DET KGL. DANSKE VIDENSKABERNES SELSKAB
BIOLOGISKE MEDDELELSER, B ind XX, N r. 9
THE SPONTANEOUS
FORMATION OF HAPLOID, POLYPLOID,
AND ANEUPLOID EMBRYOS
IN SOME ORCHIDS
BY
0. HAGERUP
^
KØBENHAVN,
I KOMMISSION HOS EJNAR MUNKSGAARD
1947
-y
Det Kgl. Danske Videnskabernes Selskabs Publikationer i 8” :
,
'
.
Oversigt over Selskabets Virksomhed,
Historisk-filologiske Meddelelser,
'
Arkæologisk-kunsthistoriske Meddelelser,
Filosofiske Meddelelser,
Matematisk-fysiske Meddelelser,
Biologiske Meddelelser.
_^
, Selskabet udgiver desuden efter Behov i
Skrifter med samme
Underinddeling som il Meddelelser.
Selskabets Adresse: Dantes Plads 35, København V.
Selskabets Kommissionær: Ejnar Manksgaard, Nørregade 6,
København K.
-
DET KGL. DANSKE VIDENSKABERNES SELSKAB
BIOLOGISKE MEDDELELSER, B ind XX, N r. 9
THE SPONTANEOUS
FORMATION OF HAPLOID, POLYPLOID,
AND ANEUPLOID EMBRYOS
IN SOME ORCHIDS
BY
0. HAGERUP
KØBENHAVN
I KOMMISSION HOS EJNAR MUNKSGAARD
1947
CONTENTS
'
Page
1. Introduction...............................................................................................
3
2. Listera ovata R. B h................................................. ; ................................
4
3. Platanthera chlorantha
( C u s t e r ) R c h b .....................................................
9
4. Orchis strictifoliiis Opiz . ( = O. incarr^atiis L . ) ......................................
11
5. Cephalanthera longifolia (L . ) ....................................................................
11
6. Cephalanthera Damasonium (Mill . ) .................................
12
7. Aneuploidy (Epipactis s p .).......................................................................
14
8. The Formation of New Species...............................................................
9. Su m m arj'...................................................................................................
17
19
10.
Literature................................................................................................
Printed in Denmark
Bianco Lunos Bogtrj'kkeri
21
1. Introduction.
I
t is a fact that polyploid forms are o f common occurrence in
nature and play an important part both in the spontaneous
formation o f new species as well as in their ecological orientation.
The problems o f polyploidy therefore affect central biological
questions, and the study o f these is of decisive importance.
W e know very little, however, of the w a y s in which the
species change their degree o f polyploidy in nature, and inde­
pendently o f man’s intervention.
It has come to light, however, that the chromosome number
o f a species can undergo even very considerable changes during
the f e r t i l i s a t i o n , which may differ remarkably in the different
ovula found in the s a me ovarium. In the collective species
Orchis maculatus L., embryos thus develop either n, 2n, 3n, 4n,
or 6n (and perhaps also other numbers o f) chromosomes
( H a g e r u p , 1944).
It would seem therefore that Embryology, one o f the neglected
children o f Botany, like Cytology, will prove to be an important
auxiliary science.
O f the spontaneous change of the chromosome number o f a
species from 2n to 3n, 4n, . . . . etc. in nature little is known.
In Orchis maculatus, however, it sometimes happened that more
than one male nucleus penetrated into the female nucleus during
fertilisation and the consequence was that a p o l y p l o i d e m b r y o
wa s p r o d u c e d b y p o l y s p e r m a t y .
Further it will also happen quite normally that some few
per cent. (e. g. 5— 10) of the ovula in an ovarium never receive
any male nucleus but nevertheless continue their development
and form a p a r t h e n o g e n e t i c e m b r y o w h i c h is h a p l o i d ,
with the chromosome number n.
1*
4
Nr. 9
Since the various embryos receive difiering numbers o f genes
from the father, they become genetically different (new species),
and also react in different ways to the environment.
To throw light upon conditions o f such decisive importance
as the abovementioned it is necessary to use as large a material
as possible. In addition to Orchis, therefore, Epipactis laiifolin
Figs. 1— 0. Listera ovata. First stages in development of embryo sac.
x .550.
was studied ( H a g e r u p , 1945), with the result that this species,
too, forms haploid embryos by “ facultative parthenogenesis” .
Below it will, moreover, be shown that the same is the case
with several other orchids, which also develop haploid embryos
without being fertilised.
These species were all gathered in nature in Denmark. They
were fixed on the spot according to L ew itsky and stained with
F e u l g e n , with “ lichtgriin” as a contrast. This technique yields
unique results, and it should be noted that the ovaria o f the
orchids (more particularly Listera and Neottia) are ideal peda­
gogic objects, because the most delicate details, otherwise so
difficult to see in most other plants, are easy to study here.
2. Listera ovata
R. B
r.
Several investigations, recent too, are available both on the
haploid and the diploid chromosome number ( T uschnjakova ,
1929 and R ichard son , 1933). Most commonly n is 17, but often
n may also be 16, 18 or 19. T uschnjakova has given an excellent
description o f how these interesting aneuploid numbers arise by
irregularities o f meiosis (non-disjunction).
So it will here suffice to append some figures showing that
plants from Møn and the vicinity o f Copenhagen have n = 17
5
Nr. 9
9
10
11
Figs. 7-—^11. Listera ovata. Fertilisation. T, pollen tube; ¡^, male nucleus;
female
nucleus; P, polar nucleus; X , tube nucleus. The two male nuclei often adhere
to each other, x 550.
(Figs. 20 and 21), whereas n is 18 (Figs. 18, 19) in plants from
calcareous soil in central Sealand (Alindelille).
The development of the remarkable embryo sac has also been
well investigated by T uschnjakova , so I will here merely figure
(Figs. 1—6) the first stages of the development. No antipodals
are formed, and the mature embryo sac merely seems to contain
4 nuclei; the lower o f these (the polar nucleus) may, however,
divide, so that it consists o f tv\^o or more partly fused nuclei.
T uschnjakova even states that she has found as many as 8
nuclei in embryo sacs o f plants from Russia, but that I have
6
Nr. 9
never seen (her fixations in C arnoy were probably not good.
My Car noy fixations have always been poor).
The fertilisation process is remarkably easy to follow in the
short and broad embryo sac, even when its position in the section
Figs. 12— 14. Lisiera ovata. Polyspermaty. Fig. 12. 2 male nuclei simultaneously
fertilising the egg. x550.
is oblique. The male nuclei (cJ in Fig, 8) are very large and
stain so deeply that they catch the eye at once, even at low
magnification. The polar nucleus ( P in Fig. 8) is dead and shrivelled
already before fertilisation. In this way the female nucleus will
be easy to identify as it cannot, either, be mistaken for the much
smaller synergids. It is therefore possible in a very short time to
follow a large number of fertilisation stages and obtain a reliable
numerical material.
When the tip o f the pollen tube enters the embryo sac, it
kills one synergid and swells considerably. Most frequently all
the 8 nuclei o f the pollen tube enter the embryo sac. The 2 male
nuclei frequently pass together to the female nucleus; and often
they even adhere (Figs. 7, 11) so closely to each other that they
b o t h fuse with the female nucleus s i m u l t a n e o u s l y (Fig. 12).
The polar nucleus, which is dead, is never fertilised, and no
endosperm forms. Hence a male nucleus will as a rule be left
over, and this will be found lying next to the young embryo
(Figs. 25, 2(>).
7
Nr. 9
20
21
Figs. 15— 21. Lislera ovata. Fig. 15. P’acultative parthenogenesis: the female
nucleus shows a metaphase with 2n = 17. x550. Fig. Ih. Parthenogenetic em­
bryo with 2 n = 17. X 2200. Fig. 17. Parthenogenetic anaphase with 2 n = 17.
x 2200. Figs. 18 and 19. Metaphase I in the pollen mother cell, n = 18. x2200.
Fig. 20. Metaphase I in megaspore mother cell with n = 17. x2200. Fig. 21.
Metaphase I in microspore mother cell with n = 17. x2200.
When the male nucleus fuses with the female (Figs. 8, 14, 22),
the male swells, becomes lighter in colour, and its contents are
resolved into fine grains.
It is a common occurrence that an embryo sac receives more
than one pollen tube, and more than 2—3 male nuclei will then
lie next to the female nucleus (Figs. 13, 14). In one case (Fig. 12)
it was even seen that a f e m a l e n u c l e u s wa s f e r t i l i s e d by
2 m a l e n u c l e i s i mu l t a n e o u s l y . That this may lead to the
formation o f triploid embryos was found in Orchis inaciilatas,
but not in Listera whose chromosome number is relatively difficult
to determine.
.
The distribution o f the numerous pollen tubes among the
ovula does not merely go wrong in that one ovulum may receive
Nr. 9
8
25
26
Figs. 22— 26. Listera ovata. Development of twins. Fig. 22. Both egg and synergid
seem to be fertilised. Fig. 23. The female nucleus forms a diploid embryo (2 n
= 34), and the synergid also has begun to develop an embryo. Fig. 24. The egg
is undivided but the synergid has begun to form an embryo. Figs. 25— 26. Fewcelled twins. x550.
more than one pollen tube. It may also sometimes happen (in
about 5 p.c. o f the ovula) that an ovulum does not receive any
pollen tube at all, or the latter may come too late (Fig. 15). Such
an unfertilised ovulum does not die, however, but the female
nucleus begins to divide and develop a p a r t h e n o g e n e t i c emb r y p w h i c h w i l l t he n be h a p l o i d . That this is actually the
9
Nr. 9
case can be decided in such instances in which it is possible to
count the chromosomes in the young embryo. Figs. 15— 17 show
mitoses from such young embryos which have developed by
“ facultative parthenogenesis” . For comparison Figs. 18—21 show
meiosis with n = 17 or 18.
Not rarely are 2 embryos found in a seed (Figs. 28—26). One
0
29
30
O
31
32
O 'j
34
33
Figs. 27— 34. Platanthera chlorantha. Stages of fertilisation. The male nuclei keep
apart. Figs. 27— 28 x 700. Figs. 29—-34 xl500.
o f these has then been formed of a s y n e r g i d , which in some
instances (Fig. 22) seems to be fertilised, hence it must be diploid.
If a synergid develops without fertilisation, the result is a haploid
embryo.
3. Platanthera chlorantha
(C
uster)
Rchb.
The structure and development o f the embryo sac have been
closely studied by A f z e l iu s (1922), so a reference to his work
will suffice.
The tip o f the pollen tube sometimes contains only the 2 male
nuclei. One of the synergids is killed by the pollen tube, which
swells considerably at the tip. A f z e l iu s states (p. 377) that one
o f the male nuclei fuses with the polar nucleus. This I have
never seen, though I have examined many thousands o f ovula
10
Nr. 9
and seen many hundred fertilisation stages. Moreover the polar
nucleus is dead when the egg is fertilised, and I have never
found any endosperm. The 3 small antipodals too are dead in
the ripe embryo sac and soon j^erish.
1 he fusion o f the two sexual nuclei is remarkably easilv
o
36
41
37
42
Figs. 35— 42. Plalanthera chloranfha. Stages of fertilisation. The male nuclei
adhere firmly to each other (superfertilisation?). Fig. 35. One synergid has devel­
oped as a sexual cell (cause of twins).
studied because this process is very slow in Plalanthera (Figs.
27— 34). In some instances the 2 male nuclei do not pass together
to the female which is then only fertilised by one nucleus (Figs.
27— 34), and the embryo will then be diploid (2n = 42).
Nor is it rare that the 2 male nuclei adhere so closely to each
other (Figs. 36—38) that they must both enter the egg s i m u l ­
t a n e o u s l y . In addition it also often happens that an embryo
sac receives more than one pollen tube, the male nuclei o f which
then place themselves in the immediate vicinity o f the egg, which
means that there is a chance o f polyploid embryos being formed
(Figs. 39—41).
As in the above-mentioned species, it may also happen in
Plalanthera that an ovulum which does not receive any pollen
tube develops a p a r t h e n o g e n e t i c embryo, which is h a p l o i d
(Fig. 43) with n = 21.
Nr. 9
11
Fig. 44 shows an embryo sac, one synergid o f which is devel­
oped as a female nucleus. If the latter is not fertilised, a haploid
embryo will arise in this way too (2 n = 21, Fig. 45); it lies
beside the normal diploid embryo, but may often be distinguished
from the latter by a difference in the size o f the nuclei.
Figs. 43— 45. Platanthera cblorantha. F"ig. 43. A haploid embryo (2 ii = 21) is
formed by facultative parthenogenesis. Fig. 44. 2 female nuclei may cause the
formation of twins. (H g. 45) x 800.
4. Orchis Strictifolius O p iz . ( = O. incarnatus L.).
The embryo sac contains 8 nuclei (Fig. 46) of which both the
antipodals and the polar nucleus are dead when fertilisation
takes place, so that no endosperm develops.
Fig. 47 shows that a p a r t h e n o g e n e t i c embryo has devel­
oped (with 2n = 20) in a embryo sac which has not received
any pollen tube.
In an embryological respect the species shows similar con­
ditions to O. maculatus.
5. Cephalanthera longifolia (L .).
Owing to their rarity the Cephalanthera species have not been
subjected to embryological investigations. A fze liu s (1943) found
12
Nr. 9
that C. longifolia has n = 16 in Sweden, and I have found the
same number in plants from S. Sealand (Oreby Forest, Fig. 52).
The development and structure o f the embryo sac entirely
resemble that o f Epipactis; the ripe embryo sac contains 8 nuclei.
In contrast wdth most other orchids the polar nucleus is really
50
Hgs. 46— 50. Orchis striclifolius (incarnatus). Stages of fertilisation. Fig. 47.
Development of a haploid parthenogenetic embryo with 2 n = 20. x 800.
fertilised and develops an endosperm consisting o f quite few'
nuclei that die quickly, so that the ripe seed does not contain
an endosperm.
In this species too a few' p a r t h e n o g e n e t i c h a p l o i d e m ­
b r y o s develop (2n = 16, Fig. 51) when an ovulum is not
fertilised.
6. Cephalanthera Damasonium (M il l .).
O f this magnificent plant abundant material w'as gathered in
Møn, where the fertilisation stages occur at the close of July.
B ar ber found that n = 18, but the plants from Denmark
showed n = 16 and 2n = 32 (Fig. 53). It is possible therefore
that the species contains aneuploid forms.
13
Nr. 9
The structure of the embryo sac is as in C. longifolia and
Epipactis; here too there are 8 nuclei in the embryo sac. The
polar nucleus is also fertilised and develops a paucinuclear endo­
sperm (Fig. 54) which is soon absorbed again.
52
53
Figs. 51— 53. Cephalanthera. Fig. 51. C. longifolia. Development of a parthenogenetic haploid embryo with 2n = 16. x500. Fig. 52. C. longifolia. Metaphase
I in megaspore mother cell with n = 16. x2400. Fig. 53. C. Damasonium. Meta­
phase in young embryo \vith 2 n = 32. x 2400.
Not rarely more than one pollen tube (Fig. 54) enters the
embryo sac and superfertilisation is then possible.
It is also a fairly common occurrence that one o f the synergids
forms an embryo so that the seed will contain t wi n e m b r y o s
(Fig. 55). •
.
.
.
It is, however, of special interest that in this species too the
f e m a l e n u c l e u s m a y d e v e l o p w i t h o u t f e r t i l i s a t i o n , if for
instance the pollen tube should “ come too late” , as shown in
Fig. 56. The consequences o f such a “ facultative parthenogenesis”
will then again be that a p a r t h e n o g e n e t i c embryo will develop,
with 2n = 16.
14
Nr. 9
7. Aneuploidy (Epipactis sp.).
The species grouped around the main species, E. latifolia,
are interesting subjects o f study because they are markedly
p o l y m o r p h o u s ( N a n n f e l d t , A b e r c r o m b i e ) . W hile the isolated
E. palustris has n = 20, B a r b e r states that E. latifolia has
n = 19. In Denmark this species has, however, n = 20 ( H a g e RUP, 1945). SuGiURA even found 2n = 24 in E. falcata, and I
Pigs. 54— 55. Cephalanthera Damasonium. Fig. 54. 2 pollen tubes in embryo sac.
Incipient formation of endosperm, p'ig. 55. Twins, x 500.
found 2n — 36 in E. leptochila (F'ig. 58). It would seem there­
fore that the genus presents an interesting subject for studies on
the bearing o f aneuploidy on the formation of species. Hence
the genus Epipactis should be made the subject o f thorough
research in as many countries as possible.
N a n n f e l d t has made a thorough and excellent revision of
the Scandinavian Epipactis species. I have been able to fix most
ol these forms in nature. E. pérsica H ausskn . was gathered in
Mon, and Chief Veterinarian G. H a r b o u gave me a living spe­
cimen o f E. leptochila ( G o d f . ) from S. Funen (Fig. 58). My special
thanks are, however, due to Dr. C. H e u s s e r who after great
difficulties managed to fix the smallest species, E. microphylla
( E h r h .), in Switzerland (Fig. 57).
Examination o f the root tips showed that 2n = 40 in E.
Nr. 9
15
microphylla (Fig. 57). Altogether the following chromosome num­
bers have been recorded within Epipnctis:
E.
E.
E.
E.
E.
E.
E.
E.
E.
n=
palustris......................................... . . 20
atropurpúrea...................................... 20
latifolia..................................
19 and 20
pérsica..................................................
20
microphylla.........................................
20
leptochila............................................... 18
falcata (S u g i u r a ) .................................
schizuoi ( M i d u n o ,1938)......................... 16
thunbergii (M i d u n o ,1938).....................
20
12
If it be assumed that most of the available numbers are cor­
rect (some of them should perhaps be revised, as they are difficult
to count), there are several different basic numbers within the
genus Epipactis, though many o f the species are so closely related
that they are hard to distinguish from each other. But how, now,
have these species developed from each other?
It would seem that at some time or other polyploidy has
played a part in the development o f some o f the species; for in
particularly well suited stages of division with 2n = 40 the
different size classes o f chromosomes are present in a number
o f 4, and often lying near each other, as indeed is frequently
the case with polyploids.
But the phenomenon of polyploidy does not give the whole
explanation o f how species with such basic numbers as 12, 16,
and 18 can have developed or been derived from each other or
perhaps from 20. These numbers are perhaps aneuploid? To
throw light on this question numerous pollen tetrads were ex­
amined, and it then turned out that in every single micro­
sporangium some few per cent, o f the tetrads were very regularly
found which, in addition to the normal 4 microspores, also con­
tained one or more extra microspores (Figs. 59, 60, 70). The
accessory pollen grain is remarkably small, not only in volume,
but the nucleus evidently contains much less chromatin than
normal pollen grains.
Similar dwarfish pollen is known from many other orchids
and in many other plant families, and their development has been
thoroughly investigated, e. g. by A f z e l i u s , F e r n a n d e s and T u s c h -
16
Nr. 9
57
58
60
Figs. 56. Cephalanthera Damasonium. Facultative parthenogenesis. The egg forms
a haploid embryo with 2 n = 16. x 1100. Fig. 57. Epipactis microphylla (Switzer­
land). Metaphase from root tip with 2 n = 40. x 2400. Fig. 58. Epipactis leptochila. Metaphase from root tip with 2 n = 36. x2400. Figs. 59— 60. Epipactis
persica. Pollen tetrads with extra dwarf pollen. xlOOO. See also text.
NJAKOVA, who found that one or several chromosomes may be
entirely ejected in meiosis and form an independent small pollen
grain. In other instances two sister nuclei do not receive the same
number of chromosomes, one or several gemini migrating, divided
or undivided, to one single nucleus, which thus receives more
chrosomes than the sister nucleus; the latter has then a lower
and aneuploid number ( n o n - d i s j u n c t i o n ) .
In our Danish Epipactis species there are, almost in every
Nr. 9
17
section through a pollen sac, certain microspores from which
arise gametes with a deviating chromosome number. Already
prior to the prophase stages in meiosis, some few nuclei may
thus be found, scattered among the normal pollen mother cells,
which are predestined to form tetraploid pollen grains (Figs. 65,
66). These nuclei have a particularly dense content and are there­
fore also comparatively highty susceptible to staining. In suc­
cessful staining it may even be possible to get the normal nuclei
stained green, and between these the tetraploid mother nuclei
will then appear, stained a vivid scarlet and therefore especially
conspicuous.
Some o f these large nuclei (Fig. 65) do not participate at all
in any meiosis but develop directly into a s i ng l e pollen grain
(Fig. 66) lying isolated among normal tetrads. In other cases
(Fig. 65) the giant mother cells divide once in a mitotic division,
and each o f the daughter cells grows into a t e t r a p l o i d micro­
spore (Fig. 69).
It may also happen that one daughter cell forms two normal
(n = 20) pollen grains (Fig. 67), while the other remains un­
divided and has n = 40. In an apparently normal tetrad, too,
there may occur p o l y p l o i d g i a n t n u c l e i (Fig. 71).
If a polyploid female gamete is fertilised by a similar male
gamete, a p o l y p l o i d e m b r y o may be formed. Polyploid Epipactis plants should be looked for in nature where giant plants
are sometimes met with.
8. The Formation of New Species.
Thus Epipactis seems to be a standard example of how
g a me t e s w i t h a d e v i a t i n g c h r o m o s o m e n u m b e r m a y
d e v e l o p s p o n t a n e o u s l y in nat ure. And it is important to
note that, though the species do not seem to be direct hybrids,
yet there is n o r m a l l y d i s t i n c t n o n - d i s j u n c t i o n in the forma­
tion o f a certain small number o f pollen grains in e a c h pollen
sac. This alfords a chance for the development o f individuals
with aneuploid chromosome numbers; such individuals must also
have new genetic characters, and so they must also have the
chance o f becoming founders o f new species. And as a matter
D. Kgl. Danske Vidensk. Selskab. B iol. M edd. XX, 9.
*
2
18
Nr. 9
f
61
64
62
^
63
/ P
B
T
65
66
O
67
Figs. 61— 71. Epipactis laiifolia. Non-disjunction. During meiosis one or more
uni- or bi-valent chromosomes are ejected (Figs. 61— 64), and microspores are
formed with different aneuploid numbers and nuclei of different sizes. The largest
nuclei are polyploid (Figs. 65, 66, and 69). x 1000. See also the text.
o f fact, a number o f such microspecies with deviating aneuploid
numbers occur in nature. (But it must be borne in mind that
there also occur microspecies with the same chromo.some number,
which have not developed in this w ay.)
The genus Orchis ( H a g e r u p ) affords a particularly fine ex­
ample of what an important part the fluctuations in the degree
o f polyploidy in nature may play for the s p o n t a n e o u s forma­
tion of species. In many other orchids too haploid embryos may
develop by “ facultative parthenogenesis” . The higher degrees of
polyploidy may also develop either by (1 ) “ s u p e r f e r t i l i s a ­
t i o n ” or (2 ) by the normal formation o f single p o l y p l o i d
p o l l e n g r a i n s and gametes.
Quite schematically these processes may be expressed numeric­
ally by the fact that a chromosome number (e. g. n = 20) can
19
Nr. 9
be multiplied (or divided) by e. g. 2, 3, 4, etc. or it may be
subjected to a subtraction or an addition so that it is changed
from n = 20 to n = 20 i 1 zb 2 etc. Or a given number may
be subjected to more than one o f these processes.
That the above-mentioned conditions also occur perhaps in
most other plants is illustrated by the fact that e. g. Pyrolaceae
( H a g e r u p ) has the basic number 8. But in addition the family
also contains the polyploid number 3 X 8 as well as the aneuploid number 3 X 8 - r 1 and even ( 3 x 8 - r l ) x 2 . Others
again o f the family have n = 13 or 19, which numbers have
presumably also arisen by non-disjunction. Within many other
smaller or larger systematic units we find similar numerical con­
ditions due to polyploidy and aneuploidy.
Most o f the many chromosome numbers already known from
other orchids seem to be aneuploid. It may be conjectured there­
fore that an essential part o f the causes o f the remarkably rich
species formation in the orchids may partly be explained as
phenomena connected with (1 ) a n e u p l o i d y and (2 ) fluctuations
in the degree o f p o l y p l o i d y .
Such changes in the number o f chromosomes (and the corre­
sponding genetic composition) of the species thus take place
s p o n t a n e o u s l y in nat ure. In this I see s o me o f the chief
causes of the spontaneous formation of species. How this species
formation is then again dependent on, for instance, pollination
and other e x t e r n a l factors should be studied more closely.
My respectful thanks are due to the C a r l s b e r g F o u n d a t i o n
for tbe grants enabling me to pursue these studies, and to Pro­
fessor C. A. J ø r g e n s e n who has given me much help with the
difficult chromosome counts.
9. Summary.
1. The following 7 species were studied: Listera ovata, Platanthera chlorantha. Orchis incarnatus, Cephalanthera longifolia,
C. Damasonium, Epipactis microphylla, and E. leptochila.
2. In nearly all o f these species some few per cent, o f the e m ­
bryos we r e d e v e l o p e d by “ f ac ul t at i v e p a r t h e n o ­
g e n e s i s ” and w e r e thus h a p l o i d .
2*
20
Nr. 9
3. In some, polyploid embryos may perhaps also be formed,
because (1 ) more than one male nucleus enters the egg ( p o l y s p e r m a t y ) or ( 2) by p o l y p l o i d g amet es .
4. After irregularities in meiosis ( n o n - d i s j u n c t i o n ) g a me t e s
ar e f o r m e d , w i t h a n e u p l o i d c h r o m o s o m e n u mb e r s .
5. It is conjectured on general grounds that the circumstances
associated with (1 ) a n e u p l o i d y and with the degree o f fluc­
tuation in (2 ) p o l y p l o i d y ar e a m o n g the mo s t i m p o r t a n t
o f the s p e c i e s - f o r m i n g f a c t o r s in nat ure. The depen­
dence o f these factors on external conditions should be sub­
jected to close investigations.
Botanical Museum, Copenhagen 19A7.
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{Epipactis latifolia) in the Peak district. Northwest Nat. Bd. 20,
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A f z e l iu s , K. (1922): Embryosackentwicklung und Chromosomenzahl
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— (1943): Zytologische Beobachtungen an einigen Orchidaceen.
Svensk Bot. Tidskrift. Bd. 37, Hf. 3, S. 266.
B a r b e r , H. N. (1942): The Pollen-Grain Division in the Orchidaceae.
Journ. of Genetics. Bd. 43, p. 97.
D u n c a n , R. E. (1945): Production of variable aneuploid numbers of
chromosomes within the root tips of Paphiopedilum Wardii. Amer.
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F e r n a n d e s , A. (1946): Sur le devenir des micronoyaux formés à la
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G u ig n a r d , L. (1884): Recherches sur la structure et la division du
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32, S. 6— 14.
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latifolia. Det Kgl. Danske Vidensk. Selskab. Biologiske Medde­
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H eusser , c . (1938): Chromosomenverhältnisse bei schweizerischen
bastionen Orchideen. Ber. Schweiz. Bot. Ges. Bd. 48.
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Phanérogames. II. Listera ouata. La Cellule. Bd. 36. Se Schürhof
S. 501.
M id u n o , T. (1940): Chromosomenstudien an Orchidazeen. III. Über
das Vorkommen von haploiden Pflanzen bei Bletilla striata R e ic h e .
f. var. gebina R e ic h e , f. Cytologia. Tokyo. Bd. 11, S. 156.
— (1940): Chromosomenstudien an Orchidazeen. VI. Cytologia,
Bd. 11, S. 179— 185.
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N a n n f e l d t , J. A. (1946): Tre for Norden nya Epipactis-artev, E. pér­
sica H a u s s e n ., E. leptochila (G o d f .) och E. purpúrala Sm. Bota­
niska Noliser, S. 1.
R ic h a r d so n , M. M. (1933): Chromosome Variation in Listera ovala
R. BR. University of California Publications in Botany. Vol. 17,
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T u sc h n ja k o v a , m . (1929): Embryologische und zytologische Beob­
achtungen über Listera ovala. Planta. Bd. 7, S. 29.
V er m o ese n , Ca m il l e (1911); Contribution à l’étude de l’ovule, du sac
embryonnaire et de la fécondation dans les angiospermes (Neottia,
Orchis latifolia, O. macúlala, Epipactis palustris, E. latifolia). La
cellule. Vol. 27.
Indleveret Ul Selskabet den 14. Januar 1947.
Færdig fra Trykkeriet den 26. November 1947.
DET KGL. DANSKE VIDENSKABERNES SELSKAB
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their Structural Interpretation. 1942 ............ ......................
3. L emche, H en n in g : Studien über die Flügelzeichnungen der In­
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posits from the Ice Age and the Post-glacial Warm Period.
1942......... .......... ................. ........................... < ..............
5. B ørgesen, F.: Some Marine Algae from Mauritius. III. Rhodophyceae. Part 1. Porphyridiales, Bangiales, Nemalionales. 1942
6. H agerup , O.: The Morphology and Biology of the CorylusFruit. 1942.......... '.................. ...................................... .
7. B røndsted , H.V.: Further Experiments on Regeneration-Problems in Planarians. 1942........................................... ........
8. V. E uler , H. und v. H evesy , G.: Wirkung der Röntgenstrahlen
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10. B ørgesen , F.: Some Marine Algae from Mauritius. III. Rhodophyceae. Part 4. Ceramiales. 1945 .........................................
11. H ÅGERUP, O.: Facultative Parthenogenesis and Haploidy in
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5. H agerup , O.: Studies on the Empetraceae. 1946.....................
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nium Robertianum L. 1947 ............................................... .
9. H agerup , O.: The Spontaneous Formation of Haploid, Poly­
ploid, and Aneuploid Embryos in some Orchids. 1947 ........
10. Jørgensen , C. B arker : On the Spicule-Formation of Spongilla
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Id: 228
Forfatter: Hagerup, 0.
Titel: The Spontaneous Formation of Flaploid, Polyploid, and Aneuploid Embryos
in some Orchids.
Ar: 1947
ISBN:
Serietitel: Biologiske Meddelelser
Serienr: B 20:9
SerienrFork: B
Sprogkode: Eng