it is
quite extensive, hut in many paraSitic 'forms tho mycelium is
localised at the region of infection. The parasitic mycelium may
be· entirely intra-cellular or it lives in the intercellular spaces of
the host tissue and frequently develops special hypha! branches
which penetrate the living cells and fUllction as ahsorbing organs
l.:a11c<l
hallstoria.
r 12
STHUCTURE AND IlEVJ\LOl']\·mNT OF PL,\NT cl{()UPS
The problem of ~;exllal rvproduniol1 in AscorllyC(·tc~ is vcry
yuria ble :ind has receivl:cl cOJ1sidcrabl~ at tCl1tioll durinp; recent:
years. In general it: may be slll11marisetl thai a gradual decline in
~exlla1ity can he traced ill the gl'OlljJ and the 1'ml\.\'(' includes from
a well-clevdnped (log-allly. in which hoth :llltheridia and OOg'Ollia
are present and functional. tTl complete suppressioll of sex O1'g~lllS.
although perhaps there alway~ remaim, a fusion '()f nuclei at a (,(Ttain stage in the life cycle. l'ep)'(','\CJHill~' th(' csseJlrials of ~l'xllal
reproduction. Tn hetween these two extn:J;ne:; there are intvrnwcliate forms in which the oog(lnia art' always present hut the
antheridia arc either ahsent or when present (:ulirclv funcrionll'ss.
The ';l'~ org"n~- may he mdnnclt'ate 0]' l11111tin\lc!t·;nc.
The Ascomycetes have heen hrnadly divided into three main
suhdivisions. They nre(a) Plectomycetes: Charactcri~ed in having dosed ascocarp~
witlwu( any definite opcning, within which the asci either arise
from the floor and stand parallel to one another. or they arc irregularly arranged; in Sf,ll11e cases a clcfinitc fructification is wanting. Examplcs-Sacclzaromyces, Eurot1'wn, Penicillium, etc.
(b) . Discomycetes: Characterised in having a well-devcl<;pccI
fruit body. an (/potheciu1Il, which lJecoll1cs more or less cup-shaped
at maturity; the asci intermingled with paraphyses stand ill
parallel series forming a hyl11eniul11 which occupies the concavity
of the cup. Examples-Peziza, Morchell(.l, etc.
(c) Pyrenomycetes: Characterised, in having; a flask-shaped
fructification, the perithecium, opening at the top by an' ostio\e
and containing -.vithin it asci in parallel series. EXa1nple~­
C[(lvicej)s, Xylaria, etc.
Saccharomyces (Yeasts)
(Fmnily Saccharomycetacex)
Saccharomyces or yeasts are mostly saprophytes which arc·
They ar~ commonly found on such media as fruits, llectaries of flowers, exudates
of plant-tissues containing sugar, soih of vineyards, etc. Some
arc distinctly parasitic on plants and animals including mnn.
Some Saccliaromyces arc of economic importance and arc largely
used in various industries involving fel·mentation.
widely distributed on suhstrata containing sugar.
THALLOPI-IYTA-FUNGI
113
Vegetative body
The body of yeast plant is mostly unicellular, but at the time
of vegetative reproduction several cells arc founel to remain united
with onc another forming colonies. Certain ~pecieR under special
conditions of nlltritiolls may forlll
distinct mycelium which is very
umtahle, hecause with slight alter a- !ion in the composition of the
medium it hreaks up into small
cells.
Cell structure:
Each ccll is
rounded or elliptic in form C011si8ti11"_'
of it delicate cell-wall and Volutin granules
h
containing within it granulated alld
84. AN ygAST men
vacuolated protoplast with a single
((lfll'l" jJ'''!lrr).
nucleus. The chemical nature of
the cell,waU ,is obscure. It is neither made lip of c!tllul()~e
nor of chitin. 1 he nucleus is Dot of the normal type but
of a degenerated one, hecame the nudcolns is fOllnd at the
periphery 'of a hil~ central vacuole con willing within it the nuclear
reticulum only. Hence, the vacuole is not all ordinary sap-vacuole
hut: lluclear-vaCilolc. Food-reserves in the form of glycogen, drop- .
~ctR .of oil .and refractive granuleg of: volutin are distrihuted in the
cytoplasm.
Reproduction
Yeast i'cprodllces hy vegetative. ascxual ,wet sexual metbode .
. 'r. Vegetative: Vegetative
iissi(;n or by hudding.
reproduction
takes
place
hy
(a) Fission-This process is well-illustrated by Schizosacclwro1nycl!s octospOrtls. In this case the vegetativc~ multiplication
takes place by cell-division. The nucleus of the mother cell first
divides by karyokinesis (mitosis) into two daughter nuclei and is
followed hy the division O[ the cytopla\\lU (cytokine,is), thus formtwo daughter cells nearly oE equal size. Afrcr a time, these two
daughter cdls separate {rom each other hy splitting oJ the commOll
wall.
(b) Buclding.-Common bll(lcling. yeasts arc Saccharomyces
(40 spp.) and ZygoStlccha.rom)lCcs. At the time of hudding a small.
S
STHUCTURE AND DEVELO!'ivIENT OF PLANT (alOUI'S
outgrowth, a bud is formed at one pole of the mother cell. Till'
divides by amitosis into two daughter nuclei. One
daughter nucleus \;/ith wme amount of cytoplasm migrates into
the bud. Gradual constriction (If the plasma l11el1l hrane at the
point of odgiD of the hud brings about the clivi~i()n into two
Buclcn~
a
b
c
r'·if(. 85.
e
d
811""'/(11'111111/1'1','.
SI)CCg~~[\-g STAla:H IN UUIl]lINO ,INI) j.'I)It~r.\TJ<)N (IF
HAUGH'['lm CELLs.
daughter celis of 1111e(1ll(11 size. The small cell SOOll ('nlarg('s and
it is detached from thl' IJHlther cclI. III
such cases the daughter cells of sllC(:e~sivc diviAions remaili
attached with one another for sOllletime hefore sl'paration.
hud~ ill its turn before
2. Asexual:
Under suitable conclitiom the cell-contents may
round themselves up and form 1"8 endosllores, known itH ascospores and the mother cell i~ callcel an ascus. These spores arc"
eventually liberatl'd by tht' rnpture of
of tbe ascll~-wall Hnd ullder suitable
conditions reproduce by the process of
hudding. Until recently it was thought
tlltt the majority of the ~pt:des. of
Saccll(JT(nnyccs have this type of reproduction (parthenogullcsis).
[t is also
a
b found in Zygosacc/lilromyct's,
Fig. 86.
Sal'r!t a 1'0111./1"1'.,.
a, [.'( .(; "rATION OF ASCnHI'OIlIJH ;
GEHM!NA'I'WN OF AN AH('n~J>OItE A.ND FOlurATIOl, OF NEW
b,
1.
'.
Sexual:
::leXlial
repro([UC(lOll
was formerly thought to he found only
in it few cases as in Schizosaccharo'/TEyces' odosportts. In this case there is conjugation between two
vegetative cells. Each of the two conjugating cells produces a
short protuberance and two such protuberance!; ultimately uuite
to form a conjugation tube. The two nuclei of the two conjugatiu;s
.
I'LANTH BY nUllllINU,
THALLOPHYTA-FUNGI
cells migrate into tll(; conjugation tuhe, with each other and
1'orm a diploid nucleus. The conjugation tube then grac1uall;'
broadens and ultimately forms a more or les& (hul1hd-shapcd
zygote containing the diploid nucleuB. Then, there follows three
succt:ssive divisiollS forming eight haploid daughtcr nuclei, the first
division being reduction division. About each of these nuclei eight
A
B
o
c
E
G
F
AiCU.
J
Ascospor."
K
Fig. 87.-Sclt iZ,WIC,·l!(/I'('IIl!/I'f'''.
H~J[)C'E~HIVB H'1'AI\@ ()I,' {'ONJllUA'!'WN .. l--K., H'rA<HlH
HHOWING TIm ~'On~IA'!'!oN OF AKeITH WITH AHI 'OHPnn':H,
A--H,
aSC()SjJOre.I'
arc delimited within the mother cell (zygote) called the
ascus; At maturity Ithe ascus-wall
hurst~,
the aScospOl'es arc
liberated and these under favourable conditions nntltiply by
fissioll.
It has already been pointed out that lllost of the species uf
Srtcdlaromyces llntil receutly were thought to be wholly parthenogenetic, but recent researches of Dr. Winge (193.1) have shown
that: it is not so.
Sexual reproduction oct:urs in the genus
Sacclwrolnyces and he has been able to demonstrate conjugation
ht:twet:n the ascospores and also between the vegetative cells, as
given below, which will clearly indicate that there is a definite
al t(Tnatioll of generations in the life cycle.
I
r6
STRUCT[JRE AND DEVELOPI\IENT OF PLANT (;JWUl'S
Alcoholic fermentation
When yeasts grow in sugar solution alcoholic fermentation is
set up, sllgar is decomposed by an enzyme (zymilse) inlo ak{)hol
and carbon dioxide, The gas is given off in stJ'(:allls of hu hhks
LlFE-HlSTORY
Reduction
Vegetative nell ----7- AsctlS
(2X)
Aacospores
(X)
Division
(2X)
t
J.
Vegetative rsprod uction
(by budding) of the
cell-zygote
GermInatlOll of
ascospOfOS (by
budd.ing)
(2X)
(X)
t
Sexual
{----- Conjllgl1ticm l)etwaen
Union
2 such vegetative
(lells
(X+X)
Ccll'7.ygotc
(2X)
+--
+
Vegetative cells
(X)
A
Vegetative cell
Reduction
- 7 ABCUS
(JlX)
---40
(flX)
Di'uision
vegetatlV! reproduction
(by budding) of ~ Spore,zygote
tbe spore·zygote
(2X)
(JlX)
Asaospores
(. K)
~
Sexual Conjugo.tion bet W Qelt
+-- 2 suoh aSCOSpores
Union
(X+X)
B
Fi!-,;, 88.
Sr:rlE:~rATl<: gm'ItBKEN'I'ATInN (A
81l(:r:/11I /'(1/1/ ,/(,(,N
Sl!()\\'lNf:
& [~)
Ar.'I'EIlNA1'ION'
or 'I'IIN 1.11'1<: CYC'Lg~ (ll"
(II'
UlCNlmA'I'WNH,
forming froth, while the alcohol remains in the solutioll, ff the
supply of oxygen be in excess, very little alcohol is 1'orllll'd, but
when the supply of oxygen is least more alcohol is formed. The
chemical change can be represented as follows:
C,JI 12 0(l
=
2C~HIiOI-I'I-2CO"
TH,\LLOPHYTA-FUNGI
Eurotium
(Family AS/lcrgillace;:e).
l\IosL of the species of Eurotium arc saprophytes and
on a wide variety of organic substrata.
parasites and
A
few
OCCllr
species
arc
cause diseases of the skin, car and respiratory
organs of higher anim.als including mall.
They are commonly
found as filamentous mouldy growth on the surf<lce of clamp
fruits and vegetables, preserved fruits, moist breads, jams and
various conserves, and also on imperfectly dried herbarium speci"
Many species are commercially important on account of
mens.
their hydrolysing powers on starch and sugars and cause fermentation to citric and oxalic acids and rarely to alcohol.
The generic name Aspergillus was given to the conidial stage
or
the fungus long before its aseospores were found and this
name
~till
survives in the name of the f<llllily.
Vegetative body.
The vegetative budy is a much-hranched mycelium consist·
ing of usually colourless, septate hyphre.
It ramifies in or on
the sllrface of the bubstratUl11, or through the intercellular spaces
of the host-tissue.
Each hyphal cell contains granulatecl, vacuo-
hued and llluitinucleawd protoplasm with oil globules as fooel·
reserves.
Reproduction.
Eurot:iu11Z reproduces both asexually and sexually.
(n) Asexual.
During
asexual
reproduction
numerOllS
!;traight, thick-walled, aseptate and upright hyphre shoot up in
the air.
These arc called Gunidiophorcs.
The free end of each
conidiophore swellH up and usually becomes spherical. This
vesicle buds out a large number of peg-like outgrowths, called
sterigmata. From the tip of eacb sterigma spherical or nearly
sphcrical, smooth or roughened conidia arc pinched olT in basipetal
~ 18
STRUCTURE AND nEVELOPlVIENT OF PLANT GROUPS
succession. The cytoplasm and nuclei stream up the conidiophore into the sterigmata and finally to the developing conidia.
The number of nuclei in each conidium is variable and it varies
Conidia in chains
A
B
Vesicle
Conidiophore
c
Fig, a9, Nllltlfill/ll (.1.~jJel'(lillIl8 stago),
A-D, ~(1COFJS,~In; S'l'AGEH IN '{'I{1C DEVELOPlIrJ;N'1' (W CONIIltOl'1I0itE
1'ORMATION Ill" FIRST CONIDIA ON S'{'EIlH1MNI'A; l~, A CtlNIllIOl'llOTlI;
WITH S'{'EHWlIfA'I'A llEAllING CONIIlIA rN f~HArNi; (NEC'J'LO NAI{),
ANn
THALLOPHYTA-FUNGI
119
from species to species. Usually, it is multinucleate, but
III
some
rare cases there may be one nucleus in each conidium. '1 he
conidia, as they are formed. are not separated from one another.
for the time being, but they remain in rows or chains on the
sterigmata till they become ripe.
They are produced in enor-
mous quantity :mu at maturity lwcol1lt'. deciduous and arc
readily carried away by the wind.
Each conidium under favour-
able conditions germinates on a suitable substratum and produces
a mycelium directly. It has already been stated that it is
to
this conidial stage of the fungus, the generic name Aspergillus
was g'iven.
(b) Sexual.
Sexual reproduction of Eurotium will he des-
cribed for the best known species E. hcrbarioru1ll (=Asjlcrgilllls
hcrbariorum).
In the species the sallle mycelium, producing the
conidia. eventually hears the sexual organs.
The fr;male hranch, or the arcliic{wp, is a specialised hypha
which becomes coiled, at first loosely but later on very closely,
in a helix. This archicarp. at first one-celled. is soon divided
into several multinucleate cells. At this stage it becomes differentiated into three portions:
oogonium and
the
it
11
multicellular stalll, an unicellular
terminal unicellular trichogYl1e. It differs from
fetnale sex otgam with which we have already become
familiar in that it reprcsents Duly
11
Illultinucleated segment of
a narrow hypha and its protoplasm is not rounded off to form
an ovum,
After t.he diITerentiatioll of the archicnrp there appears
mlOthel' sept<lI'C hypha from the tip of which the unicellular.
111111tinuclea Ie au tlwl'idiu'Ill. is ell t ofL The allthericliU11l develops
either independently of the nrehicarp on
formed on two
I'he archicarp,
01'
another hyph or
three slender bl'anciteH aI'iRing fron1 beneath
Afw]' its formation. the anthcridi.l1l1l appears t:o
120
STRUCTURE AND DEVELOl'lVIENT OF PLANT GIWUl'S
clirnb Up the side of the coiled archicarp. The lIni.on between
the artheridium :md the a1'c11ica1'p hag not heen observed in any
c
Fig.
"\-F,
90.
A8j"'I'[fillu"
7/1'I'!wl'iol'lIlIl.
H!lt'I.'E~SIVg H'J'Amm IN 'l'Im IlEV1~H)l'~mN'1' In' A l'lml'l'lIEI'111~1
(=I:I.]U" '1'O '['Ill, ('lll~l);
Iiltnul' IW YOUNI: AHI'I;
H, A MA'!'rlltE A~G()H \\,ITll AHL'OHI'OlW:;.
n,
case and possibly cIoes not take place. The anthcriclium appears
to be rudimentary and its nuclei llRually degenerate hefore it:
attains the full size. The growth of the anthericliull1 may e\'e1\
he checked, or the an thcl'icliul11 may not dcvelop it l all.
However, the oogonium soon becomes septate alld forms
binucleate cells. From these binucleate cells small olltgrowtb~
THALLOPHYTA-FUNGI
J21
cleYl~l()p
which grow and form branched hyph,e, called ascogcllolls
hyphx.
From the terminal or sub-terminal cell of an ascogcnolls
hypha an ascus develops.
When young each ascus is binucleate.
The two nuclei fuse to form a deflnitive nucleus.
It undergoes
three karyokinetic divisions ill which reduction in chromosomelllllllber takes place forming eight daughter nuclei arollnd which
asc(}sj)ores arc delimited by the process of free cell-formation.
The cytoplasm which is not used up in the formation of ascospores constitutes the cpipZasm containing fnoel. substances especially glycogen.
Each
ascospore
has
sculptured
a
spore-wall
(cpispore) and is of characteristic form and when seen laterally
somewhat
r~semhles
a pulley wheel or butcher's tray.
A little lJcfore the septatioll of the oogonium some vegetative hyphrc grow lip and Cover the
~exllal
organs. These hyphrc
hy interweaving and septation form a thick outer wall of smallcelled, pseudo-parenchyma which cOll1pletely enclose
organs.
the sex
Some of the hyplJ<e grow inwards and form a nutritive
tissue ahout the
~eX
organs. The entire structure, thus formed,
is the frm:tification of EIITotiu1n
<l.1lCl
is termed periLhccium.
The wall of the perithccium becomes invested with
sllhstance.
it
hrittlc yellow
At maturity the ascoge]10llS byph1e, th(' cells of the
nutritive tissue and the walls of the asci disintegrate and are
llltimatcly ahsorbed so that the ascospores lie free within the
Ollll'f
hrittle pseudo-parenchymatous sheath of the pedtheciu11l.
III
This wall finally (kcays and the ascospores arc Het free.
Each
ascospore under favourable conditions germinates on a witable
suhstratulll and J)]'oduces the myceliulll.
Peziza.
(Family Pcziz{{ccw)
;\lost species of Pcziz({ arc saprophytic on
wood or on clung.
~rolllld, 011
dead
122
STRUCTURE AND lJlcVEI.OPlI.!ENT OF PLANT GROUPS
Vegetative body.
The mycelium generally grows in soils rich in organic IlHltter,
or
ll1
decaying wood. Th!.: mycelial filaments arc divided by
septa into multinucleate cells and the branching
Fig. 91.
A
FBW F'nrnT-ll!)IlJEH
<)I,'
PI'Z.;'"
OJU)lI'lNCl
ON
IS
extensive.
(lUfllJNI>.
Reproduction.
At the time of reproduction there arises from the mycelium
a conspicuous fruit-hocly known as the af)()thechl'1n. Usually the
apothecium is a iIcshy, fwssile or sub-sessile cup or a saucer-shaped
body, regular in ~()rnil, often hrightly coloured,
diameter and without any hair.
apothccium
shows
that
the
:2
to 40 C.rn. in
A vertical section through the
upper
surface
constitutes
the
hymenium, a layer of elongated cells standing at right angles
to the surface like a palisade.
It consists of asci intermingled
with ~upporting and protective filamen'to\ls hyphre, the f)araph yscs.
Immediately below the hymcnium is a layer, thin
OJ"
fairly thick,
the hypolhecium, consisting mainly of light·coloured hyph,(' and
THALLOPI-IYTA-I'UNGI
running parallel to the surface of the hymenium. The basal
portion of the cup is known as the excipulum.
:Fig. 92.
VlmTlCA]',
HgC"I'IflN
1'/!:izfI.
'l'IlHO!Jfm TIn;
Al'O'I'IlU'1 f) ,II.
Development of asci: In several opecies of Pez'iza so far
investigated, the development of asci. takes place without the
o
"
A
B
C
D
Fig. 93.
S UC:<;ESSIVE
RTAm,s OF
E
l'r.ziZfl.
DEVEr...Ol'.MI~N'l\
F
G
OE'
ASCUS.
U-J-
STRUCTURE AND DEVEI_OPl\IENT OF PLANT GROUPS
formation of sex organs. The asei arise as sub-terminal cells
of special hyph~c, called the (/scogcnotls hyp/u:c, and these cOl1Rist
of hinucleate cells. In 1894 Dangcard £0 II lKi that in Pcziz{l
'vesiculosa the terminal cell of the ascogenous hypha elongates
and l1eIllIs over forming a crozier, its two nuclei divide simultalleoLisly, the curved suh-terminal segmcllt of the branch retaining one daughter nuclells of each division, while the other arc
cut off by transverse walls, one in the terminal ccII or tip, the
other in the hasal region or stalk below the curve. The sub-
Fig. 94.
PAll/.l~ OF A ~l.;r:'l'lON '.l'HllOUllH 'l'llJD H~MENIITl\r ~HowrNCl AS!"']
\\'l'l'll
AH('O~I'OlH:s
ANll
l'~ ltAPHYSg~.
terminal cell then dongates, its two nuclei fuse anel this cell
becomes an aSCllS. The fusion-nucleus of each aSCllS then um]t:rgoes three successive divisons forming eigh t nuclei. One of these
diviAions is a reduction division. Each of thc eight nuclei with
a considerahle amount of surrounding cytoplasm then cuts out
af; a spore. Usually a certain am.ount of cytoplasm is left out
in the ascus after the spores are CII tout; this is known as
THALLOPHYTA-FUNGI
I~
-,)
ej)iplasm whit:h is rich in food substance and glycogen. The
fully formed spores are oval, unicellular and hyaline. Whell the
spores become mature, each ascus opens explosively by a lid
and the spores are shot out in a jet of liquid. Each spore under
favourable conditions germinates and forms a new myccliurn.
C.
BASIDIOMYCETES
The class Basidiomycetes includes such forms as the lllushrooms, toadstools, bracket fungi and their alli~s (HymcIUJIIlYcetales), the puff halls, hire1's nest fungi and their allies (Gasteromycetales), the smuts (Ustilaginales) and the rusts (Uredillfllc~s).
The smut and rust fungi are obligate parasites on higher plants
for at least a portion of their life cycle, while others are usually
saprop h ytic.
Tbe Basidiomycetes is a heterogel\ous group but all the
memhers are characterised by the production of specialised
asexna[ reproductive units called the basidiospores, which arc
produced l!xternally on a mother-cell called the basidium. fll
most cases the basidium develops directly hy the elongation of
the terminal cell of a clicaryol1 hypha (as ill Agaricus) but it
may also develop as a result of germination of a specialised
hinucleate spore called Ic{1'osjJore (as in smu ts and rusts). Usually
the basidia are cluh-shaped and unicellular hut they vary COllsiderably in structure, some being transversdy 4-celled while
others arc longitudinally 4-cellecl. The hasidia are mostly arranged siele' hy siele in a palisade-like I ayc]' forming the hyme'llill 111.
which may cithcr he cxpo\\ccl to thl~ external atlTlosphcrc, eit\1C1"
directly or inelin'cdy (e.g. Hymenomycetes), or may form the
lining of completdy closed chambers (e.g. GllsLcromycclcs). The
hymenia are produced UpOll or within fructifications, which
usually attain grear complexity in structure, form and size.
These are the familiar structures which arc ordinarily referred
to as 'the fun~lls' hut arc in reality fruit-bodies only, the vep;etalive body or the mycelium proc\ncing these fructifi.cations
remaining hidden withill the substratum. The basicliospores are
typically horne Oil horn-like projections, tile sterigmata, deve·
loped usually from the top of the basidium. The spores produced hom the basidium an~ generally 4 ill llumber, but sometimes may be 2, 6 or more. A basidiospore is always unicellular
126
sTll.UCTURE . AND DEVELOPMENT OF PLANT GROUPS
and uninucleate, thin-walled or thick-walled, and may he hyalille
or colourcd. Besides basicliospores, conidia and chlarnyclospores
arc formed in some "pedes but they play minor part in reproduction.
The basidiospore on germination usually produces an extellsive. much-branched, septate mycelium which may hI,; primary
(monucaryon) or secondary (dicaryon). The primary mycelium
consists of uninucleate hyphal cells and represents the Iwploj,hnse, whereas t'he secondary mycdimD with tUllstantly binucleate cells represents the diploplwsc in the entire life cycle,
The diplophase ('nds with the basidial development and the
formation of basidiospores marks the l)l~gillning of the haplophasc,
These two phases arc eithcr rcpresented ill ditTerent mycelia or
combined in the same mycelium,
There is ncver any development of typical ~cx organs in
Basidiomycetes, but never thc less a change ill the nuclear COll"
clition from the haplophasc to the diplophase takes place in the
life cycle, as stated beforc, and the mycelium may exist in two
or 1110re sexually different strains. In such cases any cell of a
mycelium of onc sexual phase may unitc with any cell of the
mycelium of opposite sexual phase as it result of which a sporophytic or diplophasic (dical'yon) mycelium is produced.
The Basidiomycetes have been classified into three main
suh-divisions, as follows:
(fl) Hemibasidiomycetes:
Characterised by the faq that
more than 4 basicliospores ale produced on the basidium whicl~
is either aseptate or divided transvcrsely into 4 cells. It includes
such obligate parasites on the higher plants as thc smut~ or
bunts (U stilagirLales).
(h) Protobasidiomycetes:
Characterised by the production
of regularly septate (transverse, longitudinal or oblique) basidium
which always bears a definite numbcr of basidiospol'cS, usually 4It includes such obligate parasites as the rusts (Uredinales) and
saprophytic gelatinolls fungi (Aw-iclllrwiales and Tremel/ales).
(e) Autobasidiomycetes: Characterised in
lar basidium which produces a definite number
usually 4 but lUay be 2, 6 or more; basidia arc
in a hymenium which may either be cxpoRcd
having unicellu.
of basidiosporcs,
always arranged
to the external
THALLOPIIYTA-FUN(:I
atmusphere either directly or indirectly (Hymenumycetes), or
may form the lining of completely closed chambers (Gasteromycetes). It includes such common forms of fungi as mush-
rooms, toadstools, bracket fungi, puff balls, birers nest fungi,
btink-horns, etc.
UstUago
(Family U stilaginace<e)
The species of Ustilago, commonly knowll as
i.
smut fungi,'
bdong to a group of obligate parasitic basidiomycetes which arc
n.:spomible for the diseases known as "smut'·· diseases. They an:
so called
bCcaUSl!
of their black soot-like spore-masses formed
externally on the host plant. The spores are known as smut
sj>ores (also chlamydosporcs, brand spores, resting sj)orcs or
teleut.ospres).
A mature chlamydospore contains single diploid
nucleus and js surrounded by a thin endospore and a thick,
smooth or sculptured exospore. Smut spores, as they arc formed,
(:itlu:r separate as individual units, or
~n
some cases remain in
compacted aggregations of several spores, each termed siwre
bal/s.
At maturity .these smut spore-masses
e~ther
break up into
fine dust-like powder and arc readily carried away by the wind
(loose smut), or they remain finn, compacted together and more
or less covered (covered or hemel smut).
Smut fungi arc of considerahle economic importance, Sll1ce
they attack
111.08t
of
Olll'
cultivated cereals and a few wild and
cultivated grasses. The most affected par.ts of plants are the
grains or tbe entire inflorescences, thus reducing the yield of the
cereal grains by 25 to 50%. Most species of Ustihlgo grow
parasitically upon a selective host species.
Smuts of our cultivated crops may be grouped into three
kinds on the basis of the time of germination of the smut spores
128
STRUCTURE AND DEVELOPMENT OF PLANT GROUPS
and also or the type of infection as follows: (a) shoot infectiuJl
or general -infection type e.g. corn smut (U stilago may dis = Ustilrtgo zea:), (b) bloss()m infection lyjJe c.g., loose smut of wheat
"
A
Fig. 96.
B
S:-llJ'l'TEI) lNFLOltmlCllNCE OF WHlc,\'l'
c
(A-B),
D
AND OF OAT
(C-D) ..
A-B, U,,'li7(l!lo tl';ti"i; C-D [l.~lill1l1() (/l'l"II(r'~
(U. trili~i)"ari(l (c) seedl·ing infection tyjJC c.g. loose smut of (Jats:
(U. aVe'/ue)'.
TIIAJ_LOPHYTA-FUNGI
12 9
(Jorn smut (U. Hlaydis=U. zex).
The corn smut infects the corn plant during its growing
period. Usually The ears and the tassels of the corn plant arc
attacked, but sometimes variolls other aerial parts, such as stems,
leaves or aerial roots, arc also infected. The infection is localised
and docs not pervade the whole system o.f the plant. The chiamydospores, formed during the last growing season of the host
plant, usually lie dormant on the dried stems, in the soil or in
c
B
A
Fig. 97.
Usl j"'!I(}
D
ZI''''.
OERMINA'!'INC! l'IlL!l.MYIln~I'OIIT';S SHOWING 'l'III~ "TArlE!; rN'
THE ~'OllMA'l'ION IW HAHIIlIA AND 'l'I'm I'JtOll11CnON 01' CONIDIA
BY TilE II{)])))ING OF ']'m: Di\HlproHl'OREH.
A-E, ,
other favourable places. With the advent of the spring or the
following ~lImmer they germinate in abundance. Each chlamydospore containing a diploid nucleus on germination produces
it small tubular outgrowth called the epibasidiwn.
Its nucleus.
divides reductiol1::Jlly into tour haploid nuclei all of. which either
remain within the elongated epibasidium or only three of them
mi):!;rate into the epibasidium and the other remains within its
9
130
STRUCTURE AND DEVELOPMENT OF PLANT GROUPS
old spore wall. The epibasicliull1 is then divided by tranRVertie
walls into four uninucleate cells. The llucleus of each cell
divides into two daughter nuclei, of which une migrates into a
hasidiospore which buds of[ from any point on the celi wall and
the other remains within the mother-ccll. This process may he
repeated so that a few more basicliospores lllay be produced from
a sipgle cell. Corn smut is hcterothallic and Oll t
four cclls
formed in the epibasiclium, two cells contain nuclei of one sex
and the other two of opposite sex. Thus, the basicliospores
derived from these cells arc of two sexes. Each basidiospore
before or after detachment from the epibasidiul11 may sometimes bud otI cunidia of the same sex.
The basicliosporcs OJ' conidia an: Ctissetninatecl by the wil1l1
and when they reach (he cor11 plant hring- ahom infectioll.
Typical infectioll is only possi hIe if the host plant is infected
with the basicliospol'es OJ' the conidia of hoth S<':Xt'S. A hasidiospore or conidium germinates on any part of the host plant and
sends out a germ tube which soon penetrates the epidermis of
the host, enters rhe intercellular spaces and grows more or less
horiz()ntally formillg a haplophasic (monocaryon) l1lyceliulll of a
few uninucleate ('clls. Soon unioll follows between cd Is of two
haplophasic mycelia uf opposite s(·xes. Tn some cases this union
may take place carly, just after the pellettatioll of the genu
tubes l'esulti.ng from the basicliospol'es or conidia of opposite
sexes. During union it ccli of a hilplophasic mycelium of Oll<':
sex fllS<:~ with a ('ell of it haplophasic mycelium of oppoHite l;;l>X
and the nucleus' of ODe is introducecJ into the other and it
binucleate condition (cliplopluli;ic 01' dicaryon) is e~tablished.
This cell, usually a terminal one, now elongates, its two unfu!lcd
nuclei divide simultaneously forming four daughter nuclei and
a cross wall is r,mned containing it paired nuclei of opposite
sexes. The process is repeat<.:cl several times as a result it Call·
Hiderable amount of cliplopbasic ((lieary()n) mycelium is formed.
which ramifies through the intercellular spaces of the host tissu<.:s.
It draws nOllr1shmellt from the living cells by means of short
hyphal branches, the haustoria, which penetrate them.
or
During the period of vegetative activity of the diplophasic
mycelium the cells of the localised regions begin to divid(~ and.
l'e-dividc actively due to stimulation caused by the presence of
THALLOl'HYTA-F'UNCI
the parasite, As a result the infected region swells to an
cnonnom size forming gulfs or tumors, Ultimately the cens o£
Piii, 98,
[,7 .. /illlllo
Z('((
AN BAR OJP COUN IN"Bcn'rCD WITI! ('OUN
R~IU~L' ]'ORMIN[J (;,ILLS,
the galls helow the epidermis are killed ancI the diplophasic
mycelium begins to form the chlamydospores, Details of chla-
132
STRUCTURE AND DE\'ELOPlvmNT OF PLANT GROUPS
mydospore-formatlOll are not yet known with certainty. However, when first formed they are binucleate and as they attain
maturity the two nuclei of each chlamydospore fuse to form a
diploid nucleus "and its protoplast becomes surrounded hy a
thick waiL
At this stage the gall consists of the epidermis
surrounding the masses of chlamydospores and a few sterile
hyphre and the remains of the host cells. Ultimately the epidermis l'llptures and the powdery mass of chlamydospores are blown
away by the wind.
The chlamydospores are resting spores amI
usually do not germinate until the following spring or carly
snmmer, the growing season of the host plant.
Loose smut of wheat (Ustilago tritid).
Loose smut of wheat infects the healthy wheat plants" at
the time of flowering. Just when the wheat plants head out the
chlamydospores of U. tritid arc blown ahout hy the wind and
numerous spores are lodged between the s;lumes where
reaching the feathery stigmas germinate. Each spore
011
th(~y
on
gCl'll1ina-
tion produces a germ tube which grows down the style and enters
the ovary.
It then pierces the integllments of the ovule and
then through the nuctllns. endosperm and scutellllm and finally
enters the axis of the embryo.
Here the fungus continues to
grow within the embryo without doing any injury to it ancI as
the seed matures it passes into the stage of dormancy along with
the seed.
These seeds though infected with the fungal rnvce-
limn appear perfectly healthy.
In the following spring when
these seeds are planted the internal dormant mycelium resumes
its activity and grows as an internal parasite keeping pace with
the growth of the developing seedling. When the plant attains
maturity and at the time of flowering the" fungus
makes a
vigorous developnlCnt and destroys the spikclets of the flowering
heads which arc fmally transformed into hlack powdery masses
THALLOPHYTA-FUNGI
133
of chlamydosporcs. In most 'cases' the spikelets arc completely
destroyed and when the chlamydospoI'cS are blown about by the
wind or washed away by rain, only the bare stl'uctlll'e of the
]!'ig. 99.
:~, r.'1IJ~A~I'lDOHPOI\rn~
(r"lilo!!" tritid.
m.'AGES OF (lIm~UN,\1'ION
OF Onr,AMYllOspnUlcS IN '\VA1'lill.
j
B-IE, VAnLOU~
central axis of the head is left behind. The disease is systeinic
and not localised as in the case of corn smut, since the mycelium
pervacles the whole systein of the plant bocly.
134
STRUCTURE AND DEVELOPl\IENT OF PLANT GROUPS
LOose smut of oat (Ustilago
(17)£11111:).
The infection of an oat plant chiefly take~ place in very
young seedlings. The chlamydospol'l's. produced on the sl1llltted
iniiorescnces of oat pbnrs. are Llsllallv lodged Oil the surface of.
healthy grains. These spores can retain their vitality at least for
a year. In the next season when the~e smutted healthy grains
are planted. they germinate and also the eblamydospores resume
their activity. Each spore 011 germination produces a basidium
which bears the hasidiospores of two sex(~s in the usual nH1I\1\Cr.
The basicliospores of two ~excs. on corning in contact with each
other. unite. From this cell so formed. a short hypha develops
'which immediately infects tbe very young seedJin~. The myceliUln keeps pace with the growth of the plalll and in\'ade~ the
new tissues as they are formed. The infected plan t appears to
11e sOlll.ewhat stunted and the el1't:ct of this infection is sometimes
RO serious that the plant never comes to Hower.
As the plant
comes to hlooming the mycelium penetrates the floral parts and
for a time becomes more aggressive as a result the neighhouring
structurcs arc also affected. The' chlamvdospores Hre finally
formed by the mycelium essentially ill the same way as in the
case of corn smut. The chlamydospores occupy the place of
the grains and sometimes aho some of the surrounding chaffy
structurcs. These spores arc finally liherated and carricd away
by winds to healthy flowers and may also bring about infection
in :flowers instead of seedlings. Like the loose smut of wlwar
the disease is of the systemic - type.
ContrQl of the disease.
(a) Corn smlll.-Since the infection is localised and restricted
to the aerial parts of plants oilly. spraying- of healthy com plant
with Bordeaux mixtures can prevent the spread of the disease.
Thcre are also recommended lllethods: (I) Rotation of Cl"0ps. i.e ..
corn plants arc not cultivated on the same field for at least
three years. (2) destruction of the infected parts. such as.
inflorescences and the stalks. hefore the spores are disseminated
and (3) use of manure free from Slllut spores.
(b) Loose smut of ~c,hc{/t.-In Fe('tioll cluc to loose smut can he
ctlcctivcly controlled by treating the infected seeds with hot water
THALLOPHYTA-FUNGI
135
in ~uch a way that the internal mycelium i~ killed without killing
the embryo. This is done by immersing the seeds for a period
of tCll minutes in hot water hath, maintained at a temperature
of 1250 F. to 1290 F. Great care should he taken during treatment, sincc, any rise of temperature above 1310 F. will kill the
embryo and a temperature below [23'S o F. will not kill the
fungus at all.
(c) Loose smut of Oat.-Thc loss clue to this disease is
prevented hy treating the seeels with fungicides that kill the spores
lodged OIl the; surface of the grains without affecting the vitality
of the seeels. For this purpose, an equal part of commercial
formaldehyde and water when sprayed or sprinkled on oats give
effective results.
Puccinia
(Family Pucciniaccre).
Pucci1l'irl includes a group of parasitic hasidiomycetes which
li\'(~
upon a few fcl'llS but in the main on various species of seedplants (Gynll!n~l)('rms and Anginspenns). They are commonly
known as "rllst fnne;i" owing to the fact that they cause hro'wn or
rmty spots, 01' ~treaks on living- plant!\, p3rticlIlatly on the leaves.
/\11 arc obligate parasites and most of them grow on particular.
host plants or on a Hmall group of closely related hosts. The
ravages made bv the111 are well known wherever plants arc cllltiyatcc!. as they callse dal11a~e to various cereals worth thousands
of rupees evcry veal'. They produce at least two distinct types
of spores, others have three, foul' or even nvC' different kinds of
spore-forms in a complete life cycle. A rust is said to he .jJ(JZy11WI'/l/Zic when several spore-forms occur i11 its complete life cycle.
When a rust prod lIces all the spore-forms in the life cycle on a
particlllar host planr or on closely related bosts, it is called
tluia:cioliS. A large numher of specieg, howevcr, producc their
clifIerent spore-forms on distantly related hosts amI they arc saiel
to he lW/,cro.'cious.
The best known species of rust fungi is Pu('cinia gl'mninis,
commonly known as the "blr{cll stem-rust of wheat", which
causes greatest economic loss and is responsible for one of the
most important plant-diseases known. It is polymorphic, since it
136
STRUCTURE AND DEVELOPMENT 01" PLANT GROUPS
exhibits a total of five difi'en.:nt spore-forms in its complete lifl:
cycle and these are; (a) 1tTcd().lj)()res (urudinios/J()J"l's), (1)) telio.lpures
(telell tospores). (c) hllsidiospores (sporidia),
(el) Pyclliosjmre.I'
Fig. lOa.
['IIt:t:iuirl
(l1'1/1I1£lIi,<,
A.-B, LlCJ\]o'
AND HTF.M OF W!llo:r\'C INI,'\o:(':Clm WITI! "111,,\('K
STEM ltU~'I'" nJo;AltlNG UI\EnOHOltf Ai'll) 'l'Er,IW'],OHOltr
lteHI'E("I'IVELY; C, [',lTV!: OF '],1IE INJ'IlO~l'mD HTRM
SHOWING HWHLY MAGNU'lED 'n;LI':UTn~(l]tl,
(sperrnatia) and Ie) reciospores (rccidiospores). Besides the basidiospores anel pycniosporcs which arc uninucleate, all other HpOl'l~-
137
THALLOPHYTA-FUNGI
forms are always binucleate. P. grmninis is, therefore, a nlacrocyclic rust) since it produces, beRides the telcutospores, ,two other
additional .types of binucleate sporeR. This rust is a hetcro.:cious
species producing certain of its spore-forms on wheat plants and
others on the leaves of berberry plant. Besides wheat plant it
may also attack oat, rye, barley and many other grasses during
the growing season of these plants.
The life history of. P. gramillis can be divided into five
dillerent stages as follows:1. Uredinial or red rust stage.-In late spring there
appear on the stems and leaves of wheat !)lants vertically
elongated reddish-brown pustules (sod) or hlisters called uredosori
Spines
Intercollular mycelium
Fi~.
101.
1'1I(:"inifl
!/1'(illlilli,<.
S,:C'l'ION 'l'llltOUllll A U.lIEDOHOHUH HllOWING UltgIH1HI'OltES
VAItIOUH H'PAGES OF DluVELOl'MgNT.
IN
(l.Iredillilt), each of which at maturity contains a powdery mass
of innml1cl'abk' small orange-red spores called uredospores
(urcdiniosjmrcs, summer spores, reel rust spores). A Ul'cclospore is
HOmewhat ovoid in form, hinucleate, always unicellular, minutely
spiny and with a constant numher of germ pores. At maturity
the epidermis of the blister ruptures and the ul'edospol'cS of a
~l1'edosorus arc freely exposed and disseminated by various means,
especially hy the wind, to other
wh~:at
plants. On reaching
<:\
J 38
STRUCTUHE AND DEVELOPMENT OF PLANT GROUPS
wheat plant a uredospore germinates within a few hours by
sending out usually a single germ tube which OIl reaching a
stolIla penetrates it and eventually ramifies through the intercellular spaces of the host tiSSll('S forming a dicaryon (cliplophasic)
mycelium comisring of. short binucleate cdb. The myccliull1
SUb.stomatal vesicle
Fig'. 102.
A,
j'llI'l'illifl
111"11111 ill i ••.
n,
A GEnMINA'I'IN'~ uTtgnOSl'OHE;
INI·'g("l'lON 0J0'
WHIM'I' [,L,IN'!' BY TUN IHlOW'l'1i Ill-' THE JNFI';O·
'I'ION HYPHA IW A (;J<;!tMINA'l'I'Nf: TTnM)f)~l'Ol!g
'l'l-IllIlUfm A :<'I'OMA.
derives its nOl!ri~hment from the ncighhourillg cdls hy l1leans
of short haustoria! hyphal hranches. The growth of the mycelium
is localised and docs not grow deep into the tissues of the hOS1.
Benearh the epidermis of the host the hypha1 hl'1\!\ches h('come-
THALLOPHYTA-FUNGI
139
more numerous and within 5-6 clays after infection begins to
form nreclosori with ul'edospo)'es. vVhen very young a ureclosorus
consists of a layer of parallel binucleate basal cells which are
pressed directly agaimt the inner wall of the epidermis. Each
of these. cells elongates vertically and divides transversely; the
lower daughter cell, thus formed. remains undivided and is called
a foot cell. The upper daughter cell divides again to form two
cells, the terminal one matures into a uredos/JOre and the lower
one is a stalll cell. Like the cells of the mycelium the foot cell,
the stalk cell and the lll'eclosj)ore are all hinucleate. The maturation of the ureclospol'es is followed by rupturing of the overlying
epidermis of the host plant resultiIlf!; in their final dissemination.
Other wheat plants 11ecome gradually infectcd by these ll1'cdospores and within 1O,:I2 days a new crop of uredospores is produced on the newly infected plants and these may repeat the
~ame Rtage. It is for this reason the urec1ospores arc often spoken
of as "repeating spores". In this way the lln:dosporeo arc 1110wn
ahollt from one field to a l1eil!;hhollring nne and the di~ease
within a very short time spreads like a wild firc.
2, Telial (teleuto) or black rust stage.- Towards the ~end
of summer, as the wheat, plants attain maturity, the mycelium
which npto this time how urecJospOl'es hegins to producc another
type of spores callecl telelltospOYCS (lidiospnrcs, winter spores, hlack
mst spores) within the tclcltios(Jri (lelia). At first the rc1eutospores
arc produced in a sorns containing urcdospores, bll t later on new
teleutosori containing tcleutnspol'cs only develop on the host plant.
The developmcnt of a tcleutospore is similar to that of a. ureclospore except that the upper sister cdl of the stalk cell instead
of directly developing into a uredoRpore divides into binucleate
cclls which mature into it two-celled, thick-walled tdeutosporc.
The tclelltospol'e~ arc dark-hrown hm in mass black in colour.
Each spore when young is binucleate and with a single germ
pore, hut as it attains matnrity the twO nuclei fuse to form a
diploid nucleus. The spores appear on wheat stalks as narrow
hlack streaks 01' sori bursting through the epidermis of the host.
The tclclltospol'es arc resting spores and do not germinate until
J40
STRUCTURE AND DEVELOPMENT OF PLANT GRaUl'S
the following spring. They tide the fungus over tbe winter,
remaining either on the ground or attached to the old sorus 011
the wheat stalk. By this rime the wheat crop matures fully and
.furthcr growth of the fungus is stopped.
Telutospores
Intetcellular
Fig. 103.
myce~!um
1'IIccinia (//'(l/lliliiN.
fJm)'fmN THUOUOH A l'ELEU'fOSORVS SHOWING cl'ELrm'I'OHI'Oll};t;
IN VARIOUS Wl'AGES OF DEV],]LOPMEN1'.
H. Basidial stage.-Under suitable conditions of lemperntUl'e
.<U1(1 moisture n tcleutospore germinates and from each of its
cells a tubular outgrowth is formed. This tubular outgrowth
elongates at its apex and becomes curved at its free cnd. The
fusion nucleus migrates into lhis cl11'ved terminal portion. divides
reductionally into four daughter nuclei. after which transverse
walls are laid down forming four uninucleate cells. more Of less
equal in size. This is the basidium (p),omycelium). Each ccll
devciopg a ~malt lateral projectioll. the sterigma, through which
pass the nucleus and most of the cytoplasm. The swollcn apex
of the sterigma containing the nudem; he comes separated as a
basidiospore (sporidium). A spore forms a small pl'Ojection.
·<tt one side of it called the hilum, wherc· it jllim; a stcrigma.
At maturity all the foUl' sporcs are attached to the stcrigmata
THALLOPHYTA-FUNGI
somewhat obliquely and are soon shot away in succession to the·
air from the sterigmata with considerable fOl:ce. Just before spo1'edischarge a smail drop of water is excreted at the spore-hilum.
This water drop gradually increases in volume and the spore ainng
with the ,drop is violently shot away from its sterigma. P. graBlIB1dlospores
.
~ Basidium
'"
A
B
J!'ig, 104.
c
IJllC~illi(l
(11'(1"1111111,',
A,
A MA'J:URE TELEUTosrORE; B-D. STAGES IN THE
(llnnUNA'rroN m' A 'l'ELlm'J'OSrOl\E HIIOWINO THE
SUC(Jr~~SIVIl B'J:AGES OF DJlVI~r,c)l'~mN'I' OF 'rHR
lIASIDIUM AND THE lIARlIlIOSPORl(S.
is heterotballic.
The basidiospores, thu~ formed, aretherefore of different sexes (-I- ancl-), two (Irc of one Sex ::md'
the other two of the opposite sex. The hasidiosporcs are incapable of infecting wheat plant but can germinate only when they
come ill contact with the alternate hOGt, the. berberry.
?nUHS
'1. Pycnial or sperroagonia,l stage.-The . basiciiospol'cS are
carried away. in all directions by the wind and when they rt~ada
142
STRUCTURE AND DEVELOPMENT OF PLANT GROUl'S
a berbcrry plant they begin to germinate. A hasidio~porc
(+ or -) on falling on a leaf, twig or fruit of berherry puts forth
a germ tube, which penetrate~ directly t}mmgh the ~'pidennal
cells and branche~ through the intercdlu1ar spaces of the host
tissue forming a brandu;c1 haplophasic (monocaryon) mycelium
consisting of uninncleate Cl'Jl~. The illfccted area~ SOUlI become
swollen and yellowish in colour,
\Vithin 4-S days afler infection there appear hetween the
upper epidermis and the pali~ade riswl', isolated hyphal mats,
which at maturity hecollle Hask-shaped and each d~'vcl()ps a porelike opening, the (}.I'li()/c. These ostioles appear as minute dark
spots on the upper surface of (lisco]olll'ecl areas on I he ll'a\'l'~
Wig.
105.
1'I/I'I'illill (/mlllillis.
:-iv;:lfI-IlIAG JtAMM/\'L'I(, 1tl~I'JtEHEN'rA'j'!ON OF A 1'/\'11.'[' 01' A HI,;C'['[ON 'I'H1WIJUJ[
THE IlI'PEn ~IJIlYACE OF 11 LEAl' OF BElllJliBlty KHOWING :-ll'l'HM()(\ONI.\
C(lVEnIW BY /\ BJ(l DJtOI' OF NI,(~,/,AIt IN WHICH Hl'ETlMNI'I/\ ,\HE
mUNG EXlT]Jlo:Il.-(iI','r['I'(I'l(/1l a/I,'1' 11'111/,,1').
of bcrberry. Th,!sc are known as tJycnia (spcrmogo'lli(/). InwarcU), projecting hy'ph~. lining the cavity of each spcrmog-oniul11,
Cllt off from their tips a succession erE small uninucleate ~pore-
TIIALLOPHYTA-FUNGI
143
like cdts, called pycniosjmres (spermatia), which gradually accumulate imide the spcrmogonial cavity. The pycniospores have
gelatinous wall and these arc extruded in a drop of nectar
exuded through the ostiole. Besides the p),cniospol'es, each
pycnium sends out through the ostiole lllllnerous straight, pointed
red hairs, the jJl:rij)/tyses" and a small n umber of simple or
branched /lcxiwus hy jJ/zrc projecting beyond the cloud of spores
into the nectar. The haplophasic mycelium, the pycnict and the
pycniospores are all haploid strllCtllreS and may be either of the
+ or of the - sexual strain, depending on the nature of 'the
basidiospore from which they devdop. Individually each pycniospore cannot re-infect the berberry plant, aIld was previously
thought to be spore that has become fUllctil III less. BlII. it has
cleHnitely been proved that they arc essential structures which
arc responsible for the initiation of the diplnphase. This initiatirm of cliplophasc is rcmkrecl possihle by the tramfcrcnce of
pycniospores from it pycninm of one sex to another of the
opposite sex with the help of insects. The fragrance and sugary
contents of the llectal' arc attractive to the insects and induce
tbem to crawl from Ol1e pycniul1l to another, thereby mixing the
pyenial exuclates d the two opposite sexes. A pycniospure of
one sex usually fuses with the tip of a flexuous hypha of the
opposite sex and its protoplasmic contents finally cntt'r into the
latter: this is the initiation of the diplophasc. How the entire
haplophasic mycelium becomes cliplophasic iN not known with
cel'tainty.
iJ. Aecial {a-9Cid i al) or clu,ster-cup stage.-While the pycnia
an: being formed towards the upper infL:cted rcgiClll~ of the
Ilerberry leaf, masses of hyplla,; accumulate at \'ariom points jmt
within the lower epidermis of the infected area. These are the
rudiments of IIccill ('jm!l(J-llcr.:idia' of Buller)' and arc haploid
~tructures.
Presumahly after diplodisat:ion the nuclei migrate
through the hypha to an aecial initial, and as a resnlt it is
.;timnlatccl to further cle\,c]opment. Some cells of the aerial
initial become binucleate and a layer of binucleate hasai cells
is formed in a manner similar to that produced in a Borns.
Eaeh basal cell hy nuclear and cell-divisions produces a chain
of alternately large and small binucleate cells. The larger cells
mature into [CciospoycS and the smaller ones disintegrate. These
STRUCTURE AND DEVELOPJ'vmNT OF PLANT GROUPS
144
chains of spores arc surrounded by a continuouR protective layer
of fungal tissue known as the peridiu11Z in w!~ich ih~ radial and
outer tangential walls arc greatly thickened. I he enUre structure
is known as the xcium (xcidiztm or cluster-cup). At maturity
Perldlum (ruptured)
B
Ruptured epidermis
A
li'ig. 106.
A,
Pl/~~inia
g)'{/'IIlini .•.
A SECTION l'HHOlTnH AN 3WIUM SnOWING .:WJIOi:\P01tW,
VAUIOlTS BTA[H;H OF DEVELOPMEN'J'; B, FOHMA'l.'lON
OF .},;CI08I'OREH,
IN
the pcridium ruptures, the entire ~ciul1l becoJ11es distinctly cupshaped and the hinucleate ~ci(Jsporcs arc liberated. The xciospores are always unicellular, orange or yellow in colour and with
minutely warty hyaline wallR:
In late spring when these ;eciospores are liberated, they arc
disseminated hy wind. They cannot re-infect the hcrbcrry, but
if a spore reaches a wlu.:at plant, it germinates, puts forth a
germ tube, which penetrates a stoma, and ultimately ramifies
through the intercellular spaces of the host and again forms a
diplophasic mycelium, which within 10-12 days begins to form the
first crop of uredospol'es. Thus, in typical cases, the first infection: of the wheat plant is brought aho'Ut hy the reciospores.
145
TIIALLOPHYTA-FUNGI
Agaricus
!Family Agaricacea:) .
Agaricus campeslris {Psalliola campeslris) , the COliU1l011 edible
:gilled mushroom, is the ~pecies that ig cultivated for the
market, It is a saprophyte which grows singly, or ill groups,
during the rainy season in pastures, grassy' places, richly manured
unploughed fields, but never in thick woods. Tn open field, someltimes the fruit bodies of the fungus come up forming small or
large ring, the so-called tmry ring:
The body of the fungus consists of t"'~o parts, namelY-(I) the
'Vegetativ.e portion Of the mycclil·(.tn and (2) the sporophore (fructification) or the fruiting /J()d.)" cOIlccrned with the reproduction of
the plant,
Vegetative body.
The myceliulll, which is perennial and sllbtcrranean, consists
_(r[ extensively bra11ched strands of septate, white hyphre, by means
Fip;, 107,
ivI.Y('J:J,lTDl' AND FIW1:'I'-BODIE~ fH'
1.'(tlnjJe,~tri",
Ar/ll7'icll"
of which th(;' plant not only vegetates hut also drawH nourishment from the substratllll1, The hyphal cells COl1ta,i,:(!' granulated, vacuolated and l1mltiuucleated (in. most cases'. twelve or
more) pro~oplasm containing. droplets' of oil as l'ese~ve f<.lild.
10
146
STRUCTURE AND DEVELOPMENT OF PLANT GROUPS
HYljhre of a centrifugally developing mycelium may be free
[rem
olle another or' may unite to form Hll1all rope-like strands. called
rhizmnorphs. When reproduction becomes necessary and arter the
mycelium' has accumulated considerable stores of food, sjmroplwres or the reproductive bodies of plants arc produced on the
rhizomorphic portion of the mycelium .
. The sporophore. Typically a mature sporophorc consists of'
two parts: (1) the stijJC (2/1 to 3/1 inches long and )1) to ~- inch
in diameter) is the stalk-like portion which is composed of united
aerial hyphre. It is at first' solid bulhous, but later cylindricai
and tapering below, ap.d whitish in colour. On the stalk a broad,
fle~;l
~........ .
~
.
.
1.;,
<
mg.
108.
Aya·riIJu8.
WfNDUN I,ONGlTUDINAI. HllOTION THROUGH 'L'lIN I'IW['['-IJIlTl.ms
SHOWING ])n"FJi]nJi]N~I' PAnTS.
thin, white., fragile ring or (IIllIlI!US (tlte n:maillH (If the partial
veil) is also prcsem. Tht' stipe bears at its top all lllllhrella-like
structure known a~ (2) the pilelts (I~/I to 4" inches in diameter)
which is at firRt more or lesR convex. then fhit, dry, smooth, soft,
llHually satiny white in colou r, sOlllctimes wi tl1 minutc browllish
scales (triangular) and with a thin wavy, while and delicate mar.
gin. The upper- thick and white part of the pileus is known as
the flesh, on the underside of which SOllle delicate whitt: to ,pink
or flesh-coloured, thin, plate-like strllcturcs arc seCll to hang-.
TUALLOPHYTA-FU~GI
These are called the gills or /amellx (0.6 to 1.6 <.:.m. broad in the
middle, 300 to 600 gills per pileus). The gills which arc free from
the stipe ultimately become purple-brown to chocolate-brown to>
almost black with age and they radiate outwards from the stalk
towards the margins of the pilells.
A cros!> section of the gill reveals, under tllC microscope, the
following regions: (a) a cent.ral portion, the tmnUl, consists of
elongated: multinucleated hyphal Cl'lI~. which te['lninnte bothway~,
:q8
STRUCTURE AND DEVELOPMENT 0,1' PLANT GROUl'S
right and left, to (b) sub-hymen-iu'llt layers consisting of more or
'less circular hyphal cells (innermost cells multinucleated, outer
.cells billucleated) which end in (c) hymenitim mainly composed
.of closely-packed, club-shaped cells known as basidia. Thus each
surface of the gill is covered with a layer of hymcniul11" the cells
,of which grow at right anglcs to its surface.
b
,<I
c
e,
f
n"i)!'. 110.
I.lIAUHA;\I
d
9
HHnWINH HUCCEHHIVI-; ,,'!'AGBH TN '['liE
DEVELOl'~mN'I,'
O~'
A llAHIDfUM,
The h,isidia are really the spore mother-cells. Each basid iUlll
binucleate in Its first Eormation. These nuclei Euse to' form a
Jdiploid nucleus which soon undergoes reduction division. After
'lS
TIIALLOPHYTA-FUNGI
reductiOli division, four haploid daughter nuclei are formed which!
furni~h the nuclei of the basidiospores. Each basidium produces,
four ster'igrnata, through each of which a nuclells passes out to'
form a pUl'ple-brown 01' violet-brown, slightly kidney-shaped, thickwalled, uninucleate basidiospore (usually with a highly refractive oil globule) at the tip so that four hasidiospores are produced:
on each, basidium. Each spore, when separated, is provickcl with'
a small, eccentrically placed spine-like projection at the basal end,.
the former point of attachment of ,the .sterigma. At mHturity ..
just before spore-discharge, a drop of water appears at the spore.,
hi/lIlII. 'When the water-drop attains full size the spore is shot
'0B; with considerable violence. * The Hpores fall to the'
ground and under suitable
conditions begin to germinate_
Each spore,' at tht: time of
germinatioll, becoll1t:s multinucleated and contains oil'
globules. On germination, it:
puts forth one, two, or even
three, spht:ric'al or irregularly
shaped gcrm-tubes from 'any
point which ramifying profusely P~'O(~llt:e a new mycclimn.
There arc irregular waves
of basidial development in <1'
hymeniul11 of Agaricus which
Fig. 11L A (lfl'l'ic1l8.
consists of five typcs of def'FUU]'}NRIVE STAGES IN TIm DIlVllT,Ol'MNN']'
ll1entroi' viz .. (I) basidia of past
OF ~lYC'I'r.I{TiI1 F.lWM A (lElt~UNA'l'ING
I
1
1 I
HAHmJOSl'OlUl.
generation t utt lave a .reue y
discharge(l
their
SP()l'CR',
(~) hasidia of present generation with' mature spores ready
--------------:-._ "_,--_._-----.-.-._",, .. _._ ...... _..........----,,_----.' "A Hinp;le spore (1) takas 30 t{_) 40 miuuteR to grow. from II.. till?
I'udillllmt to hill size, (2) l'cmnins eololll'less fOl' the next 2 hOUl'S,. (3) ~1'I1d\1l1!ly
l,ecolllcs pigmentHu during the nc:x;1. 2 llO~;l'~, (4) remains .in the fully plg~
mellted condition on' the md of ]t,s sterlgmlt fo1' a furtllCl' ·3 hours and
"bout 10 minutes, and. (5) is then dischal'ged"-R~171er, 1942.
i' Buller.
150
STRUCTURE AND DEVELOPMENT OF PLANT GROUPS
'for discharge, (3) basidia of Rllccccding gencration with developing Htcrign;~ta and immaturc sporcs, (4) basidia of future generation (erroneously called paraphyses) which have not yet formed
:sterigmata and spores, and (s) paraphyses.
Thc paraphyses arc. destined to he sterile from the first, hecome vacuolated carly, and swell up considerably during th(;
gradual development and final collapse of the basidia. The paraphyses arc much smaller in size than the basidia and are visible
:as living cells when all the basidia in thc hymenium a1'e' collapsed
:aud have clischar_l;ed their spor(,s.
The basidia of wild form. of' Agaricus campestris arc tetraand (]lladrisporolls, while the basiclia of thc cultivated
ones arc mmally distcrigmatic and hispol'ous. In some cases, in
the latter variety, a fair proportioll of lllonostcrigmatic and 11l1ii'POroUS basidia are .met with in the hymcnium.
~terigmatic
III.
SCHIZOMYCETES
(=BACTERIA*)
The Schizomycclcs or Bacteria arc the simplest' of all plants
ami are present almost everywhere, in watcr, in air, in soil and in
all organic bodies. living or dead. Some can withstand extreme
heat and cxtreme cold. Most of them live in the presence of
oxygen and arc sclid to he a::robic, but a fcw can livc only in the
ahsence of oxygen, when they 'arc said to be' anxrobic; others
,can live in both conditions.
Structure.
Bacteria arc usually unicellular, and the cell is very small in
!iize, in extreme case less than 1/ roo m.m. in diameter. The cell
Inay he spherical. rod-shaped, or spiral. In a few cases cells are
hrcuichcd, and in some cases united together to form filaments.
': In many cases, many bactel'iJ;.l remain togcther ill a mucilage
forming zooglca stag:c. Sometimes thcy arc provided with delicate
protoplasmic cilia.' Each cell has a distinct cell-wall which is
ncither of cellulose, nor of chitin. Thc protoplasm is homogeneolls alld is generally colourless, though occasionally it may
.• The great. Clc!I'lll[lll In\','o]"giHI, and p!J(llj', p:lilw]ou:iHL Alltoll de Hilty
(1831-1888) exelll,]t,ci til(' B,lI'L"ria frolli the fungi. Since 1,]1ll1l. OW'llIYC(JlogISts a)'(\ lllHlllirnnu, ill following ,lp Bary's pntCtiec.
TIIALLOl'HYTA--BAl:TERIA
contain pigments, such as green, red, blue, etc. True nucleus is
absent in bacterial cells. Chromatin granules are present in the
cell and perhaps perfofm the function of lludeuH.
The unicellular hactetia are classified according to their
Hhapes: (1) Cocci, whell spherical in shapt' and arc very minute.
-®~
_83
ii4fia
m:
,
i
~
~
'I' 4fl»
~
1J;fI'
0
Q)
rJ·:
(1
Dlp!acott;i
---..
II "
'I
I "
0e6lll&
(j
~,
rt')
(j
"'~
~
ttl
•.,f.,..>
®e@
(i~(j!)
®1I'll1!l
S!ophylococcl 8<
Sarcinae
Slrcpl"eoeti
~
af)o
@1Il
~
,;;.:,:1
r~
Ib'
m
~ ~ -di':3"
#
lee~~
Rod blJoIel'ia
B
;f
D
0
~
" I
Bacteria with .pores
, ;\
Capsulated bacteria
They m,ay remain singly Of in pairs «UploeocCtts); if two cells are
surrounded hy a common'membrane, capsulated diploeocetIS;' or
in regular gl:OUpS of 4-8,' sarcina.~. (2) Bacilli" when rod-like in
shape. Many of them afC pwvided with one or more :flagella.
IS:!
STRUCTURE AND DEVELOPMENT OF J'LANT GROUPS
Sometimes the rod may be curved ,uid loob like a comma. such ,~
form if> called comma bacillus. (:~) Sjririlll, when coiled spirally.
Nutrition.
Most bacteria either live sapropbytically Oil d.ead or~ani("
inatter. or parasitically 011 the living plants and animals. In very
rare cases, bacteria live exclw,iscly 01\ li"in)!; plants or animals, in
which case they :ll'{, said to he o hlig;atl' /wrilsittJs. Some bacteria
arc peculiar in their mode of nutrition. They ohtain thdr energy
from the oxidation of certain inorganic substances ane! from the
nxation of nitrogen, etc. They are neither parasitic nor sapruphytic and arc said to he autotrophic.
Reproduction.
r. Vegetative. The bacteria commonly l1lultiply hy fissioll
or fragmentation. A constriction appears in the middle of a cell.
which gradually deepens and the cell is ultimately divided into<
two,. which then usually separate.
z, Asexual. Many bacteria multiply hy ll1C'am of SPOrt'S and'
the process is known. as sporulation. When the nutrient suhstance
in the medium is exhausted, sporulation takes place. In the unicelllliar forms, there is a contraction of the protoplaHt, .which then
sun'oul1ds itscIf with a' wall, thus forming an' clldos/JOrc within
the mother-cell. These thick-walk'cl spores arc very resistiyc and
can tide over the periods of drought, heat, cold. etc. When
favourable conditions con~e, the wall or tlle parent-cell bursts anc!
the sporc' produces a bacterium. "l~cproducti[)n in the higher
forms takes place l)y means of conidia. The filamentous fnrm~
bud off conidia at their ends. Thesc conidia an~ set free, and
arc sometimes motile and rod-shaped. The conidia, llnlike tlw
encl()spore~, have no thick wall and an~ lwt rl'sistive. After dispersal they settle and multiply by division.
Importance of Bacteria.
Bacteria are the malu agents for the process of putrefaction,.
fermentation, digestion, nitrification, disease-productioll, etc.
(a) Saprophyte bactcria attack the dead bodies or the organic
products of plants ancf animals, therel_JY produce plltrefaction and
fermentation. This is a process in nHtUl'e'S economy hy which the
THALLOPHYTA-LICHENS
IS3
dead bodies of vCf!;ctable and animalorganisms are disposed of by
the -forma tion of. RU hstanccs llseful -£01' the growth of other vcge~
cahlc and animal life. By the process of putrefaction, hacteria act
as scavengers by removing the dead remains of animals and vege~
table organisms hy collverting them illto simpicr organic COlllpounds which act as manLll'es ancl. thereby -forms the basis for
higher animal and .H·getable life. By fermentation alcohol is·
produced.
(h) Pathogenic hacteria usually calise cliseasl.:s in living organism. The disease may be due to a direct attack upon the tissues,.
or to tbe excretion lJf poisolls (toxins) or to both. Diseases, such
a,<; tuherclllosis, diprh(:ria, typhoid fever, tetanus, cholel:a, etc., are
due to these bacteria. Some of the pathogenic bacteria arc always
pre~ellt your alimentary tract and help in the process o£ diKestion. '!f(/~illus coli is a familiar example of such bacteria.
(c) N'itrogcn hacteria arc 'present in the soil. They are able·
l11ilisc thl.: £ree l)itrogen of the soil-air ull1ikl.: the ordinary green
plallts. They illfl.:ct the r:)()lK of leguminous plants causing nodules· and thereby enrich soils deficient in nitrogen.
t()
(d) Nitrifying bllcteria are always present in the soil. Theil'nitrilicatinn' comist~ in taking amn:lOnia and oxidising it to
nitrous acid with the production o-f nitrites which arc ultimately
converted into nitrates and arc thus available for the green plants.
IV.
LrCHE.N'S·
Lichens are dorsin~ntrally differentiated thallophytic organisms
comisting of two dilII.:I·ent types of plants, one of which is usually
illl alga and the other ',l,fungus. The alga always remains enveloped by the fungns and the two remain ill such a close association
rh,lt a lichen loob like a single plant. In the majority of cases therelationship between the two component orglmisl1ls seems to hesYll1hioti.c partnership. The algal partner may belong to tIl(>
l\tyxophyce:t' or to the Chl()l'ophycere, while the fungal one is
usually an Ascomycete, exceptiollS heing found in a few cases only.
where it is it BasiclioJ1Jycete,
Lichens grow in very varied habitats ill1d' are ~o~mopolital1 in
habit, in HOme cas(~s they grow in. such places, where it is practically
impossihle for other vegetations to thirve at all. They arc found
154
STRUCTURE AND DEVELOPMENT OF PLANT GROUPS
grow on the leaves of other plants, bark of trees, on the surface
of soils and even on bare rocks, and arc extremely droughtresistant.
to
The economic importance of iichens is also well-known. One
<Of them yields a purple dye, which is used for staining purposes.
Some of them containing oleo-resinuous substances arc used widely
in the perfume lllclustry. Some of the lichens are of pharmaceutical interest and some of them f01'm the only fodder in the
,arctic regions for the reindeer.
1!'ig-.
A,
IlORHAL
114.
VIEW;
IiIlS£dioliche.lI.
B,
Vl'~N'l'HAL
V'll~W,
The Lichens arc usually divided into two su h-classes:
(a) Ascolichens, where the fuugHs is an ascomycete,
(b) Basidiolichens, where the fungus is it hasidiomycetc,
'lJId
Depending on the nature oJ the thallus, the Ascolichcns may
be:
lay crusto$e-whelc the thallus is crustaceous alld attaches itself very closely to the substratum. In this type both the com-
ISS
TlJAl.LOPIIYTA-LICHENS
ponelit partners (i.e. the alga and the fungus) are distributed
throughout a gelatinous or Don-gelatinous body in a uniform
manner.
(b) Foliose-Wherc thc thallus is somewhat leaf-like in appear;mce, highly differentiated internally and remains fixed to the
c
A,
~ubstratum
Fig'. 115. .·t~clili"JlCn8.
R, l'ItU~I:ICOSJ,; G, ORUSTOHE,
J.'OJ,ln~B;
by means of rhizoid-like outgrowths. whicb develop
from the ventral surface of the thallus.
Internally there arc four distinct regions in most of the foliose
lichens. The uppermost ):egion is known as the uNJcr corl'ex,
which is llsually composed of vertical hyphoc and may he hounded
externally hy a single layer of hyph!c representing an epidermislike structure. Below this region is the algal !({yer (also known
as gonicUal layer) consisting of ulg!c intermixed with loose hyphal
clements. The third layer is known as the 111 Cdllll(l , which is
made up of very loosely interwoven hypluc. Beneath the medulla
is the lowcr cortex, composed of highly compact hyphre, wJJich arc
either perpendicular to the ventral sll1.'face of the thallus or al'C
parallel to it. Thi~ region (the lower cortex) gives rise to the
rhizoid-like outgrowths (rhizines) from its under smface.
156
STRUCTURE AND nEVELOl';\IENT OF PLAt\T Gnou.ps
(c) Fruticose-Where the thallus is also illtc;'nally dilfnen.
[iared, is either ribbon-like or much·branched amI cylinrlrical and
l<'ig-.
A.
D,
116.
Auoli('lil'//'<,
SUCCESSIVE (;'I'I\OI':S IN THE nEVEr.lll'Mj,:N'!' m' ~(lmmL\ ;
AT,GAI, m~Lr,s' Bl1RnOlJNDBll UY ~'UNGAT, c:I']LLH WI'I'H ITAl.IH'['OltlA;
E, ASCUH WI'!'U ASCOSI'OnNS ANn PAll,\PIIY:;E:H; Ii', Hl,]("l'ION 010'
~l'OTIIECIlIM; G, S,:C'I'JON \)1' '\'TTAl,LU!-I,
A LICHEN;
11-0,
TIl:\LLOPIIYT,\-LICHENS
157
rt:mains attached 10 the substriltum hy a distinct basal part; fIlIti·
cose lichens may he either erect or han~ing,
Some foliose and frutieDse licheIlR possess breathing porcs in
their upper cone:.::, which help in the inlerehangc of gases, between
rlw thallus and i he external atmosphere. In some cases some
coral-like outgrowths, known. as isidia. develop from the fret: surface of the thalltis.: they help in photosynthesis and also function
as v('getatin: reproductive bodies. Gall-like outgrowths, called
cejlhaZ()dia, cOlltllining hoth the algal' and fungal elements haw
also been found to be within or ·ou tside the body of the thallm
of a lichen.
Reproduction.
Lichens reproduce by vep;ctativl.', asexual cwe! sexual methods.
(a) Vegetative, Vegetative reprocluction may take: place by
any portion of it fragmented "hallus, which ('ontains both the
symbiotically dCI'cloping or~anisms, It also takes place with the
Itdp of 1:sidia Ol' by meHllS of son:dia which al'l~ very small bud-like
(Jl1tgrowths developed on the (lm'sal sllrface of the thallus.
(b) Asexual, Asexual !lpores, like oidia 01' Pycllospores are
regularly ·formcd by the funp:uH of an ascolichcn. TheRe spores
falling on suitable sllbstratum germinate very easily and WhL'1l the
hYlihre developed frobl them come in contact with the witable
alga, a lichen is produced. In SOlne cases the alga of tlle lichen
gi I't'H rise to typical zoospores.
'(c) Sexual. The rcprnclllcrivc orgClns . ."!Jemwgonia and (ISCOgonia.. arc always produced hv the fungal constituent. The male
reproductive organs, called the :'j)('nll()grmic/, are fiasl(-shap~cl
cavitie,~ developed on the boely of the thallus, whic:h contain illsiltc
them ltllnt('roUf. sinall mall' cells calied sperl1wtia. The femal!'
orgalJ, the (,.,·c:(Jgol1iu1n, is a multicellular srrllc;ttlre, the lolve!' part
of which is spirally coiled and is known as the archicarp.; the
upper end i~ usually diffe.l'l~ntiatcd inti) a trichogyne, whose tip
in most of the species pr.ojucts slightly beyond the surface of the
th al1 us. The spermatin hecol1w· attached to the tips of the trichogyne and the contents of the Hpern1'ltilllll pass into the trichogync,
but actual migration of the mHlc llllCkuB l111S not'yet been: ol~served
"Ltd practicall y noth ing is known aboll t nuclear fusion.
r 58
STRUCTURE AND DEVELOPMENT OF PLANT GROUPS
After fertilization, flscogenous hyph<l~, are developed from the
bas::tl portion of the ascogonium and finally an ascocarp (either
ajJOtheciu1ll, when cup-shaped, or l}(~rithccium. when nask-shaped)
is produced containing many asci and paraphyscR, Each asclls
usually contains eight ascosj>ore.I·, Ascospol'CS arc discharged in
wet weather, and falling on suitable soil. germinate and give rise to
hyph<.e, These hyph<.e coming in contact with suitahle algae give
rise to new lichens.
In some cases ascogel1olls hyphlC arc ckvelopcd parthenogenetically without any formation of ascogonia.,
CHAPTEH. II
BRYOPHYTA
The Bryophytes comprise a iitnaU grollp of tcnestl'ial plai1ls
which grow mostly in moist slwatiol1s. They are more or less
Cosl1lopolitan in distribution and OCCllr in all climateH whC're
there' is plenty of moisture for the maintenailcc' of life. They
have a >\'r.l1-defin(~d alternation of generations in their lifc-cyclcH
and the sexual generation, or the gametoplzyte, is always 1//1 in(li~pnldent jJ[arit amI. carryon photosynthesis owing ,to the presence of chloroplasts in their bodies, The asexual generation, or
the stloTophyte, on the other hand is '/lot all indej>endent 'plant
but is always attached to l'he gamewphyte and is partially, 01'
wholly, dependent on it: for nutrition:, The plant body is llSually
a thallus without a'lY differentiation into roots, stems and 1cavef,
hut in higher forms it is dif'fercntiatecl ,externally into stemil .and
kavcs, though the, roots are entirely absent. Instead, springing
from the lower stu'face of tbc thallus or from tlw hase of the
'stern there arise a number of unicellular or multicellular tllamclltom structures called l'hizoid.\' which pcrfonn both the functions
of absorption and fixation like the roots. All Bryophytes rcproduce sexually by the process of fertilization. The sex orgam,
(/Iltheridi({ and archegonia. are alwaY,I; IIwlticcl1l1/al' stl'llc[:'IIrl!.I' and
the gametes, the spermatozoid.\' and (lV'IIIII" arC' alwitys SllrrOlllHl('cl
by an outer jtlclwt cf sten'le cells.
The Bryophytes h,H'C been divided illto the following thrl'e
classes:
RRYOPHYTA
159
Class 1. Hepaticre. The
Hcpatic:e have dorsiventrally
diifcrcntiated gametophytes which arc either externally simple
(e.g .. Riccia and Marchantia) or differentiated into stems and
leaH'~ (e.g., Jung;lJrmannia). Interally they may be homogeneous
or ("()mpo~ed of 'different kinds of tissul~s. Sex organs are always
fOl"lncd on the dorsal surface of the' thallus. The sporophytes may
b<: extremely simpk (e.g., Ricc'ia) or dilTerentiated into a foot, it
scta and a capsule (e.g., Jllarchmltia) and these arc always entirely
parasitic upon the gametophytes for nourishmelit.
Olass II. Anthocerotre. The gametophytcs of the Anthoecrotre· have distinct dorsiventrality and arc of simple external
forms. The internal construction is homogeneous. The sex organs
arc developed on the dorsal surface. and arc embedded hita the
tissue of the thallus. The sporophytes arc differentiated into a
capsule and a foot. The lower part of the capsule corresponding
to the position of the ~eta is highly mcristematk. The sporogenous tissne is developed from the amphithecium instead of from
the endothecium. which is transformed into columella.
Class III. Musci. The gamcwphytcs of the Musd have a
transitory prostrate stage bearing radially symmetrical, leafy sexual
hranches which continue to grow a~ independent plants after the
disappearance of the prostrate portion. Sex organs are developed
ncal' about the tips of the sexual branches and are produced either
on· the same plant (molla'cious) or on different plants (direcious).
The sporophytcs arc differentiated 'into a foot, a seta and a capsule
.anc! are semi-parasitic upon the gametophytes for nourishment.
Riccia
(Fam.ily R.icciacere)
Riccia) a comlllon liverwort, grows usually during the rainy
Oil damp wall~. moist places, etc., in dense patches, or
rarely in pouls of water as frce-flnatinp; scum.
!;eaSOl1
Vegetative body
of the gametophyte.
The vegetative body of each plaut is a flat, dorsiventral thallus,.
wholly prostrate and typically rosette-like. It branches dichotomOllsly. Each branch of the thallus.is wedge-shaped and duckened
Oil the middle line. On the vCl1tl"Ill side of the thallus, there are
u60
STRUCTURE AND DEVELOPMENT OF pLANT GROUPS
numerolls scale-like srr.ucwres, OlH~-CelJ in thicknl.'ss, amI many
rhizoids which perforn1 the function of the root. Rhlzoids arc
.of two kinds, smooth-walled and pegged i.e., with variolls types
'of ingrowth~ of tl1(' wall projecting- into the lumen of the rhizoids.
When a traw,n:rsc
section of the' thallus of
Riccia is eXHmined under
the
microscope it: is
fonnel that the npper or
dorsal portion consists
of vertical tiel's .of cells
contammg
chloropla:.;rs,
while the lower or velltral
:"'ig. 117. CiAWc'I'Ol'lfY'I'Il' WIALLIJR OF Ril'I'i(l.
part is a tissm: of colonrJess parenchyma cdls,
which may contailJ starch. Theft: is a single row of canals extending thro\lghout thl~ entire length of the chlorophyll-hearing
tissue; these canals arc the air-chambers. The air-chamhers arc
perfectly smooth and arc without allY ingrowths. At: thc top of
the air-chambers ~here is RO- callcel "epidermis", which is only (Inc
".
.~
Fi~.
118.
'['It INHVEIlSE SEf"II[()N OF
'I'~m 'l'I1ALLITH OF !iil'l'io.
'ccll ill tlll·C·]'llC",';'. 1"1'1';C .'
. . 1e tlmct'
. II \I Iar spaces
<ul'-pores are s11np
,,b<)unded by several "epidermal" celk In older portioll ()f rhc
'
M
'
BRYOPHYTA
161
thallus and on the vertical stu,face arc: observed the unicellular
rhizoids lying between the multicellular scales.
Sexual reproductive organs.
Most species of Riccia an.: Il1ona;ciom (ho11lotlzallic) i.e., anthcridia and archegonia are borne on the same plant, but a few arc
direcious (hctcrothallic) i.e:, antheridia and archegonia are born<;
on different plants. Sex organs, antheridia aml archegonia,
are borne in acropetal succession in a more or less linear row within the longitudinal furrow on the dorsal side of the vegetative body.
Antheridium. Anthcl'iclia occur in discoid meas above the
general level of the thallus. Each antheric1inm is completely endosed in an anthericlial chamber
formed hy the growth of the adjacent tisslles and connected to the
exterior hy a narrow slit-like 0pellil1g. Each anthcridiul11 is a pearshaped hOlly, stalked at the broader
end. It is sUlToumkrl hy a sin~lc
layer of sterile cells at the exterior,
forming the wall of the :l.I1theridiuJ11.
Enclosed hy this wall. there arc
llumerous cells, each with a relatively large llucleus and dense
A
cytoplasm.
These:
arc
sperm
Each
mother-cell
mother-cells.
undergoes a single nuclear division
and by oblique partition forms two
Fig;. 119, Rircill.
cells, each of which is ll1etamol'- A, "\ VElt:rWAT, SJWTION THltOUGJI
A MATum;. AN'['HEltTDITTJI!; n,
phoscd into a single hiciliated
A 8J'JUtMA'fOZOID.
spermatozoid. When the spermatozoids mature, there is a complete dissolution of the cell-walls
within the antheridiulU so that the spcrmatozoids lie in a
common cavity and are ultimately discharged.
Archegonium. Archegonia lie in the deep pits or furrows and
arc partially enclosed by the overgrowth of the surrounding
tissues.
Each archegonium is a flask-Rhaped body with a
II
IG:l
STRUCTURE AND DEVELOPMENT OF PLANT GROUPS
very short stalk anel consists of two parts, an enlarged hasal
portion called the vel/lel', and an elongated, comparatively large,
tuhu1ar portion called the ncd,.
The venter consists of vcntral
canal cells all(1 a brge o()sj)ilCl"c or IlV1!IH or egg, and neck cnllsists
of a number of '/Iccll cmwl cells.
Fertilization.
\Vhcn the archegonium matures, there is a complete disi:iolution of the canal-cells, so that: a passage is estahlishecl,
sperm<tt()zoicls
Biciliate
enter
the
into
venter and one 01' which eYl'llluallv
fertilizes
fertilizec[
the
()\'l1l11 IS
egg.
The
then surround-
ed by a thin celllliose wall an( 1
IVitll fcr-
becomes an ()()sj)()re.
of
tilizaliotl (llld fOrlllllli(J1l
liOn:, the
Ovum
sp()'r()i)hylc
gC1lcrati(J1I
()()s-
tliJ)/oid
()l'
bl.~f!:i/ls.
Formation of the sporophyte.
The
zygote,
as
formed,
increases
111
soon
as
size until
the venter of the archegoniullI
is almost completely f1l1ecl lip, ami
then llllllergoes a sing!.c division
Ri,,(·;u.
Fig. 120.
to
form
This
of repeated cell-division
ma1\y
times
consists of
the
20-JO
grOWi-i
zygotc
III
a
em bryo
twu-cdlcd
hy
em bryn.
the
JlroCl'S~i
into a rnulticellu1ar structure,
size.
The
sporophyte,
when
cells, becomes differelltialed into an outer laycr
of'stei'ile cells, called the (/lIlj)/Zitlzecillm, and an inner mass of fertile sporogenous cells, calleel the cllcZot/wcium.
Ml~anwhilc
venter
also increases in size, and the entire sporophyte rClllains enclosed
LRYOPHYTA
within the gametophytic tissue.
Each cell of the endotheciulll,
consisting of a relatively large nucleus and dense cytoplasm, is a
The spore
spore mother-cell.
mother-cells llllckrgo contrac-
tion of protoplast.
tegration of the
The disinwall~
of the
spore mother-cells and of the'
sterile cells, except the wall of
the venter, result in
fluid
III
it
viscous
the
spore
1'e111<1111
sus-
which
mother-cells
Then
pClltleel.
each
iPore
l1lothL:1'-ccll unciergoes reduction divisioll and forms spores.
The
spores,
whell
mature,
have a wall of threl' layers
nncl they arc liberated hy the
Fig. 119.
A
Hic!'irr.
YOIJNt! i:'J'l)l:lJl'JI},'l'E EAlJlEJ)]));J) Wl'l'H.lN
'I'Hg n.\ME'I'()Pll\,1'J<' 'I'THHlTE.
death <Incl. decay of the surrounding tissue;s. With n:duction d'ivisio'll (Iud forma tion of
sp()res, the gtlmeLophytic
haploid generation hegins.
or
Formation of the new gametophyte.
Spores, at the advent of
favourahle conditions, germi-
Fig. 120.
'l'U.INHVEHHE
NIDWI~Y
l!i,,,·i(l.
'.ruwmnn
~EC'l'lnN
MATnnE Hl>OIlOl'lIl;n;
"'IT!! SI'Oltr,-'I'ETTtAllH.
A
nate: the two outer walls burst
and the inner wall protrudes to
form a germ-tube which hy the
process of cell-division forms a
gal11('wphytt'.
164
STRUCTURE AND DEVELOl'MENT OF PLANT GROUPS
Marchantia
tFmnily Marclwntiacem)
l\1archantia a common liverwort, is generally fonnd
moist soils, rocks, etc.
J
Oil
Vegetative body of the gametophyte.
The thallus is found creeping on the surface of the
substratum. in the form of a 1'Osette and is closely attached
to it by means of rhizoids found Oil the under surface of the
thallus. The branching of the thallus is dichotomom; and
there is a prominent midrib.
]'ig. 121.
THALLUS
WITH
.l/m"i'll(lillill.
AN'l'.IIEUID[Ol'HOllE ANll
Ancm.;f:ONl<WITOUl·:.
In transverse section of the thallus, it shows an IIpper
epidermis which contains many air-pores wliich open to the
external surface. Beneath the upper epidermis lies the air·
chamber containing hranching filaments of cells, growing
upwards from the layer of cells that compose the lIoor of th~
chamber. The cells of these filaments contain chlorophyll and
constitute the main photosyntbetic tissue of the plant. Beneath
r65
BRYOPHYTA
tIle air-chambers there are several layers of cells containing a
few chloroplasts.
scale~
From the lower surface of the rhallns grow
and rhizoids.
Fig. 122.
The rhizoids are of two different kinds;
1'RANSVEltrm HI,C"l'lON O~' THE 'l'HALLUS OF
,1/(/1'1'11 £III li((.
some arc simple, others are pegged, the inner wl'face of the
walls of which are marked by localised thickenings.
Reproduction.
1.
Vegetative. The vegetative multiplication takes
place by apical growth and branching, and by progressive death
of the older parts of the thallus due to which the number of
plants is increased.
It also takes place hy the formation of
lens-shaped structures (gclIunce) which are produced in great
numbers in shallow cups known as gemm;r-cltj}s. Each gemma'
is attached to the thallus by means of a one-celled stalk, from
which the gemma is easily detached.
Each gemma is more
or less round with .two notches in the middle and. when l.t
falls on the sub~tratulll, cell-divisions begin at the notcbes
and two plants are cOllSe(lucntly formed.
166
STRUCTURE AND DEVELOPMENT OF ,PLANT GROUPS
'2.
Sexual. The sex organs of 111 {[rc/ulIllia are horne
on special erect hranches. cadl composed of a stalk and a
terminal horizontal disc. The male and female branches may
j,;ig. 123.
J\I ([,,·/trw! iu.
'['UA!.LUll WI'I'H (ll'M~U,;-C(JP~ !"ONTATNINll m:MM_T.:, AN gNLAIHiEV
OF ON[~ OF WHICH IH SHOWN ON 'l'r!!'; J,EFT HAND ~IDE.
I'JEI\'
he borne on the same plant (monn.:dllw;) or on different plants
(direcious).
Fig. 124,
A
Jl/!ll'd/(/I/Iill.
VERTICAL ST;C'l'lIlN OF '('HI':
nISK OF A MAL~: IlHAN(.·JI
FiHOW:N(: ANrl.'IrII~lt[DTA.
The disc borne by a
male branch is lobed and
the antheridia arc embedded on the upper surface of each lobe. The
oldest:
antheridium
is
found at the centre and
the youngest towards tbe
outer extremity of the
lobe.
There are airc h a 111 b e r s with porcs
hetween the cavities C011taining anthcl'idia. When
npe, the wall (If the
anthtTidium ruptures antI
llRrOPHYTA
llUlllerom biciliate spermatozui(is or antherozoicls arc liberated
III a drop oI water.
The Iemale receptacle IS divided in to rays and the
archegonia at first develop on the upper surface. hut due to
growth of the central part of the
upper
side
of
the
elisc.
the
archegonia become inverted with
neck downwards and the youn.\5est
archegonium is found towards the
centre and the oldest one towards
the extremity of the ray.
Each
archegonium has a long narrow
neck with many
lll'ch
Cfl1lfll
cells
and a swollen venter with a veil"
t ral callal cell and an
OV1I1'Il
or egg.
Fertilization.
l·'iii. 125.
Fertilization
presence
of
takes
water
pace
in
il/(lrl"/t II II I ill.
J\ VEIl'I'IL'AL ~EC~'I'ION TH]loncnr
A ~rA'l'UUl~ AN1'UEHIJ)] llM.
when
the
spcrmatozoic1s enter into the venter through the neck of the
archegonium, the n(.'ck canal cells 11Hving heen disorganised hefore fertilization.
fertilizes the egg.
One of the spermatozoids eventually
The fertilized· egg is then surrounded by
a thin cellulose wnll and }Jecomes an ()()sjJnre (zygote). With
[('rlilizat'ioll and jrmnatirJll of o oSj)()rc , the sj)()}'ophyfic or
dilJ/()id gnzcmtio/l hegills,
Formation 01 t.he sporophyte.
The zygote illlmediately develops into a sporophyte within
the venter of the archegOllium. When fully developed it is
dittcl'cntiatecl into (il a hroad ha~aI fool, (it) an elongated stalk
or ,1'('/(/ and (iii) it Lerminal capsl/le.
168
STRUcTURE AND DEVELOl'J\IENT OF l'L,\NT CROUPS
As a result of fertilization the ventral cells of the archego.
nium arc stimulated to divide and re-divide forming a lisslle
known as clli'vplra, which surrounds the developing sporophYI'C
till the latter attains maturity, SOIlIC of Ihe cells at'
B
Fi/.(. 126.
A,
J!IIJ'dllllli ill.
'VBH'l'lC,\L SBl:'I'WN OF TilE llr~r' OF ,\ F~:AI~Ll': llIlAN('JI WITll
INVlm:n:n AltClIEI:I1NIA .. B. A YOrlNU All('IlI-:t;()NlIT~I i
C. A ~lA'l'{lllB AHC'fn:r.ONWM.
the ]1ase Df the archegonium abo divide and form 11
cylindrical sheet-like outgrowth, known as ilsclIr/o/Jcri({'/l/.h,
surrollnding; the archegonial venter with its enclosed sporn:
phytc. The zygote after fertilization firflt divides transversely
into an upper and lower ccII. Second division is, however, at
right angles to the lirst so that a fom-celled emhryo jg formed,
BRYOPHYTA
The two uppermost cells. the e11ibasal cells, hy division and
reclivisiol1 give rifle w the capsult; and the upper part of the seta.
~'lllcl the two lowermost cells, the hypo basal cells, by suhflequent
divi~ion form the lower part of the seta ancl the foot. The
foot is a hroad, expandecl tissue \\ hich fixes the sporophyte to
P.~udoperianth
B
Fig. 127.
A-C,
ll/m·clwiltiu.
HUGCBRSrV/1 S'l'ACa:S IN 'I'HE lIEVELOP.lmNT
DE' THE SJ'DlWl'HY']"l.
the gametophyte and absorbs water and nutrient solu~ions
from it. The !leta consists of vertical rows of more or less
isoclbmctric cells which during the latter part of the develop"
menJ of the sporophyte elongate considerably. Due to the
elongation of seta the calyptra ruptures' and the capsule is
pushed outvvards beyond tbe pscucloperianth. Early in the
J 70
STRUCTURE AND DEVELOPl\IENT OF PLANT GROUPS
development of the embryonic spuropbyte its capsule portion
is difIcrentiatec1 into an oLlter a1Hj)h£t/tccium and an inner
cllllothccizl'fn.
The amphithecium remains one-celled in
thickness and forms the ()I[tCI' covering, or outer jacket layer,
of the capsule. The first cell generation of the endotheciull1 is
the arc/zcsjmrill17l which divides and re-divides to form a mass
of sjJorogellolls tisslie. A few apical cells of this tissue remain
.l4\;H-~ft Spore,
C.poule
~
~
i·
Fig. 128.
LnNi>l'L'lll'INAL
A,
flEUL'rnN
A HI'nltE;
.1/,1/"'''"111;(/.
(W
n,
'l'ILg' ~L'(ILt()not,;rlt,1 :
AN E[,,\TIW.
sterile, while others elongate and divide n11liquely. Finally,
half of the sporogenolls cclls by two or thl"l'e sliccessive divisions
give risc to more 01' less isocliamel'ric spore mother-cells. The
other half of the sporogenous cellg become much elongated,
each with two spiral thickenings on its wall, and form tlle
c/aters. The spore ll1otl1el"-cdls ai1Cl claLet's are llsually evenly
nRYOPHYTA
17 1
distributed within the wall of the capsule. Each spore mothercell by reduction division forms four spores. With reducti()/l
divis'ion and formatioll of sf)orcs, the gamrtaj)hvf'ic or haJ)laid
gCllcra/,ioll llegins.
At maturity, when the capsule is pushed outward heyond
the pseudoperianth clue to the sudden increase in length. of
seta, the jacket of the capsule splits up from the apex to about
tIle middle into an indefinite number of segments and the
spores are liberated. During tbe process the elaters coil and
uncoil due to hygroscopic changes in their walls and mlsil'lt in
the liberation of spores.
Formation of the new gametophyte.
The spores, after lilleration, are dispersed and carried away
l)y the wind. Each spoye under suitahle conditions germinates.
increases considerahly in size, divides to form a six to eightcelled irregular filament from which a typical gametophytic
thtllus is grad ually differentiated.
Anthoceros
(Family' A ntlzocol'otacex)
1'los1 species of Antlwceros, commonly known as horn
liverworts, ocelli" frcC[uently along hillside roads on very moist
clay hanks. They rliffer so greatly from the liverworts that
the present-clay writers separate them as a distinct class Coordinate with the classes Hepatica: and Musci.
Vegetative body of the gametophyte.
The vegetative hody of each plant is a small, clorsiventral
and very simple greasy clark green gametophytic tballus which
is inconspicllously hranched or somewhat lobed. and without
any internal dilT:erelltiation of tissues. There arc ntlluCrous
slr{ooth-wallec1 rhizoids on the uncler side of the thallus. the
scales heing entirely absent. On the ventral side of the thallus
there are numerous large intercellular spaces, each of which
opens externally 1>y a narrow slit. These cavities arc usually
172
STRUCTURE ilND DEVELOPMENT OF NANT G1WUPS
filled up with mucilage and often contain colonies of an
endophytic l1Iue green alga (NOSfOC), Each cell of the thallus
Fi!!:,
THALf,U~
12g,
cl 1/ II/ "/'/''/''''',
Wi'l'H Hl'Oltol'JiY'I'I':H,
usually contains a single large chloropla~t with a conspicuuus
pYl'cnoicl wbich is made lip of 11l1ll1CI'0lIS disc or spindle-shaped
BRYOPHYTA
Ij3
bodies destined to he metamorphosed into small starch grains.
Thus, it is evident that simplicity is the most prominent feature
of the thallus in comparison with those of Riccia and
jVfarchantia.
Reproduction.
I.
Vegetative, The vegetative reproduction is usually
effected hy progressive growth and death of the thallus. Under
certain conditions of prolongecl desiccation the gametophyte
often produces 'tubets' formed due to marginal thickenings.
Each tuber is externally protected by a cork layer and under
favourable conditions gives rise to a new thallus.
2. Sexual. Antjwceros i~ homothallic, though in some
Rpecies the antheric1ia may attain maturity early (protandrous).
Tt is a noteworthy feature that the sex organs are entirely
Aniberldllll el,.mber
Antherozoid-lJlotnor-oell.
Fig. 130.
A,
Anlh,.'/"·IIIN.
Vgl\ITWAf, Sk:CTI(}N OF A J;'OltTION m·' 'fHALI,US;
AN AN'rHERIlllUM (ENLARGED).
n,
embedded in the dorsal side of the thallus and not borne on
special receptacles as in Jl.iarclulIlt'ia,
Antheridia develop in clusters within dosed ca vitics
(afLllwl'idial clumd)crs) just beneath the upper surface of the
thallus. From the floor of each ulltheridial chamber two TO
four <lntberidia develop. The sterile layet over-roofing each
antheridial cbamher may he one or more cells in thickness.
174
STRUCTURE AND DEVELOPMENT OF PLANT GHOUl'S
Each antheridium develops a. stalk of several cells in height.
Numerous biflagellate antherozoids are produced from each
antheridium. When the anthcridia attain maturity the sterile
layer ot cells over-roofing each antheridial chan;ber disintegrates and the antherozoids are liberated.
Archegonia develop singly and are closely embedded in
The vegetative cells of the thallus are confluent"
with ;l part of the neck and venter of each archegonium, the
extreme end of the neck being· only protruding. \Vhen fully
the thallus.
Fig. 131.
AH('IlE(lONTA,
,·1 11th OI'I'I"I/'<.
YOUNI1
ANi)
~1A'I'{1HJ';.
developed there is a single axial row of cells in each ill'chegoni LIm,. consisting of four to six neck canal cells, a yen 1:ral
canal cell and an egg cclI. I\t maturity, the neck canal cells
and ventral canal cclI cligorganise aile\ fertilization ot the ovum
it': hrought about: by one of the anthcrozoicls passing down the
neck into the venter. After fertilization the fertilized egg
secretes a wall around it and forms an QusjJOrc, TVil h fertilization I1lId formation of oos/)ure, t1w spu'I"olJhylic, or diploid
f!;cllL'ration
beghzs.
Development of sporophyte.
The oospore, without: any period of rest, divide~ and n:cli vicles and forms a sporophyte. The sporophyte is gradually
tlitIerentiated into a basal foot, and an upper slender cylindrical
structure of mote or less uniform thickness, the ca/lsille. The
zygote usually first divides longitudinally and then transversely,
BRYOPHYTA
175
This is followed by another longitudinal division of the foul',
daughter cells forming an eight-celled embryo, made up of
two tiers of four cells each. The foot develops by division
and re-division of the cells of the lower tier. When fully
funned it becomes a massive inverted cap-like structure,
means of which the sporophyte is not only anchored to the
gametop.hyte but also ahsorbs nourishment therefrom. The
cells of the upper tier also by repeated divisions form the
capsule. which when very young becomes differentiated into
mnj)/titlzecillm and cndothcciu1ll. When fully developed the
capsule stands erect on the thallus and attains a l1eight of one
inch or more in some cases.
The structure of a mature sporophyte is very complex.
At the centre there is a sterile tissue of elongated cells, called
columella. It- appears r6-celled in rectangular arrangement in
cross sectioll. The entire columella is derived from the
endotbcciull1. Surrounding and over-arching the top of the
columella there is a cylindrical sheet of sjJorogenous tisslle .. the
(l}'c/tcspori1l1ll. The sporogenous tisslie either remains one
cell in thickness throughout its developlllent or hecomes two
to four-celled in thickness in some cascs. Alternate groups
of sp01'ogenolls cellH develop int() spores and daters. Those
sporogenouH cells which hehave itS spore lIlother-cells llndergo
reduction division anel from each a spore-tetrad is formed.
by
With reduction divisirJ'll lind frmrwtiolL of slmn:s the ganwto1)/zytic or haj)[oid generation hegills. The cells developing
info daters are joined with one another forming filaments of
3-..j. cells eacb. Their walls are either smooth or thickened.
The sporogenous tissue is again externally surrollllc1cd by a
cylinder of sterile tisslle possessing an epidermis. This jacket
layer of sterile tissue and the entire arcbe8porium are derived
in mogt ca~es from the amphithedull1. The outer ceBs of the
jacket layer contain chloroplasts and the epidermis jg provided
with numerous stomata, each with a typical pair of guard
cells. Thus, the sporophyte is able to carryon photosynthesis
from the raw food materials ahsorhed from the soil by the
gamctophyte and ~upplied to it and carbon dioxide ~bs9rbed
from the air. This ability to synthesize carbohydrates
is more highly developed than o.thcl' liverworts. . The'
lower portion of the capsule is provided with a meristbna c
176
STRUCTURE AND DEVELOPMENT OF PLANT GROUPS
tic tissue, which continllally adds new cells to the upper pnrtiort
}\,
Fig. 132. c(lIl/wi""/"rm,
~ R.\O~\lA; }). 1(" NOI'l'Ul:'INAL SECTION (}J1' THB HPOUOUONIUl\[ ill ;,,)'il.ll;
("-1., r,ONGl'l'l7JJINAL YIEWt> OF 'rUE H,\ME A'I' nIFl'I~IUJN'I: LI'V'lI,~.
and as a resul:t the capsule grows and produces spores over
an extended period, The spore-production begil18 at the
BRYOPHYTA
upper end of the capsule and as the capsule grows the spores
are produced successively from lower layers. As they attain
maturity the capsule dehisces at the apex into two valves and
the split is continued downwards. with gradual formation,
maturation and liberation of spores. During the early stages
of development of sporophyte the gamctophytic tissue
sllJ'rouncling the archegonium also grows upwards. finally stops
and forms a sheath surrounding the base of the developing
capsule.
Formation of the new gametophyte.
Each spore under sui table conditions germ ina tes ancl
Jonns a new gametophytic thallus.
Polytrichum
(Family Polytriclwccx)
Poly trich 1I11I, often known as squirrel tail inoss, is one
of the common mosses of Indian Archip1egn and Australia
which grows in the rainy season on damp grollnd, ncar the
hases of tree trunks and side-walls of cities forming dense
tufts and patches.
Vegetative body of the gametophyte.
The gametophyte is differentiated into two portions: a
prostrate and much-hranched alga-like filamclltouR portion, the
proionem({J and un upright peristcnt leafy shoot, the gametoj)hore. The filamentous protonema is transitory and shows
two kinds of branches: the ordinary green ones with straight:
transverse septa, and the hrowll-walled ones with strongly
ohlique walls, the 1·hizoids. If abundant moisture is present
this protonema grows to a comidel'ahle extent and S0011er 01'
later there arise, from its distal end of the cells, lateral pearshaped I11Ulticcllular cell-masses (buds), hom each of which
a leafy gametophorc is produced.
The gametophore, which is independent at maturity. often
reaches, a height of 20-40 cms. ancl is always differentiated
into. an angular stem and closely-set, thick, l'igid. spirally
12
178
STRUCTURE AND DEVEl.OPMENT OF PLANT GHOUl'S
arranged (with angular divergence S/13. 13/34. etc.) kavt:s.
The leaves are small, very numerous, lanccolate to linear in
outline and with a very 1;road and strong midrih, proje~ting
beyond the apex 01 the lamina. The lamina which devclopf\
-OPI)I'('U]IIJn
"
, ---CII[ISlllc
c
A
B
Fig. 133.
A,
A ;\IALE
])(li!lil'idl/I/I/.
PLAN'l'; H. A m,;i\IAU; PLANT WI'I'II HPI)I\OGON,ll1~l;
C, CAI'HULE WIT]! CAI.YI"I'HA IU;MOVI';Il.
only at tl1e extreme margin of the midrib is ll~[[ally rl1<>re or
le~s incurved. A leaf. when viewed with a pocket lcm, ::;110W8
BRYOPHYTA
that as if 1here arc several narrow midrihs. Hut when sectioned
and cxaminccl uncler microscope these are in reality t.hin
vertical plates of cells with numerous chloroplasts al()~lg the
micldle region of the leaf and arc protected by the incurve<t
Fil-!:. 134.
/'ul/itJ','·,"h11!!i.
·TllANKVEl!.~E KEC'I'ION OF LEAF (IN J'All'!').
margins of the lamina in dry weather. At the base of the
shoot: numerous rhi7:oids develop and these often become
closely-twisted together to form cable-like strands,
A cross senion of the stem shows three distinct regions:
a linn epidermis .. a comparatively thick curtex and a central
cylillder. A few outer layers of cells of the cortex are thickwalled and dark-coloured like the epidermis hut more compaCT
than the inner cololll']ess parcnchymatolls ground tissue. The
central cylinder is composed of two tissue elements: thickwalled, t1ark.colo'ul'cd cells with living protoplast" (stereids)
especially abundant towards the centre, a11(l larger, thin-walled,
empty cells (hyrlroids), almost destitute of protoplasm and
resemhling vessels of true vascular plants. Starch has been
uoted in the outer cellg of the cortical region.. This central
cylinder is separated from the cortex hy' an in:complete
180
STRUCTURE AND DEVELOPl\IENT OF PLANT GROUPS
peri cycle-like sbeath of tbin-walleclliving cells and lies enclosed
hy a xylem sheath. Leaf-traces are also present in the cortex:
and these are structurally similar to the central cylinder.
Sexual reproductive organs.
Polytricll.1l1n is diceci()llS and the sex organs, flllthcJ'idill
and arc:hc.wmia, are borne separately at t11c apices of male
and female gametophores respectively forming .the so-called
"inflorescences". Each inflorescence consists of a group of
sex organs which are surrounded hy specialised leaves, j)(:ric/zteJ:ia/ leaves, Cjllile difIerent in form ant] colour from those
on I-he stem.
Fig. 135.
'l'ItAN;;VEn~g HI\C'l'ION (lJo' 'l'H~; HTICM OF
l'olytrich1l'l1l..
The conspicuour. male inflorescence consists of group of
antherirlia intermingled with peculiar' sterile green hairs
(jJ(/mjJ/tyses) and is surrounded by broad, reddish antI membralleous peric1u-etial leaves. The growth of the apical region
of the f;tem is, however, not stopped by the formation of
antheric1ia and its further growth may he resumed when the
llR\:,OPHYLA'
181
formation of antheridia is totally stopped. This inflorescence
is regarded as a compound structure, since groups of antheridi,t
develop at the base of each leaf of the inflorescence and it is
cjuite probable that each group represents a condensed branch.
Antheridium. Each anthericlium is a shortly stalked clubshaped body cont.aining within it many n{other-cells of
the spermatozoicls (sper1llatozoid mother-cells) and within
each of which a biciliate spcnnatozoid is developed.
SI,erm·mothcl··cell
©
c
Sperm atazoid
B
Fig. 136.
11,
D
Polyt'r'iclLllm.
r,ONGl'fUDINAT, HmCTION THltOUGH ~rHJl] Al'mX 1)10' A .\[,l.LI'~ I'I,AN~'
SHOWING ANTHgItIDIA AND l'AUAI'J!YAI~S; B, A MA1'lTUJoJ
AN'l'llleRIIHUM !lISCIlAltGINU Sl'EltMA'l'OZOIDS.
vVhen ripe, the anthel'ic1ium have a yellowish or orange colour
and open at the top (multicellular Oi)CrClIlar cap), the whole
mass of spermatozoid l1lother-cellH escape and finally from
these mother-cellH the spermatozoids are discharged in the
surrounding lilm or water which· wets the surface of moss
bcd.
lih
STRUCTURE ,\ND 1,EVELOPl\IENT OF I'LANT GROUP:-;
Archegonium.
The archegonia, borne on
separate plant,
arc also in a duster at tlw apex. of the garnetophore and the
it
perich1ctial leayes lllmally remain folded over them. Each
archegoni\lm is a llask-s11aped body with a very short stalk
and consists of 1\'.'(1 pans: a hasal slwlllen portion, the V(.'Iz/Cl',
and a c()lllparalivelv long upper portion, the lIt~ch. The venter
Archegonict
Ventral canal calf
Ovum
A
B
Fig'. 137.
"\,
l'oly/.ri'·"·/II1'.
LnNl'il'l'UIliNAL Cl];)("I'JnN THItOI.lI:U 'I'l{{': .11']";'\
FBl.AI.Jo: PLANT Rl{OW1Nn AIll'IIEtHlN1A:
H,
A
',II,HlTtlE
A[\(·In:r:nNl1J~I.
OF
.\
'
cOlltains a ventral callal cell and a female cdl. the ()().\·/J!tC/'I'.
or OVUIIl, or egg. In this case there is a variahle number of
1/{.'c/z cdls.
F el'tili.zaLion.
vVhen an archegonium matttl'l's. it passage i<; l'stahlisil('(l
aue to rhc disorganisation of the canal cells. Thi:; passage
becomes li11c(l with a mucilagl'llolls substance containing emu'
,wg;ar. Fertilization takL's Id;1C(' in walet'. Biciliate spcrrnat<12:oids, swimming by means of cilia. come ill the neighhourhood of archcgnnillll1; thc~e hcim r attracted by ('he cane
wgar penctral~ tht' \led.;:, hLlt' one"of them fl1S~'S with the
DRYOPHYLA
The fertilized ovn111 then ~llrounds itself with a cellwall and hecame~ an oospore. The ova nf sc\'eral al'clle~onia
may be fertilized forming oospores. hut 1'hc nne whi~h is
forilled firs1' hegins to grow on getting footl while the rest
elry up so tha1' only one sporophyte develops over a leafy
gametophore. With fertilization and formlltioll of uos/>ore,
Ihe sjJOrtJhvi£c or dij>Z()id gencrlltion hegilZs.
ovum.
Formation of the sporophyte, .
The oospore gradually passes into an emhryo. which
ultimately gi vcs rlse to the s/)orogollilllll, the ~porphytic
generatioll of I-he moss plant. Due to the rapid growth of
tIle sporngonium. Ihe upper portion of the archegonium-neck
becomes torn oif so that it is carried ott in the form a cap.
ultimately forming- a very large hood-shaped C({lYl>lra covered
with a dense growth of ImirR.
Sporogonium. The sporngnniuIll consists of three parts:
(a) a sac-like upper part. the capslfle, (b) a sknder st'alk calleel
sela and (c) a small foot hy lllcam of which it is attached
to the gametnphyte. The capsule is at f1rst green in colom
owing to the P()sst'~Ri()ll of chloroplastR and in its lower portion
it I,eal'S a few stomata. \Virhin the capsule the spore-hearing
tisslle, the S!WfOP;C}/()US tissuc, develops frOIl1 which 111timately
spores :U'c formed (folll' spores from each spore mother-cell
(Iue to reduction diyision). A large part of the central tissue
of the capsule rel1laim sterile forming the so-<;aIIcrl columella
and the conical upper part. the o/>cl'l'1I1u1H, which 1)ecomeg
detached from the lower part as lid in order t:o allow these
spores to escape. Jll~t hene:t.i"h the (Jperculum there is a complicated structure known as j>crislo112c consisting of 6+ "teeth"
in 11 circle around the mouth of the sp()re-cav~ty of the capslIle.
These are nothing Inlt hundles oj' I-hkketwd (-ilm.lus c('ll~, 1'("
,e;l1larly arranged in crescent form rcsc.mhlin~ the spokes in
a wheel. These teeth hell I lO scalter the spores. There
are two large intercellular spaces surrounding the sporogenOlls tisslle, nne 011 its ower ~ide and the other between it
and the columella and arc traversed by narl"Ow lllamentoUR
strands of cells Ct)lltaining cllloroplasfs. At maturity the
184
STRUCTlJH!i AND DEVELOPMENT OF PLANT GROlll'S
capsule finally becomes horizolltal and elorsivcntral. With
redllctiull divisioll and formal'ion of sl)orcs, the gaml't()phylic
or haploid p:encratieJ7l begins.
AlIlIulus
-Oulel' ste1'ile tissue
win.
clilor'oll!zISlS
Fig. 138.
l.d)N(UTfTflINAL
l'lily/rid'lIlIl,
HW"l'ION
(1J'>
A 1_' .. \I'~rrLE.
Formation of tlie new gametophyte.
Whell the spores matll1'C they are shed by means o[
peristo1l1e. These may rest for sometime but whell they germinate, lIneler favourahle conditions. dirccl"ly give rise lo
protonemata. On germination the exo~p()rc bursts and tht.:
endospore protrlldes and ultimately by repeated cell-divisions
give rise to prlltonema.
CI-IA PT'ER III
PTERIDOPHYTA
rhe Ptericloph y lCf; include plan ts like ferns. horsetails,
du b-U1osses and their allies and arc widely distributed in the
temperate and tropical regions. They al:e frequently fOlillCl
in moist terrestrial habitats but many grow as lloating
aCluatics or may even he epiphytes on .tree trunks. They
])ave a well-defined alternation of generations in their lifecycleH and. the sjJ()1'()jJhyLc -is always lUI indetJC1UZCllt plant and
free from the gametophyte at maturity. The p;ametophytc on
111e other hand .is either wholly hulependc1l1 of lhc sporophyll'
or
be p(lrlillllv or wholly tlcpenliL'llt rm the SJ1()},O jJlty te
for its nutrition and arc alway~; smaller than the sporophyte.
'1II1Iy
Thc plant hody is u:-;\lally wcll-clifEercntiated into stem, root
and leaves and with an internal conducting system consisting
of xylem and phlocm. The asexual generation or the sporophyte may be /1O'fI!o.-;porolls (with sporeR of one kind) or
Izl'terospo'I'O'IIs (with spores of two kinds, viz.-small 01' microsj)()1'CS and large or mIJgas1)orcs). The Pteridophytes differ
from the Hryt;phytes in having an independent sporophyte
with well-differentiated vascular strLlctures, They also differ
from the seed-bearing plants (Spcrrnatophytes) in the liheratio]) of the female gamctophyte from the sporangium. The
method o[ sexual reproduction resembles that In the
Bryophytes.
The principal feature of the stem is its conducting system.
This is known as sicle; it is worth noting the different kinds
of StelcR with their names as in all pteridophytcs and. aU plants
abq"c t1Wtn have steleR of one kind or another, Tbe principal tiRSIlCS of the steIes are xylem and jJIIllJcm. Outside the
r;tclc there is always a cortex limited externally by an epidermis: and inside it there is oft-en a pith, The names of
ditTeren1' kinds of steieR depend upon the relative positions of
these parts. It may he a protostclu, where the xylem represents a central Holicl cylinder sllrrollnuccl by phloem (e.g,
Ly(;oj)_odiutn, Glcid/c1/ia-a fern, etc.). In an mnjJhijJhloic
186
STRUCTURE liND DEVELOl'l\lENT UF 1'1.,\NT CROUPS
siplzollostele the xylem is in- the form of it IlOllow cylinder
with phloem on both sicles, external and ill ternal, and there
is always a central pirh (e.g. Adimltll'lll-Maiden hair fern,
Mtlrsclia, elT.). 'Vhen it: is an cCIIJ/Jh/(Jic Sij)/tolwslc/c' the
xylem has the form of a hollow cylinder SlilTOllllding- it central
A
B
D
I"i 1,':. 139.
A,
lJU'J"EllENT
Pno'POSTEt.l;;
IUNUS OF SH.LES
IN
"/l'I'it/(/j)/'Y/"".
A1\lPITlPJILnlC ~LP!l(l1\In,";'['ELE j
SII'HONOH"'ELl':; D, ~'nrly\';'I'ELJI:.
H,
<\
]<:{"I'O'l'IJLOl('
pith bm rhere is phloem only on the outside (e.g. OS11W/lila
-Royal fern. also charac:terisl"ics ()f Dicotylc(lollS and Gymnosp~nns). vVhen there arc several s1rands, ~ach one is a Pl'~)t()­
stele, it: i~, called the jJolysldr' and these sLrands are lIwally
arranged in a circk su tllar there if. a pith at the ct:ntre and
cortex ()U1Hide (e.g. Polv/){)(/iulIl, P/I'ris, etc.).
PTERIJ)OPIIYTA
The Pteridoplytes have heen divided intI) four classes:
Class I. Psilophytinoo.
The sporophyte if; le:lfless or
pl'Ovidcd with very minute leaves: rO(lts arc lJS\JallV ahscnl
in the fossil fonus. The sporangia arc terminal a l~rl occur
singly at the tips of the hranches.
Class II. Lycopodinae. The sporophyte is diFferentiated
into root, stem and leaf. The leaves are millute (micl'ophyllous) and usually spirally arranged. The branching of the
stem is typically dichotomous. Leaf-gaps are absent in the
vascular cylinder. The sporangia are horne singly on the
adaxial face of the sporophylls and contain either homospores
(e.g. Lycopodium) and heterospol'es (e.g. Is(rtes and Selagillcllfl).
The spol'ophylls mayor may not form a cone or strobilus.
Sperms arc usually biciliate excepting in Isa~lcs.
Class Ill. Equisetinre. The ~porophyte is differentiated
into root, stem and leaf. The Htem i~ provided with distinct
nodes and il1tcrn(Jde~. The sterile leaves are either micruphy1l0UR or lll<tcropllyllolls and arc mmally arranged in whorls.
Leaf-gapH are absent in the vascular cylinder. The Rporangia
are borne iil groups on the under surface of the pcltate SP0l'(Jphylls arranged Oil a special S1TllctLll'e c;tllcd the spo1'({llgiojlll()re and form a distinct COliC or stmbilus. The sporophyte
i~ wmally homosporous. Sperms are always mu1ticiliate.
Class IV, FUicinm. The sporophyte is dilTercntinted into
root, stem and leaf. In some exccpti()nal cases roots arc entirely lacking. Thc leavc~ are usual1y large (macl'ophyllous)
and are <11'l'anged spirally. Morphologically the sporophylls
and sterile leaves nrc alike and they never form any c()ne 01'
strohilus. The sporangia are borne in groups forming sori,
either on the margins or near about the centre on the under
(ahaxial) surface of the sporophylk Leaf"gaps are present in
the vascular cylinder. Sperms are always 11111hiciliatc.
Lycopodium
(Family [,_-Vw jJ()di((C('m)
Lycopodium, commonly known as c!u1HnosR and ground
pine. grows chiefly in tropical and suh-tropical forests 1mt
STRUCTURE AND DEVELOprvI~i:NT OF l'L,\NT GROUPS
188
some species are also distrihu ted in arctic and .te1l1peratc
regions.
Vegetative body of the sporophyte.
In habit all species vary widely, hut all have sJcnucr,
weak-stellUTIerl, cornpal'atively small, herhaceous or shruhby.
1<'ig. 140.
A,
PIJANT;
B,
A r.V::\lI';
J,!lI'''l",tlill'lll.
(\ A HPOn,OPlfl'LL \Vl'l'lL ,.\ KI'nllANf:IlT~\1.
sporopbytes. Many species are wmcwhat prostrate with
stems creeping above or helow lhe surFac(' of d1l' soil. Other
PTERIDOPIIY'l'A
terrestrial species have upright or semi-erect stems, which later
on become more or less borizul1taL
Some species may algo
l)l' epiphytic witb pendent bodies. whilc still othe'l's are twining to some extent.
In the simple~t case the sporophyte has a simple stem
covered with
ll11merOltS,
moss-like leaves. each bearing
large sporangiulll on its upper side,
a
single
Tn this sense the whole
s/)()rojJhVtc.' is thcll. (/ strobilus (e.g. L. sc/rtgn. L. pitheyoidcs.
etc.). Tn more complex types, the sporophytes have lUnchhranc11ecl stems whose lower leaves are sterile and act :ts
foliage Jea ves and this gradual sterilization process can be
trace!l to forms 'where the sporophyte is distinctly differen-
liawd into a vegetative region hearing foliage leaveR ilnd
reprodllcdve regioll bearillg the sporophylls.
!l
Tn 811(:1) ca.~cs
the s]1nrophylls are quite (liirencnt in form from the foliage
leaves and are localised and compacted to form a distinct
strobilus (e,g. L. clilva/.um).
The~e strohili
arc often separa.ted
from the vegetative hotly aml arc horne on slender stalks with
ru(Hmentarv leaves.
Branching of 1'11c stem is charilcteristically dichotomolls.
the two branches of a forking may he equal or uneCJual. The
leaves are very
l1Umel'OllS.
sirnple and small (usually
2-10
m.m.
long. sometimes llptn 25"30 111.1'11.). arranged in close spirals,
whorls or opposite pairs, or the arrangement may he sotnewhat irregular.
The primary root is short-lived but many.
adventitious roots arii'c. singly or in i\('l'opetal dusters, from
the under side of the older part::; of the stem and the hranch-
ing is. strikingly \lichotomolls. Root hair!'; arc abuncla6t and
persistent in some terreRtrial species and lateral roots do nor
develop.
Iya
STRUCTURE AND DEVELOPi\lENT OF PLANT GROUPS
A eross section of the stern shows two distinct regions,
the cortex and .the cellI ral Cyilldcr or the sIde. The cortex
is hounded externai Iy by all epidermis. one cell in t:hickness
and with stomata.
in structure.
The cortex varies in thickness as well as
In somc species it is soft and parenchymatous
tbroughout, in others the olltc:r or the inner portion of the
cortex un(1ergoes sclerili.cation, while in still others the entire
ProioxyJem
Phloem
Endodei-m18
Pericyelo
Fip;. 141.
/'/I(·oIJl/t/ilill/.
TltAN!,VEJU:HC SECTION OJ.' TIlE :-;'/'El\l.
cortex become.s sclel'itie.cl.
The cortex is limited i.n\cmally
hy
an l:ndodermis with characteristic radially rhic1{cncd walls.
Lying within the endodermis is thc pericyck. 3-6 cells
thickness.
Internal
to
III
the pCl'icyclc is the central core O:l
va~clljal' cylinder which is a protostrlc with xylem exarch.
In
tI1e simplest ca~e the xylem appem's as a star-like mass, with
a varia hie numher of rays.
Til hctwcen the ~'ays lies the
l'TERIDOP!-lYTA
19 1
phloell1, being separated from the xylem by narrow ~trip of
parcncl1yma.
In more advanced' types of sporophytes
llumerous furrows appear in the xylem cylinder so that the
xylem hreaks up into isolated strands forming plate"like
lohes or mesh"like mass, with inc]urkd phloem hand!'.
Sporangium
Spol'opbyll
mg.
142.
1;;ljcllji(!(/iulJI.
T,ON(II'1'l1ll1NAL Hl·:(."l'ION'
m'
H'1'W\JIILlTl-l.
Asexual reproduction.
(a) Vegetative. There are several means hy which
:vcgctative reproduction takes place.
(I) Tips of lateral
hranches hecome tlattened and with wing"like leaves, known
as hulbils or gemma:_>, annually fall to the grouno.. take roots
and form new plants. (2) The rhizome progressively grows
at the apt~X and its oleIer part dies. the hranches become
Hcparated an(l :form new plantH. (3) In some species during
winter the entire plant dies, hut the apical portion behaves
as it resting hud. (4) In epiphytic species portions of. plan1'
hotly may give rise· to new plants .. (5) Roots il!ld detached
leaves of lmlbils can also gh;c rise .to new it'i.dividuals.
19 2
STRUCTURE lIND DEVELOPMENT OF PLANT GROUPS
(b) By spores. Lycopodium is homosporolls ape! the
spores are produced within large, shortly-stalked, reniform to
somewhat sub-globose sporangia borne singly either in the
axils or on the stem a little above the sporophylls. The sporophylls are variable in form, size and colour in di1Terent species,
sometimes resembling foliage leaves.
These sporophylls
usually become localised and aggregated to form cOlles or
slrobili, at the apex of the main stem or on lateral branches.
The strohili are either stalked or sessile. The sporangiulll io
Spore
mothel··cella
Fig. 143.
/,yt:()}Jllilili III.
LONGrl'U.TJlNAr, KI';c:'l'JOl'l 0]0' 'l'IIJo: i:\pnllhN[lI{J~l
CONTAINING HI'Ortl'; MO'I'llJm-C'JlJ.r.H.
eusporangiate in dcve]opll1cnt*. Within the jacket of the
spOl'<lngiulU the .1}orogc1l0US tissue is surrounded hy a special
nutritive layer known as laj)ciulll. Tbe cells of the sporogcnOUH tissue ultimately cease to divide to form spore mothcr-cellR .
Supcl'fic~111
J_(l'onp of 6-12 cells in t.he axil of HflOJ'()j1hyll miLy aet, H.i!
"hich hy repeatml rliyiHioll ultimately forllls I.h ..
Rp0l.'illlgium. Eaeh of ,thoso C('JlH <1ivi<jpH by pCl'il'lin:tl wall (i."., 1':1,1'1\1101 Ltl
the snrfnce) fOl'lning l'OWR nf iun!)l' IIllci ()1l1!>,1' !\t111~. The illlWl' cldlH, Lit"
'1))'i-JtlIlI'J1 '~lJ01'()(I(',7W1(.q' (,P,UB, hy l'cjlcat,'d (livisioll give rise to thn IIjllI)'ogmlOm
[,iSSlI.C .while the ont.or cells lllLinud,oly form tltt! wall (If (,1w H]lOl'IIIIgilllll
C()nSIH~1llg of 11 few lnyol'll .of eol!. 'rIds lllethod of HIHll'l1l1ginlll r]t,v(dol'mont lB known I1R M(,Q1Wl"(IIf1W/.(', III(!tlwrl ,md i~ (']\al'Hdel'istie of all \"\Hl'.n1ar
plants excepting tIle mo<1Cl'n ferBs.
.,.
"))()1"(11/.{/illln-illIf i(ll
l'TERIDOPHYTA
each of which by reduction division gives rise to a spore-tetrad.
lVith reduction division and formatioll of
sj)OH'S
the gmne;o-
j)/zytic or !zaploid generation begills. Each spore shows a
weak tri-radiate ridge and its wall is 'either smooth or shows
l]()Iley-cOlhb or net-like thickenings.
The gametophyte,
When the spores are mature a narrow transverse strip
of cells (slomillm) is gradually differentiated at the apex of
fhe sporangium which ruptures transversely and liberate the
spores.
Each spore under favourable conditions germinates
and produces t11e gametophytic plant.
There are 1wo main
types of gametophytes. In tropical speci~s (L cCrJlllum) usually the spores after liheration germinate quickly and form
qllOft-livccl gametophytes. on the surface of the )!;round, which
arC very small, grecn (excepting the basal porlion), some-
In other
cases especially in creeping and epiphytic species (L. clavatum), the spores after a shorter or longer period of rest (:-\-8
what cylindrical to ovoiil hodies wit11 lobed apices.
years) gerrninate and form non-green, subterranean, somewhat tuherous or can:o~-shapecl, much larger gametophytes,
sometimes milch convoluted, and these grow to maturity very
slowly, taking several years (6-I5 years) and nourishing the
young
sporophytes.
In
other
species
transitional
forms
occur and these gametophytes are partly suhterranean with
a l\"reen. lobed,. aerial portion (crown) bearing the sex organs.
Usually both hypes of gametophytes are assocIated with an
endophytic fungus forming a mycorrhiza which is a prominent feature of the gametophyte.
The gametopbyte of Lycoj)oclium is monceciolls (homo,
thallic) and numerous sex organs, antheridia and archegonia.
13
IY4
STRUCTURE foND DE'lELOP}'IENT OF PLANT CROUPS
are borne either on the crown Of in between its lobes or on
the central cushion in flattened types of the gametophytes.
Crown
Primary tubercle
A
l<'ig. 144.
A. (lAAUJ'l'Ol'n1:Tl~; 13,
LlII'I11I()(hllll/.
I.Ol-WITlllllNAL Hl']CTtnN (H' THE HAm,
~llOWJN(j A DIWgLOI'IN(; RI'OlWPIlY'I'E.
PTERIDOPHYTA
195
Antheridia. The antheridia vary in size, shape and
!lumber of spermatozoids and either project slightly or remain
wholly embedded within the gaemtophytic tissue. There are
many spennatozOld mother-cells within the single-layered
antheridial wall and each gives rise to a biciliated (rarely
three) spermatozoid resembling the spermatozoid of Bryophyta.
mg.
A,
145.
Lyc()jJodilllll.
B, ANTHETW7.i)Ill~.
AN AN'fHEltlDIrlM;
Archegonia. The archegonia are either short or long and
embedded In the dSSllC of the gametophytes with their necks
protruding upwards.
At maturity each archegonium cantains
Fig. 146.
LycopodiulII.
STA(lES IN THE DEVEr.OPlIIENT
OF THE Alt(JHEOONIl'l\{'
an egg cell. a ventral canal cell and 6, sometimeI' 10- I 3, neck
canal cells (hut only one neck canal cell in shorter arrhcgonium).
F ertiliza tion.
\Vhen the antheridium attains' lnaturity .its neck canal
{:elJs and ventral canal cell disiritegrate forming II passage
196
STRUCTURE AND DEVELOl',MENT OF I'L/\NT GROUI'S
open to the ovum for .the spennatozoids to fertilize. The
walls of the antheridiu11l breaks up; .the spermatozoids are
set free, these are washed to the arcbegonium and one of them
finding its way through the neck ultimately fertilizes the
ovum. The fertilized ovum soon covers itself with a wall and
forms the oosj)ore. With fertilization and fonnatio}l of
oospore the spofophytic or diploid gmzeratimz begins.
Formation of the new sporophyte.
The oospore by repeated division gives rise to an emllryn
consisting of a SlIsj)ClZsor cen, an ahsorhing organ, calletl the
foot, the stem. a leaf ano a root helated in development. From
this embryo the young sporophyte gradually develops and this
may be supported and nourished hy the gamctophyte for
several years. In some caSl~S several young spnrophyt:es may he
borne simultaneously on the same gametophytc.
Selaginella .
(Family Sc/(/gillcllaceEt')
Most species of Selaginellu in habit clamp forests of tropical climates and are distributed all over the world; Home
species also grow in the temperate regiom. These are found
in the hills and are ahundantly cultivated in private gardc·ns.
Some are xerophytic and grow on rocky cliffs or dry sandy
soil. They are mostly perennial. a few arc small, delicate
annuals.
Vegatative body of the sporophyte.
In general appearance, they arc lIsually long, slender,
much-hranched. dorsivcnlTal, creeping stems.
All for111s
branch freely, chiefly in one plane, and the hrnnching is in
most cases dichotomous or pseudo-monopodia],
.
The stems are thickly-clothed with numerous small, more
or less ovate leaves, usually of two distinct killtls: some
large and some small, arranged usually in four longitudinal
rows, two of which spring from the lower and two from tlw
upper part of the stem. The leaveR of the lower surface are
l'TERlDOPHYTA
197
much larger than the upper ones, one small leaf and one
large leaf arise at each node'~, At the base of the ventral
surface of the leaf, there is a membraneoLis ligule which IS
characteristic of the genus Sclaginclla,
Micro- Sporangium
I",i'.,rosporophyll
B
Fill',
147,
Sr/Il!lindlil,
,\, HPOltOl'HY'J.'E ~HOWIN(I HABl1', ltHIZOI'HOm, AND ~l'nItAN({JFlm01JH
Hl'IJml4; .13, A rONGI'l'lTllINAL HEfTl'rON TJTIU)t1(}H A HI'DltANGIFJo:JtO!lB
SI'IKI'; SHOWING MWIlO-ANlI MAGAHl'nnANUI,\,
The roots are mostly adventitious, hecause the first root
dieH early, The branching of the roots is dichotomous in
al fern ate planes. At each ramification of the stem, a root"
like organ, tIle Thizoplwl'C t is developed which on reaching
the soil produces the root!; ['here,
A cross section of the stem shows two regions clearly
differentiated, the corte,'),.' anll the sIde or stdes. The cortex
is many-layered consisting of either entirely thin-walled
* In Home
CII~(jH t;Jw le[lVl'~ are filiform lIud t,lu' 1l1'l'IlUI-(PlIlcnt, is eithel'
01' ill deCllssa,te pilil'~,
,', '1~he morphological lHltlll'u is donhLful. HOW!)Vl'I', it appears to Le
1l01'lIlii lIy a h~ilf·lo~H skill and IlHt,V Honwt,imes heal' leaves aHd even C!JlleS,
in
~pil'als
198
STHUCTURE ,\:-;D DEVELOPl\lENT OF PLANT GROTJPS
parenchyma or the outermost parr of it being thick-walled and
highly lignified (sclcrified parcllchyma). with or without intercellular spaces and is hounded on the outside by a singlelayered upidermis consisting of thick-walled cells and with
a cuticle. The number of stele ranges from one (rn01wsfclic)
to three or more (polystelic), each of which is slIlT()undecl by
an air-space which is bridged by radially elongated cells with
prominent casparian strips. the ll'(!/JuW/u' .• which represenl the
enc!odermis. Surrounding each stele there is a single layer
of pericycle consisting of conspicllous parenchyma cells. The.
vascular bundles are haclrocclltl'ic; the xylem is exurch and
diarch.
Asexual repl'oduction.
SclcwiILclla is heterospurous, hecause the asexual reproductive uni~~, the sporeR, are of two kinds: the smaller ones are
micl'osporcs and the larger ones arc J1lcgas[JO/,l!s which are
PTERIDOPHYTA
produced in ditl'erent kinds of sporangia. The sporangia are
mostly reniform or ovoid, sometimes flattened, and shortly
stalked. The two kiilds of sporangia differ greatly -in size, the
megasjJorangill1Jl being much larger than the microsporangiu1Jl. The sporophylls bearing rncgaspurangia are called 1Jlcgasporophylls and those bearing microsporangia are calle(l microsporophylls. The
sporophyllfl, which are nearly of equal size,
are generally collected into more or less distinct, four-angled cone or sporangifero1lS
spi1u: or stmbilus. These cones are tenninally situated at the apices of the branches.
Each cone usually consists of both types of
~porophylb, hut in some. species only one
type of sporophvll may occur. The order
of arrangement of the two types. of sporophylls is variable in different species. Each A
n~egasporophyll hears in its axil a megaRporangium within wllich occurs only one
jUllctional 117cgns1JOrl' 11wthcr-ccll and it
gives to fOlll" megaspores* due to reduction
division. On the contrary each microsporophyll hears in its axil a micro sporangium
containing 1nany microsporc mother-cells, B
eac}) of which produces four microspores c111'~
to reduction division" so that many microspores occur in each microsporangium. Both Fig. 149. SI'1f1!/in"zla.
types of spores nrc tetrahedral ann the wan A MA'1'lnm MI(:JtOSl'Oshows a tri-radiatc ridge and ornamerita- RANGllTM wl'm MW'
tions. With reduction division and formaM~~~:R~~~;~~_
tinn of s/JOres, the gametophvtic or ha1JZoid l'OltANClJUM WITH
,
1 '
MIWASPOTIES.
gClwratWIl JCgZtls.
The Gametophyte,
Male gametophy'~e. The microsporcs, when still included
within the microsporangiulll, hegin to germinate but are
...- ..... ----_.._--_.-------.-.-_.... _---------_..
_._.._..- - - - - - - -
• OeeaRiOlllllly 8 to 40 llwgasplll't'R art' fOllnd in
D
lll<1gaSptJl'f111ghllll:
200
STRUCTURE AND :UEVELOl'MI;NT OF PLANT GHOUl'S
ultimately set free by transverse rupture of the sporangil.llllThe re~mlt of germinatioll of each :nicrospore is a mille
prothalllls (protlwllial cell) which is extn:mcly reduced to a
wall.
single cell.
tipel'm'U1olhel'-oclls
c
Sllel'llIH
MicrOSllOl'e coat
o
Fip:. 150.
A-D,
SI'7oUilll'7lll.
STJI.:c:f;~KIYJ·;
S'fAGES IN THE nIWEr.I)PMI~N'I' (W )1,11.1';
GAlIIKI'Ol'ilY'l'lC AN]) I'OllMATIClN (W Rl'EH~I.\1'():r.nIl)K;
lj}, 'l"Vn ~"Eltl\TA'I'OZOn):-\.
c
It hears the so-called rudimentary
r/1lllwridiu/ll
(the
II/·j/llt/}')!
spernw{oRc}Wl/S ccl!.I'--fuul' in number) !Jeill[!; SlfrrOi/ Iulcd liy
a .lac/eel of sterile cells (}aclwl cells) and the whole remains illc111detllVithin the sp(irc-wall. From the primary Spel'malo),!;cnolls
cells about nil to 1.56 speI'1Halo,zo'itl IIwtlie'l'-cdls are Ill'oclllced.
Biciiatcd spennat()znids are developed from the spermatozoid
mother-cell of the so-called antheridium and these ultimately
Hoat freely in the cavity of the spore-wall. The spore-wall
hllrst~
and liherates tlle spermat(lz()ids ill tbe slirrounding lilla,
of water.
Fem.ale gametophyte. Similarly.
hefore fhey are
S('l
free
froll1
111 egosplll'l'S
gel'millate
the megas)l(]ranginm.
On
PTEIU[J()PHYTA
germination the spore-wall docs not hurst and there
folow8 within it free nuclear divisions forming large number
of nuclei which arc distributed in the general mass of. cytoplasm surrounding a large central vacuole. As the nuclei
.Fi;.;. 151.
IN
A
IlEf:A"I'(IIll':
IiW"I'InN.
l"ig. lS2.
SJJll\\,INli
]\{lcllAHI'OIU: OF S"far/lud/a
'1'111, FE'IA].!':
1';Xl'OHEIJ rrHIHHTnH TilE
(~uli'mlI'HYI'J:
'I'nI~lIAIllA'(,I';
HlIHiE.
increase in number the cytoplasmic layer becomes thicker and
the vacuole becomes smaller and smaller mHil it is completely
tilled lip with cytoplasm. Wall-formation ahom the nuclei
c
Fig, 153. 8dl![/illdll/,
A-C,
S'I'AClEel IN '1.'l'm I)!o]\'JolLOI''MEN'I' rlF ~'I';MA'I,r·: (;A~H:'I'OI'HI"n:
ANI> FOUMN1''[()N OI!' Aitr'TTlWIlN WM'.
follows from the periphery ncar the apical region. (towards the
tri-rarliat·c ridge) forming a tisslle which gradually extl>nds
2()2
STRUCTURE AND DEVELOP:\IE1-:T OF PLANT GROUPS
inwards. In wme cases, after forming 11 tissue consisting of
3-10 layng of cells from the periphery, the wall-formation
~rops temporarilY .aud the inner walls of the lowermost layer
of cells hecnmes thickened to form !'.o-called diaphragm which
;;epal'ates the peripi;eral ti~sllc from the nOIl-lcllular portion.
The megaspores. at abollt thi~ stage. are liberated from the
megagporangium and the \Vall of each me~aRpore ultimately
hursts along the tri-radiate ridge exposing the archegonia and
part of the female gametophyte. The female gametophyte
then becomes gl'f"en and also deyelops rhizoids which
come out through the tri-radiate fissure. The female gametophyte thus ultimately becomes independent of the sporophyte
but not free from the megaspore being still enclORcct within
the spore-wall. \Vithin each archegonillm the ovum 01' oosphere
dc,'elops.
Fertilization.
When the archegonium attains maturity. the lieck cells
and ventral canal cells disorganise. The l;iciliate spermato
Fig. 154.
S/·!I'yiw-llil.
A
LONGITUDINM. ~ECTION TITR01l1iH TIm
FE)[ALE GAMETOl'HY'I'E SIWW1Nf: THE
E~mnYO srOHOl'HYTE.
zoids
discharged from the antheridium of the neighbourin{Y
•
b
rudImentary male prothallus, swim towards the archegonium
in dew or rain-water and ultimately fcrtili?:e the ovum. The
PTERIDOPHYTA
fertilizecl ovum, on gecreting a wall round itself, becomes an
oospore. With fertilization and [ormatioll of oospore thl?
sporoplzy tic Or diploid generatioll begins.
Formation of the new
sporophyte.
The oospore gradually
gives rises to an embryo
possessing a stem two cotvledons, a foot, a root, and a
.suspensor
and
from
this
F'ig. 155.
E31I1RYO OF
Sdar/illl,llll
,., SUSPENSOR: 'r, HOOT; j,
E'oo'r; 7, LEAVES; ,st, STE)['
embryo the Selag'inella plant
is derived, thus completing the life cycle.
Isoetes
(Family Isretace<e)
A great majority of the species of ha:tes, commonly
known as quillworts, are hyclrophytes that grow in water or
on swampy land, A fe~ species, however, grow in habitat~.
that are' completely dry for greater part of the year.
Vegetative body of the s)JoroJlhyte.
Isa'tes wggests the appearance of a tufted grass which
consists of a very short. two or three lobed. tuberous axis
densely covered hy rOBette of overlapping hases of, stiff awJshaped leaves, From tbe lower surface of the stem many
dichotomously branched roots develop. The leaves are
unique in structure being arranged in a close spiral on the
upper surface of the stem.' Each - leaf is a sporophyll, the
outermost and lowermost leaves lJeing sterile: successively
within tl1ese are sporophylls with mature and immature
:20..[
STRUCTURE AND DEYELOPl\lENT OF pr~ANT GROUPS
sporangIa. In this sense the entire plant body suggests the
COllstructioll of ([ strobilus. Each leaf consists of a basal
Rporangium-bearing region and a terminal foliage region. The
awl-shaped foliage portion of the
leaf contains within it four
cylindrical air-chambers whicb
lllay be transversely septate at
intervals.
At the j unction of the blade
and basal por'i:ion of the leaf
there appears on the adaxial side
a ligule being socketed in a small
pit. Below this ligule the broad
sporangium-region occurs. There
is a single flattened sporangium
on the adaxial face of each leaf.
Leaf
This sporangium IS situated
within a depression 1Il the leafbase and is more or less completely or incompletely shut off
from the outside by a curtain of
tissue (veI1lm) arising just below
the ligule.
The anatomy of the stem
has been interpreted variously
as it appears to he somewhat confusing. The stem is so much
compressed that
cylinder appears
}fig. 156,
AN ENTIHE
[.<"'11'.'.
PLANT,
the vascular
to be a little
more than a vasc'ular plate and is
a pro/()slele The xylem elements,
PTERIDOPHYTA
however, do not completely fill up their region and the
phloem elements are not completely recognisable. Some sort
of secondary growth takes place by means of cambium.
•
Vascular bundle
Fi~.
157.
1.0w/,·,<,
TRAWSVERHE SECTION
OF LEAl'.
Asexual reproduction.
Iswles is 11etcr08po1'ou5, Both
microspo~'es
and megaspores
are produced in different types of sporangia, microsporangla
and mega sporangia, borne on microsporophylls and megasporophylls respectively. The method of development of hath
types of sporangia is somewhat alike in early stages. Within
each sporangium a large mass of sporogenous tissue (upto
10,000-15,000 cells) is developed.
At this stage the differences
l'esulting in heterosporous conditions start. In those sporangia
which are destined to become microsporangia differentiation
of the sporogenom tissue begins. SOlne of the cells of the
206
STRUCTURE ,\ND ilEVELOPl'\IEl'\T OF PLANT GROUPS
sporogenous' tissue form alternating plates of sterile cells
(trabecula:) across the sporangium with fertile cells which
function as microspore-mother-cells. In those sporangia which
are to become megasporangia the trabeculre appear to he
more· massive and ~lUt of the thousands of sporogenous cells
only
4~-75
megaspore mother-cells are fertile, others perform-
A Sporangium
Fig.
A,
158.
180:/ e.~.
OAtiAL I'Olt1'ION OF A LEAF; B. 'l'HAN~\,ER8E ::menON
OF THE HA;\fE; C, LONflITiJDINAL SEcnON.
iug nutritive function. Reduction division of the spore
mother-cells follow and from each four spores are produced
with the initiation 'of the gametophytic or haploid generation.·
The total output of microspores in a single microsporangiuI11
is 15,000-300,000 and that of megaspores in a single megaspOl'angiull1 is 150-300. At maturity .the sporangia an:
illdehiscent in most cases and both types of spores are ultimate-
ly liberated by the death and decay of the sporophylls.
The Gametophytes.
Male gametophyte. The 111lCrOSpores after liberation gerInmate immediately ami fonn male gametophytes within a
1.0j
l'TERIDOPHYTA
few days. The nucleus of each micros pore divides and the
microspore is divided asymmetrically into a small prothnll£al
cell and a large antheridi{l/ illitial cclI. The prothallial cell
.....:" ..
Antheridium
Froth.llial cell
c
o
"'ig.
A-D,
159.
Iswt, N.
SnGES IN THE DEVELOI'~[ENT OF ANrm:rWZmll.
j'cmains undivided but the anthericliai initial divides rep~atedly and ultimately forms a so-called rudimentary antheridiullL consisting of an outer jacket layer of four cells and.
four inner spermarozoid mother-cells. Each spermatozoid
mother-cell is ultimately metamorphosed .into a large, spirally
coiled, mlliticiliate spermatozoid. The prothallial cell 'and
:l08
STRUCTURE ,\ND DEVELOPllJE;\;T OF PLANT GROUPS
the four jacket cells disintegrate and the !Spermatozoids are
ultimately liberated by the decay of the spore-wall.
Female gametophyte. Each megaspore germinates and
forms a female gametophyte and its mode of development
resembles that of Sclagillella with the fo11owing differences:
The germination starts with a series of free nuclear
division and a conspicuous central vacuole is never formed in
the protoplast (as in Selaginella) in any stage of development. The nuclei gradualIy becmllc more numerous in the
~(n~:>:----l1egDspore
cont
W¥.,.}+~---Arehcgouium
o
Fiy;.
A,
160.
Jso:II·.~.
LONGITlJDINAL :'ECTION OF )!EG srORE RHOWING
AN ARCHEnONIUM; B-D. STAGF.S IN THE
DEVELOPMENT OF AnCUEGONIUM.
apical ponion of the multinucleate gametophyte and an
apical tissue is formed at this stage. The lower multinucleatJ;'
portion of the gametophyte ultimately becomes cellular but
this process may he considerably delayed till the development
of an adult embryo. "The first formed apical prothalJial tissue
is exposed by cracking of the spore-wall along the tri-radiate
PTERIDOPHYTA
ridge and is de\'oid of chlorophyll. The gametophyte does
not protrude through the megaspore-wall but may produce
numerous rhizoids, The archegonium is hroad and short,
and consists of a single uninucleate neck canal cell, a ventral
canal cell and an egg .
.Fertilization.
When the archegonium attains maturity the neck canal
.cell and ventral canal cell disorganise. The lllulticiliate spermatozoids swim towards the archegonium in dew or rain
water and one of them ultimately fertilizes the ovum. The
fertilised ovum Oll secreting a wall round itself becomes an
oospore.
With ft'J'/ilizfltir)J] and for1l1ation of o,ospore the
sporophytic stage or diploid generation begills .
.Formation of the new sporophyte.
The oospore gradually gives rise to an embryo posses~ing
.a massive foot, a root. the stem and a leaf (cotyledon) with
It ligule.
It is a peculiar feature that the emhryo of /S(ctcs
Fig;.
A,
161.
13,
A DEVEr,Ol'lNG E~[BnYO;
/,,,,'11'8.
nIWELOl'lNI: >;l'(lllOl'IlYTE.
has no suspensor. Of the various parts of the embryo the
stem apIJears to be helated member. From this embryo the
ls~/es plant is derivecl thus completing the life cycle.
Equisetum.
(Family Equ£sctace;e)
Species of Equisctwu, commonly known as horsetails, are
JOllnd allover the world excepting Australia and New Zealand
14
2IO
STRUCTURE ,\:\1) DEVELOPi\IENT OF PLANT GROUPS
and are mostly inhabitants of tile cool. and temperate regions,
Equisetwn is usually found in hills, especially in dark and
marshy places, wet fields. gravdly or loamy soil.
Vegetative body of the sporophyte.
The plant is herbaceous, perennial one and many are
evergreen. The siz;:; of the plant is very variahle, usually not
Tubers
Fig,
162.
l!Jqllisetll1n.
SPOROPHYTE ~HOWING THIil HOltIZON'J:AL RHIZOMK
WITH STlillULJ,
.u·m
FERTILE
SHOOTS.
PTERIDOPHYTA
2U
exceeding a metre in length. But E. giganteunl, a South
American tropical species, grows to a height of about 10-201
metres in length.
The stem is a much-branched. dorsiventral, horizontal.
rhizome which gives off many erect subaerial 81100t8, usually
of two distinct types, sterile and fertile. The sterile shoots
are green in ullom, usually hranched, perennial and
\egetative in function. The fertile shoots are pale or
hrownish 1ll colour. without chlorophyll, unbranched.
short-lived and wi ther after discharging their function (the
production of spores). Transitional forms between these two
types are not uncommon. The stem is jointed with nodes
and internodes, and each internode consists of distinct ridges
and furrows, the number of ridges is equal to the number
of leaves present at each node. At each node there is a whorl
of minute scale leaves, which are mostly non-green and ~oon
become dead. These are free at the tips hut fused laterally
with one another forming a sheath closely enveloping the base
of each internode The function of photosynthesis is.
however, taken hy the stem and hranches. The hranches are
in whorls and usually equal in numher to the leaves, a branch
always developing between a pair of leaves. The whorls of
leaves and branches of successive nodes alternate with one
another.
Roots are slender, fibrous. adventitious in nature and arise'
endogenously from the bases of the lateral branches 01'
dormant buds of the rhizome. .
A cross section of the stem shows two regions clearly
differentiated, the cortex and the stde. The cortex is bounded
on the outside by an epidermis which is single layered and
provided with a number of alternate ridges and furrows. The
outer walls of the epidermal cells are highly silicified. Stomata
are present in two vertical rows in each furrow. The cortex
is highly dilferentiatecl into the following: (a) hypodermis
consisting of sclerenchyma which may be restricted to the
periphery of the cortex or may extend inwards to the stele;
below each ridge sclercnchyma is well-developed, (b) general
cortex consisting of many-layered parenchyma with large air
cavities (vallecular C(f'uities) , each corresponding to a furrow
::217,
STRUCTURE .'ND DEVELOPIYlliNT OF PLANT GROUPS
,and these alternate in position with usually water-filled cilyities
(carillal cavities) in the vascular bundles. The peripheral
.portioll of the general cortex. lateral to the sclerenchyma, is
<chlorenchymatous with intercellular spaces and especially
.conspicuous just beneath the stomata. ancI (c) endoder'lllis
surrounding the entire stele with pro.~ninent casparian strips.
In some species each vascular hundlc is surrounded by an
individual enelodermal layer. Lying internal to the elld~)der.mis there is the pericycle consisting of a single layer of pal'en-chyma cells. The vascular huncHes are closed, collateral, and
,conjoint being arranged in a ring and each containing a carinal
]!'i~.
A,
163.
R'llli8elll'lll.
n,
TRANVERHE SEc'rION 01' THE S'rEM;
A PORTION
OF ~tAGNIFna) Y lEW OF TIlE SA:i\[E
.cavity: they a[c laterally separated from one another hy a
-small parenchyma cell. The p!'Otoxylem is end arch and in
,mature bundles these are found in a more or les~ cli~organised
,condition within the carinal cavities. Outside the carinal
.cavity is a mass of phloem consisting of phloem parenchyma
,and sieve-tubes. On hoth sides of the phloem mass is a
small metaxylem mass consisting of tracheids only_ The pith
:Iies at the centre. Occupying most of the pith tllere is a
conspicuous space (the central cavity) in the internodes of the
lwimal'y branches of the aerial shoots and this central cavity
PTERIDQPHYTA
may. he entirely ahsent in tllc internodes of smaller branches
and ol the rhizome; these' ca vitic~; also are usually ,vater.filled.
Asexual reproduction.
At the apex of the fertile hranch thcre is a conc-like'
structure, the sl)()rangiter()l1.~ spike or strobilus, which consists,
of a central axis hearing a \'ariable number of sporan~illm­
hcaring orgam, thc sporangiophores, in distinct b~n cUl~lpact
whorls. Each sporangiophore is a peltate structure with a'
somewhat f-lattcned hexagonal disc amI is attached to the mailr
axis at right angles to each otht:r. \Vhen young, these:
Ann
A
c
o
Fi". 164. IiJquisetlllll .
•/\, A I'Oll'I'IDN OF THE l'mJ.'l'll,l> SH001' BEAHING .~ 'J'En;\IINAL
STJWBII,UK; B & 0, SPORER W['l'H EIA'rEllH; D, A ~POltA~'
GIDPHORg WITH SPORANGIA ON ITS l!NIlErt SUm"ACK
sporangiophores remain closely-fitted together, but later Cll1l
separate as distinct whorls. At the hase of the strobilus, in
some cases, a modified leaf-whorl is present forming the so·,
called annulus.
On the under surface of each sporangiophore, towards,
the circumferencc, sporangia, llslIaJly S-IO in number, arC'
borne on a ring and are projected horizontally towards theaxis of the cone, Each sporangium is an elongated, sac-likebody containing many spore mother-cells hom each of which
foul' spores are formed due to reduction division, so that ~t
:214
STRU(''TURE ,\2,,1) DEVELDl']I,lENT OF PLANT GROUPS
Jnaturc ~porangium contains mal~y sporeR inside.
TVith
r-ecil(C-
,Ii(m cii'i.)isiull tlild ,oilh Jurllliltioil vj spores, the garnetophytic
or haploid generation begins.
"The Gametophytes.
The sporangium. at maturity, bursts longitudinally and
a large number of green-coloured spOTe~. Each
hesides its usual two coats. has a delicate cuticular
-sets free
~pore,
Archegonium
Fig.
165.
IvfcNowious PROTHALLUS OF Bl/lliset1l.71I.
layer and a thick pcrispore.
Later
011,
this last layer splits
into four ribhon-Iike appendages, called elaters; with spoon.like tips and these remain attached to a com.mon point.
These daters are hygroscopic in nature, which uncoil in dry
air and recoil around the spore in moisture. The function
PTERIDOPHYTA
of the elaters is uncertain.
Possibly, this expansion may assist
in the dehiscing of the sporangia, or possibly their expansion
and contraction may assist in spore-dispersal. The spores are
.all of one kind. Hence Equiseturn is homosporous.
On germination each spore forms a small green prothallus
which differs in form and in the position of sex organs
(antheridia and archegonia) from that of a fern.
At maturity
it looks like a disc-shaped, thick cushion of tissue consisting
·of several layers of cells.. from the upper surface of which
there arise irregularly-lobed flattened branches, each one-cell
in thickness.
It produces rhizoic1s from its lower side.
Antheridia usually develop at the upper ends of these flattened
and vertical hranches. while the archegonia on the upper
surface of cushion near the bases of these branches. Thus,
the prothallm is
mon~cious.
On the ()ther hand if the
gametophytes remain small, each one-cell in thickness, probably
due to nutritional deficiency, they bear antheridia only and
it is for these reasons they were once thought to be direcious.
In some cases (E. flr'venS! half of the spores develop male
gametophytes and other half female gametophytes unclet
controlled conditiollR. In the latter case if fertilization of
the archegonia fails prothal1ia proceed to develop antheridia.
The prothallia may he long-lived and may persist for more
than two years.
Antheridia. Eael) antheridium COllRlsts of an outer
jacket layer, one-cell in thickness, surrounding a number of
Rperl1latozoid mother-cells. each of which is ultimately metamorphosed into 11 "pirally-coiled anrherozoid with numerous
flagella.
Archegonia. The archegonium consists of an egg. nech
(3 or 4 cdb in height), and a central cell projecting vertically
-:n6
STRUCTURE ,. Xl) flEYELCI':\IE);T OF PUNT GROUPS
abm-e the prothallus. Thc central cell divides transversely
inw a jJri11lary cailal cell and a primm_\' '-'I'!ltral cell. The
primary canal cell
n~rticall'v
Fig.
A •.\
166.
di\'icles i.nto two !lee/? canal cells"
E'jllj"l'tlJlll rrrvfJ/i'.
Fr;~[ALE l'HOTHALLUS;
13,
AN ARCHlWONUD-r;
C ..\ 1t!.LE l'ROTHALLUS.
while the ventral cell asymmctrically
dividc~
into a ventral
crillal cell and an egg. At maturity the canal cells disintegrate
and the egg is ready for fertilization.
Fertilization.
Fertilization is effected by <lntherozoicls which 8W11n clown
the canal of thc archegonium and only one fuses with the egg.
The fertilizecl egg then surrounds itself with <l wall and forms
an oospore. With fertilizatioll (lild formation of oos/)ore, the
sporophytic or diploid gelleration begins.
l'TERIDOPHYTA
21 7
Formation of the new sporophyte.
This oospore passes into an embryo (consisting of stem,
root. cotyledon and foot) which, without any period of rest.
continues to grow until the Equiset1l1ll
plant is established and thus completing
the life-cycle.
It has been observed in
the case of E. debile a single gametophyte
may bear eight to ten young sporophytes.
Polypodium.
(Family Pnlypodiacerc)
Poly podillm is commonly found In
tropical ,mel temperate regions gnHving
in the woods, hedge rows and near
streams.
Though it prefers shady paces.
it is sometimes found in more exposed
Fig. 167.
AN
AN1'TIEllOZOI D OF
Eqllisdmn.
sit-wttiOl1S sLlch as hill sides.
Vegetative body of the sporophyte.
The stem of Polypodill III is a perennial. sparingly hranchecl. erect or creeping rhizome which when destitute of fronds
(lcayes) has the <lppearance of some kind of sea polypus.
USllally the greater part of the rhizome is subterranean but
it grows ohli(luely upwards and its apex
rise~
a little above
the ~urface of the ground and bear~ the leaves.
This erect
or ascending region is known as the c(1ude.Y., often clothen.
with dense growth of scales, epidermal hairs or adventitious
routs.
The older portion of the stem shows the presence of
persistent leaf-bases of the dead fronds and this portion when
dies the hranches become disconnected and coiltinue to
c1evelop as separate new plants.
::u8
STRUCTURE AND DEVELOP:,\IENT OF PLANT GROUPS
The primary root die~ early, all subsequent roots are
adventitious and arise from lower side of the rhizome. Each
root has a root-cap and root-bairs.
Fig
168.
Polypodium.
AN ENTIRE PLANT.
21 9
PTERIDOPHYTA
The leaves, often called fronds, are either Rimple, entire
or pinnatij-jed or pinnately compound and whe!-l young show
characteristic circinate 'C'urnation. Annually resette of leaves
unfold from the caudex portion of the rhizome and these
ultimately die at the close of the growing season. The petioles
(stipes) arc short or slightly longer. tufted and are often clothed
with numerous hrown hairs known as rmnenta which are
Fig.
169.
'J'nAl'1SVEHSE SECTION
OX'
Q}'
STEM
l'al!llIO(li'llTli.
characteristic of ferns. These hairs are also present on the
rachis. The veins of the leaf-segments are either simple or
forked and ultimately bear groups (sori) of asexual reproductive organs (sporangia) and are, therefore, soriferous.
A crosS section of the stem shows ,two distinct regions,
the cortex and a number of steles. The cortex is bounded on
220
STRUCTURE AND DEVELOPl\IENT OF PLANT GROUPS
the outside by an epidermis consisting of a single layer of
nanCllY cells 'with thick walls. The cortex is differentiated
into two regions: (a) hypodermis consisting of a few layers of
sc1erenchyma, (b) general cortex consisting of many layers of
parenchyma cells with or witham intercellular spaces: this
ti:;slle is mainly concerned with the storage of food and water.
The vascular bundles i'al'Y in number. some of which are
large and some are small <~nd are generally found near about
-"'x:*-T-Pericycie
~~~~~~~~~-j---Phloem
Fig.
170.
OF PolY1lOclilt1ll.
enlarged)
STELE
(ll1U~h
the centre of the stem. Each vascular lmudlc is discrete and
hadrocentric and is surrounded by a typical cll!lodcrmis,
lying internal to which there is a single layer of pericycle ;
the protoxylem is exarch.
The phloem consists of sievetuhes and 'conjunctive' parenchyma, and the xylem consists
of vessels varying in width with thick lignified walls
ancl 'conjunctive' parenchyma like that of phloem.
There are two or three well-defined gtl'ancis of sclerenchyma
near the centre of the stem. Leaf-tracc' lJll1ldlcs are present
in the cortex.
PIERIDOPIIYTA
Asexual reproduction.
Early in summer, the foliage leaves bear
011
their under
surface many greenish l1rowl1 structures, called son, which
aer developed directly over the veins so that the foliage lea\'cs
now spoken of as sporophylls. Thus in Polypodi1l11l there is
Fip;.
A
171.
l'"l!lporliu III ,
Port'I'ION OF 'I'HE SPOIlOPHYLL
"}lOWING !-10m.
no differentiation into
f~)liage
leaves and sporophylIs, both the
functions of photosynthesis and spore-production are taken
over hy all the leaves. The sori are generally round, large
or small, and sometimes are mixed with hairs, They are
generally terminal on the veinlets or at their bases forming
a regular row on each side.
Each sorus is naked and consists
of a group o£ sporangia which arise from a tissue of the leaf,
called jJ/({ccllia.*
Each sporangium develops by the lepta-
sporallgiatl! 11lcthod.t "fIle
fu]ly~formed
gpOrangnl111
18
a
.• III "Dille IIthu!' ~'l'!lt'l'H flf f''''IlX it is proteded by an illtill.,illlll, ontgrowth fl'om the plaeenllL.
t It !neallS !IH"~ the developmeu( IIf tit" "porogell(]IlS tissue takc~ pla<'"
fl'lllll tlte Ollfl'l' cell !t.llflwing the p(·\·ic·linal didl'fion of the Rupedicial initial
illstead of fJ'Dm the ifllll"l' eellR ItR ill !,!I('IJjJodilllll.
222
STRUCTURE AND DEVELOP;l.lE"'T OF PLANT GROUP':;
lenticular calJS1.tle attached to the stalk.
On the capsule there
is a specialised, cutinised, incomplere cellular layer called
annulus.
When the annulus stops short, the cells are thin
and form wbat is called
si()1Jlilllll.
\Vithin the single-layered
wall of each sporangium there are one or two layers of nut~itive
tissLle, the tapetum, SlllTOLlntling a mass of sporogenolls ceib
Fig. 172.
TU.\r-;SVEn:ll:
,'OHtI>; OF
~E('l'.ln:-l
THltOIlUH
A
1'"IYJl"r/i1l1il.
which ultimately form about sixteen spore mother-cells. From
each cell, by reduction division, a spore-tetrad is fonned. When
mature, the spores are dark brown
ll1
colour and morpho-
logically alike,-hence Polypodiu1H is homosporous.
With
1'er/lIction division a1ld for11latio/l of spores the gametoplzytic
01'
haploid genera/ioll begins.
The gametophyte.
\Vhen the sporal:tginm npens it bursts at the stomium
owing to the hygroscopic l1lCH'ement of the annulus and the
223
PIERlDOPHYTA
spores escape.
Each spore has two coats: the outer coat is
called e:l:Ospore and the inner coat. endospore.
Under proper
conditions of temperature and moisture
each spore germinates.
On
tion the ollter coat hursts and the inner
one elongates and protrudes into a multicellu1ar
filamentous
structure.
which
when fully developed form;; a flat. green.
heart-shaped body called pro thallus.
The prothallus gives out from its uncleI'
Rurface
many
delicate,
multicellular.
hair-like structures called rhizoid.l· hy I!"
Ilg. 173. A
means of which the prothalJus is not
sponAN(JIU~I.
only attached to the substratum hut it also draws nourishment
therefrom. The prothallus is. therefore, an independent plant
Fig. 174. Polypodium.
A-E,
SUCCESSIVE S~I'AQES IN THE DISPERSlOl>! OF'
SPORES FROM SPORAl>!GIUM
IAfter A.tkinson)
:22+
STRUCTURE AND DEVELOP1>IEKT OF PLANT GROUPS
which can absorb raw food materials from the substratum and
can carryon photosynthesis. The prothallus bears on its under
surface., scattered among the rhizoids, especially on the thicker
part of it, several cellular bodies of two distinct kinds: (I)
Fig,
A
P"ll/podiulJI.
175,
~L\TUnE I'RO'l'IlALLt'H
~H()WING
AS ~LLN FlW;\I nm.()W,
AHf'HEGONH
HliTZOIUf<.
AN~'HERTDlA,
AND
fllltheridia or the male sexual organs and (::!) archegollia or
the female sexual organs.
Antheridium.
Each antheridium is a spherical hotly and
cOllt:lins about thirty-two spennato::;oid mother-cells, from each
of which a
spirally-twisterl.
(I1lthcro.'Zoid is prorluced.
multiciliate,
When
spermatozoid or
mature the anrhcriclium
opens at the top, the mother-cells are liberated: the spermatozoids set themselve..; free from the mother-cells and hegin to
>;wim in the film of water already present on the surface of
the prothal1lts,
Archegonium. Each archegonium consists of two parts:
(i) a basal swollen portion called the ,-'cilter and (i) an elongated
upper portion, the Jlccll. It contains only one elongated neck
Spermatozoid
!
c
lTig. 176.
A,
l'nl!lliOrlillm.
A ~f.\TURE .\NTHEIUDIU.I[; B. 'I'IIE HA~m SHOWING
LIBERATION OF HI'ER~[A'I'OZOIl)S; C. A
HPEIUIATOZOIlJ.
canal cell, one ventral canal cell and an oospherc or ovum or
egg. The archegonium wben matures, its neck canal cell and
ventral canal cell become disorganised so that a thorough
passage is established between the exterior and interior of the
archegonium.
This passage becomes filled with a mucilage-
neous substance containing malic {(cid.
Fertilization.
The spermatozoids, set free by the antheridium. moYe
ahout by means of their cilia in the film of water already
present on tbe surface of prothallus and arc attracted towards
the archegonimu by the malic add given out by the archegonium for the purpose,
The spermatozoids enter the canal,
pass .down the venter but only one fertilizes the ovum. This
fertilized ovum on secreting a wall round itself becames an
IS
STRUCTURE A~n DEVELOPME;-,:T OF PL\1'<T (;ROUPS
1.:::1l
(JOS/JOrt'.
H'itll ,i<'rliliz(ltioll (/Wl tormatiol! Of oospore, Iho
sporojJhytic or dijlloid generation begins,
It is to be nnt;:r1 that altllollgh the prothallus hears. as a.
rule, buth kinds of seX urgans. the antheridia and archegonia,
c]'()sR-fertiiizatioI1 generally takes place. i.e.
pa~s
dercopL'd on one prothallus
spermatozoids
into the archegonia of
Neck canal-cell
,/
r:-'f.>;"+ _ _
Egg-_,_..,....:..-r.~"r3
'_'_'_""'-o
A
l?iy'. 177.
A,
A YO!';N;:
,\](CHE"C:-NrrT~l:
GIlA/WING
anotlHT, Thil;
~f1'('lr.AI;E
i~ neccs~ary
/I,d!/IJ(/(hlll/l,
B.
A ~l,\'I'l!lm
CONTAININtl
AIH'HEt:ONI"\1
~rALrc
IllS-
A('1l).
hecltul:'c antheridium and archego-
nium ar(' not rleveloped on the same prothailllS "il11ultaneollSly.
Formation ox the new sporophyte.
The coo,pore grarlual1y forms an embryo consisting of foot.
root. primary leaf and stem, and from this embryo "ultimately a new sporophyte is developed.
After the establish-
meill: of new sporophyte, the prothallus dies down and tlms
it becomes inrlepcnden t.
PIERIDOPHYTA
.2'27
Marsilea
(Family i\1arsil('(lce:e)
In hahit j'l,jarsi/f!{l (water [I:rn) grows in shalluw water or
III
wct places. often (TCl~)ing our upon the shores and growing
111
all directions.
A few species. hc.wc:ver, grow in dry situa-
tions througholl t the vear.
Vegetative body of the sporophyte.
fhe
~item is rhizul!lCltOllR.
dichotomollsly branchccl and
creeps on· or jllst below the surface of the suhstratlilu.
internodes mav he s110rt or long.
The
Oil the llpper side of the
rhizome there are two rows of <lite] nating erect leaves.
The
branches arc either axillary or arising below or lateral to each
Ach"enririolls roots de"elop on the ollter side of each
leaf.
The leaves an: typically peltate and
node of the rhizome.
ljuadrifoliate, each with a considerably long petiole.
leavc8
towal'dR
the
growing
apex
cllaracteril'tic circinate vernati1ll1.
the
of
The
veill~
Young
~tt'lll
show
111 the a wl-
shaped leaflelH are dichotomuusly branched and arc ultimately
connected by short vcinletH to form a rericuillm.
Internally. tlw rhizome of all
spccie~
of AllIl'silell have
an amphiphloic siphollostde hein~ limited internally and externally hy cndoc\crmal layers and with a central pith.
The
pitb may be either parenchymatouH or sclerotic depending
upon environmental conditions in which the plant grows and
i~
separated from the inner enc\ndennis by a single layer of
parenchymatous pericyele.
In some Hpecies the protoxylem
elements arc not recognisabk.
Outside the outer endodermi,
there is a single layer of parenchymatous pericyc1e. External
to the outer pericyde lieR a comparatively thick cortex extt:nding
UplO
the epidermis.
This is differentiated int,' :m inner
:228
STRUCTURE AND DEVELOP)'IEKT OF PLANT GROUPS
F~g.
A:"1
178.
lIlarsilea.
ENTIRE PLAXT \Yll'H SPOROC.-IRPS.
pmRIDOPI-IYTA
solid thin-walled or sclerotic parenchyma and an OUler aerechyma with a single ring of conspicuolls air-space, being
limited externally by one to several layers of parenchymatous
tissue.
Pig. 179.
llIlll'silea.
'l'T\ANSYERSll ~llCTlON OF H'l'I':;IL.
Asexual reproduction.
At the time of reproduction prominent reproductive
structures, known as sporoc({rtJs, which are usually bol'ne
laterally on short or long pechlllclc~ inserted a little above
tbe base 01 the petioles (sometimes apparently adaxially or
axillary). The sporocarps are stalked and somewhat beanshaped to ovoid nut-like bodies. The wall is very hard and
and thick, strongly resistant to external influences and is
capable of retaining its vitality
for sevel'al years.
The
.:!30
STRUCTliHE AND
DEVELnp~n:I'T
()F 1'["IN1' l;fHJUl's
peduncle mav be unbranched with a solitary terminal
carp. or in
~--20
SPI)I"O-
species branches dichutllll1UllSlv and bears
80111('
()r more sporocarps,
that the sporocarp
or
It has gL'nerally been interpreted
Alarsilm 11-\ "a modified fertile segment
from the lower part of a leaf, hU.r it has also heen considered
to he
h()molognu~
with tbe whole leaf',
Outer endoderDl[.
Fig', 180.
I'AI('I'
OF
A
'I'nAN~\ Ens!:
~I-:<'TJON
IIF
sTim
OF
JI(lr.~il"f{.
\Vitllin the inner wall of the sporocarp and attached
it there are two
nlWf;
1"0
of elongated. close-packed sori onc on
each side filling up the sporocarp-cI"ity and these extend
PIERII)OPIIYTA
transversely to the longitudinal axis of the :-:purOl'<lrp.
soniS is enclosed
bach
hv a delicate indusiuiJl. ;\;Jarsib, is hcrtero-
spOrollS and each sorus contains a row uf Inegasporangia
surrollnded hy many microsporangia. Thec-;c
to
it mucilagenou~ ii~Slle
~;nr~ arc :'. l:tached
which swells n.:markahly on coming
~
-~
B
A
l:<'ig-. 181.
A',
:\f"r.,il,.lI.
V~ltTWAL Hf,CTlllN TH{!OFClJ[ Tj[~ KFOHO('AI\I'
[y, THANSVlm><l, HH''!'ION OJ,' 'l'ln: HA~lE,
III
contact with water at the time of germination.
mother-cells
of
the
microsporangiul1l
division and form micruspores,
undergo
All the
reduction
Within the mcgasporangium
only one mother-l:el.l matures and by reduction division forms
a spore-tetrad, of which only one megaspore matures while
With red1lclioll division and formation of
the gmnetojJhytic or hapl(Jid generatio1Z begins,
others degenerate.
Sj)ores
. The gametophytes.
When the sporeR attain maturity the spol'ocarp germinates
and Opf'I1S in water along its ventral side and apex, splitting
::!3:!
STRUCTURE AND DEVELOP;\IENT OF PLI;\1T GROUPS
ill a spreading hi-valved structure.
The ring of internal
mucilagenous ti!'sue within the sori ahsorbs water, swells remarkably, comes
Ollt
of the ruptured sporocarp and thus drags
Sporocarp
Fig. 182.
Jla/,.,ilcll.
STAf:ES IN TIRE nEIL\UNA'J'lON OF TIlE :-;POl{OUAHP.
out the sori which are attached to the ring by their ends.
Gradually the indusia and the sporangia! jackets undergo
geiatillisariol1 and the spores remain embedded in the galatinous matrix during early stages of germination.
Male gametophyte. The development of the male gametophyte from the micrnspore resembles that of ScZagillclla
and [sertes. It does not elnergc out of the spore-wall.
A
small prot/III/1illl cdl is first cut oil as llsual anf1 a single
PIERIDOPHYTA
anrheridium is ultimately formed making up the whole
gametophyte. The antheridiull1 consists of a jacket of sterile
initial
A
D
E
Fig. 183. Jf(II'.,iha.
A-E,
s'r.\Gf.S
IN
THE
Df;I'ELOPMlJNl'
OF ~l'r·:lnr'\'I'OZO!l)S.
-cells surrounding two inner spermatogenous cell, by tIle
successive divisions of which 16 ll1ultici.liate. spirally-coiled.
spennato2oirk are produced. The spcrmatozoids are ultimately set free hy the bursting of the spore-wall.
2,1{
:-;TRUCTURE AND lJEVELOP:"IE1\T OF PLA?>iT GROUP:;
Female gametophyte. The megaspore germinates s()on
after it comes in contact with water. Its nucleus divides near
its apex and a small apical ccII is cm off by a wall. The
large basal cell. with its undivided llucleus. contains abundant
food materials including starch grains and is nutritive in
function.
The slllall apical cell protrudes through the
megaspore-wall and forms a small groups 01' cells. the game-
Megaspore cout
Nutritive cell
Fig. 18'1.
. . \-E.
.If,fl"il,.,r .
~~T.H~E~ lK THE IH':VJ:l.llr .\H .. Y;'I
nr I,:)IHHYO.
tophyte proper, lwaring a !~ll1all and ,;imple archegonium. The
archegonium is hroad but lllw and has- only one neck canal
cell.
FertHiza ~ion.
Thl: spermatozuids swim toward;; an al'chegonimll and
only one hnding its way down through the neck fertilizes the
OVUlU and forms an o(Jsj)()}'c.
TVilli jertii1:zaLio1l and form(/tion of ()(HpoJ'e the sjlC)rnfJ/zylic 0)' difJ/oid generation hegins.
Forma.tion of tlle new sporophyte,
The oospnrc deve1t'-ps into an embryo consisting of a
leaf, a root, a foot and the stem. ilnd from this emhryo the
n{llrsilca plan t is ul rima tell' c1cH~lopc(1.
CHAPTER IV
GYMNOSPERMS
The Gymnosperms or i'naked-seeded" plan(~ an.: tht: mOB!:
primitive of all seed plants. They are regarded as an intermediate group between the Vascular cryptogams or Ptnidophytes and Angiosperms. The plant always represents the
sporophyte and ig heterosporous. The sporotJhvlls are aggregated 'into cone-like structures or sirohili which are usually
unisexual and do not contain any accessury wl1orl. In the
Gymnosperms the carpels do not unite to form (l closed chamher or ovary but the megasporangi1l1ll OJ' ovule is borne
directly on Ihe surface of the meglispol'jJlzyll as in the case
of Pteridophytes and the pollhuttioll is direct i.e. the pollen
grains are tram;ferred directly to the surface of the ovule. As:
in Selaginella, two hinds of ganlclophytcs lire produced, but
the)' arc 11l1lch more reduced. Archegonia arc stilI presenr.
The fertilization is eflected by means of motile spcrmatozoids
in lower GylIlIlospel ms, hut in 11igher ones hy means of nonmotile gametes. The endosjJerm is formed before and 1I0i
after fertilization as in the case of Angiosperms. As the
carpel or carpels do not unite to form an ovary, so the seeds
arc naked and tliere is IlO slIch orgall as fruit in the
Gymnosperms.
Gymnosperms are divided into seven classes of which
t1l1'ee are altogether extinct. These are as follows:
(I) C:vcar/(J{ilica les
(2)
Bennettitales
C~)
Cvcada/es
(4)
COTdailalrs
(5)
Gin l~goales
(6) Com/erales
(7) Gnetales
Extinct.
Extinct.
Extillcr.
Extinct and living.
Extinct and living.
Extinct and living.
Living.
23fl
STRUCTURE AND DEVELQP:-'IENT OF PLANT_ GROUPS
ORDER CYCADALES
Plan ts woodv, usually hranched and di<rcious: leaves
hipiullate cnmpuLllHl: sporophylls generally borne in cones
(bu t not in the case uf the megasporophylls of Cycas) ; microsporophylls hearing sporangia in gJ"Gups of sari on the under
surface; spcrmatozoicls multiciliate, motile and lIsually z in
numher ; megasporophylls usually hearing one to several erect.
sessile, naked nvu]ei-i; ern bryn in a ripe seed with generally
two cotyledons and attached to a long much-coiled sllspensor ;
stems with large pith, little wood and thick cortex: true vessels
abscnt.
It incll1de~: only line family, Cvcadacefc.
Cycas
(Family CVc(II/acL'!e)
CyC([S is the most prominent gellus of the Eastern hemis-
phere heing confined to the tropical and subtropical zunes of
India. Japan, Australia and Polynesia.
They are usually
cultivated in gardens as ornamental plants and their leaves
are extensi\'ely used for (kcorating purposes.
Vegetative body of the sporophyte
The vegetative body of the sporophyte externally resemhIes a palm tree.
The stem is typically unbranched, short,
thick. cylindrical and more or less columnar, covered by an
armour of persistent leaf-bases and bearing a crown of leaves.
Leaves are pinnate, tough, leathery, .large. sometimes may be
llpto
3 mctres in length, anel arc spirally arranged round the
free growing apex of the stem.
Each leaHet has only one
midrib without branches: the midrib and pinnuks show
H'l'llUrion characteristic of fern);.
The primary roOl: elongates
as a strong tap root with scanty branches but numerolls
geconclary roots arc present.
These secondary roots near the
(;Y:-'INOSPERi\JS
:137
surface of the ground branch profusely and dichotomollsly
forming coralloid masses known as "rOM tubcrcles"*. whicb
possibly serve both in aeration and in nitrogen assim.ilation.
A cross section of the stem shows a large pith. a comparatively thin vascular cylinder with con juint, collateraL open
and endarch bundles, and
;1
very thick cortex showing
numerous leaf-traces (girdles) and limited externally by an
epidermis.
Numerous canals f1llecl with mucilage also ocelli'
in the cortex and in the pith, and these are connected with
one another through leaf-gaps forming a network.
The
primary cambium is short-lived and a succession of secondary
cambiums is formed in the cortex producing concentric series
of vascular cylinders,
The first cortical cambium produces a
prominent secondary vascular cylinder, the second produces
* Ront tubercles rrc fDl'med (lue to the entrance and snbseqllent multilllication of "bacterioid6" frmn the soil cansing cDnsiclel'alJle enla.l'gement
of the intercelllll:tl' spaces anel clis()l'ganisatiOlI of Rome of the cells. Alg're
(A lIalimna; pORsibly N o.. toc 111so) soon occnjJY these spa('es and their multiplication still flll'thel' enlllrges the size of theRe cavities.
238
STRU(:TIl!{E .\:\Il
or n:I 01''' 1E~1'
OF PLANT
cnoups
much narrower one~ with widely !'('parated va~cuJar hundles
nncl as this process is cunrinucd thl:: constructive power of the
successive camhillll1 Iayer~ is greatly reduced. ultimately forming isolated parche,.; (If smallar va;;cuJar bundles here and
there at the periphery. Tllc,;e !'tT(lIldarv cunical hundles are
concentric.
A cross senion of the !caf shows strongly curinise:! l'f)idermis on IJurh sides of if and with deeply sunken stcmat'l
only on rhe under
~1lrfacc.
Below rhl' upper epidermis rher('
Spongy p.nl'crll::h.}'mn
Lower epJderml_s
Fi~:.
A.
enos;;
185.
R.
s~:r'l'''lN OF ., LE,\F;
IHFFElLENT
'l'lS:-'rIEt-;
('.'1"118.
rOH'I'WN (II-' TilE
OF
~A1TE sI[O\Y1N"~
;ur:-:;OIIHYLL.
is a h}I/)()demlis collsisting of a fl'w layers of thick-walled cells
and this layer gi\'e[; a tough and Ic~lthery texture of the leaf.
The mesophyll rissue is ditrtrenriated into an upper 1)/di.\'(/(/{'
and a lower spollg,\' jlal'cllchv iIl{/, full of chloropla:;rids, and
these two tissues are separated hy colourless. elongated cells
which run parallel to the lcaf-slIl'frrce. The vaRculal' hundle
is wHlall" mesarch.
.:439
c;Y!\INOSPER~IS
Asexual reproduction
CYC(f.l is strictly clift'ci(Ju~ and heterosporous. the l1licrnand mega-Rpo)"ophylb hein_e; horne (In diflncnt plant~. In this
B
A
Fii(. 187.
A,
O.llI)({8.
A MALE S~'ROBILUR; E, A MICltOSl'OROI'Rjjp,; C, l'ORTION OF
A Ml(!R()~POROl'HYLL SHOWINO A nlW HORl.
'240
.
STRUCTURE AND DEYELOP:\IENT OF PLANT GROUPS
case the microsporophylls only are in compact strobili, while
the megasporophylls are arranged spirally like the ordinary
crown of foliage leaves around the terminal vegetative bud of
the shoot-axis.
The staminate strobili are apparently ter-
minal ill position hut in reality lateral. being situated close
to the growing apex.
Staminate (or male) strobilus, It consists of a central axis
on which numerous micrnsporophylls are arranged in acropetal
sllccession forming a compact. elongated and ()\'oicl structure,
often attaining a length of 50 c.m. or more.
~,trobili
One or more
maY grow simultaneously about the growing point.
The terminal and l)a531 microsporophylls arc however sterile.
while the remaining ones bear
700
or more microslJOrangia
or pollcH StlCS on their abaxial (lower) surface in twO,
more or Jess distinct patches, separated hy a sterile
median line.
The microsporangia occur in definite groups
of 5, 4, 3,
sometimes
2, forming
sori.
Each micr03-
porophyll, which is not leafy in nature, is narrow below and
broadened ahove into a more or legs sterile expanded portion.
The sporangium is eusporangiate in development and consists
of a wall of several layers of cells surrounding an inner large
mass of sporogenous tisslIe, from the surface of which a comparatively scanty tapetum is developed.
From each spore
mother-cell by reduction division four micmsjJorcs or pollcll
grains are produced.
Ovulate (or female)
s~robilus.
The megasporophylls do
nOl
form compact str~bili, as in the case of microsporophylls, bur
are spirally and loosely arranged like ordinary crown of foliage
leaves around the terminal vegetative bud of the shoot-axis.
The megasporophylls bear considerable resemblance to foliage
leaves (e.g., C. rcvoll/ta, C. circiJUllis, etc.) devoid of clliorophyll.
GY:\INOSPER:-IS
and covered with short brownish .hairs.
241
Several ovules -or
mcgaspormzgia, sometimes only two (C. Sialllellsi.~), are borne
on the margins of the megasporophyll. In a specie~ of Cyms
(C. cil'cinalis) the ovules are largest:
lueasuring about 6 x 4- c.m. and in some
cases they are densely hairy (C. rec}o/lIta).
The ovule consists oE a Illicelius
~LlITOUllclecl
by a single massiye integu-
ment which develops a testa of three
layers: an outer fleshy,
<l.
middle stony
and an inner fleshy layer. The nucellllR
is fused with the thick integument for
most part of its length, except at he
apical region, where it forms a
beak-lik~
structure called llucellal'-bcah.
Witbin
the nucellar-hcak develops a conspicuous
chamber, called. pollen
cjUlmbcl', in
The
vascular supply of the ovule is divided
into two sets, the outer set enters the
outer fleshy layer and. the inner set
Fig. 18B. (.'Y(·(/·<.
traverses the inner fleshy layer just wi~h­
MEGASl'OIWPRYLI,
WITH OVULE!;.
in the stony coat and continues beyond
the free porion of the nuccllus. Deep withill the tissue of the
llncellus a spore mother,cell becomes soon differentiated which
by reductioi1 division forms a linear tetrad of four megaspores
or embrvo-s(/cS, of which the innermost one is functional whiie
others disorganise.
which the pollen grains collect.
The gametophytes.
Male gametophyte. The microspore, the first cell of the
gametophyte, has two coats: the exine and. the intine. It
16
Z.F
STRUCTUHE '\":>;1) DEYELOP;\!E:'IiT OF PLAN'!' t:ROUPS
~;enninates while still ,,-irhin thc microsporangium. its nuclells
dilides and twu unequal cells are formed, a small persistent
protilallial ccl! or ;_Icgc/ativc ccli and a large cell, the {liltizeri.
dial lllitilli. The btter ill turn divides again into two unequal cells. one a small cell closely in contact with the prothallial cell is the gc;,t'I'{/fi~lc cell and the other large cell, the tube
cell. It is at fhi:, three-celled condition the microsporcs or
-Ii
t,
!
Outer
MilhHe
Innet'"
Fig. 189.
(/.'1"(/'-"
STlll;Cl'rTfiF: OF OVFLE.
pollen grains are clischargeC+ from the microsporangilll11 and arc
disseminated by wimL it has heen accepted that Cycas is windpollinated. The three-celled microscopores arc carried hy tllG
wind to the uvules oi the neighbouring female plants They are
caught by a mucilagenom secretion from the micropyle and as
the fiuici dl'icg up they arc sucked into the pollen chamher. The
tube cdl e1qngatc~ and penetrates the tissue of tllC llucellus
forming pollcil [Ilbe and the tube nucleus passes into it. The
pollen tuhe often branches" and always functions as an abHOrpti\-e organ. The generative cell then divides into a stal!~ cell
and a IJOdv cell. The former is functionless but the latter
again undergoes division producing two spermatozoid "mothered!s, in each of which a large, spirally-coiled, 111l1lticiliate
sj)C/'1Iwtozoid is produced. These spcrmatozoids are remarkably large, larger than any known in other plants and animals,
GYl\JNOSPERi\IS
243
and are easily visible to the naked eye through the transparent
pollen tuhes.
Female gametophy'te. Similarly, the megaspore is the lirst
cell of the female gametophyte. It germinates within the
l11egasporangium (or ovule) and is never shed but is retained
within ir. The development of the gametnphyte can he
broadly divided into five stages: (1) the megaspore cniarges, its
nuclells divides freely forming a variable number of free nuclei
distributed in its general mass of cytoplasm; (2) due to the
development of a large central vacuole all the nuclei are placed
at the periphery of the megaspore: (3) free nuclear clivisinl1 con-
A
·
·
A
,·
E
l~ig
A-E,
SUr:C:E~~IVE
(:,UIT,'l'Ol'HYTE;
TUBE;
F,
n,
190.
('yra".
1'HE DEVELOl')rEN'f m' TIn: ~[AL"
TWO )!A'J'Ulll) Hl'rcllll[S INHIDl, THE POLLEN
SIDE VIEW m' A MA'l'UIU~ HPl)lnr.
~'l'AGES IN
tiuucs: (+) a peripheral tissue is gradually developed by the
formation of cell-walls separating the free nuclei; (5) this
process is continued and the tissue grows centripetally until
it hlls up the cavity of the megaspore. This gametophytic
244
STRUCTURE AND DEVELOP;'IENT OF PLANT GROUPS
tissue which is developed hefore fertilization is known as the
rndnsperm, which at maturity contains abundant starch grains.
It consists of two regions; (a) a region of large cells near the
hase performing nutritive function and (h) a region of small
cells near the micropylar region. Vlithin the latter region
develop a variahle number of archego1lia (2-8 in C. re'uoluta).
Any superficial cell of the gametophyte may he come an archeg()JZiWll
initial. which divides periclinally into an outer primary
1IC('1~
cell and an inner celliml cell. The primary neck cell
divides vertically to form two ned cells, while the central cell
enlarges remarkably and gradually becomes surrounded by a
special jacket of nutritive cells, known as the archegonial
jacket. The nucleus of central cell finally divides to form a
'velltral llllClcus and an egg ilucleus around which an 008p11ere
is gradually differentiated. The ventral nucleus soon disorganises. The oosphere and its nucleus have
been described as the largest among plants.
During the development of the archegonia at
the micropylar surface of the gametophyte.
its neighbouring cells continue to grow upwards so that the archegonia are left in a
shallow depression. known as the archegonial
clutnzber. .
Fertilization.
Fi!!;. 191.
('!Jell".
E),[llRYO WITH THE
LONG COILED
SURPENSOR.
After penetrating the nucellus the pollen
tube bursts when the spermatozoids are set
free 111 the archegonial chamber.
The
spermatozoids then make their way into the
archegonium and one of them fertilizes the
oosphere. The fertilized oosphere surroumh
iNeH by a wall :llld forms an oospore.
G',::\IXOSPER:\IS
Formation of the new sporophyte .
•\fter f::rtilization the oospore enlarges, its llllclcll~ by free
. cell-formation produces as many as 256 or probably more IC.
rc;:()ZlIta)
nuclei distributed through the cytuplasm of the
oospore.
A large central vacuole soon appears (C. circillaZis)
f()llo~\'ed by the formatioll of peripheral tissue.
Fig. 192.
SUC'()ERSIVE STA!H,S
This tissue is
IN THE DEVET,OI'MENT OF '('HE
EMBIlYO IW A ('Yl~An (ZlIlIIill); i\, FltEE NUi'LEAR T>iVJflION
IN 'rBE DEVELOPING ZYGotE j
FOn~[A'I'ION I'lL' A
TIH~I'E A1' TH}~ LOWEn IU:G10N OF THE SA~m.
n,
the pro-embryo,
Further details is not known in Cyeas.
But
in another genm Zami(l., the development has been fairly
In Zmnia the pro-embryo is formed only at the
lower end of the developing oospore. The cells below the
tip-cells of this pro-embryo elongate remarkably and ultimately
form a long coiled flexuous and massive filamentous structure,
called the suspensor, which forces' the tip-cells out of the archegonium into the nutritive gametophytic tissue (endosperm).
From the tip-cells a dicotyledonous embryo is produced. The
worked out.
cq6
STHUC'l'URE AND
DEVELOP~rENT
Ot' PLANT l;ROU1'8
embryo and the endosperm remain within the three-layered
testa and the ovule is gradually transformed into a seed,
The
seed on germination gives rise to a
new seedling-sporophyte and the
mode ()f gel minatiol1 is hypogeal.
ORDER CONIFERALES
Fig, 193.
IJIFFEHEN1 u'rrON OF
TIm j'!W-j,;;\lllIt yo BY THT':
ELONClATION 01' 'l'ITE' C'cLI,R
or 'I'HE S[]SI'ENSOJ! !:EGION
llEHIND THE APICAL GHOUl' Ill'
:m:nI~TE)IA'I'IC CELLS
(l']\n.E,lIluyn),
Plants highly hranched, evergreen shrubs or trees. mOl1a:cioliS.
or dio:cious with exstipulate SImple.
acciculal' leaves: sporophylls usually
forming cOlles,. microsporophylls
bearing only a few sporangia (liniloclllar) on the ventral surface.
winged microspore,
con tallung
(pollen grains): male cells represented lw male nuclei and non-motile:
naked ovules generally borne upon
. 07.-'1Ilifcrolls scales: seeds llwally
wingcd and enclospcnnic : embryo
with a varying l1umber of cotyledons and generally attached to a'
short suspensor: stems with small
pith. thick wood and scant)' cortex.
true vessels absent: large num her
of prominent resin canals,
The
order has heen divided into ~ix
families, one of which is Pin<lCc':c,
Pinus
(Familv PiJl[Jcc;l')
Pin liS. the familiar pine t~-ee, has a large
11UI111>el'
of species
which is widely distributed througbollt the l10rtllcrn hemisphere, especially in cxtra-tropical regions,
r;Y"-I1\:OSPEiL\IS
::!47
Vegetative body of the sporophyte.
The plants are tall trees which arc characterised hy the
excurrent type of branching and fascicles of slender n~cfl1c·
like evergreen foliage leaves. The main stem is stolLt. cylindrical hearing a series of wide-spreading branches by a ~caly
hark. At its apex Lhcrc is a reJati\'c!y large terminal lJUcl. It
bear~ two kinds of shoots: (0) one of llnlimited grll\vth or [allg
slzoot and (b) the other of limited growth or dwarf shoo/. The
long shoots 11sually hear scale leaves at the axils of which
n11merous dwarf shoots appear. There is a fascicle of two or
FI.L(.
A
194.
j';IIWJ.
BUJ\N('H BMHINt:; WI'A~nN,\l'E ;;TllnIlILr.
more needle-like leaves closely held together at the hase by a
circle of scales at the apex of each dwarf shoot. The primary
root-system is persistent and perennial and consists of a large
and deeply-penetrating tap root which branches extensively.
111 some SpCciCR the tap root may die early.
The primary structure in a cross section of a young stem
shows three distinct regions: epidermis" cortex and slele.
At the centre of the stele is a parenchymatous pith which is
surrounded by a ring of yascular bundles, separated from one
anorher by primary medullary rays. Each vascular hundle is
conjoint, collateral and open. The xylem contains tracheict&
and not trach~e or true yessels characteristic of the xylem (It
an angiOsperm. The phlcem consists of Ricvc-tuhes and phkem
Fi!.(. 195,
T'AI1T OF A
(,H()~K SEt"I'ION
0[' 'J'lHI-YEAltH
OLD STRM OF' j}i )/118.
parenchyma. In bet ween xylem and phloem there is a strip of
c~l1lbium. The cortex is made up of parenchyma frequently
WIth choroplasts and is traversed hy longitudinal resin canals
(ducts). On the outside there is epidermis with he<lvily-
GY~IlmSPER:'>JS
curinisecl ollter wall. During ~econdary growth secondary
xylcm and phloem are produced by the cambial activity as in
the dicotylcdons and conspicuous annual rings are gradually
developed. Secondary medullary rays are funned in the usual
way. Resin canals also appear in [he second:Il"V xylem. Al
rhc time of camhial activity within the stele a complete ring
of cork camhiull1 appears in the hYI)(Idcrmal region of the
cortex: which eventually gives rise ro the periderm. Later,
sllccessive layers of cork cambium appear deeper and dceper
in the cortex and finally in the oLltt;r part of the phlm:m. In
this way a thick protective bark develops on tl1c outside of the
stem of Pin liS.
A cross section from rhe mirkl1c of a leaf of the current.
Year ~1J(l\\,~ from olltside inwards a singlc-hycl'ed epider11lis
Cuti.ele
Fig. 196.
Pili/I,'.
UROSn SECTION OF A
N~;EllLE.
2.'i0
STRUCTURE AND DEVELOPi\lENT OF PLANT GROUPS
composed of thick-walled cells with a heavy clIticle, the lumen
of each cell heing often nearly ohliterated. The hypodermis
is sclerenchymatous, with fine pits on the lignified walls: it is
s(;wral cells deep, Rpecially at the ridges. A few Rtomata are
noted, each "toma interrupting the epidermis and the hypodennis. and opening into a respiratory cavity in the 1nesojJhyll,
which consists of several layers of large, polygonal, thin-waHed
parenchyma containing cytoplasm, nucleus and abundant
chloroplasts: tlleir cellulose walls are infolded to form peculiar
projections into the cell-cavities. A fcu' resin ducts, lined hy
a thin epithelial layer and surrounded hy a sheath of sclerenchyma are also presen:_ in the mcsophylL There are nm
7_11lSCulat lJlmdl('s, each olle having its xylem towards the upper
side of the leaf and its phloem facing the lower side, which is
llsually more or less convex: the hundles are embedded i.n a
man y- layered ground tisslle" the jJcricvclc, which is surrounded
bv an {'luloderm!s, consisting of a sin\;'le layer of parenchyma
clearly separating the central region from the mesophyll. The'
pcricyde comists oi two kins of parenchyma C(~l1s. termed
collectivcly the tmns/IISiOIl lissl/I,'. and an irregular hand of
sclcrenchyma lying across and helow the phlrem of each
hundle and cr;nnecring them. The tr:msfusillll tisslle consists
of (a) albllmillol/.I' cells-·-living cells with cellulose walls. containing protein and starch ane[ serving for the translocation of
prepared foods from the mesonhyll to the phloem. all(l (II)
tmchcirlaZ cells ·--empty dead cells with lignified walls possessing horclered pi ts, function ing as channels for water and rli~­
sll]vnl salts from xylem to mesophvll.
The primary structure of a root in a cross section shows
as usual three distinct regions. viz .. pili/emus laver, corle:,: and
side. There are I.wn. three or four groups of primary xylem
alternating with the corresponding numher of phloem groups.
A srn.aIl parenchymatous jlitlz mayor may not be present.
Outer region of the stele constitutes the /Jcricyclc consisting of
several layers of cells. Sometimes resin callal is Jormerl just
olltside each primary xylem. Outside the stele is the parenchymatous cortex, limited internally hy the clldocZel"lnis with
characteristically thickened walls. Next comes the pili.ferous
laver as that in a dicnl'vlcdnl1olls root. The secondary groW1'll
GYMNOSPEH;\IS
in thickness takes olacc in the same manner as in a dicotvle"
donous root by lh; activity of a layer of secondary C:llnbil~m,
which first appears as strips of cambium from the thin-walled
cells between primary xylem and primary phloem. The corle
cambium also originates [rom the outermost cells of the
pericycle and gives rise to cork outside so that the cortex and
the piliferolls layer die to form a hark.
Asexual reproduction.
Pinus is l11onrecious and hears hath microsporophylls in
stami1late strobili and mcgasporophylls in carpcllate sfrohili
or cones. But hisporangiate strobili may occur in exceptional
cases as in P. 111arilillw and P. lilricio.
'~:C~P
O
~:_:Uff:'
A
B
E
Fig. 197. Pill 1/8.
"\,
S'l'A~llNAl'E
S'J'ILOBILUS IN LONIH'1' [lnrN,\T, SECTION; B, AN
gNTIRT~ STA~IINA'rE S'l'UOllILUS; C-D. MICROSl'oitol'HYLLg
WITH ~lWl:,OSl'OJtoNGIA VLEWED FltnM !lELOW AND HIE
SIDP.; E, A MATrllU; ~!ln](OSI'ilItE.
Staminate strobilus. The staminate strobilus is found in
clusters towards the apex of some branchcH. It is simple in
nature and consists of a short axis in wllich there are micro~
sf)()rophylls (oJ' stamens) arrange(l spirally. Each microsporo-
::!5~
STRUC'TURE AND DEVELOP;\IENT OF PL\NT GROUPS
phyll consists of a stalk subtending an expanclcd scale-like
portion, On the under side of this scale and to the side of the
stalk there an: two microsporrmgia (or pollen sacs). The wall of
the microsplll':lngiull1 consists of several layers of ceJls. whose
inner laver at least forms the tapetum surrounding the spore
muthcr-~elb as in the pteridophytes, As a result of reduction
di,jsion four microsporcs (or pollen graills) are produced from
each J11icro~porc mother-cell. Uwally the microspores arc shed
wirhin a few weeks after the appearance of the strobili. which
Fig, 198, 1';111/.,.
P HllT();IlIt.'nOGILlI'II OF THE )IWH()~I'OI~E~,
haling performed their function ultimately wither and fall
frnl1l tIle tree. Each microspore cOllsists of an oval cell with a
compicllously large nuclells and has two baloon-like, air-tillecl
wings. formed by the separarioll of the exine layer from the
imine at two places and SlI bs('cluent inflation of the spaces thus
formed between the two layers,
Cal'pellate strobilus. The carpclbte strobili remain on
the tree for a lllllch longer period tlmn do the staminate ones.
\Vhen fir~t formed near the tip~ of certain hranches they are
deep red in colour and ahout one c.m, in length. Each' 8t1'o-
G Y2>lNOSPERMS
bilus is compound and consists of a central aXIS on which
mcgaspornphyllus (or carples) are spirally arranged. A mega~porophylI, when removed ancl ,·ie-wed with a pocket lens, is
found to consists of a very short stalk and a scale (ovIIlifenllls
Fig. 199. /'ill/l.,.
A,
A CARPEJ,LAU; ~TROIlIL{JS AT 'J'HE '['DIE OF Ff:ll'J'JLEATION.
B, THE ~A~[E SEVERAL ~roN'l'IT~ LAl'ER WI'l'H S{'ALES
~pnr,An APART ANn REEU, HHED,
scale) to which a bract is attached on rhe lower side. At the
base of this ovuliferous scale and on its upper side there are
two rounded megaspoTangia or ovules. Each ovule consists
Megaspore lTIot~er cell
Fig. 200.
AN
OV1TI.F. OF /'iliIlN,
of an oval mass of tissue, the nucellus, .surrounded hy a single
integument and its micropyle is directed towards the stalk of
the carpel. At the chalazal end the tissue of the integurncat
254
STRUCTURE AND DEVELOP:'IIENT OF PLANT GROUPS
and nucellus is fused with that of the oniliferous scale.
vVithin this nucellar tis~lIe there is a single central megaspore
mother-cell whose nucleus by two sllccessive division (reduction dlyisinn) form:'. a linea~' tetrad of four megaspores (or
MeQ'a.porophyll
Fig. 201.
A,
1';11118.
A l\IEGASl'OltOl'HYLL AT TILE TD\E OF I'IlLLINAI'ION;
B,
THE SA,;I,1'E ,VITH I\IATTjHElJ
SEEn~.
ClIIhrYO-SilCS), of which the one furthest away [rom the micropyle functions and enlarge;; considerahly at the e~pense of
three others which are fina lIy absorhed.
The gametophytes.
Male gametophyte. The microspores (pollen grains) begin
to germinate about a month before 'they are set free from the
megasporangiulll. The nucleus first eli vides to form two
daughter nuclei, one of which flattens Ollt against the sporewall and is cut off from the other daughter nucleus alld most
of the cytoplasm by formation of a thick wall. The cell,
thus Cllt off, is the first vegetative ccll (/)'}'ol//(/I/i([/ cell) whose
nucleus rapidly degenerates. The nuclells of the large sister
cell di\'ide~ again and form" a second 'Uegl'l(/li7J/~ cell (second
prot/llllliaZ cell) wllose nucleus also hehaves in the same
manner, while large persistent cell with its prominent nuclells
255
(;Y:\INOSl'EK\IS
and cytoplasm is ,alle(l the 1I11!/tericiial cell. A little before
the micros pores are liberated the anrheridial cell eli "ides tl~
form a smaller cell. the gC'Jlt'rltti'vc cell, cut off against the
sccoml vegetative ccli and a larger cell, the Ill[)(~ ccli. It is
abol1t this stage th;; microsporangia burst longitudinally and
the microspores (pollen grains) arc liberated. The amoLlnt of
pollen graim liberated by the microsporangia is astonishingly
large which Jill the surroLllltling atmosphere. commonly known
as "flowers of sulphur", and are disseminated by wind. During
transport most oE the pollen grainf are wasteel but some of
them reach the mature carpelJate c(lnes with megasporophylls
RetnnJJ!t of vegetative c::dla
Fig. 202. Pili/I.,.
SIJ('C.b!S~IV1~ !,-:"J'A.(.ms IN 'fHE lH~VBLnp-;\[ENT nr~ ')[ArJr~
nAMg'I'O['HY'l'E,
(or carpels) being slightly separated at this time. The
microspores glide between them and remain in close proximity
of the micropyles of the ovules. During this time pollinationdrop consisting of a sticky fluid appears at the. tip of the
ovule which catches some of the pollen grains. As the drop
dries up the pollem an; sucked inside the nllcellus. After
this process the carpellary leaves close up. Following this
during the subsequent eleven montl1s, male gametophytes do
not further develop considerahly, bu.t a short pollen tlI he
may be formed from each pollen grain. The tube may somewhat branch, penetrates the Illlcellus and growH very slowly
till winter sets in.
::,56
STRUCTURE AND DE'·ELOP;>.JEZ'.'T OF PLANT GROUPS
Female gametophyte. During the year following pollination de\'dopment of the female gamctophyte takes place. The
megaspore germinates within the mcgasporangiut1l and it i~
never set" free. It first enlargc~ at the expense of the nucellar
ti%ue, its nuclens cliyides· rcpe<ltedly without wall-formation
for a c(Jnsiderable length of tillie terming large number of
free nuclei distributed in the general mass of cytoplasm of
the megaspore. Vi/alls are ultimately laid down between the
• nuclei and their result is a solid maS~1 of gamctophytic tissue
known as the t'IIdospt't11l which is not homologuus with the
Fig. 203.
Pill II.'.
LONGITUDINAL ~ELTmN OF AN ARCHEGONIUM.
endosperm in the seeds of angiosperms. Nearly a year after
pollination there c!e,'elop, at the micropylar end of the female
gametophyte (endosperm), a number of archegonia (n,'o or
three usually), each having its origin from a superficial cell
of the gamewphyte. \\Then fully developed each archegonium
consists of a nech of eight cells. in two tiers of four, the
'ventral ca1lal cell and a very big cavity containing an egg.
Before fertilization the ventral canal cell disorganises. The
neck canal cells arc entirely wanting and the large cavity,
containing the egg is surrounded by a jacket layer of cells,
257
GY:-'fNOSPERl\lS
which supplies food to the egg-cell and ultimately to the
.dcye1oping embryo. The- archegonia mature and are ready
.for fertilization until about a year after pollination.
Subsequent changes upto fertilization.
During the second spring the pollen tube grows slowly
·downwards. penetrates the nucellus and finally its tip reaches
the surface of the female gametophyte. During development
the tuhe nucleus first enters the pollen tube. The generative
Micropyle
t::;::·;~,_--
Fig. 204.
Integument
['jlll/s.
PAR'!' Ob' A LONGI'l'UJJJNAL SECTION THROUGH A
~IEGASrORANGI1IM (OV1.'LE); THREE rOLLEN ~rllBES
GROWN DOWN INTO 'rHE NUCET,LUS AND EI'FECTINa Jo'ER'l'ILIZATION.
·cell also divides into a stalk nilcleus and a body nucleus which
also enter into it, where the body nucleus again divides to
form two male or sperm nuclei. About the s,talk nucleus
cytoplasm is organised to form a definite stalk cell around
which there i~ a definite membrane. The male gametes have
dearly differentiated cytoplasm and a large nucleus.
17
258
STRUCTURE AND DEVELOPl\IENT OF PLANT GROUPS
Fertilization.
The tip of the pollen tube on reaching an archegonium
at the surface of the female gametophyte destroys the neck
cells and discharges its contents into the cytoplasm of the egg.
The nucleus of one male cell moves towards the egg-nucleus
and fertilizes it. The other male nucleus and the tuhe and
stalk nuclei soon disintegrate. The fertilized egg surrounds
itself with a wall and forms an ooslJOre.
Formation of the new sporophyte.
The fusion nucleus then passes to the base uf the oospore
B
A
D
E .
Fig'. 206.
A-F.,
c
F
i>iIlI18.
STAur,;,; F'1011 Flmnr.lZ.\;I'ION OF 'I'HE ],Gu TIl'TO 'I'HE
DEVELOP.1IEH1' OF 'i'HE PRO-E:VlDRYO.
and hy repeated division forms folll' nuclei which become
arranged at right angles to the long axis of the oospore.
GYi\lNOSI'ER:\IS
Three further divisions Occur resulting in the production of
tour tiers, each tier containing four nuclei. Panition walls,
develop separating all the nuclei excepting those of the uppermost tier. The three lower tiers are known respectively, from
below upwards, as the embryo tier, sllspellsor tier and roseltC'
tier. and the whole structure is termed pro-embryo. The
embryos develop from the lowermost or embryo tier: tbe other
Stony layer of BCeeI
Inner fle.by layer of Iced
Cotyledons
PluMule
Female GlUl'Ielophl'te
(EndDIIp!!lrml
c
Fig. 206.
A-B,
O.
f'jllll.'
STAGES IN THE DEVELOl'MEN'1" OF A SImnLING
LONGITUDINAT. S]\(TIO:, ,11' ,\ ;I[A'l'lJRE sElm.
tiers being only nutritive in function. The suspensors rapidly
elongate and diverge so that the emhryos are pushed deep
within the tissue oi' the female prothalllls which now he comes
laden with food matters diffusing into it from the placenta.
Each suspensor bears at its apex one of the fOllr embryo cellf>.
FOll1" potential emhryos are produced '1)y rapid division of each
::260
STRUCTURE ,\ND DEVELOl':llEKT OF PLANT GROUPS
,of the embryo celk It is to he noted that as more than lln~
oosphere may be fertilized 111.<111Y potential embryos may alsu
J)e produced. This is ralled polyembryony and is a wry
.characteristic feature of the Conifers. Only one. 11owen~r .
.attains maturity and the rest perish during development. A
.fully developed emhryo consists of a radicle. the hypocotyl,
.three to many cotyledons and a small plumule. As the
endosperm expands the nucellus is generally crushed out hut
sometimes it pen.;ists as a thin lay~>r forming the so-called
·perisperm. The integument is gradually converted into the
:seed-coat and the ovule develops into a seed.
ORDER GNETALES
Plants woody. sparsely branched and usuall~' diceciou$;
:leaves simple, opposite and net-veined li~e those of the dicoty'ledons ; "flowers" with a distinct perianth and generally forming cones; embryo with two cotyledons; endosperm copious ;
"true vessels present in the secondary wood; resin canals
,ah,ent. The order includes only one family. Gnetace:e.
Gnet"!lm
(Family Gllt'lm:ea:)
Giletuni grows luxuriantly in tIle tropical forests of 'hoth
11emispheres being mostly di~tribllted in tropical Asia and in
·the islands between Agia and Australia. A few species
IC. sc([ndens, C. [ali/olium, C. gllc1Ilon) are also found in India.
-Vegetatlve body of the sporophyte.
The plants are mostlv lianc:; (C. lila) which climhs
·or trail over other vegetation. often reaching the tops of tallest
'trees. A few specie:, are. however, small trees (G. gil e11lO I! ,
·G. costatum) and shrubs. The leaves are simple. large. oval,
. entire, exstipulate. leathery with short petioles. They show
:pinnately reticulate venation resembling the foliage leaves of
·dicotyledons and are arranged en the stem in opposite-decussate
·pairs. The branches are of two kinds: one of limited growth
·or dwarf shoo! and the other of unlimited growth or lOllg
GYi\INOSI'I::RMS
Iu c1imhing species the foliage leaves arc horne anI
dwarf shoots only, while those on long shoots arc usually
reduced to scales. In case of tree (G. gllClIUlIl) the diffcl'cnces
between these shoots arc very much reduced.
shoot.
The vascular anatomy of the stem of
Gllctlllll
showt):
;r
striking angiospermic character, since its wood in additionc to·
gymnospermous tracheids with hordered pits pOflsesses
vessels of angiospermolls type.
tn/{:
A section through the inter-·
uode shows, according to species, 8-:2.0 vascular hundles arranged
in a ring surrounding a small central pith. The central region
of the 'pith is thin-walled and contaim alnmciallt starch grains,
while the peripheral region is lignified. It ultimately' disorganises. The vascular bundles are Mrong, conjoint, collateral.
open and endarch. The protoxylem elements are scanty and
show spiral, annular or reticulate thickenings, among which
bordered pits occur at intervals. The end-walls of the vessels·
of metaxylem are oblique and with a single long or round
perforation, 01' with several rollnd perforations. The phloem
does not contain fibrous elements. The sieve-tubes are' Iarge·
and the sieve-plates occur on the oblique end-walls or on lateral
radial walls. Alternating with the sieve-tubes there occur
i-egular radial rows of alhuminous cells. The regular arrange'
ment is ultimately disturbed and they arc forced to occupy
po:::;itions at the corners of the sieve-tubes where they look like
"extremely like companion cells." These cells are short, narrow
with thin walls and contain a mass of proteid and a few starch
grains and crystals of calcium oxalate. The medullary rays;
between the vascular bundles are large, broadening as they
pass outward and are made up of parenchymatous cells whose'
walls may also he lignified. Outside the vascular cylinder the
parenchymatous cortex is comparatively thin ann in older
Z62
STRUCTURE AND DEVELOP;\IENT OF PLANT GROUPS
;!'tems contains an irregular ring of stone cells and numerous
simple fihres with cellulose walls at the outer region. Just
,outside the phloem region stellate fibres (spicular cells) are
Fig. 207.
(furtum ..
POIlTION OF (,RnR~ Sl,cnON OF Sl'E~l.
,common In a section through the node, but in the internodaL
region these are "cry rare. Latex vessels are also conspicuous
,clements of the cortex.
On the epidermis of young stem
GYMNOSPERMS
vertical rows of stomata also occur. The primary cambium
is short-lived and during secondary growth successive layers
of cortical cambiums produce concentric series of vascular
bundles. The secondary cambium first arises at the various
points in the phloem parenchyma and these extend laterally,
unite and produce a continuous ring which gives rise to
normally oriented rings of xylem and phloem separated into
wedge-shaped vascular bundles hy broad medullary rays.
A cross section of the leaf of Gnelum seem to differ in
no essential feature from that of a dicotyledon. The upper
epidermis is provided with a thick cuticle. Numerous stomata
occur entirely on the lower epidermis. The mesophyll consists
of a single layer of upper pa1isade cells ?-nd well-developed
lower spongy tissue. Stellately-branched acicular cens occur
particularly ncar the lower epidermis. Simple or shortlyhranched fibres with thick cellulose walls are very numerous.
Asexual reproduction.
In Gnetllm the microsporophylls and megasporophylls
form different strohili and are mostly dioecioU8.
Staminate strobilus. It consists of a slender axis with
numerous pairs of decussate bract~ whieh are connate throughout and thus making them look like cups. In the axils of
these cups, surrounding the axis, numerous staminate flowers
develop. Eaeh staminate flower consists of a stalk bearing at
its tip two anthers, each with a single micrbsporangium, and
invested at the base hy two connate bracts (the "perianth").
The strol1iJi are axillary or terminal, solitary or in catkin-like
clusturs and are compound structures, since the microsporangia
are borne on secondary axes (the so-called flowers) and the
investing bracts at the base of each flower are regarded· as
perianth. The presence of perianth is a striking angiospermic
characte'r. The flowers mature in acropetal order. Our
knowledge about the development of microsporangium and
microspores (pollen grains) is still very incomplete. Within
the microsporangi.um gradually sporogenous cells become
differentiated and, from these ultimately, by reductio.n division,
spore-tetrads are formed. The outer wall of the anther
264
STRUCTURE AND DEVELOl';I.!E~T OF l'L.\:-IT GROUPS
consists of a single layer of cells and the t~petum is formed:
from the outer sporogenom; tissue aUel not from the walL A~
Fig.
A,
208.
(hiP["}/I.
n,
CLflirI'ERS OF STAlIlINATE R"l'IWBILI;
A I'OItl'WN OJ.' 'IHE
SAnIE (ENLAllGlm), C, A STNGLE "FLOWEll".
the microsporangia mature all the cells between the microspores
and the epidermis break and the microspores are liberated.
GYMNOSPER:\IS
Ovulate strobilus. The structure of the ovulate strobili
resembles in general that of stamit'iate strobili, ovules or
megasporangia arising in the axiIs of connate bracts. There
are nve or six whorls of ovules surrounding the axis and with
five to seven ovules in each whorl. Sometimes the axis is
terminated by a single ovule. Though there are numerous
Pistillate "flowers"
B
A
Fig. 209.
A,
Olltlllln.
A C[,UHTEIt OF OVULATE STROBILI; 13, l'IS'L'ILLA'rE
'FLOWERS' WITH llllACl'fi.
ovules only a few attain maturity. Each ovule is invested with
two integuments, but the inner one becomes prolonged into a
micropylar tube,. which is a characteristic feature of the genus.
The llucellus has all the characteristic features of a gymnosperm.
266
STRUCTURE AND DEVELOPIVIENT OF PLANT GROUPS
consisting of a heavy mass of sterile tissue overlying the
megaspore mother-cell. 1t is quite probable that in some cases
more than one megaspore mother-cell is organised within a
single ovule. The tip of the nucellus becomes more or lesR
disorganised and shallow (G. gllemon) and this is only trace
of the pollen chamber found in other gymnosperms. A deeper
and narrower pollen chamber may he formed in some cases
(G. af:rica nll 111). The megaspore mother-cell, as usual by reduction division, forms two cells. each of which may become an
embryo-sac: thus when seyeral megaspores begin to function
several gametophytes may he produced within a single ovule.
Other details abollt the development of embryo-sac is still incomplete.
The gametophytes .
. Male gametophyte. The microspores (pollen grains) after
liberation are disseminated by wind and ultimately reach the
ovules. Insects may also play an important role in it (G.
gnc1noll). A drop of sweet fluid is exuded at the tip of the
micropylar tube and the pollen grains are conveyed to it. Due
to evaporation the drop shrinks and the pollen grains arc
sucked in and finally reach the top of the nucellus. Germination of the microspore starts while it is in the micropylar tube.
The nucleus of the microspore first divides into two nuclei
which lie free in the cytoplasm. In wme species (G. aIricallUm)
a delicate and evanescent wall may he formed after 111'st
division of the nucleus of the mic1'c;spore. However, of the
two free nuclei. one again eli "ides so that the adult microspore
contains three free nuclei. In some species the num11cr oj"
nuclei may he two (C. jllnicul((re: in G. gllemoll either two
or tbree). One of the three nuclei usually disappears hefore
or after pollination, or even if it persif'ts it docs not enter the
pollen tube formed as a result of gennination and this nucleus
may he regarded as a reduced homologue of the pl"othallial
cell. Thus, in the elimillation of even a single protlwllia/
cell GlictUnl has reached the angiosperm cOlldition. The
generative cell is not organised before pollination. During
germination, either in the micropylar tube or in the pollen
chamber. the exine of the microspore is cast off and the in tine
GYMNOSPERl\IS
growR into a tube which grows through the base elf the pollen
chamber into the tissue of the nucellus and reaches the apex
of the embryo-sac. Of the three nuclei, one doeR not enter the
tube and of the other two, one iR the tube 1lUCleliS which finally
clisorganises. The second ~lUcleus organises i tseH into a ccli,
A
Generative
ccII
D
8
c
E
Fil,(.
210.
linN 11m.
])EVllLOJ'1fEN'1' OP ~fALE ClA)IETOPHYTIC.
the generative cell. The nucleus of the gcnetative cell divides
into two more or less spberical st)erm nuclei. Smaller of the
two spernl nuclei may disintegrate. It is to be noted that the
germination of the microspore at a distance from the flllcelllls
is another angiosperm feature.
Female g,ametophyte. Our knowledge about the development of the megaspore (embryo-sac) and endosperm is still
268
STRUCTURE AND DEVELOPMENT OF PLIINT GROUPS
yerv incomplete. The account as far as available reveals that
a~ a result of germination of the megaspore and consequent
divi~ion of the nucleus, there appears within the megaspore a
CDnspicuous central vacuole and fOllr free nuclei distributed in
tl)e peripheral layer of cytoplasm. Subsequen t divisions of
tllcse nuclei increase their number but wall-formation does not
Illig.
211.
(i1ll'tlf'IJI.
~~, A ~!EGASI'OHAGGIU2\I; H, l\IAGNIFIEf) VIE\V (IF ~rr-;GASPOnE
AND GLANIlliLAR 'rrSSlfE (l1''l'~IllE IT.
take place. As the embryo-sac enlarges the nuclei he come
more closely aggregated at the chalazal end. The lower llalf
of the sac then becomes separated into compartments or cells
hv the formation of walls and each cell contains more than
one nucleus (five Ol' more). Towards the micropylar end of
GYMNOSPERMS
the sac there is no sign oj' septation and the nuclei remain
free in the irregularly vacuolated cytoplasm and commonly
remain in this condition. Each free nucleus organising some
cytoplasm around it functions as an egg. Therefore, c.acil free
nucleus is tI free potential egg-nucleus and this is another
angiosperm condition. The nuclei in each cell of the 10lrer
half finally fme and form a prominent nucleus. This tissue
is the "primary endosperm" whose cells further undergo
division and form a group of uninucleate cells. Endospcrmformation may proceed upwards towards the micropylar end
and if in the meanwhile fertilization is not effected it may
completely fill lip the cavity of the sac. Outside the emhryosac a remarkable nutritive (glandular) tissue is formed whicll
is really a part of the nuce11us.
Fertilization.
Information regarding the details of fertilization is mcagn:.
Fertilization llsually takes place either before (G. rumph-i(I/I~l1n)
8
A
Cellular parL of female h
gametop !_YLe
Fig. 212.
. _.Ie-C,
(/-netllln .
HIlCCEH,,;I\'g STAGES IN FEI\TILIZATION.
and after (G. gnel1lrm) the formation of the primary endospenn
~l.l1d it is confined OIily to the micropylar region of the nuclei.
270
STRUCTURE AND DEVELOPMENT OF PLANT CROUPS
fhe pollen tube cnters the embryo-gac and the sperm nuclei
are discharged. These meet the egg-nuclei and fertilization
of anyone of them may he effccted leading to the formation
of an o,ospore. Aftcr fertilization the endosperm increases
greatly and becomes differentiated. It has two growing points.
()f which the lower one grows and destroys the glandular tissue.
Development of the new sporophyte.
The nucleus of the oospore immediately undergoes a series
offree nuclear divisions which enter into the organisation of n
~mall mass of free cells. called pro-t:mbryonal cells (one proembryonal cell in C. gnemon). Each pro-embryonal cell.
elongates to form a long tortuous cell (suspensor) containing
a numher of free nuclei and penetrates the endosperm tissue.
Further details of the development of embryo are not known.
hut in one species (G. gnelllon) transverse walls are formed
hetween the free nuclei. An uninucleate cell at the tip 01
D
Ifig. 213.
A-D,
SUCCESSI\'Jc
Oll['tllili.
S'l',\(!ES IN THE IJE\'ELOI',\IENT
OF E~TBIt\'L).
the suspensor is finally cut off in the same way which contain~
numerous starch grains. From this terminal cell (embryonal
eel!), by free nuclear divisioll, a multintlc1eat~ emhryo i~
formed. When fully developed it consist~; of two coty1cdol1s,
a central apical cone (stem-apex) and a root-apex. The ()vule
is ultimately converted into a seed and contains only one
embryo.
OALCUTTA UNIVERSITY
B.A. & B.Sc. QUESTrON PAPEH.
1949
Jl'IHST P,\PEH
1.
\Vhat are
lhl:
chief agencies by which seeds and fruits
Give examples.
of difFerent plants are di~persed?
Give a comparative account of Solanacetr and SCI'()Mention two economic plants belonging to the
family of Sn/a/Ulcc;;c.
2.
1)/tIlZfll'iacet'I'.
3. Describe the main characters of the family of
Laliiat[l}. Illustrate the structl11'e of the Hmvcr hy means of a
floral diagram.
.
t. What are the main differences in the internal structures
of stem and root of a dicotyledonous plant?
S. Descrihe how the growth in thickness takes place in
the stem of Pz'/ll/s.
6. Give an account of the morphological and anatomical
adaptations exhibited hy some of the rooted and floating
water plants.
7. Write short notcs on any fOllr of the following:(a) Cladode; (h) Bulbil; (c) Conn; (d) Em bryo"sac.:
(e) ACTCIlCllY1Hll; (f) Trachece.
SECOND PAPER
I.
Either, Give a general account of the structure, modes
of reproduction and aRinities of the Cyanophycere, mentioning
the types studied hy you.
Or, Give a detailed account of the structure and life-·
history of Vallcheria and compare its sexual reproduction with
that of Spirogyra.
2.
Either, Describe the life-history of any Ascomycete
you may have sudied and compare it with that of a Phycomycete.
l
ii ~
Or, Dcscirhe the ~tructure and
Zygomyccte you may have ~tudied.
life-hi~t(Jry
3. Either, Descrihe the distribution of
tissue in the thalloid liverworts.
nf
:iny
phorosyllth~["ic
Or. Descrihe the types of stelaI' structure found
Pteridophytes studied by you.
III
the
+ Either, Define Geotropism and describe some cxpenments to show dw rda tionship hetween "stimulus" and
·'responsc·'.
Or,
s.
Give a general account of respiration in grecn plants.
\Vrite short notes on the following:-
Adaptation: Variation: Reduction division: AlleloJl1orph~:
Crossing oyer.
INDEX
B
A
AI>IJ:l"put'e, .),).
Aecia, 143.
Aecial stage, 143.
AecidiodpOl'eS, 136.
Aeddinm. 144
Aeciospores, 136, 144.
A!lrtl'icl(;;.
145.
Akinete, 6, 12, 15, 19, 29, 53.
Albumino11!; cell, 249.
Algre, 2.
A Ig<L[ byer, 155.
Algill, 65.
Arnphip;YIlUllS, 104.
Amphiphloic sipllOlloslele, 185.
Amphit.hccillm, 162.
Amylase shtrs, 57,
Androspurangia, 31.
Andl'{)spuI'C, 32.
AllisDl-(ametes. 19.
Anisogamv 2. 16. 66.
Alltheridial cell. 67 119 158.
chaUluet', 173.
Jilnmellt, 60.
initi'LI cell. 242.
Allthl3riuinll1, 2. 16 60.
Alititel·01.Oid, 2, 21. 75.
AntI, (/c«(nJ.<, 171.
Anthocel'Otm, 159.
Annulus .. lA5. 213. 222.
Apical 9!lP, 27.
Aplallospnre, 15. 18. 23. 53. 95.
Apothec.i(Lm. 111, 122, 158.
Archegonial l'hambl'l', 244.
jacket. 244.
Archegllui nUl , 158.
Archesporillm. 170 175.
Al'chi",lI'IL 119 157.
Al'chi!llvede~
77.
ASCt)(,!ll:P 158.
Ascogennns hypha, 121. 124. 15~.
Aseogollia, 157.
AseOSfl0l'(!~, 94. 11.0. 114, 115.
158 212.
Ascoii<:hells. 154.
ARl!omyceteR. 96, 110.
A~OllH. 94 111 114. 115. 124. 158.
A"'l/l(/'(rill/l.~, 117, 119.
All~imilat.Ql's, 47.
AutoLasidimllv~etes. 126.
Antrecious. 135.
Autuphytes, 2.
Auxillial'Y 'I'!ells. 90.
Aux()spol'es, 78, 81.
Azygospol'e. 41. 46 110.
Bu,cillariopliyce(c, 3. 78.
Bacilll 151.
comma,. 152.
Bacteria, 150.
Basltl cell, 61.
Bltsidia, 94, 125, 150. 148.
Ba~idial stage. 140.
Basidiolichen. 154.
Basidiomycetes. 96 125.
BasitiiosporeH, 94, 125, 136, 140.
149.
/JlIlr/l('/;o8jJl'rmUJII,
Black rust
st~Lge.
84.
139.
Blepharoplnsts, 29,
Blight, 99.
Body cell, 257.
Brand spores. 127.
Bryophyta. 15B.
Bud. 95. 177.
13nclrling. 95.
Ilull.ib. 57. 191.
c
(:alyptm, 168, 183.
Capsule. 167, 183.
Carinal cavity, 212.
G:ll'p"g,)!!hl filameut. 86 90.
OarpogouiL'm. 82. 86. 90.
C;\l'Jlo~pol'angiulll. 91.
lla,l'p(Jsnol'~,
91.
Uandex, 217.
Oaule'/"/)((, 46.
Central bnrly. 4, 5.
e;tvity, 212.
Uenti'ic (lin,toms. 80. 81.
Cephalodia,. 152.
Uh:lJltI'!Ln~iH stltg'C.
88.
f'/u'J'{I, 55.
('h7I/1/l!/rl/)m(J"'Il.~.
16.
ChlamvdoKpores, 94 103,
Chlol'ophycom, 3, 12.
Chl'0U10plasrn, 4. 5.
Clustel' cup, 144.
stage, 143.
Cocci, 151.
(:()enl)cyLe, 93, 106.
Oolumella, 1.07. 175,
plasm, 107.
COll(;eptaclcs, 73.
Cone. 198.
Conidia, 95. 117. 152.
C(ll1idioph()l'e, 99. 117.
Cfmifcl'uloR 246.
(\,njugatiOJ1. 35-,
1~{.
(
Fl~8h,
lateral, 36.
sea larifol'm.
ii
2:6.
t.uLe. 36 . .
eontractilc vacllole. 17.
I!ol'll smut, 129.
Cortex, 72.
UOl'tiuated, 56.
('o'~lIul]'itUil, 41.
Crown, 193.
Crnst OliO, 152.
Cranophycere, 3_
Cwurlales. 236.
('~l/en8, 236.
C:ystoelll'p, 91.
D
146.
Fltixu(JU5 ltyphm, 143.
Fl,,!'idclln sta1'(']', 83.
l;'lol'itlosirle. 83.
FnlioRe. 255.
Foot _ 167, 183, 196.
Fmgmcntat.ioll, 152.
Fl'(,;id. 72, 217, 219.
Fl'llctititntioll, 145.
Fl'ui.ting body, 145.
Fl'1I5t.111~, SO.
l"l'uticLJ"", '255.
FUCO,xHut,hin. 64.
FiI~/I-' ••72.
Fllugi. 2, 92.
il11Jlcrfel·ti. 96.
Th .'II/ids, 4l.
Diaphragm, 202.
Diatom, 78.
DiatomaceouB earth. 80.
Diatomin, 98.
DiclLl'YOll phll5e, 93.
Diplococcns, 151.
-~, capsulllted. 151.
Diplop}Jase, 126.
Discom:ycet<~s, 112.
Dry rots, 99.
Dwarf male, 29.
shoot, 247. 260.
E
R~iocnrpIl8,
67.
l<Jctollhloin siphonllRtele. 185.
Elat:~l', 170, 214.
EmlH'yo, 217, 225.
Embl·Yo-Sn.c. 254.
- _ ti.~l'. 259.
ElldophytBS, .3, 10.
1<~ll<l(J:lperm, 235.
EndoSI10l'€, 6. lOa. 152.
Endllthr,cinJ'Il, 162.
E]lib"sa1 cell, 169.
Epihasidium, 129.
Ejliplusm, 121. 125.
EpisJ')ol'e, 121.
Ellithec'l, 80.
E'1uisetiIlffi, 187.
H'/lIiMtllllJ, 209
l~lI)'otillm, 117.
Enspornngi'lte.. 192_
e Exciptllum, 123.
Exospor~, 108.
Extl'U,ion papillm. 49.
Eye spot, 11, 17. 23.
F
Fair~
ring, 145.
Filicimc. ] 87.
FissiOlI. 152.
G
'(iamel,wgia, 1. 35 108.
('Hlllcte. 1, 95.
(lameoophol'e, 177.
f: am etophytc, 158:
---, fmnale. 200, 207.
- - , male, 199, 206.
Gii~tel'Omycetes, 127.
G(,mmm, 165, 191.
- - cnps, 165.
Oenerativc cell. 255, 267.
nel'mlinp;, 32.
Ciel'm'pore, 92_
- - spora.ngiull1. 108.
- - .j.uhe, 93.
(1i1l~, 131, 147.
nirtll('~, 237.
lil,'o"(/li.~(/.
7,
Glolmle. 57.
tilll'/ iIIl/. 260.
Gonirhllgiollhol'e, 106.
Goilidia, 106.
.
({cllidial laver. 155.
(1ollimnhla3t filami1nt~_ 88. 91.
(;YllHndl'ORporons. 32.
Hall<lle cell, 58.
Ha[llophas~, 126.
HaptCl'll, 33.
HauRt.Ol'ia. 99, 111. 130.
HemihaRi(liomyc('tcs, 126.
Hppaticm, 159.
Het.el·ocyst, 6.
Hetel'~ei()ns, 135_
. Heteroph);tc,. 2.
H etel'(}spol't)l1s. 185.
Het.el'othalli(', . Ill. 53, ·1§1.
Hilum, 140.
Holdf:lRt, 22, 27. 33, 89.
HomnspOI'OIlS, 185.
rr"ntothall ie, 19. 53 161.
jii
HUl'lllogolles, 6, 9, 11.
HOl'Il liverwort, 171.
Hydl'oids, 179.
Hymenomycetes, 127.
IIymeniurll, 111, 122, 125, 148.
Hyphre, 92', 105.
Hypllo~pore, 15, 53.
Hyp()basal eell, 169.
HYp(,theca, 80.
Hypo.theeium, 122.
I
Idil)alllll'o,p()rou~,
1viicI'Ilspure, 185, 198, 240. , . '
- - mo.thel'-eell. 199. Z()6.
Microopol'ophylle, Hi9, 240.
MOJlOCarVOil ph"s", 93.
~10Jl(Jspllrungi\lHl. 86.
MOlWSPOr<;s, 84, 86.
l\I[ucilai-!;illOllR ring. 232.
Mucor" 10[,.
MnsC'i. 159,
1.[yreiium. 92. 105. 145.
l'iIYrorrlliza. 92, 193.
:\lyxophyeete, 3.
32.
N
[udusiuUl, 231,
Inflorescences, 180.
lsidia, 157,
1.,o;te~, 203.
hogametes, 19.
Isogmny, 2, 66, 95.
IstlunuR, 42.
N annandrillIll, 29.
Narrnnndrous, 29.
N ontral sporangium, 66, 70.
- - Hporos, 84.
- - zoospores, 66. 70.
Nos/I)c, 10.
N \lc,'llar
J
:racket cell, 200.
he~Il{.
241.'
N nenle, 5"(,
o
K
Kernel smut, 127.
L
Lamelloo. 147.
Lamiuarin, 65.
Late hlip;ht, 99 .
. Lateral eonjllgation, 36.
I"cafy shoots. 47.
Lelw'es, 56. '
Leptosporangiatc, 221.
Lichens. 153.
Ligule, 197. 240.
Liv~rwort, 164.
Loose smut, 127.
- - of oaL, 134.
- - of wheat., 132.
Lycopodillre, 187.
Lycollniliu1II., 187.
M
29.
MacrocycJic rust, 137.
Mannitol. 65.
Manubrium, 58.
;l/arclumtia, 164.
,11rJ.r8ilra, 227.
Medulla, 72, 155.
Megasporangium, 199, 205.
Megaspore, 185, 198.
_ - mother-cell, 199, 205,
Megasporophylls, 199.
'
Micl'os[lorungium. 199, 205, 240.
.Mat:l·UIlUl'OllS,
241.
Nll('elll1~,
()lJligate pal'Usitt',;, 152.
Or.do(fOllium., 26_
Oi(lia, 110, 159.
Oogamy, 2, 16, 66, 95.
Oogonium, 2, 16, 61.
Oomycetes, 97.
Oosphere, 95.
Oospore, 22, 104.
Operculum, 183,
- - cap, 181.
{),s"iUatlJrill, 9,
Ostiole, 73, 111, 142.
Ovule, 235.
OVlllifcl'()uS seale, 253.
Ovum, 225.
.
p
PalmtlJltl ~tage" 19.
Pltl'aphyses, 73. Ill. 122,' 150, 18t
Parthenogenesis, 16.
Pal'thenospol'oS, 16., 41, 46. 72. nO .
Pedicel cell, 61.
Penuate diatoms, 80, 82.
Pel'ichrotial leaves, 180.
Perirjillm, 111. 144.
Peripllyses, 143.
I'oriplasm, 104,
PeriRpOl'e, 214.
:Peristome, 183.
Perithecium, 111, 121, 158.
Peziza, 121.
, Phreophycere, 3, 64_
Phycoeyanin 4.
[
I' lt~· l'uwytbl'in, 82.
Phycomycetes, 96.
l'h!ltuphtlw/'(/, 98.
Pileus, 146.
Placenta, 221.
Plankton, 3.
Plpf'ienchyma, 93.
- - , pam, 93.
- - , Pl'OSO, 93.
Plectomycetc~, 112.
Polar lll)d ule, 7.
I'olleu ulHll1lbul', 241.
- - grain, 240.
- - ~acs, 240.
Pillyembryony, 260.
PolylllOl'pllie, 135.
]'oi.llI'0lillOIl J 217.
Pol!l.~il)"ultia, 88.
PoJystele, 186.
i'olytJ'irhulll, 177.
Poud·scllm, 34.
Prinun'y capitulum, 58.
pl'otonema, 63.
Pro-emuryo, 259.
Progametangia, lOB.
Promycclium, 108, t40.
Pl'Opl1gula, 66.
Prosenchyma, 93.
Protha.Jlial cell, 207, 233.
Prothallus, 223.
Proto-:eci(lia, 143.
basidiomycetes, 126.
ProtocOCC7l8, 25.
Prot,onema, 177.
Prc>tostele, 185.
PRtlUdo-pluenchyma, 93.
perianth, 16B.
plemnenceus sta)l;e, 26.
Psilophytinem. 187.
Pteridopliyta, 185.
P1Jr,cinia, 135.
Pycnin, 142.
Pycn~al ~tage. 141.
;ycllloepores, 136, 143.
1 Y"I1ospores, 157.
Pyrenoid, 35.
Pyrsnomycrtes, 112
Q
Qnadrifiagellate, 23.
R
Ramellta, 219.
Hed rust stage, 137.
Replicate. 35.
Rhizine, 156.
Rhizoid, 15B, 177, 223.
iv
Hhi:widlLl appendagps, 63.
initial, 63.
Rhiznmorph, 94, 145.
Rhizophol'e, 197.
Hhodophycere, 3. 82.
Ri"('ia, 159.
Hoot tubercles. 237.
Rose.Ue tiel', 259.
llllst fnngi, 135.
8acc/WI'lJln',l/ce."
112.
BmJariiol'm conjugatioll. 36.
Schizomycete~, 150.
Schizosacchal'omyees, 113. 114.
Sclel'ilied p<LrellchYllllt. 19B.
Sclerotium, 94.
Secondm'Y capitula 60.
protonemaI a)lpellrlage~. 63.
rhizoids, 63.
Srl(l!7in~lla, 196.
S£)mi-cells, 42.
8E1pal'<Ltion disk, 9.
Set,1, 183.
Sheath, 4. 8, 191.
Shi<:'ld cell, 58.
Smut clisea.~e, 127.
fungi, 127.
lip0l'eS, 127.
SOl'edia. 157.
SOl'i, 219, 230, 240.
Sperrnagonial ~tage, 141.
Spl)t'h1:ttangia, 86 90.
Spermatin. 86. 90. 136. 143. 157.
SI'Bt·matozoid. 2, 95.
Spel'mogonia, 142. 157.
Rpienlar cl,lls. 262.
R"iriia., 152.
8piroYlltil. 33.
Spol'alll!ia 1. 15 95. 106. 219.
. meMa. 199, 205.
micro 199. 205.
l'lpol'angiferous "]lib). 199 213.
~1")]·aIll!!()p'!lJl'e8. 213.
94. 105.
RpflJ'e, 1. 94. 106.
hillis, 127.
hilum, 149.
plasm, 107.
Sporidium, 136, 140.
SP"l'OCl1l'}J, 229.
Spol'ogonium. 183.
Sp')l'ophol'e, 145. 146.
Spol'ophylls. 221.
Sporonhyt,p, 158.
Rpol'ula,l,ioll. 152.
Stalk-mil. 42.
!-llJ('l'[ll1gtnSn(}l'p~,
v
Siele, 185.
Stel'eids, 179.
Sterigml1ta, 125, 140.
Stigm:L, 14,
Stipe, 65, 72, 219.
Stomillm, 193, 222.
StrolliluB, 1S9, 199.
carpollate, 252.
ovulate, 240, 265.
,taminate, 240. 263.
Stroma, 27.
Snb-hymenium, 148.
Snffultory cell, 30.
Suspensor, 108 196.
tiel'. 259.
Symbiosis, 92.
]
u
CI"I",;;I'. 22.
U redinal stag;e, 137.
Uredinia, 137.
lhedinuspores, 136, 137.
Ul'edosori, 137.
Ul'erlospol'es. 136, 137.
F8lilaqo, 127.
.
V
V"llel'nlar clIvity, 211.
Fa Il"lw' ill , 50.
Vegtlltath-e cell, 24::.
fir~t.. 254.
second. 254.
Vp]llm 204.
Fnlro.'t, 19.
w
T
'l'apetum, 192, 222.
'feleutosori, 139.
Teleutospores, 127 136, 139.
'J.'elia. 139.
'felia! stage, .139.
~reliosp()res, 125, 136, 139.
Tetras)Jol'e, 88, 92.
Tetrasporic plant, 88, 91.
Thallus, 1.
Tl'abeClhlre, 48, 198, 206.
Tl'<tma, 147.
Tracheidal cell. 250. ,
Tl'ansfllsion tisslle, 249.
'I'richoblast, 90.
'rl'ichogYlle, 86, 90. 95, 119, 157.
Tube cell. 63.
TlIUIf)I"~, 131
X
:Xyl~m
sheath, 179.
y
z
Zoodclt
~ta.ge,
150.
Z(Jo~IJOran!!:inm, 52 95, 101.
ZOORpOl'e, 15, ,23. 52, 95. 101.
Zygolllycetes, 98.
Z:'I!Inelfl{1, 39.
ZygosaceharomyceB, 113.
Z~'goBpOl'e, 40,
Z~'got(1 2.