ALGAE ANP
PVNOl
DATitENTERH*
E. K. SEIVASTAVA, M. Sc.
Indian Administrative Service
/
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<b'^
CENTRAL BOOK DEPOT
ALLAHABAD
9J
.^Q!
Published by
CENTRAL BOOK DEPOT,
AUfthabs^d
Printed at
VANGUABD PRESS
Allahabad
PREFACE
In tlie Mlo^^ring pages an attempt has been made to present
a. concise account of the Algae and the Fungi. The entire
subject matter has been diviaed into two main sections dealing
with Algae and Fungi and a subsidiary section dealing with the
Bacteria. A general introduction to the Thallophyta is given at
the beginning and three appendices for special topics, Seaweeds,
Lichens and Fungi Imperfecti are included at the end. The
object throughout has been to give a brief and yet comprehensive
description.
In preparing the text, help has been taken from authoritative
texts. Original papers and researches have been referred to in
most of the cases. All account has been brought uptodate and
in specially controversial topics, all views have been given.
Illustrations have been drawn from specimens and slides which
the author had the opportunity to examine. Wherever this was
not possible, original drawings of the investigator have been
simplified and adopted. Most of the common species were examined by the author through his ow n preparations.
In dealing with types, effort has been made to give a short
narrative of the order or class to which the type belongs. This
has been done to enable the student to place the type in proper
perspective and to avoid a disjointed description.
The author's thanks are due to all who helped during the
preparation of the text.
Suggestions for improvement would be welcome.
R. K. S. •
CONTENTS
Iiitroiluction
SECTION
I
6
Algae-Introduction
Myxophyceae
11
Chlorophyceae
17
Pliaeophyceae
41
Rhodopliyceae
53
SECTION
II
Fungi-Introduction
67
Saprophytism, Parasitism, Specialisation, Symbiosis
71
Phycomycetes
77
Ascomycetes
91
Basidiomycetes
106
Economic Importance of Fungi
122
SECTION
III
125
Bacteria
Appendix
Appendix
Appendix
129
I—Seaweeds
II—Lichens
..
I I I — F u n g i Imperfect!
132
135
INTRODUCTION
There is a very general consensus of opinion among
Botanists that the vegetable kingdom can be broadly classified
into THallophyta, Bryophyta, Pteridophyta and Spermatophyta.
Following Darwin's theory of evolution, phylogeny and ascending complexity took hold of the field of systematic Botany and
agreement on the above-mentioned broad divisions of the vegetable kingdom was the natural outcome. Amidst such trends
in classification, Eichler proposed, in 1886, a scheme which
established Thallophyta as the most primitive of plants. Eiehler's
Thallophyta comprised two classes, Algae and Fungi.
The original Greek term literally meant plants with undifferentiated shoots and included in its fold practically all plants
below the Mosses and Liverworts in complexity of organisation.
B u t this range of component individuals is so large and
varied that the Thallophytes appear to be an unnatural assemblage of plants.
I n the light of detailed investigations on
life-histories of plants, it appears that a more plausible and
acceptable classification is needed to remove this unwieldy group
from plant-systematics.
Thallophytes possess a great variety of transitional forms.
Morphological differentiation proceeds irom the
^B boay
simplest forms which display neither specialisation nor division of labour, to others which exhibit both external
and internal complexity. I n the simplest case the individual
consists of a single small cell with thin cell-wall and protoplasm.
I t contains chlorophyll and boundaries between various inclusions are not defined. Progress from the holophytic unicell is,
in the first instance, towards perfection in shape and contents.
Delimitations in the increased volume of the unicell result in the
formation of a complex unicellular organisation which is unknown elsewhere in plant kingdom.
XJnicells may also be colourless. They multiply by simple
fission and uniplanal division. As the evolutionary stages are
crossed, aggregation of cells appears to occur among undifferentiated forms. This may assume the form of a simple globulat
colony or a filamentous strip. Colonies of cells may increase in
size and attain a very high measure of specialisation in which
the identity and autonomy of component cells may be lost.
Filaments may branch and divisions in more planes may produce
thalloid multicellular plant bodies in which division of labour
teads to restrict the physiological independence of various parts.
-5
INTRODUCTION
The primitive THallophytes might possess 'undifferentiated
shoots' but higher up in the evolutionary sequence, definite rootlike, stem-like and leaf-like parts can be distinguished.
With a wide range of structural variance is accompanied a
. .
variable pattern of metabolic systems.
The
pigmented unicells are holophytic and fiutotrophie, i.e., they can marrafactxire their ovm food. I n the cQlourl^ss
forms, heterotrophism appears as the adaptation. Saprophytism
and parasitism are ^he two divergent modes of heterotrophic
nutrition. I n the former, the plant body absorbs nutriment from
decaying organjc matter and dead remains of living organisms.
In the latter, absorption is confined to living bodies alone. Many
Thallophytes lead a life which is part saprophytic and part
parasitic. Even the same individual may, at times, be capable
of changing its mode and is then designated facultative. However, certain forms are unable to alter their metabolic habit and
either remain saprophytes or parasites throughout. These are
termed obligate. Obligate parasites show a considerable specialisation and a study of pathogenic forms suggests that in the series
of progress, specialisation confines the parasitism of species to a
narrower range of hosts.
„
I n the simplest Thallophytes, reproduction is coincident with
, ,.
oudinary cell-multiplication. The organism grows
epro uc ion
^^^^ attains maturity. Division takes place and
the resultant cells begin life anew. The process of division is"
repeated and continuation of life achieved.
^
I n colonies of cells and filaments, the work of reproducing
is allotted to a specific part of the organism and differentiation
results in the production of definite reproductive cells. The
thallus continues to grow for a longer time. Reproduction by
splitting is common in primitive filamentous forms and this may
be considered analogous to the simple binary fission of unicells.
I n asexual reproduction, the vegetating individual or its specific
p a r t undertakes the formation of 'spores'which are capable of
growth and cell-division. In primitive unicellular Thallophyta,
the spore is simply a smaller rounded cell which has to undergo
a size increase to attain to the status of the vegetative individual.
Later in the evolutionary scale are seen dividing individuals
which do not separate and form colonies. As, in the plant-body,
so in the germination of spores, the colonial stage is followed by
multicellular segmented filaments.
Asexual spores are variously modified to suit the environments
and in the way of such an adaptation, chlamydospores, aplanospores, tetraspores, teleutospores and piolyspores find their place.
Their thick outer cover serves to preserve the protoplasm within
and continues life in the adverse circumstances.
INTRODUCTION
3
Gases Have, however, been recorded where the spores produced
by the organism are extremely small and incapable of independent development. Such a condition may be due to a paucity
of nutrition when quick division into small motile individuals
may serve to carry off the species to more favourable environs.
Occasional fusion of such motile individuals seemed to be an
adequate stimulus for further growth and adequate protection
for future generations. The need of such a process was, in all
probability, soon felt widely and as a consequence union of
motile division products waa estalilished in plant kingdom.
T he origin of sexual reproduction must be traced back to stfme
such unconscious process in the history of plante. It appeared
that the reproductive unit which was liberated from tEe parent
plant was almost always a single cell; but exceptions to this were
often seen. Further, these fusing cells greatly varied in origin
and function.
Initially, they appeared' to be alike in form and structure.
Slowly came in a physiological differentatioii between'strains'
which may be regarded as the rudimentary precursor of actual
sex differentation. Structural variation completed the series and
even among the members of a single genus the whole series of
forms could be traced. This was the origin of Isogamy and
Heterogamy.
It Has been pointed out that adverse conditions were the
cause of sexual fusion. Usually these conditions were manifested in the absence of a liquid (aqueous) medium. In these
cases, it was increasingly important for the female of the species
to secure a protected place. In the advancing series this fact
was achieved by loss of movement in female'gametes'(fusing
individuals). This was the oogamous type of reproduction.
The female gamete was perched on a protected' thallus while the
motile male swam in for fertilisation. At this level of sexual
advancement, the difference in the structure of the gametes
was remarkable. The sex organs, however, remained unicellular
and devoid of any sterile jacket layer.
The fusion product represented the second generation in the
Alternation of 1^^^ ^^ ^^^ P^P* and'was_ elaborately protected:
generations
^^ 'iructmcations' 01 various shapes and sizes.
However, fusion brought in another significant
difference. It 'doubled' the contents of the spores. Chromosomes,
the bearers of hereditary traits were doubled also and the fusion
product became a 'diploid'.
Thus, the same plant possessed two distinct phases of life:
normal (haploid appears to be a misnomer) and" diploid. It is
obvious that in a continuous cycle of life, the diploid phase should
be halved or reduced to reach the normal, Nuclear division for
4
INTRODUnCTION '
this end Has been designated 'Reduction', THe two pliases have
also been called Gametophyte and Sporophyte.
The phenomenon of continuous concomitance of two distinct
phases, of different chromosomal composition, in the same lifeieycle has been termed as Alternation of Generations. The limits
are marked by fusion and reduction. In primitive cases the two
generations were very much alike in form (Isomorphic) but
later, with increasing complexity of vegetative body, their form?
differed to a considerable extent (Heteromorphic).
In the Thallophytes, therefore, trends in evolution appear to
pursue a course of progressive complexity, from isogamy to
heterogamy and from isomorphism to heteromorphism.
Variance in habitat, form and structure makes the Thallophyta
a predominantly heterogenous group. The different modes of life
viz. holophytism, saprophytism and parasitism also tend to
modify and widen their scope of function, and ecology. Protected by mucilage or living and dead organic matter, or incrustations of inorganic minerals, and perennating by a series of
elaborately constituted spore-forms, the Thallophytes appear to
be cosmopolitan in distribution. However, they are essentially
aquatic in habit and their sex organs do not possess sterile
envelopes. Their diploid generation is a gradually increasing
structure and attains a measure of differentiation in form and
function.
Eichler (1886) divided the Thallophyta into Algae and Fungipio<,=-f« +•
This division is based essentially on charactoiHssitication
eristics relating to the mode of life. The Algae
are mainly chlorophyllate and autotrophic; the Fungi mostly
heterotrophic, saprophytic or parasitic, and devoid of chlorophyll.
More recent investigations have elucidated the morphological
and reproductive similarities of the two classes. Some parasitic
genera of Algae are known and several Algae are now known to
be devoid of chlorophyll. In cellular structure the Coenocytic
Alga Vaucheria volunteers close comparison with the Oomycetes
(Cystopus). The same can be said of their reproduction. CoiLsiderable resemblance is observed beween the reproductive
processes of the red Algae and certain Ascomycetes (Laboulbeniales), and this has been emphasised by Dodge (1914).
It is certain that the various families of Algae and Fungi
show distinctive f-eatures but whether these alone are sufficient
to instal them as separate phyla is a controversial point. Pascher
(1931) and Smith (1938) have given the algal classes and Fungi
(Eumycet^e) the rank of phyla but Fritsch (1935) has treated'
them as classes. It is believed that the Fungi originated from
the Algae due to a difference in environment which led to the
diffe'rence in niitrition. In the present st9.te of knowledge, the
INTRODUCTION
5
TKallophyta must be accepted as a tentative pHylum for basic
morphological treatment.
Questions
Give a full account of the differences between Algae and
Fungi with regard to (a) mode of life and nutrition, (b)
method of reproduction.
{Allahabad. 1949).
Accepting the view that Fungi, in general, have originated from the Algae, what striking features do you observe
between certain forms of Fungi and Algae?
{Ag a, 1949).
ALGAE
Introduction
Algae are universal in occurrence and cosmopolitan in
habitat. TRey are invariably associated -with, moist media and
are present in fresh as well as salt water. In snow and
geysers, the Algae thrive well but still waters are their most
favourable haunt.
They may be floating, immersed or submerged .forms. In
flowing water they appear as elongated tresses attached to
submerged rocks and in lakes and ponds as scums of slimy
mucilage. Floating unicellular forms are called planktons while
attached multicellular ones benthos. They also occur as epiphytes on larger aquatic plants, or as epizoics on aquatic animals.
A large number falls in the categoiy of endophytes. Some of
the endophytes are merely space-parasites, occupying the intercellular spaces for shelter but others may be .symbionts living
for mutual benefit or parasites. Endophytes like Nostoc in
'AnlJioceros are typical space-parasites; species of Scylonemu are
symbiont-partners in Lichens and Cephaleuros is a simple
parasite on tea.
Algae can exist under various temperature conditions. They
can survive freezing in arctic climates. Ghlamydomonas nivalis
is found in snow as the red pigmented protophyta. It has been
claimed that they can exist in hot water upto 200°F. Such
forms are usually encrusted with silica or calcium carbonate and
play an important role in the formation of rock-deposits. Variations in the acidity and alkalinity of the surrounding media
So not affect Algae to a large extent. Species of Oedogonium and
(Spircjg'j/ra can withstand salinity of water. The marine Algae
or sea-weeds are among the largest plant bodies found in saline
water.
It is not true that all Algae are aquatic. Among terrestrial
forms, several thrive well on rocks and in sub-soils. These forms
are adapted to resist drought and display capacity to retain
normal structure in prolonged dry periods.
Algae exhibit periodicity. In standing water, they generally
undergo a periodic (often seasonal) succession. Some forms
are perennials, e.g. Cladophova, while others are annuals e.g.
Spirogyra and Myxophycete. Volvox and Ghlamydomonas are
ephemeral forms. Diatoms appear to occur in all seasons.
Algae can be best studied in the living state. Species of
fresh water forms can be kept for study in water for sometime,
ALGAE—INTRODUCTION
7
HoweveT, for longer preservation, 2% to 4% formalin is adequate.
FortHe study of yitemal structure, Heidenhain's iron-alumJiaematoxylin serves as a good stain. For laboratory culture of
Algae, Knop's nutritive solution is frequently used. This consists of four parts calcium nitrate, and one part eacli, magnesium
sulphate, potassium nitrate and potassium phosphate, in 1000
parts of water. The solution can be solidified by mixing agar.
I n a study of the algal types, four major vegetative constructions appear to have developed during
Plant body
evolution. The simplest among these is the
motile unicellular form with a more or less pearshaped body and a cup-shaped chloroplast. I t is Uiflagellate and
the flagella are anterior. The nucleus and chromatophores are
definitely arranged in the body. The cell-wall is usually thin
{Chlainydomonas) or thick and striated (Sphaerella).
I n certain
cases the chromatophore may be absent.
The next form is the motile colony (Pati^orina, Tolvox).
The
unicellular individuals are aggregated here to form spherical
ball-like groupingiS. I n these forms, division of labour appears
among the cells.
I n the life of certain motile forms loss of cilia and subsequent
cell-division gives rise to a palmelloid condition. The thalloid
multicellular forms are considered to have arisen due to a permanency of this condition.
The colon'ies
mucilage.
and
multicellular
thalli are
enveloped
in
The more highly evolved forms possess a vegetative divisionmechanism by which the body becomes septate. This is the
origin of the filamentous habit {Ulolhrix, Spirogyra).
Development of filaments in one direction leads t o broad flattened
thalli of Prasiola but more frequently multiplanal development
leads to branched forms like Sligeoclonium and Batrachospermum. But the most evolved filaments exhibit a prostrate and
an erect system of branching (Ghaetophora)
and display
elaborate parenchymatous bodies as in some Red and Brown
Algae.
Loss of septation gives ri^e to the siphonaceous condition,
characteristic of the Vaucheriaceae.
A marked parallelism in evolution is seen in the Algae, in the
evolution of the thallus.
The cellular structure of the group, however, shows remarkable constancy. Embedded in the cytoplasm can be distinguished a single nucleus in unicellular and septate forms.
Except in the blue-green Algae, this has a definite structure
8
ALGAE—INTRODUCTION
akin to tHat of higher plants. The photosynthetic pigments
are usually present in special chromatophor^ except in Myxophyceae, where the pigment is dissolved in the general cytoplasm.
The main pigment is chlorophyll but except in Chlorophyceae,
it is masked by the presence of a variety df other pigments,'
phyeocyanin, phycoerythrin, fucoxanthin etc. Associated with
the chromatophores are pyrenoids which are protein-globules,
surrounded by a layer of small starch grains. Probably the
pyrenoid represents stored food and plays some part in carbonassimilation.
I n most of the free-moving unicellular forms and colonies,
the cells possess an eye-spot or stigma. The movement of these
forms is due to the flagella which* are exterior projections of the
cytoplasm.
The reproductive processes of the group can be distinguished
as vegetative, asexual and sexual.
„
..
I n the first of these, the whole plant body
cpro uc ion
splits or breaks into small units which grow
independently. I n Asexual form, zoospores may be formed.
These are small, globular, biflagellate, naked protoplasts which
appear as division products of the parent body. Their number
varies from 4, 8, 16, 32 to 64. I n some cases, the zoospores may
not be liberated as motile cells but their outer plasma membrane
may become a definite cell-wall (aplanospores). These membranes, in other forms may undergo thickeniiTg anff form
hypnospores for prolonged rest. For a similar purpose are
produced cysts and akinetes.
The study of the reproductive processes of the Algae is
instructive in so far as it throws considerable light on the origin
of sex in the plant kingdom. In the primitive Cyanophyceae,
reproduction is entirely asexual and vegetative. Unfavourable
conditions are counteracted by the formation of cysts, hormospores and other resistant spoi'e bodies. I n the Chlorophyceae,
reproduction is vegetative, asexual and sexual. I n the asexual
type, small flagellate bodies called' zoospores are formed by
division of the cell-contents. I n a simple genus like Ghlamydomonas, the zoospores are like the parent, only smaller in size.
I n UlolJirix they are like small chlamydomonads. But differentiation occurs at this level. Smaller zoospores (micro),
formed by more divisions of the parent protoplast, and larger
ones (macro) are characteristic of Ulothrix. Probably smaller
zoospores are formed in unfavourable circumstances when
available nutriment is scarce.
I n both Chlamydomonas and TJlothrix, more unfavourable
conditions produce certain very small motile bodies designated
gametes. These are identical with Hhe zoospores, only smaller
ALGAE—INTRODUCTION
d
in size. For normal asexual development), therefore, tJie contents
of these are inadequate. Possibl;^ sexual reproduction and
sexual fusion originated, in forms similar to Clilamydomonas
and Ulothrix, by a more or less accidental fusion of these very
small bodies. Since this fusion proved to be advantageous to
the plai^^t, it was permanently adopted. I t is possible to visualise
the origin of sex amid starvation conditions. The production of
very small reproducing units, and their inability to produce a
strong plant by simple growth, combined with the exigencies of
an adverse environment resulted in a pooling of resources —the
sexual fusion. Evidence of such an origin is also available from
forms like Oedogonium where the zoospore is similar to the male
gamete but for the size.
Evolution, from this base of similar gametes (isogamy), proceeded towards their dissimilarity. I n Chlamydomonas, itself,
certain species possess the anisogamous form of reproduction.
I n C. coccifera, heterogamy is introduced. I n Volvox, oogamy
is seen. Filamentous forms like Oedogonium and VaucJieria
do not liberate the female gametes and produce the male gametes
only from differentiated cells set apart for the purpose (gametang^a). This localization is the precursor of definite sex organs.
Ectocarpus, like Ulothrix, shows similarity in its gametes and'
zoospores. Forms like Ghara represent complications in the
protection of sex organs. Same is true of Fucus,
Batrachospermum and Polysiphonia.
The simple oogonium of simple forms
becomes the carpogonium of Ehodophyceae, -while the antheridium is converted into the nannandrium in Oedogoniales.
The zygote, which results, undergoes a period of dormancy
and is not so much a reproducing stage as it is a protection
against extermination during extremely unfavourable circumstances.
The Algae show an alternation of generations, which is not
marked enough in lower forms even upto Chlorophyceae.
Feldmann (1952) has studied the life-cycle of Algae and their
reproduction from the viewpoint of evolution. He has shown
that alternation of geaeratioas has considerable phylogeaetic
significance and" becomes increasingly complex in higher forms.
An excellent review of the schemes of classification of the
Algae has been published in the
Botanical
Classification
Review by F . E. Fritsch (1944). I t appears
that since the detailed account of West (1916),
the main criterion of classification has beea pigmentation. The
study of food-reserves, morphology and reproduction has justified
this basis to a large exteat. Wast (1916) e a ^ h i s i z e d the characteristics of fiagella in algal classification.
9.
10
ALGAE—INTRODUCTION
Fritsch (1935) has divided Algae into eleven principal classes
on the combined characters of plastids, food-reserves and
reproduction. Important of these are Myxophyceae (blue-green),
Cryptophyceae (brownish), Dinophyceae (golden-broTvn), Xanthophyceae (yellow-green), Ohrysophyceae (yellow-orange), Bacillariopbyceae (golden brown), Chlorophyceae (green), Phaeophyeeae (brown to orange green), Rhodophyceae (red). Des-.
criptions in this section, will be restricted to genera of Myxophyceae, Chlorophyceae, Phaeophyceae and Rhodophyceae.
Several Algae are of economic importance.
Spirogyra
maxima is used for human consumption. Chondrus is dried and
given to cattle. Several sea-weeds are used as sources of iodine
and agar (appendix I ) . The calcareous and siliceous deposits
of diatoms are used in various industries. The nitrogen-fixing
powers of several blue-green and green Algae are yet to be
exploited.
Questions.
1. Give an account of the structure and range of the form of
thallus in Algae studied by you. {Allahabad, 1942).
2. Give a brief description of the reproductive processes
in the Algae and illustrate from the types studied by you.
3. "Write a brief note on the origin of sex in the Algae and
give two examples of types which illustrate your
viewpoint.
4. Describe the different modes of perennation in the freshwater and subaerial Algae you have studied. {Agra, 1949).
CHAPTER I
MYXOPHYCEAE
THe group comprises those primitive forms in which' the
nncleiis and chromatophores do not possess the usual defined
structure but appear as rudimentary precursors of these parts.
Usually the pigment is uniformly distributed' in the peripheral
protoplasm and the central portion remains colourless, representing the nucleus. The Myxophyceae are blue-green and
are also called Cyanophyceae.
The Myxophyceae are a very clearly circumscribed group and
are cosmopolitan in habitat. They arc peculiarly adapted to
resist adverse conditions and probably their mucilage envelopes
and low plane of differentiation are mainly responsible for their
easy occurrence in fresh water, seas and hot springs. Their
presence in great abundance as planktonic forms often colours
the water and gives rise to 'water blooms.' Certain Chaemosiphonales are important constituents of flowing Avater.
The plant body of the Myxophyceae is rarely unicellular,
more often the cells are grouped into colonies (Aphanocapsa).
The simple filamentous forms are very numerous and others
display a heterotrichous differentiation into basal and erect
branches.
Cellular structure of the blue-green Algae poses a problematic
constancy. The internal structure is extremely simple. The
protoplast possesses two regions: a peripheral region with pigments, oil drops and glycogen. There are no definitely differentiated chromatophores but the pigment is found in small
granules (cyanoplasts) which are comparable to the grana of
the definitive chromoplasts. The chief pigment is phycocyanin
which gives the characteristic blue-green colour but relative
proportions of chlorophyll a, carotin, xanthophyll and phycoerythrin are also present. Besides the pigment, the periplasm
contains cyanophycin granules which are in the nature of a
protein reserve. Their presence depends upon external conditions. They disappear in dark and during cell-division and are
easily dissolved by weak acids.
In planktonic forms, certain pseudovacuoles are present.' It
is considered that they contribute towards the buoyancy of the
forms, and have gaseous contents.
The centroplasm of the cell is a speck of colourless alveolar
protoplasm called the central body. Iti contains neither a
32
MYXOPHYCEAE
nuclear membrane nor nucleolus, and cannot be called a nucleus
In filamentous forms it often appears as an irregular body with'
idented surface. Scott (1887), Kohl (1903), Olive (1904) and
Gardner (1906), are of opinion that it contains definite chromatin
granules and is, th'erefore, of a nuclear nature. Fischer (1905)
considers these granules to be of the nature of a carbohydrate
reserve called anabaenin which is stored in the central body and
falsely gives the nuclear staining reaction. Acton (1914) calls
them metachromatin granules and claims to have seen transition
stages from a little differentiated to a definitely nuclear centnl
body. While Zacharias (1903, 1907) contends that there is no
mitotic division, Hegler (1901), Kohl (1902) and Phillips ('19041
report the - presence of a rudimentary spindle. Geitler n922Y
denies it a nuclear status altogether and recent investio'atioTiq of
Haupt (1923), HoUande (1933) and Prat (1925) at least d i /
prove any mitotic activity. Mockeridge (1927.) has been able to
identify nucleic acids in the centroplasm, while Cassel ri952)
describes nuclear structures in Synechococcus cedorum and
Microcoleus vagmatus in three stages: oriented rod-like stase
net-like stage and condensed stage. Arena (1951) has-shown
that ribonucleic acid is absent from the centroplasm of CalothriT
It appears possible, as West has suggested, that the central bodv
IS an incipient nucleus which appears in various stages of evolu
tion m the Myxophyceae.
The protoplast is surrounded by an inner investment which
IS only a modified plasma membrane, /phe mucilage envelone
also contributes towards the protection of the filament and forms
a firm cell sheath formed mainly of peetic compounds Tt vanV^
m composition in the various groups and seems to be'denendenf
upon environmental conditions in its chemical characteristics.
The pigment being modified, the photosynthate is not starch
bugars and glycogen has been distinguished. Oil drops are also
present. Myxophyceae have also been reported to be able to fix
atmospheric nitrogen. In 1937 Allison, Hoover and Morris had
reported the nitrogen-fixing activities of Nostoc muscorum. Their
™ T ^ 7
^T confirmed l?y Fogg (1947) who enumerated
some general problems concerned with the nitrogen fixing nroperties of blue-green Algae. Watanbe (1951) and Watanbe
Nishigaki and Konishi (1951) investigatid thi n-fixing power'
of thirteen species belonging to the genera Tolypothrix, Plecto(1947) believed that only members of the Nostocaceae could fix
autrogen Williams and Burris (1952) d'escribe nitrogen fixation
by several algae Among the chief products of algal n ™ e n
MYXOPHYCEAE
13
Nosioc commune is used as foo3 for human consumption.
Tlie MyxopEyceae lack sexual reproduction. Multiplication
is usually by cell division and formation of hormogones or split
parts of filaments. Akinetes and gonidia have been reported, in
some genera, to reproduce the forms asexually.
Classification of the blue-green Algae has been based by
Fritsch, in the first instance on mode of reproduction. Five
orders have been distinguished on the basis of vegetative body.
Three of these, Chro'ococcales, Chaemosiphonales, and Pleurocapsales, reproduce by single cells while two, Nostocales and
Stigonematales, reproduce by hormogones. Smith calls these
latter, Hormogonales.
The Myxophyceae will be represented here by important
genera of Nostocales.
NOSTOCALES
These are filamentous, non-heterotrichous forms which reproduce by hormogones, hormocysts or akinetes. They may be
branched. Heterocysts are commonly present. Oscillatoriaceae,
Nostocaceae and Rivulariaceae are important families.
1.
OSCILLATORIA
It is a cosmopolitan alga. The plant body is filamentous and
the trichomes (filaments) "are free and smooth. They often form
tangled masses and are devoid of the mucilagenous sheath. The
component cells, of the septate filament are more broad than long.
The septa are usually concealed by rows of fine granules.
The filament shows no differentiation. In certain cases, however, the apical cell may differ in shape from the rest of the
filament. It is sometimes pointed or attenuated or capitate or
furnished with a calyptra.
The filaments of OscUIatoria are capable of spontaneous movement. This is usually a slow alternate lateral shift of the apical
parts of the trichome. The movement becomes rapid with increasing illumination and is doubled for each 10° rise of temperature upto 30°C. At 60°C the cells die and movement ceases.
Burkholder (1934) correlates this movement with osmotic changes
and diameter of the filament. Harder (1918) and Schmid (1918)
consider it to be due to a rapid swelling of the gelatinous mass
which is secreted through a system of pores arranged in a double
spiral. Schmid (1923) has shown that trichomes whose apical
cells have been killed are also capable of movement. Ullrich
(1929)
ascribes, forward progression,
to rhythmically
expanding and contracting waves along the trichomes.
14
MTXOPHYCEAE
Oscillaioria reproSuees by liormogones. At certain places in the
filament biconcave discs of gelatinous material arise, probj^bly
due to degeneration of cells. These discs serve to separate parts
of filaments two to three cells in length. The hormogones are
also capable of forward and lateral movement and can grow into
mature filaments.
Fig. 1,—Jfyxophyceae. A, B, Oscillatoria; G, Nostoe; D, BivUlaria; "Si,
Gloeotrichia,
2.
NOSTOC
It occurs as a solid or hollow gelatinous colony of a va,rieff
size, floating in water. The limiting layer of the colony is firm
and contains numerous interwoven contorted filaments of beadlike cells. Individual filaments may contain inconspicuous
sheats but these may ofHener be absent.
Interspersed among the'globular vegetative cells, are seen
certain larger, thick-walled, transparent cells called Heterocysts
which originate by a metamorphosis of the ordinary cells. These
may be terminal or intercalary. In their formation, a new wall
is first secreted" within the older one. Pores develop at the two
poles of the wall layer and through them the protoplasm of the
heterocyst is connected to that of adjacent cells. Towards maturity, the pores are closed by button-like plugs of the wall-material. These plugs are termed polar nodules. In terminal heterocj'sts, there is a single nodule. The protoplasm gradually turns
MtX0PHYCEAl3
15
yellow and soon becomes transparent. Probably it is transformed
into a viscus homogenous mass.
The heterocysts have been the topic of much speculatioi^
and controversy. _ Kohl (1903) and Borzi (1878) considered
them to be delimiting devices for trichomes. In this case the
utility of terminal heterocysts presents a powerful objection.
Turchini (1918)also considered the heterocj^sts to be delimitations of trichome lengths.
Hegler (1901) and JPritsch (1904) suggest tEat they are
store-houses for reserve food. Cannabaeus (1929) thought they
stored enzymes.
Bomet and Thuret (1880) noted germination of heterocysts
in Noatoc elUpsosporum, and Brand (1903) recorded liberation
of the contents in heterocysts of Nostoc.
Geitler (1921) adopts the view that heterocysts may be
archaic reproductive cells but according to Fritsch abortive
repi'oduetive cells donot usually persist so manifestly.
Fritsch (1951) states that the development of heterocysts
in blue-green algae appears to b& relatively uniform despite
differences in their structure and frequency. Their formation
involves disappearance of granules, "increase in thickness of
sheath, maintenance of cytoplasmic connections with adjacent
cells and formation of localised thickenings. The study suggests
high chemical activity. Probably the terminal heterocysts
secrete substances which promote growth and cell-division. As
cells become farther removed by growth, intercalary heterocysts
are formed. Heterocysts are also perhaps concerned in the
secretion of growth promoting substances which induce enlargement, accumulation of food reserve and modification of, cellmembrane as in the case of akinetes. This is further evidenced
by the frequent association of akinetes and heterocysts e.g., in
Gloeotrichia.
The nature and function of heterocysts is still in a very
controversial state.
Besides forming hormogonia, Nostoc reproduce by akinetes.
These are thick-walled individ'uals which are capable of producing a new filament with the' return of favourable conditions.
3.
RiVULiRIA
It occurs in spherical or irregular gelatinous colonies whicli
are attached to some stone or plant substrate. Inside the gelatinous mass are a large number of radiating branched filaments.
The branching is false. Each branch is apparently drawn out
16
MYXOPHYCEA^
into a terminal colourless hair, anS is surrounSed by a rattier
conspicuous mueilagenous sheath. The individual sheaths are
distinct at the base of the trichomes but outwards they become
diffluent.
Incrustations of lime have been reported in the thallus.
Heteroeysts are basal.
4.
GrLOEOT.aCHIA
The thallus of this form is soft and globose. In the younger stages of formation, it appears as an atftached spherical mass,
but later in course of development it becomes free-floating.
Embedded in the gelatine are a group of radiating whip- .
like trichomes, falsely branched as in Bivularia. The sheaths of
individual filaments are conspicuous only at the base but farther
up they merge into each other to give an undifferentiated homogenous consistency to the peripheral mucilage. The trichomes
are usually torulose and sharply taper outwards. Immediately
foUowi'ng the terminal heterocyst is developed a large cjdindrical
spore which is thick-walled and filled with reserve food.
Keproduction takes place by germination of these spores
or by separation of the trichomes.
Questions.
1. Describe the cell organization and reproduction in the
Cyano phyceae.
{Allahabad, 1947.)
r
2. Write a short note on the habit and distribution of bluegreen Algae, and give a full description of Nostoc and
its life-history.
{Agra, 1944, 1950.)
3. State what you know about the structural organization of
an algal cell in Cyanophyceae.
4. Write a short note on Heterocyst.
(Agra, 1947.)
{Allahabad, 1944.)
5. Write illustrated note on the vegetative structures of
Oscillaioria,
{Allahabad, 1948.)
CHAPTER I I
CHLOROPHYCEAE
—Volvocales, UlotricJiales, Oedogoniales—
The OhloropHyceae include a very large number of diverse
forms which enjoy^ world-wi3e distribution. Usually they are
freshwater forms but some members are terrestrial while others
marine.
They are usually green forms which manufacture their
own food by photosynthesis. A few species, e.g. Endoderma,
Chlorochytrium are parasitic while others participate in the formation of lichens, e.g., Carteria and Chlorococoum.
The plant ho3y shows a very high degree of diversity, unusual for a class. The primitive Ghlamydomonas is unicellular
with a small nucleus, a cup-shaped chloroplast, a pyrenoid and
an eye-spot. There are two equal flagella. Volvox represents a
colonial form with a large aggregation of Ghlamydomonas like
cells. Both these forms are motile. Upwards, in the Ulotrich'ales,
the filamentous habit has been acquired. The individual cells
of the filament are similar uninucleate with band-shapeJ
chloroplasts and^ several pyrenoids. Differentiation in the filaments appears to have proceeded on two distinct lines, one leading
to the branched Chaetophorales, the other to non-septate Siphonales.
Each cell of the Chlorophyceae is usually uninucleate but a
multinucleate condition is present throughout the Siphonales.
The cell-structure is uniform in the class. The protoplasts possess a definite wall which is rigid and gives a definite shape to the
Alga. The wall is generally two-layered, the inner lamellate of
cellulose and the outer of pectose. In Siphonales and Charales a
third cuticular layer can often be distinguished. In several Conjugales mucilage envelopes are present.
The green chlorophyll, which is identical with that of higher
plants, is lodged in delimited plastids called chloroplasts which
vary in shape in the various orders. In a great majority of cases
the chloroplasts contain pyrenoids (absent in Vaucheria). These
have a central protein crystalloid and' numerous surrounding
starch-grains.
The protoplasts usually possess a central vacuole round
which the protoplasm spreads out in a thin film. The vacuole is
18
CHLOROPHYCBAlJ
often traversed by eytoplastnxc strauds. Vacuoles are absent iti
the Volvocales.
Several genera of Chlorophyceae are reported to be able to fix
atmospheric nitrogen.
The reproductive processes are very varied". Vegetative multiplication is accomplished by- fragmentation and ordinary cell-'
division.
The usual mode of a sexual reproduction is by formation of
zoospores. They are by to quadri-flagellate naked protoplasts,
which can be' produced by any vegetative cell. Aplanospores are
produced and perehnating akinetes are of frequent occurrence.
All forms reproduce sexually, all stages from isogamy to
oogamy being present. The zygote possesses a highly sculptured
wall and germinates by reduction to form the gametophytic plant.
There is regular alternation of gametophytic and sporopHytic generations, although the latter is only an inconspicuous
stage in the life-cycle.
West (1916) classified the green Algae on the basis of
flagellar characters into Isokontae (equal flagella), Akontae (no
flagella), Stephanokontae (crown of flagella) and Heterokontae
(unequal flagella).
Fritsch (1935), however, stresses the morphological and
reproductive features and divides Chlorophyceae into 9 orders :
Volvocales, Chlorococcales, Ulotrichales, Cladophorales, Chaetophorales, Oedbgoniales, Conjugales, Siphonales and Charales.
VOLVOCALES
The group" contains unicellular (Chlamydomonadaceae) to
colonial (Volvocaceae) forms which are principally motile.
1.
CHLAMYDOMONAS
This unicellular alga is usually floating on temporary
stagnant pools or in foul water.
The body is ellipsoid' or pyriform in shape, ranging from
3 fi to 20 IJ-. The protoplast is enclosed in a thin wall which may
possess an inconspicuous mucilage cover. There is a distinct
anterior and posterior part. The two flagella are situated in the
anterior portion and project out of two distinct pores in the
cellrwall. Traced backwards, they are seen to arise in a pair of
basal granules called blepharoplasts whose function is not known.
The granules are connected by a transverse protoplasmic thread
CHLOROPHTCEAB
19
from the middle of wHicli a longitudinal strand .runs posteriorly
to join the centrosome of the nucleus. The nucleus is situated
in, the hollow of a cup-shaped chloroplasfc and contains a distinct
proximal centrosome and a distal nucleolus. The ehloroplast
varies in shape. In C. reticulata, it is reticulate, in C. alpina of
small discoid components and in C. biciliata, H-shaped. Embedded
in the ehloroplast is the characteristic chlorophycean pyrenoid.
The system of flagella and the transverse and longitudinal
fibres, the basal granules and the centrosome constitute the
neuro-motor apparatus which appears to act in coordination with
a stigma or eye-spot. This photoreceptor is situated anteriorly
in the protoplasm and is made up of a colourless lens-like disc
with a basal disc of pigment. In C. pluristigma, there aje two
to three eye-spots.
Two contractile vacuoles have been seen at the anterior end
of the cell. They have been ascribed respiratory and excretory
functions.
During asexual reproduction, the motile condition is temporarily lost due to a shedding of flagella. The resting cell
divides longitudinally into 8 to 16 zoospores which are liberated
20
CHLOEOPHTCEAE
as motile units. In C. Braunii and G.gToeogama,iS.e ^rst division is vertical but the septum is reorientated in such a way by
rotation that it looks transverse.
When water is not abUndanK, the daughter cells are not
liberated but are retained in the mother protoplast, in a gelatinised matrix. Gradually the daughter cells may also divide and
division may go on to form innumerable cells in the same amorphous colony. The cells may now develop flagella and swim
away. Such aggregations are called palmella stages. In some
cases the contents of the entire cell may round off and the wall
may become resistant. These are the akinetes or aplanospores
to tide over adverse conditions.
"».
In sexual reproduction, normally the contents of a cell are
cleaved into 32 to 64 small motile cells, gametes which differ from
the parent only in size. The gametes may be equal and naked
as in C. deBaryana and C. longistigma or walled as in G. media.
In the latter the naked protoplasm comes out to fuse. Anisogamy is seen in C, monoica and G. media where each individual
forms 4 female or 32 male gametes. 0. Braunii also shows
marked anisogamy. In C coccifera, anisogamy leads to oogamy
but complete loss of motility is not seen in the female fusing
component. The parent produces only one female cell but 16
male cells.
Kuhn (1939—49) and Moewus (1949—51) have proved
that the sexual process in the genus is chemically re'gulated.
The zygote has a thick-walled structure with' reticulate or
stellate and spiny outer cover. In ripening zygotes the red
pigment, haematochrome, appears. The zygote germinates to
form four zoospores by reduction. The zygote may remain motile
for a considerable time as in G. botryoides but the four flagella
are soon shed.
Chlamydomonas shows the origin and differentiation of
sex. The zoospores and gametes are remarkably similar in
structure and differ only in size. This difference can be brought
about only by a greater number of divisions of the parent body.
The small individual thus loses the power of independent development and takes recourse to fusion as a first step towards the
establishment of the sexual process in the Algae.
Differentiation in the size and mobility of gametes produces
evolved forms.
Chlamydomonas possesses both hetero
forms,
and
homothalljc
CHLOROPHYCBAB
2.
n
VOLVOX
It is a colonial form. The colonies are hollow spEeres or
globes with a single peripheral layer of biflagellate Chlamydomonas—like cells. The number of cells in a colony is fixed and
specific in nature. The small colonies of Volvox aureus have
nearly 500 cells while in giant V. Globator 20,000 cells may be
present. Colonies with definite shape and cell number are called
coenoBia.
The colony is covered by mucilage and external pressure
renders the soft cells angular. These are connected by stout
protoplasmic processes (F. Gloiator) or by thin delicate strands
(F. aureus). The cells are provided with' characteristic neuromotor apparatus and stigmata which are three layered. The
stigmata of the anterior part of the colony are well developed
and the concerted action of their differential photo-reception and
flagella helps the forward progression of the colony.
Fig. 3.— Volvox. A, A single coJony; B, A portion enlarged; 0, Protoplasmie connections; D—L, Stages in tlie origin and inveision
of a daugliter colony; M, cells in a daughter colony; Nj Eye-spot
of Chlamydomonas; P, Eye-spot of Volvo^.
The majority of cells are somatic in character. During
asexual reproduction, parthenogonidia are formed in the posterior part) of the colony by simple size-increase of vegetative cells.
These divide longitudinally to form an eight-celled plakea. At
the 16-celled stage the plakea becomes hollow and hangs iutp the
fe2
CHLOROPHYCEAE
cavity of tHe parent." GraSual invagination converts it into a
daughter colony with cells pointing outwards. These colonies
are liberated by pushing themselves out of the posterior part.
Sexual reproduction is oogamous. The androgonidia are
large posterior cells whfch divide longitudinally into> 64 to 128
cells. This plakea becomes slightly curved" and each component
cell is converted into a single spermatozoid.
The zoids are
biflagellate and liberated in a group.
In the formation of gjoiogonidia, certain posterior cells are
pushed back into the mother cavity. Enlargement takes place
•and the cilia are lost. The number of pyrenoids increases.
During fertilization, the zoids swarm roun3 the egg, fusion
takes place and the zygote secretes a three-layered sculptured
wall around itself. Haematochrome is developed.
Fig, 4.—Volvox. A—0, Formation of And^ogonidiuIn'^and Spermatozoid;
D, Gynogonidium; E, fertilization; F, Zygote; Gr—H, Germination of Zygote in 7. oapensis.
The zygote germinates by splitting the exospore. The
mesospore also breaks and the endospore comes out in the form
of a vesicle. The protoplast is either liberated as a biflagellate
zoospore {V. capensis) or develops directly by reduction division
- into a plakea ( 7 , aureus).
dSLOROPHtCEAB
t^
Goen.ohia.-of-yolvox may be completely sexual or asexual.
In some cases the same colony bears botH partheno and sexual
gonidia. If the colony is sexual, it may be monoecious ( F .
aureus) or dioecious (V. Olobator). In some cases functional
heterothallism is manifested as protandry (prior .development
of males) or protogyny (prior development of females).
Volvox represents the highest stage in the development of
colonial forms of Algae, and shows a pronounced division of
labour.
IJLOTRICHALES
The order consists mostly of unbranched vegetative filaments capable of limitless division. In some instances the plant
body may take the shape of flattened parenchymatous expanses
as in TJlva and Prasiola.
1.
ULOTHEIX
The plant is inhabitant of cold flowing water. The unbranched filaments are attached to the substrate by a modified basal cell
which often ramifies to form a distinct rhizoid or holdfast. The
filament otherwise consists entirely of uninucleate almost square
cells which contain bandshaped chloroplasts. Several pyrenoids
are embedded in the matrix of the chloroplasts. In Ulothrix
zonata the chloroplast-ring is complete. The nucleus hangs in
the central vacuole and is supported by protoplasmic strands.
Vegetative reproduction takes .place by fragmentation of
the filament.
During asexual reproduction a large variety of swarmers
or zoospores is formed. In their formation the protoplasm of the
cell divides by cleavage into a number of uninucleate parts.
Usually there are 16 such units. They are liberated in an
ephemeral vesicle and are known as Macrozoospores. Each is
g[uadriflagellate.
Often, however, the protoplast is cleaved into 32 parts so
that the uninucleate units liberated are smaller in size. These
are known as Microspores and are quadriflagellatg.
In adverse conditions, the Microspores may be biflagellate
also.
All these asexual motile zoospores are pear-shaped and
contain typical chlamydomonad structures. There is a cup*
shaped chloroplast and an eye-spot. During germination, a
transverse division separates an upper, filament forming and a
lower, holdfast forming cell.
CHLOROPliYCBAE
Asexual reproduction may also take place by thin-wall ed
aplanospores, or thick-walled akinetes.
Fig. 6.—VlothrU. A, Filament with holdfast and band-shaped chloroplasts;
B, Liberation of quadriflagellate macro-zoospores; C, Liberation
of quadriflagellate micro-zoospores; D, Biflagellate mierozoospor^s; E, gametes; F, Germination of a zoospore; G—M,
Eormatlon and Germination of a Zygote; N, Germinating
aplanospores and an akinete.
The vegetative filaments produce gametes at certain periods
of the life-cycle. The gametes are usually 64 in number and are
distinctly smaller than the zoospores. They are not capable of
independent development and have to unite in pairs. In almost
all cases of sexual fusion, isogamy is seen but in some heterothallic forms the fusing individuals may differ in size. Ulothrix
illustrates tlie origin of sex by the similarity of zoospores an3^
gametes.
It has been observed that the development of gametes is
initiated at the apex and the stimulus travels downward.
The quadriflagellate zygote remains motile for a short time
but finally comes to rest and secretes a thick wall around it.
The rest period lasts for 5—9 months, after which meiosis occurs
and the protoplast is divided into 4—16 aplanospores or
zoospores.
Ulothrix is also found in saline water, the chief species being
JJ. flacca.
/^>'^
CHLOROPHYCEAE
25
OEDOGONIALBS
The order contains simple or branched filamentous forms
which divide vegetatively by a peculiar cap formation and. reproduce asexually by forming multiflagellate zoospores (Tiffany,
1936). West (1916) had separated the group into Stephanakontae.
1.
OEDOGONIUM
In Oedog^ojiiwrn the filaments are unbranched. When young,
the filaments are attached by a basal ramifying holdfast to
leaves or stones in a stagnant pond. Mature filaments are,
however, free-floating.
The component cells of the filament are usually cylindrical,
sometimes swollen at upper ends. The apical cell of the filament
may be tapering or drawn out into a long hair as in 0. ciliata.
-Oedogonmm. A,Filam.&nt with net-shaped ehloroplast and caps;
B—F, Stages in eell-division; G—J, Formation^'and liberation
of a zoospore; K," Germination of a zoospore. ^
The cell walls are firm and rigid and are composed of three
layers: an outermost chitinous, the middle pectic and the inner
made of cellulose. Inside the wall is an elaborate reticulate
ehloroplast which contains in its meshes numerous pyrenoids.
The meshes of the ehloroplast run in an obliquely parallel direction and completely encircle the protoplasm.
4
26
CHLOEOPHYCBAE
The cells are uninucleate. The nucleus lianga rarely in the
centre but more commonly occupies a peripheral position. In
it, chromosomes are clearly visible possessing dark thickened
segments at intervals.
Vegetative division starts by an upward shift of the nucleus.
A rim of cellulose and pectin or hemicellulose (Steinecke, 1929)
is formed inside the cell, close to the upper transverse wall. The
nucleus starts mitotic division. The deposition of wall material
on the rim continues till the outer wall invaginates. By this*
time the nucleus divides completely. The outer wall breaks near
the invagination and the tension causes a pulling-out of the
substance of the ring. Thus a new cylindrical piece of cell wall
is intercalated between two old ones. Elongation of the cells
takes place now and the transverse wall dividing the nucleus is
orientated in such a way that the upper daughter cell consists of
a small protruding old wall and a major part of the new wall
while the lower daughter cell is made u p entirely of the old'
wall.
Due to such a disposition each young daughter cell appears
possess an apical cap. The young wall soon thickens up and
repeats the process of division so that at certain places in the
filament series of caps are present.
Vegetative reproduction takes place by fragmentation.
In asexual reproduction akinetes and multiflagellate zoospores are known. The latter are formed singly in the cells of a
thread. The entire contents of a densely protoplasmic cell are
organised into a more or less pyriform structure by retraction of
cell contents. The anterior beak-like portion is colourless and at
its lower margin are a number of blepharoplasts in a ring. Out
of this fringe arise the numerous cilia.
The zoospore comes out in a short-lived vesicle and is soon
liberated outside. I t contains a single cup-sHaped chloroplast
and a single pyrenoid. There is jilso one eye-spot (Fritsch,
1902),
I t is held that this swarmer has developed from the ulotrichalean zoospore by several divisions of the two original blepharoplasts.
Zoospore formation is stimulated by increase iii the carbon
dioxide concentration of the surrounding medium.
D,uring germination the zoospore fixes itself by the colourless anterior end" and a transverse wall is laid down. The lower
part develops into a holdfast while the upper forms the filament.
GHLOROPHYCEAE
27
Sexual reproduction takes place by an advianced type of
oogamy. The formation of sex organs is assisted by an alkaline
medium.
In some species the oogonia and antheridia are borne oa the
same filament (monoecions). In dioecious forms the sex organs
are borne on distinct male and female plants. These two types
constitute the Macrandrous section of the genus. In these the
antheridia are produced in normal filaments. More than half the
macrandrous forms are monoecious.
In the Nannandrous section of Oedogonium, filaments produce special androspores which are liberated" to form small filamentous dwarf-males. Often the androsporangia and oogonia occur
in the same filament (monoecious) but usually they are borne on
separate plants (idioandrosporous). Even in the monoecious or
gynandrosporous forms, heterothallism is present.
Ftg. 7.—Oedogonium. A, Filament forming antheridia; B, Gametes; 0,
Filament -with an oogonium, germinating dwarf-male and gametes;
D, Androspore; E, Dwarf-male; Fj Zygotes, with one showing
formation of zoospores.
In all types, the oogonia are spherical or ellipsoidal cells
formed from the upper-most daughter cell of a oogonial mother
cell. It is seen that oogonia are usually solitary, but there are
exceptions. The lower stalk cells of an oogonium may remain
28
CHLOPOPHYCEAE
sterile or function as oogonial mother cells.
behave as antheridial mother cells.
I n rare cases they "
The contents of the oogonium are organised into a single
uninucleate oosphere with a colourless receptive spot.
The
oogonial wall next to this spot is ruptured or possesses a-pore
through which a certain amount of protoplasm is exuded out
forming a canal of mucilage. Through this a spermalozoid
passes during fertilization. The nucleus lies next to the hyaline
receptive spot at maturity.
The development 0 f the oogonium is similar in both macrandrous and nannandrous forms.
I n macrandrous species, repeated divisions of a vegetative
cell may give rise to a number of antheridia. Such a vegetative
cell can be termed antheridial mother cell. The antheridia vary
from 2-40 in number. The contents of the antheridium are
cleaved vertically and each of the daughter protoplasts is liberated
as a single multiflagellate antherozoid in a delicate mucilagenous
resicle. The zoids are similar to zoospores exeejit in size.
In nannandrous species, the vegetative cells form androsporangia which are similar to antheridia. But the androsporangia
liberate a single androspore. These are simply small zoospores
but after swimming about for some time they settle in the
vicinity of an oogonium and germinate to form a snuill nannandrium or dwarf male. Each of these is composed of a rhizoidal
holdfast and a few antheridial cells. The latter produce two
antherozoids each with the usual structure.
During fertilization, the male and female nuclei are approximately equal in size.
The zygote secretes a thick wall around itself. The wall is-usually of 2-3 layers and reddish. Liberation of zygotes takes
place ijy disintegration of the oogonial wall.
The zygote nucleus divides meiotically into four and thus
four zoospoi'es are liberated in an ephemeral vesicle. They
develop in the same way as asexual zoospores. Segregation of
sexes is said to take place when division of the zygote nucleus
occurs. Mainx (1931) reported in one species that out of four
zoospores, two develop into male and two into female filaments.
The androspqres are probably equivalent to the small asexual
zoospores of Uloihrix which have lost the faculty of independent
development. They may also be considered as prcjmaturely liberated antheridial mother cells. The first view holds the nannandrous
forms as primitive while the second holds the macrandrous
forms as primitive.
CHLOROPHYCEAE
29
Questions.
1. Describe the life history of Chlamydomonas. What light
does it throw on the origin of sex in plants?
(Allahahad, 1948, 1950)
2. Give an account of the structure and reproductive processes of Chlamydomonas.
{Allahabad, 1944)
3. Describe in detail the method by which gonidia are formed
in Volvox.
{Allahalad, 1944)
4. Describe the method of sexual reproduction in Oedogonium.
How does it differ from that of Vlothrix'^.
{Allahalad, 1946)
5. Describe the structure and methods of reproduction in
Oedogonium.
{Allahchad, 1952)
6. Describe in detail the life history of Uhthrix, commenting
upon any points of morphological and physiological
interest.
(Agra, 1942)
7. Describe the method of sexual reproduction in Oedogonium.
{Agra, 1943)
8. Describe the features of special interest in the structure
and life history of Oedogonium.
{Agra, 1947,1950)
9. Write an essay on the origin and evolution of sex in the
green Algae.
{Agra, 1951)'
CHAPTER III
CHLOROPHYCEAE
—Conjugales, Chaetophorales, Siphonales—
The oi'ders Conjugales and
sent direct evolutionary forms
honales, However, appear to have
by loss of septation. The plant
Conjugales.
Chaetophorales probably repreof the Ulotrichales. The Siparisen from filamentous forms
body is usually unbranched in
CONJUGALES
The order is distinct from the rest of the Chlorophyceae in
the entire lack of flagellate reproductive cells. It is probably
evolved from a very early stage of the chlorophycean complex.
1.
SPIBOGYRA
The filaments of Spirogyra grow in stagnant water and
often form yellowish green slimy masses at the bottom or on the
surface. The plant body is free-floating although S. adnata is
an attached species.
Each cell of the filament is a cylinder, considerably longer
than broad,with a very delicate peripheral protoplasmic layer
and" a large central vacuole. The protoplasmic layer is often
called "primordial utricle". The replicate end wall next to
the protoplasm is largely of cellulose but the mucilagenous
sheath outer to it forms a firm inner pectic layer which serves as
an outer investment.
The single nucleus of each cell hangs in a small protoplasmic mass in the centre which is supported by delicate protoplasmic strands. The chloroplast may be a single parietal spiral
band with numerous pyrenoids projecting into the vacuole on the
inner side. The number of band's may be more and in these
cases the bands cross each other at regular intervals forming a
beautiful lattice-work.
Vegetative multiplication by fragmentation is of commonest occurrence. In cell disjunction, a mucilagenous mass
may develop between split parts of a septum or the dissolution of
the middle lamella and subsequent invagination of the rings on
the septum may force the cells apart (replicate fragmentation).
In some cases a tq shaped piece may develop between two cells
and this may slip off separating two filaments.
CHLOROPHYCEAE
31
I n most filaments apical and basal portions are not distinguishable.
_,8.—Spiro'gyra. A, Filament with a single spiral of ehloroplast; E,
Sealariforni conjugation j C—F, Development of a zygote; G—J,
Stages in lateral conjugation.
Homo and' heterothallic filaments are known. There is
marked periodicity in the formation of sex organs.
During conjugation, two filaments come nearer by mucilage
secretion and their cells put out lateral papillae. These grow
rapidly and push the cells away from each other. Meanwhile
the contents of conjugating cells contract due to the appearance
of ^contractile vacuoles which pump out water. The male
cytoplasmic mass then travels through the conjugation tube and
merges with the female counterpart. The male chloroplasts
usually degenerate.
Conjugation of this type is known as scalariform and is
present in heterothallic forms. I n monoecious species, conjugation is lateral. Conjugating filaments contain oil reserve.
The whole process leading to fertilization is divided into
two p a r t s : maturation phase upto the formation of conjugation
tubes and phase of gametic union upto the formation of zygotes.
The zygotes have a three layered wall. On germination,
four reduction nuclei are formed. Of '^these, three degenerate
and the fourth forms the holdfast and filament.
32
CHLOEOPYCEAE
CHAETOPHORALES
In these Chlorophyceae the branching of the filament shows
a basal and an erect system. The thallus is, therefore, called
heterotrichoiis. Most Chaetophorales possess abundant hairs, a
character from which the group derives its name.
The forms included' in this genus are usually terrestrial,
unicellular to colonial globose cells. The cells form a small green
patch on soil, trees or rocks and are adapted to telerate
prolonged desiccation.
1.
PLEUKOOOCCUS
The individual cells are round with firm cellwalls. The
protoplasm has no vacuoles, A parietal lobed chloroplast i s
present. There is no pyrenoid
Fig. 9.—A—C, Pleurooocous,, single cell and colonies showing formation
of hairs; T>,Goleochaete; E, A marginal filament magnified; F,
Branch with antheridia; G, Branch with carpogonium.
Reproduction is exclusively by cell-division and cases where
zoospores are recorded are extremely doubtful.
Slow separation of daughter cells results in the formation of
colonies. I n these, branching is often apparent. I t Ms always
in one plane and peripheral cells often show a tendency to taper;,]
outwards.
CHLOROPHYCEAE
33
There is only one species, P. Naegelii.
2. COLBOCHAETE
Among tEe more advanced Ciiaetophorales are the prostrate
cushion-like thalli of Coleochaete which are fresh water forms.
The species are usually epiphytic upon submerged plants,
but one species is endophyte in the Charales. Some forms
are truly heterotricEous while others only possess the prostrate
basal portion.
The discs are one layered and possess several outgrowing
hairs. The hairs grow apically while the thallus possesses a
marginal meristem. The hairs are sheathed basally.
Component cells of the thallus are uninucleate with a single
parietal chloroplast. Pyrenoids are present and are embedded
in the irregular cEloroplast.
Asexual reproduction is effected by the production of ovoid
biflagellate zoospores which are formed singly from ordinary
vegetative cells. The zoospores escape from a round orifice in
the parent cellwall by amoeboid movement. After a short motile
Fig. 10.—Coleochaete. A—B, Maturation of the zygote and formation
of a spermocarp; F, Zoospore.
phase, the zoospore settles down. In C. scutata, the first division
of the spore is transverse. Of the two cells formed, the upper
produces the hair and the lower forms the disc. In other cases,
a vertical division may take place first but very soon during
development sheathed hairs arise.
Aplanospores have been recorded.
U
CHLOROPHYCEAB
Coleochaete is oogamous, the plants being either dioecious
or monoecious.
I n C. pulvinata the oogonium (earpogonium) appears as a
flask-shaped structure with a short neck or trichogyne. The
protoplasm of the oogonium is usually colourless. The oogonia
arise terminally on the margins of the prostrate system but are
shifted to a lateral position due to continued growth of the thallus.
The antheridia in Coleochaete are borne in clusters at the
end of branches ( 0 . pwlvinafa) or develop from prostrate cells
(C. scutata).
Each antheridium produces only one biciliate
green antherozoid ( C scutata) which is liberated by r u p t u r e of
the antheridium.
The neck of the trichogyne gelatinises and the antherozoid
enters to fuse with the egg. The trichogyne is cut off and the
oospore enlarges considerably secreting a thick wall around itself.
The adjacent cells give rise to enveloping branches which close
over the oospore. This fructification is now known as a
spermocarp, and it undergoes rest.
Allen (1905) states that the zygote on germination undergoes
meiosis and divides into 8-32 wedge-shaped protoplasts which are
organised into biflagellate zoospores.
The zoospores directly develop into new thalli.
SIPHONALES
The outstanding feature of this group is the ecenocytic construction of the branched filaments. Septa are produced only
during the formation of reproductive organs, or on injury.
1. VAUCHEEIA
The genus Vaucheria is an essentially temperate form inhabiting aerated streams or saline mud flats. V. Debaryana is
encrusted with lime. The filaments appear as interwoven masses,
of coarse threads which grow apically. In young stages the
threads are attached by a broadly ramifying rhizoidal portion
called fiapteron.
In the filaments of the ccenocyte, a continuous vacuole runs
from base to apex. Bounding it on all sides is a moderately thick
lining of cytoplasm which contains a parietal layer of small
ellipsoidal chloroplasts (no pyrenoids) and an inner layer of
rounded nuclei. The cell wall surrounding these structures is
thin and contains cellulose and pectose.
The chloroplasts contain a greater proportion of xanthophyll.
Hence the product of photosynthesis is oil. According to Meyer
(1902) this oil is not a true fat. Tiffany (1924), however,
reports starch formation in continued illumination.
Vegetative reproduction is secured through fragmentation.
CHLOKOPHYCEAE
35
Prolific asexual multiplication occurs by means of large
multiciliate zoospores. The zoospores are produced singly in
cliib-shaped sporangia which are cut off by a septum from the
parent filament. Numerous chloroplasts and nuclei aggregate
in the club-shaped" sporangium before the septum is laid down.
An inversion in the relative position of the chloroplasts and
nuclei is eifected so that in the protoplast of the sporangium,
nuclei are peripheral.
The contents of the sporangium contract and opposite each
nucleus, two flagella .are projected. The pear-shaped zoospore,
escapes through a rather narrow aperture in the sporangium wall
and often divides into two.
This compound structure probably represents a group of
biflagellate zoospores which have failed to separate. The zoospores include a central vacuole. In V. omithocephala, cilia are
fully developed only on the anterior half of the zoospore. In
V. piloioloides, the zoospores are elongated.
Fig. 11.—TaucMria. A, A young filament with holdfast;_B, .Details of
cellular structure; C—F, Formation, liberation and germination
of a zoospore; Q, Aplanoapores in a filament, with one
liberated aplanospore germinating; H, Antheridium and
oogonium of V. sessUs; J, Zygote and mature sex organs of
V. terrestris; K, Spermatozoids.
Germination of the compound zoospore starts by a withdrawal
of c'ilia and is completed by the formation of a number of filamentous processes. One of these attaches itself bj^ a hapteron,
36
CHLOROPHYCEAE
In a"ry conditions thin-walled aplanaspoi'es have been recorded.
I n T. sessilis and V. geminata cysts are formed. These may
germinate directly but more often they liberate amoeboid units
which form the plant.
Sexual reproduction is distinctly oogamous. Both moncEcioiis
and difficious species are known.
The position of the sex organs is- very variable. I n V. sessilis
and y . dichotoma they are borne on the male filament, while in V.
geminaia, V. hamata and V. lerrestris they are produced on
lateral branches. V. dichotoma is a dioecious species.
Antheridia develop as papillate protruberanees of the main
filaments in the vicinity of oogonia. Each stores a large number
of nuclei and dense cytoplasm. The antheridium gradually
becomes hook or horn-shaped and a septum appears high up in
the curved part. Thus the antheridium is stalked. The chloroplasts degenerate. Around each nucleus, a little protoplasm
accumulates and the arrangement of the uninucleate protoplasts
is parietal round a central vacuole. Liberation of antherozoids
is by an apical pore in the distal end of the antheridium. • Each
antherozoid is a pear shaped body with two anterior or lateral
heterokont cilia (Koch, 1951).
The oogonia are shortly stalked or sessile and arise as globose
papillae on the filament. A small amount of cytoplasm and
nuclei accumulates below the bulge and later enters the oogonium
us'wanderplasm'. Before a septum is formed, the extra nuclei
are said" to migrate back into the main filament (Oltmanns, 1895;
Couch, 1932). Davis (1904) and Williams (1926), however,
consider that degeneration of nuclei takes place after the septum
is laid down.
«
The mature oogonium has no vacuole. On one side of it a
beak like projection develops. Prior to fertilization the oogonial
wall opposite the beak gelatinises and a hyaline receptive spot
develops in the beak. A small amount of protoplasm is excuded
out and' the antherozoids enter through the mucilagenous
conduit.
The male nucleus usually increases in size before fusion.
The zygote possesses a very thick wall of 3-7 layers and undergoes a long hibernating period. Germination is direct and
a new filament is formed.
Mundie (1929) holds that the sex organs are reduction products so that the plants belong to a diploid generation.
Gross (1937) considers first zygotic division to be reductional.
Thus the plants are haploid. Probably this view is more correct.
CHLOEOPHYCEAE
37
Parthenogenesis of the oogonia is known to occur through
artificial stimulus.
Lotsy (1910) believes that the FazjcAeWa-like forms arose as
a side line during the transition between Algaj and Fungi. More
probably the fungal characters of the genus are due to parallel
evolution.
Vaucheria resembles the Phyeomyeetes in the possession of a
ecenocytic thallus, conidium-like compound zoospore and clubshaped sex organs.
Vaucheria was always included in the Chlorophycea? but
Bohlin (1897), Feldmann (1946), Pritsch (1935) and Printz
(1927) have expressed doubts about its position. The predominance of yellow pigments in the plastids, formation of oil are
probably grounds on which Vaucheria differs from other ChlorophycesE. Strain (1949) has reported that pigments of Vaucheria
are typical of Xanthophyceas rather than Chlorophycea; and Koch
(1951) has shown that the cilia are unequal in authrozoids.
Smith (1950) has included Fawc/ieria in Xanthophycese among
Chrysophyta and placed it near Botrydium.
Questions.
\.
2.
Describe carefully the. structure of the sexual organs and
the process of reproduction in Vaucheria.
I n what
respects does it differ from other green Algae 1
{Allahahad, 1945, 1947, 1949).
Give a diagrammatic representation of the life-cycle
illustrating the relative length of the haploid and the
diploid phases in Vaucheria.
{dgra, 1943).
3.
Give an account of the sexual reproduction, in TJlolhrix
and Vaucheria.
(Agra, 1946).
4.
Give an account of the life history of Coleochaete, and
describe the significance of the spermocarp.
From your studies of the types of Chlorophycea3, give a"
general account of the asexual modes of reproduction in
the group.
{Allahalad,Wi3).
5.
CHAPTER IV
CHLOROPHYCEAE
Charales
The order includes green submerged Chlorophyceae with
segmented axes bearing whorls of leaf-like appendages at the
nodes. The forms occur commonly in ditches, ponds and brackish water.
1. CHARA
Chara fragilis is the commonest species of the group with a
cosmopolitan distribution. I t has an erect branching axis which is
negatively geotropic and positively phototropie. The axis is- attached .to the substratum by branched rhizoids. I t is equisetoid
in habit with distinct nodes and intemodes. At each node the
whorl of branches is of limiHed growth and' is ofted called a
leaf-whorl. These branches are also difEerentiated into nodes
and intemodes. At their nodes, in t u r n , they bear spiny
emergences called stipules.
Branches of unlimited growth are also present on the main
axis. These repeat the axial structure.
During growth, the apical cell of the filament divides to form
a plate of three basal cells and an apical part. The basal cells
form the two outer intemodes and one central node. The internodal initials enlarge while the nodal cell divides vertically only
to form a small biconcave plate of cells.
The basal cells of branches often grow up to form corticating
branches of the axis. Such corticating filaments contain unicellular intemodes and three-celled nodes. However, the nodal
cells usually elongate and the distinction between them and
intemodes is lost.
The cell-walls of the filaments are made u p of an inner cellulose sheet and an outer callose layer which is impregnated with
calcium carbonate. Inside the wall, the .cytoplasm revolves
continuously in a longitudinal direction round a central vacuole
I n the cytoplasm are a large number of small ellipsoidal ehloro
plasts arranged in a long spiral. Yoiing internodal cells ar(
uninucleate but in older cells, amitosis produces a plurality o:
nuclei.
Asexual zoospores are not formed. Bulbils may be forme(
on rhizoids, or protonema-like threads may grow up on nodes
Round the lower nodes asteroid starchy cells may be formed fo
vegetative propagation (C. stelligera)
CHLOROPHYCEAE
39
Oogamous sexual reproduction is known. Species may be
monoecious or dioecious. THe male and female fructifications are
definitely orientated on the branches and the nucule always
lies above the globule.
Fig, 13.—Chara. A, A mature filament with zygotes; B—E, Division
of tlie apical cell to form nodes and internodes; F—Hj
Development of an antheridiuin; J—M, Development of an
oogonium and sheath-eells; N, Germinating zygote; O,
Spermatozoids; P, A filament -with mature sex organs.
Antheridia arise from the projections at the base of peripheral nodal cells. The initial cell divides to form a lower-nodal and
upper pedicel cell. It becomes globose and' divides verticallj'- into
four cells. A transverse wall is laid down in each of these and
the octant stage is reached. The first periclinal division of the
octants results in a group of eight central head cells and eight
peripheral cells. Next, the peripheral cells again divide peri^
clinally to form outer eight shield cells and inner manubrial
cells.
The antheridium enlarges and a cavity is formed in which the
manubrial cells stretch.
The primary head cells or capitula may form secondary and
subsequent capitula. Finally, antheridial filaments arise from
the head cells. At maturity each cell of the antheridial filameat
functions as an antheridium and its contents are liberated as a
• single biflagellat'e antherozoid (globule).
30
CHLOEOPHYCEAE
The nucule-initial develops next to tHe pedicel cell. I t
elongates repidly to form a plate of three cells, the lower pedicel,
the middle nodal and upper oogonial. The last enlarges greatly
and is uninucleate. Soon an apical cell is cut off but it degenerates. By this time the node sends' out 5—6 erect tCiicelled'
filaments called sheath cells. They arrange spirally round the
oogonium. Apically, the sheath cells cut off small crown cells
which are one layered and characteristic off the nucule of
Ghara.
The antherozoids enter the oogonium through angular slits
which are formed due to the separation of sheath cells below
the crown. The zygote wall gets thickened. The inner walls of
sheath cells also become firm and persist on the zygote like screwthreads, when the sheath coils disintegrate.
The zygote undergoes rest and when favourable conditions
return, its nucleus undergoes reduction division to form four
nuclei. One of these nuclei forms a distal biconvex cell while
others prepare to degenerate. A vertical division of the distal
cell separates a rhizoidal and a protonematal initial which grow
into segmented filaments.
Chara is haploid and the zygote is the only diploid p a r t of
the life-cycle.
Questions.
1.
Describe the features of special interest in the structure
and methods of reproduction of Vaucheria or Ghara.
(Agro, 1948).
2.
Describe the sexual reproduction in Chara.
{Agra, 1944,1947).
CHAPTER V
PHAEOPHYCEAE
—Ectocarpales, Fucales—
The Algae composing this group are predominantly marine
forms with greatest development in colder regions of the sea.
A few inhabit warm temperate oceans and rare fresh water
forms are known. Together with the Red Algae they make up
the bulk of marine algal vegetation and form sea forests.
The Brown Algae exhibit zonation in the intertidal zones
of the sea. The larger kelps, Laminaria, Postelsia etc. grow in
the lower littoral zone while Pucus is founds in the upper
littoral. In the sub-littoral zone are Sargassum, Nereocystis and
Macrocystis.
Fig. 13.—Sea-weeds. A, Laminaria Sinolairii; B, L, Saccharina,
Nereocystis; D, Macrocystis; E, Postelsia.
0,
The plant body of the Phaeophyceae varies from simple
filaments of Eciocarpus to laminate parenchymatous thalli as
in Fucus. The large sized filaments need additional support
from coi'ticating branches and haptera. In still more developed
42
PHAEOPHYCEAE
forms, regular dichotomy of a stiped lamina may give rise to
sea-palms. Unicellular forms are unknown.
The cellular structure is uniform.
Each cell possesses
a double wall, an inner rigid cellulose membrane and an outer
of gelatinous consistency. The outer wall is said to be made up
of algin, a pectic compound, probably tli,e calcium salt of
alginie acid. Cells are uninucleate and possess n.umel'ous discoid
chromatophores. The pigments of chromatophores have been
variously described but chlorophyll deficient in chlorophyll h
is usually present. The brown pigments have been collectively
termed Phaeophyll consisting of chlorophyll and fucoxanthin
(C4oH540g). Fucoxanthin has also been considered a n i n d e - '
pendent pigment, au oxidation product of
Xaiithophyll
(C40H56).
Kylin (1927) opines that fucoxanthin is a mixture of two
components, a and 6. Molisch considers that the brown pigment is
Phycophein. Naked' pyrenoids are pxesent in the chromatophores.
The general cytoplasm is vacuolated. Scattered in it, can
be distinguished dark dots called fucosan vesicles. Formerly
these were considered to be insoluble food reserves but Kylin
(1918) considers them to be tannin-like metabolic bye-products.
Due to modified pigmentation, starch is absent. Simple
sugars and pentoses are present but are immediately converted
into complex polysaccharides. Laminarin has been described to
be the chief photosynthate. Mannitol and fat are also present.
The reserve food is stored in a dissolved state.
The thalli grow by a long apical cell which forms an intercalary row of. cells (trichothallic growth). The meristematic
region of larger thalli is situated at the junction of the stipe and
lamina.
Vegetative reproduction may take place by fragmentation
or by development of special propagules
{Sphacelaria).
Asexual reproduction is secured by biflagellatc zoospores
which are formed in special sporangia. The zoospores are elongated pyriform bodies with two lateral flagella inserted in a
vestibular fossa (Chaudefaud, 1948), the superior being longer
and upturned. There are 1-2 chromatophores and a lateral eyespot. This structure is uniform throughout Phaeophyceae.
Zoospores are produced in unilocular sporangia. Proliferation is usual. The zoospores germinate into gametophytes.
Plurilocular sporangia are formed on Gametophytes.
These form the gametes which have to fuse before forming the
sporophyte.
PHAEOPHYCEAB
43
I n sexual reproduction, besides the isogamous process
mentioned above, oogamy is found, Antheridia and oogonia are
formed in uni to muitilocular gametangia.
Kylin (1933) based his classification of the group on facts
of life-history. Three families were distinct:
1.
Isogeneratae:
Similar generations.
2.
Heterogeneratae:
3.
Cyclosporae: '
Dissimilar generations, sporophyte
larger.
Only sporophyte is known.
I n thfe Phaeophyceae evolution takes place from an isomorphic to a heteromorphic alternation of generations.
Dwarf gametophytes are known as Diplonema and dwarf
sporophytes as Plethysmothalli.
Fritsch (1935) consicL'ers that structure of thallus and
sexual reproduction are more important systematic factors than
life-cycles which may be similar due to environment factors.
He divid'es the group into nine orders: Ectocarpales, Tilopteridales, Cutleriales, Sporochnales Desmerestiales, Laminariales,
Sphacelariales, Dietyotales and? Fucales.
ECTOCARPALES
The order contains some of the simplest brown Algae. The
alternation of generations is isomorphic in most cases. Growth
is triehothallic.
1.
ECTOCiEPUS
The representative genus Ectocarpus is very common on
Indian shores. E. conifer and E. breviarticiilahis
are epiphytes
on sea-grass. The best known species is E. siliculosus.
The branched thallus of uniseriate filaments is coinposed
of both erect and prostrate portions. Growth is intercalary.
The individual cells are uninucleate with 16 chromosomes
(diploid"). I n each cell there a r e a few disc-shaped" chromatophores. The cell-wall consists of three pectic-cellulose layers.
Reproduction is by typical biflagellate swarmers which are
formed by reduction, in-unilocular sporangia. The sporangia
arise by the considerable swelling of the apical cell of a lateral
branchlet. The initially single nucleus undergoes meiosis to
form haploid nuclei which divide equationally to pi'oduce 32 free
nuclei. Walls are not laid down. Protoplasm aggregates around
each nucleus and the protoplast formed thus is liberated as the
phaeophyeean zoospore.
The plant body of Ectocarpus
was a diploid sporopyte,
44
PHAEOPHYCEAE
The reduction zoospores produce, on germmation, a gametophyte which is morphologically similar to the sporophyte. The
gametophytes are heterothallic.
The gametophyte bears pluriloeular gametangia. During
their formation, a lateral papilla arises on a main branch and it
is cut oiJ by an oblique wall. Its length increases and' a number
of transverse divisions take place. A row of 8-12 cells is formed.
Longitudinal divisions also take place now beginning from the
central rows. The result is a pyriform to conical structure
composed of hundreds of cubical cells. These protoplasts are
liberated as bifiagellate gametes.
The gametes fuse in pairs anS produce the zygote in which
the diploid number of chromsomes is restored. I t is, However,
seen tliat sometimes the gametes develop independently and
reproduce the gametophyte asexually. Hence some authors
prefer to designate them also as zoospores and the gametangia
as pluriloeular sporangia.
Fig. l4!.—Eetocarpns. A, A sporophytic filament with uniloculer and
pluriloeular sporangia; B—G, Development of a pluriloeular
sporangium; H—K, Development of a unilocular sporangium;
h, Haploid zoospores; M, A gametophytic filament with pluriloeular gametangia; N, Gametes; 0—R, Development of a
zygote.
The sporophyte generation also reproduces asexually by
pluriloeular sporangia. The bifiagellate diploid zoospores in this
structure germinate to form the sporophyte again.
PHAEOPHYCBAE
of
45
Thus there are three types of sporangia in the life-history
Ectocarpus.
1. Unilocular sporangium to form the reduction zoospores,
on the sporophyte.
2. Pluriloeular sporangium to form diploid zoospores to
reproduce the sporophyte asesually.
3. Pluriloeular gametangium (sporangium) on the gametophyte, to form the gametes which fuse to form the sporophyte.
Sometimes gametes reproduce the gametophyte asexual] y.
Pappenfuss (1935) -worked out the complete life-cycle of
£ctocorpj(s and found that there was an alternation of isomorphic generations.
Knight (1929). however, observed that in British waters the
plants were only spoi'0])hytes and the haploid swarmers fused to
form the zygote.
I n the Mediterranean, Knight found only gametophytic plants.
The swarmers produced by these did not fuse but germinated
independently to form the haploid plant.
Fig. 15,—Ectoearpus. A, B, Life-histoiy in British waters; 0, D, Lifehistory in Mediterranean; dotted lines complete the life-cycle.
I t appears from such a variance of phases, that the life-cycle
of Ectocarpiis is considerably altered by environmental conditions.
46
PHAEOPHYCEAE
The sexual reproduction of Ectocarpus is predominantly isogamous. I n E. siUculosus sometimes gametes differ in size. I n
E. secundus larger female gametes are produced. These come
to rest earlier than the males which swarm to form a cliimp •
around them. I n E. Padineae three types of plurilocular sporangia are known: micro, meio and mega. The last produces
apogamous zoospores.
Anisogamous forms were formerly grouped in the genus
Giffordia which is now considered to he untenable.
FUCALES
The order is characterised by the possession of a dominant
sporophyte which produces gametes by reduction. The extent
of the gametophyte is thus extremely shortened. The plant body
is large and flattened parenchymatous lamina with considerable
tissue diflierentiation.
1. F u c u s
The chief representative of the group, FMCIIS, forms a conspicuous feature of the shore-vegetation of northern seas.
It
is present in the inter-tidal zone and is adapted to resist
desiccation due to tide ebb.
The thallus is flattened and ribbon-like, branching dichotomously and attached to rocks by a sucker-like holdfast. There
is usually a short stalk connecting the holdfast and the laminate
frond and this is continued in the frond as its midrib. With
increasing age, tides scratch away the soft tissues of the frond
and only the midrib persists as a stipe.
The plant is perpetually covered by mucilage to protect the
parts from drought.
The whole of the expanded thallus is covered with sterile
pits or conceptacles called cryptostomata. I n the fruiting plants,
however, only the tips of the thallus are expanded a n d are
studded with little rugosities indicating the presence of fertile
conceptacles.
Morphologically, the thallus shows distinct differentiation of
tissues. The outermost is the limiting layer consisting of small
cells with abundant plastids. I t is the chief assimilatory tissue.
The cortex which follows, is composed of compactly arranged
parenchymatous cells which tend to elongate and form the storage
tissue. The centre of the lamina is constituted by elongating
interwoven filaments, which have thin walls and incomplete septa.
This web of filaments is called the medulla and probably functions
PHABOPHTCEAE
47
for translocation. Secondary growth of the thallns takes place
by the activity of the limiting layer and inner cortical cells.
Fig, 16.—Puovs. A, Fuous vesiculosus (dotted apical regions possess
conceptacles) ; B, Transverse section of a fertile blade; C—B,
Development of a eonceptacle; F, A species of Fncus sho-wing
dichotomous branching of the thallus.
Growth is due to an apical cell which comes to lie in a depression due the rapid growth of surrounding tissue. Each apical
cell is a large truncated pyramid with five cutting surfaces.
In the formation of the conceptacles, a superficial cell of
the ] imiting layer divides transversely into two unequal cells;
the upper cell degenerates while the lower divides anticlinally.
The products of this division are arranged in a curved manner
to form the wall of the eonceptacle. The sterile pits arise in a
similar manner but tKey are usually very small and full of
paraphyses.
>»
There is no asexual reproduction. The thallus may, however, reproduce vegetatively by fragmentation.
The sex organs are lodged in the fertile conceptacles. The
plants may be dioecious as in F. vesiculosus and F. serratus or
monoecious as in F. spiralis and F. platycarpus.
I n the latter
case, both sex organs are present in the same eonceptacle in
48
PHAEOPHYCEAE
F. platycarpus but in F. spiralis they occur in different conceptacles of the same plant.
Fig. 17.—Fiious. A, A male coneeptacle; B, Antlieridia; 0, A female
oonceptacle; D—E, Development and liberation of oospheres.
Each antheridium or micro-sporangium is a globular body
with tliree walls. I t is borne on the tip of a filament
which arises from the cells at the base of the coneeptacle. The
antheridium is at first uninucleate but the number of nuclei is
increased to four by meiosis. At this stage of development, a
pause follows and the antheridium appears to rest in a fournucleate stage. After some time divisions start again and 64
nuclei are formed. Around each of these nuclei, protoplasm
accumulates and an antherozoid is delimited. The antherozoid
has been studied by Manton and Clark (1951). I t possesses two
laterally inserted unequal flagella.
A large number of stalked antheridia are entangled among
the paraphyses, in the coneeptacle. As the antheridium matures,
the outer wall (exochite) bursts and the antherozoids remain
enclosed by the mesochite and endochite. When the tide ebbs,
the antheridia are forced out of the osteole due to the collapse
of the latter. The tide returns, the two walls of the antheridium burst and antherozoids are liberated.
For the formation of the oogonium, a cell at the base of the
coneeptacle divides by a transverse wall, after considerable
PHAEOPHYCBAE
49
enlargement. THe lower cell functions as the stalH while the upper
cell is the oogonium initial.
-'^ig. 18.—Fuoius. A—B, Development of an antheriaium; F—J, Formation of oospheres; pause is denoted by the long dash.
Initially, the oogonium is uninucleate. Meiosis takes place
and the number of nuclei is increased to four. Division stops
a n d the oogonium undergoes rest. After a short while, nuclei
divide a'gain and the resultant eight nuclei organise themselves
as eight oospheres. The oogonia are dark green in colour and
eggs are liberated in a way similar to that of antherozoids.
The mature oosphere is released into the sea and a large
number of antherozoids surrounds it, resulting in clump-formation by which the oospheres rotate. "Fertilization is, thus,
external. Cook and Elvidge (1951) have established that in the
Fucaceae, fertilization is chemotactically controlled. The zygote
secretes a wall around itself and starts germination atonce, as the
tide returns. There is no rest period.
The first Stage in zygotise development is elongation., The
first wall is usually transverse. Perhaps it is laid at right
angles to the plane of incident light. Subsequent divisions t u r n
it into a three celled structure. The lower cell forms the rhizoid.
The upper part elongates and grows by a three sided apical cell.
Divisions of this portion are irregular but finally the apical cell
comes to lie in a depression. A large number of hairs are also
formed. These show trichothallic growth. The hairs soon fall
PHAEOPHYCBAB
5&
off but the basal cell of one of them functions as a four-sided
apical cell and continues to increase the plant, in dimensions.
Fig. 19.—Fuous. A, Liberation^ of antherozoids;'i|,B, A single oosphere;
C, Clump-formation; D, Zygote; E^G^ Germination of
zygote.
Partheiiogenetic oospheres have been described in Fucus,
FuGUs plant is a diploid or sporophyte. I t is interesting to
observe that the sporophyte produces the sex cells by reduction
division, a phenomenon parallel to that found" in the animal
kingdom. There appears to., be no gametophyte generation as the
sex cells unite atonce to form the zygote. Thus there is no apparent alternation of generations.
Strasburger (1906), however, believes that the pause in the
development of sex organs subsequent to meiosis, represents the
haploid phase and thus the predominant sporophyte alternates
with a one-celled gametophyte;
Diploid Fucus has 64 chromosomes.
9
2.
SARGASSUM
The genus, Sargassum, which is confined mainly to tropical
waters is very varied with about 150 species. I t occurs most
abundantly in the Atlantic and is responsible for the formation
of Sargasso Sea near the "West Indies. The forms are mostly
pelagic and floating (S. natans, S. iacciferum) but 8, vulgare
(ind S. Hystrii/> are examples of attached species.
PHAEOPHYCEAE
51
Sargassum is distingTiished by its high differentiation. The
monoecious or dioecious sporophyte forms an erect radially branching plant body which has an irregular, warty holdfast and a
cylindrical stipe. The first branch of the axis is sterile and
bears the cryptostomata or sterile conceptacles. The second
branch is also sterile and is present as an air-bladder. Subsequent branches are fertile and bear the fertile conceptacles.
The microsporangia or antheridia of this genus are characteristicallj' phaeophycean and liberate sixty-four antherozoids
each. The pause occurs in their development when the 4-nucleate
stage is reached. The antherozoids are biflagellate.
Fig. 20.—Sargassum. A, A part of the mature plaat j B, Deyelopmeat of
an antheridium; 0, A spermatozoid; D, Development of
oogonia; Ej^, Eg, Liberation of oagoaia; E, Germination of
zygote.
The megasporangium has a single ovum at maturity.
Initially the ovum contains all the eight nuclei but seven degenerate. The whole megasporangium is liberated at maturity, but
remains attached to the wall of the conceptacle by a stalk of
mucilage.
The first transverse wall is laid down in the zygote while it
is still attached to the conceptacle. The lower cell usually forms
the rhizoidal holdfast while upper gives rise to the erect plant.
Sargassum represents the highest evolved stage of Fucales
in increasing embryonal complexity.
B2
t'HAEOPHYCEAE
TKe Pucales are regarded as the most aclvanced among tKe
PKaeopKyceae. Their origin is, however, a problem of considerable controversy.
The fossil NematopJiyton was formerly grouped under
Phaeophyceae but now it has been removed to a new order Nematophytales.
Questions.
1. Write an account of the habit, structure and modes
of reproduction of Ectocarpus. Discuss alternation
generations in this plant.
(AllaJiahad, 194:1)
2. Describe the habitat and structure of Fucus, and state
the gametophytic and sporophytic parts of it.
{Allahabad, 1950)
3. Give an account of the life-history of Fucus, and
discuss the question of alternation of generations in
the geiius.
{Agra, 1949)
4. Give an account of the habit and habitat of Fucus.
Explain how its form and structure is adapted to its
environmental conditions.
{Agra, 1950)
C H A P T E R VI
RHODOPHYCEAE
—Nemalionales,
Ceramiales—
The Rhodophyceae are characterised by a total lack of motile
reproductive units. They are almost entirely marine, growing
chiefly in deeper waters. However, nearly 50 species occur in
fresh water, constituting the algal flora of swift flowing streams.
The marine forms are usually red or purple but the fresh
water species exhibit a variety of colours from green to golden
brown.
Several views have been put forward regarding the
pigmentation of this class. One hypothesis suggests that the
red pigment serves to alter the wave-length of the predominant
blue rays which reach tliese Algae, and thus allows the chlorophyll to manufacture food. I t may be that the red pigment
screens the protoplasm from the harmful effect of blue light
and only Alters red rays for use by the chlorophyll-corpuscles.
Another view suggests that the red pigment is itself assimilatory
in nature.
However, the chief pigment of all Rhodophyceae is Phyo erythrin. Occasionally Phycocyanin is also present and produces
a shade-variation of the red. Chlorophyll deficient in chlorophyll j8 is also iacludei in the chromatophores. I n the fresh
water forms, phycoerythrin is absent.
The pigments of these Algae are found in cHromatophores
which^may be discoid and small or irregularly lobed' and large.
I n certain forms the chromatophore may be axial and stellate
while in others it may be band-shaped. The chromatophores of
primitive Rhodophyceae have naked pyrehoids but in advanced
members of the group pyrenoids are lacking.
The chromatophores are dispersed in the cytoplasm of the
rhodophycean cell. The cells generally lack vacuoles and may
be from uni to multinucleate. I n the Florideae, the mucilaginous
and pectic cell walls are broken at the two poles to provide
cytoplasmic connection for adjacent ^cells.
The product of photosynthesis is iloridean starch and a sugar
floridoside.
The vegetative structures of the Rhodophyceae range from
delicate filaments to large parenchymatous expansions. From the
simple filaments of CalUthamnion to corticated ones of Polysiphonia and Geramium and the fleshy thalli of Gracilaria, no distinct
54
RaODOPHYOBAl^
series can be traced. However, the reproductive features of the
group establish in it an evolutionary; series of growing complexity.
Vegetative reproduction by fragmentation is rare.
Most Rhodophyceae reproduce asexually by forming either
monospores or tetraspores. The sporangia producing these
spores are globular swollen structures with abundant reserve
food and a large number of chromatophores. The spores are
naked and germinate directly into the new thallus. Usually,
however, the tetraspores are products of a meiotie division. Each
spherical sporangium is capable of forming a single monospore
or four tetraspores.
The sex-organs of the Ehodophyceae are termed as antheridia or spermatangia and carpogonia.
The antheridium produces only a single non-motile sex cell
called the spermatium. This is carried to the female organ
through water and lodged against its distal projection, the trichogyne.
The carpogonium is borne on a special branch consistmg
of a varying number of cells, constituting the procarp. The
carpogonium usually terminates the procarp. I t is a swollen
flask-shaped structure with a lower bulb-like part and an upper
neck-like trichogyne. Before fertilization, the single female
nucleus divides, one daughter nucleus migrating into the colourless
trichogyne to degenei'ate. The bulbous p a r t of the trichogyne
contains reserve food and chroma uophores.
I t has been observed that the
organise itself into a definite cell.
female nucleus does not
Fusion of the sex nuclei takes place at the base of the carpogonium.
I n Nemalioa
and Batraohospsrmum,
the male
nucleus undergoes a division but in other forms only a single
nucleus from the spermatium passes through the trichogyne,
>vhich shrivels up after fertilization and is cut off from the basal
part.
The zygote gives rise to a diploid generation called the
carposporophyte. I n the Nemalionales, however, the carposporophyte is a result of the meiotie division of the fusion nucleus
(Svedelius, 1933).
Thus there may be two types of alternation of generations.
I n the first type, a gametophyte and a hapliod carposporophyte
alternate (Nemalionales), while in the second a gametophyte and
a diploid carposporophyte {Liagora). I n yet other cases, the
diploid carposporophyte may produce carpospores which develop
into independent plants, 'the tetrasporophyte. These are also
idip.loid but their tetrasporangia are reduction products and
EHODOPHYCEAE
55
produce gametophytes. Thus tHere are three generations Haploi'd
gametophyte and dii)loid earpo and tetrasporophytes.
From this account, it becomes clear that alternation of generations in the Rhoffophyceae is not necessarily accompanied by
a change in chromosome number. Meiosis appears to occur at
different phases in their life-cycle. Svedelius (3931) called the
Nemalionales, Haplobionts as there was only the haploid biont or
plant in the life-cycle. Higher Florideae are Diplobionts as the
gametophyte and diploid earposporophytes (two types of bionts)
alternate.
The Ehodophyceae have been divided into two classes:
1.
Proto-Plorideae or Bangiales: "Without pit connections between adjacent cells, with Intercalary growth
and direct division of the zygote into carpospores;
stellate chromatophores with naked pyrenoids.
2. Florideae: With pit connections, terminal growtK
and carposporophyte formation; chromatophores not
stellate, pyrenoids absent.
The Florideae have been divided into several orders of
which Nemalionales and Ceramiales are the most important.
NEMALIONALES
The order contains both marine and fresh water forms comprising about 35 genera and 250 species.
The thallus consists of simple branched filaments which are
corticated in higher forms. The cortical investment is generally
formed by the downward growth of the inner cells of branches at
the nodes.
In several genera the fusion nucleus passes into an auxiliary
cell which develops a carposporophyte. This latter is invested
with a layer of sterile cells which develops from the hypogenous cells of the female procarp.
The alternation is haplobiontic.
1.
BATKACHOSPERMUM
The chief genus Batrachospermum is a fresh water form
growing in swift streams of the tropical and temperate regions.
The characteristic beaded filament consists of an axfal row of
large cells which are somewhat wider at the septa or nodes.
Each of these cylindrical cells is uninucleate with a lobed"
parietal chromatophore and a pyrenoid. The chromatophores
lack the red pigment and thus the whole plant is bluish green
to violet in colour. The cells of the axial filament are joined
to each other by protoplasmic-pit-connections.
56
RHODOPHYCBAE
From the nodes, dense whorls of branches (laterals) arise.
Each branch is composed of monoliform cells. The presence of
whorls of branches give the thallus its bead-like appearance.
The whole thallus is. a thick, soft structure enveloped in
mucous. Growth is due to a hemispherical apical cell. In mature
filaments, the basal cells of branches grow downwa,rd to form the
cortex of the axial thread.
These erect floating thalli of Batrachospermum arise from a
juvenile ehantransoid stage which grows attached to rocks or submerged stones and gives rise to 'the axial filaments"'"as lateral
branches. The Chantransia is prostrate and' filamentous and con-'
sists of similar uninucleate cells ("West, 1904).
Fig, 21.—Batrachospermum. A, Developing Chantransia
with erect
filaments; B, Erect filament (dotted) with branches showing
origin of cortieating filaments; C. A filament showing origin
of branches below a node; D—J, Formation, liberation and
germination of a monospore.
Asexual reproduction of the ehantransoid stage takes place
by monospores. In their formation, a branch-tip swells up and
cuts off a single or a number of globular uninucleate monosporangia. The contents of each sporangium are liberated as a
single spore which is naked and non-motile. The wall of the
sporangium often continues to remain attached to the filament,
and proliferates to form more monospores.
The Chantransia does not reproduce sexually.
^tlODOPHYCEAI^
57
Sex organs ate formed on the erect filaments. THe' plants
are dioecions, i.e., sexes are separate.
The antheridia arise as spherical globules at the ends of
the ultimate branchlets of laterals. The tip of the branchlet
swells up and is cut off by a septum. Further growth of the
tip pushes the antheridium to one side and cuts oif another
antheridium. This process may go on till three antheridia are
formed. Each antheridium liberates a single naked and nonmotile spermatium by the rupture of its wall. Proliferation
may take place and a large number of spermatia may be
produced.
The antheridial branches are colourless and whorled and
thus can be easily distinguished.
If
\
if p
.^y^
^P"-
W-^lf^
Fig. 22,—BatraoJiospermum. A, B. monoUforme; Bj Whorls of branches
at the nodes; C, Origin of branches; D—F, Development of
antheridia; G—J, Carpogonium; K, L, Stages in conjugation.
The carpogonia are formed on a three-celled procarp which
originates as a branch of the laterals near the central axis.
Invariably the procarp arises in a ventral, protected position.
The two lower cells of the procarp are the stalk cells of the
apical carpogonium. Each carpogonium is a flask-shaped structure with a clavate apical protruberance or trichogyne. The
carpogonium has a well developed parietal chromatophore which
may extend into the trichogyne. Initially the carpogonium is
uninucleate but 01 eland (1919) has reported division of the
single nucleus into two, one going into the trichogj'e to degenerate..
m
RHObOP&YCteAE
THe spermatia reach' the triehogyne through the ^ agency
of water. The smgle nucleus divides (Kyliti, 1916). The intervening wall dissolves and the two male nuclei travel downward
towards the female nucleus. One of the male nuclei reaches
the base of the carpogonium earlier and simultaneously a wall is
laid down cutting off the triehogyne with a male nucleus.
The triehogyne shrivels up and the male nucleus degenerates.
Meanwhile, fusion of the sex nuclei takes place in the
carpogonium. The zygote contains 2 x chromosomes (20).
Reduction division is immediate and the zygote nucleus
divides into four. Thus the diploid stage is extremely short.
The carpogonium produces lateral sporogenous protruberances into which the haploid nuclei migrate. Subsequent
divisions result in the formation of a large namber of gonimoblastic filaments. The large number of closely arranged gonimoblasts gives the fertilized carpogonium a globular appearance.
The end's of gonimoblasts are converted into si:)herical carposporangia which liberate single uninucleate carpospores.
Fig. 23.—Batraohotperthum. A, A filament with a eystocarp; B, A
zygote; C, D, Zygote with gonimoblastie filaments; E, A
diagrammatic T. S. of a eystocarp; F—J, Formation of carpospores; K, Germination of a carpospore.
Due to the formation of these carpospores, the whole structure developing from a fertilized carpogonium, is called a
carposporophyte. However, the carposporophyte is a haploid
generation.
RHODOPHTCEAE
59
While these cKanges are going on, tHe basal cells of the
procarp are also activated and by repeated divisions give rise to
a sterile investment which encloses the carposporophyte. This
enclosed structure is known as a cystocarp and at maturity,
appears like a dark nodule on the thallus.
The investment of the carposporophyte is ruptured, as the
earposporangia liberate the carpospores. Each carpospore gives
rise to the juvenile chantransoid stage on germination.
The genus shows a haplobiontic alternation of generations.
The life history of other genera of the Nemalionales is
closely similar to 'that of BatracJiospermum but the number of
component cells in the procarp and the condition of sex nuclei
at the time of fertilization may vary. Even species of Batrachospermum are variable in this respect.
CEEAMIALES
The order is characterised by the formation of an auxiliary
cell after fertilization. Into this cell, the zygote nucleus or its
division products pass and finally develop the carposporophyte.
The auxiliary cell is cut o& from the stalk cells of a carpogonium.
Carpospores of this group develop into tetrasporophytea.
The reduction in chromosome number takes place when tetraspores are formed and thus, the carpo as well as tetrasporophyte
represent the diploid generations. In the life cycle of the
Ceramiales, two distinct generations occur: haploid main plant,
and diploid carposporophyte and tetrasporophyte. The alternation of generations is diplobiontic.
1.
POLYSIPHONIA
Polysiphonia grows epiphytically on larger algal thalli,
mainly the Fucaceae, on the Atlantic coast of America.
P. fastigiata is probably hemi-parasitic on the ribbon-shaped
fronds of Ascopliyllum nodosum (Fncales).
The thallus of Polysiphonia originates from decumbent
filaments which grow attached by an irregularly lobed flattened
disc. The thallus is branched laterally and often gives a dichotomous appearance. Early in development, the basal cells of the
axis cut ofi! an enclosing tier of pericentral cells. The number
of these cells ranges from four to twenty-four. The pericentral
cells elongate and look like siphons, giving the plant a
characterstic polysiphonous appearance. However, the ultimate
branches of the thallus are not polysiphonous.
60
RHODOPHYCEAE
The axial filaments are often corticated also. This condition arises due to the formation of short cell-layers external to
the pericentral zone, in, the basal region.
Fig. 24.—FolysipJionia. A, A branching filament witli antheridia; B,
An antheridium; C—B, Development of an antheridiumj
P—K, Formation of a four-celled eaTpogonium; s—support
cell; b—basal cell; 1—lateral cells; fp—Fertile perie^tral cell.
In the formation of lateral branch, a cell of the axial row
divides diagonally and the daughter cell grows out into a multiseriate filament. In certain cases, the daughter cell may form
uniseriate trichoblasts. In this case, the trichoblast initial divides
in one plane and by repetition of this process, gives rise to dichotomously branching, delicate multicellular hairs. The trichoblasts
are sterile as well as fertile.
Polysiphonia reproduces sexually. The species are mostly
heterothallic.
In the formation of antheridia, an apical trichoblast branches dichotomously and usually one branch develops into the
fertile axis (Grubb, 1925). Two basal cells of this trichoblast are
sterile. The upper cells cut off transverse tiers of pericentral
cells. Every pericentral cell divides to form one or many antheridial mother cells which may bear two to four antheridia according to species. Proliferation is common during spermatia formation.
RHODOPHYCEAE
61
The composition of the antheridial axis is, thus, complex.
Encircling, is the layer of antheriSia which are being liberated.
Next to them occur the proliferating or empty walls of the antheridial mother cells. Inner to this comes the layer of pericentral
cells which form an enclosure round the axis.
The carpogonium develops on a fertile triehoblast. The main
axis cuts off a triehoblast initial and a layer of pericentral cells
at one level close to the apex. Often the trichblast initial looks
like one of these pericentral cells and is designated as the fertile
pericentral cell. • The triehoblast initial divides to form a 5-7
celled triehoblast. Two lower cells of this hair form pericentral
tiers. Out of these, one pericentral cells towards the axis forms
the support cell or stalk cell of the carpogonial filament.
Fig. 25.—Polysiphonia. A, Conjugation -with a spermatium (auxilia'ry
cell is dotted); B, Zygote with auxiliary cell and accessory
baflal and lateral nutrient filameats; C, Fusion of zygote and
auxiliary cell; D, Fusion of zygote, auxiliary cell, support
cell, and basal cell; E,-Development of gonimoblastio filaments.; F, A cystocarp.
The support cell undergoes division and produces a hornlike, four-celled carpogonial filament. The distal cell of this is
converted into a carpogonium, with a bulbous base and an elongate narrow trichogyne. Simultaneous with this process, is the
formation of a basal and a lateral nutrient cell from the support
cell. Kylin (1923) has described immediate division of the lateral
62
RHODOPHYCEAE
nutrient cell. Iyengar and Balkrishnan (1950) describe a three
celled carpogonial brancH in P. 'platycarpa.
Yamanonchi (1906) observed tKe process of fertilization in
Polysiphonia. The spermatia of the male plant are carried to
the trichogj'ne by water. The intervening wall between the
spermatium and triehogyne dissolves and the single male nucleus
travels downwao'd. At this stage, the female nucleus had divided into two, one migrating into the triehogyne. Unlike, Batraeliospermtim, the trichogynal female nucleus is persistent. The
male and female nuclei fuse in the base of the carpogonium.
Subsequently the lateral and basal nutrient cells germinate
into long filaments. The support cell buds off an upper
auxiliary cell which fuses with the carpogonium. The zygote
nucleus divides into two. Often both of these diploid nuclei
pass into the auxiliary cell but in P. nigrescent only one daughter
nucleus migrates. A wall is laid down between the carpogonium and the auxiliary cell.
Fig. 26.—Polysiphonia. A, A tetrasporophytic filament; B—D, liberation of tetraspores; Life-cycle showing alternation of generations.
The auxiliary cell gradually fuses with the support cell and
basal nutrient cells to form a large fusion cell. Its diploid
nucleus buds off gonimoblast initials which develop*'into gonimoblastic filaments and constitute the' earposporophyte. Meanwhile the pericentral cells, adjacent to the support cell, are
activated and these give rise to a sterile investment for the
earposporophyte. The carpospores develop from carposporangia
RHODOPHYCBAE
63
•whicK are transformed terminal cells of the two-eelled gonimol)lasts. In P . platycarpa mature cystocarp has one layered wall
(Iyengar and Balkrishnan, 3950).
Lewis (1914) rei^orted that the diploid carpospores develop
into tetrasporophj'tes. " This also has a structure similar to the
gametophyte. The tetrasporangia are, however, embedded in the
T tissue of the thallus. Their protoplasm is dense. The nucleus
"divides mciotically into four and thus, four haploid tetraspores
are formed.
Liberation of the tetraspores involves a rupture of the
tetrasporangial wall and splitting apart of the cover cells of the
tetrasporangium. The tetraspores germinate to form the gametophytic PolysipJion'ia1.
C A L L I T H AMNION
The delicate filaments of Callithamnion are usually monosiphonous. I n certain cases the filaments show cortications at'
Fig. 27.—Callithamnion. A, A portion of the mature filament with
antheridial groups; B, An antheridial filament enlarged;
0, D, I'ormation of spermatia; E, A branch with carpogonial
filament, B—K, Development of gouimoblastie filaments; L,
Two cystoearps; ao—apical cell; am—auxiliarj mother cell;
b—basal cell; fc—fertilized carpogonium; g—gonimoblastie
filament; sc—sporogenons cell.
the base bat the cortications are formed exclusively from the
basal rhizoidal cells only. The cells of this genus are multinucleate.
64
BHODOPHYCEAti
, The antheridia are borne on short lateral branches which
appear like ellipsoidal bunches. In their formation, a lateral
stalk cell is cut off. From this, by division, a number of secondary cells are formed. Each of the secondary cells is converted
into 2-3 celled branch the terminal cell of which functions as the
antheridial mother cell. The mother cells give rise to antheridia
and proliferate.
Spermatia are liberated singly from the
antheridia.
The carpogonial branch (4-celied) arises from one of a
pair of auxiliary mother cells. These mother cells are formed
in the middle of a branch. Fertilization takes place when the
spermatial nucleus fuses with the female nucleus. The auxiliary
mother cells divide to form a basal cell each. The fertilized
carpogonium forms two cells. Each of these now cuts off a
sporogenous cell, which fuses with the auxiliary cell of its side.
The diploid nucleus of the auxiliary cell divides, one daughter nucleus passing to the apex. The other daughter nucleus
and the original nucleus of the auxiliary cell remain at the base
and are separated off by a wall. The apical cell is large, its
nucleus divides and redivides, the daughter nuclei passing into
gonimoblastic initials.
Since two auxiliary mother cells are produced initially, the
cystocarps are present in pair.
The carpospores are diploid and give rise to tetrasporophytes. These sporophytes bear the tetrasporangia in acropetal
succession as lateral outgrowths of young vegetative branches.
The tetraspores are reduction ;products and germinate into
gametophytes.
In several eases, combinations of tetrasporangia and cystocarps or tetrasporangia and antheridia have been found in the
same plant. Probably in these cases, the plant is diploid and
sex organs are formed on it by reduction. Fusion of sex cells
restores the diploid number in the zygote and the carpospores
are diploid. The carpospores develop into the diploid plant
which may produce tetrasporangia (diploid) as well as sex
organs (haploid).
The Geramiales represent a very high degree of evolution
land differentiation among the Ehodophyceae.
Among the fossils, the red Algae are represented by LithO'
ihamnion, Lithaphylium and Dermatalithon.
/
EHODOPHYOEAE
65
Questions
1. Give an account of tHe structure and life history of
any Eed Alga studied by you, {BatracJiospermum).
{Allahalad, 1946,1951)
2. Give an account of the mode of reproduction of
PcKhjsiphonia,
{Agra, IdU, 1945,1946,1948)
Compare with Chara (1944); With Fern (1946,1948)
8. Write a short note on cystoearp.
4. Describe the post-fertilization changes in the life
history of Sargassum and Polysiphonia. {Agra, 1951 ^
SECTION I I
FUNGI
Introduction
Saceardo in 1889 defined Fungi as "Ciyptoganlic plants,
cellular, destitute of chlorophyll, for the most part having ;a
mycelium, either parasitic or saprogenous, for the most part
aerial." They are classed Tinder Thallophyta and are separated
from the Algae due to a distinct heterotrophic mode of nutrition.
In a large majority the thallus is composed .of filaments or hyphae
which are colourless and together constitute the mycelium. Motile
.reproductive units are absent from the higher forms.
The plant body of Fungi may be made up of non-septate
t T. ^
hyphae, where multinucleate condition of the
^^ ° ^
hyphae may impart them a eQgaflfiytio j ^ a t u r e .
The hyphae may be divided by transverse septa into uni, bi or mulr
tinucleate segmehts. In rare cases "ohlique or longitudinal septation has been described (Nichols, 1896; Kempton, 1919).. The
hyphae are, in most cases, richly branched and lie loosely on the
substrate in an amorphous form. In other cases, the hyphae are
intertwined to give a macroscopic form of definite composition.
Complexity in this interwoven felt-like mass may result in .a
pseudoparenchymatous web-like formation where the component
filaments may give the appearance of a regular arrangement. The
hyphae may aggregate in various manners for purposes of reproduction or assimilation and form compact bodies like the pileus of
Mushrooms or cups of the Aseo'mycetes.
In several Basidiomycetes, the mycelium shows anastomoses.
These may take place through short straight branches or by small
loops. In the former case, the mycelial filaments are arranged
like H-pieces where the bridge of H is formed by the small fusing
branches put out by the main filaments.
Often, adjacent cells of the same hypha are joined by clampconnections, which are short tubular protrusions from one cell
to its neighbour (Noble, 1937). Hoffman (1856) and Rj^le^^
(1877) observed that the passage between adjacent cells is soon
closed. This would appear to suggest that the clamp-connections
serve some special function and are of more th^an mere nutritive
significance.
Hyphae may be interlaced to form thick root-like strands
called rhizomorpjis, or they may aggregate in tbick-walled resting
68
FUNGI—INTRODUCTION
bodies called sclerotia. In a sclerotium, tHe peripKeral cells
are modified to form a cover for the inner vegetative mycelium.
The sclerotia are means of propagation.
In certain cases, a mycelium is not formed (Yeast). Here
the body consists of unicells which participate both in vegetative
and reproductive functions.
The cell wall consists of a special variety of cellulose known
as fmigaL_£ellulose. The space enclosed by the'wall is not completely filled with protoplasm. Differential staining by Neutral
red shows the presence^of several minute vacuoles scattered" in
the protoplasm. The general cytoplasm is granular to reticulate.
•The cytoplasm includes storage products like amylo-dextrin,
-amyloid, glycogen and oil. Besides these the protoplasm possesses
the property of secreting several kinds of ferments and enzymes
which help in the digestion of food and serve to dissolve the walls
anff protective layers of'host-;cells. Nuclear structure is usual.
The general mode of division is mitotic. In certain Basidiom^cetes the spindle is extranuclear.
'
<
Fungi reproduce asexually by forming several distinct types
- Eeproduction o^spf^es. In the lower groups of Pungi, sEheri^
cal, tubular or ovoid sporangia are formedl)y
the swelling of hypHal ends-or apices of lateral branches. In
aquatic forms the sporangium liberates motile zoospores (Phycomycetes)'but in sub-aerial members the contents of the sporangium may be liberated as walled' non-motile spores. In other
conditions, the sporangium may itself act as a reproductive unit
and is shed as a conidium. Again, a conidium may germinate
directly into the new mycelium or else divide into several zoospores in a moist medium. Conidia may be solitary and uncovered
or may occur in groups on conidiophores and aggregated in
pycnidia or coremia.
On the normal mycelium often dark coloured chlamydospores may be distinguished occurring in chains, or singly. These
are heavily walled and in many cases walls are spiny to
reticulate.
A more efficient method of asexual reproduction is by oidium
formation. Under special circumstances the hyphae are broken
into a number of small .segments which form spores. Each spore
is termed an oidium. This kind of propagation is particularly
noticed in pathogenic forms.
Development of spores may be endogenous or exogenous.
Fungi reproduce sexually by isogamy where fusing individuals are similar cells or by an advanced oogamy where definite
antheridia and oogonia are formed. The number of forms with
_ intero-rading types of sex apparatus is so large that it is easy tq
FUNGI—INTEODUCTION
'69"
picltiie a distinct' series from the primitive members of the group
to the aSvanced. The most important fact of fungal sexual
reproduction is the gradual degeneration of normal modes
and organs.
In the early forms, the distinctness of sex organs is striking.
Gradually the process of reduction sets in by a reduction in the
number of fusing nuclei. This is followed by the slow disappearance of sex organs. However, the process of sexual fusion
still occupies a definite position in the life-cycle. In the next
stage sex organs are lost and the uniting partners may either be
whole cells (vegetative) or parts of cells. The condition is then
restricted to nuclei only and finally, in a complicated vegetative
phase, it becomes difBcult to distinguish the actual sexual fusion
which varies to different positions of the life-history.
The degeneration of sex is traceable individually in every
order of Fungi ; and from order to order again there is gradual
reduction.
It has been noticed in several cases that in isogamous or
anisogamous forms two complementary myeelia are present.
These can be designated+and—strains. It has been observed that
while in some forms zygospores are formed by the union of
hyphae from the same spore (Homothallie), in others two different
sources should be harnessed for this purpose (Heterothallic).
The phenomenon of heterothallism is common in Fungi. However, in many members, there was a faculty to exhibit periodic
homo and heterothallism. Heterothallism is present even in
those genera which possess normal sex organs (Mitter, 1936).
Dodge defined Heterothallism as "the condition where
monosporous myeelia produce perfect stages only when mated with
their reciprocal haplonts." Gwynne-Vaughan considers heterothallism to be a purely nutritive phenomenon.
Thus, with the results of sexual fusion, and the formation
of a resting zygote, begins the diploid fungal generation. In
the life-history of Fungi, alternation of generations is distinct
with clearly defined haploid and diploid phases. In certain groups,
however, due to degeneration of sex, it is difficult to locate
meiosis. Sometimes even in the same life-cycle two fusions
take place at different or simultaneous stages. Nevertheless,
whereever products of syngamy are known, there is an alternation of two separate generation. The predominant phase of
the life-cycle is the gametophyte.
Gwynne Vaughan (1951) has divided the Fungi into three
great groups on the basis of the septatign of their mycelium, and
the characters of their spores,
70
UNGI—INTEODUCTION
1. PHycomyeetes—Vegetative mycelium aseptate.
2. Aseomycetes—Vegetative mycelium septate, characteristic endogenous ascospores.
3. Basidiomycetes—Vegetative mycelium septate, characteristic exogenous basidiospores.
Certain authors (Gaumann, (1928) include another group
Arehimycetes in the Fungi. This is placed before the Phycomyeetes and consists of plasmodial forms. Often the Bacteria
are also included in the Fungi but here they will be treated
separately.
All those Fungi, in which the perfect or sexual stage is not
known, are grouped under Fungi Imperfecta
Questions
1. Give a concise account of the various modes of asexual
reproduction in the Fungi studied by you.
(Allaliahad, 1943)
2. Give the chief criteria employed in the classification of
the Fungi into the three important groups. Quote
examples.
(Allahalad, 1950)
3. Write a short essay on the sexual methods of reproduction in the Fungi studied by you.
{Agra, 1946)
SAPROPHYTISM, PARASITISM, SPECIALISATION,
!
SYMBIOSIS
Fungi, being colourless, have to secure food and energy
from the substrates upon which they live. For culturing in the
laboratory they have to be grown on media which contain the
essential elements required for synthesizing their cell constituents. There appears to be no universal natural substrate or
artificial medium upon which all Fungi will thwve. Numerous
F u n g i remain sterile in culture while others do not complete
their life-cycle on synthetic media. This is especially t r u e for
parasitic forms.
Media are of three general types: natural, semi-synthetic
and synthetic. The natural media are useful for routine work
and consist oi n a t u r a l products, putxiiying oxgamc m a t t e r ,
decaying plant parts etc. The synthetic media a r e of known
composition and concentration.
The first such medium was
prepared by Raulin (1S69). Steinberg (1939) recommendedspecific concentrations of sucrose, ammonium nitrate, magnesium
sulphate and dipotassium hydrogen phosphate. For making the
media semi-solid 2 per cent, agar is used.
Before proceeding to grow the fungus in a medium, it is
better always to 'sterilize' the medium. This is done by autoclaving. For careful a n d systematic study, single-spore-cultures
are made by allowing only a solitary spore to grow on a specific
substrate.
The chemical reactions which condition the vital processes
of Fungi are governed by enzymes. I n many cases, for particular environmental conditions, adaptive enzymes may be
produced". Enzymatic secretions from fungal hyphae serve to
dissolve host tissue as -well as digest the absorbed nutriment.
Fungi, which utilize organic storage materials or waste
products or break up decaying tissues to obtain
Sapropliytism food and energy, are termed saprophytes. If
the form is not capable of changing its mode of
life, it is designated obligate saprophyte. But if environments
can influence this mode of nutrition, then the form is known as
facultative parasite, i.e., having the capability of • changing to
parasitic mode of life.
The saprophytic forms can be roughly classified accoi;ding
to the nature of their substrate.
72
SAPROPAYTISM ETC).
In aquatic types (Saprolegniales) tKe mycelium adsorbs
iood from the plant remains floating or submerged in the watery
medium. Such forms are abundant in shallow stagnant ponds
but occur in fresh water also.
Fungi also infest moist and cultivated soils. Since aeration
is necessary for the growth of hyphae, the mycelium does not
grow beyond the iirst few inches from top but it spreads laterally
and often forms filmy lattices between soil particles. Aspergillus,
Penicillium, Eurotium, Rhizopus and several Basidiomycetes
occur in the soil.
Growth of filamentous soil Fungi is usually centrifugal and
is well exemplified by the 'fairy-rings' of Agaricus. Shantz
and Piemeisel (1917) observed that in A. tabularis growth is
initiated at one point. As it spreads out, fungal action destroys
and absorbs the food. Thus the ring increases. year to year.
More than 50 species of soil Agaricus, Boletus, Lycoperdon and
Scleroderma form fairy-rings.
Several members of the Ascomycetes are completely subterranean in development.
Coprophilous Faugi grow on dang. They feed on the
nitrogenous refuse and cellulosie remains in the dung of herbivorous animals. They are capable of decomposing cellulose.
Propagation is secured by forming the spores into a projectile
which shoots out in presence of moisture. The surrounding
grass, to which the spores stick, is eaten by animals and the
spores reach the intestine only to come out associated with
dung. Generally Zygomycetes, Ascomycetes and Basidiomycetes
occur in regular succession. Perhaps the progressive development of bacteria is responsible for this succession. Light favourably influences the growth of coprophilous fox'ms. Important
examples are Muoo.r, Bhisopiis, Pilobolus, Coprinus, Ascoiolvi,
'Tesiza and Agaricus.
^
Saprophytic Fungi also occur on wood. Olomerella, Xylaria
(Ascomycetes) and Dacromyees, Tremella (Basidiomycetes) are
produced on fallen tree trunks twigs and logs. The hyphae
absorb the contents of unaltered cells by penetrating their walls
and delignifying the dead cell-walls. There is abundant secretion
of enzymes which dissolve the dead matter and help in the
penetration of the mycelium.
Moat Fungi are able to synthesize fats. Hence several genera
are reported from fatty substrate. Eurotium, Penicillium and
Aspergillus regularly occur on oily substances. Species of Empusa and Gordyceps are common on animal remains whence
they absorb and utilize fatty nutrients.
SAPRO^HYTISM ET^O.
73
TEe capacity to produce enzymes is used by Fungi in
fermentation of simple carbohydrates. It has been observed
that saprophytic species develop on the exterior of juicy fruits,
e.g., pears and' grapes. Sacharomyces, Penicilliiim glaucum,
Citromyces, and Aspergillus glaucus produce alcohol from monosaccharides. Fermentation is due to the production of zymase
which acts upon carbohydrates and breaks them into alcohol
and carbon dioxide. It has been established that the fermenting fungus acts in conjunction with species of bacteria.
Sooty molds (Meliolaceae) occur in profuse crusts on leaves
and flowers. The mycelium covers the surface of green parts but
does not usually interfere with" photosynthesis, in Gapnodium
cifrt the fungus may hinder photosynthesis. The molds usually
live on the excreta of insects and flies which visit flowers of the
host. The fungus is ephiphytic.
ThrougE forms which exhibit a variability in mode of
'tis
nutrition, the saprophytes intergrade into parasites. In the transition forms the parasites are
not obligate but can change to saproph'ytism. These are, therefore, called facultative saprophytes. De Bary showed that most
facultative saprophytes first kill the host cells and then feed
upon the dead tissue.' In obligate parasites death of the host
means death of the fungus also. Hence these forms only enter
into a close nutritional relationship with the Host, without causing necrosis.
A parasite may enter the host through stomata, lenticels or
other natural openings or through the epidermis or through
wounds. Even unspecialized hyphae may enter the host through
stomata but in most cases haustoria are produced. Direct penetration of the Host cells is partly due to mechanical and partly to
chemical means. The stimulus of contact first gives rise to an
appressorium which is a bulbous or discoid structure. The germ
tube turns inwards and enters the host cells. In several cases
enzymes are secreted to dissolve a passage for the delicate germ
tube. Rhizopus nigricans on sweet potato, Penicilliiim expansum
on apple and P. digit at urn on citrus enter mainly through
wounds.
P
The action of parasites depends upon whether they are facultative or obligate.
In facultative types, strong enzymes are produced. Toxins
are also formed. The hyphae are weak in mechanical action.
Rotting of tissues is initiated by the enzyme peetinase which
dissolves the middle lamellae of host cells allowing the cells to
separate. The soluble food is, then, readily absorbed. The insoluble matter is digested by further secretion of extracellular
fin Trirm ao:
74
SAPEOPHYTISM ETC.
In obligate parasitism tHe toxie effect of enzymes is extremely slow so that there is apparently little or no effect on the host.
Local hypertrophy or irritability-reactions soon become visible
but there is no effect on the metabolic activity of the host in early
stages. In these'balanced' parasites the power of mechanical
penetration is strong. Most of the filamentous forms produce
intercellular mycelium and send haustoria into host cells. The
h'austorium serves to absorb food from the host in the same way
as the intracellular mycelium of other forms.
There is no evidence that the prdtoplasm of the host is
attacked chemically by obligate parasites. Most of the harm is
done by the direct absorption of nutriments.
Parasitic Fungi not only attack higher plants but also other
members of the same group. A species of Penicillium has been
reported by Thom and Eaper (1945) to be parasitic on Aspergillus.
Hyperparasites are Fungi parasitic upon other parasitic Fungi.
Darluca filum, a hyperparasite, attacks Uredinales.
The existence of pathogenic forms has naturally given rise
to the phenomenon of resistance in the hosts. The basis of resistance may be mechanical or physiological. Usually the parasite
is capable of infecting two or more hosts in the same life-cycle
(Heteroecism). In other eases, the same parasite may be able to
complete the whole life-cycle on any one of a large number of
hosts. However, obligate parasites usually exhibit specialisation
in the choice of hosts. In extreme cases, one parasite is capable
of infecting a single species (monoxeny), e.g., Sclerotinia Ulcerosa
on, Anemone nemorosa and Ustilago Maydis on Zea Mays. Hosts
of several distinct species may also be attacked (polyxeny).
The researches of Eriksson have established that when a single
Sneciaiisation
species is found capable of attacking a large
*" 1 ^ "
variety of hosts, the species is usually composite,
being formed by a large number of biological forms. These
biological races donot usually differ in structure but are distinct
in their physiological behaviour. The parasitic Puccinia graminis of wheat is not able to infect barley, although the mycelial
characters of parasites occurring on the two hosts is exactly
similar.
These various 'strains', included in a single botanical species,
which differ in their capacity to infect a certain host, are termed
biological species.
To quote Butler and Jones (19i9} "Amongst those fungi which
are capable of attacking several different species of plants, many
have developed into distinct races, each of which, though outwardly similar to the others, is restricted to one or a few only, of
— thfi host plants. A special species of fungus, such as Puccinia
SAPROPHYTISM ETC.
75
graminis, may include a number of these races, similar in strueture and not to be distinguished from one another in any other
way than by their capacity for living on certain hosts
These
various races of rust are not morphologically distinct but physiologically they are
To this splitting of a parasite into specialised races on different host plants, the term 'specialisation of
parasitism' is applied..... .The races are now known as 'physiologic races'."
Elvin Stakman (1952) has done considerable work on the
genetic variations and nature and extent of phj^siologic specialization in parasitic fungi; he has attributed specialization to the
chemical heterogeneity of hosts and proved that the physiologic
races of a specialized pathogen are c[uite stable.
Parallel to this specialization of the pathogenic fungus and
coincident with it, is a specialization, of the host species. IXifferent
biological forms may also be present in a single host species, some
susceptibe and others resistent to fungal attack. Bromus racemosus is susceptible to its own Erisiphe graminis but conidia of
the fungus growing on Bromus commutatus cannot infect B. racemosus. Again, biological species of B. racemosus cannot be infected by E. graminis of the same botanical species.
It has been observed that often the specialisation of
parasite and host go hand in hand and for every biological
species of the host there is a parasitic counterpart. This specialisation is most clearly noted in case of rusts.
Besides saprophytic and parasitic forms, Fungi are also
g .. .
capable of symbiosis. In this, the fungus
ym losis
enters into a mutually beneficial relationship
with another plant body. Thus the physiological basis of Lichen
formation is primarily an advantageous metabolic alliance although it has been observed that the fungus constituent dominates
over the algal partner.
The Fungi associate symbiotically with the roots of higher
plants. This relation is known as mycorrhiza. In general, the
vascular plant derives greater benefit from such a combination
and in many cases, is unable to grow without the fungus.
In endotrophie mycorrhiza, the fungus develops profusely in
the cells of the host' with either intercellular or intracellular
mycelium, and a few branches outside. This type of association
is present in several orchids. The mycelium is restricted to nonchlorophyllous parts and is found to have a poisonous effect on
green parts. In the orchid Gastrodea elata, the basidiomycetous
Armillaria meUea is symbiotic and is said to induce flowering.
In ectotrophic mycorrhiza, the fmycelium forms a dense felt on
the rootlets. Usually the development of root-hairs is inhibited
76
SAPEOPHTTISM ETC.
and the fungus subserves their function more efficiently. In
Monotropa (Bticaceae) the fungal threads form a cushion on the
roots but leave the growing apices free. Some of the hyphae
enter the roots.
It appears that mycorrhiza is only a ease of mild parasitism.
Perhaps the attempted' attack has been controlled and utilized
by the higher plants.
Mycorrhizal infection takes 'place extensively in soils rich in
vegetable debris, humus and other refuse.
It is clear that Fungi possess a great capacity of responding
to environmental conditions. The presence of facultative forms
amply evidences this statement. Besides these they are also
capable of reacting to external stimuli concerned with nutrition
or sporulation.
Most chemotropic responses are negative and the hyphae grow
away from their toxic secretions. In nutritive media, the fungus
gives out katabolic staling substances and there are no hyphae
formed in the region of secretion.
Vegetative hyphae usually respond positivelj'^ to moisture,
although the response varies with fungal forms. Mucor has
been shown to be positively hydrotropic but Bhizopus is negatively so. Sporangiophores of Mucorales are negatively hydrotropic. Spores of rusts are discharged only when there is higli
humidity.
Light favourably affects growth and spore dissemination.
Many eoprophilous fungi such as Piloiolus, Mucor, Ascoibolus,
and Sordaria forcibly discharge their spores towards the source
of light. Light also exerts a formative influence and several
Basidiomycetes fail to form important asexual and sexual
phases unless properly illuminated.
The Fungi are positively geotropic and can grow in a wide
range of temperature conditions.
Questions
1. Give an account of the modes of nutrition in the
Fungi and illustrate with types studied by you.
2. Write a short note on specialisation of parasitism.
CHAPTER II
PHYCOMYCETES
Phycomyeetes are regarded as the primitive Fungi. The
group is rather heterogenous and approximately includes 300
genera and 1500 species.
The plant body ranges from unicellular to branched filamentous forms which typically lack septation and are coenocytic in
nature. The Chytridiales lack a true mycelium and at first show
a unicellular thallus (Karling 1932, Sparrow 1935). In Ancylistales there are simple or branched filaments. The Blastocladiales possess branched filaments differentiated into a stout
basal part and slender branches. The mycelium of Saprolegniales is also distinctly divisible into thick extra-matrical and
thin, ramose intra-matrieal parts. In Peronosporales the
mycelium is profusely branched and consists of cylindrical,
slender hyphae. The Mueorales possess thick much branched
coenocytic mycelium while in Entomophthorales the hyphae are
characterfstically septate.
It appears that while the thallus is generally coenocytic, i.e.,
non-septate and ^multinucleate', septa are commonly formed
during the development of reproductive organs or in old hyphae.
Phycomyeetes are saprophytic as well as parasitic, the latter
being intercellular or intracellular. Absorption of food is
accomplished by haustoria.
Asexual reproduction takes place by zoospores which are
endogenous, being formed in globose, multinucleate, stalked
sporangia. In aquatic forms, the sporangium commonly divides
by cleavage and the biflagellate zoospores' are naked. The
sporangia in Peronosporaceae and Albuginaceae are detachable
and" under unfavourable conditions they are capable of independent development into the mycelium. In this case the sporangium is called a conidium. Proliferation of sporangia is of
common occurrence.
THe sporangia differ in shape and size in different genera.
They may be globose, papillate, ellipsoidal or elongate. They
may occur in chains or terminally as a single bulge of the hypHal
tip.
The zoospores of saprolegniales show diplanetism (Couch
li924). The spores, when discharged from the zoosporangium,
78
PHYCOMYCBTBS
are pyriform with two apical flagella. They swim for a few
mill ates, encyst and after twenty-four hours again give rise to
zoospores with laterally inserted ilagella (Hohnk, 1933). Usually
in other orders the zoospores come to rest on a substratum and
germinate into the mycelium after discarding the cilia.
In
advanced terrestrial forms zoospores may be absent and the
sporangium may act as a conidmm (Peronospora).
Transition
forms from zoosporic to azoosporic types are also known.
Sexual reproduction also varies in the group. Forms may
be homothallic i.e., producing both kinds of gametes on the same
thallus or heterothallic, producing only one kind of gametes.
I n a few cases the gametangia are simple, undifferentiated protruberanees of the main thallus (Mucor) while in other cases
definitive gametes dissimilar in structure and function may be
formed. On this basis of isogamy and aniso or heterogamy the
Phycomycetes are clearly divisible into Zygomycetes and Oomycetes. The line dividing these two groups is, however, shown to
be hazy and intermediate forms have been described.
Gwynne-Vaughan and Barnes (1926) recognise the Phycomycetes as composed of four orders: Plasmodiophorales, Archimycetes, Oomycetes and Zygomycetes. Fitt^patrick (1930) does not
recognise these groups and enumerates eight orders while Wolf
and Wolf (1947) divide the group into eleven orders. Of these,
Peronosporales and Mucorales are the most advanced and' will
be dealt with here.
Phycomycetes are variously regarded as degenerate Algae, as
a series parallel to the Algae or as originated from Protozoa.
Bessey opined that the coenocytic condition of thalli, eonidial
formation and iso or heterogamous sexual reproduction warrant
the relationship of Phycomycetes with Alga-like ancestors.
PERONO SPORALES
The order represents the highest point of development in
Oomycetes. .There are about 300 species parasitic on higher
plants and leading a more or less terrestrial life. The aquatic
habit of the Saprolegniales is gradually lost.
The asexual reproductive bodies are borne terminally on
specialised sporangiophores and are dispersed by wind. The
zoospores are reniform.
The mycelium is usually intercellular but may be intracellular
also. The intercellular forms are obligate parasites while the
intracellular ones are "facultative saprophytes, developing well
in artificial media.
Sexual reproduction takes place by typical sex
theridia and oogonia.
PHYCOMYCETES
79
The order is divided into three families: Pythiaceae, Albuginaceae and' Peronosporaceae. Of these, only the iirst two will
be considered here.
PYTHIACEAE
The family lacks well-defined sporangiophores. The mycelium
is non-septate, eoenocytic and irregularly branched. Sporangia
are borne terminally in succession on sympodial hyphae. The
family connects Saprolegniales and Peronosporales.
1.
PHYTOPHTHOKA
PhytopMhora
is an important genus with seven Indian
species. P. colocasiae and P. infestans are the most important,
economically. The genus was first studied by de Bary (1876)
and subsequently by a number of authors (Pethybridge 1913,
Leonin 1925, and Dreehsler 1931), P. infestans which causes
potato blight was the first species to attract attention.
The mycelium is *non-septate and intercellular sending haustoria inside the host cells. It induiies pronounced hypertrophy
and rot of plant parts. P . infestans destroys the aerial as well
as subterranean parts of potato while P. palmivora attacks
palms. I n general, Phytophthora is a destructive parasite, though
saprophytic species are also known.
During asexual reproduction, slender sparsely branched
hyphae, sporangiophores, emerge from stomata in clusters. Each
sporangiophore cuts off at the apex a multinucleate, oval to obpyriform papillate sporangium. Each sporangium is a yellowish
hyaline body with a terminal papilla. The number of nuclei is
not definite.
Germination of the sporangium is governed by moisture conditions. I n absence of water the sporangium germinates directly
by germ tubes and forms the mycelium. In this case it is ffesig, nated a conidium. In presence of moisture, the contents of the
sporangium divide into a number of uninucleate, kidney-shaped,
biciliate zoospores. The sporangium ruptures due to absorption
of moisture and the naked zoospores are liberated. I n P. palmivora the zoospores are liberated" into an ephemeral vesicle, but
in most cases they are differentiated inside the sporangium and
are liberated by its rupture.
The zoospores soon cast away the cilia and become round. A
wall is secreted round them. A small germ tube comes out and
enters a host cell either through stomata or by breaking through"
tEe epidermis.
Asexual reproduction also takes place by terminal or intercalary thick-walled chlamydospores. These are non-papillate and
formed for unfavourable periods.
80
PHYCOMYCBTBS
Aiitlieridia and oogonia arise on. lateral brancKes. PetHybridge
(1013) divided the genus into two groups, infestans and cactonctn,
on the basis of the relation between antheridia and oogonia. In
the infestans group, the antheridium is amphigynous: the oogonial
brancii penetrates tbe antheridial branch and emerges on the
other side where a globose oogoniurm is cut off. The antheridium
is, thus, seen to form a collar at the base of the oogonium. In
coctoruvi group the antheridium is paragynous, i.e., laterally applied to the oogonium.
The oogonium as well as antheridium is multinucleate at origin.
Before septa delimit them, their nuclei divide so that in the
oogonium the number nearly reaches 30 while in the antheridium
it is less than 10.
At this stage, the protoplasm becomes vacuolated and nuclei
degenerate. Only 8-9 nuclei are left in the oogonium and 4-5 in
^the antheridium. Nuclear division takes place again and nuclei
" are uniformly distributed.
Fig, 28.—Phytophthora. A, An infected leaf; B, A portion of finfected
tissue with haustoria and papillate zoosporangia; G—B, Formation of zoospores; P, Germination of a conidium; G, H, Sex
organs of P . m/estans (amphigynous antheridium); J, Sex
organs of P. cactorum (paragynous antheridium) ; K, Zygote;
M, Germination of zygote.
In the oogonium, two zones can be distinguished. In the
peripheral periplasm most of the nuclei degenerate. Only one
PHTCOMYCBTES
nucleus remains in the ooplasm.
coenocentrum in P . cambivora.
81
Alain (1935) Has deseribeJa
THe antlieridium is mature by this time and contains a single
male nucleus. The wall at the contact jjoint between the antheridium and oogonium bulges into the former to form an oogonial
receptive papilla. The antheridium sends out a fertilization tube
at this point and ft liberates the single male nucleus near the
centre of ooplasm, along with some cytoplasm.
The plasm of both strains unites fplasmogamy) but the nuclei
remain distinct. A wall is laid down around the oospore. The
zygote undergoes rest in a binucleate phase. F a t globules appear
in the cytoplasm and all fuse to form a single large drop. The
fat drop is eccentric.
After a lapse of 3-5 weeks the male and female nuclei fuse
(caryogamy). The wall of the oospore is composed of an outer
exospore and inner endospore. The fat globule and endospore are
digested prior to germination. The fusion nucleus enlarges and
divides. The first division is reduction and" halves the number of
chromosomes.
The oospore gives out a germ tube which penetrates the host
cells and develops into a m^ycelium.
In the allied genus Pythium, the asexual zoospores are liberated
as well as differentiated in a short-lived vesicle (Butler 1907), as
against PhytopJithora where the vesicle is extremely rare. Fitzpatrick (1923) thinks that there is no satisfactory basis for
generic se,paration of the two forms.
ALEUGINA-CEAE
The family contains the single genus Albugo or Cystopus with
nearly 25 species. Butler and Bisby (1931) report 7 species of
Albuga from India, A. Candida and A. hliti being most important. The endoparasite is obligate and attacks members of the
Cruciferte, Amarantaee^, Compositae. and Convolvulacese. A.
Candida attacks mustard, turnip, cabbage, radish, and cauliflower;
A. hliti attacks species of Amaranthus while A. tragopaganis is
restricted to Compositae. The fungus is also termed white rust.
The fungus causes hypertrophy and deformation of plant
parts. In each botanical species, specialisation has led to the
formation of several biological forms which are restricted to
definite host species.
The mycelium is strictly intercellular. Knob-like haustoria
are sent into the host cells. There are no septa in the hyphae and
the condition is characteristically ccenocytic.
11.
82
PHTCOMTOETBS
In asexual reproduction, Eyphae collect beneatli the epidermis
of the host at several places and branch profusely. From this
mycelium arise erect sporangiophores arranged in a compact
group like a palisade layer. Each sporangiophore is short, unbranehed and broadly clavate from the apex of which sporangia
are abstricted in chains basipetally. The compact collection of
sporangiophores gives rise to a white shining pustule which appears at several places on the leaf after rupturing the epidermis.
This fact has been responsible in giving to the fungus, the name
'white rust'.
Bach sporangium is a multinucleate globose body. Between
successive sporangia a disjunctor intercalary cell is present. It
is usually made up of callose and is sterile. As the epidermis
ruptures, the sporangia and disjunctors are exposed to the atmosphere. Callose undergoes modification due to the presence of
moisture and the sporangia are liberated.
As in Phytophthora, the sporangia may germinate in two
ways^. The germination may be direct (Melhus 191.1, Palm 1932)
and IS governed by temperature conditions and lack of moistuz^e.
If the sporangium germinates directlj^ it is known as conidium.
29.—Cystopus. A, E, Infected leaves; 0," Intercellular mycelium
forming sporangiophores and sporangia; t)—F, formation of
sporangia; G, H, Fertilization; J—L, Zygote with ephemeral
vesicle and zoospores.
In presence of water, however, the contents of the sporangium are cleaved into 12-20 naked zoospores. Each of these is
PHYCOMYCETES
83
biciliate, reniform and uninucleate. After a brief perioa' of
swimming, the zoospore comes to rest, secretes a wall and gives
out the germ-tube which enters the host through a stoma.
The sex organs of Albugo begin to appear when sporangia
gradually disappear. Oogonia and antheridia are formed within
the host tissue. The delimitation of each organ is preceded by
an inflow of cytoplasm and nuclei so that both organs are multinucleate initially (De Bary).
• The details of fertilization differ in different species.
In A. Candida the oogonium contains 100 nuclei and before
it is delimited the nuclei undergo division. The antheridium
contains 6-12 nuclei. At the point of contact, the oogonial wall
pushes slightly into the antheridium to form the receptive spot,
(Wager 1896) or papilla (Stevens 1899). The papilla, however,
soon disappears and the antheridium gives out a fertilization
tube at the same spot.
Fig. 30,—Cystopiis. A, chains of sporangia; B—D, Germination of a
sporangium; E, Zoospore; F—G, Germination and infection
by a zoospore; H—J, Germination and infection by a conidium; K, Intercellular mycelium"witli haustoria.
Meanwhile, the protoplasm of the oogonium is differentiated into a peripheral denser and non-vacuolated zone called
periplasm and a central vacuolated ooplasm. The nuclei of the
oogonium migrate to the periplasm although a few are left in the
ooplasm. The nuclei of the antheridium and ooplasm undergo a
mitotic division. The periplasm nuclei remain inactive and show
a tendency to degeneration. Coincident with the mitotic division, there, appears in the centre of the ooplasm a deeply staining
84
PHYCOMYCETES
protoplasmic body called coenocentrtiin. I t is several times the
si^e of the nirclei and is granular. Following its appearance, a
single female nucleus shifts to the centre of ooplasm while the
rest pass out to the periplasm.
There is a single functional male nucleus which migrates
through the fertilization tube to the centre of ooplasm and fuses
with the female nucleus. The coenocentrum disappears and the
zygote secretes a thick wall around itself. The fusion nucleus
undergoes five simultaneous divisions (Wager 1896) and before
entering dormancy possesses nearly 30 nuclei (Fitzpatrick
1930).
I n Albugo hliti there are nearly 300 nuclei in the oogonium
and 35 in the antheridium. The receptive papilla is very prominent. I n the stage of zonation (Stevens 1901) there is an
outer periplasm, a dividing layer of nuclei and a central homogenous ooplasm with 50 nuclei. Nuclei in the antheridium number nearly 70. A division of antheridial and ooplasm-nuclei
doubles their number. After fertilization nearly 100 fusion
nuclei are formed and extra male nuclei degenerate. A similar
condition is reported in A, portulacae
(Stevens 1940) and
A. molluginicola (SafeeuUa and Thirumalaehar 1951).
I n A. tragopagonis the initial condition is similar to A. hliti, i.e.,
multinucleate. • The receptive papilla is feebly developed. The
coenocentrum is large. There is a single functional female nucleus
which fuses with a single male nucleus while the extra male
nuclei degenerate in the ooplasm. On rest the zygote is multinucleate.
The wall of the zygote is sculptured and is made up of three
layers. The sculpturing is different in different species ("Wilson
1907).
After the period of dormancy, the wall of the zygote bursts
and the endospore comes out in the form of a vesicle. The nuclei
had meanwhile divided twice or thrice. Nearly a hundred zoospores are formed, each reniform and biciliate. The vesicle bursts
and the zoospores are liberated. Each swims for a short while,
encysts and gives out a germ tube.
The important features of the life history of Albugo are the
palisade-like unbranched sporangiophores, multinucleate sex organs showing a variance in functional nuclei, coenocentrum and
coeno-zygote. The first two divisions of the zygote constitute
reduction.
MUCORALES
The Mucorales are widely distributed with about 30 genera
and 450 species. In general they are saprophytes and are called
PHTCOMYCETES
85
'black molds'. A few forms are pathogenic. Rhizopus nigricans
is concerned in the decay of sweet potatoes while Absidia corymbifera causes human bronchomycosis. Species of Piloibolus, Mucor
and Rhizopus are cpprophilous while Mortierella and Piptocephalis
are hyperparasites.
The mycelium is stout, eoenocytic and richly branched. The
older hyphae are often divided into plurinucleate segments.
Often the mycelium develops stolon-like prostrate and rhizoidal
subterranean parts.
Asexual reproduction takes place by aplanospores which are
formed in sporangia. In Pilobalus the sporangial contents divide into uninucleate parts but before liberation, divisions take
place in each so that the mature spores are multinucleate. I n
Rhizopus and Phycomyces the spores are multinucleate initially
and do not undergo nuclear division. I n these^forms the development is endogenous. In Cunninghamella
and
Syncephalastrum
exogenous sporangia are developed at the ends of sterigmata on
sporangiophores. These act directly in the former but divide to
form spores in the latter genus.
The sporangia usually possess columella in the Mucoraceae.
Sexual reproduction is isogamous. Lateral branches of adjacent hyphae act as progametangia and bear terminal aplanogametes. The zygote possessed a thick many layered wall.
I n a study of sexuality in the Mucorales, it is seen that
zygospores occur frequently in nature in certain species. I n
other forms, however, zygospores are rarely seen. Early investigators considered that the latter condition was due to environmental effect.
Blakeslee (1904) working on Mucor mucedo found that species
of Mucorales fall into two broad categories. I n the first, designated homothallic, zygospores could be formed by gametangia
arising from the same mycelium, i.e., if a single spore be allowed
to germinate in artificial medium to form the mycelium,
zygospores will be produced by fusion of gametangia formed on
this mycelium. In the second category, designated heterothallic,
zygospores could not be formed unless mycelia of two different
spores (of different sporangia) unite. Then these two mycelia
probably belong to different strains, designated + and — by
Blakeslee'. The mycelia did not differ in structure but probably there was a physiological segregation of sexes.
Sporodinid grandis, Absidia spinosa and Rhizopus sexualis
belong to the homothallic category while Mucor mucedo, Rhizopus
nigricans, and Phycomyces nitens are heterothallic.
86
PHYCOMYCETES
BurgefE (1924) believed that
segregation of sexes took
place when the zygospore germinated. Heterothallic
forms
arose by immediate germination of the zygospore whereas
homothallie forms resulted from a zyg;pspore nndergoing
dormancy.
The Mncorales have been classified by Cutter (1942) into four
patterns on the basis of nuclear behaviour. I n some forms all functional nuclei of the zygospore fuse in pairs, undergo reduction and
become dormant. In Rhizopus, paired nuclei fuse but all extra
nuclei degenerate before dormancy begins. Eeduction division
takes place when zygospores germinate. I n Phycomyces, paired
nuclei fuse when zygospore germinates, but extra nuclei donot
degenerate. I n Sporodinia nuclear fusions donot take place.
Gwynne-Vaughan and Barnes have divided Mucorales into
seven families. The order will be represented here by the
.Mucoraceae.
MUCORACEAE
The family is characterised by globose to pyriform sporangia
with numerous uni or multicluneate spores. The columella is
well developed.
The zygospore is formed from whole of the
two aplanogametes.
MucoR
In Mucor which grows commonly on dung, staling bread and
decaying cheese, the mycelium is^ non-septate and coenocytic.
The hyphae are prostrate but the sporangiophores are erect.
M. javanicus causes alcoholic fermentation while M. pusillus
is associated with human mycosis. Butler and Bisby (1931)
have reported M. glomerula, M, plumheus, M. praini and
M. racemosus from India. The species are saprophytic.
I n nutrient media, septations appear in the mycelium. Each
multinucleate cell develops an oidium or oidiospore which is
capable of budding and producing the normal mycelium. This
is known as the torula condition.
D uring the asexual phase, the prostrate ramifying mycelium
gives rise to stout aerial branches called sporangiophores. The
apex of the sporangiophore bulges and is filled with dense
cytoplasm and a large number of nuclei. A transverse septum
is laid down separating the globose aptex, the sporangium. At
maturity the sporangium possess a well-developed columella.
The older view that the columella is formed by an invagination of the septum was shown to be erroneous by Cutter (1942).
Working on_M. genevensis, he found that at maturity the
cytoplasm of the sporangium is differentiated into two zones, a
peripheral sporogenous and a central sterile. A heavy wall is
PHYGOMYCETES
87
laid down-at the line of separation and the enclosed region
forms the columella.
Moreau (1913) in M. spinescens
and
Cutter
(1942)
in M. genevensis and M. hiemalis have described spore
formation. "The sporangiophores are unbranched and at their
ends terminal swellings develop into which considerable amount
of cytoplasm is carried. Mitotic nuclear divisions take place
with great rapidity in the sporangial fundament. As the
fundament reaches its maximum size the cytoplasm becomes
differentiated into a peripheral sporogenous layer which contains
most of the nuclei and, an internal more or less sterile region
which ultimately becomes the site of the columella. This stage
is of short duration and then numerous vacuoles appear in the
fertile zone and divide the cytoplasm into many multinucleate
blocks. These blocks may contain as many as 15-20 nuclei
I t must be emphatically stated that the columella does not arise
by the upward burgeoning of the septum which is usually
formed below the sporangial fundament." {M. genevensis).
oc o
Fig. 31.—Mucor. A," Mycelium with erect sporangiophores; B—Fj
Formation and libeartion of asexual spores; Q—K, Stages
in conjugation of aplanogametes; L, Germination of a
zygospore.
The sporangium undergoes slight contraction and simultaneously vacuoles appear in the fertile zone. The vacuoles
8
PHYCOMYCETES
form the cleavage planes of multinucleate spores. All tlie
protoplasm is not used up in the formation of spores; whatever
is left gives rise to a gelatinous mass which by absorption of
water swells and ruptures the sporangium. In some species
Uninucleate spores have been described. Each spore after
liberation gives out a germ tube and forms a new mycelium.
Mucor is heterothallic. Safina and Blakeslee (1928) have
pointed out that there are biochemical differences in the sex
strains of Mucor. In M. racemosus, Harris (1948) has reported
differences of antibiotic behaviour between + and — strains.
Sex organs are formed on mycelia arising from different spores
(of different sporangia). Two juxtaposed hyphae give rise to
lateral branches called progametangia. In the apices of these,
numerous nuclei and dense cytoplasm are seen to accumulate.
The tips are then cut off by septa and are the typical undifferentiated aplanogametes. The proximal part of the progametangia are known as suspensors. The gametes are multinucleate
and are often known as coenogametes.
The wall at the point of contact is gradually absoi^bed
(isogamy) and the nuclei "fuse in pairs. According to Cutter
^1942), reduction division takes place at once and the zygospore
undergoes dormancy (9 months). It is also possible that reduction takes place after dormancy but before germination. The
zygospore is double-walled and the outer exosporium is rough
cuticularised and reticulate. Segregation of sexes is complete
at meiosis, i.e., before the formation of germ sporangiophore
from the zygospore (Cutter, 1942).
On germination, the endosporium comes out in the form of
a simple or branched germ-sporangium called promycelium. It
bears at its apex a single globular sporagium which at maturity,
possesses columella and multinucleate spores. The spores can
reproduce the plant by forming a new mycelium.
2.
EHIZOPUS
In the allied genus Bhizopus the mycelium is differentiated
into stolon-like prostrate parts which give off subterranean
rhizoids wherever they come in contact with the substratum.
There are 35 species of which R, nigricans, B. cambodja -and
B. artocarpi are common in India.
At each 'node' of the stolon, arise erect branched tufts of
sporangiophores each bearing a globular sporangium. The
columella is dome-shaped. Swingle (1903) found that vacuolar
cleavage of the peripheral sporogenous region results in the
PHYCOMYCBTBS
89
formation of mxiltmiicleate spores whicK round ;>p and form
membranes around themselves.
Fig. 32.-^Bhisopus.
A, Mycelium with stolons, rliizoids and sporangiop h o r e s ; B — P , Poi-mation of spores; E — J , Formation of
zygospore; K, G'ermination of a zygospore.
I n unfavourable conditions the mycelia of opposite strains
form zygospores (heterothallic). The lateral progametangia cut
off at their distal ends coenogamet'es which fuse (anisogamy).
The nuclei of the two non-motile gametes fuse in pairs but the
supernumerary nuclei degenerate before dormancy begins.
Reduction of chromosome number is delayed till germination of
the warted zygospore. The promycelium forms an apical sporangium as in Mucor. The spores from this develop into the
mycelium.
I n Mucor as well as Bhisopus the suspensors of gametes lack
outgrowths.
I n reviewing the principal genera of Phycomycetes tendency
toward septation and degeneration of sex become apparent. I n
Phytophthora, there were single male and female nuclei. I n
species of Cystopus theiv number was variable and the fusion
function
xvfl'.^ n o t
lVf>,friati^i^
t^
rlpfitiitA ......T,.^. _ T _ _ , . .
90
PHYCOMYCETES
Bhizopus there was drop from oogamy to isogamy and a complete
loss of definitive sex organs.
Questions
1. Describe .the life history of Cystopus.
{Allahabad, 1948, 1951).
2. Give the systematic position of Cystopus. Where does
it occur? Describe the sexual method of reproduction
in it.
{Allahabad, 1^2).
3. Describe the life history of Phytophthora on any host
you have studied, and state its mode of infection.
(Allahabad, 1950).
4. "Write an illustrated note on the structure of the thallus
and modes of reproduction in Bhizopus. {Agra, 1949).
5. Give an account of the structure and life history of
Mucor. Explain the phenomenon of heterothallism.
6. (a) Give a comparative account of the germination of
Cystopus and Phytophthora.
{b) What is meant by heterothallism ?
{Allahabad, 946).
7. Describe the process of sexual reproduction in Cystopus
and compare it with that of VaucJieria. . {Agra, 1950),
CHAPTER III
ASCOMYCETES
Bessey (1950) believes that the Ascomycetes form a group
of the higher Fungi, the Carpomyeetes. The Carpomycetes differ
from the lower Fungi, Phyeomyeetes, in their adaptations to
terrestrial conditions, septate mycelium, absence of cellulose
from cell walls, non-motile asexual spores and distinct sexual
reproduction which shows degeneration. Estimates of the number of species comprising the Ascomycetes differ from 15000
(Gwynne-Vaughan, 1922) to 25-35,000 (Wolf and Wolf, 1947).
The mycelium is richly branched and consists of septate
hyphae (except in the yeasts). The hyphal segments are uninucleate although in some forms rapid nuclear division may give
rise to the plurinucleate condition. Forms are parasitic as well
as saprophytic.
Asexual reproduction takes place by exogenous eonidia
abstricted at the apices of erect conidiophores. The eonidia may
be formed singly or in chains. The conidiophore may be branched or unbranehed.
The characteristic result of sexual fusion is the ascus, which
produces endogenous ascospores. The sexual process was first
studied by de Bary in 1870. Sexuality in the group shows progressive degeneration. A complete series is traceable from forms
with well-developed sex organe to those in which vegetative cells
subserve the gametic function.
There are mulinucleate sex
organs in Asco^desmis, Ascobolus and Pyronema, and uninucleate
in Endomyces, Erysiphe and Sphaerotheca. There are multicellular oogonial structures in .4.SCO&OZMS and Ascoplianus; unii_cellular in Erysiphe, Pyronema, Sphaerotheca. Species may have
functional trichogynes {Ascodesmis, Pyronema); non-functional
ones (Laboulbenia); or none at all {(Erysiphe, Taphrina). A
few produce spermatia, functional or otherwise, but most species
do not. Some have simple ascogenous hyphae {Ascodesmis,
Sphaerotheca); some branching ones (Erysiphe, Pyronema),
and some none at all {Eremascus). Normal sexual process is
variously modified. In all likelihood there was a time when all
the species possessed sexual reproduction of the normal type.
Evolutionary tendencies arising independently in different
orders, and at different times, have brought about many modifications of it and even its total loss,
92
ASCOMYCETES
The ascus contains 8 ascospores in the normal eases. In
Saccharomyces and Endoniyces, only 4 spores are formed due
to fewer divisions; Failure of all nuclei to organise spores may
also reduce the number to 1 in Tuber and 2 in PhyZlactinia. In
the case of Podospora curvicolla, however, additional divisions
result in 128 spores.
In most eases the fusion product is surrounded by a sterile
laj^er of hyphae, *result being a fructification called aseoearp.
In primitive forms the asci are scattered irregularly; in others
where it is present, it is at first open and cup-shaped (Apothe- •
cium). Gradually flask-shaped and closed aseocarps (Perithecia)
are developed.
Associated with the variations in the morphology of the
sexual apparatus, is the lack of uniformity in nuclear behaviour.
Fig, 33.—Nuclear plianaes in Aseotnycetes; A—D, Formation of zygote
(2x) ; F—G, Aseogenous hypha; H, Fusion in penultimate
cell (2x—double); J, Heterotypic reauetion division; K,
Homotypie division (4 nuclei); M. Braehymeiosis (8 nuclei)
resulting in the mature asens formation.
Dangeard (1894) observed nuclear fusion in the ascus of
Peziza vesiculosa, but interpreted the ascus as an egg cell. . In
1895, Harper reporting his studies on Sphaerotheea Jiumuli
confirmed Dangeard's observation on the nuclear fusion in the
ascus but showed that it is preceded by a regular fertilization
process in the-oogonium. Harner found that the antheridium
ASCOMYCETBS
93
and the oogonium were unimicleate at the time of fusion. Fertilization was effected after tlie discharge of the male nucleus into
the oogonium. The resultant zygote, however, developed into an
aseogenous hypha which was crozier shaped at the apes. The
penultimate or subterminal cell of this hypha contained two
nuclei. Each of these nuclei was diploid. The two nuclei
fused to give rise to a definite nucleus (double-diploid).
The
ascus was formed' from the penultimate cell.
The complete process of nuclear fusion and division can be
summarized t h u s :
1. First nuclear fusion, of haploid nuclei in the oogonium;
result: diplaid number of chromosomes in the zygote.
2. Formation of an aseogenous hypha, the penultimate
cell containing 2 diploid nuclei.
3. Second nuclear fusion, of diploid nuclei in the penultimate cell; result: doitSJe-cZipJoi'd number of chromosomes in the
definite nucleus.
4. First division of the definite nucleus (double-diploid) —
heterotypic (resulting in daughter nuclei different in constitution
from the p a r e n t ) ; result: 2 diploid nuclei formed.
5. Second division of the 2 diploid nuclei
homMypic
(resulting in daughter nuclei similar to the parent in constitution) ; result: 4 diploid nuclei formed.
Divisions 4 and 5 together constitute the first reduction
division.
6. Third division of each of the 4 diploid nuclei into
8 haploid nuclei. There is again a reduction in the number of
chromosomes, and this division constitutes the second reduction,
also called brachymeiotic division.
I t is known that in the life-cycle of most Fungi, a single
sexual fusion takes place and the zygote (diploid) undergoes a
single reduction division to restore the haploid number of chromosomes in the gametophyte. But according to Harper, in the
life-cycle of Sphaerotheca, there are two fusions and consequently two reduction divisions. Harper confirmed these steps
for Enjsiphe polygoni (1896) and Pyronema confluens (1900).
Harper's contentions in regard to two fusions and two
reductions have been upheld by Blackman and Fraser (1905),
and Gwynne-Vaughan and Williamson (1931).
Dangeard (1907) also investigated Pyronema but did not
believe that there was a migration of male nuclei to oogonium.
Claussen (1906, 1907, 1912) studying the same fungus
stated that although there was a migration of male nuclei, there
was no sexual fusion.
Instead, the sexual nuclei united in a
94
ASCOMYCETBS
dicaryon phase and fused only in the penultimate cell. Thus
there was a single fusion.
Tandy (1927) thought that in P. domesticum some of the
antheridial and oogonial nuclei fused while others did not.
Morean and Moreau (1931) reject the view of Claussen,
They did not find any nuclear migration in the oogonium.
The case of two fusions and two reductions has been
vigorously stated by Gwynne-Vaughan and Williamson (1932),
but evidence as to the absence of these is equally convincing for
certain other aseomycetous species. Swingle (1934) in a review
of the various views has concluded that there are two fusions in
Erysiphe, Humaria, Pyronema and Sphaerotheca ; but only one
fusion takes place in Eremascus, Taphrina etc. I t cannot be said
that either all Ascomycetes have two or one nuclear fusion in
their life-cycle.
Martens (1946), in a critical essay on the developmental
cycles and sexuality of Ascomycetes has held that the theory of
Dangeard and Moreau regarding a parthenogenetic development
of asci stands refuted. Shear and Dodge (1927) and Dodge
(1931) have also proved this point. Martens (1946) believes that
brachjmeiosis can hardly be considered to be general or validly
demonstrated and that brachymeiotic species represent, at best,
exceptional cases.
Hirsch (1950) has shown that there is no brachymeiosis in
Pyronema confluens, but Wilson (1952) has again demonstrated
the opposite view*.
Whitehouse (1951) contends that genetic studies of most
Ascomycetes do not support the two-fusion-two-reduction theory
of Harper.
The universal occurrence of asci and ascospores in
Ascomycetes supports the view that they are monophyletic.
Sachs (1875) proposed that they originated from RhodophycesE
while d e B a r y (1887) considered them to be phycomycetean in
origin.
Gwynne-Vaughan and Banies (1951) divide the group
into three classes:
1. Plectomycetes: Asci irregular, open or covered with a
shield-shaped perithecium.
2. Discomycetes: Asci regular in an apothecium.
3. Pyrenomycetes: Asci regular in a perithecium.
Only the first two classes will be described here.
PLECTOMYCETES
The group includes forms which lack the apothecial and
perithecial ascocarps of advanced types but contain either no
ASCOMTCETES
95
ascocarp or one witH no ostiole. TEe asci are arranged irregularly and are club-shaped, pyriform or oval. I n some forms
there is no mycelium (SaccharomycetaceEe).
Classification has been based on the characters of ascus and
ascocarp. In the Plcctaseales the asci are irregular with a loose
sterile waft of gametophytic filaments in some cases. I n the
Erysiphales the asci are grouped together in globular perithecia which open either by decay or an irregular rfUpture or
slit. I n the Exoascales, the asci are exposed. They are parallel
and grow out between epidermal cells of the host.
The Plectascales are divided into three parts, with naked
asci, with subserial ascocarps and with subterranean ascocarps.
The important families are Saccharomycetaeeae and Aspergillaceae.
The perithecia of Erysiphales have a thin and membranous
peridium. The number of asci in a fructification varies but,
where numerous, they are more or less parallel to each other.
The perithecia possess appendages in the family Erysiphaeeae.
The Exoascales are obligate parasites. The asci are naked.
Asexual reproduction is not known, neither are the details of •
sexual reproduction.
1.
YEAST
Saccharomyces or Yeast was first studied by Leeuwenhock
in 1680. I t occurs on fruits especially grapes and apples and
on all kinds of sugary media. Important species are iS*.
cerevisiae, S. elUpsoideus or wine yeast, S. piriformis or gingerbeer yeast and S. sake. The genus is a saprophyte.
There is no mycelium. The fungus occurs as separate cells
but in rare cases a tendency to form chained mycelium is seen.
iS. Ludwigii
behaves in this way when grown on gelatin and
-S. pomie grown on beer-wort. The individual cells are round
to elliptical with a delicate cell-membrane enclosing a large
vacuole. I n the cytoplasm refractive granules of volutin, globules
of oil and particles of glycogen are present. Mitochondria have
been seen by Guilliermond (1902). Wager and Peniston (1910)
thought that the vacuole is, in reality, a nucleus with traversing
chromatin filaments, and an external nucleolus. Guilliermond
(1910), however, established that the nucleolus of Wager is the
t r u e nucleus and there is a central vacuole. Lindegren (1945)
after extensive genetic studies on yeast, has supported Wager
a n d Peniston. Eanganathan and Subramaniam (1948) criticize
Lindegren and agree with Guilliermond. Delamater (1949) also
supports Guilliermond in considering the nucleus and vacuole
of yeasts.
96
ASCOMYCETES
Vegetative reproduction is by budding or fission. Each
cell gives oS. a small round protruberance. The nucleus divides
amitotically and a daughter nucleus goes to the bud. It is then
cut off by a septum and separated. By repetition of this process,
a large number of cells may be formed.
Asexual reproduction is by endospores which are formed
in enlarged cells called sporangia. The nucleus divides twice
to form four nuclei which organise themselves into endospores.
All protoplasm is not used up in this process, a little epiplasm
being left. Each endospore grows and buds off new cells.
Fig. 34.—Yeast. A, A mature cell witli Bueleus and vacuole traversed by
chromatin filaments (Wager, 1910); B—B, Vegetative multiplicatiou by budding; E, F, Formation of endospores; G-,
Germination of endospores; H—K, Isogamous conjugation
and germination of zygote.
Definite sex organs are lacking but often vegetative cells have
been observed in the process of copulation. The fusing individuals
come nearer and give out copulating processes which join each
other. A bridge is formed by the dissolution of the intervening
wall. The fusion nucleus divides immediately and the two
daughter nuclei return to the two cells. Another division takes
place here and the four resultant nuclei are formed into ascospores. The whole structure can be called an ascus. There is a
single fusion, a single reduction and only four ascospores.
The fusing individuals may be similar (isogamy) or dissimilar
(heterogamy). Intermediate stages are also present. The rupture of ascus wall liberates the ascospores which bud off new
cells.
In (S'. Ludwigii the ascospores have been observed in the process of conjugation.
ASCOMYCETES
97
QUiUiermond (1920) has sHown tHat two types of alternations
can be possible:
1. The -vegetative cells are diploid; spores haploid and
fusion of spores restores the diploid number.
2. The vegetative cells are haploid; they unite to form diploid aseus which forms haploid ascospoi'es.
Guilliermond (1909) postulated that yeasts are derived from
forms which possessed the normal mycelium. The unicellular
condition is due to their peculiar mode of nutrition. According
to this view yeasts are reduced forms.
Yeast is included in Fungi due mainly to the absence of chlorophyll from its cells, saprophytic nutrition, torula condition and
presence of fungal cellulose in cell walls.
The occurrence of torula condition and formation of asci and
ascospo^'es places the genus under Ascomycetes.
2.
ASPERGILLUS
The genus is also known as Eurotium. and occurs saprophytically or parasitically on a wide variety of media. It has been
studied thoroughly by Thorn and Church (1926) and Thorn and
Raper (1945).
The mycelium is richly branched, of septate multinucleate
cells. The hyphae ramify in and" on the substratum.
In asexual reproduction, the prostrate hyphal system gives off
erect conidiophores which are non-septate. The distal end of the
conidiophore swells up into a globose to elliptical head bearing irradiating bottle-shaped sterigmata. The starigmata bear conidia in
chains. Often there are two layers of sterigmata, one above the
other. Nuclei stream up through the conidiophore to the conidia.
In the figures described by Thom and Church, the conidia are
separated by sterile disjunctors.
The perithecial stage was first described as Eurotium Jierbariorum and de Bary (1854) showed that it is genetically connected
with Aspergillus glaucus described as conidial stage.
The female organ, archicarp arises at the end of a hypha which
becomes coiled. Three parts can be distinguished, terminal unicellular trichogyne, middle unicellular ascogonium and basal
multicellular stalk. Like the segments of the mycelium, each
part of the archicarp is multinucleate. From the same mycelium,
there arises a multinucleate antheridial branch at the base of the
archicarp. It cuts oif a terminal antheridium which archeg over
the archicarp and sometimes coils round it. The intervening
wall dissolves and probably the male and female nuclei fuse in
pairs. In some cases the antheridium was found to fuse with the
98
ASCOMYCETBS
Mchiogyne. Dangeard (1907) found no antheridium in A. flavus
and A. fischeri and in these cases, perhaps, the ascogonial nuclei
fuse in pairs.
Fig. 35,—Aspergillus.
A, Branched myeeliumj B—E, formation of
conidia; J1, Germinating eonidium; G, H, Sex organs; J,
Ascogenous hypha in a perithecium; K, Asci in a perithecium.
The fusion product develops ascogenous hyphae whose penultimate cells form asci. A loose sterile tissue is developed from the
stalk cells of the archicarp and antheridium and encloses the
developing oval asci. On maturing the perithecium is ruptured
and small multinucleate ascospores are liberated. Bach of these
can germinate to form the coenocytic mycelium,
Thom and Eaper (1945) divide the genus into 14 groups on
the basis of. colour of stalks and heads, shape of heads, shape of
conidia and one or two series of sterigmata.
Among important species are A. glaucus, A. flavus, A. oryzae
and A. wentii causing walnut-rot; J., nzfirer causing rot of figs,
dates and pomegranates; A. fumigalus, A. flavus, A. niger and
A. nidulans causing human otomycosis. A. glaucus occurs on
ASCOMYCBTES
99
stale bread, soiled clothes and drenched leather, several species
are capable of inciting fermentation.
3.
SPHAEROTHECA
The fungus occurs as obligate parasite on young shoots, leaves
and intlorescenes of dicotyledons. S. mors-ii-uae is the gooseberry
mildew, S. humuli strawberry mildew, S. pannosa rose mildew
and S. casiagnei hopmildew.
The mycelium is made up of uninucleate cells and is richly
branched, forming a soft felt-like mass on the attacked parts of
the host. The profusion of this ectoparasitie mycelium imparts
to the infected parts a mealy appearance. The mycelium sends
haustoria in epidermal cells of the host.
?
While reproducing asexually, the superficial mycelium forms
erect aerial conidiophores arising as simple protruberances. At
the apex of each conidiophore, oval uninucleate hyaline conidia
are formed in basipetal chains. The conidium can put out a
germ tube which ramifies into a mycelium.
Fig. 36.—Sphaerotheca. A, A portion of the branched myeelium; B—H,
Formation of conidia; J, K, Stages in conjugation; L, M,
Development of a the perithecium.
Sex organs arise as erect appendages of the prostrate myeelium. The antheridium and oogonium are closely juxtaposed.
The antheridium is a cylindrical uninucleate organ borne at the
top of a small stalk, The oogonium is ellipsoidal and uninucleate.
100
V >~^
J
ASCOMYCBTES
Fusion of sex nuclei takes place when the intervening wall dissolves (Harper 1895). The zygote becomes septate, the penultimate cell containing two nuclei. A second fusion takes place
here and the cell enlarges to form a single large aseus. Other
cells of the ascogenous hypha degenerate. Meanwhile, as the
definite nucleus undergoes two reductions to form eight ascospores, the stalk of the oogonium branches to produce a sheath of
sterile cells, the peridium. These cells branch inwards and two
zones of cortex and nurse cells are formed^. The mature perithecium possesses branched or unbranched appendages originating in superficial cells.
According to Blaekman and Fraser (1905) two fusions and
two reductions take place (cf. page 108, 109) but Dangeard
(1907) and "Winge (lOll) are of opinion that fertilization does
not take place in the oogonium. Male and female nuclei associate
in a dicaryon condition and the only fusion t^ikes place in the
penultimate cell. Thus there is only one fusion and one reduction.
The rupture of perithecium and ascus membrane liberates
the uninucleate ascospores which germinate to form the mycelium.
A high degree of specialization has been developed in these
powdry mildews.
DISCOMYCETES
The Discomycetes possess disk-like or cup-shaped fructifications with the hymenium exposed at maturity. There are nearly
500 species. Initially the ascoearp is closed by a thin peridium
but this ruptures at maturity due to the growth of asci and
paraphyses.
The group has been classified on the basis of the extent to
which the hymenium is exposed at maturity. In the two orders
Pezizales and Helvellales, the hymenium is completely exposed.
In the Pezizales the ascoearp is cup-shaped and in the Helvellales
convoluted and stalked. The Phacidiales and Hysteriales possess
incompletely exposed hymenia, the round ascoearp opening by a
stellate aperture in the former order. In the Hysteriales the
ascoearp is elongate and opens by a slit. The hymenium is completely covered at maturity in the Tuberales.
In the Pezizales, there are 100 genera and about 3300 species.
The genus Peziza has 160 species, Ascoholus 60, and Morchella 40.
Ascocarps of Discomycetes were once designated as gj'mnocarpic and angiocarpic. Corner (1929) showed that both types
may occur in the single genus Ascobolus. Helvellales were also
shown to possess intermediate forms. Hence the distinction does
not appear to be well-defined.
ASCOMYCETES
101
Pezisa and Ascobolus have been included by Gwynne-Vauglian
in Pezizaceae and Ascobolaeeae, of the Pezizales. The two
families differ from each other in that in Pezizaceae the asci
do not rise above the surface of the apothecium at maturity and
the ascospores are uniseriate while in Ascobolaceae the asci
protr,ude out at maturity and the ascospores are coloured and"
multiseriate. In both families, the peridium is well-developed.
1.
PEZIZA
Species of Peziza are saprophytic E^ungi growing on decaying
organic matter. P. vesiculosa occurs on manures in the form of
dense clumps, P. venosa and P. hadia are common on the
ground in deciduous forests. The apothecia of P. vesiculosa
are contorted and crimped while the hymenial surface of P.
venosa is convolute.
Mycelium is septate, uninucleate and forms but an insignificant portion of the fungus.
Asexual reproduction is rare although P. repanda and
"• vesiculosa are reported to produce conidia.
Fig. 37.—Pesiza. A, Cups of Pezisa; Bj Diagrammatic T->,'S. of the eup;
C, A portion of the hymenium enlarged; D, Ascospores; E—H,
Nuclear fusions in Pe^iscj; J, Development of asci from tlie
penultimate cell.
Peziza is characterised by a typical apothecium which is fleshy
without hairs. Formerly, all form» with such an apothecuim
were grouped under the genus Peziza. Later, however, the name
was retained only for the larger species with sessile or subsessile
102
ASCOMYCETES
apothecia varying from 2 cm. to 7'5f em. in diameter.
The
smaller forms were called Humaria.
Sexual reproduction has been worked out in Humaria
granulata (Gwynne-Vaughan and Williamson, 1930) and Eiimaria
rutilans (Fraser 1908). Rosenberg (1933) is reported to have
observed a lars^e twisted antheridium which coils round the
trichogyne of a globose oogonium in H. aggregata.
I n H. granulata there is no antheridium but the nuclei of
the oogonium fuse in pairs and finally ascogenous hyphae are
formed.
I n H. rutilans the sexual apparatus is absent. Nuclei of
adjacent cells have been observed to migrate by dissolution of
cell walls. Fusion takes place in the vegetative hypha and the
fertilized cell gives rise to ascogenous hyphae. From the surrounding cells, paraphyses and peridium cells arise.
The ascogenous hypha possesses a subterminal crozier-shaped
cell in which the second fusion takes place. A single elongate
club-shaped ascus arises from this cell. Several nuclear migrations and fusions ^result in the formation of a large number of
regularly arranged asci intermingled with paraphyses.
The
palisade layer of these structures constitutes the h^raenium of
the mature apothecium. Below the hymenium is a layer of
hyphae in which nuclear migrations were taking place. This
layer is called the sub-hymenium or .hypothecium. Lower to
this is the compact aggregation of the original mycelium with a
pseudoparenchymatous appearance called excipulum (Bessey,
1950).
The mature apothecium is covered by a sterile cell layer, the
peridium.
The apothecium arises from a tuft of hyphae (excipulum of
mature apothecium) in which nuclear fusions give, rise to a
binucleate layer (sub-hymenium). From this arises the hymenium of asci and paraphyses.
Each ascus contains eight
ascospores. There are two fusions and two reductions (see
page 108).
Most species of Peziza lack sexual organs and the apothecial
development is of Humaria rutilans type.
The ascospores are liberated through a pore formed on the
apex of the ascus. They are capable of germinating to form the
mycelium.
2.
ASCOBO-LUS
Sexual reproduction in Ascobolus varies from fusion between
definite male and female nuclei formed in sex organs to simple
vegetative fusions as in Humaria rutilans. A. strol>ilinus and
103
ASCOMYCETES
A. magnificus possess distinct sex organs formed on the older
hyphae of two distinct strains. The sex organs are multinucleate
and stalked.
Fig. 38.—Ascololus. A—C, Stages in coajugation (earpogonium coiled) ;
Dj Zygote; E, Vertical section of an apothecium.
The antheridium is cylindrical or clavate while the oogonium
is globose. There is a terminal trichogyne of about seven cells
and it is twisted round the antheridium at maturity.
The
intervening wall between antheridium and trichogyne dissolves
and the male nuclei migrate to the oogonium through perforations formed in the septate tricbogyne. The male and female
nuclei fuse in pairs.
Ascogenous hyphae arise from the oospore. They are narrow
with the nuclei lying in a single row. Formation of ascospores
involves brachymeiosis—according to Fraser and Brooks (1909)
but Schweizer (1931) opines that there is no brachymeiosis.
Dodge (1912) has described the formation of numerous conidia
from the septate uninucleate mycelium of A. carbonarius.
3.
MORCHELLA
i
Morchella of Helvellales is a saprophytic fungus growing on
damp soil and decaying branches and leaves. The mycelium
forms a small tuft of soft hyphae at the base of a large stipitate
fructification. In M. crassipes and M. esoulenta, the fructifications are 8—10 cm. tall.
104
ASCOMYCETES
The stalk or stipe of the apothecium is a compact pseudoparenchymatous region coi3.tinued as
the hypothecium in the head. The
fertile region is distinctly marked oS.
from the stalk.
In the sub-hymenium, nuclear
f asions similar to those in Huniaria
rutilans have been observed by Maire
(1905).
The hymenium is covered by a
membrane in the young stages. The
hymenial surface is alveolate being
made up of several laterally united
discs. The whole club-shaped head
has a convolute appearance. Bach
ascus is cylindrical and contains 8
uniseriately arranged ^hyaline ascospores. Morchella is edible.
*
*
I n reviewing the principal types
of reproductive activities fn
the
Ascomycetes, one is struck by the
gradual discardment of the sexual
process. Sphaertkeca can, perhaps,
be placed first for possessing
an
Fig. 39.—Morchella, Mature elaborate sexual apparatus. There is
fructification showing
a definite male and a definite female
stipe and pileus.
nucles. From here, a series can be
traced through Aspergillus,
Pyroncma
confluens,
Ascobolus
magnificus and Humaria aggregata where, with the elaboration
of accessory trichogyne and stalk, there has been a distribution of
the caryogamic act so that a large number of male and female
nuclei are present. Next in the series come forms like Humaria
granulata and Peziza theleboloides where there is a multinucleate
oogonium and fusion of female nuclei. I n Humaria
rutilans
and Pi-ziza vesiculosa even the oogonium is absent and the nuclear
fusions in the vegetative hyphae are considered equal to sexual
caryogamy. I n Saccharomyces, there is a fusion of discrete
vegetative individuals.
In any attempt at interpreting evolution, a series of forms
can be viewed from two directions; either there is a progi essive
complexity from simple to advanced forms or a gradual degeneration from seemingly elaborate individuals to really complex but
apparently simple forms. The study of the Ascomycetes tends
to conform to the latter type. It would, thus, appear that forms
like Sphaerotheca and Aspergillus are primitive because they
ASCOMYCETBS
105
possess well-developed sex organs; whereas forms like Peziza are
ad.vanced as they have dispensed with the traditional sexual
apparatus.
Q uestions
1. Give an account of the structure and life history of
Yeast. (Allahabad, 1951);—habit, hahit and adaptations.
(Agra, 1950).
2. Describe the life history of Sphaerotheca.
(Allahabad, 1946,1948).
3. Describe the development of the Ascus and ascospores
in any typical Ascomycete, and show how it differs
from the corresponding structures in the life history
ot Agaricus.
(Agra,W4:7).
4. Give an account of the reproduction in Peziza, with
special reference to the cytological changes.
(Allahabad, 1944),
5. Write an illustrated note on the structure of the thallus
and modes of reproduction in Morchella. (Agra, 1944).
6. Write an account of the structure and life history of
'Eurotium.
(Agra, IMS).
7. Give an account of the habit and habitat of Euriatium.
Explain how its form and structure is adapted to its
environmental conditions.
(Agra, 1950.)
14
CHAPTER IV
BASIDIOMYCETES
The Basidiomycetes include about 2000 species of . Fungi
which vary widely in the range of habitat, mode of nutrition, and
structure of plant body. However, varied as they are in structural and nutritional denominations they, show a marked constancy
in their sexual reproductive processes. Their sexual spores are
borne exogenously on a septate or non-septate bagidium. The
spores are called basidiospores and are products of sexual fusion.
The structure of the basidium and number of basidiospores have
been used as criteria for classifiying the Basidiomycetes.
The primary mycelium, in this group, consists of ramifying
or sparse septate filaments of uninucleate cells. However, in
almost all recorded cases, the secondary mycelium which forms
the bulk of the adult plant body, is binucleate. Hoffman (1856)
observed peculiar clamp connections between adjacent cells of
hyphae in the group and these have been correlated with the
presence of binucleate cells. BuUer (1941) has given a clear
significance to clamp-connections and interpreted them as modes
in the process of diploidization. Leach and Ryan (1946) consider
that the binucleate mycelium is not in a dicaryon phase but is
truly diploid.
Fig. 40.—Clamp-connection in Basidiomycetes.
In the formation of a clamp-connection, first a curved hornlike process appears between two nuclei in a filament. The
BASIDIOMYCETES
107
nuclei soon undergo division and simultaneously one daughter
nucleus of tlie terminal cell passes into the curved process giving
rise to a uninucleate clamp cell. A septum is laid down at the
base of the clamp cell. Another septum separates the second
daughter nucleus of the terminal cell with one daughter nucleus
of the basal cell. Finally, the clamp cell grows inwards and
fuses with the basal cell. The arrangement of nuclei is, therefore,,
such that the terminal cell contains one terminal and one basal
nucleus and the basal cell also contains the two complements.
I t would appear that the process of clamp-fusioin is a method
of bringing different nuclei together.
The binucleate mycelium of Basidiomyeetes maj' be saprophytic and ramifying in decaying wood, dung and organic matter
or parasitic, inter and intracellular. The mycelial strands may
be delicate as in Ustilaginales or may be thick and stout as in
Agaricales. I n Armillana mellea there are rhizomorphs.
Asexual reproduction is uncommon though conidia, oidia,
chlamydospores and gemmae have been reported in a few species.
According to Hirschorn (1945) the chlamydospores are truly
diploid.
Most BasidiomycetJes lack sexual organs which can be definitely demonstrated" only in the Uredina,les. The binueleate phase
of the mycelium is representative of the approximation of complementary nuclei. I n Ustilaginales, the binucleate stage is
reached by fusion of the uninucleate promycelium of opposite
sexes or fusion of the basidiospores. In Uredinales, the nuclei of
sex organs donot fuse but are associated in a dicaryon phase.
There is a regular alternation of generations but often due to
the presence of more than one host in the life-cycle it is diiScult
to lay down a demarcating line in parasitic forms.
Gwyhne-Vaughan and Barnes (1951) have divided the Basidiomyeetes into three groups :
1. Hemibasidiomycetes—Indefinite number of basidiospores.
2. Protobasidiomycetes—Usually four basidfospores on a
septate basidium.
3. Autobasidiomycetes—Four basidiospores on a non-septate basidium.
The Hemibasidiomycetes comprise nearly 600 species of pathogenic fungi placed^ under a single order Ustilaginales. These are
commonly called brand fungi or smuts. Usiilago is atypical
example.
The Protobasidiomycetes include nearly 6000 species majority
of which are obligate parasites (Uredinales) or saprophjrtes
108
BASIDIOMYCETES
(Auriculariales and Tremellales). In the TJretiinales or rusts
there are approximately 100 genera parasitic upon angiosperms,
gymnosperms and ferns. Heteroecism, polymorphism and specialisation are seen in highly developed forms in this order. Pticcinia
is a typical genus.
The Autobasidiomyeetes are parasites as well as saprophytes
numbering nearly 14000 species. They are cosmopolitan in distribution and occur as large mushrooms, toadstools and other pileate
fungi. They are divided into Hymenomycetales with exposed
hymenium and Gasteromycetales with covered hymenium. The
former order is typified by forms like Agaricus and" Polyporus
while the latter by Lycoperdon and Scleroderma.
• USTILAGINALES
The order is characterised by the presence of a basidium which
develops an indefinite number of basidiospores. The dicaryon
mycelium usually gives rise to a large number of thick-walled
binueleate brand spores or chlamydospores which break through
the hypertrophied host tissue at maturity. Though the species
are obligate parasites, the germination of brand spores is a saprophytic phase.
The mature brand' spore is uninucleate, the fusion of two
nuclei being equivalent to sexual fusion. Basidiospores are produced on a basidium which is formed from a brand spores. The
nucleus of the brand spore does not migrate into the basidium
but sends a daughter nucleus to it after first division. Subsequent
divisions of the parent nucleus furnish nuclei for successive
spores. The basidiospores may bud indefinitely in a yeast-like
manner.
The basidfospores are uninucleate. I n the formation of a
binueleate mycelium, fusion takes place either between basidiospores or their promycelia or sometimes between the septate cells
of the basidium. However, only plasmogamy takes place, the
nuclear fusion occurring in the brand spore. There are no sex
organs.
Kniep (1919), Rawitscher (1922), BaucE (1925), and Stakman
and Christiansen (1927) have shown that there are strains in
Ustilaginales. For each sexual fusion, mycelia or spores of
different strains are required. "Whitehouse (1951) reports
heterothallism in 30 species.
The order includes important genera. Ustilago, Urocystis,
Tilletta and Sphacelotheca,
which infect crop plants. All
species show specialisation of parasitism.
1.
USTILAGO
TJstUago is a cosmopolitan genus with nearly 200 species on
all kinds of hosts. The mycelium is intercellular as well as
intracellular. The brand spores are borne singly.
BASIDIOMYCETES
109
THere are several species of economic importance; V. carho
occurs on oat, wheat and barley; TJ. zeae on corn ; TJ. avenae anU
TJ. lev is on oais-yJJ. tritici on wYieat, and TJ. nuda and TJ. liordei
on barley.
The mycelium is septate, the nuclei being associated in the
dicaryon phase in each cell. The vegetative mycelium does not
cause any distortion of the host tissue.
I n the formation of brand spores, hyphae form dense tangled
masses in the host tissue. This accumulation causes hypez'trophy.
The cells of this binucleate mycelium (Dangeard, 1894) are
readily separable because the cell walls undergo rapid gelatinisation. Very soon a new wall is laid down within the gelatinised wall. By this time the cells separate and the new wall
thickens to form a sculptured exospdre. The two nuclei unite
(caryogamy), and a brand spore is formed. The mass of spores
swells and ruptures the host tissue.
Sori containing brand spores are formed in all parts of the
host. Commonly they are present on stems, leaves, inflorescen-
Flg. 41.—Ustilago. A, An infected inflorescence o£ Zea mays; B, Intracellular mycelium; C—P, Formation of brand spores; Gt,
Germination or brand spore; H—L, Conjugation between
basidiospores.
ces and even roots. I n U. avenae, TJ. levis and TJ. liordei, the
mycelium is intercellular and is lodged at the shoot apex. In
V, zeae the mycelium is intracellular.
110
BASIDIOMYCBTBS
The brand spores lead a saprophytic existence. Germination
takes place immediately or after a variable period of dormancy.
I n v. zeae the exospore ruptures
and
the cndospore
protrudes out in the form
of
a promycelium.
The
nucleus of the brand spore divides meiotically to form four
haploid daughter nuclei. The promycelium becomes septate and
a four-celled basidium is formed. Each cell buds off a single
uninucleate basidiospore which may again bud to form sporidia.
The basidiospores are capable of infecting host plants.
Each basidiospore germinates to form a small germ tube.
The germ tubes arising form basidiospores of different strains
unites to form a binucleate mycelium. Before actual conjugation, the germ-mycelium may be formed in a large quantity or
there may be only a unicellular germ tube. Variations in the
extent of germ-mycelium occur. Nuclei donot fuse.
The binucleate condition of the mycelium is also brought
about by a direct conjugation of .basidiospores. The basidiospores of opposite strains give out small conjugation tubes
which fuse. The two nuclei come to the tube and are associated
in the discaryon phase. Later they migrate to one of the
spores from whicH the binucleate mycelium arises.
Conjugation tubes may also be formed between cells of
different or the same basidium. Even a cell of one basidium fs
capable of conjugating with a free basidiospore.
I n Z7. carta, there are two distinct strains, in Z7. zeae four
strains and in TJ. antherarum more are reported. Conjugation,
however, always takes place between cells or spores of compatible strains.
Smuts may attack any part of the host. " Brefeld (1895) was
able to lay down definite modes of infection. Infection is caused
only by basidiospores and their germ tubes.
The basidiospores are produced by brand spores which
germinate on ground. Thus the basidiospores are associated
with the seeds, and the mycelium enters the seedling before it
emerges from the soil. This type is seen in oat-smut, Ustilago
avenae.
Infection can also take place through embryonic tissues,
viz. young stems and roots, unrolled leaves, young inflorescences
a n d soft joiiits. This is seen fn U. zeae.
I n TJ. tritici and If. nuda the basidiospores germinate on
the elongated styles and- stigmas and the promycelium passes
down into the ovary. "When such infected seeds germinate, the
mycelium grows along with the host and spores are produced
BASIDIOMYCETES
111
only in the flowers. Thus the fungus .is hidden throughout the
life-cycle and appears only in the form of spores in seeds, and
the crop is destroyed.
Smuts have been distinguished as loose and covered. I n
loose smuts, e.g., U. tritici on wheat, Z7. nuda on barley, the
spikelets are converted into sori and instead of the grains powdry
masses of spores are formed. Each spore mass is covered with
a delicate membrane which ruptures as the ears emerge. Thus
loose smuts are able to produce spores even on very young inflorescence and thus cause infection of other healthy plants. I n
covered smut of bafley, U. hordei, the spore mass is developed
as a compact assemblage in the ovary and is covered by ovary
wall and glumes of the spikelet. The membrane covering the
spores remains intact till the crop ripens. The spores are liberated when the grain is thrashed, and here mixing of seeds and
spores takes place.
UEEDINALES
Nearly 6000 species comprising this order are obligate
parasites and are commonly known as rusts. The mycelium, in
m'ost cases, is intercellular and consists of branched septate
hypH'ae in dicaryon phase. Haustoria penetrate the host cells
and cause hypertrophy, distortion and malformation of infected
parts. Usually the host is not killed but a nutritional balance is
maintained between the parasite and the host.
The rusts display several spore forms (polymorphism):
uredospores, teleuto or teliospores, basidiospores, pyenidiospores,
and aeciospores. If the teliospores and aeciospores occur on
the same host, then the species is designated autoecious but if
these spore forms are produced on different hosts then the
fungus is termed heteroecious. The spores are produced in a
cup-shaped structure, the sorus, which arises by a dense aggregation of hyphae below host epidermis. The several spore forms
were confused to be separate parasites for a very long time but in
1865 De Bary established a genetieal connection between aecidiospores and teleutospores of Puccinia graminis and since then
the life-history of heteroecious forms has been clarified.
Of the several important genera included in the order are
Puccinia, Gymnosporangium,
Cronartium,
Melanipsora, TJromyces and Pucciniastrum.
1.
PUCCINIA
Butler and Bisbey (1931) have reported 147 species of
Puccinia from India. AH species are known to exhibit speeiali, sation of parasitism.
Infection of wheat by P . graminis tritici takes place
through aecidiospores, which come from barberry.
Thus
112
BASIDIOMYCETES
Pucdnia
is Eeteroeeious, completing its life-cycle on two
hosts, wh6at (Triticum vulgare) and Barberry (Berieris
vulgaris).
The mycelium produced by aecidiospores ramifies in the
tissues of wheat host and is septate with nuclei in dicaryon
phase. The mycelium sends out haustoria into host cells. Near
about the months of December and January, the mycelium
aggregates beneath the host tissue in stems and leaves and forms
brown patches called IJredosori. A section of host tissue through
uredosorus shows a dense accumulation of superficial dicaryotic
hyphae beneath the epidermis. From this mass ' arise erect
sporophores which bear at their apices sculptured, ellipsoidal,
brown uredospores. Each uredospore is stalked and binucleate.
The development of uredospores ruptures the epidermis and
the spores are carried away^by wind.
aredo spores
epidermis
Fig. 42.—•Puocinia. A, Infected stem of -wheat with uredosori (dark
patches); B, T. S. through a uredosorus; 0, Uredospore; D,
Germinating uredospore.
Bach uredospore has four germ-pores. On germination, a
promycelium comes out through one of these and develops again
into, a dicaryotic mycelium. The uredospores can again infect
wheat and thus serve to spread the rust asexually.
- Towards the end of the growing season, in the month of
March elongated black streaks are noted at several places on
stems of infected plants. These represent teleutosori. I n a
section of the teteutosorus are seen a large number of stalked,
SASIDIOMYCETES
113
bieelled dark teleutospores in compact aggregations. Their
formation ruptures the overlying tissue and exposes them to
the atmosphere. Each cell of the teleutospore is binucleate and
possesses a conspicuous oil globule and a germ pore. The spore
usually remains dormant for a considerable time (winter in
colder regions and summer in hotter regions).
D
Seleatospore
Fig. 43.—Puceinia. A, Infected stem and leaf of -wheat' -with teleutosori
(dark patches) ; B, T. 8. through a teleutosorus; C, Teleutospore; D, Germinating teleutospore.
Prior to germination, the nuclei in each cell of the teleutospore
fuse. A short curved hypha comes out of each cell through the
germ pore. The fusion nucleus divides and the resultant four
haploid nuclei come out in the hypha which becomes septate. It
is now called the basidium. Each cell of the basidium is uninucleate. Soon from each basidial cell, a pointed sterigma
arises. Its end dilates into an ellipsoid basidiospore and the
entire contents of the basidial coll pass into it. Four basidiospores are formed from each basidium. These belong to two
distinct strains + and - .
The basidiospores are airborne and infect barberry leaves. A
short germ tube is given out which penetrates the cuticle and the
cell wall between epidermal cells. This germ tube is uninucleate.
On entering the host, it elongates and branches into an extensive
intercellular septate mycelium which is monocaryotic, i.e.,
composed of uninucleate cells.
15
ill
BASIDIOMYCETES
Grra'dually Hyphal aggregations appear on the upper surface of
barberry leaf. These form themselves into small globular bodies
called pyenia (pycnidia, spermagonia). I n each pycnium the
hyphae form a -curved sheet of sporophores which cut off
terminally a large number of pycniospores or spermatia. At
maturity, the pyenia break through the upper epidermis. Thefr
opening is called ostiole. Interspersed among the sporophores are
certain long unicellular hyphae which penetrate deep in the
tissue of the leaf and reacE the lower surface. These were termed
flexuous or receptive hyphae-by Craigie (1927).
Fig. 44.—Pucoinia. A, Basidium witt basidiospores of -f- and—strain;
B, A part of the Barberry plant with leaves showing patches
of spermagonia; C, Germinating basidiospore; D, T, S of an
infected Barberry leaf with spermagonium on the upper and
a^eidium on the lower surface. (Flexuous hyphae are drawn
by dotted lines).
Bach pycnium with its flexuous hyphae and spermatia belongs
to one strain since it develops from a basidiospore of either
4- or — strain.
The researches of Craigie (1931), Piej;son (1933) and Duller
(1938) have established t h a t spermatia and flexuous hyphae are
the functional sex organs of Pucoinia. I t has been observed that
spermatia of opposite strain are carried by wind to the flexuous
hyphae. Both structures are haploid and uninucleate.
The
intervening wall dissolves and the nucleus of spermatium migrates
BASIDIOMYCETES
115
into tHe flexuous hypha. Both nuclei are now associated in a
dicaryon phase and they travel rapidly downward. Only plasmogamy takes place.
Meanwhile, mycelium was also collecting in patches near the
lower epidermis. Into this mycelium was the flexuous hypha
penetrating at the lower end. The aggregation of this monoearyotic mycelium is termed protoaeeium. The conjugate nuclei
of the flexuous hypha reach the lower mycelium and are cat off
as a long binueleate sporophore. Since several such sporophores
are cut off towards the lower end, a cup-sbaped structure called
aecidium is formed in the tissue of the barberry leaf. The
innermost layer of the aecidial cup is a tangled web of monocaryotic hyphae called sub-Kymenium. Following this is the
sheet of sporophores which are binueleate, hymenium. Successive
divisions of the sporophore tip give rise to basipetal chains of
aecidiospores. When young, the aecidial cup is covered by a thin
membrane, the peridium. The developing aecidiospores exert
pressure on the leaf tissue and rupture the peridium as well as
the lower epidermis to expose the aecidiospores. Inside the cup,
the aecidiospores are polygonal with six germ pores but on
p-la8nid=^
infection
Fig. 45.—Puceinw. A, Nuclear association in flexuous hypha; B Diagrammatic section of an aecidium; 0, Lower surface of
J^ar berry leaf with groups of aecidia; D, Aecidiospore-E,
trerminatmg aecidiospore infecting wheat.
liberation they assume a more or less spherical shape. They are
bright yellow and binueleate. Sterile disjunctors have been
observed between these spores.
116
BASIDIOMYCBTBS
The aecidiospores can infect wheat plants. On germination
they give rise to a dicaryotic mycelium which enters the host
through stomata. The mycelium ramifies in the intercellular
Spaces of the host.
The study of sexuality in rusts has revealed that the aecidial
cup is a direct result of nuclear association accomplished in the
pyenidium. Andrus (1931) and Allen (1934) are of opinion
that flexuous hyphae extend out from uninucleate cells of the
protoaecinum. Allen (1932) reports that receptive hyphae may
emerge from stomatal openings -or from between cell walls.
Brown (1935) found evidence that hyphae fusions of opposite
strains bring about the diploidization of aecidial hymenium.
Most species of Puccinia are heterothallic, i.e., mycelium of
opposite strains is required for aecidium formation. Important
heterothallic species are P . gratninis, P . heliantJii, P. sorghi,
P. triticinia and P . coronata. However, P. xanthi and P,
grindeliae are homothallic.
I t is clear that for completion of the life-cycle, Puccinia
requires two unrelated hosts. I n the plains of India, however,
barberry is not present. Nevertheless the attack of the fungus
is regular. Much speculation has centred about attempts to
explain this phenomenon.
One theory suggests that uredospores persist on accidental
wheat plants or allied graminaceous hosts and cause infection
in the next season. But their presence has not been demonstrated nor have the accidental host plants reported from the
hottest parts of the country. Moreover, it has been found that
uredospores cannot germinate beyond an optimum temperature.
The uredo-infection theory also does not take into account the
intense specialisation of parasitism among the rusts.
The conjectures regarding the persistense of uredospores in
soil have also been disproved.
Eriksson (1894) had stated the Puccinia hibernates inside
the protoplasm of the seed. According to him, the fungal
plasma is indistinguishably mixed up with the protoplasm of
the host. With the return of favourable growth season, the
promycelial strands are organised and these grow out in the
intercellular^spaces of the host. I t is more likely however, that
Eriksson's se'eds were inflected on germination. The mycoplasm
hypothesis cannot be applied to tropical conditions due to intense
heat which would kill all fungal protoplasm.
Mehta (1940) reported that infection on plains^of India is
due to oversummered uredospores. He could find infected wheat
on the hills upto June and produced evidence to the effect that
air-borne uredospores migrate from the hills to tarai regions
BASIDIOMYCBTES
and finally descend on the plains.
produced on the plains.
117
Thus aecidiospores are not
Universal and extensive damage by Puccinia to cereals has
resulted in attempts to breed resistent varieties of seeds. The
fungus has, however, shown remarkable adaptability in this
respect and developed several physiological races within a
single species. "Wolf (1947) has listed seven races in P.
graminis. Efforts have also been made to develop early maturing,
forms. F o r Indian conditions Mehta (1940) has suggested
cessation of cultivation in hill and tarai regions.
The outstanding features of rusts are their polymorphism,
(production of many types of spores in the same life-cycle) and
heteroecism (presence of two unrelated hosts in the same
life-cycle).
Puccinia has several species. P. graminis with its races
tritici and avenue is very destructive for wheat and oats. 1'.
triitcina also infects wheat. P. corojioia attacks oats. p . sorghi
and P . dispersa are rusts of corn and rye. P . glumarum, P .
suhnitens and P . asparagi are other harmful species on wheat,
beets and asparagus.
H YMENO MYCET ALES
This is the largest alliance of the Basidiomycetes and contains over 11000 species. Forms are parasitic as well as
saprophytic.
I n most species the mycelium is binneleate to multinucleate,
the latter condition arising due to lateral fusion of adjacent
hyphae. The mycelium is usually composed of stout hyphae
which develop sporophores. The sporophores show a wide
variety of form and form the conspicuous part of the plant
body.
Sexual apparatus is absent but the non-septate young basidium is binucleate. The fusion of nuclei is considered to be
the equivalent of earyogamy and results in the formation of
four haploid basidiospores borne exogenously on sterigmata.
The basidia form the outermost layer, hymenium, of the large
fructifications which consist of a central tissue or trama of
parallel hyphae. The hyphae in the trama are interwoven and
give off lateral branches which constitutes the subhymenium of
each fructification. I n Polyporus the hymenium lines the
pores of expanded fructifications while in Agaricus it is spread
over gills.
118
BASIDIOMYCETES
THe spores are airborne and are produced in huge quantities.
1.
AGARICUS
I n ^.^rancMs or PsaZHoia (Aitkinson 1906, Hein 1930, Colson
1935) the mycelium is composed of thick strands of multinucleate septate hyphae which ramify in the soil. There is an
erect stipe capped with a convex pileus or head over every tuft
of hyphae strands.
I n the development of the fructification, a little knot or
bulb of interwoven hyphae is formed. Soon three regions are
distinguishable: an upper convex rapidly growing pileus, central
ring of elongated deeply staining hyphae or gills and a lower
slow growing mass of erect interwoven filaments or stipe. Rapid
growth in the upper region pushes the gills into an annular
cavity to the centre of which the stipe is attached. The gills
curve inwards and finally come to lie on the ventral surface of
the pileus. They are covered by a membranous velum in young
stages but at maturity the membrane ruptures and leaves only
an annulus attached to the stipe.
Fig. 46.—Agaricus, A—D, Development'Of the fruetifieation; E,-Enlarged portion of the T. S. of a gill; F—K, Development of
basidiospores; L, M, Basidiospores of a wild and a cultivated
variety.
The transverse section of a free gill or lamella shows a
central pseudo-parenchymatous region, the trama which is
BASIDIOMYCBTES
119
composed of elongated interwoven hyphae. From this arises a
sub-hymenial layer by lateral branching. I n the outermost
layer of the gills, hymenium, there are basidia and sterile paraphyses.
The trama consists of multinucleate cells although binucleate
cells are also seen. The subhymenium and hymenium are
typically binucleate. Nuclear fusion takes place in the basidium. The fusion nucleus divides meiotieally into four haploid
nuclei, which lie at the swollen upper end of the basidium.
Sterigmata appear as pointed projections on the apex and
cytoplasm flows into them. Their apices swell and form small
delicate spores. The spores enlarge probably due to inflow of
more cytoplasm. The wall thickens and one nucleus migrates
into each spore.
When young, the gills are flesh coloured and the spores are
purple.
Bach basidiospore is uninucleate in the beginning but
nucleus divides at least onee in the spore. Thus mature basidiospores are binucleate. I n cultivated species of
Agaricus,
only two basidiospores are formed on each basidium. These are
initfally binucleate. Nuclear division soon makes them four
nucleate.
Cultivated varieties of Agaricus are hpmothallic. The spores
fuse and' their promycelia form multinucleate hyphae.
2.
POLTPORUS
Species of Polyporus are commonly associated with decay
of timber. The genus includes a large number of forms which'
contain pileate, stalked or bracket-shaped fructifications, fleshy
when young but hardened and corky at maturity. I n P.
henzQinus the pileus is 9-12 cm. wide and 10-20 cm. thick, woody
and shell shaped. The pileus of P. arculanus is 1-3 cm. broad,
pliant and umbilicate with a 10-25 mm. long stipe. I n P.
nodulosus there is a triquetrous pileus with nodules. The mature
fructification is rugose and corky with pores nearly 5 mm. long,
p . leucomelas has a large pileus and a thick stipe with hyaline
spores, p . umhellatiis, p. frondosus and P . leucomelas are edible
species. P. sulphureus is luminiscent.
Species of Polyporus
may also be terrestrial viz.
P.
tomentosus, P. cinnamomeus.
There are saprophytic as well
parasitic forms.
I n a tyi^ical life history, the fungus starts as an inconspicuous web of hyphal strands either in the soil or on wood.
The mycelium develops from wind-borne uninucleate basidio-
120
BASIDIOMYCETES
spores. Usually tlie mycelium soon becomes binucleate due to
the formation of clamp-connections.
Fig. 47.—Polyporus.
Mature fructification.
From the subterranean or prostrate mycelium arise numerous compact hyphae which finally form the fructification.
The fructification may be fleshy, cheesy, coi'iaceoas or corky
and at maturity may attain a high degree of woody consistency.
The conspicuous part is the expanded pileus which may be
coloured. Beneath it and around the stipe are several pores
which are commonly produced inwards into contiguous tubes.
The substance of the pileus is made up of a pseudo-parenchymatous hyphal mass which gives rise to a subhymenium. The
erect basidia and paraphyses arise from this and line the pores
as well as the tubrs to a certain distance. The whole fructification can be called hymenophore.
Fusion of nuclei probably takes place in the basidium.
The basidiospores are haploid.
Often in the hymenium multinucleate cystidia are produced. P. saptirema and P. mylittae alpo form giant sclerotia
BASIDIOMYCETES
121
Among parasitic species of economic importance are
p . sulpliurens, P. schweinitzii, P. betulinus and P. adustus.
Questions
1. Describe in detail the life history of any syecies of
Ustilago that you have studied.
{Allahabad, 1944, 1947, 1951).
With special refei*eaee to the modes of infection and
methods of control of the smut disease.
(Agra, 1944, 1947, 1950).
2. Describe in detail the life history of the h'eteroecious
rust fungus Puceinia gramiriis. {Allahabad, 1945,
1947,1949),{Agra, 1946, 1948).
With special reference
{Allaliabad, 1949) ;
to
•
cytological changes.
{Agra, 1942).
Explain how the initial annual infection of wheat crop
is caused in the plains of India.
{Allaliabad, 1947);
{Agra, 1942).
3. Give an account of the aecidial formation in Puceinia.
What methods would you adopt for preventing the
incidence of Rusts in plants ? How does it) spread in
your province ? {Allahabad, 1943);
{Agra, 1951).
4. Describe t)He life history of Agaricus. {Allahabad,
1946,1948.);
{Agra, 1943,1949).
16
CHAPTER V
ECONOMIC IMPORTANCE OF FUNGI
The study of Fungi is important from many view points.
The Fungi are an important source of certain drugs and synthetic
products and can be used as food. As disease producing organisms
they are responsible for doing immense harm to food crops.
Fungi act as scavengers by decomposing organic plant and
animal remains. The result of this process of decomposition is
carbon, dioxide which is assimilated by green plants. Rolfe and
Rolfe (1926) have designated saprophytic Fungi, 'vegetable
vultures'.
The mushrooms were probably the first fungi to be used as
food by man. Psalliota campestris, Cantharellus- cibarius, Boletus
edulis and Morchella esculenla are important* as protein sources.
Psalliota. campestris is cultivated for this reason. Fungi are able
to synthesize fats. Species of Endomyces, Penicillium, Aspergillus, Mucor and Fusaritim are important in this respect. Burkholder (1943) found Candida guilliermondi to be able to produce
riboflavin, a constituent of vitamin B. Species of Aspergillus
and, Fusarium- could also manufacture riboflavin. Streptomyces
griseus produces vitamin B^^.
Fungi are the source of enzymes of commercial interest viz.,
amylase, pectinase and sucrase. Penicillium, Asper,gillus, Rhizopus
delemar and jg. Oryzae are largest producers of amylase. Yeasts
also produce enzymes (zymase complex) which have been used in
fermentation and production of alcohol. Penicillium glaucum,
Aspergillus glaucus, Mucor racemosus, species of Citromyces and
Fusarium are able to produce alcohol. The enzymatic nature of
alcoholic fermentation was studied by Buchner (1897). The
properties of yeast in bakery and brewery have also been of
considerable importance.
Many fungi synthesize organic acids. Aspergillus niger, A.
glaucus, A. clavatus, Penicillum divaricatum, P. glaucum, Citromyces glaher, G. citricus, and Mucor pyriformis have been suggested for production of citric acid (Von Loesecke, 1945). Gluconic
acid is produced by Aspergillus Oryzae, A. niger, Penicillum
crustaceum and P. cJirysogenum. Rhizopus cJiinensis, R. elegans,
R. nodosus, Mucor rouxii and Monilia are important sources of
lactic acid.
The production of antibiotics which are capable of inhibiting
the growth of pathogenic micro-organisms Has received increasing
ECONOMIC IMPORTANCE OP FUNGI
123
attention in recent years. Selected mutants of Penicillium
notatum an3 P. cJirysogenum and Aspergillus flavus are sources
of Penicillin. Streptomycin is synthesized by Streptomyces
griseus. Streptomyces aureofaciens produces aureomycin and S.
venezuelae produces Chloromycetin.
Fungi produce important plant diseases. Since in most
cases the fungus mycelium remains inside the host, it is difficult
to know a diseased plant but for the external symptoms. Infected host shows early maturity, wilting, malformation and
hypertrophy, temporary and slow rotting, leaf fall and" leaf spot,
curling of parts, tumor and gall formation, and finally necrosis or death. Dissemination takes place usually through the
ruptured parts by air-bome spores. Insects are important
carriers of disease. Claviceps purpurea or ergot of rye is borne
by flies. Rusts viz., P. graminis, P. glumarum a n d P . coronata
are maintained on weeds and accidental plants. The researches
of Mehta (1933) prove that in India uredospores of P. graminis
are disseminated by air. Rapid spread by wind is known in
case of TJstilago sea, Gystopus, Erysiphe etc.
Important diseases of crop plants are due to obligate
parasites.
TFheat is attacked by several fungi to produce black stem
ru.st (P. graminis tritici), leaf rust (P. triticina), yellow rust
(P. glumarum), bunt {Tilletia Levis), loose smut (Ustilago
infici),flag smai (Urocystis tritici) audi leal spot {Helminthosporium sativum). Erysiphe graminis tritici, species of Pythium
and Fusarium also infect wheat.
Among common diseases of barley are dwarf rust (Puccinia
anomala), covered smut (Ustilago liordei), loose smut (Z7. nuda),
spot blotch, late blight and stripe disease (Helminthosporium
sativum, B. teres and H. gramineum) and root rot due to
Fusarium and Sclerotium.
Oats are attacked by Ustilago levis and U. avenae. Maize
smut is caused by U. seae while maize rust by Puccinia
maydis.
Potatoes are affected by Phytophthora infestans, Altemaria
solani; Tomatoes by species of Pythium, Fusarium and Alternan a : Brinjals by Cercospora solanacea, Bhizoctonia and Phoma
solani. Red rot of sugarcane is due to Colletotrichum falcatum.
Methods of disease control are as old as the diseases themselves. A fungicide is an agent capable of killing fungi. Fungistatic agents cause inhibition of fungal growth. Fungicides
may be protectants or eradicants. In the past, fungicides were
m o s t l y innrrranin
in natnTO inirl nawtpg or s n r a v s of s a l t s
of
124
ECONOMIC IMPOETANCB OF FUNGI
copper, mercury and sulpHur were found to be very useful.
Bordeaux mixture is a fungicide of copper and lime, but it
bums tender foliage and softer plant parts. The relative concentrations of copper and lime are very variable. Fungicides
of heavy elements are said to cause fuugistasis by precipitating
proteinous enzymes produced by the fungus. Enzyme inhibition is usually the basis of the action of all fungicides. Copper
sulphate, copper carbonate, mercurous chloride, mercuric acetate,
boiled lime-sulphur, hydrogen sulphide are important fungicides
and enzyme preeipitants. Recently organic or organometallic
compounds have come into use as fungicides. Formaldehyde,
p-b enzoquinone, naphthaquinones, dithiocarbamates and several
unsaturated ketones are active fungicides. Probably these
substances act upon the fungus by inhibiting the production of
sulfhydryl enzymes of the fungus. There is no universal fungicide and usually there are specific inhibitory substances for
particular diseases.
Questions
1. Write a brief essay on the economic importance of
bacteria and Fungi.
{Agra, 1935).
SECTION III
BACTERIA
Bacteria were first seen by Anton van Leeuwenhoek in 1683,
w ho considered them to be tiny animals because of their motility.
This opinion was held by zoologists for nearly a century after
the discovery. Soon the pioneer researches of Pasteur, Fuchs,
Lister and von Hessling demonstrated that bacteria are intimately associated with fermentation, souring of milk and
human diseases. Jacob Henle gave the germ theory of disease
which stated" that a given disease is caused by a given
organism.
Schlasing and Muntz (1873) reported" that the change of
organic forms of nitrogen and ammonia into nitrates was caused
by bacteria and in 1889 Winogradsky isolated the species. The
• symbiotic nature of bacteria was definitely established by
Hellriegel and'Wilfarth in 1887.
During these early years of the rise of bacteriology, little
was known about the structure of the bacterial cell. However,
the shapes were recognized to be rods, spirals or spheres. The
rod-like forms are called bacilli; spirally coiled forms spirilla,
and round forms cocci. Their size varies from 0. 2 microns to
80 microns. They are unicellular or multicellular forms.
Bacteria are best regarded as a separate division of Thallophyta. They were placed with Algae as Schizophyta and with
Fungi as Schizomycetes. But they differ in certain important
' respects from these lower group of plants. The bacterial cell is
destitute of chlorophyll.
The cell wall is a distinct structure. It does not contain
cellulose but some chitinous substance. In Acetohacter xylinum,
however, cellulose is reported". Some bacteriologists regard the
wall as a firm outer layer of protoplasm. Inside the wall is
granular cytoplasm. Vacuoles are present. Pigments occur in
the form of granules or as dissolved matter but plastids are
absent. There is no organised nucleus. The chromatin granules
are scattered in the protoplasm and there is no nuclear membrane. Some bacteriologists consider that the entire bacterial
cell is taken up by a nucleus and there is little or no cytoplasm.
Others are of opinion that there is no nucleus but the dense
cytoplasm alone occupies the whole cell. The inclusions
most resembling chromatin are metachromatin or volutin
granules. Glycogen, fats and proteins are also dispersed' in the
cytoplasm.
126
BACTERIA
Bacteria are often capable of movement due to flagella. The
number of flagella on each cell varies and a definite terminology
has been established to define the number and position of flagella.
Monotrichic forms have one flagellum at one end, lophotrichic—
a cluster of flagella at one end, amphitrichic—a cluster of
flagella at each end and Peritrichic—flagella over the entire
body.
Fig. 48.—Bacteria. A, Diplodoocus; B, Staphylococcus; G, Sarcina-D
Streptococcus; E, B. sporogenes; F, B. subtilis; Q' S'.
typhosus; Hj B, proteusi I, Ihiospiriilum;
J, Spirillum
undulum; K,Vibri cholerae; h, Spirochaete; M, Cladothrix
dichotoma ;_Nj Beggiatoa alha.
The shape of bacteria varies during a single life-cycle. The
same form may be coceoid, rod-shaped, smooth or flagellate at
different period of life-history. The cell-shape is, therefore,
more properly called growth form. The flagella are regarded as
protoplasmic protrusions or as simple wall projections.
Bacteria reproduce by fission. The cocci and bacilli divide
by constriction. A ring-shaped furrow appears exactly in the
centre and progresses inwards till the cell divides. Over the
newly formed parts of cells, a wall is laid down. The process is
called binary fission. Active bacterial cells divide repeatedly
in this fashion. Division usually takes place in a single plane
but in Micrococcus and Sarcina there are two or three planes.
In Staphylococcus successive furrows are not at right angles to
each other.
BACTERIA
127
Clostridium and Bacillus reproduce by endospores. These
are resistant resting bodies and are usually formed in the
zoogloea stage when several cells of the bacterium are embeddedin a mucilagenous mass. I n the formation of endospores the
protoplasm of each cell rounds off in some part of the cell, the
position being characterstic of the species. I n Clostridium the
spore is larger than the width of the rod but in Bacillus it is
smaller. A new wall is formed around the aggregated protoplasm. The spore is released by disintegration of the parent
cell wall. More than one spore may be formed in a cell. On
germination, the outer wall of the spore ruptures and the
contents flow out in the shape of a normal cell. I n some cases
the spore wall softens and stretches out to assume the shape
normal to a vegetative cell.
I n Bhizoiium,
small reproductive bodies called gonidia are
described originating in considerable numbers in each cell.
Their development to vegetative cells appears to be a simple
growth phenomenon.
Studies on the life-cycle of bacteria are considerably hindered
due to the small size of these organisms. I t is, however, certain
that a bacterium shows polymorphism in its life cycle. I n the
life history of Bhizohium, which lives symbiotically in rootnodules of Leguminosae, cocci, monotrichic spheroids, banded
rods and unhanded" rods and peritrichic forms appear successively.
If the bacteria are considered as grouped under a single
class Schizomycetes,
then
they are divided into
seven
orders : Eubacteriales, Actinomycetales, Chlamydobaeteriales,
Caulobacteriales, Thiobacteriales, Myxobacteriales, and Spirochaetales.
Bacteria are more conveniently grouped as autotrophic and
heterotrophic. Important autotrophic bacteria are Nitrosomonas
which oxidizes ammonium compounds into nitrites, Nitrobacter
which converts nitrites into nitrates, Beggiatoa which produces
sulphur from hydrogen sulphide, Pseudomonas denitrificans or
denitrifying bacteria. Heterotrophic forms may be parasitic as
Phytomonas and Erwinia or saprophytic as Spirillum,
Bacterium
mycoides, B. iermo or symbiotic as Bhizobium and Pseudomonas.
Bacteria play an important role in the carbon cycle as decomposers of organic matter and in the nitrogen cycle as agents of
128
BACTERIA
ammonification, nitrification, a^enitrification and nitrogen fixation.
' They are cultivated in the laboratory on artificial culture media
similar to those employed for fungi.
Question
1. Describe the forms, structne,mod.and er of reproduction
in bacteria. Mention briefly tHe points of their economic
importance. {Allahabad, 194,5, 1952);
(Agra, 1944).
2. "The beneficial effects of bacteria outweigh the harm
which they do". Justify the above statement, giving
suitable examples.
(Agra, 1951).
APPENDIX I
SEAWEEDS
Seaweeds is the term applied roughly to the marine algae
belonging to the classes PhaeopEyceae and Ehodophyeeae. They
are attached" forms inhabiting the sea shore in well-marked
zones.
The most conspicnons components of the marine algal flora
are usually the diiferent kinds of brown seaweeds although a
moss-like carpet of red algae is present towards the low-water
mark. In European waters the vertical zonation roughly follows
the pattern : Pelvetia canaliculata near high-water mark, Fucus
spiralis and Fucus platycarpus with broad branching thalli
attached by a stipe terminating in a discoid holdfast, Ascophyllum
nodosum ancf Fucus vesiculosus near the middle of the shore,
Fucus serratus near the low-water mark. Below the low-water
mark, where chances of an exposure are extremely rare, occurs
Laminaria digitata and Laminaria saccharina followed by L.
cloustoni'. Growing in sandy or rocky places below the lowwater mark are sometimes seen Saccorhiza hulhosa and 'Alaria
Fig. 49.—Zonation of Sea-weeds, a, Fuous spiralis; h, Fucus vesioulosusi
Cj Ascophyllum;
d, F^icus serratus; e, f, Laminaria.
esculenta. Besides these brown weeds, the carpet of red algae is
present iji the lower half of the zone exposed at low tide. Chondrus
130
SEAWEEDS
crispus and Gigartina stellata are often present in tliis zone.
Two more red algae, Porphyra umhilicalis
and
Rhodymenia
palmata usually occur at high and low-water marks respectively.
On the Pacific coast of America, larger Kelps are distributed.
Nearer the shore is present Macrocystis integrifolia and farther
off, Macrocystis pyrifera easily exceeding 100 ft. in length and
rooted 10-15 fathoms deep. Along with th^is is the giant alga,
Nereocystis
luetkeana
commonly known as "bladder kelp".
Larger still is the "elk-kelp" or Pelagophycus growing in patches
associated with Macrocystis.
Besides are the species of Alaria,
Fucus, Egregia, ThalassiophyUum and Gostaria.
I n warmer waters the zonation of littoral seaweeds is not so
obvious. Near Japan, red seaweeds esp. Porphyra,
Gelidium
amansii and Gloiopeliis are very common. Brown algae ax'e
represented by species of Laminaria, Ecklonia, TJndaria etc.
Knowledge of the economic importance of seaweeds extends
back for several hundred years. They were used as source of
food, pigments and medicines. 'Giant kelps were also utilized as
manures. Commercial uses of sea weeds have, recently been
reviewed by Kirby (1951).
One of the chief industries flourishing entirely due to the
marine algal flora is the Kelp Industry producing iodine, potash
and soda. The industry has now developed in all countries with
coastal strips rich in seaweeds. The species employed" are those
of Laminaria^
Saccorhiza hulbosa, Fucus vesiculosus,
Fucus
serratus, Aseophyllum,
Himanthalia lorei (Europe) ; Laminaria,
Ecklonia cavo, Eisenia
bicyclis, Sargassum natans (Japan) ;
•Macrocystis, Nereocystis, Alaria fistulosa (America).
Usually the kelps are harvested at definite periods, dried in
the sun and packed into iron retoi'ts for distillation at low red
heat. The distilled material separates out into tar, ammonia
and an illuminating gas. The residue in the retort is treated
with water to dissolve the sodium and potassium salts of iodine
and bromine. The final residue is an efficient decoloriser and
deodorant. I n good kelp prepara1,ions the percentage of potash,
soda and iodine is as follows (Hendrick 1883);
Potash
Soda
Iodine
..
..
..
15-1—21-95 per cent.
13-7—16-85 per cent.
0-55—0-67 per cent.
In Japan, uearly 115 tones of iodine were produced per
year in 1929. Usually the amount of iodine varies from 0-02—
0-76 per cent, of dry weight. Parker and Lindemuth (1913)
have found that American species of Macrocystis contain nearly
23 per cent. KCl and Nereocystis nearly 28 per cent. KCl.
SEAWEEDS
131
Another important product of seaweeds is agar.agar. I t is
chiefly prepared from boiled extracts of Gracilaria
lichenoides,
G. confervoides, Eucheiima muricatum and E.
deuticulatum.
Agar is used, mostly in bacteriological and fungal culture work.
It^is also used in sizing of fabrics and as a constituent of high
grade adhesiv.es. Agar is used for clarifying beer in western
to
countries.
Spoon (1951) has reported that J a p a n produces
90 per cent, of the world's supply of agar-agar.
Importance of seaweeds as food is two-fold; they are
used as cattle feed as well as for human consumption. Laminaria saccharina, Ithodymenia
palmata,
Alaria
esculenta,
Fucus serratus, Chorda filum, Blossevillea, Sargassum.
Hormosira are used in cold countries as cattle fodder.
Laminaria
saccharina, Ghondrus crispus, Porphyra, Gracilaria compressa,
Durvillea antarctica and Sarcophycus potatorum are used in
various countries as parts of human food.
Manurial value of the seaweeds can be easily gauged from
the following table, showing the composition of a ton of wet
weeds:
Nitrogen Phosphoric Potash Common Organic
acid
1 ton wet weed:
71b.
2 1b.
22 1b.
salt
matter
351b.
400 1b.
Certain red seaweeds produce lime.
I n 1883, Stanford discovered Algin. This organic substance
is obtained by macerating the seaweeds with dilute hydrochloric
acid and' extracting by a solution of sodium carbonate. Soluble
salts of alginic acid are used in textile industrj' for dressing a n d
polishing. I n the U. S. A., it is now being used for stabilising
ice-cream.
Rose (1949) has emphasized that for a successful seaweed
industry a cheap and efficient extrajction process is yet to be
found.
A P P E N D I X II
LICHENS
Lorrain Smith (1920) has described Lichens as "pereunial
aerial plants of somewhat lowly organisation. I n the form of
spreading encrustations, horizontal leafy expansions, of upright
strap-shaped fronds or of pendulous filaments, they take possession of the tree trunks, palings, walls, rocks or even soil that
afford them a suitable and stable foot hold." This view is
maintained by Abb ayes (1951) in his treatise on Lichenology.
Lichens are symbiotic associations of two dissimilar organisms, an alga and a fungus. The fungus is the predominant
part of this association and is usually an Ascomycete, though
rarely in tropieal Heheiis, a b'asidiomyeet<3 is present.
The
association is mainly physiological, alchough the term "lichen"
was first used by theophrastus to denote a superficial composite
growth on bark of trees.
The components of a lichen are chara,cterised by a very
low plane of differentiation.
The algae are mostly unicellular
and multiply by cell-division. The fungus component consists
of profusely branching filaments which provide the matrix of
the plant body. Lichen thalli lack true pa^'enchyma but a kind
of pseudoparenchymatous ground tissue is formed by the fungus
by coherent growth. Lindau (1899)_ proposed the name "plectenchyma" for the lichen-matrix.
Zukal (1895) divided lichen tKalli into endogenous and
exogenous forms according to the predoniinance of algal or
fungal component. The thallus shape hiis been made the
basis of classification of exogenous thalli by H u e (1899). Thalli
may be stratose with a prominent dorsiventrality, radiate with
cylindrical or strap-shaped body or stratose radiate with primary dorsiventral body and secondary u p r i g h t radiate
structures.
Lichens are classified into two subclasses: Ascolichens
and Hymenolichens. Ascolichens are the raore important a n d
have been subdivided into Pyrenocarpeae with perithecial f r u i t s
and Gymnocarpeae with apothecial fruits.
Reproduction is by ascospores in a large number of ascolichens. I n discolichens like Collema niicrophyllum
coiled
carpogonia are formed and these are fertilized by conidia. I n
Physcia and Usnea barbata, similar sex organs have been described. Moreau fl926') studied reoroductioii of several lichens
LICHENS
133
an3'refuted tlie reports of fertilization. It seems, however.
that both apogamous and perfect forms are present.
B
Fig, 50.—Liehen. A, A typical Lichen thallus (1) growing on an angio,
sperm stem (st) ; B. Transverse section o f an Ascoliclien; CAn ascus magnified, a, ascus; al, algal cells; as, ascospores;
p, paraphyses.
The presence of functional triehogyne has been taken by
Bessey as signifying relationship with the FloriSae of Rhodophyceae. Van Tiegham (1891) and Zukal (1895) considered
the triehogyne as an apparatus for respiration.
Lichens grow slowly and therefore their food requirements
are rather low. They are capable of enduring complete desiccation and possess no special organs for water ab'sorption. The
hyphae on the under surface act primarily as holdfasts but
can absorb the water beneath, by capillary action. Larger
lichens are provided with rhizinae which are absorptive only to
a limited extent. Through this water come the inorganic nutrients essential for the goowth of lichens. Orga"nic food of lichens
is derived by saprophytic fungus from the substratum as well
as by manufacture in the green alga. Zukal has pointed out
that in associations of mosses and lichens, the latter playeff a'
parasitic role for subsistence. Some authors are of opinion
134
LICHENS
that the fungus is actually parasitic on the algal p a r t n e r but
these reports have been widely contradicted.
I t has been reported that insects use lichens as food.
Larvae of certain Lepidoptera, mites, wood lice, caterpillers live
on lichens. Cladonia rangiferina is used as fodder for reindeer
while Getraria islandica is used for horses and pigs. I n India
a species of Parmelia has been used for human consumption and
for medicinal purposes. Lichens are widely used as popular
medicines. Species of Cladonia and Getraria in intermittent fever,
Peltigera camana in hydrophobia, and Evernia furfuracea in
cough. Letharia vulpma is a poisonous lichen. Lichens have
also been used in dye-industry and as purfumes.
Koursanov
(1945) has listed several commercial and industrial uses of
Lichens.
Church (1920) has attributed to the lichens, an important
role in the origin of plants. According to him lichens "present
an interesting case of an algal race deteriorating along the
lines of a heterotrophic existence...',
by the adoption of
intrusive algal units of lower degree to subserve photosynthesis".
A P P E N D I X III
FUNGI IMPERFECTI
Apart from tHe great groups of F u n g i : Phy<3omycetes, Ascomycetes and Basidiomycetes, there is still left a whole assemblage
of forms only partly known to the mycologist. Usually only the
conidial or asexual stages of these forms are known. Since the
knowledge about their life-cycle is not yet complete, these forms
are called Imperfect Fungi or Fungi Imperfect! or Deuteromyeetes.
I t is believed that these partly known organisms are asexual
stages of ascomycetous forms and much evidence has been gathered
in this connection by the discovery of 'perfect' or sexual stages of
somft gertCTa. Some species axe probably basidiorayeetoMs m n a t u r e
and rarely some may belong to the Phycomycetes. I t appears
that in many forms sexual reproduction is wholly lost and
the fungus has completely acquired the faculty of conidial
tpropagation.
To such imperfect forms, systematists hesitate to apply generic
and specific names. Nevertheless, for purposes of identification
and description latin nomenclature has been given to them. Some
mycologists consider the names only as temporary 'form genera'
and 'form species', and defer from
making statements about
their affinity till the knowledge of their perfect stage is available.
Classification of these fungi is, thus, based on morphological
resemblance only. There are three orders : Sphaeropsidales,
Melanconiales and Hyphomycetales.
I n the Sphaeropsidales eonidia are produced from a hymenium
which is enclosed in a flask-shaped pycnidjum. Ejection of
eonidia is through a narrow slit or pore, the osteoli. Important
genera are Phoma, Phyllosticta, Diplodia, Septoria,
Bhizosphaera
and Phomopsis.
The eonidia of Melanconiales are borne on crowded conidiophores. The conidiophores arise from a sunken stroma in a cavity,
the outer walls of which are formed from host tissue. Such a
structure is called an acervulus. Among other genera, Gloeosporium,
Golletotrichum,
Pestalotia and Cyliiidrosporium
are
important.
In the third order, Hyphomycetales, both pycnidia and acervuli
are absent. Conidiophores originate superficially from mycelial
congi-egations which may be organised into a strand or wart-like
cushion or pseudoparenchyma. There are seijeral
genera,
136
FUNGI I M P E R F B C T I
'Alternaria, Fusarium, Helminthosporium,
rium, Gephalosporium etc.
Cercospora,
Glddospo-
Genera of Deuteromycetes occur botE as saprophytes and
parasites. Several of them are important economically since they
are responsible for producing important crop diseases. Amoiig
diseases of cereals, Black mould of wheat caused by Cladosporium
Jierharum (Bennett, 1928) is mildly harmful. Fusarium avenaceum
and F. culmorum cause Brown Foot Rot and E a r Blight disease
of wheat and is very destructive (Sadasivan, 1939 ; Greaney,
1938). The conidia of Fusarium
are septate and elliptical to
crescent shaped. Fusarium caeruleum, CoUetotrichum
atramentarum on Potato and Phoma lingam on Turnip are fatal to the crops.
Species of Fusarium, Colletotrichuni, Cladosporium and Helminthosporium are capable of attacking a wide range of plants. These
pathogenic forms are often narrowly specialized in their parasitism but they are generally facultative parasites.
AUTHOR INDEX
Abb ayes, 132
Action, 12
Aitkinson, 118
Alain, 81
Allen, 34, 116
Allison, 12
Andrus, 116
Arena, 12
Balkrisbnan, 62, 63
Barnes, 78, 86, 94, 107
de Bary, 79, 83, 91, 94, 97
Bauch, 108
Bennet, 136
Bessey, 91, 102
Bisby, 81, 86, 111
Blackman, 93,100
Blakeslee, 85, 88
Bomet, 15
Borzi, 15
Brand, 15
Brefeld, 67, 110
Brown, 116
Brooks, 103
Buchner, 122
BuUer, 106,114
Burgeff, 86
Burkhiolder, 13
Burris, 12
Butler, 74, 81, 86, 111
Oannabaeus, 15
Cassel, 12
Chaudef and, 42
Christiansen, 108
Church, 97, 134
Clark, 48
Claussen, 93
Cleland, 57
Colson, 118
Cook, 49
Corner, 100
Couch, 36, 77
Craigie, 114
Cutter, 86, 87, 88
Dangeard, 92, 93, 98, 100, 109
Darwin, 1
Davis, 36
Delamater, 95
Dodge, 4, 69, 94, 103
Dreschler, 79
Eichler, 1, 4
Elvidge, 49
Eriksson, 116
Feldmann, 9, 37
Fischer, 12
Fitzpatrick, 78, 81, 84
Fogg, 12
Eraser, 93,100,102, 103
Fritseh, 4, 9,15,18, 26, 37, 43
Fuchs, 125
Gardner, 12
Gaumann, 70 .
Geitler, 12,15
Greaney, 136
Gross, 36
Grubb,60
Guilliermond, 95, 97
Gwynne-Vaughan, 69, 78, 86,
91, 93, 94,102,107
Harder, 13
Harper, 93,100
Harris, 88
Haupt, 12
Hein, 118
Hegler, 12,15
Hellreigel, 125
Hendrick, 130
Henle, 125
Hessling, 125
Hirsch, 94
Hirschorn, 107
Hoffman, 67,106
HoUande, 12
Hohnk, 78
Hoover, 12
Hue, 132
138
Iyengar, 62, 63
Jones, 74
Karling, 77
Kempton, 67
Kirby, 130
Kniep, 108
Knight, 45
Koch, 36, 37
Kohl, 12,15
Konishi, 12
Koursanov, 134
Kuhn, 20
Kylin, 42, 43, 58, 61
Leach, 106
Leonian, 79
L'eeuwenhock, 125
Lewis, 63
Lindau, 132
Lindegren, 95
Lind'emuth, 130
Lister, 125
Loesecke, 122 .
Lorrain-Smith, 132
Lotsy, 37
Mainx, 28
Maire, 104 ,
Manton, .48
Martens, 94 .
Mehta, 116,117, 123
Melhus, 82
Meyer, 34
Mitter, 69
Mockeridge, 12
Moewus, 20
Moliseh, 42
Moreau, 87,94, 132
Morris, 12
Mundie, 36
Muntz, 125
Nichols, 67
Nishigaki, 12
Noble, 67
Olive, 12
Oltmanns, 36
AtiTHOB INDEi
Palm, 82
Pappenfuss, 45
Parker, 130
Pascher, 4
Pasteur, 125
Peniston, 95
Pethybridge, 79, 80
Phillips, 12
Piemeisel, 72
Pierson, 114
Prat, 12
Printz, 37
EanganatEan, 95
Raper, 74, 97, 98
Raulin, 71
Rawitscher, 108
Rolfe, 122
Rose, 131
Rosenberg, 102
Ryan, 106
Saecardo, 67
Sachs, 94
SafeeuUa, 84
Satina, 88
Sehlossing, 125
ScEmid, 13 .
Schewiezer, 103
Scott, 12
Shantz, 72
Smith, 4, 37
Sparrow, 77
Shear, 94
Spoon, 131
Stanford, 131
Steinberg, 71
Steinecke, 26
Strasburger, 5 0
Stackman, 75,108
Stevens, 83, 84
Strain, 37
Subramaniam, 95
Svedelius, 54, 55
Swingle, 88, 94
Tandy,94 "
Thirumalachar, 84
Von Tiegham, 133
Tiffany, 25, 34
Thuret, 15
AUTHOR INDEX
Thorn, 74, 97, 98
Turchini, 15
Ullrich, 13
Wager, 83, 84, 95
Watanbe, 12
West, 9,12, 18, 25, 56
Whitehouse, 94 108
Wilfarth, 125
Williams, 12, 36
Williamson, 93, 94, 102
Wilson, 84, 94
Winge, 100
AVolf, 78, 91, 117
Yamanouchi, 62
Zaeharias, 12
Zukal, 132,133
139
SUBJECT INDEX
Aecidiospore, u s
Aecidium, 115
Agar, 10, 131
Agarieales, 118
Agricus, 118
Akinete, 8, 13, '26
Albuginaceae, 81
Albugo, 81
Algae, 6
Algin, 131
Alternation of generation, 3,
9,69
Anisogamy, 9, 68
Aplanogamete, 85
Ascocarp, 92
Ascogenous hypha, 93
Ascogonium, 93
Ascolichens, 132
Ascomyeetes, 91
Ascospore, 91
Ascus, 91
Aspergillus, 97
Bacillariopliyceae, lO
Bangiales, 55
Basidiolichens, 132
Basidiomycetes, 106
Basidiospore, 106,107
Basidinm, lOfi, 107
Blepharoplast, 18
Capitulum, 39
Carpogonium, 57
Carposporangium, 58
Carpospore, 58
Carposporophyte, 58
Chaetophorales, 32
ChantranSiaj 56
Chara, 38
Charales, 38
Chlamydomonas, 18
CMamydospore, 68, 79
Chlorophycea^, 17
Cliloroplast, 17
Chromatophore, 42, 53
Giixysophyceae, 1 0 '
Clamp connection, 107
Coenobium, 2l
Coenocyte, 34
Coleochaete, 33
Columella, 86
Conceptaele, 46, 51
Corticating branch, 56, 60
Cyanophyceae, 11
Cyclosporae, 43
Cystocarp, 59 61, 64
Diatoms, 10
Discomycetes, 94, 100
Dwarfmale, 27
Ectoearpales, 43
Ectocarpus, 43 '
Erysiphales, 95
Exoscales, 95
Eyespot, 19, 21
Ploridae, 55
Ploridean starch, 53
Fucales, 46
Pucus, 46
Fucosan vesicles, 42
Fucoxanthin, 42
Fungi, 67
Fungi imperfeeti, 135
Gametophyte, 3, 9, 50, 69
Germpore, 112, 113
Globule, 39
Gonimoblast, 58
Haematochrome, 22
Hapteron, 34
Hauslorium, 73
Heterocyst, 14,15
Heterothallism, 69
Holdfast, 25, 46
Horniogonales, 13
142
SUBJECT INDEX
Hormogone, 13
Hymenium, 102, 119
Hymenomyeetes, 108
Hypothecium, 102
Inversion, 22
Isogamy, 9, 68
Isogeneratae, 43
Rhisopus, 88
Ehodophyceae, 53
Bivularia, 15
Eusts, 111
Laminarin, 81, 129, 130
Laminarin, 42
Lichens, 132
Monospore, 56
Mucorales, 84
Mucor, 86
Mycorhiza, 76
Myxophyceae, 11
Nannandrons, 27
Nemalionales, 55
Nostoc, 14
Nucule, 39
Oedogoniales, 25/
Oedogonium, 25
Oogamy, 9, 68
Oomycetes, 78
Oscillatoria, 13
Ostiole, 114
A
Paraphyses, 102, 104
Parthenogenesis, 21
Parthenogonidia, 21
Pericentral cell, 59
Perithecium, 92
Peronosporales, 78
Pezizales, 100
Phaeophyceae, 31
Phyeocyanin, 11
Phycoerj'thrin, 11
Phycomycetes, 77
Plakea, 21
Plectomycetes, 94
Plenrococcus, 32
Polysiphonia, 59
Progametangium, 88
Pseudovacuole ,11
Puccinia, 111
Pycnidium, 114
Pyronema, 93
Pythiaceae, 79
^
A
Saccharomyces, 95
Sargassum, 50
Siphonales, 34
Smuts, 107,108
Spermatium, 114
Spermogonium, 114
Spirogyra, 30
Sporophyte, 3, 9, 50, 69
Stephanekontae, 25
Sterigma, 113,119
Stipe, 118
Subhymeniiim, 102,119
Suspensor, 88
Symbiosis, 75
Teleutospore, 112
Tetraspore, 54
Trichogyne, 57,103,13J
Trichome, 16
Trichothallic growth, 42
JJlothrix, 23
Ulotrichales, 23
Uredinales., I l l
Uredosorus, 112
Uredospore, 112
Ustilaginales, 108
Vstilago, 108
Vacuoles contractile, 19
Vaucheria, 34
Vaucheriaeeae, 34
Volvoeales, 18
Volvox, 21
Xanthophyceae, 10, 37
Xanthophyll, 42, 37
Yeast, 95
Zygomycetes, 78, 84
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