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THE DIFFERENT FORMS OF
FLOWERS ON PLANTS OF
THE SAME SPECIES
BY
CHARLES DARWIN, M.A., F.R.S.
WITH ILLUSTRATIONS
NEW YORK
D. APPLETON AND COMPANY
1896
bean
QK
ARG
D2!
IS
Authorized Edition.
TO
PROFESSOR ASA GRAY
THIS VOLUME IS DEDICATED BY THE AUTHOR
AS A SMALL TRIBUTE OF RESPECT AND AFFECTION,
CONTENTS.
InrRoDUCTION ve te ae ae te wee we) Page 1-18
CHAPTER IL
UsteRostyLeD Dimorpyuic PLants: PRrimuLAcEs.
Primula veris or the Cowslip—Differences in structure between the
two forms—Their degrees of fertility when legitimately and ille-
gitimately united—P. elatior, vulgaris, Sinensis, auricula, &e.—
Summary on the fertility of the heterostyled species of Primula—
Homostyled species of Primula—Hottonia palustris—Androsace
Vitalliana fooled): ate EA Sie. Gh! ase ae. Se dod
CHAPTER II
Hysrip Primunas.
The Oxlip a hybrid naturally produced between Primula veris and
vulgaris—The differences in structure and function between the
two parent-species—Effects of crossing long-styled and short-
styled Oxlips with one another and with the two forms of both
parent-species—Character of the offspring from Oxlips artificially
self-fertilised and cross-fertilised in a state of «ature—Primuia
elatior shown to be a distinct species—Hybrids between other
heterostyled species of Primula—Supplementary note on spon-
taneously produced hybrids in the genus Verbastum .. 55-80
Vi CONTENTS.
CHAPTER III.
TletenostyLep Dimorputio PLaNrs—continucd.
Linum grandiflorum, long-styled form utterly sterile with own-form
pollen—Linum perenne, torsion of the pistils in the long-styled
form alone—Homostyled species of Linum—Pulmonaria offici-
nalis, singular difference in self-fertility between the English
and German long-styled plants—Pulmonaria angustifolia shown
to be a distinct species, long-styled form completely self-sterile—
Polygonum fagopyrum—Various other heterostyled genera—
Rubiacex—Mitchella repens, fertility of the flowers in pairs—
Houstonia—Faramea, remarkable difference in the pollen-grains
of the two forms; torsion of the stamens in the short-styled
form alone; development not as yet perfect—The heterostyled
structure in the several Rubiaceous genera not due to descent in
common ., .. «eee ee we ee we~S Page 81-186
CHAPTER IV.
HETEROSTYLED TrimorPHic PLaNts,
Lythrum salicaria—Description of the three forms—Their power and
complex manner of fertilising one another—Eighteen different
unions possible—Mid-styled form eminently feminine in nature
—Lythrum Greefferi likewise trimorphic—L. thymifolia dimor-
phic—L. hyssopifolia homostyled—Neswa verticillata trimorphic
—Lagerstreemia, nature doubtful—Oxalis, trimorphic species of
—O. Valdiviana—O. Regnelli, the illegitimate unions quite
barren—O. speciosa—O. sensitiva—Homostyled species of Oxalis
—Pontederia, the one monocotyledonous genus known to include
heterostyled species .. «2 «2 0. 0.) we )=-187-187
CHAPTER V.
ILLEGITIMATE OFFSPRING OF HETEROSTYLED PLANTS
Illegitimate offspring from all three forms of Lythrum salicaria—
Their dwarfed stature and sterility, some utterly barren, some
CONTENTS. vii
fertile—Oxalis, transmission of form to the legitimate and il-
legitimate seedlings— Primula Sinensis, illegitimate offspring in
some degree dwarfed and infertile—Hqual-styled varieties of P.
Sinensis, auricula, farinosa, and elatior—P. vulgaris, red-flowered
variety, illegitimate seedlings sterile—P. veris, illegitimate
plants raised during several successive generations, their dwarfed
stature and sterility—Equal-styled varieties of P, veris—Trans-
mission of form by Pulmonaria and Polygonum—OConcluding
remarks—Close parallelism between illegitimate fertilisation and
hybridism .. 0. 4. 4. eee) Page 188-243
CHAPTER VI.
Coxctupinc Remarks on HetTerosTyLep PLants.
The essential character of heterostyled plants—Summary of the
differences in fertility between legitimately and illegitimately
fertilised plants—Diameter of the pollen-grains, size of anthers
and structure of stigma in the different forms—Affinities of the
genera which include heterostyled species—Nature of the
advantages derived from heterostylism—The means by which
plants became heterostyled—Transmission of form—Equal-
styled varieties of heterostyled plants—Final remarks 244-277
CHAPTER VII.
cd
Ponyeamous, Diccious, anD GyNo-pi@cious PLANTS,
The conversion in various ways of hermaphrodite into dicecious
plants—Heterostyled plants rendered dicecious—Rubiaceee—
Verbenacex—Polygamous and sub-dicecious plants—Kuonymus
—Fragaria—The two sub-forms of both sexes of Rhamnus and
Epigwa—Ilex—Gyno-dicecious plants—Thymus, difference in
fertility of the hermaphrodite and female individuals—Satureia
—Manner in which the two forms probably originated—Scabiosa
and other gyno-diecious plants—Difference in the size of the
corolla in the forms of polygamous, dicecious, and gyno-dicecious
plants -. ue ue ee eee ete ee 278-809
viii CONTENTS
CHAPTER VIII.
CLeIstogaAMic Flowers.
General character of cleistogamic flowers— List of the genera pro-
ducing such flowers, and their distribution in the vegetable
series—Viola, description of the cleistogamic flowers in the
several species; their fertility compared with that of the perfect
flowers—Oxalis acetosella—O. sensitiva, three forms of cleisto-
gamic flowers—Vandellia—Ononis—Impatiens—Drosera— Mis-
cellaneous observations on various other cleistogamic plants—
Anemophilous species producing cleistogamic flowers—Leersia,
perfect flowers rarely developed—Summary and concluding
remarks on the origin of cleistogamic flowers—The chief con-
clusions which may be drawn from the observations in this
volume tee nee wee ewe Page 810-845
INDEX! gg.) say GS Me Re ee ee ee eS es 18 4E S852
THE
DIFFERENT FORMS OF FLOWERS
on
PLANTS OF THE SAME SPECIES.
INTRODUCTION.
THE subject of the present volume, namely the dif-
ferently formed flowers normally produced by certain
kinds of plants, either on the same stock or on distinct
stocks, ought to have been treated by a professed bota-
nist, to which distinction I can lay no claim. As far as
the sexual relations of flowers are concerned, Linnzus
long ago divided them into hermaphrodite, monecious,
dicecious, and polygamous species. This fundamental
distinction, with the aid of several subdivisions in each
of the four classes, will serve my purpose; but the
classification is artificial, and the groups often pass
into one another.
The hermaphrodite class contains two interesting
sub-groups, namely, heterostyled and cleistogamic
plants; but there are several other less important
subdivisions, presently to be given, in which flowers
differing in various ways from one another are pro-
duced by the same species.
Some plants were described by me several years ago,
in a series of papers read before the Linnean Society,*
* “On the Two Forms or Di- of Primula, and on their remark-
morphic Condition in the Species able Sexual Relations.” ‘Journal
2 INTRODUCTION.
the individuals of which exist under two or three
forms, differing in the length of their pistils and
stamens and in other respects. They were called by
me dimorphic and trimorphic, but have since been
better named by Hildebrand, heterostyled.* As I
have many still unpublished observations with respect
to these plants, it has seemed to me advisable to re-
publish my former papers in & connected and cor-
rected form, together with the new matter. It will be
shown that these heterostyled plants are adapted for
reciprocal fertilisation ; so that the two or three forms,
though all are hermaphrodites, are related to one
another almost like the males and females of ordinary
unisexual animals. I will also give a full abstract of
such observations as have been published since the
appearance of my papers; but only those cases will be
noticed, with respect to which the evidence seems fairly
satisfactory. Some plants have been supposed to be
heterostyled merely from their pistils and stamens
varying greatly in length, and I have been myself
more than once thus deceived. With some species the
of the Proccedings of the Linnean
Society,’ vol. vi. 1862, p. 77.
“On the Existence of Two
Forms, and on their Reciprocal
Sexual Relation, in several Species
of the Genus Linum.” Ibid. vol.
vii. 1863, p. 69.
“ On the Sexual Relations of the
Three Forms of Lythrum salicaria,
Ibid. vol. viii. 1864, p. 169.
“On the Character and Hybrid-
like Nature of the Offspring from
tho Illegitimate Unions of Dimor-
hic and Trimorphic Plants,”
Pid. vol. x. 1868, p. 393.
“On the Specific Differences
between Primula veris, Brit. Fi.
(var. officinalis, Linn.), P. vulgaris,
Brit. Fl. (var. acaulis, Linn.), and
P. elatior, Jacq.; and on the
Hybrid Nature of the Common
Oxlip. With Supplementary Re-
marks on Naturally Produced Hy-
brids in the Genus Verbascum.”
Ibid. vol. x. 1868, p. 437.
* The term“ heterostyled” docs
not express all the differences be-
tween the forms; but this is a
failure common in raany cases.
As the term has been adopted by
writers in various countries, I am
unwilling to change it fur that of
heterogone or heterogonous, though
this has been proposed by so hish
an authority as Prof. Asa Gray:
see the ‘American Naturalist,
Jan. 1877, p. 42.
INTRODUCTION. 8
pistil continues growing for a long time, so that if old
and young flowers are compared they might be thought
to be heterostyled. Again, a species tending to become
dicecious, with the stamens reduced in some individuals
and with the pistils in others, often presents a decep-
tive appearance. Unless it be proved that one form
is fully fertile only when it is fertilised with pollen
from another form, we have not complete evidence
that the species is heterostyled. But when the pistils
and stamens differ in length in two or three sets of
individuals, and this is accompanied by a difference in
the size of the pollen-grains or in the state of the
stigma, we may infer with much safety that the species
is heterostyled. I have, however, occasionally trusted
to a difference between the two forms in the length
of the pistil alone, or in the length of the stigma
together with its more or less papillose condition; and
in one instance differences of this kind have been
proved by trials made on the fertility of the two forms,
to be sufficient evidence.
The second sub-group above referred to consists of
hermaphrodite plants, which bear two kinds of flowers
—the one perfect and fully expanded—the other mi-
nute, completely closed, with the petals rudimentary,
often with some of the anthers aborted, and the re-
maining ones together with the stigmas much reduced:
in size; yet these flowers are perfectly fertile. They
have been called by Dr. Kuhn* cleistogamic, and they
* «Botanische Zeitung,’ 1867,
p. 65. Several plants are known
occasionally to produce flowers
destitute of a corolla; but they
belong to a different class of
cases from cleistogamic flowers.
This deficiency seems to result
from the conditious to which the
plants have heen subjected, and
partakes of the nature of a mone
strosity. All the flowers on the
same plant are commonly affected
in the same manner. Such cases,
though they have sometimes been
ranked as cleistogamic, do not
come within our present seope :
see Dr. Maxwell Masters, ‘ Vege:
table Terutology,’ 1869, p. 402
4 INTRODUCTION.
will be described in the last chapter of this volume.
They are marifestly adapted for self-fertilisation, which
is effected at the cost of a wonderfully small expendi-
ture of pollen; whilst the perfect flowers produced by
the same plant are capable of cross-fertilisation. Cer-
tain aquatic species, when they flower beneath the
water, keep their corollas closed, apparently to protect
their pollen; they might therefore be called cleisto-
gamic, but for reasons assigned in the proper place are
not included in the present sub-group. Several cleis-
togamic species, as we shall hereafter see, bury their
ovaries or young capsules in the ground; but some few
other plants behave in the same manner; and, as they
do not bury all their flowers, they might have formed
a small separate subdivision.
Another interesting subdivision consists of certain
plants, discovered by H. Miller, some individuals
of which bear conspicuous flowers adapted for cross-
fertilisation by the aid of insects, and others much
smaller and less conspicuous flowers, which have often
been slightly modified so as to ensure self-fertilisation.
Lysimachia vulgaris, Euphrasia officinalis, Rhinanthus
crista-gallt, and Viola tricolor come under this head.*
The smaller and less conspicuous flowers are not closed,
but as far as the purpose which they serve is con-
cerned, namely, the assured propagation of the species,
they approach in nature cleistogamic flowers; but they
differ from them by the two kinds being produced on
distinct plants. é
With many plants, the flowers towards the outside of
the inflorescence are much larger and more conspicu-
ous than the central ones. As I shall not have occa-
* H. Miiller, ‘Nature,’ Sept. 25, ‘Die Befruchtung der Blumen,
1873 (vol. viii.), p. 433, and Nov. &e., 1878, p. 294.
20, 1873 (vol. ix.), p. 44. Also
INTRODUCTION. 5
sion to refer to plants of this kind in the following
chapters, I will here give a few details respecting them.
It is familiar to every one that the ray-florets of the
Composite often differ remarkably from the others; and
so it is with the outer flowers of many Umbellifera,
some Cruciferee and a few other families. Several
species of Hydrangea and Viburnum offer striking
instances of the same fact. The Rubiaceous genus
Musseenda presents a very curious appearance from
some of the flowers having the tip of one of the sepals
developed into a large petal-like expansion, coloured
either white or purple. The outer flowers in several
Acanthaceous genera are large and conspicuous but
sterile ; the next in order are smaller, open, moderately
fertile and capable of cross-fertilisation; whilst the
central ones are cleistogamic, being still smaller, closed
and highly fertile; so that here the inflorescence con-
sists. of three kinds of flowers.* From what we know
in other cases of the use of the corolla, coloured bractez,
&ec., and from what H. Miller has observed} on the
frequency of the visits of insects to the flower-heads of
the Umbelliferee and Composite being largely deter-
mined by their conspicuousness, there can be no doubt
that the increased size of the corolla of the outer
flowers, the inner ones being in all the above cases
small, serves to attract insects. The result is that
cross-fertilisation is thus favoured. Most flowers wither
soon after being fertilised, but Hildebrand states} that
the ray-florets of the Composite last for a long time,
until all those on the disc are impregnated; and this
clearly shows the use of the former. The ray-florets,
* J. Scott,‘ Journal of Botany,’ men,’ pp. 108, 412.
London, new series, vol. i. 1872, t See his interesting memoir,
pp. 161-164. ‘Ueber die Geschlechtsverhiltniss
+ ‘Die Befruchtung der Blu- bei den Compositen,’ 1869, p. 92.
§ INTRODUCTION.
however, are of service in another and very different
manner, namely, by folding inwards at night and
during cold rainy weather, so as to protect the florets
of the disc.* Moreover they often contain matter
which is excessively poisonous to insects, as may be
seen in the use of flea-powder, and in the case of
Pyrethrum, M. Belhomme has shown that the ray-
florets are more poisonous than the disc-florets in the
ratio of about three to two. We may therefore believe
that the ray-florets are useful in protecting the flowers
from being gnawed by insects.t
It is a well-known yet remarkable fact that the cir-
cumferential flowers of many of the foregoing plants
have both their male and female reproductive organs
aborted, as with the Hydrangea, Viburnum and certain
Composite ; or the male organs alone are aborted, as
in many Composite. Between the sexless, female and
hermaphrodite states of these latter flowers, the finest
gradations may be traced, as Hildebrand has shown. }
He also shows that there is a close relation between
the size of the corolla in the ray-florets and the degree
of abortion in their reproductive organs. As we have
good reason to believe that these florets are highly
serviceable to the plants which possess them, more
especially by rendering the flower-heads conspicuous
* Kerner clearly shows that gnawed, and thus the organs of
this is the case :‘ Die Schutzmittel —_fructitication are protected. My
des Pullens,’ 1873, p. 28. > grandfather in 1790 (‘Loves of
+ ‘Gardener’s Chronicle,’ 1861, the Plants,’ canto iii, note to lines
p. 1067. Lindley, ‘Vegetable 184, 188) remarks that “The
Kingdom, on Chrysanthemum, flowers or petals of plants are
1853, p. 706. Kerner in his in- perhaps in general more acrid
teresting essay (‘DieSchutzmittel than their leaves; hence they are
der Bliithen gegen unberufene much seldomer caten by insects.”
Giste” 1875, p. 19) insists that $ ‘Ueber die Geschlechtsver-
the petals of most plants contain hiltnisse bei den Compositen,’
matter which is offensive to in- 1869, pp. 78-91.
sects, so that they are seldom
INTRODUCTION. 4
to insects, it is a natural inference that their corollas
have been increased in size for this special purpose ;
and that their development has subsequently led,
through the principle of compensation or balance-
ment, to the more or less complete reduction of the
reproductive organs. But an opposite view may be
maintained, namely, that the reproductive organs
first began to fail, as often happens under cultiva-
tion,* and, as a consequence, the corolla became,
through compensation, more highly developed. This
view, however, is not probable, for when hermaphrodite
plants become dicecious or gyno-dicecious—that is,
are converted into hermaphrodites and females—the
corolla of the female seems to be almost invariably
reduced in size in consequence of the abortion of the
male organs. The difference in the result in these two
classes of cases, may perhaps be accounted for by the
matter saved through the abortion of the male organs in
the females of gyno-dicecious and dicecious plants being
directed (as we shall see in a future chapter) to the for-
mation of an increased supply of seeds; whilst in the
case of the exterior florets and flowers of the plants
which we are here considering, such matter is expended
in the development of a conspicuous corolla. Whether
in the present class of cases the corolla was first af-
fected, as seems to me the more probable view, or the
reproductive organs first failed, their states of develop-
ment are now firmly correlated. We see this well illus-
trated in Hydrangea and Viburnum; for when these
plants are cultivated, the corollas of both the interior
and exterior flowers become largely developed, and
their reproductive organs are aborted.
* I have discussed this subject xviii. 2nd edit. vol. ii. pp. 152,
in my ‘Variation of Animals and 156.
Plants under Domestication,’ chap.
2
8 INTRODUCTION.
There is a closely analogous subdivision of plants,
including the genus Muscari (or Feather Hyacinth)
and the allied Bellevalia, which bear both perfect
flowers and closed bud-like bodies that never expand.
The latter resemble in this respect cleistogamic
flowers, but differ widely from them in being sterile
and conspicuous. Not only the aborted flower-buds
and their peduncles (which are elongated apparently
through the principle of compensation) are brightly
coloured, but so is the upper part of the spike—
all, no doubt, for the sake of guiding insects to the
inconspicuous perfect flowers. From such cases as
these we may pass on to certain Labiate, for instance,
Salvia Horminum, in which (as I hear from Mr. Thisel-
ton Dyer) the upper bracts are enlarged and brightly
coloured, no doubt for the same purpose as before, with
the flowers suppressed.
In the Carrot and some allied Umbellifers, the cen-
tral flower has its petals somewhat enlarged, and these
are of a dark purplish-red tint; but it cannot be sup-
posed that this one small flower makes the large white
umbel at all more conspicuous to insects. The cen-
tral flowers are said* to be neuter or sterile, but I
obtained by artificial fertilisation a seed (fruit) appa-
rently perfect from one such flower. Occasionally two
or three of the flowers next to the central one are simi-
larly characterised ; and according to Vaucherf “cette
singuliére dégénération s’étend quelquefois & Pombelle
entiére.” That the modified central flower is of no
functional importance to the plant is almost certain.
It may perhaps be a remnant of a former and ancient
zondition of the species, when one flower alone, the
* The English Flora, by Sir d’Europe,’ 1841, tom. ii. p. 614
J. E. Smith, 1824, vol. ii. p. 39, On the Echinophora, p. 627,
{ ‘Hist. Phys. des Plantes
INTRODUCTION. 9
central one, was female and yielded seeds, as in the
umbelliferous genus Echinophora. There is nothing
surprising in the central flower tending to retain its
former condition longer than the others; for when ir-
regular flowers become regular or peloric, they are apt
to be central ; and such peloric flowers apparently owe
their origin either to arrested development—that is, to
the preservation of an early stage of development—or
to reversion. Central and perfectly developed flowers
in not a few plants in their normal condition (for in-
stance, the common Rue and Adoxa) differ slightly in
structure, as in the number of the parts, from the other
flowers on the same plant. All such cases seem con-
nected with the fact of the bud which stands at the
end of the shoot being better nourished than the
others, as it receives the most sap.*
The cases hitherto mentioned relate to hermaphro-
dite species which bear differently constructed flowers ;
but there are some plants that produce differently
formed seeds, of which Dr. Kuhn has given a list.f
With the Umbelliferze and Composite, the flowers that
produce these seeds likewise differ, and the differences
in the structure of the seeds are of a very important
nature. The causes which have led to differences in
the seeds on the same plant are not known; and it is
very doubtful whether they subserve any special end.
We now come to our second Class, that of moncecious
species, or those which have their sexes separated but
borne on the same plant. The flowers necessarily
differ, but when those of one sex include rudiments
* This whole subject, including Domestication,” chap. xxvi. 2nd
pelorism, has been discussed, and edit. vol. ii. p. 338.
references given, in my * Variation t ‘Bot. Zeitung,’ 1867, p. 67.
of Animals and Plants under
10 INTRODUCTION.
of the other sex, the difference between the two kinds
is usually not great. When the difference is great,
as we see in catkin-bearing plants, this depends
largely on many of the species in this, as well as in
the next or dicecious class, being fertilised by the
aid of the wind;* for the male flowers have in this
case to produce a surprising amount of incoherent
pollen. Some few moneecious plants consist of two
bodies of individuals, with their flowers differing in
function, though not in structure; for certain indivi-
duals mature their pollen before the female flowers on
the same plant are ready for fertilisation, and are called
proterandrous ; whilst conversely other individuals,
called proterogynous, have their stigmas mature before
their pollen is ready. The purpose of this curious func-
tional difference obviously is to favour the cross-fertili-
sation of distinct plants. A case of this kind was first
observed by Delpino in the Walnut (Juglans regia), and
has since been observed with the common Nut (Corylus
avellana). I may add that according to H. Miller the
individuals of some few hermaphrodite plants differ in
a like manner; some being proterandrous and others
proterogynous.t On cultivated trees of the Walnut and
Mulberry, the male flowers have been observed to abort
on certain individualstf, which have thus been converted
into females; but whether there are any species in a
state of nature which co-exist as moncecious and female
individuals, I do not know.
The third Class consists of dicecious species, and the
* Delpino, ‘Studi sopra uno
Lignaggio Anemofilo” Firenze,
1871.
t Delpino, ‘Ult. Osservazioni
sulla Dicogamia,’ part ii. fase. ii.
p. 337, Mr. Wetterhan and H.
Miller ou Corylus, ‘ Nature,’ vol.
xi. p. 507, and 1875, p. 26. On
proterandrous and proterogynous
hermaphrodite individuals of the
same species, see H. Miiller, ‘Die
Befruchtung,’ &., pp. 285, 339.
t ‘Gardener’s Chron,’ 1847 pp.
541, 558.
INTRODUCTION. 11
remarks made under the last class with respect to the
amount of difference between the male and female
flowers are here applicable. It is at present an in-
explicable fact that with some diccious plants, of
which the Restiacee of Australia and the Cape of
Good Hope offer the most striking instance, the dif-
ferentiation of the sexes has affected the whole plant
to such an extent (as I hear from Mr. Thiselton Dyer)
that Mr. Bentham and Professor Oliver have often
found it impossible to match the male and female spe-
cimens of the same species. In my seventh chapter
some observations will be given on the gradual con-
version of heterostyled and of ordinary hermaphrodite
plants into dicecious or sub-dicecious species.
The fourth and last Class consists of the plants which
were called polygamous by Linnzus; but it appears to
me that it would be convenient to confine this term to
the species which co-exist as hermaphrodites, males and
females; and to give new names to several other com-
binations of the sexes—a plan which I shall here
follow. Polygamous plants, in this confined sense of
the term, may be divided into two sub-groups, accord-
ing as the three sexual forms are found on the same
individual or on distinct individuals. Of this latter or
trioicous sub-group, the common Ash (Frawinus ex-
celsior) offers a good instance: thus, I examined during
the spring and autumn fifteen trees growing in the
same field; and of these, eight produced male flowers
alone, and in the autumn not a single seed ; four pro-
duced only female flowers, which set an abundance of
seeds; three were hermaphrodites, which had a dif-
ferent aspect from the other trees whilst in flower, and
two of them produced nearly as many seeds as the
female trees, whilst the third produced none, so that it
12 INTRODUCTION.
was in function a male. The separation of the sexes,
however, is not complete in the Ash; for the female
flowers include stamens, which drop off at an early
period, and their anthers, which never open or dehisce,
generally contain pulpy matter instead of pollen. On
some female trees, however, I found a few anthers con-
taining pollen-grains apparently sound. On the male
trees most of the flowers include pistils, but these like-
wise drop off at an early period ; and the ovules, which
ultimately abort, are very small compared with those
in female flowers of the same age.
Of the other or monoicous sub-group of polygamous
plants, or those which bear hermaphrodite, male and
female flowers on the same individual, the common
Maple (Acer campestre) offers a good instance; but
Lecoq states * that some trees are truly dicecious, and
this shows how easily one state passes into another.
A considerable number of plants generally ranked
as polygamous exist under only two forms, namely, as
hermaphrodites and females; and these may be called
gyno-dicecious, of which the common Thyme offers a
good example. In my seventh chapter I shall give
some observations on plants of this nature. Other
species, for instance several kinds of Atriplex, bear on
the same plant hermaphrodite and female flowers; and
these might be called gyno-moneecious, if a name were
desirable for them.
Again there are plants which produce hermaphrodite
and male flowers on the same individual, for in-
stance, some species of Galium, Veratrum, &c.; and
these might be called andro-monecious. If there
exist plants, the individuals of which consist of her-
maphrodites and males, these might be distinguished
/
* ‘ Géographie Botanique,’ tom: v. p. 367.
INTRODUCTION. 13
as andro-diecious. But, after making inquiries from
several botanists, I can hear of no such cases. Lecoq,
however, states,* but without entering into full details,
that some plants of Cultha palustris produce only male
flowers, and that these live mingled with the her-
maphrodites. The rarity of such cases as this last one
is remarkable, as the presence of hermaphrodite and
male flowers on the same individual is not an un-
usual occurrence; it would appear as if nature did
not think it worth while to devote a distinct indi-
vidual to the production of pollen, excepting when
this was indispensably necessary, as in the case of
dicecious species.
I have now finished my brief sketch of the several
cases, as far as known to me, in which flowers differing
in structure or in function are produced by the same
species of plant. Full details will be given in the fol-
lowing chapters with respect to many of these plants.
I will begin with the heterostyled, then pass on to
certain dicecious, sub-dicecious, and polygamous species,
and end with the cleistogamic. For the convenience of
the reader, and to save space, the less important cases
and details have been printed in smaller type.
I cannot close this Introduction without expressing
my warm thanks to Dr. Hooker for supplying me with
specimens and for other aid; and to Mr. Thiselton
Dyer and Professor Oliver for giving me much in-
formation and other assistance. Professor Asa Gray,
also, has uniformly aided me in many ways. To Fritz
Miller of St. Catharina, in Brazil, 1 am indebted for
many dried flowers of heterostyled plants, often accom-
panied with valuable notes.
* ‘Géographie Botanique,’ tom. iv. p. 488,
14 HETEROSTYLED DIMORPHIC PLANTS. Cuar, L
CHAPTER I.
HETEROSsTYLED Dimorpuic PLanTs: PRIMULACES.
Primula veris or the Cowslip—Differences in structure between the
two forms—Their degrees of fertility when legitimately and ille-
gitimately united—P. elatior, vulgaris, Sinensis, auricula, &c—
Summary on the fertility of the heterostyled species of Primula—
Homostyled species of Primula—Hottonia palustris—Androsace
Vitalliana,
It has long been known to botanists that the common
Cowslip (Primula veris, Brit. Flora, var. officinalis,
Lin.) exists under two forms, about equally numerous,
which obviously differ from each other in the length
of their pistils and stamens.* This difference has
hitherto been looked at as a case of mere varia-
bility, but this view, as we shall presently see, is far
from the true one. Florists who cultivate the Polyan-
thus and Auricula have long been aware of the two
kinds of flowers, and they call the plants which dis-
play the globular stigma at the mouth of the corolla,
“ pin-headed ” or “ pin-eyed,” and those which display
the anthers, “thrum-eyed.” + I will designate the two
forms as the long-styled and short-styled.
The pistil in the long-styled form is almost exactly
twice as long as that of the short-styled. The stigma
* This fact, according to von
Moh] (‘Bot. Zeitung,’ 1863, p. 326)
was first observed by Persoon in
the year 1794.
t In Johnson’s Dictionary,
thrum is said to be the ends of
weavers’ threads; and I suppose
that some weaver who cultivated
the polyanthus invented this name,
from being struck with some degree
of resemblance between the cluster
of anthers in the mouth of the
corolla and the ends of his
thieads,
Cuar. L PRIMULA VEBRIS. 15
stands in the mouth of the corolla or projects just
above it, and is thus externally visible. It stands
high above the anthers, which are situated halfway
down the tube and cannot be easily seen. In the
short-styled form the anthers are attached near the
mouth of the tube, and therefore stand above the
stigma, which is seated in about the middle of the
tubular corolla. The corolla itself is of a different
Fig. 1.
av, [Sycoati 5
Long-styled form. Short-styled form,
PRIMULA VERIS.
shape in the two forms; the throat or expanded
portion above the attachment of the anthers being
much longer in the long-styled than in the short-
styled form. Village children notice this difference,
as they can best make necklaces by threading and
slipping the corollas of the long-styled flowers into
one another. But there are much more important
differences. The stigma in the long-styled form
16 HETEROSTYLED DIMORPHIC PLANTS. Cuar. L
is globular; in the short-styled it is depressed on
the summit, so that the longitudinal axis of the
former is sometimes nearly double that of the latter.
Although somewhat variable in shape, one difference
is persistent, namely, in roughness: in some speci-
mens carefully compared, the papillae which render
the stigma rough were in the long-styled form from
twice to thrice as long as in the short-styled. The
anthers do not differ in size in the two forms, which
I mention because this is the case with some hetero-
styled plants. The most remarkable difference is in
the pollen-grains. I measured with the micrometer
many specimens, both dry and wet, taken from plants
growing in different situations, and always found a
palpable difference. The grains distended with water
from the short-styled flowers were about *038 mm.
(42-11 of an inch) in diameter, whilst those from the
long-styled were about +0254 mm. (_,5, of an inch),
which is in the ratio of 100 to 67. The pollen-grains
therefore from the longer stamens of the short-styled
form are plainly larger than those from the shorter
stamens of the long-styled. When examined dry,
the smaller grains are seen under a low power to
be more transparent than the larger grains, and
apparently in a greater degree than can be ac-
counted for by their less diameter. There is also a
difference in shape, the grains from the short-styled
plants being nearly spherical, those from the long-
styled being cblong with the angles rounded; this
difference disappears when the grains are distended
with water. The long-styled plants generally tend
to flower a little before the short-styled : for instance,
I had twelve plants of each form growing in separate
pots and treated in every respect alike; and at the
time when only a single short-styled plant was in
Caar. I. PRIMULA VERIS. 17
flower, seven of the long-styled had expanded their
flowers.
We shall, also, presently see that the short-styled
plants produce more seed than the long-styled. It is
remarkable, according to Prof. Oliver,* that the ovules
in the unexpanded and unimpregnated flowers of the
latter are considerably laiger than those of the short-
styled flowers ; and this I suppose is connected with the
long-styled flowers producing fewer seeds, so that the
ovules have mote space and nourishment for rapid
development.
To sum up the differences :— The long-styled plants
have a much longer pistil, with a globular and much
rougher stigma, standing high above the anthers. The
stamens are short; the grains of pollen smaller and
oblong in shape. The upper half of the tube of the
corolla is more expanded. The number of seeds pro-
duced is smaller and the ovules larger. The plants
tend to flower first.
The short-styled plants have a short pistil, half the
length of the tube of the corolla, with a smooth de-
pressed stigma standing beneath the anthers. The
stamens are long; the grains of pollen are spherical
and larger. The tube of the corolla is of uniform
diameter except close to the upper end. The number
of seeds produced is larger.
I have examined a large number of flowers; and
though the shape of the stigma and the length of the
pistil both vary, especially in the short-styled form, I
have never met with any transitional states between
the two forms in plants growing in a state of nature.
There is never the slightest doubt under which form a
plant ought to be classed. The two kinds of flowers are
* ‘Nat. Hist. Review,’ July 1862, p. 237,
18 HETEROSTYLED DIMORPHIC PLANTS. Cuar. I.
never found on the same individual plant. I marked
many Cowslips and Primroses, and on the following
year all retained the same character, as did some in my
garden which flowered out of their proper season in the
autumn. Mr. W. Wooler, of Darlington, however, in-
forms us that he has seen early blossoms on the Polyan-
thus,* which were not long-styled, but became so later
in the season. Possibly in this case the pistils may not
have been fully developed during the early spring. An
excellent proof of the permanence of the two forms may
be seen in nursery-gardens, where choice varieties of
the Polyanthus are propagated by division ; and I found
whole beds of several varieties, each consisting exclu-
sively of the one or the other form. The two forms exist
in the wild state in about equal numbers: I collected
522 umbels from plants growing in several stations,
taking a single umbel from each plant; and 241 were
long-styled, and 281 short-styled. No difference in
tint or size could be perceived in the two great masses
of flowers.
We shall presently see that most of the species of
Primula exist under two analogous forms; and it may
be asked what is the meaning of the above-described
important differences in their structure? The ques-
tion seems well worthy of careful investigation, and I
will give my observations on the cowslip in detail.
The first idea which naturally occurred to me was,
that this species was tending towards a dicecious
condition; that the long-styled plants, with their
longer pistils, rougher stigmas, and smaller pollen-
grains, were more feminine in nature, and would pro-
duce more seed ;—that the short-styled plants, with
their shorter pistils, longer stamens and larger pol-
“I have proved by numerous that the Polyanthus is a variety
experiments, hereafter tobe given, of Primula verés.
Cuap. I, PRIMULA VERIS. 19
len-grains, were more masculine in nature. Accord-
ingly, in 1860, I marked a few cowslips of both forms
growing in my garden, and others growing in an
open field, and others in a shady wood, and gathered
and weighed the seed. In all the lots the short-
styled plants yielded, contrary to my expectation, most
seed. Taking the lots together, the following is the
result :—
TaBLe 1.
Number | Number | Number | Weight
— of of Umbels of Capsules/ of Seed in
Plants. | produced. | produced. | grains.
Short-styled vowslips . . . 9 33 199 83
Long-styled cowslips . . . 13 51 261 91
If we compare the weight from an equal number of
plants, and from an equal number of umbels, and from
an equal number of capsules of the two forms, we get
the following results :—
TABLE 2,
| | ,
Weight: Weicht
_ Number of Sed Number Weight Nuaaher of Seed
| Plaats, valid [vase seed. | sules. erainst
Short-styled cowslips . | 10 92 | 100 | 251 100] 41
Long-styled cowslips .} 10 70 || 100} 178 100 | 34
So that, by all these standards of comparison, the
short-styled form is the more fertile; if we take the
number of umbels (which is the fairest standard, for
large and small plants are thus equalised), the short-
styled plants produce more seed than the long-styled,
in the proportion of nearly-four to three.
In 1861 the trial was made in a fuller and fairer
20 HETEKOSTYLED DIMORPHIC PLANTS. Caap. 1
manner. A number of wild plants had been trans-
planted during the previous autumn into a large bed
in my garden, and all were treated alike; the result
was—
TABLE 3.
Number | Number Weight
— of of of Seed in
Plants. Umbels. grains,
Short-styled cowslips. . 47 173 745
Long-styled cowslips . 58 208 692
These figures give us the following proportions :—
TasBLe 4, :
Number | Weight Number | Weight
—_ of of Seed in at of Seed in
Plants. grains. Umbels. | grains.
Short-styled cowslips . 100 1585 100 430
Long-styled cowslips 100 1093 100 332
The season was much more favourable this year than
the last ; the plants also now grew in good soil, instead
of in a shady wood or struggling with other plants in
the open field; consequently the actual produce of
seed was considerably larger. Nevertheless we have
the same relative result; for the short-styled plants
produced more seed than the long-stvled in nearly the
proportion of three to two; but if we take the fairest
standard of comparison, namely, the product of seeds
from an equal number of umbels, the excess is, as ip
the former case, nearly as four to three.
Looking to these trials made during two successive
years on a large number or plants, we may safely con-
clude that the short-styled form is more productive
than the long-styled form, and the same result holds
Cuap. L. PRIMULA VERIS. 21
good with some other species of Primula. Conse-
quently my anticipation that the plants with longer
pistils, rougher stigmas, shorter stamens and smaller
pollen-grains, would prove ‘to be more feminine in
nature, is exactly the reverse of the truth.
In 1860 a few umbels on some plants of both the
long-styled and short-styled form, which had been
covered by a net, did not produce any seed, though
other umbels on the same plants, artificially fertilised,
produced an abundance of seed; and this fact shows
that the mere covering in itself was not injurious.
Accordingly, in 1861, several plants were similarly
covered just before they expanded their flowers; these
turned out as follows :—
TABLE 5,
Number | Number
oa, of of Umbels Product of Seed.
Plants. | produced.
cre 1-3 grain weight of seed,
Short-styled . . 8 24 { or about 50 in number.
Long-styled . . . 18 74 Not one seed.
Judging from the exposed plants which grew all round
in the same bed, and had been treated in the same
manner, excepting that they had been exposed to
the visits of insects, the above six short-styled plants
ought to have produced 92 grains’ weight of seed
instead of only 1:3; and the eighteen long-styled
plants, which produced not one seed, ought to have
produced above 200 grains’ weight. The production of
a few seeds by the short-styled plants was probably due
to the action of Thrips or of some other minute insect.
It is scarcely necessary to give any additional evidence,
but I may add that ten pots of polyanthuses and
22 HETEROSTYLED DIMORPHIC PLANTS. Cuar. L
cowslips of both forms, protected from insects in my
greenhouse, did not set one pod, though artificially
fertilised flowers in other pots produced an abundance.
We thus see that the visits of insects are absolutely
necessary for the fertilisation of Primula veris. If the
corolla of the long-styled form had dropped off, in-
stead of remaining attached in a withered state to
the ovarium, the anthers attached to the lower part of
the tube with some pollen still adhering to them
would have been dragged over the stigma, and the
flowers would have been partially self-fertilised, as is
the case with Primula Sinensis through this means.
It is a rather curious fact that so trifling a difference
as the falling-off of the withered corolla, should make
a very great difference in the number of seeds pro-
duced by a plant if its flowers are not visited by
insects.
The flowers of the cowslip and of the other species of
the genus secrete plenty of nectar; and I have often
seen humble-bees, especially B. hortorwm and muscorum,
sucking the former in a proper manner,* though they
sometimes bite holes through the corolla. No doubt
moths likewise visit the flowers, as one of my sons
caught Cucullia verbasci in the act. The pollen readily
adheres to any thin object which is inserted into a
flower. The anthers in the one form stand nearly, but
not exactly, on a level with the stigma of the other;
for the distance between the anthers and stigma in the
short-styled form is greater than that in the long-
styled, in the ratio of 100 to 90. This difference is
the result of the anthers in the long-styled form
standing rather higher in the tube than does the
stigma in the short-styled, and this favours their
* H. Miiller has also seen An- sucking the flowers. ‘Nature,
thophora pilipes and a Bombylius Dec. 10th, 1874, p. 111.
Cuap. I. PRIMULA VERIS. 23
pollen being deposited on it. It follows from the
position of the organs that if the proboscis of a
dead humble-bee, or a thick bristle or rough needle,
be pushed down the corolla, first of one form and
then of the other, as an insect would do in visiting
the two forms growing mingled together, pollen from
the long-stamened form adheres round the base of
the object, and is left with certainty on the stigma
of the long-styled form; whilst pollen from the short
stamens of the long-styled form adheres a little way
above the extremity of the object, and some is
generally left on the stigma of the other form. In
accordance with this observation I found that the
two kinds of pollen, which could easily be recog-
nised under the microscope, adhered in this manner
to the proboscides of the two species of humble-
bees and of the moth, which were caught visiting
the flowers; but some small grains were mingled
with the larger grains round the base of the proboscis,
and conversely some large grains with the small
grains near the extremity of the proboscis. Thus
pollen will be regularly carried from the one form
to the other, and they will reciprocally fertilise one
another. Nevertheless an insect in withdrawing its
proboscis from the corolla of the long-styled form
cannot fail occasionally to leave pollen from the same
flower on the stigma; and in this case there might
be self-fertilisation. But this will be much more
likely to occur with the short-styled form; for when I
inserted a bristle or other such object into the corolla
of this form, and had, therefore, to pass it down be-
tween the anthers seated round the mouth of the
corolla, some pollen was almost invariably carried
down and left on the stigma. Minute insects, such
as Thrips, which sometimes haunt the flowers, would
3
24 HETEROSTYLED DIMORPHIC PLANTS. Cuar. L
likewise be apt to cause the self-fertilisation of both
forms.
The several foregoing facts led me to try the effects
of the two kinds of pollen on the stigmas of the
two forms. Four essentially different unions are pos-
sible; namely, the fertilisation of the stigma of the
long-styled form by its own-form pollen, and by that
of the short-styled; and the stigma of the short-styled
form by its own-form pollen, and by that of the long-
styled. The fertilisation of either form with pollen from
the other form may be conveniently called a legitimate
union, from reasons hereafter to be made clear ; and that
of either form with its own-form pollen an «legitimate
union. I formerly applied the term “ heteromorphic”
to the legitimate unions, and “ homomorphic” to the
illegitimate unions; but after discovering the exist-
ence of trimorphic plants, in which many more unions
are possible, these two terms ceased to be applicable.
The illegitimate unions of both forms might have been
tried in three ways; for a flower of either form may be
fertilised with pollen from the same flower, or with that
from another flower on the same plant, or with that
from a distinct plant of the same form. But to make
my experiments perfectly fair, and to avoid any evil
result from self-fertilisation or too close interbreeding,
I have invariably employed pollen from a distinct
plant of the same form for the illegitimate unions of
all the species; and therefore it may be observed that
I have used the term “own-form pollen” in speaking
of such unions. The several plants in all my experi-
ments were treated in exactly the same manner, and
were carefully protected by fine nets from the access of
insects, excepting Thrips, which it is impossible to ex-
clude. I performed all the manipulations myself, and
weighed the seeds in a chemical balance; but during
Ouap. I. PRIMULA VERIS. 25
many subsequent trials I followed the more accurate
plan of counting the seeds. Some of the capsules con-
tained no seeds, or only two or three, and these are
excluded in the column headed “good capsules” in
several of the following tables :—
TaBLe 6,
Primula veris.
Number Total Calculated
of Number | Number ; Weight | Weight of
Nature of the Union. Flowers of of good | of Seed in | Seed from
fertilisea, | Capsules | Capsules. | grains. | 100 good
erased. | produced. Capsules.
Long-styled by pollen
of short-styled. Le- 22 15 14 8°8 62
gitimate union.
Long-styled by aya |
form pollen. Ille- 20 8 5 2-1 42
gitimate union .
Short-styled by pollen |
of long-styled. Le- 13 12 11 4°9 44
gitimate union . J
Short-styled by own-
form pollen. Ille- 15 8 6 1:'8 30
gitimate union.
SUMMARY:
The two legitimate - 3
ieee *} 35 27 25 | 138-7 | 54
The two illegitimate 35 16 11 3:9 35
unions. . . .
The results may be given in another form (Table 7)
by comparing, first, the number of capsules, whether
good or bad, or of the good alone, produced by 100
flowers of both forms when legitimately and illegiti-
mately fertilised; secondly, by comparing the weight
of seed in 100 of these capsules, whether good or bad;
or, thirdly, in 100 of the good capsules.
26 HETEROSTYLED DIMORPHIC PLANTS. Cuar. I.
TABLE 7.
Number |v mber [Number Weight anadies| West Number| Weieht
of 3
f f good | of Seed of of Seed || of good | of Seed
ae Bigwa's Cap- |°cap- |> in. || Cape in Cap- | in
tilised gules. | sules. | grains. || sules, | grains. || sules. | grains,
The two le- |
gitimate}| 100] 77 71 39 100 | 50 100} 54
unions ;
The two il- |
legitimate>} 100] 45 31 11 100 | 24 100 | 35
unions |
We here see that the long-styled flowers fertilised
with pollen from the short-styled yield more capsules,
especially good ones (i.e. containing more than one
or two seeds), and that these capsules contain a greater
proportional weight of seeds than do the flowers of the
long-styled when fertilised with pollen from a distinct
plant of the same form. So it is with the short-styled
flowers, if treated in an analogous manner. Therefore I
have called the former method of fertilisation a legiti-
mate union, and the latter, as it fails to yield the full
complement of capsules and seeds, an illegitimate
union. These two kinds of union are graphically re-
presented in Fig. 2.
If we consider the results of the two legitimate
unions taken together and the two illegitimate ones,
as shown in Table 7, we see that the former com-
pared with the latter yielded capsules, whether con-
taining many seeds or only a few, in the proportion of
77 to 45, or as 100 to 58. But the inferiority of the
illegitimate unions is here perhaps too great, for on a
subsequent occasion 100 long-styled and short-styled
flowers were illegitimately fertilised, and they together
yielded 53 capsules: therefore the rate of 77 to 53, or
as 100 to 69, is a fairer one than that of 100 to 58.
Cuap, I. PRIMULA VERIS. 27
Returning to Table 7, if we consider only the good
capsules, those from the two legitimate unions were to
those from the two illegitimate in number as 71 to 31,
or as 100 to 44. Again, if we take an equal number of
capsules, whether good or bad, from the legitimately
and illegitimately fertilised flowers, we find that the
former contained seeds by weight compared with the
latter as 50 to 24, or as 100 to 48; but if all the
Fig. 2.
Legitimate union.
Complete fertility.
7 ~S.------------------
i \ .
[Megitimate / \ Illegitimate
union, = { + union.
Incomplete | { Incompleta
fertility. \ { fertility.
‘ i
4 I! a
\ /
* ea ee eer OR x
Legitimate union.
Complete fertility.
fo
Long-styled Short-styled
form. form.
poor capsules are rejected, of which many were pro-
duced by the illegitimately fertilised flowers, the propor-
tion is 54 to 35, or as 100 to 65. In this and all other
cases, the relative fertility of the two kinds of union
can, I think, be judged of more truly by the average
number of seeds per capsule than by the proportion of
flowers which yield capsules. The two methods might
28 HETEROSTYLED DIMORPHIC PLANTS. Cuap. L
have been combined by giving the average number of
seeds produced by all the flowers which were fertilised,
whether they yielded capsules or not; but I have
thought that it would be more instructive always to
show separately the proportion of flowers which pro-
duced capsules, and the average number of apparently
good seeds which the capsules contained.
Flowers legitimately fertilised set seeds under con-
ditions which cause the almost complete failure of
illegitimately fertilised flowers. Thus in the spring of
1862 forty flowers were fertilised at the same time in
both ways. The plants were accidentally exposed in
the greenhouse to too hot a sun, and a large number
of umbels perished. Some, however, remained in mo-
derately good health, and on these there were twelve
flowers which had been fertilised legitimately, and
eleven which had been fertilised illegitimately. The
twelve legitimate unions yielded seven fine capsules,
containing on an average each 57°3 good seeds; whilst
the eleven illegitimate unions yielded only two cap-
sules, of which one contained 89 seeds, but so poor,
that I do not suppose one would have germinated, and
the other contained 17 fairly good seeds.
From the facts now given the superiority of a legi-
timate over an illegitimate union admits of not the
least doubt; and we have here a case to which no
parallel exists in the vegetable or, indeed, in the
animal kingdom. The individual plants of the pre-
sent species, and as we shall see of several other
species of Primula, are divided into two sets or
bodies, which cannot be called distinct sexes, for
both are hermaphrodites; yet they are to a certain
extent sexually distinct, for they require reciprocal
union for perfect fertility. As quadrupeds are di-
vided into two nearly equal bodies of different sexes,
Cnar. L PRIMULA VERIS. 29
so here we have two bodies, approximately equal in
number, differing in their sexual powers and related to
each other like males and females. There are many
hermaphrodite animals which cannot fertilise them-
selves, but must unite with another hermaphrodite.
So it is with numerous plants; for the pollen is often
mature and shed, or is mechanically protruded, before
the flower’s own stigma is ready; and such flowers ab-
solutely require the presence of another hermaphro-
dite for sexual union. But with the cowslip and various
other species of Primula there is this wide difference,
that one individual, though it can fertilise itself im-
perfectly, must unite with another individual for full
fertility ; it cannot, however, unite with any other in-
dividual in the same manner as an hermaphrodite
plant can unite with any other one of the same species ;
or as one snail or earth-worm can unite with any other
hermaphrodite individual. On the contrary, an indi-
vidual belonging to one form of the cowslip in order
to be perfectly fertile must unite with one of the other
form, just as a male quadruped must and can unite
only with the female.
I have spoken of the legitimate unions as being
fully fertile; and I am fully justified in doing so, for
flowers artificially fertilised in this manner yielded
rather more seeds than plants naturally fertilised in
a state of nature. The excess may be attributed to
the plants having been grown separately in good soil.
With respect to the illegitimate unions, we shall best
appreciate their degree of lessened fertility by the
following facts. Géartner estimated the sterility of the
unions between distinct species,* in a manner which
allows of a strict comparison with the results of the
* *Versuche tiber die Bastarderzeugung,’ 1849, p. 216,
30 HETEROSTYLED DIMORPHIC PLANTS. Cnar. L
legitimate and illegitimate unions of Primula. With
P. veris, for every 100 seeds yielded by the two le-
gitimate unions, only 64 were yielded by an equal
number of good capsules from the two illegitimate
unions. With P. Sinensis, as we shall hereafter see,
the proportion was nearly the same—namely, as 100
to 62. Now Gartner has shown that, on the calcula-
tion of Verbascum lychnitis yielding with its own pollen
100 seeds, it yielded when fertilised by the pollen of
V. Pheenicewm 90 seeds; by the pollen of V. negrum,
63 seeds; by that of V. blattaria, 62 seeds. So again,
Dianthus barbatus fertilised by the pollen of D. superbus
yielded 81 seeds, and by the pollen of D. Japonicus
66 seeds, relatively to the 100 seeds produced by its
own pollen. We thus see—and the fact is highly re-
markable—that with Primula the illegitimate unions
relatively to the legitimate are more sterile than
crosses between distinct species of other genera rela-
tively to their pure unions. Mr. Scott has given* a
still more striking illustration of the same fact: he
crossed Primula auricula with pollen of four other
species (P. Palinuri, viscosa, hirsuta, and verticillata),
and these hybrid unions yielded a larger average
number of seeds than did P. awricula when fertilised
illegitimately with its own-form pollen.
The benefit which heterostyled dimorphic plants de-
rive from the existence of the two forms is sufficiently
obvious, namely, the intercrossing of distinct plants
being thus ensured.t Nothing can be better adapted
for this end than the relative positions of the anthers
and stigmas in the two forms, as shown in Fig. 2; but to
™* «Journ. Linn, Soc. Bot., vol. fertilisation’ how greatly the off-
viii. 1864, p. 93. spring from intercrossed plants
+ I have shown in my work profit in height, vigour, and
on tle ‘ Effects of Cross and Self- _ fertility.
Ouap. I. PRIMULA VERIS. 31
this whole subject I shall recur. No doubt pollen will
occasionally be placed by insects or fall on the stigma
of the same flower; and if cross-fertilisation fails, such
self-fertilisation will be advantageous to the plant, as
it will thus be saved from complete barrenness. But
the advantage is not so great as might at first be
thought, for the seedlings from illegitimate unions do
not generally consist of both forms, but all belong to
the parent form; they are, moreover, in some degree
weakly in constitution, as will be shown in a future
chapter. If, however, a flower’s own pollen should first
be placed by insects or fall on the stigma, it by no
means follows that cross-fertilisation will be thus pre-
vented. It is well known that if pollen from a distinct
species be placed on the stigma of a plant, and some
hours afterwards its own pollen be placed on it, the
latter will be prepotent and will quite obliterate any
effect from the foreign pollen; and there can hardly
be a doubt that with heterostyled dimorphic plants,
pollen from the other form will obliterate the effects of
pollen from the same form, even when this has been
placed on the stigma a considerable time before. To
test this belief, I placed on several stigmas of a long-
styled cowslip plenty of pollen from the same plant,
and after twenty-four hours added some from a short-
styled dark-red polyanthus, which is a variety of the
cowslip. From the flowers thus treated 30 seedlings
were raised, and all these, without exception, bore
reddish flowers; so that the effect of pollen from the
same form, though placed on the stigmas twenty-four
hours previously, was quite destroyed by that of pollen
from a plant belonging to the other form.
Finally, I may remark that of the four kinds of
unions, that of the short-styled illegitimately fertilised
with its own-form pollen seems to be the most sterile of
32 HETEROSTYLED DIMORPHIC PLANTS. Cuapr. L
all, as judged by the average number of seeds, which
the capsules contained. A smaller proportion, also, of
these seeds than of the others germinated, and they
germinated more slowly. The sterility of this union is
the more remarkable, as it has already been shown
that the short-styled plants yield a larger number of
seeds than the long-styled, when both forms are fer-
tilised, either naturally or artificially, in a legitimate
manner.
In a future chapter, when I treat of the offspring
from heterostyled dimorphic and trimorphic plants
illegitimately fertilised with their own-form pollen, I
shall have occasion to show that with the present
species and several others, equal-styled varieties some-
times appear.
PRIMULA ELATIOR, Jacq.
Bardfield Oxlip of English Authors.
’ This plant, as well as the last or Cowslip (P. veris,
vel officinalts), and the Primrose (P. vulgaris, vel acaulis)
have been considered by some botanists as varieties of
the same species. But they are all three undoubtedly
distinct, as will be shown in the next chapter. The
present species resembles to a certain extent in general
appearance the common oxlip, which is a hybrid be-
tween the cowslip and primrose. Primula elatior is
found in England only in two or three of the eastern
counties ; and I was supplied with living plants by Mr.
Doubleday, who, as I believe, first called attention to
its existence in England. It is common in some parts
of the Continent; and H. Miiller* has seen several
kinds of humble-bees and other bees, and Bombylius,
visiting the flowers in North Germany.
* ‘Die Befruchtung der Blumen,’ p. 347,
Cuap. I. PRIMULA ELATIOR. 33
The results of my trials on the relative fertility of
the two forms, when legitimately and illegitimately
fertilised, are given in the following table :—
TABLE 8.
Primula elatior.
eum Per | Number ee Menem prerese:,
. f good f Seed f Seed un ts)
Nature of Union. Flowers Cnpeales inure in ae oad Becds ne
fertilised. produced.| Capsule. | Capsule. | Capsule.
Long-styled form,
pollen of short- tye 10 6 62 34 46°5
Legitimate union
Long-styled form, b
own-form pollen. I. 20 4 49* 2 27°7
legitimate union,
Short-styled form, by
pollen of long- styled 10 8 61 37 ATT
Legitimate union
Short-styled form, iy
own-form pollen. 17 3 19 9 12-1
legitimate union,
The two legitimate 9 .
unions together . j ao | i 82 ay aoa
The two illegitimate rs 2
unions together , } an . =e 2 pare
* These seeds were so poor and small that they could hardly have germinated.
If we compare the fertility of the two legitimate
unions taken together with that of the two illegitimate
unions together, as judged by the proportional number
of flowers which when fertilised in the two methods
yielded capsules, the ratio is as 100 to 27; so that by
this standard the present species is much more sterile
than P. veris, when both species are illegitimately fer-
tilised. If we judge of the relative fertility of the two
kinds of unions by the average number of seeds per
capsule, the ratio is as 100 to 75. But this latter
34 HETEROSTYLED DIMORPHIC PLANTS. Cuap. I.
number is probably much too high, as many of the seeds
produced by the illegitimately fertilised long-styled
flowers were so small that they probably. would not
have germinated, and ought not to have been counted.
Several long-styled and short-styled plants were pro-
tected from the access of insects, and must have been
spontanecusly self-fertilised. They yielded altogether
only six capsules, containing any seeds; and their
average number was only 7°8 per capsule. Some,
moreover, of these seeds were so small that they could
hardly have germinated.
Herr W. Breitenbach informs me that he examined,
in two sites near the Lippe (a tributary of the Rhine),
894 flowers produced by 198 plants of this species; and
he found 467 of these flowers to be long-styled, 411
short-styled, and 16 equal-styled. I have heard of no
other instance with heterostyled plants of equal-styled
flowers appearing in a state of nature, though far from
rare with plants which have been long cultivated. It
is still more remarkable that in eighteen cases the
same plant produced both long-styled and short-styled,
or long-styled and equal-styled flowers; and in two
out of the eighteen cases, long-styled, short-styled, and
equal-styled flowers. The long-styled flowers greatly
preponderated on these eighteen plants,—61 consisting
of this form, 15 of equal-styled, and 9 of the short-
styled form.
PRIMULA VULGARIS (var. acaulis, Linn.),
The Primrose of English Writers.
Mr. J. Scott examined 100 plants growing near
Edinburgh, and found 44 to be long-styled, and 56
short-styled ; and I took by chance 79 plants in Kent,
of which 39 were long-styled and 40 short-styled ; so
Cuar. I. PRIMULA VULGARIS. 85
that the two lots together consisted of 83 long-styled
and 96 short-styled plants. In the long-styled form
the pistil is to that of the short-styled in length, from
an average of five measurements, as 100 to 51. The
stigma in the long-styled form is conspicuously more
globose and much more papillose than in the short-
styled, in which latter it is depressed on the summit;
Outlines of pollen-grains of Primula vulgaris, distended with water, mucn
magnified and drawn under the camera lucida. The upper and smaller
grains from the long-styled form; the lower and larger grains from
the short-styled. :
it is equally broad in the two forms. In both it stands
nearly, but not exactly, on a level with the anthers of
the opposite form; for it was found, from an average
of 15 measurements, that the distance between the
middle of the stigma and the middle of the anthers
in the short-styled form is to that in the long-styled
as 100 to 93. The anthers do not differ in size in the
two forms. The pollen-grains from the short-styled
36 HETEROSTYLED DIMORPHIC PLANTS. Cuap. L
flowers before they were soaked in water were decidedly
broader, in proportion to their length, than those from
the long-styled ; after being soaked they were relatively
to those from the long-styled as 100 to 71 in diameter,
and more transparent. A large number of flowers from
the two forms were compared, and 12 of the finest
flowers from each lot were measured, but there was no
sensible difference between them in size. Nine long-
styled and eight short-styled plants growing together in
a state of nature were marked, and their capsules col-
lected after they had been naturally fertilised; and
the seeds from the short-styled weighed exactly twice
as much as those from an equal number of long-styled
plants. So that the primrose resembles the cowslip in
the short-styled plants, being the more productive of
the two forms. The results of my trials on the fer-
tility of the two forms, when legitimately and illegi-
timately fertilised, are given in Table 9.
We may infer from this table that the fertility of the
two legitimate unions taken together is to that of the
two illegitimate unions together, as judged by the pro-
portional number of flowers which when fertilised in
the two methods yielded capsules, as 100 to 60. If we
judge by the average number of seeds per capsule pro-
duced by the two kinds of unions, the ratio is as 100
to 54; but this latter figure is perhaps rather too low.
Itis surprising how rarely insects can be seen during the
day visiting the flowers, but I have occasionally observed
small kinds of bees at work ; I suppose, therefore, that
they are commonly fertilised by nocturnal Lepidoptera.
The long-styled plants when protected from insects
yield a considerable number of capsules, and they thus
differ remarkably from the same form of the cowslip,
which is quite sterile under the same circumstances.
Twenty-three spontaneously self-fertilised capsules from
Cuar, I. PRIMULA VULGARIS. 37
TABLE 9.
Primula vulgaris.
\ : a
Maximum | Minimum
Npubee ee Number | Number eee
Nature of Union. Binreea Gupsules of Seedsin| of Seeds |’ Gangs Bey
fertilised, pruduced. Supaule, “Capnale: © Capsule.
Long-styled form, by pol- |
len from eee ia 2 | it a7 47 66°9
Legitimate union . l
Long-styled form, 5
own-form pollen, 21 | 14 66 30 52-2
legitimate union . :
Short-styled form,
pln rom ong yd 8 | 7 75 .48 65:0
Legitimate union .
Short-styled form, al i
own-form pollen. 18 | 7 43 5 18°8*
legitimate union .
The __ two legitimate 20 | 18 77 aq 66°0
unions together .
The _ two rr aes 39 21 66 5 35°5*
unions together .
* This average is perhaps rather too low.
this form contained, on an average, 19:2 seeds. The
short-styled plants produced fewer spontaneously self-
fertilised capsules, and fourteen of them contained only
62 seeds per capsule. The self-fertilisation of both forms
was probably aided by Thrips, which abounded within
the flowers ; but these minute insects could not have
placed nearly sufficient pollen on the stigmas, as the
spontaneously self-fertilised ‘capsules contained much
fewer seeds, on an average, than those (as may be seen
in Table 9) which were artificially fertilised with their
own-form pollen. But this difference may perhaps be
attributed in part to the flowers in the table having
been fertilised with pollen from a distinct plant be-
38 HETEROSTYLED DIMORPHIC PLANTS Caar. L
longing to the same form; whilst those which were
spontaneously self-fertilised no doubt generally received
their own pollen. In a future part of this volume some
observations will be given on the fertility of a red-
coloured variety of the primrose.
PrimuLa SINENSIS.
In the long-styled form the pistil is about twice as
long as that of the short-styled, and the stamens differ
in a corresponding, but reversed, manner. The stigma
is considerably more elongated and rougher than that
of the short-styled, which is smooth and almost
spherical, being somewhat depressed on the summit;
but the stigma varies much in all its characters, the
result, probably, of cultivation. The pollen-grains of
the short-styled form, according to Hildebrand,* are
7 divisions of the micrometer in length and 5 in
breadth; whereas those of the long-styled are only
4 in length and 3 in breadth. The grains, there-
fore, of the short-styled are to those of the long-
styled in length as 100 to 57. Hildebrand also re-
marked, as I had done in the case of P. veris, that the
smaller grains from the long-styled are much more
transparent than the larger ones from the short-styled
form. We shall hereafter see that this cultivated
plant varies much in its dimorphic condition and is
often equal-styled. Some individuals may be said to
be sub-heterostyled ; thus.in two white-flowered plants
the pistil projected above the stamens, but in one of them
* After the appearance of my that I erred greatly about the
paper this author published some size of the poll-n-grains in the
excellent observations on the two forms, I suppose that by
present species (‘Bot. Zeitung,’ mistake I measured twice over
Jau. 1, 1864), and he shows pollen-grains from the same form.
Ouap. I. PRIMULA SINENSIS. 39
it was longer and had a more elongated and rougher
stigma, than in the other; and the pollen-grains from
the latter were to those from the plant with a more
elongated pistil only as 100 to 88 in diameter, instead
of as 100 to 57. The corolla of the long-styled and
short-styled form differs in shape, in the same manner
asin P. veris. The long-styled plants tend to flower
before the short-styled. When both forms were legiti-
mately fertilised, the capsules from the short-styled
plants contained, on an average, more seeds than those
from the long-styled, in the ratio of 12:2 to 9:3 by
weight, that is, as 100 to 78. In the following table
we have the results of two sets of experiments tried
at different periods.
TABLE 10.
Primula Sinensis.
a ise eevee enter ae sala a
of good eight o:
Nature of Union. Flowers Gieeules Seeds per ase an a
fertilised. | produced. | Capsule. subsequent
occasion,
Long-styled form, by rei
of short-styled. a 16 0°58 50
mate union .
Long-styled “form, by own-
form pollen. mand 20 13 0°45 35
mate union. .
Short-styled form, by pol-
len of ent aaa Le- 8 8 0°76 64
gitimate union .
Short-styled form, by own-
form pollen. de vi 4 0°23 25
mate union. .
The two legitimate unions :
together. . . eee ne ae ee oe
The two aa unions)|
together. . na) ae ut ree a
40 HETEROSTYLED DIMORPHIC PLANTS. Cuar. 1
The fertility, therefore, of the two legitimate unions
together to that of the two illegitimate unions, as judged
by -the proportional number of flowers which yielded
capsules, is as 100 to 84. Judging by the average
weight of seeds per capsule produced by the two kinds
of unions, the ratio is as 100 to 63. On another occa-
sion a large number of flowers of both forms were
fertilised in the same manner, but no account of their
number was kept. The seeds, however, were carefully
counted, and the averages are shown in the right-hand
column. The ratio for the number of seeds produced
‘by the two legitimate compared with the two illegiti-
mate unions is kere 100 to 53, which is probably more
accurate than the foregoing one of 100 to 63.
Hildebrand in the paper above referred to gives the
results of his experiments on the present species; an
these are shown in a condensed form in the following
table (11). Besides using for the illegitimate unions
pollen from a distinct plant of the same form, as was
always done by me, he tried, in addition, the effects of
the plant’s own pollen. He counted the seeds.
It is remarkable that here all the flowers which
were fertilised legitimately, as well as those fertilised
illegitimately with pollen from a distinct plant be-
longing to the same form, yielded capsules; and from
this fact it might be inferred that the two forms were
reciprocally much more fertile in his case than in
mine. But his illegitimately fertilised capsules from
both forms contained fewer seeds relatively to the
legitimately fertilised capsules than in my experi-
ments; for the ratio in his case is as 42 to 100,
instead of, as in mine, as 53 to 100. Fertility is a
very variable element with most plants, being deter-
mined by the conditions to which they are subjected, of
which fact I have observed striking instances with the
Cuap. I. PRIMULA SINENSIS. 41
TABLE 11.
Primula Sinensis (from Hildebrand).
Number Number ereTaee
3 f good
Nature of Union, Flowers Caphules Heeta gee
fertilised. | produced. | Capsule.
Long-styled form, by pollen of short-
styled. Legitimate union . age ut 4 #1
Long-styled form, by own-form pollen, from ;
a distinct plant. Illegitimate union i} 28 ae is
Long-styled form, by pollen from same
flower. Mlegitimate union, eal at a Ww
Short-styled form, by pollen of long-
styled. Legitimate union . a oe - =
Short-styled form, by own-form pollen, 16 16 20
from a distinct plant. Illegitimate union
Short-styled, by pollen from the same 21 7] 8
flower. Illegitimate union.
The two legitimate unions together . . 28 | 28 | 43
The two illegitimate unions together
(own-form pollen) gS *} ee aa tS
The two illegitimate unions together (pol- |
len from the same flower). . } 8 | 2 is
1
present species; and this may account for the differ-
ence between my results and those of Hildebrand. His
plants were kept in a room, and perhaps were grown in
too small pots or under some other unfavourable condi-
tions, for his capsules in almost every case contained a
smaller number of seeds than mine, as may he seen
by comparing the right-hand columns in Tables 10
and 11.
The most interesting point in Hildebrand’s experi-
ments is the difference in the effects of illegitimate
fertilisation with a flower’s own pollen, and with that
42 HETEROSTYLED DIMORPHIC PLANTS. Cuap. IL
from a distinct plant of the same form. In the latter
case all the flowers produced capsules, whilst only 67
out of 100 of those fertilised with their own pollen pro-
duced capsules. The self-fertilised capsules also con-
tained seeds, as compared with capsules from flowers
fertilised with pollen from a distinct plant of the same
form, in the ratio of 72 to 100.
In order to ascertain how far the present species was
spontaneously self-fertile, five long-styled plants were
protected by me from insects; and they bore up to a
given period 147 flowers which set 62 capsules; but
many of these soon fell off, showing that they had not
been properly fertilised. At the same time five short-
styled plants were similarly treated, and they bore 116
flowers which ultimately produced only seven capsules.
On another occasion 13 protected long-styled plants
yielded by weight 25:9 grains of spontaneously self-
fertilised seeds. At the same time seven protected
short-styled plants yielded only half-a-grain weight of
seeds. Therefore the long-styled plants yielded nearly
24 times as many spontaneously self-fertilised seeds as
did the same number of short-styled plants. The chief
cause of this great difference appears to be, that when
the corolla of a long-styled plant falls off, the anthers,
from being situated near the bottom of the tube are
necessarily dragged over the stigma and leave pollen
on it, as I saw when I hastened the fall of nearly
withered flowers; whereas in the short-styled flowers,
the stamens are seated at the mouth of the corolla,
and in falling off do not brush over the lowly-seated
stigmas. Hildebrand likewise protected some long-
styled and short-styled plants, but neither ever yielded
a single capsule. He thinks that the difference in our
results may be accounted for by his plants having
been kept in a room and never having been shaken;
Cuap. I. PRIMULA AURICULA. 43
but this explanation seems to me doubtful ; bis plants
were in a less fertile condition than mine, as shown by
the difference in the number of seeds produced, and
it is highly probable that their lessened fertility would
have interfered with especial force with their capacity
for producing self-fertilised seeds.
PRIMULA AURICULA.*
This species is heterostyled, like the preceding ones; but
amongst the varieties distributed by florists the long-styled form
is rare, as it is not valued. There is a much greater relative in-
equality in the length of the pistil and stamens in the two forms
of the auricula than in the cowslip; the pistil in the long-styled
being nearly four times as long as that in the short-styled, in
which itis barely longer than the ovarium. The stigma is nearly
of the same shape in both forms, but is rougher in the long-styled,
though the difference is not so great as between the two forms
of the cowslip. In the long-styled plants the stamens are very
short, rising but little above the ovarium. The pollen-grains of
these short stamens, when distended with water, were barely 7255
of an inch in diameter, whereas those from the long stamens of
the short-styled plants were barely ggg, showing a relative dif-
ference of about 71 to 100. The smaller grains of the long-
styled plant are also much more transparent, and before disten-
tion with water more triangular in outline than those of the
other form. Mr. Scott + compared ten plants of both forms grow-
ing under similar conditions, and found that, although the long-
styled plant produced more umbels and more capsules than the
short-styled, yet they yielded fewer seeds, in the ratio of 66 to
100. Three short-styled plants were protected by me from the
* According to Kerner our gar- _short-styled 98 seeds per capsule:
den auriculasare descended fromP. see his “Geschichte der Aurikel,”
pubescens, Jacq., which is ahybrid —_‘ Zeitschr. des Deutschen und est.
between the true P. auricula and Alpen-Vereins,’ Band vi. p. 52.
hirsuta. This hybrid has now been _Also ‘ Die Primulaceen-Bastarten,’
propagated for about 300 years, ‘ Oest. Bot. Zeitschrift, 1835, Nous.
and produces, when legitimately 3,4, and 5. __
fertilised, a large number of seeds ; _t ‘Journ. Linn. Soo, Bot.’ vol
the long-styled forms yielding an viii. 1864, p. 86.
average number of 73, and the
44 HETEROSTYLED DIMORPHIC PLANTS, Cuap. [
access of insects, and they did not produce a single seed. Mr.
Scott protected six plants of both forms, and found them ex-
cessively sterile. The pistil of the long-styled form stands so
high above the anthers, that it is scarcely possible that pollen
should reach the stigma without some aid; and one of Mr,
Scott’s long-styled plants which yielded a few seeds (only 18 in
number) was infested by aphides, and he does not doubt that
these had imperfectly fertilised it.
I tried a few experiments by reciprocally fertilising the two
forms in the same manner as before, but my plants were un-
healthy, so I will give, in a condensed form, the results of Mr.
Scott’s experiments. For fuller particulars with respect. to this
and the five following species, the paper lately referred to may
be consulted. In each case the fertility of the two legitimate
unions, taken together, is compared with that of the two ille-
gitimate unions together, by the same two standards as before,
namely, by the proportional number of flowers which pro-
duced good capsules, and by the average number of seeds per
capsule. The fertility of the legitimate unions is always taken
at 100.
By the first standafd, the fertility of the two legitimate unions
of the auricula is to that of the two illegitimate unions as 100
to 80; and by the second standard as 100 to 15.
Priva SIKKIMENSIS.
According to Mr. Scott, the pistil of the long-styled form is
fully four times as long as that of the short-styled, but their
stigmas are nearly alike in shape and roughness. The stamens
do not differ so much in relative length as the pistils. The pollen-
grains differ in a marked manner in the two forms; “ those of
the long-styled plants are sharply triquetrous, smaller, and more
transparent than those of the short-styled, which are of a bluntly
triangular form.” ‘The fertility of the two legitimate unions to
that of the two illegitimate unions is by the first standard as
100 to 95, and by the second standard as 100 to 81.
PRINULA CORTUSOIDES.
The pistil of the long-styled form is about thrice as long as
that of the short-styled, the stigma being double as long and
covered with much longer papillw. The pollen-grains of the short
Cuar. I. SUMMARY ON PRIMULA. 49
styled form are, as usual, “larger, less transparent, and more
bluntly triangular than those from the long-styled plants.” The
fertility of the two legitimate unions to that of the two ille-
gitimate unions is by the first standard as 100 to 74, and by
the second standard as 100 to 66.
PRIMULA INVOLUCRATA.
The pisti! of the long-styled form is about thrice as long as
that of the short-styled; the stigma of the former is globular
and closely beset with papille, whilst that of the short-styled
is smooth and depressed on the apex. The pollen-grains of the
two forms differ in size and transparency as before, but not in
shape. The fertility of the two legitimate to that of the two
illegitimate unions is by the first standard as 100 to 72; and by
the second standard as 100 to 47.
PRIMULA FARINOSA.
According to Mr. Scott, the pistil of the long-styled form is
only about twice as long as that of the short-styled. The
stigmas of the two forms differ but little in shape. The pollen-
grains differ in the usual manner in size, but not in form. The
fertility of the two legitimate to that of the two illegitimate
unions is by the first standard as 100 to 71, and by the second
standard as 100 to 44.
Summary on the foregoing heterostyled species of Pri-
mula.—The fertility of the long and short-styled plants
of the above species of Primula, when the two forms
are fertilised legitimately, and illegitimately with
pollen of the same form taken from a distinct plant,
has now been given. ‘The results are seen in the fol-
lowing table; the fertility being judged by two
standards, namely, by that of the proportional number
of flowers which yielded capsules, and by that of the
average number of seeds per capsule. But for full
accuracy many more observations, under varied condi-
tions, would be requisite.
46 HETEROSTYLED DIMORPHIC PLANTS. Cauap. I.
TABLE 12.
Summary on the Fertility of the two Legitimate Unions, compared
with that of the two Illegitimate Unions, in the genus Primula,
The former taken at 100.
Ilegitimate. Unions.
Name of Species. Judged of by the Judged of by the 7
Proportional Number | Average Number (or
of Flowers which |Weight in some cases)
produced Capsules. | of Seeds per Capsule.
Primula veris . 2. 1. 69 65
4 (Probably
Pielatioy 4 « «© © © 4 27 a(t high.)
: (Perhaps
P. vulgaris .. es 60 saf too Low.)
P, Sinensis eae ke ¥ 84 63
45 (second trial) . ? 53
$5 (after Hildebrand) . 100 42
P. duricula (Scott) . . . 80 15
P. Sikkimensis (Scott) . : 95 31
P. cortusoides (Scott) . . . 74 66
P. involucrata (Scott) . . . 72 48
P. farinosa (Scott) . . . . 71 44
Average of the nine species . 88°4 | 61°8
With plants of all kinds some flowers generally fail
to produce capsules, from various accidental causes ;
but this source of error has been eliminated, as far as
possible, in all the previous cases, by the manner in
which the calculations have been made. Supposing,
for instance, that 20 flowers were fertilised legiti-
mately and yielded 18 capsules, and that 30 flowers
were fertilised illegitimately and yielded 15 cap-
sules, we may assume that on an average an equal
proportion of the flowers in both lots would fail to
produce capsules from various accidental causes; and
the ratio of 38 to 48, or as 100 to 56 (in whole
Cuap. I. SUMMARY ON PRIMULA. 47
numbers), would show the proportional number of cap-
sules due to the two methods of fertilisation; and the
number 56 would appear in the left-hand column of
Table 12, and in my other tables. With respect
to the average number of seeds per capsule hardly
anything need be said: supposing that the legiti-
mately fertilised capsules contained, on an average,
50 seeds, and the illegitimately fertilised capsules
25 seeds; then as 50 is to 25 so is 100 to 50; and
the latter number would appear in the right-hand
column.
It is impossible to look at the above table and doubt
that the legitimate unions between the two forms of the
above nine species of Primula are much more fertile
than the illegitimate unions; although in the latter
case pollen was always taken from a distinct plant of
the same form. There is, however, no close corre-
spondence in the two rows of figures, which give,
according to the two standards, the difference of fer-
tility between the legitimate and illegitimate unions.
Thus all the flowers of P. Sinensis which were illegiti-
mately fertilised by Hildebrand produced capsules ;
but these contained only 42 per cent. of the number
of seeds yielded by the legitimately fertilised capsules.
So again, 95 per cent. of the illegitimately fertilised
flowers of P. Sikkimensis produced capsules ; but these
contained only 31 per cent. of the number of seeds in
the legitimate capsules. On the other hand, with
P. elatior only 27 per cent. of the illegitimately fer-
tilised flowers yielded capsules; but these contained
nearly 75 per cent. of the legitimate number of seeds.
It appears that the setting of the flowers, that is, the
production of capsules whether good or bad, is not
so much influenced by legitimate and illegitimate fer-
tilisation as is the number of seeds which the capsules
48 HETEROSTYLED DIMORPHIC PLANTS. Cuap. L
contain. For, as may be seen at the bottom of Table
12, 88°4 per cent. of the illegitimately fertilised
flowers yielded capsules; but these contained only
61°8 per cent. of seeds, in comparison, in each case,
with the legitimately fertilised flowers and capsules
of the same species.
There is another point which deserves notice,
namely, the relative degree of infertility in the several
species of the long-styled and short-styled flowers,
when both are illegitimately fertilised. The data
may be found in the earlier tables, and in those given
by Mz. Scott in the Paper already referred to. If we
call the number of seeds per capsule produced by the
illegitimately fertilised long-styled flowers 100, the
seeds from the illegitimately fertilised short-styled
flowers will be represented by the following num-
bers :—
Primula veris, 71 Primula auricula, . . 119
P. elatior 44{(Probably P. Sikkimensis . . . 57
as . too low.) P.cortusoides . . . 93
: (Perhaps P.involucrata . . . 74
PE giels 36 too low.) | P.farinosa . . . . 63
P.Sinensis . 71
We thus see that, with the exception of P. auricula, the
long-styled flowers of all nine species are more fertile
than the short-styled flowers, when both forms are
illegitimately fertilised. Whether P. auricula really
differs from the other species in this respect I can form
no opinion, as the result may have been accidental.
The degree of self-fertility of a plant depends on two
elements, namely, on the stigma receiving its own pollen
and on its more or less efficient action when placed
there. Now as the anthers of the short-styled flowers of
several species of Primula stand directly above the
stigma, their pollen is more likely to fall on it, or to
be carried down to it by insects, than in the case of
Cuap. I. HOMOSTYLED PRIMULAS. 49
the long-styled form. It appears probable, therefore,
at first sight, that the lessened capacity of the short-
styled flowers to be fertilised with their own pollen, is
a special adaptation for counteracting their greater
liability to receive their own pollen, and thus for
checking self-fertilisation. But from facts with respect
to other species hereafter to be given, this view can
hardly be admitted. In accordance with the above
liability, when some of the species of Primula were
allowed to fertilise themselves spontaneously under
a net, all insects being excluded, except such minute
ones as Thrips, the short-styled flowers, notwith-
standing their greater innate self-sterility, yielded
more seed than did the long-styled. None of the
species, however, when insects were excluded, made
a near approach to full fertility. But the long-styled
form of P. Stnensis gave, under these circumstances,
a considerable number of seeds, as the corolla in falling
off drags the anthers, which are seated low down in
the tube, over the stigma, and thus leaves plenty of
pollen on it.
Homostyled species of Primula.—lt has now been
shown that nine of the species in this genus exist under
two forms, which differ not only in structure but in
function. Besides these Mr. Scott enumerates 27 other
species* which are heterostyled ; and to these probably
others will be hereafter added. Nevertheless, some
species are homostyled; that is, they exist only under
a single form ; but much caution is necessary on this
head, as several species when cultivated are apt to
become equal-styled. Mr. Scott believes that P.
Scotica, verticillata, a variety of Sibirica, elata, mollis, and
* H. Miiller has givenin ‘Na- viz. the Alpine P. villosa, and
tare, Dec. 10, 1874, p. 110, a shows that it is fertilised exclu
drawing of one ot these species, sively by Lepidoptera.
50 HETEROSTYLED DIMORPHIC PLANTS Cuap. 1
longiflora,* are truly homostyled ; and to these may be
added, according to Axell, P. stricta. Mr. Scott ex-
perimented on P. Scotica, mollis, and verticillata, and
found that their flowers yielded an abundance of seeds
when fertilised with their own pollen. This shows
that they are not heterostyled in function. P. Scotica
is, however, only moderately fertile when insects are
excluded, but this depends merely on the coherent
pollen not readily falling on the stigma without their
aid. Mr. Scott also found that the capsules of P.
verticillata contained rather more seed when the flowers
were fertilised with pollen from a distinct plant than
when with their own pollen; and from this fact he in-
fers that they are sub-heterostyled in function, though
not in structure. But there is no evidence that two
sets of individuals exist, which differ slightly in func-
tion and are adapted for reciprocal fertilisation ; and
this is the essence of heterostylism. The mere fact
of a plant being more fertile with pollen from a
distinct individual than with its own pollen, is com-
mon to very many species, as I have shown in my
work ‘On the Effects of Cross and Self-fertilisation.’
HoTronia PALUSTRIS.
This aquatic member of the Primulacez is con-
spicuously heterostyled, as the pistil of the long-styled
form projects far out of the flower, the stamens being
enclosed within the tube; whilst the stamens of the
short-styled flower project far outwards, the pistil being
enclosed. This difference between the two forms has
attracted the attention of various botanists, and that
* Koch was aware that this Sprengel und Darwin,” ‘ Bot. Ze:
species was homostyled: see“ Tre- tung,’ Jan. 2, 1863, p. 4.
Virauus iiber Dichogamje nach
Cusp. I. HOTTONIA PALUSTRIS. 51
of Sprengel,* in 1793, who, with his usual sagacity,
adds that he does not believe the existence of the two
forms to be accidental, though he cannot explain their
purpose. The pistil of the long-styled form is more
than twice as long as that of the short-styled, with the
stigma rather smaller, though rougher. H. Millert
gives figures of the stigmatic papilla of the two forms,
and those of the long-styled are seen to be more than
double the length, and much thicker than the papille
of the short-styled form. The anthers in the one form
do not stand exactly on a level with the stigma in
the other form; for the distance between the organs is
greater in the short-styled than in the long-styled
flowers in the proportion of 100 to 71. In dried speci-
mens soaked in water the anthers of the short-styled
form are larger than those of the long-styled, in the
ratio of 100 to 83. The pollen-grains, also, from the
short-styled flowers are conspicuously larger than those
from the long-styled ; the ratio between the diameters
of the moistened grains being as 100 to 64, according
to my measurements, but according to the measure-
ments of H. Miller as 100 to 61; and his are probably
the more accurate of the two. The contents of the
larger pollen-grains appear more coarsely granular
and of a browner tint, than those in the smaller
grains. The two forms of Hottonia thus agree closely
in most respects with those of the heterostyled species
of Primula. The flowers of Hottonia are cross-fertilised
according to Miller, chiefly by Diptera.
Mr. Scott} made a few trials on a short-styled plant,
and found that the legitimate unions were in all ways
more fertile than the illegitimate ; but since the pub-
2
* «Das entdeckte Geheimniss t ‘Journ. Linn. Soc. Bot.’ vol
der Nature,’ p. 103. viii. 1864, p. 79.
t ‘Die Befruchtung,’ &c., p.350.
52
HETEROSTYLED DIMORPHIC PLANTS.
Cuap. I,
lication of his paper H. Miller has made much fuller
experiments, and I give his results in the following
table, drawn up in accordance with my usual plan :—
TABLE 13.
Hottonia palustris (from EH, Miller).
Average
Number
Nature of Union. of Capsules gisele
examined, Capsuie,
Long-styled form, by Een of lier tan | 34 91-4 -
Legitimate union .
Long-styled form, by own-form pollen, from ‘ 18 17°53
distinct plant. Illegitimate union .
Short-styled form, by saad of ies) 30 66:2
Legitimate union. .
Short-ssyled form, by own-form pollen, from a 19 18 7
distinct plant. Illegitimate union .
The two legitimate unions together . . . 64 | 78°8
The two illegitimate unions together . . . 37 | 48°1
The most remarkable point in this table is the
small average number of seeds from the short-styled
flowers when illegitimately fertilised, and the unusually
large average number of seeds yielded by the illegiti-
mately fertilised long-styled flowers, relatively in both
cases to the product of the legitimately fertilised
flowers.*
The two legitimate unions compared with
* II. Miiller says (‘Die Be-
fruchtung,’ &c., p. 352) that the
long-styled flowers, when illegiti-
mately fertilised, Yield as many
seeds as when legitimately fer-
tilised; but by adding up the
number of seeds from ull the cap-
sules produced by the two methods
of fertilisation, as given by him,
I arrive at the results sliown in
Table 13. The average number
in the long-styled capsules, when
legitimately fertilised, is 91:4,
and when illegitimately fertilised,
77°5; or as 100 to 85. H. Miiller
agrees with me that this is the
proper manner of viewing the
case.
Cuar. I. ANDROSACE. 53
the two illegitimate together yield seeds in the ratio
of 100 to 61.
* _H. Miller also tried the effects of illegitimately fer-
tilising the long-styled and short-styled flowers with
their own pollen, instead of with that from another
plant of the same form; and the results are very
striking. For the capsules from the long-styled
flowers thus treated contained, on an average, only
15:7 seeds instead of 77°5; and those from the
short-styled 6°5, instead of 18°7 seeds per capsule.
The number 6°5 agrees closely with Mr. Scott’s result
from the same form similarly fertilised.
From some observations by Dr. Torrey, Hottonia
inflata, an inhabitant of the United States, does not
appear to be heterostyled, but is remarkable from pro-
ducing cleistogamic flowers, as will be seen in the last
chapter of this volume.
Besides the genera Primula and Hottonia, Androsace
(vel Gregoria, vel Aretia) vitalliana is heterostyled.
Mr. Scott* fertilised with their own pollen 21 flowers
on three short-styled plants in the Edinburgh Botanic
Gardens, and not one yielded a single seed; but
eight of them which were fertilised with pollen from one
of the other plants of the same form, set two empty
capsules. He was able to examine only dried speci-
mens of the long-styled forms. But the evidence seems
sufficient to leave hardly a doubt that Androsace is
heterostyled. Fritz Miller sent me from South Brazil
dried flowers of a Statice which he believed to be hete-
rostyled. In the one form the pistil was considerably
longer and the stamens slightly shorter than the cor-
responding organs in the other form. But as in the
shorter-styled form the stigmas reached up to the anthers
* See also Treviranus in ‘ Bot. Zeitung,’ 1863, p. 6, on this plant
being dimorphic.
.
54 HETEROSTYLED DIMORPHIC PLANTS. Cuap. I.
of the same flower, and as I could not detect in the
dried specimens of the two forms any difference in their
stigmas, or in the size of their pollen-grains, I dare not «
rank this plant as heterostyled. From statements made
by Vaucher I was led to think that Soldanella alpina was
heterostyled, but it is impossible that Kerner, who has
closely studied this plant, could have overlooked the
fact. So again from other statements it appeared prob-
able that Pyrola might be heterostyled, but H. Miller
examined for me two species in North Germany, and
found this not to be the case.
Cuar. IL HYBRID PRIMULAS. 55
CHAPTER IL.
Hysrip PrIMULAs.
The Oxlip a hybrid naturally produced between Primula veris and
vulgaris—The differences in structure and function between the
two parent-species—Effects of crossing long-styled and short-styled
Oxlips with one another and with the two forms,of both parent-
species—Character of the offspring from Oxlips artificially self-
fertilised and cross-fertilised in a state of nature— Primula elatior
shown to be a distinct species—Hybrids between other heterostyled
species of Primula—Supplementary note on spontaneously produced
hybrids in the genus Verbascum.
THE various species of Primula have produced in a
state of nature throughout Europe an extraordinary
number of hybrid forms. For instance, Professor
Kerner has found no less than twenty-five such forms
in the Aips.* The frequent occurrence of hybrids in
this genus no doubt has been favoured by most of the
species being heterostyled, and consequently requiring
cross-fertilisation by insects; yet in some other genera,
species which are not heterostyled and which in some
respects appear not well adapted for hybrid-ferti-
lisation, have likewise been largely hybridised. In
certain districts of England, the common oxlip—a
hybrid between the cowslip (P. vers, vel officinalis)
and the primrose (P. vulgaris, vel acaulis)—is fre-
quently found, and it occurs occasionally almost every-
* “Die Primulaceen-Bastarten,” ‘ Bull. Soc. Bot. de France,’ tom. x.
*Oesterr. Bot. Zeitschrift, Jahr 1853, p. 178. Also in ‘ Revue des
1875, Nos. 8,4, and 5. See also Sciences Nat.’ 1875, p. 331.
Godron on hybrid Primulas in
5
56 HYBRID PRIMULAS. Cuap. IL
where. Owing to the frequency of this intermediate
hybrid form, and to the existence of the Bardfield
oxlip (P. elatior), which resembles to a certain extent
the common oxlip, the claim of the three forms to
rank as distinct species has been discussed oftener
and at greater length than that of almost any other
plant. Linneus considered P. veris, vulgaris and
elatior to be varieties of the same species, as do some
distinguished botanists at the present day; whilst
others who have carefully studied these plants do not
doubt that they are distinct species. The following
observations prove, I think, that the latter view is
correct ; and they further show that the common oxlip
is a hybrid between P. veris and vulgaris.
The cowslip differs so conspicuously in general ap-
pearance from the primrose, that nothing need here
be said with respect to their external characters.*
But some less obvious differences deserve notice. As
both species are heterostyled, their complete fertili-
sation depends on insects. The cowslip is habitually
visited during the day by the larger humble-bees
(viz. Bombus muscorum and hortorum), and at night
by moths, as I have seen in the case of Cucullia. The
primrose is never visited (and I speak after many
years’ observation) by the larger humble-bees, and
only rarely by the smaller kinds; hence its ferti-
lisation must depend almost exclusively on moths.
There 1s nothing in the structure of the flowers of the
two plants which can determine the visits of such
widely different insects. But they emit a different
odour, and perhaps their nectar may have a different
taste. Both the long-styled and short-styled forms of
* The Rev. W. A. Leighton seed, in ‘ Ann. and Mag. of Nat.
nas pointed outcertain differences Hist.’ 2nd series, vol. ii. 1848,
mm the form cf the capsules and ___p. 164.
Cuar. II THE COMMON OXLIP. 57
the primrose, when legitimately and naturally fert:-
lised, yield on an average many more seeds per capsule
than the cowslip, namely, in the proportion of 100 to 55.
When illegitimately fertilised they are likewise more
fertile than the two forms of the cowslip, as shown by
the larger proportion of their flowers which set cap-
sules, and by the larger average number of seeds which
the capsules contain. The difference also between the
number of seeds produced by the long-styled and short-
styled flowers of the primrose, when both are illegiti-
mately fertilised, is greater than that between the
number produced under similar circumstances by the
two forms of the cowslip. The long-styled flowers of
the primrose when protected from the access of all in-
sects, except such minute ones as Thrips, yield a con-
siderable number of capsules containing on an average
19:2 seeds per capsule ; whereas 18 plants of the long-
styled cowslip similarly treated did not yield a single
seed.
The primrose, as every one knows, flowers a little
carlier in the spririg than the cowslip, and inhabits
slightly different stations and districts. The primrose
generally grows on banks or in woods, whilst the cow-
slip is found in more open places. The geographical
‘range of the two forms is different. Dr. Bromfield re-
marks * that “the primrose is absent from all the in-
terior region of northern Europe, where the cowslip is
indigenous.” In Norway, however, both plants range
to the same degree of north latitude.
The cowslip and primrose, when intercrossed, be--
* ‘Phytologist,’ vol. iii. p. 694. centre de la France,’ 1840, tom. ii.
t H. Lecog, ‘Géograph. Bot.de p. 376. With respect to the rarity
l'Europe,’ tom. viii. 1858, pp.141, of P. veris in western Scotland,
144. See also‘Ann.and Mag. of see H. (©. Watson, ‘ Cybele Britan-
Nat. Hist. ix. 1842, pp. 156, nica,’ ii. p. 293.
515. Also Boreau, ‘Flore du
38 HYBRID PRIMULAS. Cuar. IL
have like distinct species, for they are far from
being mutually fertile. Gartner* crossed 27 flowers
of P. vulgaris with pollen of P. veris, and obtained
16 capsules; but these did not contain any good
seed. He also crossed 21 flowers of P. veris with
pollen of P. vulgaris; and now he got only five
capsules, containing seed in a still less perfect
condition. Gartner knew nothing about hetero-
stylism; and his complete failure may perhaps be
accounted for by his having crossed together the
same forms of the cowslip and primrose; for such
crosses would have been of an illegitimate as well as
of a hybrid nature, and this would have increased
their sterility. My trials were rather more fortunate.
Twenty-one flowers, consisting of both forms of the
cowslip and primrose, were intercrossed legitimately,
and yielded seven capsules (7.2. 33 per cent.), contain-
ing on an average 42 seeds; some of these seeds,
however, were so poor that they probably would not have
germinated. Twenty-one flowers on the same cowslip
and primrose plants were also intercrossed illegiti-
mately, and they likewise yielded seven capsules (or
33 per cent.), but these contained on an average only
18 good and bad seeds. I should, however, state that
some of the above flowers of the primrose were fertilised |
with pollen from the polyanthus, which is certainly a
variety of the cowslip, as may be inferred from the per-
fect fertility inter se of the crossed offspring from these
two plants. ‘To show how sterile these hybrid unions
* ‘Bastarderzeugung,’ 1849, p.
721.
+ Mr. Scott has discussed the
nature of the polyanthus (‘ Proc.
Linn. Soc.’ viii. Bot. 1864, p.
103), and arrives at a different
conclusion; but I do not think
that his experiments were suffi-
ciently numerous. The degree of
infertility of a cross is liable to
much fluctuation. Pollen from
the cowslip at first appears rather
more etticient on the primrose than
that of the polyanthus; for 12
flowers of both forms of the prim-
rose, fertilised legitimately and
>
Cuar. II. THE COMMON OXLIP. 59
were I may remind the reader that 90 per cent. of the
flowers of the primrose fertilised legitimately with
primrose-pollen yielded capsules, containing on an
average 66 seeds; and that 54 per cent. of the flowers
fertilised illegitimately yielded capsules containing on
an average 35:5 seeds per capsule. The primrose,
especially the short-styled form, when fertilised by the
cowslip, is less sterile, as Gartner likewise observed,
than is the cowslip when fertilised by the primrose. The
above experiments also show that a cross between the
same forms of the primrose and cowslip is much more
sterile than that between different forms of these two
species.
The seeds from the several foregoing crosses were
sown, but none germinated except those from the
short-styled primrose fertilised with pollen of the
polyanthus ; and these seeds were the finest of the
whole lot. I thus raised six plants, and compared
them, with a group of wild oxlips which I had trans-
planted into my garden. One of these wild oxlips
produced slightly larger flowers than the others, and
this one was identical in every character (in foliage,
flower-peduncle, and flowers) with my six plants,
excepting that the flowers of the latter were tinged of
a dingy red colour, from being descended from the
polyanthus.
We thus see that the cowslip and primrose can-
not be crossed either way except with considerable
difficulty, that they differ conspicuously in external
appearance, that they differ in various physiological
illegitimately with pollen of the
cowslip gave five capsules, contain-
ing on an average 32°4 seeds,
whilst 18 flowers similarly fertil-
ised by polyanthus-pollen yielded
only five capsules, containing only
‘226 seeds.
On the other hand,
the seeds produced by the poly-
anthus- pollen were much the
finest of the whole lot, and were
the only ones which germinated.
60 IIYBRID PRIMULAS. Cuap. IT,
characters, that they inhabit slightly different stations
and range differently. Hence those botanists who
rank these plants as varieties ought to be able to prove
that they are not as well fixed in character as are most
species ; and the evidence in favour of such instability
of character appears at first sight very strong. It
rests, first, on statements made by several competent
observers that they have raised cowslips, primroses, and
oxlips from seeds of the same plant; and, secondly,
on the frequent occurrence in a state of nature of
plants presenting every intermediate gradation between
the cowslip and primrose.
The first statement, however, is of little value;
for, heterostylism not being formerly understood,
the seed-bearing plants were in no instance* pro-
tected from the visits of insects; and there would
be almost as much risk of an isolated cowslip, or of
several cowslips if consisting of the same form, being
crossed by a neighbouring primrose and producing
oxlips, as of one sex of a dicecious plant, under similar
circumstances, being crossed by the opposite sex of
an allied and neighbouring species. Mr. H. C. Wat-
son, a critical and most careful observer, made many
experiments by sowing the seeds of cowslips and of
various kinds of oxlips, and arrived at the following
conclusion,t namely, “that seeds of a cowslip can
produce cowslips and oxlips, and that seeds of an oxlip
can produce cowslips, oxlips, and primroses.” This
conclusion harmonises perfectly with the view that in
* One author states in the‘ Phy-
tologist’ (vol. iii. p. 703) that he
eoveredwith bell-glasses some cow-
slips, primroses, &c, on which he
experimented. He specifies all
tle details of his experiment, but
does not say that he artificially
fertilised his plants; yet he ob-
tained an abundance of seed,
which is simply impossible.
Hence there must have been
some strange error in these ex-
periments, which may be passed
oe a3 ee : i
* Phytologist,’ ii. . 217,
852; iii. p. 13 o
Cuap. IT. THE COMMON OXLIP. 6k
all cases, when such results have been obtained, the
unprotected cowslips have been crossed by primroses,
and the unprotected oxlips by either cowslips or
primroses ; for in this latter case we might expect, by
the aid of reversion, which notoriously comes into
powerful action with hybrids, that the two parent-forms
in appearance pure, as well as many intermediate gra-
dations, would be occasionally produced. Nevertheless
the two following statements offer considerable diffi-
culty. The Rev. Prof. Henslow* raised from seeds of a
cowslip growing in his garden, various kinds of oxlips
and one perfect primrose; but a statement in the same
paper perhaps throws light on this anomalous result.
Prof. Henslow had previously transplanted into his
garden a cowslip, which completely changed its ap-
pearance during the following year, and now resembled
an oxlip. Next year again it changed its character,
and produced, in addition to the ordinary umbels, a
few single-flowered scapes, bearing flowers somewhat
smaller and more deeply coloured than those of the
common primrose. From what I have myself observed
with oxlips, I cannot doubt that this plant was an ox-
lip in a highly variable condition, almost like that of
the famous Cytisus adamt. This presumed oxlip was
propagated by offsets, which were planted in different
parts of the garden; and if Prof. Henslow took by
mistake seeds from one of these plants, especially if it
had been crossed by a primrose, the result would be
quite intelligible. Another case is still more difficult
to understand: Dr. Herbert raised, from the seeds of
a highly cultivated red cowslip, cowslips, oxlips of
various kinds, and a primrose. This case, if accurately
* Loudon’s ‘ Mag. of Nat. Hist.’ iii. 1830, p. 409.
¢ ‘Transact. Hort. Soc.’ iv. p. 19.
62 WYBRID PRIMULAS. Cuar. II
recorded, which I much doubt, is explicable only on
the improbable assumption that the red cowslip was
not of pure parentage. With species and varieties
of many kinds, when intercrossed, one is sometimes
strongly prepotent over the other; and instances are
known* of a variety crossed by another, producing
offspring which in certain characters, as in colour,
hairiness, &c., have proved identical with the pollen-
bearing parent, and quite dissimilar to the mother-
plant; but I do not know of any instance of the off-
spring of a cross perfectly resembling, in a consider-
able number of important characters, the father alone.
It is, therefore, very improbable that a pure cowslip
crossed by a primrose should ever produce a primrose
in appearance pure. Although the facts given by Dr.
Herbert and Prof. Henslow are difficult to explain, yet
until it can be shown that a cowslip or a primrose,
carefully protected from insects, will give birth to at
least oxlips, the cases hitherto recorded have little
weight in leading us to admit that the cowslip and
primrose are varieties of one and the same species.
Negative evidence is of little value; but the follow-
ing facts may be worth giving :—Some cowslips which
had been transplanted from the fields into a shrubbery
were again transplanted into highly manured land.
In the following year they were protected from insects,
artificially fertilised, and the seed thus procured was
sown in a hotbed. The young plants were afterwards
planted out, some in very rich soil, some in stiff poor
clay, some in old peat, and some in pots in the green-
house ; so that these plants, 765 in number, as well as
their parents, were subjected to diversified and un-
* I have given instances in my tication,’ chap. xv. 2nd edit. vol
work ‘On the Variation of Ani- ii. p, 69,
mals and Plants under Domes-
Onap, II. THE COMMON OXLIP. 63
natural treatment; but not one of them presented the
least variation except in size—those in the peat at-
taining almost gigantic dimensions, and those in the
clay being much dwarfed.
I do not, of course, doubt that cowslips exposed
during several successive generations to changed con-
ditions would vary, and that this might occasionally
occur in a state of nature. Moreover, from the law
of analogical variation, the varieties of any one species
of Primula would probably in some cases resemble
other species of the genus. For instance I raised a red
primrose from seed from a protected plant, and the
flowers, though still resembling those of the primrose,
were borne during one season in umbels on a long foot-
stalk like that of a cowslip.
With regard to the second class of facts in support
of the cowslip and primrose being ranked as mere
varieties, namely, the well-ascertained existence in a
state of nature of numerous linking forms* :—If it can
be shown that the common wild oxlip, which is inter-
mediate in character between the cowslip and prim-
rose, resembles in sterility and other essential respects
a hybrid plant, and if it can further be shown that the
oxlip, though in a high degree sterile, can be fertilised
by either parent-species, thus giving rise to still finer
gradational links, then the presence of such linking
forms in a state of nature ceases to be an argument
of any weight in favour of the cowslip and primrose
being varieties, and becomes, in fact, an argument on
the other side. The hybrid origin of a plant in a
state of nature can be recognised by four tests: first,
by its occurrence only where both presumed parent-
* See an excellent article on in the ‘Phytologist,’ vol. iii, p
this subject by Mr. H. C. Watson 43, ;
64 HYBRID PRIMULAS. Cuap. II,
species exist or have recently existed; and this holds
good, as far as I can discover, with the oxlip; but the
P. elatior of Jacq., which, as we shall presently see,
constitutes a distinct species, must not be confounded
with the common oxlip. Secondly, by the supposed
hybrid plant being nearly intermediate in character
between the two parent-species, and especially by its
resembling hybrids artificially made between the same
two species. Now the oxlip is intermediate in cha-
racter, and resembles in every respect, except in the
colour of the corolla, hybrids artificially produced be-
tween the primrose and the polyanthus, which latter
is a variety of the cowslip. Thirdly, by the supposed
hybrids being more or less sterile when crossed inter se:
but to try this fairly two distinct plants of the same
parentage, and not two flowers on the same plant,
should be crossed; for many pure species are more
or less sterile with pollen from the same individual
plant; and in the case of hybrids from heterostyled
species the opposite forms should be crossed. Fourthly
and lastly, by the supposed hybrids being much more
fertile when crossed with either pure parent-species
than when crossed inter se, but still not as fully fertile
as the parent-species. if
For the sake of ascertaining the two latter points,
J transplanted a group of wild oxlips into my
garden. They consisted of one long-styled and
three short-styled plants, which, except in the co-
rolla of one being slightly larger, resembled each
other closely. The trials which were made, and the
results obtained, are shown in the five following
tables. No less than twenty different crosses are
necessary in order to ascertain fully the fertility of
hybrid heterostyled plants, both inter se and with
their two varent-specics. In this instance 256 flowers
Cuap. II. THE COMMON OXLIP. 65
were crossed in the course of four seasons. I may
mention, as a mere curiosity, that if any one were to
raise hybrids between two trimorphic heterostyled
species, he would have to make 90 distinct unions
in order to ascertain their fertility in all ways;
and as he would have to try at least 10 flowers in
each case, he would be compelled to fertilise 900
flowers and count their seeds.
This would probably
exhaust the patience of the most patient man.
TaBLe 14,
Crosses inter se between the two forms of the common Osalip.
Mlegitimate union.
Short-styled ox-
lip, by pollen of
short-styled oxlip:
20 flowers fertilised,
did not produce one
capsule,
Legitimate union.
Short-styled ox- .
lip, by pollen of
long-styled oxlip:
10 flowers fertilised,
did not produce one
capsule,
Mllegitimate union.
Long -styled ox-
lip, by its own
pollen: 24 flowers
fertilised, produced
five capsules, con-
taining 6, 10, 20,
8, and 14 seeds.
, Average 11:6
Legitimate union.
Long -styled ox-
lip, by pollen of
short-styled oxlip:
10 flowers fertilised,
did not produce one
capsule.
Tasie 15,
Both forms of the Oxlip crossed with Pollen of both forms of the
Cowslip,
P, veris,
Mlegitimate union.
Short-styled ox-
lip, by pollen of
short-styled cow-
slip: 18 fowers fer-
tilised, did not pro-
duce one capsule.
Legitimate union.
Short-styled ox-
lip, by pollen of
long- styled cow-
slip: 18 flowers
fertilised, produced
three capsules, con-
taining 7, 3, and 3
wretched seeds, ap-
parently incapable
of germination.
Illegitimate union.
Long - styled ox-
lip, by pollen of
long -styled cow-
slip: 11 flowers
fertilised, produced
one capsule, con-
taining 13 wretched
seeds,
Legitimate union.
Long -styled ox-
lip, by pollen of
short-styled cow-
slip: 5 flowers
fertilised, produced
two capsules, con-
taining 21 and 28
very fine seeds,
66
HYBRID PRIMULAS.
TabLe 16.
Cuap, IL
Both forms of the Oxlip crossed with Pollen of both forms of the
Primrose, P. vulgaris.
Nlegitimate union.
Short-styled ox-
lip, by pollen of
short-styled prim-
rose: 34 flowers
fertilised, produced
two capsules, con-
taining 5 and 12
seeds,
Legitimate union. | Illegitiinate union.
Short-styled ox-| Long-styled ox-
lip, by pollen of lip, by pollen of
long-styled prim- long-styled prim-
rose: 26 flowers'rose: 11 flowers
fertilised, produced fertilised, produced
six capsules, con-' four capsules, con-
taining 16, 20, 5,10, taining 10,7, 5, and
19, and 24 ‘seeds. 6 wretched seeds,
Average 15'7. Many Average 7°0.
of the seeds very
poor, some good.
Legitimate union,
Long-styled ox-
lip, by policn of
short-styled prim-
rose: 5 flowers
fertilised, produced
five capsules, con-
taining 26, 32, 23,
28, and 34 seeds,
Average 28°6.
Both forms of the
Tasue 17.
Cowslip crossed with Pollen of both forms of the Oalip,
Mlegitimate union.
Short-styled cow-
slip, by pollen of
short-styled oxlip:
8 flowers fertilised,
produced not one
capsule.
Legitimate union. | Illegitimate union.
Long-styled cow-' Long-styled cow-
slip, by pollen of slip, by pollen of
short-styled oxlip: long-styled oxlip:
8 flowers fertilised, 8 flowers fertilised,
produced one cap- produced three cap-
sule, containing 26 sules, containing 5,
seeds, 6, and 14 seeds,
| Average 8°3.
|
Legitimate union,
Short-styled cow-
slip, by pollen of
long - styled oxlip:
8 flowers fertilised,
produced eight cap-
sules, containing 58,
38, 31, 44, 23, 26,
37, and 66 seeds.
Average 40°4,
TaBLe 18.
Both forms of the Primrose crossed with Pollen of both forms of the Oxtip.
Mlegitimate union.
Short-styled prim-
rose, by pollen of
short-styled oxlip:
8 flowers fertilised,
produced not one
capsule.
Legitimate union. | Illegitimate oa
Long-styled prim-! Long-styled prim-
rose, by pollen of rose, by pollen of
short-styled oxlip: long-styled oxlip:
8 flowers fertilised, 8 flowers fertilised,
produced two or produced eight cap-
sules, containing 5 sules, containing 15,
and 2 seeds. 7, 12, 20, 22, 7, 16,
and 13 seeds, Ave-
rage 14:0,
Legitimate union.
Short-styled prim-
rose, by pollen of
long-styled oxlip:
8 flowers fertilised,
produced four cap-
sules, containing
52, 52, 42, and 49
seeds,some good and
some bad. Average
48-7,
Cuar. IL. THE COMMON OXLIP. 67
We see in these five tables the number of capsules
and of seeds produced, by crossing both forms of the
oxlip in a legitimate and illegitimate manner with one
another, and with the two forms of the primrose and
cowslip. I may premise that the pollen of two of the
short-styled oxlips consisted of nothing but minute
aborted whitish cells; but in the third short-styled
plant about one-fifth of the grains appeared in a sound
condition. Hence it is not surprising that neither
the short-styled nor the long-styled oxlip produced a
single seed when fertilised with this pollen. Nor did
the pure cowslips or primroses when illegitimately fer-
tilised with it; but when thus legitimately fertilised
they yielded a few good seeds. The female organs of
the short-styled oxlips, though greatly deteriorated in
power, were in a rather better condition than the male
organs; for though the short-styled oxlips yielded no
seed when fertilised by the long-styled oxlips, and
hardly any when illegitimately fertilised by pure cow-
slips or primroses, yet when legitimately fertilised by
these latter species, especially by the long-styled
primrose, they yielded a moderate supply of good
seed.
The long-styled oxlip was more fertile than the
three short-styled oxlips, and about half its pollen-
grains appeared sound. It bore no seed when legiti-
mately fertilised by the short-styled oxlips; but this
no doubt was due to the badness of the pollen of
the latter; for when illegitimately fertilised (‘Table
14) by its own pollen it produced some good seeds,
though much fewer than self-fertilised cowslips or
primroses would have produced. The long-styled ox-
lip likewise yielded a very low average of seed, as may
be seen in the third compartment of the four latter
tables, when illegitimately fertilised by, and when
68 HYBRID PRIMULAS. Cuap. II.
illegitimately fertilising, pure cowslips and primroses.
The four corresponding legitimate unions, however, were
moderately fertile, and one (viz. that between a short-
styled cowslip and the long-styled oxlip in Table 17)
was nearly as fertile as if both parents had been pure.
A short-styled primrose legitimately fertilised by the
long-styled oxlip (Table 18) also yielded a moderately
good average, namely 48°7 seeds; but if this short-
styled primrose had been fertilised by a long-styled
primrose it would have yielded an average of 65 seeds.
If we take the ten legitimate unions together, and the
ten illegitimate unions together, we shall find that 29
per cent. of the flowers fertilised in a legitimate manner
yielded capsules, these containing on an average 27°4
good and bad seeds; whilst only 15 per cent. of the
flowers fertilised in an illegitimate manner yielded
capsules, these containing on an average only 11:0
good and bad seeds.
In a previous part of this chapter it was shown that
illegitimate crosses between the long-styled form of
the primrose and the long-styled cowslip, and between
the short-styled primrose and short-styled cowslip, are
more sterile than legitimate crosses between these two
species; and we now see that the same rule holds good
almost invariably with their hybrid offspring, whether
these are crossed ¢nter se, or with either parent-species ;
so that in this particular case, but not as we shall pre-
sently see in other cases, the same rule prevails with
the pure unions between the two forms of the same
heterostyled species, with crosses between two distinct
heterostyled species, and with their"hybrid offspring.
Seeds from the long-styled oxlip fertilised by its
own pollen were sown, and three long-styled plants
raised, The first of these was identical in every
character with its parent. The second bore rather
Cuap. IL. THE COMMON OXLIP. 69.
smaller flowers, of a paler colour, almost like those of
the primrose; the scapes were at first single-flowered,
but later in the season a, tall thick scape, bearing many
flowers, like that of the parent oxlip, was thrown up.
The third plant likewise produced at first only single-
flowered scapes, with the flowers rather small and of a
darker yellow; bué it perished early. The second
plant also died in September; and the first plant,
though all three grew under very favourable con-
ditions, looked very sickly. Hence we may infer that
seedlings from self-fertilised oxlips would hardly be
able to exist in a state of nature. I was surprised to
find that all the pollen-grains in the first of these seed-
ling oxlips appeared sound; and in the second only a
moderate number were bad. These two plants, however,
had not the power of producing a proper number of
seeds; for though left uncovered and surrounded by
pure primroses and cowslips, the capsules were esti-
mated to include an average of only from fifteen to
twenty seeds.
From having many experiments in hand, I did not
sow the seed obtained by crossing both forms of the
primrose and cowslip with both forms of the oxlip,
which I now regret; but I ascertained an interest-
ing point, namely, the character of the offspring
from oxlips growing in a state of nature near both
primroses and cowslips. The oxlips were the same
plants which, after their seeds had been collected, were
transplanted and experimented on. From the seeds
thus obtained eight plants were raised, which, when
they flowered, might have been mistaken for pure
primroses; but on close comparison the eye in the
centre of the corolla was seen to be of a darker yellow,
and the peduncles more elongated. As the season ad-
vanced, one of these plants threw up two naked scapes,
10 HYBRID PRIMULAS. Cuapr. II
7 inches in height, which bore umbels of flowers of
the same character as before. This fact led me to ex-
amine the other plants after they had flowered and
were dug up; and I found that the flower-peduncles
of all sprung from an extremely short common scape,
of which no trace can be found in the pure primrose.
Hence these plants are beautifully intermediate be-
tween the oxlip and the primrose, inclining rather
towards the latter ; and we may safely conclude that the
parent oxlips had been fertilised by the surrounding
primroses. .
From the various facts now given, there can be no
doubt that the common oxlip is a hybrid between the
cowslip (P. veris, Brit. Fl.) and the primrose (P. vul-
garis, Brit. F].), as has been surmised by several
botanists. It is probable that oxlips may be produced
either from the cowslip or the primrose as the’ seed-
bearer, but oftenest from the latter, as I judge from
the nature of the stations in which oxlips are generally
found,* and from the primrose when crossed by the
cowslip being more fertile than, conversely, the cowslip
by the primrose. The hybrids themselves are also
rather more fertile when crossed with the primrose
than with the cowslip. Whichever may be the seed-
bearing plant, the cross is probably between different
forms of the two species ; for we have seen that legiti-
mate hybrid unions are more fertile than illegitimate
hybrid unions. Moreover a friend in Surrey found
that 29 oxlips which grew in the neighbourhood of
his house consisted of 13 long-styled and 16 short-
styled plants; now, if the parent-plants had been
illegitimately united, either the long- or short-styled
form would have greatly preponderated, as we shall
* See also on this head Hardwicke’s ‘Science Gossip, 1867, pp
114, 137,
Cuap. II. THE COMMON OXLIP. 71
hereafter see good reason to believe. The case of
the oxlip is interesting; for hardly any other in-
stance is known of a hybrid spontaneously arising
in such large numbers over so wide an extent of coun-
try. The common oxlip (not the P. elatior of Jacq.)
is found almost everywhere throughout England, where
both cowslips and primroses grow. In some districts,
as I have seen near Hartfield in Sussex and in parts
of Surrey, specimens may be found on the borders of
almost every field and small wood. In other districts
the oxlip is comparatively rare: near my own resi-
dence I have found, during the last twenty-five years,
not more than five or six plants or groups of plants.
It is difficult to conjecture what is the cause of this
difference in their number. It is almost necessary
that a plant, or several plants belonging to the same
form, of one parent-species, should grow near the
opposite form of the other parent-species; and it is
further necessary that both species should be fre-
quented by the same kind of insect, no doubt a moth.
The cause of the rare appearance of the oxlip in
certain districts may be the rarity of some moth,
which in other districts habitually visits both the
primrose and cowslip.
Finally, as the cowslip and primrose differ in the
various characters above specified,—as they are in a
high degree sterile when intercrossed,—as there is no
trustworthy evidence that either species, when un-
crossed, has ever given birth to the other species or
to any intermediate form,—and as the intermediate
forms which are often found in a state of nature have
been shown to be more or less sterile hybrids of the
first or second generation,—we must for the future
look at the cowslip and primrose as good and true
species.
72 THE BARDFIELD OXLIP. Cuar. II.
Primula elatior, Jacq., or the Bardfield Oxlip, is
found in England only in two or three of the eastern
counties. On the Continent it has a somewhat dif-
ferent range from that of the cowslip and primrose;
and it inhabits some districts where neither of these
species live.* In general appearance it differs so
much from the common oxlip, that no one accustomed
to see both forms in the living state could afterwards
confound them; but there is scarcely more than a
single character by which they can be distinctly de-
fined, namely, their linear-oblong capsules equalling
the calyx in length.f The capsules when mature differ
conspicuously, owing to their length, from those of the
cowslip and primrose. With respect to the fertility
of the two forms when these are united in the four
possible methods, they behave like the other hetero-
styled species of the genus, but differ somewhat (see
Tables 8 and 12) in the smaller proportion of the il-
legitimately fertilised flowers which set capsules. That
P. elatior is not a hybrid is certain, for when the two
forms were legitimately united they yielded the large
average of 47:1 seeds, and when illegitimately united
35°5 per capsule ; whereas, of the four possible unions
(Table 14) between the two forms of the common ox-
lip which we know to be a hybrid, one alone yielded
any seed; and in this case the average number was
only 11:6 per capsule. Moreover I could not detect
a single bad pollen-grain in the anthers of the short-
styled P. elatior ; whilst in two short-styled plants of
the common oxlip all the grains were bad, as were
a large majority in a third plant. As the common
* For England, sec Hewett C. 1858, p. 142. For the Alps, see
Watson, ‘Cybele Britannica, vol. ‘Ann. and Mag. Nat. Hist.’ vol.
ii, 1849, p. 292. For the Con- ix. 1842, pp. 156 and 515.
tinent, see Lecog, ‘ Géograph. + Babington’s ‘ Manual of Brit
Botanique de I’Europe,’ tom. viii, ish Botany,’ 1851, p. 2538,
Cuap. TI. THE BARDFIELD OXLIP. 73
oxlip is a hybrid between the primrose and cowslip, it
is not surprising that eight long-styled flowers of the
prinirose, fertilised by pollen from the long-styled
common oxlip, produced eight capsules (Table 18),
containing, however, only a low average of seeds;
whilst the same number of flowers of the primrose,
similarly fertilised by the long-styled Bardfield oxlip,
produced only a single capsule; this latter plant
being an altogether distinct species from the primrose.
Plants of P. elatior have been propagated by seed in
a garden for twenty-five years, and have kept all this
time quite constant, excepting that in some cases the
flowers varied a little in size and tint.* Nevertheless,
according to Mr. H.C. Watson and Dr. Bromfield,
plants may be occasionally found in a state of nature,
in which most of the characters by which this species
can be distinguished from P. veris and vulgaris fail ;
but such intermediate forms are probably due to
hybridisation ; for Kerner states, in the paper before
referred to, that hybrids sometimes, though rarely,
arise in the Alps between P. elatior and veris.
Finally, although we may freely admit that Primula
veris, vulgaris, and elatior,as well as all the other
species of the genus, are descended from a common
primordial form, yet from the facts above given, we
must conclude that these three forms are now as fixed
in character as are many others which are universally
ranked as true species. Consequently they have as
good a right to receive distinct specific names as have,
for instance, the ass, quagga, and zebra.
Mr. Scott has arrived at some interesting results by
* See Mr. H. Doubleday in the _ p. 462.
*Gardener’s Chronicle,’ 1867, p. t ‘Phytologist,’ vol. i. p. 1001,
435, also Mr. W. Marshall, ibid. and vol. iii. p. 695.
74 HYBRID PRIMULAS. Cuar. IL
crossing other heterostyled species of Primula.* I
have already alluded to his statement, that in four
instances (not to mention others) a species when crossed
with a distinct one yielded a larger number of seeds
than the same species fertilised illegitimately with its
own-form pollen, though taken from a distinct plant.
It has long been known from the researches of Kélreuter
and Gartner, that two species when crossed reciprocally
sometimes differ as widely as is possible in their fer-
tility : thus A when crossed with the pollen of B will
yield a large number of seeds, whilst B may be crossed
repeatedly with pollen of A, and will never yield a single
seed. Now Mr. Scott shows in several cases that the
same law holds good when two heterostyled species
of Primula are intercrossed, or when one is crossed
with a homostyled species. But the results‘are much
more complicated than with ordinary plants, as two
heterostyled dimorphic species can be intercrossed in
eight different ways. I will give one instance from
Mr. Scott. The long-styled P. hirsuta fertilised legi-
timately and illegitimately with pollen from the two
forms of P. awricula, and reciprocally the long-styled
P. auricula fertilised legitimately and illegitimately
with pollen from the two forms of P. hirsuta, did
not produce a single seed. Nor did the short-
styled P. hirsuta when fertilised legitimately and
illegitimately with the pollen of the two forms of
P. auricula. On the other hand, the short-styled
P. auricula fertilised with pollen from the long-styled
. P. harsuta yielded capsules containing on an average
no less than 56 seeds; and the short-styled P.
auricula by pollen of the short-styled P. hirsuta
yielded capsules containing on an average 42 sceds
* ‘Journ. Linn, Soc. Bot.’ vol. viii. 1864, p. 98 to end.
Cuap. IT. HYBRID VERBASCUMS. 75
per capsule. So that out of the eight possible unions
between the two forms of these two species, six
were utterly barren, and two fairly fertile. We have
seen also the same sort of extraordinary irregularity in
the results of my twenty different crosses (Tables
14 to 18), between the two forms of the oxlip, prim-
rose, and cowslip. Mr. Scott remarks, with respect
to the results of his trials, that they are very surprising,
as they show us that “the sexual forms of a species
manifest in their respective powers for conjunction
with those of another species, physiological peculiari-
ties which might well entitle them, by the criterion of
fertility, to specific distinction.”
Finally, although P. veris and vulgaris, when crossed
legitimately,.and especially when their hybrid offspring
are crosséd in this manner with both parent-species,
were decidedly more fertile, than when crossed in an
illegitimate manner, and although the legitimate cross
effected by Mr. Scott between P. auwricula and hirsuta
was more fertile, in the ratio of 56 to 42, than the
illegitimate cross, nevertheless it is very doubtful,
from the extreme uregularity of the results in the
various other hybrid crosses made by Mr. Scott, whether
it can be predicted that two heterostyled species are
generally more fertile if crossed legitimately (¢.e. when
opposite forms are united) than when crossed illegiti-
mately.
Supplementary Note on some wild hybrid Verbasewms.
In an early part of this chapter I remarked that few
other instances could be given of a hybrid spontane-
ously arising in such large numbers, and over so wide an
extent of country, as that of the common oxlip ; but per-
haps the number of well-ascertained cases of naturally
76 HYBRID VERBASCUMS. Cuap, IL.
produced hybrid willows is equally great.* Numerous
spontaneous hybrids between several species of Cistus,
found near Narbonne, have been carefully described
by M. Timbal-Lagrave,t and many hybrids between an
Aceras and Orchis have been observed by Dr. Weddell.}
In the genus Verbascum, hybrids are supposed to have
often originated § in a state of nature ; some of these un-
doubtedly are hybrids, and several hybrids have origi-
nated in gardens; but most of these cases require,|| ag
Gartner remarks, verification. Hence the following
case is worth recording, more especially as the two
species in question, V. thapsus and lychnitis, are per-
fectly fertile when insects are excluded, showing that
the stigma of each flower receives its own pollen.
Moreover the flowers offer only pollen to insects, and
have not been rendered attractive to them by secret-
ing nectar.
I transplanted a young wild plant into my garden
for experimental purposes, and when it flowered it
plainly differed from the two species just mentioned
and from a third which grows in this neighbourhood. I
thought that it was a strange variety of V. thapsus. It
attained the height (by measurement) of 8 feet! It
was covered with a net, and ten flowers were fertilised
with pollen from the same plant; later in the season,
when uncovered, the flowers were freely visited by
pollen-collecting bees; nevertheless, although many
capsules were produced, not one contained a single
seed, During the following year this same plant was
* Max Wichura, ‘Die Bastard- § See, for instance, the ‘ Eng-
befruchtung, &¢, der Weiden, lish Flora, by Sir J. E. Smith,
1865. 1824, vol. i. p. 307.
+ ‘Mém. del’Acad. des Sciences || See Gartner, ‘ Bastarderzeu-
de Toulouse,’ 5° série, tom. v. p.28. gung,’ 1849, p. 590.
t ‘Annales des Se, Nat.’ 3°
série, Bot. tom. xviii. p. 6.
Cuap. IL. HYBRID VERBASCUMS. 77
left uncovered near plants of V. thapsus and lychnitis ;
but again it did not produce a single seed. Four
flowers, however, which were repeatedly fertilised
with pollen of V. lychnitis, whilst the plant was tem-
porarily kept under a net, produced four capsules,
which contained five, one, two, and two seeds; at the
same time three flowers were fertilised with pollen of
V. thapsus, and these produced two, two, and three
seeds. T’o show how unproductive these seven capsules
were, I may state that a fine capsule from a plant of
V. thapsus growing close by contained above 700 seeds.
These facts led me to search the moderately-sized field
whence my plant had been removed, and I found in it
many plants of V. thapsus and lychnitis as well as
thirty-three plants intermediate in character between
these two species. These thirty-three plants differed
much from one another. In the branching of the stem
they more closely resembled V. lychnitis than V. thapsus,
but in height the latter species. In the shape of their
leaves they often closely approached V. lychnitis, but
some had leaves extremely woolly on the upper surface
and decurrent like those of V. thapsus ; yet the degree
of woolliness and of decurrency did not always go
together. In the petals being flat and remaining
open, and in the manner in which the anthers of the
longer stamens were attached to the filaments, these
plants all took more after V. lychnitis than V. thapsus.
In the yellow colour of the corolla they all resembled
the latter species. On the whole, these plants appeared
to take rather more after V. lychnitis than V. thapsus.
On the supposition that they were hybrids, it is not an
anomalous circumstance that they should all have pro-
duced yellow flowers; for Gartner crossed white and
yellow-flowered varieties of Verbascum, and the off-
spring thus produced never bore flowers of an inter-
78 HYBRID VERBASCUMS. Cuavr. IT,
mediate tint, but either pure white or pure yellow
flowers, generally of the latter colour.*
My observations were made in the autumn; so that
I was able to collect some half-matured capsules from
twenty of the thirty-three intermediate plants, and
likewise capsules of the pure V. lychnitis and thapsus
growing in the same field. All the latter were filled
with perfect but immature seeds, whilst the capsules of
the twenty intermediate plants did not contain one
single perfect seed. These plants, consequently, were
absolutely barren. From this fact,—from the one plant
which was transplanted into my garden yielding when
artificially fertilised with pollen from V. lychnitis and
thapsus some seeds, though extremely few in number,—
from the circumstance of the two pure species growing
in the same field,—and from the intermediate character
of the sterile plants, there can be no doubt that they
were hybrids. Judging from the position in which
they were chiefly found, I am inclined to believe they
were descended from V. thapsus as the seed-bearer, and
V. lychnitis as the pollen-bearer.
It is known that many species of Verbascum, when
the stem is jarred or struck by a stick, cast off their
flowers.f This occurs with V. thapsus, as I have re-
peatedly observed. The corolla first separates from its
attachment, and then the sepals spontaneously bend
inwards so as to clasp the ovarium, pushing off the
corolla by their movement, in the course of two or
three minutes. Nothing of this kind takes place with
young barely expanded flowers. With Verbascum lych-
nitis and, as I believe, V. phaeenicewm the corolla is not cast
* ‘ Bastarderzeugung,’ p. 307. Smith,’ vol. ii, p. 210. I was
+ This was first observed by guided to these references by the
Corrca de Serra: see Sir J. E. Rev. W. A. Leighton, who ob-
Smith's ‘ English Flora,’ 1824, vol. _ served this same phenomenon with
i p. 311; also ‘Life of Sir J. E. V. virgatum.
Cuap. IT. HYBRID VERBASCUMS. 79
off, however often and severely the stem may be struck.
In this curious property the above-described hybrids
took after V. thapsus; for I observed, to my surprise, that
when I pulled off the flower-buds round the flowers
which I wished to mark with a thread, the slight jar
invariably caused the corollas to fall off.
These hybrids are interesting under several points of
view. First, from the number found in various parts
of the same moderately-sized field. That they owed their
origin to insects flying from flower to flower, whilst col-
lecting pollen, there can be no doubt. Although in-
sects thus rob the flowers of a most precious substance,
yet they do great good; for, as I have elsewhere
shown,* the seedlings of V. thapsus raised from flowers
fertilised with pollen from another plant, are more
vigorous than those raised from self-fertilised flowers.
But in this particular instance the insects did great
harm, as they led to the production of utterly barren
plants. Secondly, these hybrids are remarkable from
differing much from one another in many of their
characters; for hybrids of the first generation, if
raised from uncultivated plants, are generally uni-
form in character. That these hybrids belonged to
the first generation we may safely conclude, from the
absolute sterility of all those observed by me in a state
of nature and of the one plant in my garden, excepting
when artificially and repeatedly fertilised with pure
pollen, and then the number of seeds produced was
extremely small. As these hybrids varied so much, an
almost perfectly graduated series of forms, connecting
together the two widely distinct parent-species, could
easily have been selected. This case, like that of
the common oxlip, shows that botanists ought to be
* ‘The Effects of Cross and Self-fertilisation,’ 1876, p. 89,
80 HYBRID VERBASCUMS. Cuapr. IL,
cautious in inferring the specific identity of two forms
from the presence of intermediate gradations; nor
would it be easy in the many cases in which hybrids are
moderately fertile to detect a slight degree of sterility in
such plants growing in a state of nature and liable to be
fertilised by either parent-species. Thirdly and lastly,
these hybrids offer an excellent illustration of a state-
ment made by that admirable observer Gartner, namely,
that although plants which can be crossed with ease
generally produce fairly fertile offspring, yet well-
pronounced exceptions to this rule occur; and here we
have two species of Verbascum which evidently cross
with the greatest ease, but produce hybrids which are
excessively sterile.
Cuar. TIT. LINUM GRANDIFLORUM. 81
CHAPTER III.
HETEROSTYLED Dimorrnic PLants—continued.
Linum grandiflorum, long-styled form utterly sterile with own-form
pollen—Linum perenne, torsion of the pistils in the long-styled
form alone—Homostyled species of Linum— Pulmonaria officinalis,
singular differeuce in self-fertility between the English and German
long-styled plants—Pulmonaria angustifolia shown to be a distinct
species, long-styled form completely self-sterile—Polygonum figo-
pyrum—Various other heterostyled genera—Rubiacee—Mitchella
repens, fertility of the flowers in pairs— Houstonia—Faramea,
remarkable difference in the pollen-grains of the two forms ; tor-
sion of the stamens in the short-stylud form alone; development
not as yet perfect—The heterustyled structure in the several
Rubiaceous genera not due to desceut in common.
Ir has long been known* that several species of
Linum present two forms, and having observed this
fact in L. flavum more than thirty years ago, I was
led, after ascertaining the nature of heterostylism in
Primula, to examine the first species of Linum which
I met with, namely, the beautiful DL. grandijlorum.
This plant exists under two forms, occurring in about
equal numbers, which differ little in structure, but
greatly in function. The foliage, corolla, stamens, and
pollen-grains (the latter examined both distended with
water and dry) are alike in the two forms (Fig. 4).
The difference is confined to the pistil; in the short-
styled form the styles and the stigmas are only about
half the length of those in the long-styled. A more
* Treviranus has shown that original paper, “ ¢ Bot. Zeitung,”
this is the case in his review of my 1863, p. 189.
82 HETEROSTYLED DIMORPHIC PLANT'S. Cnap IIL
important distinction is, that the five stigmas in the
short-styled form diverge greatly from one another,
and pass out between the filaments of the stamens,
Fig. 4,
Long-styled form. Short-styled form.
88 stigmas,
LINUM GRANDIFLORUM.
and thus lie within the tube of the corolla. In the
long-styled form the elongated stigmas stand nearly
upright, and alternate with the anthers. In this latter
form the length of the stigmas varies considerably,
their upper extremities projecting even a little above
the anthers, or reaching up only to about their middle.
Nevertheless, there is never the slightest difficulty in
distinguishing between the two forms ; for, besides the
difference in the divergence of the stigmas, those of
the short-styled form never reach even to the bases
of the anthers, In this form the papille on the stig-
matic surfaces are shorter, darker-coloured, and more
crowded together than in the long-styled form; but
these differences seem due merely to the shortening
of the stigma, for in the varieties of the long-styled
form with shorter stigmas, the papille are more crowded
and darker-coloured than in those with the longer
Cnap. IIT. LINUM GRANDIFLORUM. 83
stigmas. Considering the slight and variable differ-
ences between the two forms of this Linum, it is not
surprising that hitherto they have been overlooked.
In 1861 I had eleven plants in my garden, eight of
which were long-styled, and three short-styled. Two
very fine long-styled plants grew ma bed a hundred
yards off all the others, and separated from them by a
screen of evergreens. I marked twelve flowers, and
placed on their stigmas a little pollen from the short-
styled plants. The pollen of the two forms is, as
stated, identical in appearance; the stigmas of the
long-styled flowers were already thickly covered with
their own pollen—so thickly that I could not find one
bare stigma, and it was late in the season, namely,
September 15th. Altogether, it seemed almost childish
to expect any result. Nevertheless from my experi-
ments on Primula, I had faith, and did not hesitate to
make the trial, but certainly did not anticipate the
full result which was obtained. The germens of these
twelve flowers all swelled, and ultimately six fine cap-
sules (the seed of which germinated on the following
year) and two poor capsules were produced; only four
capsules shanking off. These same two long-styled
plants produced, in the course of the summer, a
vast number of flowers, the stigmas of which were
covered with their own pollen; but they all proved
absolutely barren, and their germens did not even
swell.
The nine other plants, six long-styled and three
short-styled, grew not very far apart in my flower-
garden. Four of these long-styled plants produced no
seed-capsules; the fifth produced two; and the remain-
ing one grew so close to a short-styled plant that
their branches touched, and this produced twelve cap-
sules, but they were poor ones. The case was different
84 HETEROSTYLED DIMORPHIC PLANTS. Cuap. IIL
with the short-styled plants. The one which grew
close to the long-styled plant produced ninety-four
imperfectly fertilised capsules containing a multitude
of bad seeds, with a moderate number of good ones.
The two other short-styled plants growing together
were small, being partly smothered by other plants;
they did not stand very close to any long-styled plants,
yet they yielded together nineteen capsules. These
facts seem to show that the short-styled plants are more
fertile with their own pollen than are the long-styled,
and we shall immediately see that this probably is the
case. But I suspect that the difference in fertility be-
tween the two forms was in this instance in part due to
a distinct cause. I repeatedly watched the flowers, and
only once saw a humble-bee momentarily alight on
one, and then fly away. If bees had visited the several
plants, there cannot be a doubt that the four long-
styled plants, which did not produce a single capsule,
would have borne an abundance. But several times I
saw small diptera sucking the flowers; and these
insects, though not visiting the flowers with anything
like the regularity of bees, would carry a little pollen
from one form to the other, especially when growing
near together; and the stigmas of the short-styled
plants, diverging within the tube of the corolla, would
be more likely than the upright stigmas of the long-
styled plants, to receive a small quantity of pollen if
brought to them by small insects. Moreover from the
greater number of the long-styled than of the short-
styled plants in the garden, the latter would be more
likely to receive pollen from the long-styled, than the
long-styled from the short-styled.
In 1862 I raised thirty-four plants of this Linum in a
hot-bed ; and these consisted of seventeen long-styled
and seventeen short-styled forms. Seed sown later in the
Cuap. III. LINUM GRANDIFLORUM. 85
flower-garden yielded seventeen long-styled and twelve
short-styled forms. These facts justify the statement
that the two forms are produced in about equal num-
bers. The thirty-four plants of the first lot were kept
under a net which excluded all insects, except such
minute ones as Thrips. I fertilised fourteen long-styled
flowers legitimately with pollen from the short-styled,
and got eleven fine seed-capsules, which contained on
an average 8'6 seeds per capsule, but only 5:6 appeared
to be good. It may be well to state that ten seeds is
the maximum production for a capsule, and that our
climate cannot be very favourable to this North-African
plant. On three occasions the stigmas of nearly a
hundred flowers were fertilised illegitimately with their
own-form pollen, taken from separate plants, so as to
prevent any possible ill effects from close inter-breed-
ing. Many other flowers were also produced, which, as
before stated, must have received plenty of their own
pollen; yet from all these flowers, borne by the seven-
teen long-styled plants, only three capsules were pro-
duced. One of these included no seed, and the other
two together gave only five good seeds. It is probable
that this miserable product of two half:fertile capsules
from the seventeen plants, each of which must have
produced at least fifty or sixty flowers, resulted from
their fertilisation with pollen from the short-styled
plants by the aid of Thrips; for I made a great
mistake in keeping the two forms under the same net,
with their branches often interlocking ; and it is sur-
prising that a greater number of flowers were not
accidentally fertilised.
Twelve short-styled flowers were in this instance
castrated, and afterwards fertilised legitimately with
pollen from the long-styled form; and they produced
seven fine capsules. These included on an average
86 HETEROSTYLED DIMORPHIC PLANTS. Cuap. IIL.
7:6 seeds, but of apparently good seed only 4:3 per
capsule. At three separate times nearly a hundred
flowers were fertilised illegitimately with their own-
form pollen, taken from separate plants; and nu-
merous other flowers were produced, many of which
must have received their own pollen. From all these
flowers on the seventeen short-styled plants only fifteen
capsules were produced, of which only eleven con-
tained any good seed, on an average 4°2 per capsule.
As remarked in the case of the long-styled plants,
some even of these capsules were perhaps the product
of a little pollen accidentally fallen from the adjoining
flowers of the other form on to the stigmas, or trans-
ported by Thrips. Nevertheless the short-styled plants
seem to be slightly more fertile with their own pollen
than the long-styled, in the proportion of fifteen cap-
sules to three; nor can this difference be accounted
for by the short-styled stigmas being more liable to
receive their own pollen than the long-styled, for the
reverse is the case. The greater self-fertility of the
short-styled flowers was likewise shown in 1861 by
the plants in my flower-garden, which were left to
themselves, and were but sparingly visited by insects.
On account of the probability of some of the flowers
on the plants of both forms, which were covered under
the same net, having been legitimately fertilised in
an accidental manner, the relative fertility of the two
legitimate and two illegitimate unions cannot be
compared with certainty; but judging from the
number of good seeds per capsule, the difference was
at least in the ratio of 100 to 7, and probably much
greater.
Hildebrand tested my results, but only on a single
short-styled plant, by fertilisng many flowers with
their own-form pollen ; and these did not produce any
Cuap. III. LINUM GRANDIFLORUM. 87
seed. This confirms my suspicion that some of the
few capsules produced by the foregoing seventeen
short-styled plants were the product of accidental
legitimate fertilisation. Other flowers on the same
plant were fertilised by Hildebrand with pollen from
the long-styled form, and all produced fruit.*
The absolute sterility (judging from the experi-
ments of 1861) of the long-styled plants with their
own-form pollen led me to examine into its apparent
cause; and the results are so curious that they are
worth giving in detail. The experiments were tried
on plants grown in pots and brought successively
into the house.
First. Pollen from a short-styled plant was placed
on the five stigmas of a long-styled flower, and these,
after thirty hours, were found deeply penetrated by a
multitude of pollen-tubes, far too numerous to be
counted; the stigmas had also become discoloured
and twisted. I repeated this experiment on another
flower, and in eighteen hours the stigmas were pene-
trated by a multitude of long pollen-tubes. This is
what might have been expected, as the union is a
legitimate one. The converse experiment was likewise
tried, and pollen from a long-styled flower was placed
on the stigmas of a short-styled flower, and in twenty- _
four hours the stigmas were discoloured, twisted, and
penetrated by numerous pollen-tubes; and this, again,
is what might have been expected, as the union was
a legitimate one.
Secondly. Pollen from a long-styled flower was placed
on all five stigmas of a long-styled flower on a separate
plant: after nineteen hours the stigmas were dissected,
and only a single pollen-grain had emitted a tube,
* «Bot. Zeitung,’ Jan. 1, 1864, p. 2.
88 HETEROSTYLED DIMORPHIC PLANTS. Cuar. IZ,
and this was a very short one. To make sure that the
pollen was good, I took in this case, and in most of
the other cases, pollen either from the same anther or
from the same flower, and proved it to be good by
placing it on the stigma of a short-styled plant, and
found numerous pollen-tubes emitted.
Thirdly. Repeated last experiment, and placed own-
form pollen on all five stigmas of a long-styled flower;
after nineteen hours and a half, not one single grain
had emitted its tube.
Fourthly. Repeated the experiment, with the same
result after twenty-four hours.
Fifthly. Repeated last experiment, and, after leaving
pollen on for nineteen hours, put on an additional
quantity of own-form pollen on all five stigmas, After
an interval of three days, the stigmas were examined,
and, instead of being discoloured and twisted, they
were straight and fresh-coloured. Only one grain had
emitted a quite short tube, which was drawn out of
the stigmatic tissue without being ruptured.
The following experiments are more striking :—
Siethly. I placed own-form pollen on three of the
stigmas of a long-styled flower, and pollen from a
short-styled flower on the other two stigmas. After
twenty-two hours these two stigmas were discoloured,
slightly twisted, and penetrated by the tubes of nu-
merous pollen-grains: the other three stigmas, covered
with their own-form pollen, were fresh, and all the
pollen-grains were loose; but I did not dissect the
whole stigma.
Seventhly. Experiment repeated in the same manner,
with the same result.
Fighthly. Experiment repeated, but the stigmas were
carefully examined after an interval of only five hours
and a half. The two stigmas with pollen from a
Cuap. III. LINUM GRANDIFLORUM. 89
short-styled flower were penetrated by innumerable
tubes, which were as yet short, and the stigmas them-
selves were not at all discoloured. The three stigmas
covered with their own-form pollen were not pene-
trated by a single pollen-tube.
Ninthly, Put pollen of a short-styled flower on a
single long-styled stigma, and own-form pollen on the
other four stigmas; after twenty-four hours the one
stigma was somewhat discoloured and twisted, and
penetrated by many long tubes: the other four stigmas
were quite straight and fresh ; but on dissecting them
I found that three pollen-grains had protruded very
short tubes into the tissue.
Tenthly. Repeated the experiment, with the same
result after twenty-four hours, excepting that only two
own-form grains had penetrated the stigmatic tissue
with their tubes to a very short depth. The one
stigma, which was deeply penetrated by a multitude
of tubes from the short-styled pollen, presented a
conspicuous difference in being much curled, half-
shrivelled, and discoloured, in comparison with the
other four straight and bright pink stigmas.
I could add other experiments; but those now
given amply suffice to show that the pollen-grains of
a short-styled flower placed on the stigma of a long-
styled flower emit a multitude of tubes after an in-
terval of from five to six hours, and penetrate the
tissue ultimately to a great depth; and that after
twenty-four hours the stigmas thus penetrated change
colour, become twisted, and appear half-withered. On
the other hand, pollen-grains from a long-styled flower
placed on its own stigmas, do not emit their tubes
after an interval of a day, or even three days; or at
most only three or four grains out of a multitude emit
sheir tubes, and these apparently never penetrate the
90 HETEROSTYLED DIMORPHIC PLANTS. Cuap. IIL
stigmatic tissue deeply, and the stigmas themselves
do not soon become discoloured and twisted.
This seems to me a remarkable physiological fact.
The pollen-grains of the two forms are undistinguish-
able under the microscope; the stigmas differ only in
length, degree of divergence, and in the size, shade of
colour, and approximation of their papille, these latter
differences being variable and apparently due merely
to the degree of elongation of the stigma. Yet we
plainly see that the two kinds of pollen and the two
stigmas are widely dissimilar in their mutual reaction
—the stigmas of each form being almost powerless on
their own pollen, but causing, through some myste-
rious influence, apparently by simple contact (for I
could detect no viscid secretion), the pollen-grains of
the opposite form to protrude their tubes. It may be
said that the two pollens and the two stigmas mutually
recognise each other by some means. Taking fertility
as the criterion of distinctness, it is no exaggeration to
say that the pollen of the long-styled Linum grandi-
florum (and conversely that of the other form) has been
brought to a degree of differentiation, with respect to
its action on the stigma of the same form, correspond-
ing with that existing between the pollen and stigma
of species belonging to distinct genera. ©
Linum perenne.—This species is conspicuously hetero-
styled, as has been noticed by several authors, The
pistil in the long-styled form is nearly twice as long as
that of the short-styled. In the latter the stigmas are
smaller and, diverging to a greater degree, pass out
low down between the filaments. I could detect no
difference in the two forms in the size of the stigmatic
papille. In the long-styled form alone the stigmatic
surfaces of the mature pistils twist round, so as to face
the circumference of the flower; but to this point 1
Cuap. IIT. LINUM PERENNE. 91
shall presently return. Differently from what occurs in
Li, grandiflorum, the long-styled flowers have stamens
hardly more than half the length of those in the short-
styled. The size of the pollen-grains is rather variable ;
after some doubt, I have come to the conclusion that
there is no uniform difference between the grains in
the two forms. The long stamens in the short-styled
form project to some height above the eorolla, and
their filaments are coloured blue apparently from ex-
posure to the light. The anthers of the longer stamens
correspond in height with the lower part of the stigmas
of the long-styled flowers; and the anthers of the
shorter stamens of the latter correspond in the same
manner in height with the stigmas of the short-styled
flowers. |
I raised from seed twenty-six plants, of which twelve
proved to be long-styled and fourteen short-styled.
They flowered well, but were not large plants. As I
did not expect them to flower so soon, I did not trans-
plant them, and they unfortunately grew with their
branches closely interlocked. All the plants were
covered under the same net, excepting one of each
form. Of the flowers on the long-styled plants, twelve
were illegitimately fertilised with their own-form pol-
len, taken in every case from a separate plant; and not
one set a seed-capsule: twelve other flowers were legi-
timately fertilised with pollen from short-styled flowers ;
and they set nine capsules, each including on an
average 7 good seeds, ten being the maximum number
ever produced. Of the flowers on the short-styled
plants, twelve were illegitimately fertilised with own-
form pollen, and they yielded one capsule, including
only 8 good seeds; twelve other flowers were legiti-
mately fertilised with pollen from long-styled flowers,
aud these produced nine capsules, but one was bad ;
92 HETEROSTYLED DIMORPHIC PLANTS. Czar. III.
the eight good capsules contained on an average 8
good seeds each. Judging from the number of seeds
per capsule, the fertility of the two legitimate to that
of the two illegitimate unions is as 100 to 20.
The numerous flowers on the eleven long-styled
plants under the net, which were not fertilised, produced
only three capsules, including 8, 4, and 1 good seeds.
Whether these three capsules were the product of acci-
dental legitimate fertilisation, owing to the branches
of the plants of the two forms interlocking, I will not
pretend to decide. The single long-styled plant which
was left uncovered, and grew close by the uncovered
short-styled plant, produced five good pods; but it
was a poor and small plant.
The flowers borne on the thirteen short-styled plants
under the net, which were not fertilised, produced
twelve capsules, containing on an average 5:6 seeds,
As some of these capsules were very fine, and as five
were borne on one twig, I suspect that some minute
insect had accidentally got under the net and had
brought pollen from the other form to the flowers
which produced this little group of capsules. The one
uncovered short-styled plant which grew close to the
uncovered long-styled plant yielded twelve capsules.
From these facts we have some reason to believe, as
in the case of L. grandiflorwm, that the short-styled
plants are in a slight degree more fertile with their
own pollen than are the long-styled plants. Anyhow
we have the clearest evidence, that the stigmas of each
form require for full fertility that pollen from the sta-
mens of corresponding height belonging to the opposite
form should be brought to them.
Hildebrand, in the paper lately referred to, confirms
my results. He placed a short-styled plant in his
house, and fertilised about 20 flowers with their own
Cuar. IIL, LINUM PERENNE. 93
pollen, and about 30 with pollen from another plant
belonging to the same form, and these 50 flowers did
not set a single capsule. On the other hand he ferti-
lised about 30 flowers with pollen from the long-styled
form, and these, with the exception of two, yielded
capsules, containing good seeds.
It is a singular fact, in contrast with what occurred
in the case ot L. grandiflorum, that the pollen-grains of
both forms of L. perenne, when placed on their own-
form stigmas, emitted their tubes, though this action
did not lead to the production of seeds. After an
interval of eighteen hours, the tubes penetrated the
stigmatic tissue, but to what depth I did not ascertain.
In this case the impotence of the pollen-grains on their
own stigmas must have been due either to the tubes
not reaching the ovules, or to their not acting pro-
perly after reaching them.
The plants both of L. perenne and grandiflorum grew,
as already stated, with their branches interlocked, and
with scores of flowers of the two forms close together ;
they were covered by a rather coarse net, through which
the wind, when high, passed ; and such minute insects
as Thrips could not, of course, be excluded ; yet we have
seen that the utmost possible amount of accidental fer-
tilisation on seventeen long-styled plants in the one
case, and on eleven long-styled plants in the other,
resulted in the production, in each case, of three
poor capsules; so that when the proper insects are
excluded, the wind does hardly anything in the way of
carrying pollen from plant to plant. I allude to this
fact because botanists in speaking of the fertilisation
of various flowers, often refer to the wind or to insects
as if the alternative were indifferent. This view, ac-
cording to my experience, is entirely erroneous. When
the wind is the agent in carrying pollen, either from
94 HETEROSTYLED DIMORPHIC PLANTS. Cuap. III,
one sex to the other, or from hermaphrodite to herma-
phrodite, we can recognise structure as manifestly ad-
apted to its action as to that of insects when these are
the carriers. We see adaptation to the wind in the in-
coherence of the pollen,—in the inordinate quantity
produced (as in the Conifere, Spinage, &c.),—in the
dangling anthers well fitted to shake out the pollen —
in the absence or small size of the perianth,—in the
protrusion of the stigmas at the period of fertilisation,
—in the flowers being produced before they are hidden
by the leaves,—and in the stigmas being downy or
plumose (as in the Graminez, Docks, &c.), so as to
secure the chance-blown grains. In plants which are
fertilised by the wind, the flowers do not secrete nectar,
their pollen is too incoherent to be easily collected by
insects, they have not bright-coloured corollas to serve
as guides, and they are not, as far as I have seen,
visited by insects: When insects are the agents of fer-
tilisation (and this is incomparably the more frequent
case with hermaphrodite plants), the wind plays no
part, but we -see an endless number of adaptations to
ensure the safe transport of the pollen by the living
workers. These adaptations are most easily recognised
in irregular flowers; but they are present in regular
flowers, of which those of Linum offer a good instance,
as I will now endeavour to show.
I have already alluded to the rotation of each sepa-
rate stigma in the long-styled form of Linwin perenne.
In both forms of the other heterostyled species and in
the homostyled species of Linum which I have seen,
the stigmatic surfaces face the centre of the flower,
with the furrowed backs of the stigmas, to which the
styles are attached, facing outwards. This is the case
with the stigmas of the long-styled flowers of L.
perenne whilst in bud. But by the time the flowers
Cuap. III. LINUM PERENNE. 95
have expanded, the five stigmas twist round so as to
face the circumference, owing to the torsion of that
part of the style which lies beneath the stigma. I
should state that the five stigmas do not always turn
round completely, two or three sometimes facing
only obliquely outwards. My observations were made
during October; and it is not improbable that earlier
in the season the torsion would have been more com-
plete ; for after two or three cold and wet days the
movement was very imperfectly performed. The
flowers should be examined shortly after their ex-
pansion, as their duration is brief; as soon as they
begin to wither, the styles become spirally twisted
all together, the original position of the parts being
thus lost.
He who will compare the structure of the whole
flower in both forms of L. perenne and grandiflorum,
and, as I may add, of L. flavum, will not doubt about
the meaning of this torsion of the styles in the one
form alone of L. perenne, as well as the meaning of
the divergence of the stigmas in the short-styled
form of all three species. It is absolutely necessary
as we know, that insects should carry pollen from
the flowers of the one form reciprocally to those of
the other. Insects are attracted by five drops of
nectar, secreted exteriorly at the base of the stamens,
so that to reach these drops they must insert their
proboscides outside the ring of broad filaments, be-
tween them and the petals. In the short-styled form
of the above three species, the stigmas face the axis of
the flower; and had the styles retained their original
upright and central position, not only would the stig-
mas have presented their backs to the insects which
sucked the flowers, but their front and fertile surfaces
would have been separated from the entering insects
96 HETEROSTYLED DIMORPHIC PLANTS. Cuar. III.
by the ring of broad filaments, and would never have
received any pollen. As it is, the styles diverge
and pass out between the filaments. After this move-
ment the short stigmas lie within the tube of the
corolla; and their papillous surfaces being now turned
upwards are necessarily brushed by every entering
insect, and thus receive the required pollen.
In the long-styled form of ZL. grandiflorum, the
almost parallel or slightly diverging anthers and
stigmas project a little above the tube of the somewhat
concave flower; and they stand directly over the open
space leading to the drops of nectar. Consequently
when insects visit the flowers of either form (for the
stamens in this species occupy the same position in
both forms), they will get their foreheads or proboscides
well dusted with the coherent pollen. As soon as they
visit the flowers of the long-styled form they will
necessarily leave pollen on the proper surface of the
elongated stigmas; and when they visit the short-
styled flowers, they will leave pollen on the upturned
stigmatic surfaces. Thus the stigmas of both forms
will receive indifferently the pollen of both forms;
but we know that the pollen alone of the opposite form
causes fertilisation.
In the case of L. perenne, affairs are arranged more
perfectly ; for the stamens in the two forms stand at
different heights, so that pollen from the anthers of
the longer stamens will adhere to one part of an
insect’s body, and will afterwards be brushed off by
the rough stigmas of the longer pistils ; whilst pollen
from the anthers of the shorter stamens will adhere to
a different part of the insect’s body, and will afterwards
be brushed off by the stigmas of the shorter pistils;
and this is what is required for the legitimate fertilisa-
tion of both forms. The corolla of L. perenne is more
Onar. IIL, LINUM PERENNE. 97
expanded than that of L. grandiflorum, and the stigmas
of the long-styled form do not diverge greatly from
one another; nor do the stamens of either form.
Hence insects, especially rather small ones, will not
insert their proboscides between the stigmas of the
long-styled form, nor between the anthers of either
form (ig. 5), but will strike against them, at nearly
right angles, with the backs of their head or thorax.
Now, in the long-styled flowers, if each stigma did
Fig. 5.
\
)
Long-styled form of L. PERENNE. var. Austriacwm in its early condition
before the stigmas have rotated. The petals and calyx have been
removed on the near side.*
not rotate on its axis, insects in visiting them would
strike their heads against the backs of the stigmas ; as
it is, they strike against that surface which is covered
* I neglected to get drawings from published engravings. His
made from fresh flowersof thetwo well-known skill ensures accuracy
forms. But Mr Fitch has made in the proportional size of the
the above sketch of a long-styled parts.
flower from dried specimens and
98 HETEROSTYLED DIMORPHIC PLANTS. Casp. IIL
with papille, with their heads already charged with
pollen from the stamens of corresponding height
borne by the flowers of the other form, and legitimate
fertilisation is thus ensured.
Thus we can understand the meaning of the torsion
of the styles in the long-styled flowers alone, as well
as their divergence in the short-styled flowers.
One other point is worth notice. In botanical works
many flowers are said to be fertilised in the bud. This
statement generally rests, as far as I can discover, on
the anthers opening in the bud; no evidence being
adduced. that the stigma is at this period mature, or
that it is not subsequently acted on by pollen brought
from other flowers. In the case of Cephalanthera
grandifiora I have shown* that precocious and partial
self-fertilisation, with subsequent full fertilisation, is
the regular course of events. The belief that the
flowers of many plants are fertilised in the bud, that
is, are perpetually self-fertilised, is a most effectual bar
to understanding their real structure. I am, however,
far from wishing to assert that some flowers, during
certain seasons, are not fertilised in the bud; for I
have reason to believe that this is the case. A good
observer, resting his belief on the usual kind of
evidence, states that in Linwm Austriacum (which is
heterostyled, and is considered by Planchon as a variety
of L. perenne) the anthers open the evening before
the expansion of the flowers, and that the stigmas are
then almost always fertilised. Now we know positively
that, so far from Linum perenne being fertilised by its
own pollen in the bud, its own pollen is as powerless
on the stigma as so much inorganic dust.
Linum flavum.—tThe pistil of the long-styled form
* ‘Fertilisation of Orchids,’ t ‘Etudes sur la Géogr. Bot,
p. 108.—2nd edit. 1877, p. 84. H. Lecogq, 1856, tom. v. p. 325.
Cuap. III. LINUM FLAVUM. 99
of this species is nearly twice as long as that of
the short-styled; the stigmas are longer and the
papillz coarser. In the short-styled form the stigmas
diverge and pass out between the filaments, as in the
previous species. The stamens in the two forms differ
in length; and, what is singular, the anthers of the
longer stamens are not so long as those of the other
form ; so that in the short-styled form both the stigmas
and the anthers are shorter than in the long-styled
form. The pollen-grains of the two forms do not differ
in size. As this species is propagated by cuttings,
generally all the plants in the same garden belong to
the same form. I have inquired, but have never heard
of its seeding in this country. Certainly my own plants
never produced a single seed as long as I possessed
only one of the two forms. After considerable search
I procured both forms, but from want of time only a few
experiments were made. ‘T'wo plants of the two forms
were planted some way apart in my garden, and were
not covered by nets. Three flowers on the long-styled
plant were legitimately fertilised with pollen from the
short-styled plant, and one of them set a fine capsule.
No other capsules were produced by this plant. Three
flowers on the short-styled plant were legitimately
fertilised with pollen from the long-styled, and all
three produced capsules, containing respectively no
less than 8, 9, and 10 seeds. Three other flowers on
this plant, which had not been artificially fertilised,
produced capsules containing 5, 1, and 5 seeds; and .
it is quite possible that pollen may have been
brought to them by insects from the long-styled plant
growing in the same garden. Nevertheless, as they
did not yield half the number of seeds compared
with the other flowers on the same plant which had
been artificially and legitimately fertilised, and as the
100 HETEROSTYLED DIMORPHIC PLANTS. Cuar. IIL
short-styled plants of the two previous species appa-
rently evince some slight capacity for fertilisation with
their own-form pollen, these three capsules may have
been the product of self-fertilisation.
Besides the three species now described, the yellow-
flowered L. corymbiferwm is certainly heterostyled,
as is, according to Planchon,* L. salsoloides. This
botanist is the only one who seems to have inferred
that heterostylism might have some important func-
tional bearing. Dr. Alefeld, who has made a special
study of the genus, says} that about half of the sixty-
five species known to him are heterostyled. This is
the case with L. trigynum, which differs so much from
the other species that it has been formed by him into
a distinct genus.{ According to the same author,
none of the species which inhabit America and the
Cape of Good Hope are heterostyled.
I have examined only three homostyled species,
namely, L. usitatissimum, angustifolium, and catharti-
eum. I raised 111 plants of a variety of the first-named
species, and these, when protected under a net, all
produced plenty of seed. The flowers, according to
H. Miiller,§ are frequented by bees and moths. With
respect to L. catharticum, the same author shows that
the flowers are so constructed that they can freely
fertilise themselves; but if visited by insects they
might be cross-fertilised. He has, however, only once
seen the flowers thus visited during the day; but it
* Hooker's ‘ London Journal of
Botany,’ 1848, vol. vii. p. 174.
+ ‘Bot. Zeitung,’ Sep. 18th,
1863, p. 281.
t It is not improbabie that the
allied genus, Hugonia, is hetero-
styled, for one species is said
by Planchon (Hooker’s ‘ London
Journal of Botany,’ 1848, vol.
vii. p. 525) to be provided with
“staminibus exsertis;? another
with **stylis staminibus longiori
bus,” and another has “stamina
5, majora, stylos longe superantia.”
§ ‘Die Befruchtuig der Blu-
men,’ &., p. 168,
Cuar. III. PULMONARIA OFFICINALIS. 101
may be suspected that they are frequented during
the night by small moths for the sake of the five
minute drops of nectar secreted. Lastly, DL. Lewisii
is said by Planchon to bear on the same plant flowers
with stamens and pistils of the same height, and
others with the pistils either longer or shorter than
the stamens. This case formerly appeared to me an
extraordinary one; but I am now inclined to believe
that it is one merely of great variability.*
PuLmonaria (BoraGInEs).
Pulmonaria officinalis—Hildebrand has published f
a full account of this heterostyled plant. The pistil
of the long-styled form is twice as long as that of the
short-styled ; and the stamens differ in a corresponding,
though converse, manner. There is no marked dif-
ference in the shape or state of surface of the stigma
in the two forms. The pollen-grains of the short-
styled form are to those of the long-styled as 9 to 7,
or as 100 to 78, in length, and as 7 to 6 in breadth.
They do not differ in the appearance of their contents.
The corolla of the one form differs in shape from that
of the other in nearly the same manner as in Primula;
but besides this difference the flowers of the short-
styled are generally the larger of the two. Hilde-
brand collected on the Siebengebirge, ten wild long-
styled and ten short-styled plants. The former bore
289 flowers, of which 186 (ie. 64 per cent.) had set
fruit, yielding 1°88 seed per fruit. The ten short-
styled plants bore 373 flowers, of which 262 (ie.
* Planchon, in Hooker’s‘Lon- of Science,’ vol. xxxvi. Sept. 1863,
don Journal of.Botany,’ 1848, vol. _p. 284.
vii. p. 175. See on this subject t ‘ Bot. Zeitung,’ 1865, Jun. 13,
Asa Gray, in ‘American Journal pp. 18,
102 HETEROSTYLED DIMORPHIC PLANTS. Cuar. IIL
70 per cent.) had set fruit, yielding 1:86 seed per
fruit. So that the short-styled plants produced many
more flowers, and these set a rather larger proportion
of fruit, but the fruits themselves yielded a slightly
lower average number of seeds than did the long-
styled plants. The results of Hildebrand’s experiments
on the fertility of the two forms are given in the fol-
lowing table :—
Tasie 19.
Pulmonaria officinalis (from Hildebrand).
Number Average
Number
Nature of Union. Flowers | of Fruits pied
fertilised, | Produced. per Fruit,
Long-styled flowers, by pollen of short- 14 | |
styled. Legitimate-union . .
Long-styled flowers, 14 by own-pollen,
and 16 by pollen of other plant of same 30 0
form. Illegitimate union . . !
Short-styled flowers, by pollen of long- 7 : | 1°57
styled. Legitimate union . . I i
Short-styled flowers, 11 by own pollen
14 by pollen of other plant of same 25 0 0
form. Illegitimate union . .
In the summer of 1864, before I had heard of Hilde-
brand’s experiments, I noticed some long-styled plants
of this species (named for me by Dr. Hooker) growing
by themselves in a garden in Surrey; and to my
surprise about half the flowers had set fruit, several
of which contained 2, and one contained even 3 seeds.
These seeds were sown in my garden and eleven
seedlings thus raised, all of which proved long-styled,
in accordance with the usual rule in such cases. Two
years afterwards the plants were left uncovered, no
Cuar. III. PULMONARIA OFFICINALIS. 103
other plant of the same genus growing in my garden,
and the flowers were visited by many bees. They set
an abundance of seeds: for instance, I gathered from a
single plant rather less than half of the seeds which it
had produced, and they numbered 47. Therefore this
illegitimately fertilised plant must have produced about
100 seeds; that is, thrice as many as one of the wild
long-styled plants collected on the Siebengebirge by
Hildebrand, and which, no doubt, had been legitimately
fertilised. In the following year one of my plants
was covered by a net, and even under these un-
favourable conditions it produced spontaneously a
few seeds. It should be observed that as the flowers
stand either almost horizontally or hang considerably
downwards, pollen from the short stamens would be
likely to fall on the stigma. We thus see that the
English long-styled plants when illegitimately ferti-
lised were highly fertile, whilst the German plants
similarly treated by Hildebrand were completely
sterile. How to account for this wide discordance in
our results I know not. Hildebrand cultivated his
plants in pots and kept them for a time in the house,
whilst mine were grown out of doors; and he thinks
that this difference of treatment may have caused
the difference in our results. But this does not appear
to me nearly a sufficient cause, although his plants
were slightly less productive than the wild ones growing
on the Siebengebirge. My plants exhibited no ten-
dency to become equal-styled, so as to lose their proper
long-styled character, as not rarely happens under
cultivation with several heterostyled species of Pri-
mula; but it would appear that they had been greatly
affected in function, either by long-continued cultiva-
tion ur by some other cause. We shall see in a
future chapter that heterostyled plants illegitimately
8
104 HETEROSTYLED DIMOKPHIC PLANTS. Cuar. IIL
iertilised during several successive generations some-
times becume more self-fertile; and this may have
been the case with my stock of the present species
of Pulmonaria; but in this case we must assume
that the long-styled plants were at first sufficiently
fertile to yield some seed, instead of being absolutely
sclf-sterile like the German plants.
Pulmonaria angustifolia.mSeedlings of this plant,
raised from plants growing wild in the Isle of Wight,
were named for me by Dr. Hooker. It is so closely
allied to the last species, differing chiefly in the shape
and spotting of the leaves, that the two have been con-
sidered by several eminent botanists—for instance,
Bentham—as mere varieties. But,as we shall presently
see, good evidence can be assigned for ranking them
as distinct. Owing to the doubts on this head, I tried
whether the two would mutually fertilise one another.
Twelve short-styled flowers of P. angustifolia were
legitimately fertilised with pollen from long-styled
plants of P. officinalis (which, as we have just seen, are
moderately self-fertile), but they did not produce a
single fruit. Thirty-six long-styled flowers: of P.
angustifolia were also illegitimately fertilised during
two seasons with pollen from the long-styled P.
officinalis, but all these flowers dropped off unim-
pregnated. Had the plants been mere varieties of
the same species these illegitimate crosses would
probably have yielded some seeds, judging from my
success in illegitimately fertilising the long-styled
flowers of P. officinalis; and the twelve legitimate
crosses, instead of yielding no fruit, would almost
certainly have yielded a considerable number, namely,
about nine, judging from the results given in the fol-
lowing table (20). Therefore P. officénulis and angusti-
folia appear to be good and distinct species, in
a. ee ee ee eee Se
ae ee
Cuap., III. PULMONARIA ANGUSTIFOLIA. 105
conformity with other important functional differences
between them, immediately to be described.
The long-styled and short-styled flowers of P. angus-
tifolia differ from one another in structure in nearly
the same manner as those of P. officinalis. But in the
accompanying figure a slight bulging of the corolla
Fig. 6.
Long-styled form. Short-styled form,
PULMONARIA ANGUSTIFOLIA.
in the long-styled form, where the anthers are seated,
has been overlooked. My son William, who examined
a large number of wild plants in the Isle of Wight,
observed that the corolla, though variable in size, was
generally larger in the long-styled flowers than in the
short-styled; and certainly the largest corollas of all
were found on the long-styled plants, and the smallest
on the short-styled. Exactly the reverse occurs, ac-
cording to Hildebrand, with P. officinalis. Both the
pistils and stamens of P. angustifolia vary much in
length ; so that in the short-styled form the distance
between the stigma and the anthers varied from 119
to 65 divisions of the micrometer, and in the long-
styled from 115 to 112. From an average of seven
106 HETEROSTYLED DIMORPHIC PLANTS. Cuap. IIL
measurements of cach form the distance between these
organs in the long-styled is to the same distance in
the short-styled form as 100 to 69; so that the stigma
in the one form does not stand on a level with the
anthers in the other. The long-styled pistil is some-
times thrice as long as that of the short-styled ; but
from an average of ten measurements of both, its
length to that of the short-styled was as 100 to 56.
The stigma varies in being more or less, though
slightly, lobed. The anthers also vary much in
length in both forms, but in a greater degree in the
long-styled than in the short-styled form; many in
the former being from 80 to 63, and in the latter
from 80 to 70 divisions of the micrometer in length.
From an average of seven measurements, the short-
styled anthers were to those from the long-styled as
100 to 91 in length. Lastly, the pollen-grains from
the long-styled flowers varied between 13 and 11°5
divisions of the micrometer, and those from the short-
styled between 15 and 13. The average diameter of
25 grains from the latter, or short-styled form, was
to that of 20 grains from the long-styled as 100 to
91. We see, therefore, that the pollen-grains from
the smaller anthers of the shorter stamens in the long-
styled form are, as usual, of smaller size than those
in the other form. But what is remarkable, a larger
proportion of the grains were small, shrivelled, and
worthless. This could be seen by merely comparing
the contents of the anthers from several distinct plants
of each form. But in one instance my son found, by
counting, that out of 193 grains from a long-styled
flower, 53 were bad, or 27 per cent.; whilst out of
265 grains from a short-styled flower only 18 were
bad, or 7 per cent. From the condition of the pollen
in the long-styled form, and from the extreme varia-
Cuap. III. PULMONARIA ANGUSTIFOLIA. 107
bility of all the organs in both forms, we may perhaps
suspect that the plant is undergoing a change, and
tending to become dicecious.
My son collected in the Isle of Wight on two occa-
sions 202 plants, of which 125 were long-styled and
77 short-styled; so that the former were the more
numerous. On the other hand, out of 18 plants raised
by me from seed, only 4 were long-styled and 14
short-styled. The short-styled plants seemed to my
son to produce a greater number of flowers than the
long-styled; and he came to this conclusion before a
similar statement had been published by Hildebrand
with respect to P. officinalis, My son gathered ten
branches from ten different plants of both forms, and
found the number of flowers of the two forms to be as
L00 to 89, 190 being short-styled and 169 long-styled.
With P. officinalis the difference, according to Hilde-
brand, is even greater, namely, as 100 flowers for the
short-styled to 77 for the long-styled plants. The
following table shows the results of my experi-
ments :—
; TaBiE 20.
Pulmonaria angustifolia,
Number | Number | Average
Nature of the Union. n of on ole Tunic of
fertilised. | produced. | per Fruit.
Long-styled flowers, by pollen of short- 3
styled. Legitimate union . as 8 - sae
Long-styled flowers, by own-form tea 18 0 0
Illegitimate union .
Short-styled flowers, by-pollen of al 18 15 2°60
styled, Legitimate union . .
Short-styled flowers, by Seah ree "} 12 7 1°86
legitimate union .
108 HETEROSTYLED DIMORPHIC PLANTS. Czar. III.
We see in this table that the fertility of the two
legitimate unions to that of the two illegitimate
together is as 100 to 85, judged by the proportion of
flowers which produced fruit ; and as 100 to 32, judged
by the average number of seeds per fruit. But the
small number of fruit yielded by the 18 long-styled
flowers in the first line was probably accidental, and
if so, the difference in tne proportion of legitimately
and illegitimately fertilised flowers which yield fruit is
really greater than that represented by the ratio of
100 to 85. The 18 long-styled flowers illegitimately
fertilised yielded no seeds,—not even a vestige of one.
Two long-styled plants which were placed under a net
produced 188 flowers, besides those which were arti-
ficially fertilised, and none of these set any fruit; nor
did some plants of the same form which were pro-
tected during the next summer. Two other long-
styled plants were left uncovered (all the short-styled
plants having been previously covered up), and
humble-bees, which had their foreheads white with
pollen, incessantly visited the flowers, so that their
stigmas must have received an abundance of pollen,
yet these flowers did not produce a single fruit. We
may therefore conclude that the long-styled plants
are absolutely barren with their own-form pollen,
though brought from a distinct plant. In this re-
spect they differ greatly from the long-styled English
plants of P. officinalis which were found by me to
be moderately self-fertile; but they agree in their
behaviour with the German plants of P. officinalis
experimented on by Hildebrand.
Eighteen short-styled flowers legitimately fertilised
yielded, as may be seen in Table 20, 15 fruits, each
having on an average 2°6 seeds. Four of these fruits
contained the highest possible number of seeds, namely
Cuar. IIL PULMONARIA ANGUSTIFOLIA. 109
4, and four other fruits contained each 3 seeds. The
12 illegitimately fertilised short-styled flowers yielded
7 fruits, including on an average 1°86 seed; and one
of these fruits contained the maximum number of
4 seeds. This result is very surprising in contrast
with the absolute barrenness of the long-styled flowers
when illegitimately fertilised; and I was thus led to
attend carefully to the degree of self-fertility of the
short-styled plants. A plant belonging to this form and
covered by a net bore 28 flowers besides those which
had been artificially fertilised, and of all these only
two produced a fruit each including asingle seed. This
high degree of self-sterility no doubt depended merely
on the stigmas not receiving any pollen, or not a suffi-
cient quantity. For after carefully covering all the
long-styled plants in my garden, several short-styled
plants were left exposed to the visits of humble-bees,
and their stigmas will thus have received plenty of
short-styled pollen; and now about half the flowers,
thus illegitimately fertilised, set fruit. I judge of this
proportion partly. from estimation and partly from
having examined three large branches, which had borne
31 flowers, and these produced 16 fruits. Of the fruits
produced 233 were collected (many being left un-
gathered), and these included on an average 1°82
seed. No less than 16 out of the 233 fruits included
the highest possible number of seeds, namely 4, and
31 included 3 seeds. So we see how highly fertile
these short-styled plants were when illegitimately fer-
tilised with their own-form pollen by the aid of bees.
The great difference in the fertility of the long and
short-styled flowers, when both are illegitimately fer-
tilised, is a unique case, as far as I have observed with
heterostyled plants. The long-styled flowers when thus
fertilised are utterly barren, whilst about half of the
110 HETEROSTYLED DIMORPHIC PLANTS. Cuapr. III
short-styled ones produce capsules, and these include a
little above two-thirds of the number of seeds yielded
by them when legitimately fertilised. The sterility of
the illegitimately fertilised long-styled flowers is prob-
ably increased by the deteriorated condition of their
pollen; névertheless this pollen was highly efficient
when applied to the stigmas of the short-styled flowers.
With several species of Primula the short-styled
flowers are much more sterile than the long-styled,
when both are illegitimately fertilised; and it is a
tempting view, as formerly remarked, that this greater
sterility of the short-styled flowers is a special adapta-
tion to check self-fertilisation, as their stigmas are
eminently liable to receive their own pollen. This view
is even still more tempting in the case of the long-
styled form of Linum grandiflorum. On the other
hand, with Pulmonaria angustifolia, it is evident, from
the corolla projecting obliquely upwards, that pollen
is much more likely to fall on, or to be carried by
insects down to the stigma of the short-styled than of
the long-styled flowers; yet the short-styled instead
of being more sterile, as a protection against self-ferti-
lisation, are far more fertile than the long-styled,
when both are illegitimately fertilised.
Pulmonaria azurea, according to Hildebrand, is not
heterostyled.*
From an examination of dried flowers of Amsinckia spectabilis,
sent me by Prof. Asa Gray, I formerly thought that this plant,
a member of the Boragines, was heterostyled. The pistil
varies to an extraordinary degree in length, being in some
specimens twice as long as in others, and the point of insertion
of the stamens likewise varies. But on raising many plants
from seed, I soon became convinced that the whole case was
one of mere variability. The first-formed flowers are apt te
* ‘Die Geschlechter-Vertheilung bei den Pflanzen,’ 1867, p. 37.
Cuar. IIT. POLYGONUM FAGOPYRUM. 111
have stamens somewhat arrested in development, with very
little pollen in their anthers; and in such flowers the stigma
projects above the anthers, whilst generally it stands below and
sometimes on a level with them. I could detect no difference
in the size of the pollen-grain or in the structure of the stigma
in the plants which differed most in the above respects; and all
of them, when protected from the access of insects, yielded
plenty of seeds. Again, from statements made by Vaucher, and
from a hasty inspection, I thought at first that the allied
Anchusa arvensis and Echiwm vulga:e were heterostyled, but soon
saw my error. From information given me, I examined dried
flowers of another member of the Boraginex, Arnebia hispidis-
sima, collected from several sites, and though the corolla, to-
gether with the included organs, differed much in length, there
was no sign of heterostylism.
PoLyGonumM FAGOPYRUM (POLYGONACEZ).
Hildebrand has shown that this plant, the common
Buck-wheat, is heterostyled.* In the long-styled form
(Fig. 7), the three stigmas project considerably above
the eight short stamens, and stand on a level with the
anthers of the eight long stamens in the short-styled
form; and so it is conversely with the stigmas and
stamens of this latter form. I could perceive no differ-
ence in the structure of the stigmas in the two forms.
The pollen-grains of the short-styled form are to those
of the long-styled as 100 to 82 indiameter. This plant
is therefore without doubt heterostyled.
I experimented only in an imperfect manner on
the relative fertility of the two forms. Short-styled
flowers were dragged several times over two heads
of flowers on long-styled plants, protected under a net,
which were thus legitimately, though not fully, ferti-
ised. They produced 22 seeds, or 11 per flower-head.
Three flower-heads on long-styled plants received
* ‘Die Geschlcchtcr-Vertheilung,’ &c., 1867, p. 34.
112 HETEROSTYLED DIMORPHIC PLANTS. Cuap, IIL
pollen in the same manner from other long-styled
plants, and were thus illegitimately fertilised. They
produced 14 seeds, or only 4°66 per flower-head.
Two flower-heads on short-styled plants received
pollen in like manner from long-styled flowers, and
were thus legitimately fertilised. They produced 8
seeds, or 4 per flower-head.
Fig. 7.
Upper figure, the long-styled form ; lower figure, the short-styled,
Some of the anthers have dehisced, others have not,
PoLYGoNuM FaGopyrum. (From H. Miller.)
Four heads on short-styled plants similarly received
pollen from other short-styled plants, and were thus
illegitimately fertilised. They produced 9 seeds, or
2°25 per flower-head.
The results from fertilising the flower-heads in the
above imperfect manner cannot be fully trusted ; but
I may state that the four legitimately fertilised flower-
Cuap, III. POLYGONUM FAGOPYRUM. 113
heads yielded on an average 7°50 seeds per head ;
whereas the seven illegitimately fertilised heads
yielded less than half the number, or on an average
only 3°28 seeds. The legitimately crossed seeds from
the long-styled flowers were finer than those from the
illegitimately fertilised flowers on the same plants, in
the ratio of 100 to 82, as shown by the weights of an
equal namber.
About a dozen plants, including both forms, were
protected under nets, and early in the season they pro-
duced spontaneously hardly any seeds, though at this
period the artificially fertilised flowers produced an
abundance; but it is a remarkable fact that later in
the season, during September, both forms became
highly self-fertile. They did not, however, produce
so many seeds as some neighbouring uncovered plants
‘which were visited by insects. Therefore the flowers
of neither form when left to fertilise themselves late
in the season without the aid of insects, are nearly so
sterile as most other heterostyled plants. <A large
number of insects, namely 41 kinds as observed by H.
Miller,* visit the flowers for the sake of the eight
drops of nectar. He infers from the structure of the
flowers that insects would be apt to fertilise them both
illegitimately as well as legitimately; but he is mis-
taken in supposing that the long-styled flowers cannot
spontaneously fertilise themselves.
Differently to what occurs in the other genera
hitherto noticed, Polygonum, though a very large
genus, contains, as far as is at present known, only a
single heterostyled species, namely the present one.
H. Muller in his interesting description of several
* ¢ Die Befruchtuug,’ &c., p. 175, and ‘ Nature,’ Jan. 1, 1874, p. 166,
114 HETEROSTYLED DIMORPHIC PLANTS. Cuap. III.
other species shows that P. bistorta is so strongly pro-
terandrous (the anthers generally falling off before the
stigmas are mature) that the flowers must be cross-
fertilised by the many insects which visit them. Other
species bear much less conspicuous flowers which se-
crete little or no nectar, and consequently are rarely
visited by insects; these are adapted for self-fertilisa-
tion, though still capable of cross-fertilisation. Ac-
cording to Delpino, the Polygonacee are generally
fertilised by the wind, instead of by insects as in the
present genus.
LevucosmiA BURNETTIANA (THYMELIZ).
As Prof. Asa Gray has expressed his belief * that this species
and L. acuminatu, as well as some species in the allied genus
Drymispermum, are dimorphic: or heterostyled, I procured
from Kew, through the kindness of Dr. Hooker, two dried
flowers of the former species, an inhabitant of the Friendly
Islands in the Pacific. The pistil of the long-styled form is to
that of the short-styled as 100 to 86 in length; the stigma
projects just above the throat of the corolla, and is surrounded
by five anthers, the tips of which reach up almost to its base;
and lower down, within the tubular corolla, five other and
rather smaller anthers are seated. In the short-styled form,
the stigma stands some way down the tube of the corolla, nearly
on a level with the lower anthers of the other form: it differs
remarkably from the stigma of the long-styled form, in being
more papillose, and in being longer in the ratio of 100 to 60.
The anthers of the upper stamens in the short-styled form are
stipported on free filaments, and project above the throat of the
corolla, whilst the anthers of the lower stamens are seated in
the throat on a level with the upper stamens of the other form.
The diameters of a considerable number of grains from both sets
of anthers in both forms were measured, but they did not differ
in any trustworthy degree. The mean diameter of twenty-two
* ‘American Journal of Sci- ‘Journal of Botany,’ vol. iii. 1865,
ence, 1865, p.101, and Seemann’s __ p. 305.
Cuap, IIT. MENYANTHES TRIFOLIATA. 113
grains from the short-styled flower was to that of twenty-four
grains from the long-styled, as 100 to 99. The anthers of
the upper stamens in the short-styled form appeared to be
poorly developed, and contained a considerable number of
shrivelled grains which were omitted in striking the above
average. Notwithstanding the fact of the pollen-grains from
the two forms not differing in diameter in any appreciable
degree, there can hardly be a doubt from the great difference in
the two forms in the length of the pistil, and especially of the
stigma, together with its more papillose condition in the short-
styled form, that the present species is truly heterostyled. This
case resembles that of Linum yrandiflorum, in which the sole
difference between the two forms consists in the length of the
pistils and stigmas. From the great length of the tubular
corolla of Leucosmia, it is clear that the flowers are cross-
fertilised by large Lepidoptera or by honey-sucking birds, and
the position of the stamens in two whorls one beneath the
other, which is a character that I have not seen in any other
heterostyled dimorphic plant, probably serves to smear the
inserted organ thoroughly with pollen.
MENYANTHES TRIFOLIATA (GENTIANEZ).
This plant inhabits marshes: my son William gathered 247
flowers from so many distinct plants, and of these 110 were
long-styled, and 137 short-styled. The pistil of the long-styled
form is in length to that of the short-styled in the ratio of about
8 to2. The stigma of the former, as my son observed, is deci-
dedly larger than that of the short-styled; but in both forms it
varies much in size. The stamens of the short-styled are almost
double the length of those of the long-styled; so that their
anthers stand rather above the level of the stigma of the long-
styled form. The anthers also vary much in size, but seem
often to be of larger size in the short-styled flowers. My son
made with the camera many drawings of the pollen-grains,
and those from the short-styled flowers were in diameter in
nearly the ratio of 100 to 84 to those from the long-styled
flowers. I know nothing about the capacity for fertilisation in
the two forms; but short-styled plants, living by themselves in
the gardens at Kew, have produced an abundance of capsules,
yet the seeds have never germinated; and this looks as if the
short-styled form was sterile with its own pollen.
116 HETEROSTYLED DIMORPHIC PLANTS. Cnap. III.
LimnanTHEemoum Inpicum (GENTIANEZ).
This plant is mentioned by Mr. Thwaites in his Enumeration
of the Plants of Ceylon as presenting two forms; and he was so
kind as to send me specimens preserved in spirits. The pistil
of the long-styled form is nearly thrice as long (i.e. as 14 to 5)
as that of the short-styled, and is very much thinner in the
ratio of about 8 to 5. The foliaceous stigma is more expanded,
and twice as large as that of the short-styled form. In the
latter the stamens are about twice as long as those of the long-
styled, and their anthers are larger in the ratio of 100 to 70.
The pollen-grains, after having been long kept in spirits, were
of the same shape and size in both forms. The ovules, accord-
ing to Mr. Thwaites, are equally numerous (viz. from 70 to 80)
in the two forms.
Vittarsia [sp. ?] (GENTIANEZ).
Fritz Miller sent me from South Brazil dried flowers of this
aquatic plant, which is closely allied to Limnanthemum. In the
long-styled form the stigma stands some way above the anthers,
and the whole pistil, together with the ovary, is in length to
that of the short-styled form as about 3 to 2. In the latter
form the anthers stand above the stigma, and the style is very
short and thick; but the pistil varies a good deal in length,
the stigma being either on a level with the tips of the sepals
or considerably beneath them. The foliaceous stigma in
the long-styled form is larger, with the expansions running
farther down the style, than in the other form. One of the most
remarkable differences between the two forms is that the anthers
of the longer stamens in the short-styled flowers are conspicu-
ously longer than those of the shorter stamens in the long-styled
flowers. In the former the sub-triangular pollen-grains are
larger; the ratio between their breadth (measured from one
angle to the middle of the opposite side) and that of the grains
from the long-styled flowers being about 100 to 75 Fritz
Miller also informs me that the pollen of the short-styled
flowers has a bluish tint, whilst that of the long-styled is yellow.
When we treat of Lythrum sulicaria we shall find a strongly
marked contrast in the colour of the pollen in two of the forms.
The three genera, Menyanthes, Limnanthemum, and Villarsia,
now described, constitute a well-marked sub-tribe of the Gen-
tianez. All the species, as far as at present known, are hetero-
atyled, and all inhabit aquatic or sub-aquatic stations.
Cxap. ITI. ‘ CORDIA. 117
ForsyTHIA SUSPENSA (OLEACEZ).
Professor Asa Gray states that the plants of this species grow-
ing in the Botanic Gardens at Cambridge, U.S., are short-styled,
but that Siebold and Zuccarini describe the long-styled form,
and give figures of two forms; so that there can be little doubt,
as he remarks, about the plant being dimorphic.* I therefore
applied to Dr. Hooker, who sent me a dried flower from Japan,
another from China, and another from the Botanic Gardens at
Kew. The first proved to be long-styled, and the other two
short-styled. In the long-styled form, the pistil is in length
to that of the short-styled as 100 to 38, the lobes of the stigma
being a little longer (as 10 to 9), but narrower and less diver-
gent. This last character, however, may be only a temporary
one. There seems to be no difference in the papillose condition
of the two stigmas. In the short-styled form, the stamens are
in length to those of the long-styled as 100 to 66, but the anthers
are shorter in the ratio of 87 to 100; and this is unusual, for
when there is any difference in size between the anthers of the
two forms, those from the longer stamens of the short-styled are
generally the longest. The pollen-grains from the short-styled
flowers are certainly larger, but only in a slight degree, than
those from the long-styled, namely, as 100 to 94 in diameter.
The short-styled form, which grows in the Gardens at Kew, has
never there produced fruit.
Forsythia viridissima appears likewise to be heterostyled ; for
Professor Asa Gray says that although the long-styled form
alone grows in the gardens at Cambridge, U.S., the published
figures of this species belong to the short-styled form. ~
Corpia ‘sp.?] (CoRDIACES).
Fritz Miller sent me dried specimens of this shrub, which he
believes to be heterostyled; and I have not much doubt that
this is the case, though the usual characteristic differences are
not well pronounced in the two forms. Linum grandiflorum
shows us that a plant may be heterostyled in function in the
highest degree, and yet the two forms may have stamens of
equal length, and pollen-grains of equal size. In the present
species of Cordia, the stamens of both forms are of nearly equal
* ‘The American Naturalist,’ July 1873, p. £22.
118 HETEROSTYLED DIMORPHIC PLANTS. Cuar. U1.
length, those of the short-styled being rather the longest; and
the anthers of both are seated in the mouth of the corolla. Nor
could I detect any difference in the size of the pollen-grains,
when dry or after being soaked in water. The stigmas of the
long-styled form stand clear above the anthers, and the wholo
pistil is longer than that of the short-styled, in about the ratio
of 8 to 2.
The stigmas of the short-styled form are seated beneath the
anthers, and they are considerably shorter than those of the
long-styled form. This latter difference is the most important
one of any between the two forms.
Gin1a (IpoMopsis) PULCHELLA VEL AGGREGATA (POLEMONI-
ACE).
Professor Asa Gray remarks with respect to this plant: “ the
tendency to dimorphism, of which there are traces, or perhaps
rather incipient manifestations in various portions of the genus,
is most marked in G. aggregata.”* He sent me some dried
flowers, and I procured others from Kew. They differ greatly
in size, some being nearly twice as long as others (viz. as 30 to
17), so that it was not possible to compare, except by calculation,
the absolute length of the organs from different plants. More-
over, the relative position of the stigmas and anthers is variable:
in some long-styled flowers the stigmas and anthers were ex-
serted only just beyond the throat of the corolla; whilst in
others they were exserted as much as +4 of an inch. I suspect
also that the pistil goes on growing for some time after the
anthers have dehisced. Nevertheless it is possible to class the
flowers under two forms. In some of the long-styled, the length
of pistil to that of the short-styled was as 100 to 82; but this
result was gained by reducing the size of the corollas to the
same scale. In another pair of flowers the difference in length
between the pistils of the two forms was certainly greater, but
they were not actually measured. In the short-styled flowers
whether large or small, the stigma is seated low down within
the tube of the corolla. The papilla on the long-styled stigma
are longer than those on the short-styled, in the ratio of 100 to
40. The filaments in some of the short-styled flowers were, to
those of the long-styled, as 100 to 25 in length, the free, or
* ‘Proc. American Acad. of Arts and Sciences,’ June 14, 1870, p. 276
Suap. III. PHLOX SUBULATA. 119
unattached portion being alone measured; but this ratio can-
not be trusted, owing to the great variability of the stamens.
The mean diameter of eleven pollen-grains from long-styled
flowers, and of twelve from the short-styled, was exactly the
same. It follows from these several statements, that the dif-
ference in length and state of surface of the stigmas in tho
flowers is the sole reliable evidence that this species is hetero-
styled; for it would be rash to trust to the difference in the
length of the pistils, seeing how variable they are. I should
have left the case altogether doubtful, had it not been for the
observations on the following species; and these leave little
doubt on my mind that the present plant is truly heterostyled.
Professor Gray informs me that in another species, (. coronopt-
folia, belonging to the same section of the genus, he can see no
sign of dimorphism.
Gitta (LEPTOSIPHON) MICRANTHA.
A few flowers sent me from Kew had been somewhat injured,
so that I cannot say anything positively with respect to the
position and relative length of the organs in the two forms.
But their stigmas differed almost exactly in the same manner as
in the last species; the papille on the long-styled stigma being
longer than those on the short-styled, in the ratio of 100 to 42.
My son measured nine pollen-grains from the long-styled, and
the same number from the short-styled form; and the mean
diameter of the former was to that of the latter as 100 to 81.
Considering this difference, as well as that between the stigmas
of the two forms, there can be no doubt that this species is
heterostyled. So probably is Gilia nudicaulis, which likewise
belongs to the Leptosiphon section of the genus, for I hear from
Professor Asa Gray that in some individuals the style is very
long, with the stigma more or less exserted, whilst in others it
is deeply included within the tube; the anthers being always
seated in the throat of the corolla.
PHLOX SUBULATA (POLEMONIACEZ).
Professor Asa Gray informs me that the greater number of
the species in this genus have a long pistil, with the stigma
more or less exserted; whilst several other species, especially the
annuals, have a short pistil seated low down within the tube of
the corolla. In all the species the anthers are arranged one
9
120 WETEROSTYLED DIMORPHIC PLANTS. Cuapr. HI
below the other, the uppermost just protruding from the throat
of the corolla. In Phlox swhulats alone he has “ seen both long
and short styles; and here the short-styled plant has (irrespec-
tive of this character) been described as a distinct species (P.
nivalis, P. Hentzii), and is apt to have a pair of ovules in each
cell, while the long-styled P. subulata rarely shows more than
one.”* Some dried flowers of both forms were sent me by him,
and I received others from Kew, but I have failed to make
out whether the species is heterostyled. In two flowers of
nearly equal size, the pistil of the long-styled form was twice as
long as that of the short-styled; but in other cases the differ-
ence was not nearly so great. The stigma of the long-styled
pistil stands nearly in the throat of the corolla; whilst in the
short-styled it is placed low down—sometimes very low down
in the tube, for it varies greatly in position. The stigma is
more papillose, and of greater length (in one instance in the
ratio of 100 to 67), in the short-styled flowers than in the
long-styled. My son measured twenty pollen-grains from a
short-styled flower, and nine from a long-styled, and the
former were in diameter to the latter as 100 to 98; and this
difference accords with the belief that the plant is hetero-
styled. But the grains from the short-styled varied much in |
diameter. He afterwards measured ten grains from a distinct
long-styled flower, and ten from another plant of the same form,
and these grains differed in diameter in the ratio of 100 to 90.
The mean diameter of these two lots of twenty grains was to
that of twelve grains from another short-styled flower as 100 to
75: here, then, the grains from the short-styled form were con-
siderably smaller than those from the long-styled, which is the
reverse of what occurred in the former instance, and of what is
the general rule with heterostyled plants. The whole case is
perplexing in the highest degree, and will not be understood
until experiments are tried on living plants. The greater length,
and more papillose condition of the stigma in the short-styledl
than in the long-styled flowers, looks as if the plant was hetero-
styled; for we know that with some species—for instance, Leu-
cosmia and certain Rubiacee—the stigma is longer and more
papillose in the short-styled form, though the reverse of this
holds good in Gilia,a member of the same family with Phlox.
The similar position of the anthers in the two forms is some-
* «Proc. American Acad. of Arts and Sciences,’ June 14, 1870, p. 248
Cuar. III. ERYTHROXYLUM. 121
what opposed to the present species being heterostyled ; as is
the great difference in the length of the pistil in several shurt-
styled flowers. But the extraordinary variability in diameter of
the pollen-grains, and the fact that in one set of flowers the
grains from the long-styled flowers were larger than those from
the short-styled, is strongly opposed to the belief that Phlow
subulata is heterostyled. Possibly this species was once hetero-
styled, but is now becoming sub-dicecious; the short-styled
plants having been rendered more feminine in nature. This
would account for their ovaries usually containing more ovules,
and for the variable condition of their pollen-grains. Whether
the long-styled plants are now changing their nature, as would
appear to be the case from the variability of their pollen-grains,
and are becoming more masculine, I will not pretend to con-
jecture; they might remain as hermapbrodites, for the co-
existence of hermaphrodite and female plants of the same
species is by no means a rare event.
ERYTHROXYLUM [sp. ?] (ERYTHROXYLIDZ).
Fritz Miiller sent me from South Brazil dried flowers of this
tree, together with the accompanying drawings, which show the
two forms, magnified about five times, with the petals removed
Fig. 8.
Long-styled form. Short-styled form.
From a sketch by Fritz Miiller, magnified five times.
EryTHRoxy.oy [sp. ?].
122. WETEROSTYLED DIMORPHIC PLANTS. Cuap. IL
In the long-styled form the stigmas project above the anthers,
and the styles are nearly twice as long as those of the short-
styled form, in which the stigmas stand beneath the anthers.
The stigmas in many, but not in all the short-styled flowers aro
larger than those in the long-styled. The anthers of the short-
styled flowers stand on a level with the stigmas of the other
form; but the stamens are longer by only one-fourth or one-fifth
of their own length than those of the long-styled. Consequently
the anthers of the latter do not stand on a level with, but rather
above the stigmas of the other form. Differently from what
occurs in the following closely allied genus, Sethia, the stamens
are of nearly equal length in the flowers of the same form. The
pollen-grains of the short-styled flowers, measured in their dry
state, are a little larger than those from the long-styled flowers
in about the ratio of 100 to 93.*
SETHIA ACUMINATA (ERYTHROXYLIDZ).
Mr. Thwaites pointed out several years agot that this plant
exists under two forms, which he designated as forma stylosa et
stuminex; and the flowers sent to me by him are clearly hetero-
styled. In the long-styled form the pistil is nearly twice as
long, and the stamens half as long as the corresponding organs
in the short-styled form. The stigmas of the long-styled seem
rather smailer than those of the short-styled. All the stamens
in the short-styled flowers are of nearly equal length, whereas
in long-styled they differ in length, being alternately a little
longer and shorter; and this difference in the stamens of the
two forms is probably related, as we shall hereafter see in
the case of the short-styled flowers of Lythrum salicaria, to the
manner in which insects can best transport pollen from the
long-styled flowers to the stigmas of the short-styled. The
pollen-grains from the short-styled flowers, though variable in
size, are to those of the long-styled, as far as I could make out,
as 100 to 83 in their longer diameter. Sethia obdtusifolia is
heterostyled like S. ucuminata.
* F, Miiller remarks in his let-
ter to me that the flowers, of which
he carefully examined many spe-
cimens, are curiously variable
in the number of their parts:
5 sepals and petals, 10 stamens
and 3 pistils are the prevailing
numbers ; but the sepals and pctala
often vury from 5 to 7; the sta-
mens from 10 to 14, and the pistils
frum 3 to 4.
t+ ‘Enumeratio Plantarum Zey-
lanig,’ 1864, p. 54.
Cuar. III. ZEGIPHILA ELATA. 123
CRATOXYLON FORMOSUM (HYPERICINEZ).
Mr. Thiselton Dyer remarks that this tree, an inhabitant of
Malacca and Borneo, appears to be heterostyled.* He sent me
dried flowers, and the difference between the two forms is con-
spicuous. In the long-styled form the pistils are in length to
those of the short-styled as 100 to 40, with their globular
stigmas about twice as thick. These stand just above the numer-
ous anthers and a little beneath the tips of the petals. In the
short-styled form the anthers project high above the pistils, the
stigmas of which diverge between the three bundles of stamens,
and stand only a little above the tips of the sepals. The
stamens in this form are to those of the long-styled as 100 to 86
in length; and therefore they do not differ so much in length
as do the pistils. Ten pollen-grains from each form were
measured, and those from the short-styled were to those from
the long-styled as 100 to 86 in diameter. This plant, therefore,
is in all respects a well-characteriscd heterostyled species.
ZEGIPHILA ELATA (VERBENACEZ).
Mr. Bentham was so kind as to send me dried flowers of this
species and of 4. mollis, both inhabitants of South America.
The two forms differ conspicuously, as the deeply bifid stigma
of the one, and the anthers of the other project far above the
mouth of the corolla. In the long-styled form of the present
species, the style is twice and a half as long as that of the short-
styled. The divergent stigmas of the two forms do not differ
much in length, nor as far as I could perceive in their papille.
In the long-styled flowers the filaments adhere to the corolla
close up to the anthers, which are enclosed some way down
within the tube. In the short-styled flowers the filaments are
free above the point where the anthers are seated in the othe.
form, and they project from the corolla to an equal height with
that of the stigmas in the long-styled flowers. It is often
difficult to measure with accuracy pollen-grains, which have
long been dried and then soaked in water; but they here
manifestly differed greatly in size. Those from the short-styled
flowers were to those from the long-styled in diameter in
* ‘Journal of Botany,’ London, 1872, p. 26.
124 HETEROSTYLED DIMORPHIC PLANTS, Cuar. II
about the ratio of 100 to 62. The two forms of &. muilis
present a like difference in the length of their pistils and
stamens.
ZEGIPHILA OBDURATA,
Flowers of this bush were sent me from St. Catharina in
Brazil, by Fritz Miiller, and were named for me at Kew.. They
appeared at first sight grandly heterostyled, as the stigma of
the long-styled form projects far out of the corolla, whilst the
anthers are seated halfway down within the tube; whereas in the
short-styled form the anthers project from the corolla and the
stigma is enclosed in the tube at nearly the same level with the
anthers of the other form. The pistil of the long-styled is to
that of the short-styled as 100 to 60 in length, and the stigmas,
taken by themselves, as 100 to 55. Nevertheless, this plant
cannot be heterostyled. The anthers in the long-styled form
are brown, tough, and fleshy, and less than half the length
of those in the short-styled form, strictly as 44 to 100 ; and
what is much more important, they were in a rudimentary
condition in the two flowers examined by me, and did not
contain a single grain of pollen. In the short-styled form, the
divided stigma, which as we have seen is much shortened,
is thicker and more fleshy than the stigma of the long-
styled, and is covered with small irregular projections, formed
of rather large cells. It had the appearance of having suf-
fered from hypertrophy, and is probably incapable of fertili-
sation. If this be so the plant is dicecious, and judging from
the two species previously described, it probably was once
heterostyled, and has since been rendered dicecious by the
pistil in the one form, and the stamens in the other having
become functionless and reduced in size. It is, however,
possible that the flowers may be in the same state as those of
the common thyme and of several other Labiate, in which
females and hermaphrodites regularly co-exist. Fritz Miiller,
who thought that the present plant was heterostyled, as I
did at first, informs me that he found bushes in several places
growing quite isolated, and that these were completely sterile;
whilst two plants growing close together were covered with
fruit. This fact agrees better with the belief that the species is
dicecious than that it consists of hermaphrodites and females;
for if any one of the isolated plants had been an hermaphrodito,
it would probably have produced some fruit.
e
Cuar. III MITCHELLA REPENS. 125
RusBIAcEz.
This great natural family contains a much larger
number of heterostyled genera than any other one, as
yet known.
Mitchella repens—Prof. Asa Gray sent me several
living plants coilected when out of flower, and nearly
half of these proved long-styled, and the other half
short-styled. The white flowers, which are fragrant
and which secrete plenty of nectar, always grow in
pairs with their ovaries united, so that the two together
produce “a berry-like double drupe.’* In my first
series of experiments (1864) I did not suppose that
this curious arrangement of the flowers would have any
influence on their fertility ; and in several instances
only one of the two flowers in a pair was fertilised ;
and a large proportion or all of these failed to produce
berries. In the ensuing year both flowers of each
pair were invariably fertilised in the same manner;
and the latter experiments alone serve to show the
proportion of flowers which yield berries, when legiti-
mately and illegitimately fertilised; but for calcu-
lating the average number of seeds per berry I have
used those produced during both seasons.
In the long-styled flowers the stigma projects just
above the bearded throat of the corolla, and the
anthers are seated some way down the tube. In the
short-styled flowers these organs occupy reversed posi-
tions. In this latter form the fresh pollen-grains are
a little larger and more opaque than those of the long-
styled form. The results of my experiments are given
in the following table.
* A. Gray, ‘Manual of the Bot. of the N. Unitcd States,’ 1856,
p. 172,
126 WETEROSTYLED DIMORPHIC PLANTS. Czar. IIL
Tasue 21,
Mitchella repens,
Average
Number of | Number of | Number of
Pairs of Drupes pro- | good Seeds
Nature of Union. Flowers fer- | duced during | per Drupe in
tilised during} the second all the Drupea
the secund Season. during the
Season, tivo Seasons.
short-styled. Legitimate union
Long-styled flowers, by pollen ee 9
Long-styled flowers, by Tega
8 3 | 2-2
i
pollen. Illegitimate union ‘
sa Fs flowers, by pollen a 8 7 44,
ong-styled. Legitimate union
Short-styled flowers, by own-for' i 9 0 20
pollen. Illegitimate union .
The two legitimate unions to- oo 17 15 | 44
gether
The two swabs unions to- et 7 3 | 2-1
gether...
It follows from this table that 88 per cent. of the
paired flowers of both forms, when legitimately fer-
tilised, yielded double berries, nineteen of which con-
tained on an average 4:4 seeds, with a maximum in
one of 8 seeds. Of the illegitimately fertilised paired
flowers only 18 per cent. yielded berries, six of which
contained on an average only 2:1 seeds, with a maxi-
mum in one of 4 seeds. Thus the two legitimate
unions are more fertile than the two illegitimate,
according to the proportion of flowers which yielded
berries, in the ratio of 100 to 20; and according to
the average number of contained seeds as 100 to 47.
Three long-styled and three short-styled plants were
protected under separate nets, and they produced alto-
gether only 8 berries, containing on an average only
Cuar. III. BORRERIA. 127
1:5 seed. Some additional berries were produced
which contained no seeds. The plants thus treated were
therefore excessively sterile, and their slight degree of
fertility may be attributed in part to the action of the
many individuals of Thrips which haunted the flowers.
Mr. J. Scott informs me that a single plant (probably
a long-styled one), growing in the Botanic Gardens at
Edinburgh, which no doubt was freely visited by in-
sects, produced plenty of berries, but how many of
them contained seeds was not observed.
BoRRERIA, NOV. SP. NEAR VALERIANOIDES (RUBIACEZ).
Fritz Miller sent me seeds of this plant, which is
extremely abundant in St. Catharina, in South Brazil ;
and ten plants were raised, consisting of five long-
styled and five short-styled. The pistil of the long-
styled flowers projects just beyond the mouth of the
corolla, and is thrice as long as that of the short-
styled, and the divergent stigmas are likewise rather
larger. The anthers in the long-styled form stand
low down within the corolla, and are quite hidden.
In the short-styled flowers the anthers project just
above the mouth of the corolla, and the stigma stands
low down within the tube. Considering the great
difference in the length of the pistils in the two forms,
it is remarkable that the pollen-grains differ very little
in size, and Fritz Miller was struck with the same
fact. In a dry state the grains from the short-styled
flowers could just be perceived to be larger than those
from the long-styled, and when both were swollen by
immersion in water, the former were to the latter in
diameter in the ratio of 100 to 92. In the long-styled
flowers beaded hairs almost fill up the mouth of the
corolla and project above it; they therefore stand
above the anthers and beneath the stigma. In the
128 WETEROSTYLED DIMORPHIC PLANTS. Cuap. IIL.
short-styled flowers a similar brush of hairs is situated
low down within the tubular corolla, above the stigma
and beneath the anthers. The presence of these beaded
hairs in both forms, though occupying such different
positions, shows that they are probably of considerable
functional importance. They would serve to guard the
stigma of each form from its own pollen; but in
accordance with Prof. Kerner’s view* their chief use
probably is to prevent the copious nectar being stolen
by small crawling insects, which could not render any
service to the species by carrying pollen from one form
to the other.
The flowers are so small and so crowded together
that I was not willing to expend time in fertilising
them separately ; but I dragged repeatedly heads of
short-styled flowers over three long-styled flower-heads,
which were thus legitimately fertilised ; and they pro-
duced many dozen fruits, each containing two good
seeds. I fertilised in the same manner three heads
on the same long-styled plant with pollen from another
long-styled plant, so that these were fertilised illegiti-
mately, and they did not yield a single seed. Nor did
this plant, which was of course protected by a net,
bear spontaneously any seeds. Nevertheless another
long-styled plant, which was carefully protected, pro-
duced spontaneously a very few seeds; so that the
long-styled form is not always quite sterile with its
own pollen.
Faramea [sp.?] (RUBIACES).
Fritz Miller has fully described the two forms of this
remarkable plant, an inhabitant of South Brazil.f In
* ‘Die Schutzmittel der Blii- t ‘Bot. Zeitung,’ Sept. 10, 1869,
then gegen unberufene Gite, p. 606.
1876, p. 37,
Cuap. III. FARAMEA. 129
the long-styled form the pistil projects above the
corolla, and is almost exactly twice as long as that of
the short-styled, which is included within the tube.
The former is divided into two rather short and broad
stigmas, whilst the short-styled pistil is divided into
two long, thin, sometimes much curled stigmas. The
stamens of each form correspond in height or length
with the pistils of the other form. The anthers of
the short-styled form are a little larger than those
of the long-styled; and their pollen-grains are to
those of the other form as 100 to 67 in diameter.
But the pollen-grains of the two forms differ in a
much more remarkable manner, of which ‘no other
Fig. 9.
aoe
Short-styled form. Long-styled form.
Outlines of flowers from dried specimens, Pollen-grains, magnified 180
times, by Fritz Muller,
Faramea (sp. ?],
instance is known; those from the short-styled flowers
being covered with sharp points; the smaller ones
130 HETEROSTYLED DIMORPHIC PLANTS. Cuap. III
from the long-styled being quite smooth. Fritz Miller
remarks that this difference between the pollen-grains
of the two forms is evidently of service to the plant ;
for the grains from the projecting stamens of the short-
styled form, if smooth, would have been liable to be
blown away by the wind, and would thus have been
lost ; but the little points on their surfaces cause them
to cohere, and at the same time favour their adhesion
to the hairy bodies of insects, which merely brush
against the anthers of these stamens whilst visiting
the flowers. On the other hand, the smooth grains
of the long-styled flowers are safely included within
the tube of the corolla, so that they cannot be blown
away, but are almost sure to adhere to the proboscis of
an entering insect, which is necessarily pressed close
against the enclosed anthers.
It may be remembered that in the long-styled form
of Linum perenne each separate stigma rotates on its
own axis, when the flower is mature, so as to turn its
papillose surface outwards. There can be no doubt
that this movement, which is confined to the long-
styled form, is effected in order that the proper sur
face of the stigma should receive pollen brought by
insects from the other form. Now with Faramea, as
Fritz Miller shows, it is the stamens which rotate on
their axes in one of the two forms, namely, the short-
styled, in order that their pollen should be brushed off
by insects and transported to the stigmas of the other
form. In the long-styled flowers the anthers of the
short enclosed stamens do not rotate on their axes,
but dehisce on their inner sides, as is the common
tule with the Rubiacew ; and this is the best position
for the adherence of the pollen-grains to the proboscis
of an entering insect. Fritz Miller therefore infers
that as the plant became heterostyled, and as the
Cuap IIL, RUBIACEA, 131
stamens of the short-styled form increased in length,
they gradually acquired the highly beneficial power
of rotating on their own axes. But he has further
shown, by the careful examination of many flowers,
that this power has not as yet been perfected; and,
consequently, that a certain proportion of the pollen
is rendered useless, namely, that from the anthers
which do not rotate properly. It thus appears that
the development of the plant has not as yet been com-
pleted ; the stamens have indeed acquired their proper
length, but not their full and perfect power of rotation.*
The several points of difference in structure between
the two forms of Faramea are highly remarkable.
Until within a recent period, if any one had been
shown two plants which differed in a uniform manner
in the length of their stamens and pistils,—in the
form of their stigmas,—in the manner of dehiscence
and slightly in the size of their anthers,—and to an
extraordinary degree in the diameter and structure of
their pollen-grains, he would have declared it impos-
sible that the two could have belonged to one and the
same species.
SuTERIA (species unnamed in the herbarium at Kew)
(RUBIACEZ).
I owe to the kindness of Fritz Miiller dried flowers of this
plant from St. Catharina, in Brazil. In the long-styled form the
stigma stands in the mouth of the corolla, above the anthers,
* Fritz Miiller gives another
instance of the want of absolute
perfection in the flowers of another
meniber of the Rubiacex, namely,
Posoqueria fragrans, which is
adapted in a most wonderful man-
ner for cross-fertilisation by the
agency of moths. (See ‘ Bot.
Zcitung,’ 1866, No. 17.) In ac-
cordance with the nocturnal habits
of tiiese insects, most of the flowers
open only during the night; but
some open in the day, and the
pollen of such flowers is robbed, as
Fritz Miiller has often seen, by
humble-bees and other insects,
without auy benefit being thus
conferred on the plant.
132 HETEROSTYLED DIMORPHIC PLANTS. Cuar. IIL
which latter are enclosed within the tube, but only a short way
down. In the short-styled form the anthers are placed in the
mouth of the corolla above the stigma, which occupies the same
position as the anthers in the other form, being seated only a
short way down the tube. Therefore the pistil of the long-styled
form does not exceed in length that of the short-styled in
nearly so great a degree as in many other Rubiacesw. Never-
theless there is a considerable difference in the size of the pollen-
grains in the two forms; for, as Fritz Miller informs me, those
of the short-styled are to those of the long-styled as 100 to
75 in diameter.
HoustTonia C@RULEA (RUBIACEZ).
Prof. Asa Gray has been so kind as to send me an abstract of
some observations made by Dr. Rothrock on this plant. The
pistil is exserted in the one form and the stamens in the
other, as has long been observed. The stigmas of the long-
styled form are shorter, stouter, and far more hispid than in
the other form. The stigmatic hairs or papillae on the former
are ‘04 mm., and on the latter only ‘023 mm. in length. In the
short-styled form the anthers are larger, and the pollen-grains,
when distended with water, are to those from the long-styled
form as 100 to 72 in diameter.
Selected capsules from some long-styled plants growing in
the Botanic Gardens at Cambridge, U.S., near where plants
of the other form grew, contained on an average 13 seeds;
but these plants must have been subjected to unfavourable
conditions, for some long-styled plants in a state of nature
yielded an average of 21-5 seeds per capsule. Some short-styled
plants, which had been planted by themselves in the Botanic
Gardens, where it was not likely that they would have been
visited by insects that had previously visited long-styled plants,
produced capsules, eleven of which were wholly sterile, but one
contained 4, and another 8 seeds. So that the short-styled
form seems to be very sterile with its own pollen: Prof. Asa
Gray informs me that the other North American species of this
genus are likewise heterostyled.
OLDENLANDIA [sP.?] (RubIACEz).
Mr. J. Scott sent me from India dricd flowers of a hetero
styled species of this genus, which is closely allied to the last.
Cuar. ID. RUBIACEA. 133
The pistil in the long-styled flowers is longer by about a quarter
of its length, and the stamens shorter in about the same pro-
portion, than the corresponding organs in the short-stylerl
flowers. In the latter the anthers are longer, and the divergent
stigmas decidedly longer and apparently thinner than in tho
long-styled form. Owing to the state of the specimens, I could
not decide whether the stigmatic papillae were longer in the
one form than in the other. The pollen-grains, distended with
water, from the short-styled flowers were to those from the long-
styled as 100 to 78 in diameter, as deduced from the mean of
ten measurements of each kind.
Hupyoris [sp. ?] (Rupracez).
Fritz Miller sent me from St. Catharina, in Brazil, dried flowers
of a small delicate species, which grows on wet sand near tho
edges of fresh-water pools. In the long-styled form the stigma
projects above the corolla, and stands on a level with the pro-
jecting anthers of the short-styled form; but in the latter the
stigmas stand rather beneath the level of the anthers in the
other or long-styled form, these being enclosed within the tube
of the corolla. The pistil of the long-styled form is nearly thrice
as long as that of the short-styled, or, speaking strictly, as
100 to 89; and the papilla on the stigma of the former are
broader, in the ratio of 4 to 3, but whether longer than those of
the short-styled, I could not decide. In the short-styled form,
the anthers are rather larger, and the pollen-grains are to those
from the long-styled flowers, as 100 to 88 in diameter. Fritz
Miiller sent me a second, small-sized species, which is likewise
heterostyled.
CoccocyrsEeLum (sp. ?] (RUBIACEZ).
Fritz Miiller also sent me dried flowers of this plant from
St. Catharina, in Brazil. The exserted stigma of the long-styled
form stands a little above the level of the exserted anthers of the
short-styled form; and the enclosed stigma of the latter also
stands a little above the level of the enclosed anthers in the long-
styled form. The pistil of the long-styled is about twice as long
as that of the short-styled, with its two stigmas considerably
longer, more divergent, and more curled. Fritz Miiller informs
134. HETEROSTYLED DIMORPHIC PLANTS. Czar. III,
me that he could detect no difference in the size of the pollen-
grains in the two forms. Nevertheless, there can be no doubt
that this plant is heterostyled.
Lrrostoma [sr. ?] (RuBIAGEz).
Dried flowers of this plant, which grows in small wet ditches
in St. Catharina, in Brazil, were likewise sent me by Fritz
Miiller. In the long-styled form the exserted stigma stands
rather above the level of the exserted anthers of the other form;
whilst in the short-styled form it stands on a level with the
anthers of the other form. So that the want of strict corre-
spondence in height between the stigmas and anthers in the two
forms is reversed, compared with what occurs in Hedyotis. The
long-styled pistil is to that of the short-styled as 100 to 36 in
length; and its divergent stigmas are longer by fully one-third
of their own length than those of the short-styled form. In the
latter the anthers are a little larger, and the pollen-grains are
as 100 to 80 in diameter, compared with those from the long-
styled form.
CINCHONA MICRANTHA (RUBIACEZ).
Dried specimens of both forms of this plant were sent me from
Kew.* In the long-styled form the apex of the stigma stands
just beneath the bases of the hairy lobes of the corolla; whilst
the summits of the anthers are seated about halfway down
the tube. The pistil is in length as 100 to 88 to that of the
short-styled form. In the latter the anthers occupy the same
position as the stigma of the other form, and they are con-
siderably longer than those of the long-styled form. As the
summit of the stigma in the short-styled form stands beneath
the bases of the anthers, which are seated halfway down the
corolla, the style has been extremely shortened in this form:
its length to that of the long-styled being, in the specimens
examined, only as 5'3 to 100! The stigma, also, in the short-
styled form is very much shorter than that in the long-styled,
in the ratio of 57 to 100. The pollen-grains from the short-
* My attention was called to 3, given by Mr. Markham in his
this plant by a drawing copied ‘ Travels in Peru,’ p. 539,
from Howurd’s ‘ Quinologia,’ Tab.
Cuar. IIL. RUBIACEA. 135
styled flowers, after having been soaked in water, were rather
larger —in about the ratio of 100 to 91—than those from the long-
styled flowers, and they were more triangular, with the angles
more prominent. As all the grains from the short-styled flowers
were thus characterised, and as they had been left in water for
three days, I am convinced that this difference in shape in the
two sets of grains cannot be accounted for by uncqual distension
with water.
Besides the several Rubiaceous genera already mentioned,
Fritz Miiller informs me that two or three species of Psychotria
and ftudgea eriunthu, natives of St. Catharina, in Brazil, are
heterostyled, as is Manettia bicolor. I may add that I formerly
fertilised with their own pollen several flowers on a plant of
this latter species in my hothouse, but they did not set a single
fruit. From Wight and Arnott’s description, there seems to be
little doubt that Knoxia in India is heterostyled; and Asa Gray
is convinced that this is the case with Diodia and Spermacoce
in the United States. Lastly, from Mr. W. W. Bailey’s descrip-
tion,* it appears that the Mexican Bouwvardia leiantha is hetero-
styled.
Altogether we now know of 17 heterostyled genera
in the great family of the Rubiacee; though more
information is necessary with respect to some of them,
more especially those mentioned in the last para-
graph, before we can feel absolutely safe. In the
‘Genera Plantarum,’ by Bentham and Hooker, the
Rubiacez are divided into 25 tribes, containing 337
genera; and it deserves notice that the genera now
known to be heterostyled are not grouped in one or
two of these tribes, but are distributed in no less than
eight of them. From this fact we may infer that
most of the genera have acquired their heterostyled
structure independently of one another; that is, they
have not inherited this structure from sonie one or
even two or three progenitors in common. It furthe:
* ‘Bull. of the Torrey Bot. Club,’ 1876, p. 106.
qo
136 HETEROSTYLED DIMORPHIC PLANTS. Cuar. III.
deserves notice that in the homostyled genera, as I
am informed by Professor Asa Gray, the stamens are
either exserted or are included within the tube of the
corolla, in a nearly constant manner; so that this
character, which is not even of specific value in the
heterostyled species, is often of generic value in other
members of the family.
Cuap. IV. LYTHRUM. SALICARIA. 137
CHAPTER IV.
HETEROSTYLED TRIMORPHIO PLANTS.
Lythrum salicaria—Description of the three forms—Their power and
complex manner of fertilising one another—Highteen different
unions possible—Mid-styled form eminently feminine in nature—
Lytbrum Grefferi likewise trimorphic—L. thymifvlia dimorphic—
L. hyssopifolia homostyled—Nesea, verticillata trimorphic—Lager-
stroemia, nature doubtful—Oxalis, trimorphic species of—O. Valdi-
viana—O. Regnelli, the illegitimate unions quite barren—O. spe-
ciosa—O. sensitiva—Homostyled species of Oxalis—Pontederia,
the one monocotyledonous genus known to include heterostyled
species,
ly the previous chapters various heterostyled dimor-
phic plants have been described, and now we come to
heterostyled trimorphic plants, or those which present
three forms. These have been observed in three
families, and consist of species of Lythrum and of the
allied genus Nesea, of Oxalis and Pontederia. In
their manner of fertilisation these plants offer a more
remarkable case than can be found in any other plant
or animal.
Lythrum salicaria.—The pistil in each form differs
from that in either of the other forms, and in each
there are two sets of stamens different in appearance
and function. But one set of stamens in each form
corresponds with a set in one of the other two forms.
Altogether this one species includes three females or
female organs and three sets of male organs, all as
distinct from one another as if they belonged to dif-
ferent species; and if smaller functional differences
{88 HELEROSTYLED TRIMORPHIC PLANTS. Cuaap. IV.
are considered, there are fiye distinct sets of males.
Two of the three hermaphrodites must coexist, and
pollen must be carried by insects reciprocally from one
to the other, in order that either of the two should be
fully fertile; but unless all three forms coexist, two
sets of stamens will be wasted, and the organisation of
the species, as a whole, will be incomplete. On the
other hand, when all three hermaphrodites coexist, and
pollen is carried from one to the other, the scheme
is perfect ; there is no waste of pollen and no false co-
adaptation. In short, nature has ordained a most com-
plex marriage-arrangement, namely a triple union
between three hermaphrodites,—each hermaphrodite
being in its female organ quite distinct from the other
two hermaphrodites and partially distinct in its male
organs, and each furnished with two sets of males.
The three forms may be conveniently called, from
the unequal lengths of their pistils, the long-styled, mid-
styled, and short-styled. The stamens also aré of unequal
lengths, and these may be called the longest, mid-length,
and shortest. Two sets of stamens of different length are
found in each form. The existence of the three forms
was first observed by Vaucher,* and subsequently more
carefully by Wirtgen; but these botanists, not being
guided by any theory or even suspicion of their func-
tional differences, did not perceive some of the most
curious points of difference in their structure. I will
first briefly describe the three forms by the aid of the
accompanying diagram, which shows the flowers, six
times magnified, in their natural position, with their
petals and calyx on the near side removed.
* ‘Hist. Phys. des Plantes und dessen Formen,” ‘ Verhand.
VEurope,’ tom. ii. 1841, p. 371. des naturhist. Vereins fiir preuss.
Wirtgen,“ Ueber Lythrum salicaria Rhein).’ 5. Jahrgang, 1848, 8. 7.
Cnar. IV. LYTHRUM SALICARIA. 139
Fig. 10.
Short-
sigled.
Diagram of the flowers of the three forms of Lythrum salicaria, in their natural
position, with the petals and calyx removed on the near side: enlarged six times.
The dotted lines with the arrows show the directions in which pollen must be
carried tu each stigma to ensure full fertility.
140 HETEROSTYLED TRIMORPHIC PLANTS. Cuap. IV.
Long-styled form.—This form can be at once recog-
nised by the length of the pistil, which is (including
the ovarium) fully one-third longer than that of the
mid-styled, and more than thrice as long as that of the
short-styled form. It is so disproportionately long, that
it projects in the bud through the folded petals. It
«stands out considerably beyond the mid-length sta-
mens; its terminal portion depends a little, but the
stigma itself is slightly upturned. The globular stigma
is considerably larger than that of the other two forms,
with the papille on its surface generally longer. ‘The
six mid-length stamens project about two-thirds the
length of the pistil, and correspond in length with the
pistil of the mid-styled form. Such correspondence
in this and the two following forms is generally very
close ; the difference, where there is any, being usually
in a slight excess of length in the stamens. The six
shortest stamens lie concealed within the calyx; their
ends are turned up, and they are graduated in length,
so as to form a double row. The anthers of these sta-
mens are smaller than those of the mid-length ones.
The pollen is of the same yellow colour in both sets.
H. Miller* measured the pollen-grain in all three
forms, and his measurements are evidently more trust-
worthy than those which I formerly made, so I will
give them. The numbers refer to divisions of the
micrometer equalling 34, mm. The grains, distended
with water, from the mid-length stamens are 7-74,
and those from the shortest stamens 6-64 in diameter,
or as 100 to 86. The capsules of this form contain
on an average 93 seeds: how this average was ob-
tained will presently be explained. As these seeds,
when cleaned, seemed larger than those from the mid-
* * Die Befruchtung der Blumen,’ 1873, p. 193
Cuar. IV. LYTHRUM SALICARIA. 141
styled or short-styled forms, 100 of them were placed
in a good balance, and by the double method of weigh-
ing were found to equal 121 seeds of the mid-styled or
142 of the short-styled ; so that five long-styled seeds
very nearly equal six mid-styled or seven short-styled
seeds.
Mid-styled form.—The pistil occupies the position
represented in the diagram, with its extremity consi-
derably upturned, but to a variable degree; the
stigma is seated: between the anthers of the longest
and the shortest stamens. The six longest stamens
correspond in length with the pistil of the long-styled
form; their filaments are coloured bright pink; the
anthers are dark-coloured, but from containing bright-
green pollen and from their early dehiscence they appear
emerald-green. Hence in general appearance these
stamens are remarkably dissimilar from the mid-length
stamens of the long-styled form. The six shortest sta-
mens are enclosed within the calyx, and resemble in
all respects the shortest stamens of the long-styled
form; both these sets correspond in length with the
short pistil of the short-styled form. The green pol-
jen-grains of the longest stamens are 9-10 in dia-
meter, whilst the yellow grains from the shortest
stamens are only 6; or as 100 to 63. But the pollen-
grains from different plants appeared to me, in this
case and others, to be in some degree variable in size.
The capsules contain on an average 130 seeds; but
perhaps, as we shall see, this is rather too high an
average. The seeds themselves, as before remarked,
are smaller than those of the long-styled form,
Short-styled form.—The pistil is here very short, not
one-third of the length of that of the long-styled form,
It is enclosed within the calyx, which, differently from
that in the other two forms, does not enclose any an-
142 HETEROSTYLED TRIMORPHIC PLANTS. Cuar. LV.
thers. The end of the pistil is generally bent upwards
at right angles. The six longest stamens, with their
vink filaments and green pollen, resemble the corre-
sponding stamens of the mid-styled form. But accord-
ing to H. Miller, their pollen-grains are a little larger,
viz. 94-103, instead of 9-10 in diameter. The six
mid-length stamens, with their uncoloured filaments
and yellow pollen, resemble in the size of their pollen-
grains and in all other respects the corresponding
stamens of the long-styled form. The difference in
diameter between the grains from the two sets of
anthers in the short-styled form is as 100 to 73.
The capsules contain fewer seeds on an average than
those of either of the preceding forms, namely 83-5;
and the seeds are considerably smaller. In this latter
respect, but not in number, there is a gradation
parallel to that in the length of the pistil, the long-
styled having the largest seeds, the mid-styled the
next in size, and the short-styled the smallest.
We thus see that this plant exists under three
female forms, which differ in the length and curva-
ture of the style, in the size and state of the stigma,
and in the number and size of the seed. There are
altogether thirty-six males or stamens, and these can
be divided into three sets of a dozen each, differing
from one another in length, curvature, and colour of
the filaments—in the size of the anthers, and especially
in the colour and diameter of the pollen-grains. Fach
form bears half-a-dozen of one kind of stamens and
half-a-dozen of another kind, but not all three kinds.
The three kinds of stamens correspond in length with
the three pistils: the correspondence is always between
half of the stamens in two of the forms with the pistil
of the third form. The following table of the diameters
of the pollen-grains, after immersion in water, from
Cuar. IV. LYTHRUM SALICARIA. 1438
both sets of stamens in all three forms is copied from
H. Miller; they are arranged in the order of their
size :—
Pollen-grains from longest stamens of short-styled form 9} to 104
33 mid-styled , 9 ,,10
5 59 ” mid- -length stamens oflong-styled ,, 7 ,, 74
9 short-styled ,, 7 4, 74
Be os shortest stamens of long-styled , 6 ,, 64
” ” ” ” mid-styled ” 6 y 6
We here see that the largest pollen-grains come from
the longest stamens, and the least from the shortest ;
the extreme difference in diameter between them
being as 100 to 60.
The average number of seeds in the three forms was
ascertained .by counting them in eight fine selected
capsules taken from plants growing wild, and the
result was, as we have seen, for the long-styled (neg-
lecting decimals) 93, mid-styled 130, and short-styled
83. I should not have trusted in these ratios had I
not possessed a number of plants in my garden which,
owing to their youth, did not yield the full comple-
ment of seed, but were of the same age and grew
under the same conditions, and were freely visited by
bees. I took six fine capsules from each, and found
the average to be for the long-styled 80, for the mid-
styled 97, and for the short-styled 61. Lastly, legiti-
mate unions effected by me between the three forms
gave, as may be seen in the following tables, for the
long-styled an average of 90 seeds, for the mid-styled
117, and for the short-styled 71. So that we have
good concurrent evidence of a difference in the average
production of seed by the three forms To show that
the unions effected by me often produced their full
effect and may be trusted, I may state that one mid-
styled capsule yielded 151 good seeds, which is the
same number as in the finest wild capsule which I
.
144 HETEROSTYLED TRIMORPHIC PLANTS. Cuap. IV.
examined. Some artificially fertilised short- and long-
styled capsules produced a greater number of seeds than
was ever observed by me in wild plants of the same
forms, but then I did not examine many of the latter.
This plant, I may add, offers a remarkable instance, how
profoundly ignorant we are of the life-conditions of a
species. Naturally it grows “in wet ditches, watery
places, and especially on the banks of streams,” and
though it produces so many minute seeds, it never
spreads on the adjoining land; yet, when planted in my
garden, on clayey soil lying over chalk, and which is so
dry that a rush cannot be found, it thrives luxuriantly,
grows to above 6 feet in height, produces self-sown
seedlings, and (which is a severer test) is as fertile as
in a state of nature. Nevertheless it would be almost
a miracle to find this plant growing spontaneously on
such land as that in my garden.
According to Vaucher and Wirtgen, the three forms
coexist in all parts of Europe. Some friends gathered
for me in North Wales a number of twigs from
separate plants growing ntar one another, and clas-
sified them. My son did the same in Hampshire, and
here is the result :—
TABLE 22.
— | Long-styled. | Mid-styled. | Short-styled. Total.
North Wales. . 95 97 72 264
Hampshire . . , | 53 38 38 129
Total . . . 148 | _ 135 | 110 393
If twice or thrice the number had been collected,
the three forms would probably have been found
nearly equal; I infer this from considering the above
figures, and from my son telling me that if he had
o
Cuar. IV. LYTHRUM SALICARIA. 145
collected in another spot, he felt sure that the mid-
styled plants would have been in excess. I several
-times sowed small parcels of seed, and raised all three
forms; but I neglected to record the parent-form,
excepting in one instance, in which I raised from
short-styled seed twelve plants, of which only one
turned out long-styled, four mid-styled, and seven
short-styled.
Two plants of each form were protected from the
access of insects during two successive years, and in the
autumn they yielded very few capsules and presented
a remarkable contrast with the adjoining uncovered
plants, which were densely covered with capsules. In
1863 a protected long-styled plant produced only five
poor capsules ; two mid-styled plants produced together
the same number; and two short-styled plants only a
single one. These capsules contained very few seeds ;
yet the plants were fully productive when artificially
fertilised under the net. In a state of nature the
flowers are incessantly visited for their nectar by hive-
and other bees, various Diptera and Lepidoptera.* The
nectar is secreted all round the base of the ovarium;
but a passage is formed along the upper and inner
side of the flower by the lateral deflection (not repre-
sented in the diagram) of the basal portions of the
filaments; so that insects invariably alight on the pro-
jecting stamens and pistil, and insert their proboscides
along the upper and inner margin of the corolla. We
can now see why the ends of the stamens with their
anthers, and the ends of the pistils with their stigmas,
* H. Miiller givesa list of the one bee, the Cilissa melanura,
speci:s, ‘Die Befruchtung der almost confines its visits to this
Blumea,’ p. 196. It appears that plant.
146 HETEROSTYLED TRIMORPHIC PLANTS. Cuar. IV
are a little upturned, so that they may be brushed by
the lower hairy surfaces of the insects’ bodies. The
shortest stamens which lie enclosed within the calyx of
the long- and mid-styled forms can be touched only by
the proboscis and narrow chin of a bee; hence they
have their ends more upturned, and they are graduated
in length, so as to fall into a narrow file, sure to be
raked by the thin intruding proboscis. The anthers of
the longer stamens stand laterally farther apart and are
more nearly on the same level, for they have to brush
against the whole breadth of the insect’s body. In
very many other flowers the pistil, or the stamens, or
both, are rectangularly bent to one side of the flower.
This bending may be permanent, as with Lythrum
and many others, or may be effected, as in Déctam-
nus fraxinella and others, by a temporary movement,
which occurs in the case of the stamens when the
anthers dehisce, and in the case of the pistil when
the stigma is mature; but these two movements do
not always take place simultaneously in the same
flower. Now I have found no exception to the rule,
that when the stamens and pistil are bent, they bend
to that side of the flower which secretes nectar, even
though there be a rudimentary nectary of large size
on the opposite side, as in some species of Corydalis.
When ‘nectar is secreted on all sides, they bend to
that side where the structure of the flower allows the
easiest access to it, as in Lythrum, various Papilio-
naces, and others. The rule consequently is, that
when the pistils and stamens are curved or bent, the
stigma and anthers are thus brought into the path-
way leading to the nectary. There are a few cases
which seem to be exceptions to this rule, but they are
not so in truth; for instance, in the Gloriosa lily, the
stigma of the grotesque and rectangularly bent pistil
Cuar, IV. LYTHRUM SALICARIA. 147
is brought, not into any pathway from the outside
towards the nectar-secreting recesses of the flower, but
into the circular route which insects follow in proceed-
ing from one nectary to the other. In Serophularia
aquatica the pistil is bent downwards from the mouth
of the corolla, but it thus strikes the pollen-dusted
breast of the wasps which habitually visit these ill-
scented flowers. In all these cases we see the supreme
dominating power of insects on the structure of flowers,
especially of those which have irregular corollas.
Flowers which are fertilised by the wind must of
course be excepted; but I do not know of a single
instance of an irregular flower which is thus fertilised.
Another point deserves notice. In each of the three
forms two sets of stamens correspond in length with
the pistils in the other two forms. When bees suck the
flowers, the anthers of the longest stamens, bearing the
green pollen, are rubbed against the abdomen and the
inner sides of the hind legs, as is likewise the stigma of
the long-styled form. The anthers of the mid-length
stamens and the stigma of the mid-styled form are
rubbed against the under side of the thorax and be-
tween the front pair of legs. And, lastly, the anthers
of the shortest stamens and the stigma of the short-
styled form are rubbed against the proboscis and chin ;
for the bees in sucking the flowers insert only the front.
part of their heads into the flower. On catching bees, 1
observed much green pollen on the inner sides of the
hind legs and on the abdomen, and much yellow
pollen on the under side of the thorax. There was
also pollen on the chin, and, it may be presumed, on
the proboscis, but this was difficult to observe. I had,
however, independent proof that pollen is carried on
the proboscis ; for a small branch of a protected short-
styled plant (which produced spontaneously only two
148 HETEROSTYLED TRIMORPHIC PLANTS. Cuar. IV.
capsules) was accidentally left during several days
pressing against the net, and bees were seen inserting
their proboscides through the meshes, and in conse-
quence numerous capsules were formed on this one
small branch. From these several facts it follows that
insects will generally carry the pollen of each form from
the stamens to the pistil of corresponding length; and
we shall presently see the importance of this adapta-
tion. It must not, however, be supposed that the becs
do not get more or less dusted all over with the several
kinds of pollen; for this could be seen to occur with
the green pollen from the longest stamens. Moreover
a case will presently be given of a long-styled plant
producing an abundance of capsules, though grow-
ing quite by itself, and the flowers must have been
fertilised by their own two kinds of pollen; but
these capsules contained a very poor average of seed.
Hence insects, and chiefly bees, act both as general
carriers of pollen, and as special carriers of the right
sort.
Wirtgen remarks* on the variability of this plant in
the branching of the stem, in the length of the bractex,
size of the petals, and in several other characters. The
plants which grew in my garden had their leaves,
which differed much in shape, arranged oppositely,
alternately, or in whorls of three. In this latter case
the stems were hexagonal; those of the other plants
being quadrangular. But we are concerned chiefly,
with the reproductive organs: the upward bending of
the pistil is variable, and especially in the short-styled
form, in which it is sometimes straight, sometimes
slightly curved, but generally bent at right angles.
The stigma of the long-styled pistil frequently has
* ‘Verhand. des naturhist. Vereins, fiir Pr. Rheinl.’ 5. Jahrgang
1848, pp. 11, 13.
Cuar. IV. LYTHRUM SALICARIA. 149
longer papilla or is rougher than that of the mid-
styled, and the latter than that of the short-styled ;
but this character, though fixed and uniform in the
two forms of Primula veris, &c., is here variable, for
I have.seen mid-styled stigmas rougher than those
of the long-styled.* The degree to which the longest
and mid-length stamens are graduated in length and
have their ends upturned is variable; sometimes all
are equally long. The colour of the green pollen in
the longest stamens is variable, being sometimes pale
greenish-yellow; in one short-styled plant it was almost
white. The grains vary a little in size: I examined
one short-styled plant with the grains above the
average size; and I have seen a long-styled plant with
the grains from the mid-length and shortest anthers of
the same size. We here see great variability in many
important characters; and if any of these variations
were of service to the plant, or were -correlated with
useful functional differences, the species is in that
state in which natural selection might readily do much
for its modification.
On the Power of Mutual Fertilisation between the three
Forms.
Nothing shows more clearly the extraordinary com-
plexity of the reproductive system of this plant, than
the necessity of making eighteen distinct unions in
order to ascertain the relative fertilising power of the
and he appears to have found the
stigmatic papille differing con.
* The plants which I observed
grew in my garden, and probably
varied rather more than those
growing in a state of nature. H.
Miiller has described the stigmas
of all three forms with great care,
stantly in length and structure in
the three forms, being longest in
the long-styled form,
150 HETEROSTYLED TRIMORPHIC PLANTS. Cuapr. IV,
three forms. Thus the long-styled form has to be fer-
tilised with pollen from its own two kinds of anthers,
from the two in the mid-styled, and from the two in
the short-styled form. The same process has to be
repeated with the mid-styled and short-styled forms.
It might have been thought sufficient to have tried on
each stigma the green pollen, for instance, from either
the mid- or short-styled longest stamens, and not
from both; but the result proves that this would
have been insufficient, and that it was necessary to
try all six kinds of pollen on each stigma. As in
fertilising flowers there will always be some failures,
it would have been advisable to have repeated each of
the eighteen unions a score of times; but the labour
would have been too great; as it was, I made 223
unions, ie. on an average I fertilised above a dozen
flowers in the eighteen different methods. Hach flower
was castrated ; the adjoining buds had to be removed,
so that the flowers might be safely marked with
thread, wool, &c.; and after each fertilisation the stigma
was examined with a lens to see that there was sufti-
cient pollen on it. Plants of all three forms were
protected during two years by large nets on a frame-
work ; two plants were used during one or both years,
in order to avoid any individual peculiarity in a par-
ticular plant. As soon as the flowers had withered,
the nets were removed; and in the autumn the cap-
sules were daily inspected and gathered, the ripe
seeds being counted under the microscope. I have
given these details that confidence may be placed
in the following tables, and as some excuse for two
blunders which, I believe, were made. These blunders
are referred to, with their probable cause, in two
foot-notes to the tables. The erroneous numbers, how-
ever, are entered in the tables, that it may not be sup-
Cuar. IV, LYTHRUM SALICARIA. 151,
posed that I have in any one instance tampered with
the results.
A few words explanatory of the three tables must be
given. Each is devoted to one of the three forms, and
is divided into six compartments. The two upper ones
in each table show the number of good seeds resulting
from the application to the stigma of pollen from the
two sets of stamens which correspond in length with
the pistil of that form, and which are borne by the
other two forms. Such unions are of a legitimate
nature. The two next lower compartments show the
result of the application of pollen from the two sets of
stamens, not corresponding in length with the pistil,
and which are borne by the other two forms. These
unions are illegitimate. The two lowest compartments
show the result of the application of each form’s own
two kinds of pollen from the two sets of stamens be-
longing to the same form, and which do not equal the
pistil in length. These unions are likewise illegiti-
mate. The term own-form pollen here used does not
mean pollen from the flower to be fertilised—for this
was never used—but from another flower on the same
plant, or more commonly from a distinct plant of the
same form. The figure (0) means that no capsule was
produced, or if a capsule was produced that it contained
no good seed. In some part of each row of figures in
each compartment, a short horizontal line may be seen ;
the unions above this line were made in 1862, and
below it in 1863. It is of importance to observe this,
as it shows that the same general result was obtained
during two successive years; but more especially be-
cause 1863 was a very hot and dry season, and the
plants had occasionally to be watered. This did not pre-
vent the full complement of seed being produced from
the more fertile unions; but it rendered the less fertile
11
‘152 HETEROSTYLED TRIMORPHIC PLANTS. Cuar. IV
ones even more sterile than they otherwise would have:
been. I have seen striking instances of this fact in
making illegitimate and legitimate unions with Pri-
mula; and it is well known that the conditions of life
must be highly favourable to give any chance of suc-
cess in producing hybrids between species which are
crossed with difficulty.
Tas.eE 23.—Long-styled Form.
L
Legitimate union.
13 flowers fertilised by the longest
stamens of the mid-styled. These
stamens equal in length the pistil
of the long-styled.
Product of good seed in each cap-
sule.
36 53
81
0
0
0
45
41
38 per cent. of these flowers
yielded capsules. Each capsule con-
tained, on an average, 51°2 seeds.
ooooo
IL.
Legitimate union.
13 Howers fertilised by the longest
stamens of the short-styled. These
stamens equal in length the pistil
of the long-styled.
Product of good seed in each cap-
sule.
159 104
43 119
96 poor seed. 96
03 99
0 131
0 116
114
84 per cent. of these flowers
yielded capsules, Each capsule con-
tained, on an average, 107°3 seeds,
Ill.
Illegitimate union.
14 flowers fertilised by the short-
est stamens of the mid-styled,
ool eoooow
ooooocoo
Too sterile for any average,
IV.
Illegitimate union.
12 flowers fertilised by the mid
length stamens of the short-styled.
20 0
0 0
0 0
0 0
- 0
0 0
0
Too sterile for any average.
Cuap. IV. LYTHRUM SALICARIA. 153
TaBLe 23.—Long-styled Form—continued.
NG, Vi.
Iegitimate union. Megitimate union.
15 flowers fertilised by own-form |. 15 flowers fertilised by own-form
mid-length stamens. shortest stamens.
2 _ 4 -
10 0 8 0
23 0 4 0
0 0 0 0
0 0 0 0
0 0 0 0
0 0 0 0
0 0 0 0
Too sterile for any average. Too sterile for any average.
Besides the above experiments, I fertilised a consi-
derable number of long-styled flowers with pollen,
taken by a camel’s-hair brush, from both the mid-
length and shortest stamens of their own form: only
5 capsules were produced, and these yielded on an
average 14°5 seeds. In 1863 I tried a much better ex-
periment: a long-styled plant was grown by itself,
miles away from any other plant, so that the flowers
could have received only their own two kinds of pol-
len. The flowers were incessantly visited by bees, and
their stigmas must have received successive applica-
tions of pollen on the most favourable days and at the
most favourable hours: all who have crossed plants
know that this highly favours fertilisation. This plant
produced an abundant crop of capsules; I took by
chance 20 capsules, and these contained seeds in
number as follows :—
20 20 35 21 19
26 24 12 23 10
7 30 27 29 13
20 12 29 19 35
154 HETEROSTYLED TRIMORPHIC PLANTS. Caar. IV.
This gives an average of 21°5 seeds per capsule. As
we know that the long-styled form, when standing
near plants of the other two forms and fertilised by
insects, produces on an average 93 seeds per capsule,
we see that this form, fertilised by its own two pollens,
yields only between one-fourth and one-fifth of the full
number of seed. I have spoken as if the plant had re-
ceived both its own kinds of pollen, and this is, of
course, possible; but, from the enclosed position of the
shortest stamens, it is much more probable that the
stigma received exclusively pollen from the mid-
length stamens; and this, as may be seen in com-
partment V. in Table 23, is the more fertile of the two
self-unions.
Taste 24.—Mid-styled Form.
I.
Legitimate union.
12 flowers fertilised by the mid-
length stamens of the long-styled.
These stamens equal in length the
pistil of the mid-styled.
Product of good seed in each cap-
sule.
138 122
149 50
147 151
109 119
133 138
144 0
92 per cent. of the flowers (pro-
bably 100 per cent.) yielded cap-
sules. Each capsule contained, on
an average, 127°3 seeds.
I.
Legitimate union.
12 flowers fertilised by the mid-
length stamens of the short-styled.
These stamens equal in length the
pistil of the mid-styled.
Product of good seed in each cap-
sule,
112 109
130 143
143 124
100 145
33 12
—_ 141
104
100 per cent. of the towers yielded
capsules. Each capsule contained,
on an average, 108°0 seeds; or, ex-
cluding capsules with less than 20
seeds, the average is 1167 seeds,
Car IV.
LYTHRUM SALICARIA.
155
Tasle 24.—Mid-styled Form—continued.
ILL.
Illegitimate union.
13 flowers fertilised by the shori-
est stamens of the long-styled.
83 12
0 19
= (seeds small
. 83{ and poor.
_ 0
44 0
44 0
45 0
54 per cent. of the flowers yielded
capsules. Each capsule contained,
oa an average, 47°4 seeds; or, ex-
ciuding capsules with less than 20
seeds, the average is 60°2 seeds.
IV.
Illegitimate union.
15 flowers fertilised by the lons
est stamens of the short-styled.
130 86
115 113
14 29
6 17
2 113
9 79
_ 128
132 0
93 per cent. of the flowers yielded
capsules. Each capsule contained,
on am average, 69°5 seeds; or, ex-
cluding capsules with less than 20
seeds, the average is 102-8.
Vv.
Illegitimate unton.
12 flowers fertilised by own-form
longest stamens.
92
9
63
136? *
0
0
Excluding the capsule with 136
seeds, 25 per cent. of the flowers
yielded capsules, and each capsule
contained, on an average, 54°6 seeds;
or, excluding capsules with less than
20 seeds, the average is 77°5.
oooooo
Vi.
Illegitimate union.
12 flowers fertilised by own-form
shortest stamens,
cool ooo
oooooo
Not one flower yielded a capsule.
* TI have hardly a doubt that
this result of 136 seeds in compart-
ment V. was due to a gross error.
The flowers to be fertilised by
their own longest stamens were
first marked by “ white thread,”
and those by the mid-length
stamens of the long-styled form
by “ white silk ;” a flower fertilised
in the later manner would have
yielded about 136 seeds, and it may
be observed that one such pod ig
missing, viz. at the bottom of
compartment I. Therefore I have
hardly any doubt that I fertilised
a flower marked with “white
thread ’’ as if it had been marked
with “ white silk.” With respect
to the capsule which yielded 92
secds, in the same column with
that which yielded 136, I do
not know what to think. I
endeavoured to prevent pollen
dropping from an upper to a lower
156 HETEROSTYLED TRIMORPHIC PLANTS. Cuap. LV.
Besides the experiments in the above table, I ferti-
lised a considerable number of mid-styled flowers with
pollen, taken by a camel’s-hair brush, from both the
longest and shortest stamens of their own form: only
5 capsules were produced, and these yielded on an
average 11-0 seeds.
TABLE 25.—Short-styled Form.
I.
Legitimate inion.
12 flowers fertilised by the short-
est stamens of the long-styled.
These stamens equal in length the
pistil of the short-styled.
69 56
61 88
88 112
66 111
0 62
0 100
83 per cent. of the flowers yielded
capsules. Each capsule contained,
on an average, 81°3 seeds.
II.
Legitimate union.
13 flowers fertilised by the short-
est stamens of the mid-styled.
These stamens equal in length the
pistil of the short-styled.
93 59
“U7 69
48 53
43 9
0 0
0 0
_— 0
61 per cent. of the flowers yielded
capsules, Each capsule contained,
on an average, 64°6 seeds,
Ill.
Illegitimate union.
10 flowers fertilised by the mid-
length stamens of the long-styled,
0 14
0 0
0 0
0 0
— 0
23
Too sterile for any average.
IV,
Illegitimate union.
10 flowers fertilised by the long-
est stamens of the mid-styled.
0 0
0 0
0 0
0 0
_ 0
0
Too sterile for any average.
flower, and I tried to remember to
wipe the pincers carefully after
each fertilisation; but in making
eighteen diffurent unions, some-
times on windy days, and pestered
by bees and flies buzzing about,
some few errors could hardly be
avoided. One day I had to keep
a third man by me all the time to
prevent the bees visiting the un-
covered plants, for in a few
seconds’ time they might have
done irreparable mischief. It was
also extremely difficult to exclude
minute Diptera from the net. In
1862 [ made the great mistake of
placing a mid-styled and loug-
styled under the same huge net:
in 1863 I avoided this error.
Cnap. IV. LYTHRUM SALICARIA.
TABLE 25.—Short-styled Form—continued.
Vv. VI.
Illegitimate union. Illegitimate union.
10 flowers fertilised by own-form 10 flowers fertilised by own-form
longest stamens, mid-length stamens.
0 0 64?7* 0
0 0 0 0
0) 0 0 0
_ 0 _ 0
0 0 21 0
0 9
Too sterile for any average. Too sterile for any average.
Besides the experiments in the table, I fertilised a
number of flowers without particular care with their
own two kinds of pollen, but they did not produce a
single capsule.
Summary of the Results.
Long-styled form.—Twenty-six flowers fertilised le-
gitimately by the stamens of corresponding length,
borne by the mid- and short-styled forms, yielded 61:5
per cent. of capsules, which contained on an average
89-7 seeds.
Twenty-six long-styled flowers fertilised illegiti-
mately by the other stamens of the mid- and short-
styled forms yielded only two very poor capsules.
Thirty long-styled flowers fertilised illegitimately by
their own-form two sets of stamens yielded only eight
very poor capsules; but long-styled flowers fertilised
* I suspect that by mistake I
fertilised this flower in compart-
ment VI. with pollen from the
shortest stamens of the long-styled
form, and it would then have
yieldcd about 64 seeds. Flowers
to be thus fertilised were marked
with black silk ; those with pollen
from the mid-length stamens of
the short-styled with black thread;
and thus probably the mistake
arose.
158 HETEROSTYLED TRIMORPHIC PLANTS. Cuar. IV
by bees with pollen from their own stamens produced
numerous capsules containing on an average 21:5
seeds.
Mid-styled form.—Twenty-four flowers legitimately
fertilised by the stamens of corresponding length,
borne by the long and short-styled forms, yielded 96
(probably 100) per cent. of capsules, which contained
(excluding one capsule with 12 seeds) on an average
117-2 seeds.
Fifteen mid-styled flowers fertilised illegitimately
by the longest stamens of the short-styled form yielded
93 per cent. of capsules, which (excluding four cap-
sules with less than 20 seeds) contained on an average
102°8 seeds.
Thirteen mid-styled flowers fertilised illegitimately
by the mid-length stamens of the long-styled form
yielded 54 per cent. of capsules, which (excluding
one with 19 seeds) contained on an average 60:2 seeds.
Twelve mid-styled flowers fertilised illegitimately
by their own-form longest stamens yielded 25 per
cent. of capsules, which (excluding one with 9 seeds)
contained on an average 77°5 seeds.
Twelve mid-styled flowers fertilised illegitimately
by their own-form shortest stamens yielded not a
single capsule. :
Short-styled form.—Twenty-five flowers fertilised
legitimately by the stamens of corresponding length,
borne by the long and mid-styled forms, yielded 72
per cent. of capsules, which (excluding one capsule
with only 9 seeds) contained on an average 70°8
seeds,
Twenty short-styled flowers fertilised illegitimately
by the other stamens of the long and mid-styled forms
yielded only two very poor capsules.
Twenty short-styled flowers fertilised illegitimately
Cuar. LV. LYTHRUM SALICARIA. 159
by their own-stamens yielded only two poor (or per-
haps three) capsules.
If we take all six legitimate unions together, and
all twelve illegitimate unions together, we get the fol-
lowing results :—
TABLE 26.
Number Number eee Ransber of
Nature of Union. of Flowers | of Capsules Sead i ‘per aoe per
fertilised. roduced. ower ier-
‘ » Capsule. tilised.
The six a igi 7 56 96-29 71°89
unions. e 4%
The twelve illegiti-| 146 36 44°72 11°03
mate unions . .f
Therefore the fertility of the legitimate unions to that
of the illegitimate, as judged by the proportion of the
fertilised flowers which yielded capsules, is as 100 to
33 ; and judged by the average number of seeds per
capsule, as 100 to 46.
From this summary and the several foregoing tables
we see that it is only pollen from the longest stamens
which can fully fertilise the longest pistil; only that
from the mid-length stamens, the mid-length pistil;
and only that from the shortest stamens, the shortest
pistil. And now we can comprehend the meaning of
the almost exact correspondence in length between
the pistil in each form and a set of six stamens
in two of the other forms; for the stigma of each
form is thus rubbed against that part of the insect’s
body which becomes charged with the proper pollen.
It is also evident that the stigma of each form,
fertilised in three different ways with pollen from
the longest, mid-length, and shortest stamens, is acted
on very differently, and conversely that the pollen from
160 HETEROSTYLED TRIMORPHIC PLANTS. Cuar. IV.
the twelve longest, twelve mid-length, and twelve
shortest stamens acts very differently on each of the
three stigmas; so that there are three sets of female
and of male organs. Moreover, in most cases the six
stamens of each set differ somewhat in their fertilising
* power from the six corresponding ones in one of the
other forms. We may further draw the remarkable
conclusion that the greater the inequality in length
between the pistil and the set of stamens, the pollen
of which is employed for its fertilisation, by so much
is the sterility of the union increased. There are no
exceptions to this rule. To understand what follows
the reader should look to Tables 23, 24, and 25, and
to the diagram Fig. 10, p. 189. In the long-styled form
the shortest stamens obviously differ in length from
the pistil to a greater degree than do the mid-length
stamens; and the capsules produced by the use of
pollen from the shortest stamens contain fewer seeds
than those produced by the pollen from the mid-
length stamens. The same result follows with the
long-styled form, from the use of the pollen of the
shortest stamens of the mid-styled form and of the
mid-length stamens of the short-styled form. The
same rule also holds good with the mid-styled and
short-styled forms, when illegitimately fertilised with
pollen from the stamens more or less unequal in
length to their pistils. Certainly the difference in
sterility in these several cases is slight; but, as far as
we are enabled to judge, it always increases with the
increasing inequality of length between the pistil and
the stamens which are used in each case.
The correspondence in length between the pistil in
each form and a set of stamens in the other two forms,
is probably the direct result of adaptation, as it is of
high service to the species by leading to full and
Cuar. LY. LYTHRUM SALICARIA. 161]
legitimate fertilisation. But the rule of the increased
sterility of the illegitimate unions according to the
greater inequality in length between the pistils and
stamens employed for the union can be of no service.
With some heterostyled dimorphic plants the dif-
ference of fertility between the two illegitimate unions
appears at first sight to be related to the facility of
self-fertilisation; so that when from the position of
the parts the liability in one form to self-fertilisation
is greater than in the other, a union of this kind
has been checked by having been rendered the
more sterile of the two. But this explanation does
not apply to Lythrum; thus the stigma of the long-
styled form is more liable to be illegitimately fer-
tilised with pollen from its own mid-length stamens,
or with pollen from the mid-length stamens of the
short-styled form, than by its own shortest stamens
or those of the mid-styled form; yet the two former
unions, which it might have been expected would
have been guarded against by increased sterility,
are much less sterile than the other two unions
which are much less likely to be effected. The
same relation holds good even in a more striking
manner with the mid-styled form, and with the short-
styled form as far as the extreme sterility of all its
illegitimate unions allows of any comparison. We
are led, therefore, to conclude that the rule of in-
creased sterility in accordance with increased in-
equality in length between the pistils and stamens,
is a purposeless result, incidental on those changes
through which the species has passed in acquiring
certain characters fitted to ensure the legitimate
fertilisation of the three forms.
Another conclusion which may be drawn from
Tables 23, 24, and 25, even from a glance at them,
162 HETEROSTYLED TRIMORPHIC PLANTS. Cuap. IV.
is that the mid-styled form differs from both the
others in its much higher capacity for fertilisation
in various ways. Not only did the twenty-four flowers
legitimately fertilised by the stamens of corresponding
lengths, all, or all but one, yield capsules rich in
seed; but of the other four illegitimate unions, that
by the longest stamens of the short-styled form was
highly fertile, though less so than the two legitimate
unions, and that by the mid-length stamens of the
long-styled form was fertile to a considerable degree ;
the remaining two illegitimate unions, namely, with
this form’s own pollen, were sterile, but in different
degrees. So that the mid-styled form, when fertilised
in the six different possible methods, evinces five
grades of fertility. By comparing compartments III.
and VI. in Table 24 we may see that the action of
the pollen from the shortest stamens of the long-styled
and mid-styled forms is widely different; in the one
case above half the fertilised flowers yielded capsules
containing a fair number of seeds; in the other case
not one capsule was produced. So, again, the green,
large-grained pollen from the longest stamens of
the short-styled and mid-styled forms (in compart-
ments IV. and V.) is widely different. In both these
cases the difference in action is so plain that it cannot
be mistaken, but it can be corroborated. If we look
to Table 25 to the legitimate action of the shortest
stamens of the long- and mid-styled forms on the
short-styled form, we again see a similar but slighter
difference, the pollen of the shortest stamens of the
mid-styled form yielding a smaller average of seed
during the two years of 1862 and 1863 than that from
the shortest stamens of the long-styled form. Again,
if we look to Table 23, to the legitimate action on
the long-styled form of the green pollen of the two
Cuapr. IV. LYTHRUM SALICARIA. 163
sets of longest stamens, we shall find exactly the same
result, viz. that the pollen from the longest stamens of
the mid-styled form yielded during both years fewer
seeds than that from the longest stamens of the
short-styled form. Hence it is certain that the two
kinds of pollen produced by the mid-styled form are
less potent than the two similar kinds of pollen pro-
duced by the corresponding stamens of the other two
forms.
In close connection with the lesser potency of the
two kinds of pollen of the mid-styled form is the fact
that, according to H. Miller, the grains of both are
a little less in diameter than the corresponding grains
produced by the other two forms. Thus the grains
from the longest stamens of the mid-styled form are
9 to 10, whilst those from the corresponding stamens
of the short-styled form are 94 to 104 in diameter.
So, again, the grains from the shortest stamens of the
mid-styled are 6, whilst those from the corresponding
stamens of the long-styled are 6 to 64 in diameter.
It would thus appear as if the male organs of the
mid-styled form, though not as yet rudimentary, were
tending in this direction. On the other hand, the
female organs of this form are in an eminently efficient
state, for the naturally fertilised capsules yielded a
considerably larger average number of seeds than
those of the other two forms—almost every flower
which was artificially fertilised in a legitimate manner
produced a capsule—and most of the illegitimate
unions were highly productive. The mid-styled form
thus appears to be highly feminine in nature; and al-
though, as just remarked, it is impossible to consider
its two well-developed sets of stamens which produce
an abundance of pollen as being in a rudimentary
condition, yet we can hardly avoid connecting as
164 HETEROSTYLED TRIMORPHIC PLANTS. Cuap. IV.
balanced the higher efficiency of the female organs
in this form with the lesser efficiency and lesser size
of its two kinds of pollen-grains. The whole case
appears to me a very curious one.
It may be observed in Tables 23 to 25 that some
of the illegitimate unions yielded during neither year
a single seed; but, judging from the long-styled plants,
it is probable, if such unions were to be effected re-
peatedly by the aid of insects under the most favour-
able conditions, some few seeds would be produced in
every case. Anyhow, it is certain that in all twelve
illegitimate unions the pollen-tubes penetrated the
stigma in the course of eighteen hours. At first I
thought that two kinds of pollen placed together on
the same stigma would perhaps yield more seed than
one kind by itself; but we have seen that this is not
so with each form’s own two kinds of pollen; nor is it
probable in any case, as I occasionally got, by the use
of a single kind of pollen, fully as many seeds as a
capsule naturally fertilised ever produces. Moreover
the pollen from a single anther is far more than suffi-
cient to fertilise fully a stigma; hence, in this as with
so many other plants, more than twelve times as much
of each kind of pollen is produced as is necessary to
ensure the full fertilisation of each form. From the
dusted condition of the bodies of the bees which I
caught on the flowers, it is probable that pollen of
various kinds is often deposited on all three stigmas ;
but from the facts already given with respect to
the two forms of Primula, there can hardly be a
doubt that pollen from the stamens of corresponding
length placed on a stigma would be prepotent over
any other kind of pollen and obliterate its effects,
—even if the latter had been placed on the stigma
some hours previously.
Ouap. IV. LYTHRUM GRAFFERI. 165
Finally, it has now been shown that Lythrum salicaria
presents the extraordinary case of the same species
bearing three females, different in structure and func-
tion, and three or even five sets (if minor differences
are considered) of males; each set consisting of half-
a-dozen, which likewise differ from one another in
structure and function.
Lythrum Grafferi._I have examined numerous dried flowers
of this species, each from a separate plant, sent me from Kew.
Like ZL. salicaria, it is trimorphic, and the three forms appa-
rently occur in about equal numbers. In the long-styled form
the pistil projects about one-third of the length of the calyx
beyond its mouth, and is therefore relatively much shorter than |
in L. salicaria; the globose and hirsute stigma is larger than
that of the other two forms; the six mid-length stamens, which
are graduated in length, have their anthers standing close above
and close beneath the mouth of the calyx; the six shortest
stamens rise rather above the middle of the calyx. In the mid-
styled form the stigma projects just above the mouth of the
calyx, and stands almost on a level with the mid-length stamens
of the long and short-styled forms; its own longest stamens
project well above the mouth of the calyx, and stand a little
above the level of the stigma of the long-styled form. In short,
without entering on further details, there is a close general
correspondence in structure between this species and L. salicaria,
but with some differences in the proportional lengths of the
parts. The fact of each of the three pistils having two sets of
stamens of corresponding lengths, borne by the two other forms,
comes out conspicuously. In the mid-styled form the pollen-
grains from the longest stamens are nearly double the diameter
of those from the shortest stamens; so that there is a greater
difference in this respect than in L. salicaria. In the long-
styled form, also, the difference in diameter between the pollen-
grains of the mid-length and shortest stamens is greater than
in L. salicaria. These comparisons, however, must be received
with caution, as they were made on specimens soaked in water
after having been long kept dry.
Lythrum thymifolia.—This form, according to Vaucher,* ig
* ‘Hist. Phys. des Plantes d’Europe,’ tom. ii. (1841), pp. 369, 371.
166 HETEROSTYLED TRIMORPHIC PLANTS. Cuar. 1V,
dimorphic, like Primula, and therefore presents only two forms.
I received two dried flowers from Kew, which consisted of the
two forms; in cne the stigma projected far beyond the calyx, in
the other it was included within the calyx; in this latter form
the style was only one-fourth of the length of that in the other
torm. There are only six stamens; these are somewhat gradu-
ated in length, and their anthers in the short-styled form stand
a little above the stigma, but yet by no means equal in length
the pistil of the long-styled form. In the latter the stamens
are rather shorter than those in the other form. The six
stamens alternate with the petals, and therefore correspond
homologically with the longest stamens of L. salicaria and L.
Greffert.
Lythrum hyssopifolia.— This species is said by Vaucher, but I
believe erroneously, to be dimorphic. I have examined dried
flowers from twenty-two separate plants from various localities,
sent to me by Mr. Hewett C. Watson, Professor Babington, and
others. These were all essentially alike, so that the species
cannot be heterostyled. The pistil varies somewhat in length,
but when unusually long, the stamens are likewise generally
long; in the bud the stamens are short; and Vaucher was
perhaps thus deceived. There are from six to nine stamens,
graduated in length. The three stamens, which vary in being
either present or absent, correspond with the six shorter stamens
of L. salicaria and with the six which are always absent in L.
thymifolia. The stigma is included within the calyx, and stands
in the midst of the anthers, and would generally be fertilised
by them; but as the stigma and anthers are upturned, and as,
according to Vaucher, there is a passage left in the upper side
of the flower to the nectary, there can hardly be a doubt that
the flowers are visited by insects, and would occasionally be
cross-fertilised by them, as surely as the flowers of the short-
styled L. salicaria, the pistil of which and the corresponding
stamens in the other two forms closely resemble those of L. hys-
sopifolia, According to Vaucher and Lecoq,* this species, which
is an annual, generally grows almost solitarily, whereas the
three preceding species are social; and this fact alone would
almost have convinced me that L. hyssopifolia was not hetero~
styled, as such plants cannot habitually live isolated any better
than one sex of a dicecious species.
* ‘Géograph. Bot. de l’Europe,’ tom. vi. 1857, p. 157.
Cuar. IV LAGERSTRCEMIA INDICA. 167
We thus see that within this genus some species are hetero-
styled and trimorphic; one apparently heterostyled and dimor-
phic, and one homostyled.
Nesua verticillata—I raised a number of plants from seed
sent me by Professor Asa Gray, and they presented three forms.
These differed from one another in the proportional lengths of
their organs of fructification and in all respects, in very nearly
the same way as the three forms of Lythrum Grefferi. The
green pollen-grains from the longest stamens, measured along
their longer axis and not distended with water, were ;}3, of an
-10
inch in length; those from the mid-length stamens a and
those from the shortest stamens a of an inch. So that the
largest pollen-grains are to the smallest in diameter as 100 to
65. This plant inhabits swampy ground in the United States.
According to Fritz Miiller,* a species of this genus in St. Catha-
rina, in Southern Brazil, is homostyled.
Lagerstremia Indica.—This plant, a member of the Lythracezx,
may perhaps be heterostyled, or may formerly have been so. It
is remarkable from the extreme variability of its stamens. On
a plant, growing in my hothouse, the flowers included from
nineteen to twenty-nine short stamens with yellow pollen,
which correspond in position with the shortest stamens of
Lythrum; and from one to five (the latter number being the
commonest) very long stamens, with thick flesh-coloured fila-
ments and green pollen, corresponding in position with the
longest stamens of Lythrum. In one flower, two of the long
stamens produced green, while a third produced yellow pollen,
although the filaments of all three were thick and flesh-coloured.
In an anther of another flower, one cell contained green and
the other yellow pollen. The green and yellow pollen-grains
from the stamens of different length are of the same size.
The pistil is a little bowed upwards, with-the stigma seated
between the anthers of the short and long stamens, so that
this plant was mid-styled. Eight flowers were fertilised with
green pollen, and six with yellow pollen, but not one set fruit.
This latter fact by no means proves that the plant is hetero-
styled, as it may belong to the class of self-sterile species.
Another plant growing in the Botanic Gardens at Calcutta, as
Mr. J. Scott informs me, was long-styled, and it was equally
* «Bot. Zeitung,’ 1868, p. 112.
168 HETEROSTYLED TRIMORPHIC PLANTS. Cuap. 1V
sterile with its own pollen; whilst a long-styled plant of
L. reyine, though growing by itself, produced fruit. I examined
dried flowers from two plants of L. parviflora, both of which
were long-styled, and they differed from ZL. Indica in having
eight long stamens with thick filaments, and a crowd of shorter
stamens. Thus the evidence whether L. Indica is hetero-
styled is curiously conflicting: the unequal number of the short
and long stamens, their extreme variability, and especially the
fact of their pollen-grains not differing in size, are strongly
opposed to this belief; on the other hand, the difference in
length of the pistils in two of the plants, their sterility with
their own pollen, and the difference in length and structure of
the two sets of stamens in the same flower, and in the colour of
their pollen, favour the belief. We know that when plants of
any kind revert to a former condition, they are apt to be highly
variable, and the two halves of the same organ sometimes differ
much, as in the case of the above-described anther of the
Lagerstreemia; we may therefore suspect that this species was
once heterostyled, and that it still retains traces of its former
state, together with a tendency to revert more completely to it.
It deserves notice, as bearing on the nature of Lagerstrcemia,
that in Lythrum hyssopifolia, which is a homostyled species, some
of the shorter stamens vary in being either present or absent;
and that these same stamens are altogether absent in L. thym/-
folia. In another genus of the Lythraceze, namely Cuphea, three
species raised by me from secd certainly were homostyled;
nevertheless their stamens consisted of two sets, differing in
length and in the colour and thickness of their filaments, but
not in the size or colour of their pollen-grains; so that they
thus far resembled the stamens of Lagerstreemia. I found that
Cuphea purpurea was highly fertile with its own pollen when
artificially aided, but sterile when insects were excluded.*
* Mr. Spenco informs me that
in several species of the genus
Mollia (Tiliacewe) which he col-
lected in South America, the
stimens of the five outer cohorts
have purplish filaments and green
pollen, whilst the stamens of the
five inner cohorts have yellow
pollen. He therefore suspected
that these species might prove
to be heterostyled and trimor-
phic: but he did not notice the
leneth of the pistils. In the
allied Luhea the outer purplish
. stamens are destitute of anthers.
I procured some specimens of
Millia lepidota and specivsa from
Kew, but could not make out that
their pistils differed in length
in different plints; and in all
those which I examined the
stigma stood close beneath the
Cuar. TV. OXALIS. 169
OXALIS (GERANIACEZ).
In 1863 Mr. Roland Trimen wrote to me from the
Cape of Good Hope that he had there found species of
Oxalis which presented three forms; and of these he
enclosed drawings and dried specimens. Of one species
he collected 43 flowers from distinct plants, and they
consisted of 10 long-styled, 12 mid-styled, and 21
short-styled. Of another species he collected 13 flowers,
consisting of 3 long-styled, 7 mid-styled, and 3 short-
styled. In 1866 Prof. Hildebrand proved* by an ex-
amination of the specimens in several herbaria that 20
species are certainly heterostyled and trimorphic, and
51 others almost certainly so. He also made some in-
teresting observations on living plants belonging to
one form alone; for at that time he did not possess
the three forms of any living species. During the
years 1864 to 1868 I occasionally experimented on
Oxalis speciosa, but until now have never found time
to publish the results. In 1871 Hildebrand published
an admirable paper} in which he shows in the case of
two species of Oxalis, that the sexual relations of the
three forms are nearly the same as in Lythrum salt-
caria. I will now give an abstract of his observa-
tions, and afterwards of my own less complete ones.
I may premise that in all the species seen by me, the
stigmas of the five straight pistils of the long-styled
form stand on a level with the anthers of the longest
stamens in the two other forms. In the mid-styled
uppermost anthers. The numerous
stamens are graduated in length,
and the pollen-grains from the
longest and shorte-t ones did not
present any marked difference in
diameter. Therefore these species
do not appear to be heterostyled.
* ‘Monatsber. der Akad. der
Wiss. Berlin,’ 1866, pp. 352, 372.
He gives drawings of the three
forms ut p. 42 of his ‘Geschlechter-
Verthcilung,’ &., 1887.
t ‘Bot. Zeitung, 1871, pp. 416
and 432,
{70 HETEROSTYLED TRIMORPHIC PLANTS. Cuar. IV,
form. the stigmas pass out between the filaments of
the longest stamens (as in the short-styled form of
Linum); and they stand rather nearer to the upper
anthers than to the lower ones. In the short-stylad
Long-styled. Mid-etyled. Short-sty led.
OXALIS SPECIOSA (with the petals removed).
SS 8, stigmas. The dotted lines with arrows show which pollen must
be carried to the stigmas for legitimate fertilisation.
form, the stigmas also pass out between the filaments
nearly on a level with the tips of the sepals. The
anthers in this latter form and in the mid-styled rise
to the same height as the corresponding stigmas in the
other two forms.
Oxalis Valdiviana.—This species, an inhabitant of
the west coast of South America, bears yellow flowers.
Hildebrand states that the stigmas of the three forms
do not differ in any marked manner, but that the pistil
of the short-styled form alone is destitute of hairs
The diameters of the pollen-grains are as follows :—-
Divistons of tie
Micrometer,
Irom the longest stamens of short-styled . . . . 8to9
» mid-length ,, 7 a a oe a yg 8
7 longest stamens of mid-styled 8
5 shortest 6 4 eo 8
oF mid-length stamens of long-styled , 7
» __ Shortest 3 7" i ee te ag, 8
Cuar. IV. OXALIS VALDIVIANA. 171
Therefore the extreme difference in diameter is as 8:5
to 6, or as 100 to 71. The results of Hildebrand’s ex-
periments are given in the following table, drawn up
in accordance with my usual plan. He fertilised each
form with pollen from the two sets of anthers of the
same flower, and likewise from flowers on distinct
plants belonging to the same form; but the effects
of these two closely allied kinds of fertilisation differ
so little that I have not kept them distinct.
TABLE 27.
Oxalis Valdiviana (from Hildebrand).
ae sae epee
Nature of Union. Flowers Capsules Seeds per
fertilised. | produced. | Capsule.
Longestyled form, by pollen of longest
stamens of short-styled. ass saoan 28 28 11°9
unio. . 2. 2. . e |
‘ane etal form, by pollen of longest
stamens of mid- Gc si ees 21 21 12:0
unio. . 2. .
Long-styled form, by pollen of own and
own-form mid-length stamens. are 40 2 5:5
mate union .
Long-styled form, by pollen of own and
own-form shortest stamens. as das 26 0 0
mateunion . . . .
Iong-styled form, by pollen of shortest
stamens of eres so ea 16 1 1
union. 5
Long-styled form, by pollen of shortest
stamens of sa ea Mearns 9 0 0
union. 2. .
172 HETEROSTYLED TRIMORPHIC PLANTS. Cuar. IV.
TABLE 27—continued,
Oxalis Valdiviana (from Hildebrand).
union. .
Number Dumber Nambet
f o
Nature of Union. Flowers Capsules Seeds per
fertilised. | produced. | Capsule.
Mid-styled form, by pollen of mid-length gl 38 38 11°3
mens of long-styled, Legitimate union.
Mid-styled form, by pollen of mid-length
stamens of short-styled. Legitimate 23 23 10°4
union, . 6 2 2 6 ew we ew
Mid-styled form, by pollen of own and
own-form longest stamens. Illegitimate 52 0 0
union, . - 2 2 6 we ee
Mid-styled form, by pollen of own and
own-form shortest stamens. Illegitimate 30 1 6
union. . go ee
Mid-styled form, by pollen of shortest
stamens of oaks Illegitimate 16 0 0
union, 2 wt, oo .
Mid-styled form, by pollen of longest sta- 16 2 2:5
mens of short-styled. Illegitimate union
Short-styled form, by pollen of shortest sta- 18 18 11°0
mens of long-styled. Legitimate union,
Short-styled form, by pollen of shortest sta-
mens of mid-styled. Legitimate union | ” 10 iss
Short-styled form, by pollen of own and
own-form longest stamens. Bae 21 0 0
union. 2 . ww
Short-styled form, by pollen of own and
own-form mid-length stamens, Illegiti- 22 0 0
mate union ,
Short-styled form, by pollen of longest sta- 4
mens of mid-styled. Illegitimate union ” a
“Short-styled form, by pollen of mid-length
stamens of lorg-styled. ac amnaes 3 0 0
Cuar. IV. OXALIS REGNELLI. 173
We here have the remarkable result that every one
of 138 legitimately fertilised flowers on the three forms
yielded capsules, containing on an average 11°33 seeds.
Whilst of the 255 illegitimately fertilised flowers, only
6 yielded capsules, which contained 3°83 seeds on an
average. Therefore the fertility of the six legitimate
to that of the twelve illegitimate unions, as judged
by the proportion of flowers that yielded capsules, is
as 100 to 2, and as judged by the average number of
seeds per capsule as 100 to 34. It may be added that
some plants which were protected by uets did not
spontaneously produce any fruit; nor did one which
was left uncovered by itself and was visited by bees.
On the other hand, scarcely a single flower on some
uncovered plants of the three forms growing near
together failed to produce fruit.
Oxalis Regnelli—This species bears white flowers
and inhabits Southern Brazil. Hildebrand says that
the stigma of the long-styled form is somewhat larger
than that of the mid-styled, and this than that of the
short-styled. The pistil of the latter is clothed with a
few hairs, whilst it is very hairy in the other two
forms. The diameter of the pollen-grains from both
sets of the longest stamens equals 9 divisions of the
micrometer,—that from the mid-length stamens of the
long-styled form between 8 and 9, and of the short-
styled 8,—and that from the shortest stamens of both
sets 7. So that the extreme difference in diameter is
as 9 to 7 or as 100 to 78. The experiments made by
Hildebrand, which are not so numerous as in the last
case, are given in Table 28 in the same manner as
before.
The results are nearly the same as in the last case,
but more striking; for 41 flowers belonging to the
three forms fertilised legitimately all yielded capsules,
174 HETEROSTYLED TRIMORPHIC PLANTS. Caxar. IV.
Tasie 28.
Oxalis Regnelli (from Hildebrand).
Paraiey Puner eee
umber
Nature of Unton. Blowers Capsules Seeds per
fertilised. | produced. | Capsule,
Long-styled form, by pollen of longest sta- 6 6 | 10°1
mens of short-styled. Legitimate union
Long-styled form, by pollen of longest sta-)! 5 5 | 10°6
mens of mid-styled. Legitimate union
Long-styled form, by pollen of own mid-) 4 0 | 0
length stamens. Illegitimate union .f
Long-styled form, by pollen of own short- 1 0 0
est stamen. Illegitimate union.
Mid-styled form, by pollen of mid-length sta- F
mens of short-styled. Legitimate union ? 9 id
Mid-styled form , by pollen of mid-length sta- ,
mens of"long-styled. Legitimate union. f| ” om ae
‘Mid-styled form, by pollen of own ae 9 0 0
stamens. Illegitimate union
“Mid-styled form, by pollen of own shortest 3 0 0
stamens. Illegitimate union
Mid-styled form, by pollen of longest sta- 1 0 0
mens of shor t-styled. Illegitimate union
Short-styled form, by pollen of shortest sta- 9 9 10°6
mens of mid-styled. Legitimate union.
Short-styled form, by pollen of shortest sta- 9 2 9-5
mens of long-styled. Legitimate union.
Short-styled form, by pollen of own mid- 12 0 0
length stamens, Illegitimate union
Short-styled form, by pollen of own long-) 9 0
est stamens, Illegitimate union . f %
‘Short-styled form, by pollen of mid-length
stamens of long - Soe legitimate 1 0 0
upion. 2 wl,
Cuar. IV. OXALIS SPECIOSA. 175
containing on an average 10°31 seeds; whilst 39
flowers fertilised illegitimately did not yield a single
capsule or seed. Therefore the fertility of the six
legitimate to that of the several illegitimate unions,
as judged both by the proportion of flowers which
yielded capsules and by the average number of con-
tained seeds, is as 100 to 0.
Oxalis speciosa.—This species, which bears pink
flowers, was introduced from the Cape of Good Hope.
A sketch of the reproductive organs of the three
forms (Fig. 11) has already been given. The stigma
of the long-styled form (with the papill on its sur-
face included) is twice as large as that of the short-
styled, and that of the mid-styled intermediate in size.
The pollen-grains from the stamens in the three forms
are in their longer diameters as follows :—
Divisions of the
Micrometer,
From the longest stamens of short-styled. . . 15 to 16
ie mid-length _,, Pe * » 24 1
» longest stamens of mid-styled . . . 16
» shortest a # 11 to 12
» mid-length stamens of long-styled. . 14
» _ shortest an ” oe 12
Therefore the extreme difference in diameter is as
16 to 11, or as 100 to 69; but as the measurements
were taken at different times, they are probably only
approximately accurate. The results of my experiments
in fertilising the three forms are given in the following
table.
176 HETEROSTYLED TRIMORPHIC PLANTS. Cuar. IV
TABLE 29.
Oxalis speciosa.
upion, 5 6 6 ee ew ew
| Number Number ai
! , f be
Nature of Union. i Flowers Cupeules Sevds ne
fertilised. | produced. | Capsule,
Long-styled form, by pollen of longest
stamens of short - styled. Ges ae 19 15 57°4
union. . 6 6
Long-styled form, by pollen of longest)
stamens of mid-styled. a cated 4 3 59°0
union. 2. . .
Long-styled form, by pollen of own-form 9 2 42°5
mid-length stamens. Illegitimate unions:
Long-styled form, by pollen of own-form ll 0 0
shortest stamens. Illegitimate union
Long-styled form, by pollen of shortest
stameus of mid-styled, Illegitimate 4 0 0
union, 6 ewe ww ew Sy
Long-styled form, by pollen of mid-length
stamens of short-styled. Illegitimate 12 5 30°0
ubiOny. 6 se ee we SO ww
Mid-styled form, by pollen of mid-length
stamens of long-styled. Legitimate}, 3 3 63°6
HOB 4 ew ee 8 lh
Mid-styled form, by pollen of mid-length |
stamens of short-styled. Legitimate + 4 56°3
wnion, 2 6 6 ee ee r
Mid-styled form, by mixed pollen from
both own-form longest and shortest}: 9 2 19
stamens. Illegitimate union . .
Mid-styled form, by pollen of longest | .
stamens of short-styled. Illegitimate 12 1 8
Cuar. 1V. OXALIS SPECIOSA. 177
TaBLE 29—continued.
Oxalis speciosa.
| Number | Number | Average
N ‘ of of Number at
asure,of Unions ; Flowers | Capsules | Seeds per
fertilised. | produced. | Capsule
Short-styled form, by pollen of shortest
stamens of mid - styled. eee
unio. . 2. . .
stamens of alias ada Bakara
union. . . .
" Short-styled form, by pollen of own-form
longest starhens. Illegitimate union
Short-styled form, by pollen of own-form
Short-styled form, by pollen of eins
mid-length stamens. Illegitimate a)
Short-styled form, by both pollens mixed
together, of own-form longest and mid- 13 0 0
length stamens. Illegitimate union .
Short-styled form, by pollen of longest
stamens of mid-styled. Illegitimate 7 0 0
union, . 1 6 ew we ew
Short-styled form, by pollen of mid-length
stamens of long-styled. Illegitimate 10 1 54
union. 6 6 © 6 we we ew ww
We here see that thirty-six flowers on the three
forms legitimately fertilised yielded 30 capsules, these
containing on an average 58°36 seeds. Ninety-five
flowers illegitimately fertilised yielded 12 capsules,
containing on an average 28°58 seeds. Therefore the
fertility of the six legitimate to that of the twelve
illegitimate unions, as judged by the proportion of
flowers which yielded capsules, is as 100 to 15, and
judged by the average number of seeds per capsule as
100 to 49. This plant, in comparison with the two
South American species previously described, produces
178 HETEROSTYLED TRIMORPHIC PLANTS. Cuar IV,
many more seeds, and the illegitimately fertilised
Howers are not quite so sterile.
Oxalis rosea.—Hildebrand possessed in a living state
only the long-styled form of this trimorphic Chilian
species.* The pollen-grains from the two sets of
anthers differ in diameter as 9 to 7°5, or as 100 to 83.
lle has further shown that there is an analogous
difference between the gruins from the two sets of
anthers of the same flower in five other species of Oxalis,
besides those already described. The present species
differs remarkably from the long-styled form of the
three species previously experimented on, in a much
larger proportion of the flowers setting capsules when
fertilised with their own-form pollen. Hildebrand fer-
tilised 60 flowers with pollen from the mid-length
stamens (of either the same or another flower), and
they yielded no less tlian 55 capsules, or 92 per cent.
These capsules contained on an average 5°62 seeds;
but we have no means of judging how near an approach
this average makes to that from flowers legitimately
fertilised. He also fertilised 45 flowers with pollen
from the shortest stamens, and these yielded only 17
capsules, or 31 per cent., containing on an average
only 2°65 seeds. We thus see that about thrice as
many flowers, when fertilised with pollen from the
mid-length stamens, produced capsules, and these
contained twice as many seeds, as did the flowers
fertilised with pollen. from the shortest stamens.
It thus appears (and we find some evidence of
the same fact with O. speciosa), that the same rule
holds good with Oxalis as with Lythrum salicaria;
namely, that in any two unions, the greater the in-
equality in length between the pistils and stamens, or,
* ‘Monatsber, der Akad. dir Wiss. Berlin, 1866, p. 872
Cuar. IV. OXALIS, OTHER SPECIES OF. 179
which is the same thing, the greater the distance of
the stigma from the anthers, the pollen of which is
used for fertilisation, the less fertile is the union,—
whether judged by the proportion of flowers which
set capsules, or by the average number of seeds per
capsule. The rule cannot be explained in this case
any more than in that of Lythrum, by supposing
that wherever there is greater liability to self-fertilisa-
tion, this is checked by the union being rendered more
sterile; for exactly the reverse occurs, the liability to
self-fertilisation being greatest in the unions between
the pistils and stamens which approach each other the
nearest, and these are the more fertile. I may add
that I also possessed some long-styled plants of this
species: one was covered by a net, and it set sponta-
neously a few capsules, though extremely few com-
pared with those produced by a plant growing by
itself, but exposed to the visits of bees.
With most of the species of Oxalis the short-styled
form seems to be the most sterile of the three forms,
when these are illegitimately fertilised ; and I will add
two other cases to those already given. I fertilised
29 short-styled flowers of O. compressa with pollen from
their own two sets of stamens (the pollen-grains of
which differ in diameter as 100 and 83), and not one
produced a capsule. I formerly cultivated during
several years the short-styled form of a species pur-
chased under the name of 0. Bowii (but I have some
doubts whether it was rightly named), and fertilised
many flowers with their own two kinds of pollen,
which differ in diameter in the usual manner, but
never got a single seed. On the other hand, Hilde-
brand says that the short-styled form of O. Deppei,
growing by itself, yields plenty of seed; but it is not
positively known that this species is heterostyled ; and.
180 HETEROSTYLED TRIMORPHIC PLANTS. Cuar. IV.
the pollen-grains from the two sets of anthers do not
differ in diameter.
Some facts communicated to me by Fritz Miller
afford excellent evidence of the utter sterility of one
of the forms of certain trimorphic species of Oxalis,
when growing isolated. He has seen in St. Catharina,
in Brazil, a large field of young sugar-cane, many
acres in extent, covered with the red blossoms. of one
form alone, and these did not produce a single seed.
His own land is covered with the short-styled form of
a white-flowered trimorphic species, and this is equally
sterile; but when the three forms were planted near
together in his garden they seeded freely. With two
other trimorphic species he finds that isolated plants
are always sterile.
Fritz Miller formerly believed that a species of
Oxalis, which is so abundant in St. Catharina that it
borders the roads for miles, was dimorphic instead of
trimorphic. Although the pistils and stamens vary
greatly in length, as was evident in some specimens
sent to me, yet the plants can be divided into two
sets, according to the lengths of these organs. A
large proportion of the anthers are of a white colour
and quite destitute of pollen; others which are pale
yellow contain many bad with some good grains; and
others again which are bright yellow have apparently
sound pollen; but he has never succeeded in finding
any fruit on this species. The stamens in some of
the flowers are partially converted into petals. Fritz
Miller after reading my description, hereafter to be
given, of the illegitimate offspring of various hetero-
styled species, suspects that these plants of Oxalis
may be the variable and sterile offspring of a single
forn: of some trimorphic species, perhaps accidentally
introduced into the district, which has since been
Caar. IV. OXALIS, HOMOSTYLED SPECIES. 181
propagated asexually. It is probable that this kind
of propagation would be much aided by there being
no expenditure in the production of seed. ~
Oxalis (Biophytum) sensitiva.—This plant is ranked
by many botanists as a distinct genus. Mr. Thwaites
sent me a number of flowers preserved in spirits from
Ceylon, and they are clearly trimorphic. The style
of the long-styled form is clothed with many scattered
hairs, both simple and glandular; such hairs are much
fewer on the style of the mid-styled, and quite ab-
sent from that of the short-styled form; so that this
plant resembles in this respect 0. Valdiviana and
Regnelli. Calling the length of the two lobes of
the stigma of the long-styled form 100, that of
the mid-styled is 141, and that of the short-styled
164. In all other cases, in which the stigma in this
genus differs in size in the three forms, the differ-
ence is of a reversed nature, the stigma of the long-
styled being the largest, and that of the short-styled
the smallest. The diameter of the pollen-grains from
the longest stamens being represented by 100, those
from the mid-length stamens are 91, and those from
the shortest stamens 84 in diameter. This plant is
remarkable, as we shall see in the last chapter of
this volume, by producing long-styled, mid-styled,
and short-styled cleistogamic flowers.
Homostyled Species of Oxalis.—Although the majority
of the species in the large genus Oxalis seem to be
trimorphic, some are homostyled, that is, exist under
a single form; for instance the common O. aceto-
sella, and according to Hildebrand two other widely
distributed European species, O. stricta and corniculata.
Fritz Miller also informs me that a similarly consti-
tuted species is found in St. Catharina, and that it ia
182 HETEROSTYLED TRIMORPHIC PLANTS. Cuar. IV
quite fertile with its own pollen when insects are ex-
cluded. The stigmas of O. stricta and of another homo-
styled species, viz. O. tropsoloides, commonly stand on
a level with the upper anthers, and both these species
are likewise quite fertile when insects are excluded.
With respect to O. acetosella, Hildebrand says that in
all the many specimens examined by him the pistil
exceeded the longer stamens in length. I procured
108 flowers from the same number of plants growing in
three distant parts of England; of these 86 had their
stigmas projecting considerably above, whilst 22 had
them nearly on a level with the upper anthers. In
one lot of 17 flowers from the same wood, the stigmas in
every flower projected fully as much above the upper
anthers as these stood above the lower anthers. So
that these plants might fairly be compared with the
long-styled form of a heterostyled species; and I at
first thought that O. acetosella was trimorphic. But
the case is one merely of great variability. The
pollen-grains from the two sets of anthers, as observed
by Hildebrand and myself, do not differ in diameter.
I fertilised twelve flowers on several plants with pol-
len from a distinct plant, choosing those with pistils
of a different length; and 10 of these (i.e. 83 per cent.)
produced capsules, which contained on an average 7-9
seeds. Fourteen flowers were fertilised with their own
pollen, and 11 of these (i.e. 79 per cent.) yielded cap-
sules, containing a larger average of seed, namely 9:2.
These plants, therefore, in function show not the
least sign of being heterostyled. I may add that 18
flowers protected by a net were left to fertilise them-
selves, and only 10 of these (i.e. 55 per cent.) yielded
capsules, which contained on an average only 6°3 seeds.
So that the access of insects, or artificial aid in placing
pollen on the stigma, increases the fertility of the
Cuap. IY. PONTEDERIA. 183
flowers; and I found that this applied especially te
those having shorter pistils. It should be remem-
bered that the flowers hang downwards, so that those
with short pistils would be the least likely to receive
their own pollen, unless they were aided in some
manner.
Finally, as Hildebrand has remarked, there is no
evidence that any of the heterostyled species of Oxalis
are tending towards a dicecious condition, as Zuccarini
and Lindley inferred from the differences in the re-
productive organs of the three forms, the meaning of
which they did not understand.
PonTeDERIA [spP. ?] (PONTEDERIACEZ.)
Fritz Miller found this aquatic plant, which is al-
lied to the Liliacez, growing in the greatest profusion
on the banks of a river in Southern Brazil.* But only
two forms were found, the flowers of which include
three long and three short stamens. The pistil of the
long-styled form, in two dried flowers which were sent
me, was in length as 100 to 32, and its stigma as 100
to 80, compared with the same organs in the short-
styled form. The long-styled stigma projects conside-
rably above the upper anthers of the same flower, and
stands on a level with the upper ones of the short-styled
form. In the latter the stigma is seated beneath both its
own sets of anthers, and is on a level with the anthers
of the shorter stamens in the long-styled form. The
anthers of the longer stamens of the short-styled form
are to those of the shorter stamens of the long-styled
form as 100 to 88 in length. The pollen-grains distended
=“Ueber den Trimorphismus Zeitschrift” &c., Band 6, 1871,
der Pontedcrien”; ‘Jenaische p. 74.
13
184 HETEROSTYLED TRIMORPHIC PLANTS. Cuar. IV.
with water from the longer stamens of the short-styled
form are to those from the shorter stamens of the same
form as 100 to 87 in diameter, as deduced from ten
measurements of each kind. We thus see that the
organs in these two forms differ from one another
and are arranged in an analogous manner, as in the
long and short-styled forms of the trimorphic species
_ of Lythrum and Oxalis. Moreover, the longer stamens
of the long-styled form of Pontederia, and the shorter
ones of the short-styled form are placed in a proper
position for fertilising the stigma of a mid-styled form.
But Fritz Miller, although he examined a vast number
of plants, could never find one belonging to the mid-
styled form. The older flowers of the long-styled
and short-styled plants had set plenty of apparently
good fruit; and this might have been expected, as
they could legitimately fertilise one another. Al-
though he could not find the mid-styled form of
this species, he possessed plants of another species
growing in his garden, and all these were mid-styled ;
and in this case the pollen-grains from the anthers of
the longer stamens were to those from the shorter sta-
mens of the same flower as 100 to 86 in diameter, as
deduced from ten measurements of each kind. These
mid-styled plants growing by themselves never pro-
duced a single fruit.
Considering these several facts, there can hardly be
a doubt that both these species of Pontederia are
heterostyled and trimorphic. This case is an interest-
ing one, for no other Monocotyledonous plant is known
to be heterostyled. Moreover, the flowers are irregular,
and all other heterostyled plants have almost sym-
metrical flowers. The two forms differ somewhat in
the colour of their corollas, that of the short-styled
being of a darker blue, whilst that of the long-styled
Cuap. IV. PONTEDERIA. 185
tends towards violet, and no other such case is known.
Lastly, the three longer stamens alternate with the
three shorter ones, whereas in Lythrum and Oxalis
the long and short stamens belong to distinct whorls.
With respect to the absence of the mid-styled form in
the case of the Pontederia which grows wild in Southern
Brazil, this would probably follow if only two forms
had been originally introduced there ; for, as we shall
hereafter see from the observations of Hildebrand,
Fritz Miller and myself, when one form of Oxalis is
fertilised exclusively by either of the other two forms,
the offspring generally belong to the two parent-
forms.
Fritz Miller has recently discovered, as he informs
me, a third species of Pontederia, with all three forms
growing together in pools in the interior of S. Brazil ;
so that no shadow of doubt can any longer remain
about this genus including trimorphic species. He
sent me dried flowers of all three forms. In the long-
styled form the stigma stands a little above the tips of
the petals, and on a level with the anthers of the
longest stamens in the other two forms. The pistil is
in length to that of the mid-styled as 100 to 56, and
to that of the short-styled as 100 to 16. Its summit is
rectangularly bent upwards, and the stigma is rather
broader than that of the mid-styled, and broader in
about the ratio of 7 to 4 than that of the short-styled.
In the mid-styled form, the stigma is placed rather
above the middle of the corolla, and nearly on a level
with the mid-length stamens in the other two forms;
its summit is a little bent upwards. In the short-
styled form the pistil is, as we have seen, very short,
and differs from that in the other two forms in being
straight. It stands rather beneath the level of the
anthers of the shortest stamens in the long-styled and
186 HETEROSTYLED TRIMORPHIC PLANTS. Cuap. IV.
mid-styled forms. The three anthers of each set of
stamens, more especially those of the shortest stamens,
are placed one beneath the other, and the ends of the
filaments are bowed a little upwards, so that the pollen
from all the anthers would be effectively brushed off
by the proboscis of a visiting insect. The relative
diameters of the pollen-grains, after having been long
soaked in water, are given in the following list, as
measured by my son Francis.
Divisions of the
Micrometer.
Long-styled form, from the mid-length stamens . . . 13°2
: (Average of 20 measurements.)
” 5 from the shortest stamens . . . . 9°0
(10 measurements.)
Mid-styled form, from the longest stamens . . . . 16°4
(15 measurements.)
- $5 from the shortest stamens. . . . 9°1
(20 measurements.)
Short-styled form, from the longest stamens . . . . 14°6
(20 measurements.)
a ss from the mid-length stamens . . . 12°3
(20 measurements.)
We have here the usual rule of the grains from the
longer stamens, the tubes of which have to penetrate
the longer pistil, being larger than those from the
stamens of less length. The extreme difference in
diameter between the grains from the longest stamens
of the mid-styled form, and from the shortest stamens
of the long-styled, is as 16-4 to 9-0, or as 100 to 55;
and this is the greatest difference observed by me in
any heterostyled plant. It is a singular fact that the
grains from the corresponding longest stamens in the
two forms differ considerably in diameter; as do those
in a lesser degree from the corresponding mid-length
stamens in the two forms; whilst those from the cor-
responding shortest stamens in the long- and mid-
styled forms are almost exactly equal. ‘Their in-
equality in the two first cases depends on the grains
“Cuar. IV. PONTEDERIA. 187
in both sets of anthers in the short-styled form being
smaller than those from the corresponding anthers in
the other two forms; and here we have a case parallel
with that of the mid-styled form of Lythrum salicaria.
In this latter plant the pollen-grains of the mid-styled
forms are of smaller size and have less fertilising power
than the corresponding ones in the other two forms ;
whilst the ovarium, however fertilised, yields a greater
number of seeds; so that the mid-styled form is alto-
gether more feminine in nature than the other two
forms. In the case of Pontederia, the ovarium in-
cludes only a single ovule, and what the meaning of
the difference in size between the pollen-grains from
the corresponding sets of anthers may be, I will not
pretend to conjecture.
The clear evidence that the species just described is
heterostyled and trimorphic is the more valuable as
there is some doubt with respect to P. cordata, an in-
habitant of the United States. Mr. Leggett suspects*
that it is either dimorphic or trimorphic, for the
pollen-grains of the longer stamens are “more than
twice the diameter or than eight times the mass of
the grains of the shorter stamens. Though minute,
these smaller grains seem as perfect as the larger
ones.” Qn the other hand, he says that in all the
mature flowers, “the style was as long ag least as
the longer stamens;” “whilst in the young flowers
it was intermediate in length between the two sets of
stamens ;” and if this be so, the species can hardly be
heterostyled.
* ‘Bull of the Torrey Botanical Club,’ 1875, vol. vi. p. 62.
188 ILLEGITIMATE OFFSPRING OF Cuap. VY.
’ CHAPTER V.
ILLEGITIMATE OFFSPRING OF HETEROSTYLED PLANTS,
INevgitimate offspring from all three forms of Lythrum salicaria—Their
dwarfed stature and sterility, some utterly barren, some fertile—
Oxalis, transmission of form to the legitimate and illegitimate
seedlings—Primula Sinensis, illegitimate offspring in some degree
dwarfed and infertile—Equal-styled varicties of P. Sinensis, auri-
cula, farinosa, and elatior—P. vulgaris, red-flowered variety, illegi-
timate seedlings sterile —P. veris, illegitimate plants raised during
several successive generations, their dwarfed stature and sterility—
Equal-styled varieties of P. veris—Tyransmission of form by Pul-
monaria and Polygonum—Concluding remarks—Close parallelism
between illegitimate fertilisation and hybridism.
WE have hitherto treated of the fertility of the flowers
of heterostyled plants, when legitimately and illegiti-
mately fertilised. The present chapter will be devoted
to the character of their offspring or seedlings. Those
raised from legitimately fertilised seeds will be here
called legitimate seedlings or plants, and those from
illegitimately fertilised seeds, illegitimate seedlings or
plants. They differ chiefly in their degree of fertility,
and in their powers of growth or vigour. I will begin
with trimorphic plants, and I must remind the reader
that each of the three forms can be fertilised in six
different ways; so that all three together can be ferti-
lised in eighteen different ways. For instance, a
long-styled form can be fertilised legitimately by the
longest stamens of the mid-styled and short-styled
forms, and illegitimately by its own-form mid-length
and shortest stamens, also by the mid-length stamens
of the mid- -styled and by the shortest stamens of the
short-styled form; so that the long-styled can be ferti-
Cuar. V. HETEROSTYLED TRIMORPHIC PLANTS. 189
lised legitimately in two ways and illegitimately in
four ways. The same holds good with respect to the
mid-styled and short-styled forms. Therefore with
trimorphic species six of the eighteen unions yield
legitimate offspring, and twelve yield illegitimate
offspring.
I will give the results of my experiments in detail,
partly because the observations are extremely trouble-
some, and will not probably soon be repeated—thus, I
was compelled to count under the microscope above
20,000 seeds of Lythrum salicaria—but chiefly because
light is thus indirectly thrown on the important sub-
ject of hybridism.
LyTHRUM SALICARIA.
Of the twelve illegitimate unions two were com-
pletely barren, so that no seeds were obtained, and of
course no seedlings could be raised. Seedlings were,
however raised from seven of the ten remaining il-
legitimate unions. Such illegitimate seedlings when
in flower were generally allowed to be freely and
legitimately fertilised, through the agency of bees, by
other illegitimate plants belonging to the two other
forms growing close by. This is the fairest plan, and
was usually followed; but in several cases (which
will always be stated) illegitimate plants were ferti-
lised with pollen taken from legitimate plants be-
longing to the other two forms; and this,as might
have been expected, increased their fertility. Lythrum
salicaria is much affected in its fertility by the nature
of the season; and to avoid error from this source,
as far as possible, my observations were continued
during several. years. Some few experiments were
tried in 1863. The summer of 1864 was too hot and
190 ILLEGITIMATE OFFSPRING OF Cuar. V
dry, and, though the plants were copiously watered,
some few apparently suffered in their fertility, whilst
others were not in the least affected. The years
1865 and, especially, 1866, were highly favourable.
Only a few observations were made during 1867.
The results are arranged in classes according to the
parentage of the plants. In each case the average
number of seeds per capsule is given, generally taken
from ten capsules, which, according to my experience,
is a nearly sufficient number. The maximum num-
ber of seeds in any one capsule is also given; and
this is a useful point of comparison with the nor-
mal standard—that is, with the number of seeds
produced by legitimate plants legitimately ferti-
lised. I will give likewise in each case the minimum
number. When the maximum and minimum differ
greatly, if no remark is made on the subject, it may
be understood that the extremes are so closely con-
nected by intermediate figures that the average isa
fair one. Large capsules were always selected for
counting, in order to avoid over-estimating the infer-
tility of the several illegitimate plants.
In order to judge of the degree of inferiority in
fertility of the several illegitimate plants, the follow-
ing statement of the average and of the maximum
number of seeds produced by ordinary or legitimate
plants, when legitimately fertilised, some artificially
and some naturally, will serve as a standard of com-
parison, and may in each case be referred to. But I
give under each experiment the percentage of seeds
produced by the illegitimate plants, in comparison
with the standard legitimate number of the same
form. For instance, ten capsules from the illegitimate -
‘long-styled plant (No. 10), which was legitimately
and naturally fertilised by other illegitimate plants,
Coar. V. HETEROSTYLED TRIMORPHIC PLANTS. 191
contained on an average 44°2 seeds; whereas the
capsules on legitimate long-styled plants, legitimately
and naturally fertilised by other legitimate plants,
contained on an average 93 seeds. Therefore this
illegitimate plant yielded only 47 per cent. of the
full and normal complement of seeds.
Standard Number of Seeds produced by Legitimate Plants
of the three Forms, when legitimately fertilised.
Long-styled form: average number of seeds in each
capsule, 93 ; maximum number observed out of twenty-
three capsules, 159.
Mid-styled form: average number of seeds, 180;
maximum number observed out of thirty-one capsules,
151.
Short-styled form: average number of seeds, 83°5 ;
Lut we may, for the sake of brevity, say 83; maximum
number observed out of twenty-five capsules, 112.
Cuasses I. and II. Illegitimate Planis raised from
Long-styled Parents fertilised with pollen from the
mid-length or the shortest stamens of other plants of
the same form.
From this union I raised at different times three
lots of illegitimate seedlings, amounting altogether to
56 plants. I must premise that, from -not foreseeing
the result, I did not keep a memorandum whether the
eight plants of the first lot were the product of the
mid-length or shortest stamens of the same form ; but
I have good reason to believe that they were the pro-
‘luct of the latter. These eight plants were much more
(lwarfed, and much more sterile than those in the other
two lots. The latter were raised from a long-styled
192 ILLEGITIMATE OFFSPRING OF Cuar. V.
plant growing quite isolated, and fertilised by the
agency of bees with its own pollen; and it is almost
certain, from the relative position of the organs of
fructification, that the stigma under these circum-
-stances would receive pollen from the mid-length
stamens.
All the fifty-six plants in these three lots proved long-
styled ; now, if the parent-plants had been legitimately
fertilised by pollen from the longest stamens of the
mid-styled and short-styled forms, only about one-
third of the seedlings would have been long-styled,
the other two-thirds being mid-styled and short-styled.
In some other trimorphic and dimorphic genera we
shall find the same curious fact, namely, that the long-
styled form, fertilised illegitimately by its own-form
pollen, produces almost exclusively long-styled seed-
lings.*
The eight plants of the first lot were of low stature:
three which I measured attained, when fully grown, the
heights of only 28, 29, and 47 inches; whilst legitimate
plants growing close by were double this height, one
heing 77 inches. They all betrayed in their general
appearance a weak constitution ; they flowered rather
later in the season, and at a later age than ordinary
plants. Some did not flower every year ; and one plant,
behaving in an unprecedented manner, did not flower
until three years old. In the two other lots none of
the plants grew quite to their full and proper height,
as could at once be seen by comparing them with the
adjoining rows of legitimate plants. In several plants
in all three lots, many of the anthers were either
shrivelled or contained brown and tough, or pulpy
* Hildebrand fimt ealled atten- of Primula Sinensis ; but his re-
tion (‘ Bot. Zeitung,’ Jan. 1, 1864, sults were not nearly so uniform
p. 5) to this fact in the case as mine,
Cuar. V. HETEROSTYLED TRIMORPHIC PLANTS. 1938
matter, without any good pollen-grains, and they never
shed their contents; they were mm the state designated
by Gartner * as contabescent, which term I will for the
future use. In one flower all the anthers were conta-
bescent excepting two which appeared to the naked
eye sound ; but under the microscope about two-thirds
of thepollen-grains were seen to be small and shrivelled.
In another plant, in which all the anthers appeared
sound, many of the pollen-grains were shrivelled and
of unequal sizes. I counted the seeds produced by
seven plants (1 to 7) in the first lot of eight plants,
probably the product of parents fertilised by their
own-form shortest stamens, and the seeds produced by
three plants in the other two lots, almost certainly the
product of parents fertilised by their own-form mid-
length stamens.
Plant 1. This long-styled plant was allowed during 1863 to
be freely and legitimately fertilised by an adjoining illegitimate
mid-styled plant, but it did not yield a single seed-capsule. It
was then removed and planted in a remote place close to a
brother long-styled plant No. 2, so that it must have been freely
though illegitimately fertilised; under these circumstances it
did not yield during 1864 and 1865 a single capsule. I should
here state that a legitimate or ordinary long-styled plant, when
growing isolated, and freely though illegitimately fertilised by
insects with its own pollen, yielded an immense number of
capsules, which contained on an average 21°5 seeds.
Plunt 2 This long-styled plant, after flowering during 1863
close to an illegitimate mid-styled plant, produced less than
twenty capsules, which contained on an average between four
and five seeds. When subsequently growing in company with
No. 1, by which it will have been illegitimately fertilised, it
yiclded in 1866 not a single capsule, but in 1865 it yielded
twenty-two capsules: the best of these, fifteen in number, were
examined; eight contained no seed, and the remaining seven
eontained on an average only three seeds, and these seeds were
* ‘ Beitrige zur Kenntniss der Befruchtung,’ 1844, p. 116,
194 ILLEGITIMATE OFFSPRING OF Cuap. V.
s0 small and shrivelled that I doubt whether they would have
germinated. -
Plants 3 and 4. These two long-styled plants, after being
freely and legitimately fertilised during 1863 by the same iile-
gitimate mid-styled plant as in the last case, were as miserably
sterile as No. 2.
Plant 5. This long-styled plant, after flowering in 1863 close
to an illegitimate mid-styled plant, yielded only four capsules,
which altogether included only five seeds. During 1864, 1865,
and 1866, it was surrounded either by illegitimate or legitimate
plants of the other two forms; but it did not yield a single
capsule. It was a superfluous experiment, but I likewise arti-
ficially fertilised in a legitimate manner twelve flowers; but uot
one of these produced a capsule; so that this plant was almost
absolutely barren.
Plant 6. This long-styled plant, after flowering during the
favourable year of 1866, surrounded by illegitimate plants of
the other two forms, did not produce a single capsule.
Plant 7. This long-styled plant was the most fertile of the
eight plants of the first lot. During 1865 it was surrounded by
illegitimate plants of various parentage, many of which were
highly fertile, and must thus have been legitimately fertilised.
It produced a good many capsules, ten of which yielded an
average of 36°1 seeds, with a maximum of 47 and a minimum
of 22; so that this plant produced 89 per cent. of the full
number of sceds. During 1864 it was surrounded by legitimate
and illegitimate plants of the other two forms; and nine
capsules (one poor one being rejected) yielded an average of
41-9 seeds, with a maximum of 56 and a minimum of 28; so
that, under these favourable circumstances, this plant, the most
fertile of the first lot, did not yield, when legitimately fertilised,
quite 45 per cent. of the full complement of seeds.
In the second lot of plants in the present class,
descended from the long-styled form, almost certainly
fertilised with pollen from its own mid-length stamens,
the plants, as already stated, were not nearly so dwarfed
or so sterile as in the first lot. All produced plenty
of capsules. I counted the number of seeds in only
three plants, viz. Nos. 8, 9, and 10.
Cuar, V. HETEROSTYLED TRIMORPHIC PLANTS. 195
Plant 8. This plant was allowed to be freely fertilised in 1864
by legitimate and illegitimate plants of the other two forms,
and ten capsules yielded on an average 41°1 seeds, with a
maximum of 73 and a minimum of 11. Hence this plant pro-
duced only 44 per cent. of the full complement of seeds.
Plunt 9, This long-styled plant was allowed in 1865 to be
freely fertilised by illegitimate plants of the other two forms,
most of which were moderately fertile. Fifteen capsules yielded
on an average 57°1 seeds, with a maximum of 86anda minimum
of 23. Hence the plant yielded 61 per cent. of the full comple-
inent of seeds.
Plant 10 This long-styled plant was freely fertilised at the
same time and in the same manner as the last. Ten capsules
yielded an average of 44:2 seeds, with a maximum of 69 anda
minimum of 25; hence this plant yielded 47 per cent. of the
full complement of seeds.
The nineteen long-styled plants of the third lot, of
the same parentage as the last lot, were treated dif-
ferently ; for they flowered during 1867 by themselves
so that they must have been illegitimately fertilised
by one another. It has already been stated that a
legitimate long-styled plant, growing by itself and
visited by insects, yielded an average of 21°5 seeds
per capsule, with a maximum of 35; but, to judge
fairly of its fertility, it ought to have been observed
during successive seasons. We may also infer from
analogy that, if several legitimate long-styled plants
were to fertilise one another, the average number of
seeds would be increased; but how much increased
I do not know; hence I have no perfectly fair standard
of comparison by which to judge of the fertility of the
three following plants of the present lot, the seeds of
which I counted.
Plant 11. This long-styled plant produced a large crop of
capsules, and in this respect was one of the most fertile of
the whole lot of nineteen plants. But the average from ten
196 ILLEGITIMATE OFFSPRING OF Cuar. V,
capsules was only 35:9 seeds, with a maximum of 60 anda
minimum of 8.
Plant 12. This long-styled plant produced very few capsules;
and ten yielded an average of only 15:4 seeds, with a maximum
of 30 and a minimum of 4.
Plant 13. This plant offers an anomalous case; it flowered
profusely, yet produced very few capsules; but these con-
tained numerous seeds. Ten capsules yielded an average of
71:9 seeds, with a maximum of 95 and a minimum of 29. Con-
sidcring that this plant was illegitimate and illegitimately fer-
tilised by its brother long-styled scedlings, the average and the
maximum are so remarkably high that I cannot at all undcr-
stand the case. We should remember that the average for a
legitimate plant legitimately fertilised is 93 seeds.
Cuass III. Illegitimate Plants raised from a Short-
styled Parent fertilised with pollen from own-form
mid-length stamen,
I raised from this union nine plants, of which eight
were short-styled and one long-styled ; so that there
seems to be a strong tendency in this form to repro-
duce, when self-fertilised, the parent-form; but the
tendency is not so strong as with the long-styled.
These nine plants never attained the full height of
legitimate plants growing close to them. The anthers
were contabescent in many of the flowers on several
plants.
Plant 14, This short-styled plant was allowed during 1865 to
be freely and legitimately fertilised by illegitimate plants de-
scended from self-fertilised mid-, long- and short-styled plants.
Fifteen capsules yielded an average of 28°3 seeds, with a
maximum of 51 and a minimum of 11; hence this plant
produced only 83 per cent. of the proper number of sceds. Tho
seeds themselves were small and irregular in shape. Although
so sterile on the female side, none of the anthers were conta-
bescent.
Plant 15, This short-styled plant, treated like the last during
Cuar. V. HETEROSTYLED TRIMORPHIC PLANTS. 197
the same year, yielded an average, from fifteen capsules, of 27
sceds, with a maximum of 49 anda minimum of 7. But two
poor capsules may be rejected, and then the average rises to
82°6, with the same maximum of 49 and a minimum of 20; so
that this plant attained 88 per cent. of the normal standard of
fertility, and was rather more fertile than the last, yet many of
the anthers were contabescent.
Plant 16. This short-styled plant, treated like the two last,
yielded from ten capsules an average of 77°8 secds, with a
maximum of 97 and a minimum of 60; so that this plant
produced 94 per cent. of the full number of sceds.
Plant 17. This, the one long-styled plant of the same parent-
age as the last three plants, when freely and legitimately ferti-
lised in the same manner as the last, yielded an average from
ten capsules of 76°3 rather poor seeds, with a maximum of 88
and a minimum of 57. Hence this plant produced 82 per cent.
of the proper number of seeds. Twelve flowers enclosed in a
net were artificially and legitimately fertilised with pollen from
a legitimate short-styled plant; and nine capsules yielded an
average of 82°5 seeds, with a maximum of 98 anda minimum
of 51; so that its fertility was increased by the action of
pollen from a legitimate plant, but still did not reach the normal
standard.
Crass IV. Illegitimate Plants raised from a Mid-styled
_ Parent fertilised with pollen from own-form longest
stamens.
After two trials, I succeeded in raising only four
plants from this illegitimate union. These proved to
be three mid-styled and one long-styled; but from so
small a number we can hardly judge of the tendency
in mid-styled plants when self-fertilised to reproduce
the same form. These four plants never attained their
full and normal height; the long-styled plant had
several of its anthers contabescent.
Plant 18, This mid-styled plant, when freely and legitimately
fertilised during 1865 by illegitimate plants descerided from
self-fertilised long-, short-, and mid-styled plants, yielded an
average from ten capsules of 102°6 seeds, with a maximum of
198 ILLEGITIMATE OFFSPRING OF Cuap. V.
131 and a minimum of 68: hence this plant did not produce
quite 80 per cent. of the normal number of seeds. Twelve
flowers were artificially and legitimately fertilised with pollen
from a legitimate long-styled plant, and yielded from nine
capsules an average of 116°1 seeds, which were finer than
in the previous case, with a maximum of 135 and a minimum
of 75; so that, as with Plant 17, pollen from a legitimate
plant increased the fertility, but did not bring it up to the full
standard.
Plant 19. This mid-styled plant, fertilised in the same manner
and at the same period as the last, yielded an average from
ten capsules of 73°4 seeds, with a maximum of 87 and a mini-
mum of 64: hence this plant produced only 56 per cent. of the
full number of seeds. Thirteen flowers were artificially and
legitimately fertilised with pollen from a legitimate long-styled
plant, and yielded ten capsules with an average of 95°6 seeds;
so that the application of pollen from a legitimate plant added,
as in the two previous cases, to the fertility, but did not bring
it up to the proper standard.
Plant 20. This long-styled plant, of the same parentage with
the two last mid-styled plants, and freely fertilised in the same
manner, yielded an average from ten capsules of 69°6 seeds,
with a maximum of 83 and a minimum of 52: hence this plant
produced 75 per cent. of the full number of seeds.
Cuass V. Illegitimate Plants raised from a Short-styled
Parent fertilised with pollen from the mid-length
stamens of the long-styled form.
In the four previous classes, plants raised from the
three forms fertilised with pollen from either the longer
or shorter stamens of the same form, but generally not
from the same plant, have been described. Six other
illegitimate unions ‘are possible, namely, between the
three forms and the stamens in the other two forms
which do not correspond in height with their pistils.
But I succeeded in raising plants from only three of
these six unions. Irom one of them, forming the pre-
sent Class V., twelve plants were raised; these con-
sisted of eight short-styled, and four long-styled plants,
Cuar. V. HETEROSTYLED TRIMORPHIC PLANTS. 199
with not one mid-styled. These twelve plants never
attained quite their full and proper height, but by no
means deserved to be called dwarfs. The anthers in
some of the flowers were contabescent. One plant was
remarkable from all the longer stamens in every flower
and from many of the shorter ones having their
anthers in this condition. The pollen of four other
plants, in which none of the anthers were contabe-
scent, was examined; in one a moderate number of
grains were minute and shrivelled, but in the other
three they appeared perfectly sound. With respect to
the power of producing seed, five plants (Nos. 21 to
25) were observed: one yielded scarcely more than
half the normal number; a second was slightly infer-
tile; but the three others actually produced a larger
average number of seeds, with a higher maximum,
than the standard. In my concluding remarks I shall
recur to this fact, which at first appears inexplicable.
Plant 21. This short-styled plant, freely and legitimately
fertilised during 1865 by illegitimate plants, descended from
self-fertilised long-, mid- and short-styled parents, yielded an
average from ten capsules of 48 seeds, with a maximum of 63
and a minimum of 26: hence this plant, which was the one
with all its longer and many of its shorter stamens contabescent,
produced only 52 per cent. of the proper number of seeds.
Plant 22. This short-styled plant produced perfectly sound
pollen, as viewed under the microscope. During 1866 it was
freely and legitimately fertilised by other illegitimate plants
belonging to the present and the following class, both of which
include many highly fertile plants. Under these circumstances
it yielded from eight capsules an average of 100-5 sceds, with
a maximum of 123 and a minimum of 86; so that it produceu
121 per cent. of seeds in comparison with the normal standard.
During 1864 it was allowed to be freely and legitimately ferti-
lised by legitimate and illegitimate plants, and yielded an
average, from eight capsules, of 104°2 seeds, with a maximum
of 125 and a minimum of 90; consequently it exceeded the
normal standard, producing 125 per ccnt. of seeds. In this
14
200 ILLEGITIMATE OFFSPRING OF Cuar. V
case, as in some previous cases, pollen from legitimate plants
added in a small degree to the fertility of the plant; and the
fertility would, perhaps, have been still greater had not the
summer of 1364 been very hot and certainly unfavourable to
some of the plants of Lythrum.
Plant 23. This short-styled plant produced perfectly sound
pollen. During 1866 it was freely and legitimately fertilised by
the other illegitimate plants specified under the last experi-
ment, and eight capsules yielded an average of 113°5 seeds,
with a maximum of 123 and a minimum of 93. Hence this
plant exceeded the normal standard, producing no less than 136
per cent. of seeds.
Plant 24. This long-styled plant produced pollen which
seemed under the microscope sound; but some of the grains
did not swell when placed in water. During 1864 it was
legitimately fertilised by legitimate and illegitimate plants in
the same manner as Plant 22, but yielded an average, from ten
capsules, of only 55 seeds, with a maximum of 88 and a mini-
mum of 24, thus attaining 59 per cent. of the normal fertility.
This low degree of fertility, I presume, was owing to the un-
favourable season; for during 1866, when legitimately fertilised
by illegitimate plants in the manner described under No. 22, it
yielded an average, from eight capsules, of 82 seeds, with a
maximum of 120 and a minimum of 67, thus producing 88 per
cent. of the normal number of seeds.
Plunt 25. The pollen of this long-styled plant contained a
moderate number of poor and shrivelled grains; and this isa
surprising circumstance, as it yielded an extraordinary number
of seeds. During 1866 it was freely and legitimately fertilised
by illegitimate plants, as described under No. 22, and yielded
an average, from eight capsules, of 122°5 seeds, with a maximum
of 149 and a minimum of 84. Hence this plant exceeded
the normal standard, producing no less than 131 per cent. of
sceds,
Cuass VI. Illegitimate Plants raised from Mid-styled
Parents fertilised with pollen from the shoriest
stamens of the long-styled form.
I raised from this union twenty-five plants, which
proved to be seventeen long-styled and eight mid-
Cuar. V. HETEROSTYLED TRIMORPHIC PLANTS. 201
styled, but not one short-styled. None of these plants
were in the least dwarfed. I examined, during the
highly favourable season of 1866, the pollen of four
plants: in one mid-styled plant, some of the anthers of
the longest stamens were contabescent, but the pollen-
grains in the other anthers were mostly sound, as
they were in all the anthers of the shortest stamens ;
in two other mid-styled and in one long-styled plant
many of the pollen-grains were small and shrivelled ;
and in the latter plant as many as a fifth or sixth part
appeared to be in this state. I counted the seeds in
five plants (Nos. 26 to 30), of which two were mode-
rately sterile and three fully fertile.
Plant 26. This mid-styled plant was freely and legitimately
fertilised, during the rather unfavourable year 1864, by numer-
ous surrounding legitimate and illegitimate plants. It yielded
an average, from ten capsules, of 88°5 seeds, with a maximum
of 110 and a minimum of 64, thus attaining 64 per cent. of the
normal fertility. During the highly favourable year 1866, it
was freely and legitimately fertilised by illegitimate plants
belonging to the present Class and to Class V., and yielded
an average, from eight capsules, of 86 seeds, with a maximum
of 109 and a minimum of 61, and thus attained 66 per cent.
of the normal fertility. This was the plant with some of the
anthers of the longest stamens contabescent as above mentioned.
Plant 27. This mid-styled plant, fertilised during 1864 in the
same manner as the last, yielded an average, from ten capsules,
of 99°4 seeds, with a maximum of 122 anda minimum of 53,
thus attaining to 76 per cent. of the normal fertility. If the
season had been more favourable, its fertility would probably
have been somewhat greater, but, judging from the last experi-
ment, only in a slight degree.
Plant 28. This mid-styled plant, when legitimately fertilised
during the favourable season of 1866, in the manner described
under No. 26, yielded an average, from eight capsules, of 89
seeds, with a maximum of 119 and a minimum of 69, thus pro-
ducing 68 per cent. of the full number of seeds. In the pollen
of both sets of anthers, nearly as many grains were small and
shrivelled as sound.
202 ILLEGITIMATE OFFSPRING OF Cuar. V.
Plant 29. This long-styled plant was legitimately fertilised
during the unfavourable season of 1864,in the manner described
under No. 26, and yielded an average, from ten capsules, of
84:6 seeds, with a maximum of 132 and a minimum of 47, thus
attaining to 91 per cent. of the normal fertility. During the
highly favourable season of 1866, when fertilised in the manner
described under No. 26, it yielded an average, from nine cap-
sules (one poor capsule having been excluded), of 100 seeds,
with a maximum of 121 and a minimum of 77. This plant thus
exceeded the normal standard, and produced 107 per cent. of
seeds. In both sets of anthers there were a good many bad and
shrivelled pollen-grains, but not so many as in the last-described
plant. . ;
Plant 30. This long-styled plant was legitimately fertilised
during 1866 in the manner described under No. 26, and yielded
an average, from eight capsules, of 94 seeds, with a maximum
of 106 anda minimwn of 66; so that it exceeded the normal
standard, yielding 101 per cent. of seeds.
Plant 31. Some flowers on this long-styled plant were arti-
ficially and legitimately fertilised by one of its brother illegiti-
mate mid-styled plants; and five capsules yielded an average of
90°6 seeds, with a maximum of 97 and a minimum of 79.
Hence, as far as can be judged from so few capsules, this plant
attained, under these favourable circumstances, 98 per cent. of
the normal standard.
Cuass VII. Illegitimate Plants raised from Mid-styled
Parents fertilised with pollen from the longest stamens
of the short-styled form.
It was shown in the last chapter that the union from
which these illegitimate plants were raised is far more
fertile than any other illegitimate union ; for the mid-
styled parent, when thus fertilised, yielded an average
(all very poor capsules being excluded) of 102°8 seeds,
with a maximum of 130; and the seedlings in the
present class likewise have their fertility not at all
lessened. Forty plants were raised ; and these attained
their full height and were covered with seed-capsules
Guar. V. HETEROSTYLED TRIMORPHIC PLANTS. 203
Nor did I observe any contabescent anthers. It de-
serves, also, particular notice that these plants, differ-
ently from what occurred in any of the previous classes,
consisted of all three forms, namely, eighteen short-
styled, fourteen long-styled, and eight mid-styled
plants. As these plants were so fertile, I counted the
seeds only in the two following cases.
Plant 32. This mid-styled plant was freely and legitimately
fertilised during the unfavourable year of 1864, by numerous
surrounding legitimate and illegitimate plants. Hight cap-
sules yielded an average of 127:2 seeds, with a maximum of 144
and a minimum of 96; so that this plant attained 93 per cent.
of the normal standard.
Plant 33. This short-styled plant was fertilised in the same
manner and at the same time with the last; and ten capsules
yielded an average of 113°9, with a maximum of 187 and a
minimum of 90. Hence this plant produced no less than 137
per cent. of seeds in comparison with the normal standard.
Concluding Remarks on the Illegitimate Offspring of the
three forms of Lythrum salicaria.
From the three forms occurring in approximately
equal numbers in a state of nature, and from the re-
sults of sowing seed naturally produced, there is reason
to believe that each form, when legitimately fertilised,
reproduces all three forms in about equal numbers.
Now, we have seen (and the fact is a very singular
one) that the fifty-six plants produced from the
long-styled form, illegitimately fertilised with pollen
from the same form (Class I. and II.), were all long-
styled. The short-styled form, when self-fertilised
(Class III.), produced eight short-styled and one long-
styled plant; and the mid-styled form, similarly treated
(Class IV.), produced three mid-styled and one long-
styled offspring ; so that these two forms, when ille-
204 ILLEGITIMATE OFFSPRING OF Cuar. V
gitimately fertilised with pollen from the same form,
evince a strong, but not exclusive, tendency to repro-
duce the parent-form. When the short-styled form
was illegitimately fertilised by the long-styled form
(Class V.), and again when the mid-styled was illegiti-
mately fertilised by the long-styled (Class VI.), in
each case the two parent-forms alone were reproduced.
As thirty-seven plants were raised from these two
unions, we may, with much confidence, believe that it
is the rule that plants thus derived usually consist of
both parent-forms, but not of the third form. When,
however, the mid-styled form was illegitimately fer-
tilised by the longest stamens of the short-styled
(Class VIT.), the same rule did not hold good; for the
seedlings consisted of all three forms. The illegiti-
mate union from which these latter seedlings were
raised is, as previously stated, singularly fertile, and
the seedlings themselves exhibited no signs of sterility
and grew to their full height. From the consideration
of these several facts, and from analogous ones to be
given under Oxalis, it seems probable that in a state
of nature the pistil of each form usually receives,
through the agency of insects, pollen from the stamens
of corresponding height from both the other forms.
But the case last given shows that the application of
two kinds of pollen is not indispensable for the pro-
duction of all three forms. Hildebrand has suggested
that the cause of all three forms being regularly and
naturally reproduced, may be that some of the flowers
are fertilised with one kind of pollen, and others
on the same plant with the other kind of pollen.
Finally, of the three forms, the long-styled evinces
somewhat the strongest tendency to reappear amongst
the offspring, whether both, or one, or neither of the
parents are long-styled.
Cuar. V. HETEROSTYLED TRIMORPHIC PLANTS. 205
Tasie 30.
Tabulated results of the fertility of the foregoing illegitimate
plants, when legitimately fertilised, generally by illegitimate
plants, as described under each experiment. Plants 11, 12
and 13 are excluded, as they were illegitimately fertilised.
Normal Standard of Fertility of the three forms, when legitimately
and naturally fertilised.
Average | Maximum
(Number vf|Number in| Minimum Number in any
Form, Seeds per | any one one Capsule,
Capsule. | Capsule.
Long-styled. 2. . 93 159 no xecord was kept, as
Mid-styled . . . «| 130 151 all very poor capsules
were rejected,
Short-styled . . .| 83°5| 112 |
Cuass I. and Il.—Jlegitimate Plants raised from Long-styled
Parents fertilised with polln from own-form mid-length or
shortest stamens.
Average Num-
ig ee nan eae
Number of Plant. Form. Beets pat pe one : any ne the Poleutaee -
- Capsule. | Cupsule. | Capsule. lof the Normal
Standard.
Plant 1. . | Long-styled 0 0 0 0
» 2a % » 4:5 z 0 5
~ Se we ” 4:5 Ze 0 5
» See yy 4:5 e 0 5
53 OLS Se eS Oorl 2 0 Oorl
a we x 7 0 0 0 0
a oe ” 36°1 47 22 39
ng Bs & 7 41'1 73 11 44
we Pe « 7 57°1 86 23 61
w ADs « + 44°2 69 25 47
Cuass I1L.—Jllegitimate Plants raised from Short-styled Purents
Sertilised with pollen from own-form shortest stamens.
Plant!4 . . | Short-styled | 28°3 51 11 33
» 1B ye E 32-6 49 20 38
» 6. , 77°8 97 60 94
” 47. 1 | Long-styled | 76-3 88 57 82
206
TasLe 30—continued.
Cuass [V.—Illegitimate Plants raised from Mid-styled Parents
fertilised with pollen from own-form longest stamens.
ILLEGITIMATE OFFSPRING OF
Cuap. V.
Average Num-
Average | Maximum aroma ber of Secds,
Number of (Number in |Number in| expressed as
Namber of Plant. Form. Seeds per | any one | any one |the percentage
Cupsule. | Capsule. | Capsule. jof the Normal
Standard,
Plant 18. . | Mid-styled. | 102°6 131 63 80
ee | ee 7 W3-4 87 64 56
» 20. . | Long-styled | 69°6 83 52 95
Cuass V.—IJllegitimate Plants raised from Short-styled Parents
fertilised with pollen from the mid-length stamens of the lony-
styled form.
Plant 21 .
22 te
23 .
24,
25 4 %
Short-styled
”
Long-styled
”
43°0
100°5
113°5
32°0
122°5
63
123
123
120
149
52
121.
136
88
131
Cuass VI.—ZIlegitimate Plants raised from Mid-styled Parents
fertilised with pollen from the shortest stamens of the long-
styled form.
Plant 26 , Mid-styled. 86°0 109 61 66
TOs ok if 994 | 122 53 76
OBES ‘ 89-0 | 119 69 68
» 29. . | Long-styled | 100-0 121 97 107
» 80. , 7 94:0 | 106 66 101
* 3L. i 90-6 97 79 98
Crass VII.—Zllegitimate Plants raised from Mid-styled Parents
Sertilised with pollen from the longest stamens of the short«
styled form.
Plant 32 . . | Mid-styled, | 127-2 144 96 98
» 33. . | Short-styled | 113°9 137 90 137
Cuar. V. HETEROS'’YLED TRIMORPHIC PLANTS. 207
The lessened fertility of most of these illegitimate
plants is in many respects a highly remarkable phe-
nomenon. Thirty-three plants in the seven classes
were subjected to various trials, and the seeds care-
fully counted. Some of them were artificially ferti-
lised, but the far greater number were freely fertilised
(and this is the better and natural plan) through the
agency of insects, by other illegitimate plants. In the
right-hand, or percentage column, in the preceding
table, a wide difference in fertility between the plants
in the first four and the last three classes may be per-
ceived. In the first four classes the plants are de-
scended from the three forms illegitimately fertilised
with pollen taken from the same form, but only
rarely from the same plant. It is necessary to observe
this latter circumstance; for, as I have elsewhere
shown,* most plants, when fertilised with their own
pollen, or that from the same plant, are in some
degree sterile, and the seedlings raised from such
unions are likewise in some degree sterile, dwarfed,
and feeble. None of the nineteen illegitimate plants
in the first four classes were completely fertile; one,
however, was nearly so, yielding 96 per cent. of the
proper number of seeds. From this high degree of
fertility we have many descending gradations, till we
reach an absolute zero, when the plants, though bear-
ing many flowers, did not produce, during successive
years, a single seed or even seed-capsule. Some of the
most sterile plants did not even yield a single seed
when legitimately fertilised with pollen from legiti-
mate plants. There is good reason to believe that the
first seven plants in Class I. and II. were the offsprinz
* ‘The Effects of Cross and Self-fertilisation in the Vegetable
Kingdom,’ 1876.
208 ILLEGITIMATE OFFSPRING OF Cuar. V,
of a long-styled plant fertilised with pollen from its
own-form shortest stamens, and these plants were the
most sterile of all. The remaining plants in Class I.
and II. were almost certainly the product of pollen
from the mid-length stamens, and although very ste-
rile, they were less so than the first set. None of the
plants in the first four classes attained their full and
proper stature; the first seven, which were the most
sterile of all (as already stated), were by far the most
dwarfed, several of them never reaching to half their
proper height. These same plants did not flower at so
early an age, or at so early a period in the season, as
they ought to have done. The anthers in many of
their flowers, and in the flowers of some other plants
in the first six classes, were either contabescent or in-
cluded numerous small and shrivelled pollen-grains.
As the suspicion at one time occurred to me that the
lessened fertility of the illegitimate plants might be
due to the pollen alone having been affected, I may
remark that this certainly was not the case; for several
of them, when fertilised by sound pollen from legiti-
mate plants, did not yield the full complement of
seeds; hence it is certain that both the female and
male reproductive organs were affected. In each of
the seven classes, the plants, though descended from
the same parents, sown at the same time and in the
same soil, differed much in their average degree of
fertility.
Turning now to the fifth, sixth, and seventh classes,
and looking to the right-hand column of the table, we
find nearly as many plants with a percentage of seeds
above the normal standard as beneath it. As with
most plants the number of seeds produced varies much,
it might be thought that the present case was one
merely of variability. But this view must be rejected,
Cuar. V. HETEROSTYLED TRIMORPHIC PLANTS. 209
as far as the less fertile plants in these three classes
are concerned: first, because none of the plants in
Class V. attained their proper height, which shows
that they were in some manner affected ; and, secondly,
because many of the plants in Classes V. and VI. pro-
duced anthers which were either contabescent or in-
cluded small and shrivelled pollen-grains. And as in
these cases the male organs were manifestly deterio-
rated, it is by far the most probable conclusion that
the female organs were in some cases likewise affected,
and that this was the cause of the reduced number of
seeds.
With respect to the six plants in these three classes
which yielded a very high percentage of seeds, the
thought naturally arises that the normal standard of
fertility for the long-styled and short-styled forms
(with which alone we are here concerned) may have
been fixed too low, and that the six illegitimate plants
are merely fully fertile. The standard for the long-
styled form was deduced by counting the seeds in
twenty-three capsules, and for the short-styled form
from twenty-five capsules. I do not pretend that this
is a sufficient number of capsules for absolute accu-
racy ; but my experience has led me to believe that a
very fair result may thus be gained. As, however, the
maximum number observed in the twenty-five capsules
of the short-styled form was low, the standard in this
ease may possibly be not quite high enough. But it
should be observed, in the case of the illegitimate
plants, that in order to avoid over-estimating their in-
fertility, ten very fine capsules were always selected ;
and the years 1865 and 1866, during which the plants
in the three latter classes were experimented on, were
highly favourable for seed-production. Now, if this
210 ILLEGITIMATE OFFSPRING OF Cuap. V.
plan of selecting very fine capsules during favourable
seasons had been followed for obtaining the normal
standards, instead of taking, during various seasons,
the first capsules which came to hand, the standards
would undoubtedly have been considerably higher ;
and thus the fact of the six foregoing plants appearing
to yield an unnaturally high percentage of seeds may,
perhaps, be explained. On this view, these plants are,
in fact, merely fully fertile, and not fertile to an ab-
normal degree. Nevertheless, as characters of all
kinds are liable to variation, especially with organisms
unnaturally treated, and as in the four first and more
sterile classes, the plants derived from the same pa-
rents and treated in the same manner, certainly did
vary much in sterility, it is possible that certain plants
in the latter and more fertile classes may have varied
so as to have acquired an abnormal degree of fertility.
But it should be noticed that, if my standards err in
being too low, the sterility of all the many sterile
plants in the several classes will have to be estimated
by so much the higher. Finally, we see that the ille-
gitimate plants in the four first classes are all more or
less sterile, some being absolutely barren, with one
alone almost completely fertile; in the three latter
classes, some of the plants are moderately sterile,
whilst others are fully fertile, or possibly fertile in
excess.
The last point which need here be noticed is that,
as far as the means of comparison serve, some degree
of relationship generally exists between the infertility
of the illegitimate union of the several parent-forms
and that of their illegitimate offspring. Thus the
two illegitimate unions, from which the plants in
Classes VI. and VII. were derived, yielded a fair
amount of seed, and only a few of these plants are in
Ouar. ¥. HETEROSTYLED TRIMORPHIC PLANTS. 211
any degree sterile. On the other hand, the illegiti-
mate unions between plants of the same form always
yield very few seeds, and their seedlings are very
sterile. Long-styled parent-plants when fertilised
with pollen from their own-form shortest stamens, ap-
pear to be rather more sterile than when fertilised with
their own-form mid-length stamens ; and the seedlings
from the former union were much more sterile than
those from the latter union. In opposition to this re-
lationship, short-styled plants illegitimately fertilised
with pollen from the mid-length stamens of the long-
styled form (Class V.) are very sterile; whereas some
of the offspring raised from this union were far from
being highly sterile. It may be added that there is a
tolerably close parallelism in all the classes between
the degree of sterility of the plants and their dwarfed
stature. As previously stated, an illegitimate plant
fertilised with pollen from a legitimate plant has its
fertility slightly increased. The importance of the
several foregoing conclusions will be apparent at the
close of this chapter, when the illegitimate unions be-
tween the forms of the same species and their illegiti-
mate offspring, are compared with the hybrid unions
of distinct species and their hybrid offspring.
OXALIS.
No one has compared the legitimate and illegiti-
mate offspring of any trimorphic species in this genus.
Hildebrand sowed illegitimately fertilised seeds of
Oxalis Valdiviana,* but they did not germinate; and
this fact, as he remarks, supports my view that au
illegitimate union resembles a hybrid one between
* ‘Bot. Zeitung, 1871, p. 433, foctnote,
212 ILLEGITIMATE OFFSPRING OF Cuap. V.
two distinct species, for the seeds in this latter case
are often incapable of germination.
The following observations relate to the nature of the forms
which appear among the legitimate seedlings of Oxulis Valdiviana.
Hildebrand raised, as described in the paper just referred to,
211 seedlings from all six legitimate unions, and the three forms
appeared among the offspring from each union. For instance,
long-styled plants were legitimately fertilised with pollen from
the longest stamens of the mid-styled form, and the seedlings
consisted of 15 long-styled, 18 mid-styled, and 6 short-styled.
We here see that a few short-styled plants were produced, though
neither parent was short-styled; and so it was with the other"
legitimate unions. Out of the above 211 seedlings, 173 belonged
to the same two forms as their parents, and only 38 belonged
to the third form distinct from either parent. In the case of
O. Regnelli, the result, as observed by Hildebrand, was nearly
the same, but more striking: all the offspring from four of the
legitimate unions consisted of the two parent-forms, whilst
amongst the seedlings from the other two legitimate unions the
third form appeared. Thus, of the 48 seedlings from the six
legitimate unions, 35 belonged to the same two forms as their
parents, and only 8 to the third form. Fritz Miiller also raised
in Brazi] seedlings from long-styled plants of O. Regneili legiti-
mately fertilised with pollen from the longest stamens of the
mid-styled furm, and all these belonged to the two parent-
forms.* Lastly, seedlings were raised by me from long-styled
plants of O. speciosa legitimately fertilised by the short-styled
form, and from the latter reciprocally fertilised by the long-
styled; and these consisted of 33 long-styled and 26 short-
styled plants, with not one mid-styled form. There can, there-
fore, be no doubt that the legitimate offspring from any two
forms of Oxalis tend to belong to the same two forms as their
parents; but that a few seedlings belonging to the third form
occasionally make their appearance; and this latter fact, as
Hildebrand remarks, may be attributed to atavism, as some of
their progenitors will almost certainly have belonged to the
third form.
When, however, any one form of Oxalis is fertilised illegiti-
* « Jonaische Zeitschrift,’ &c. Band vi. 1871, p. 75.
Cuar. V. HETEROSTYLED DIMORPHIC PLANTS. 213
mately with pollen from the same form, the seedlings appear tc
belong invariably to this form. Thus Hildebrand states* that
long-styled plants of O. rosea growing by themselves have becn
propagated in Germany year after year by seed, and have always
produced long-styled plants. Again, 17 seedlings were raised
from mid-styled plants of U. hedysaroides growing by themselves,
and these were all mid-styled. So that the forms of Oxalis,
when illegitimately fertilised wth their own pollen, behave like
the long-styled form of Lythrum salicaria, which when thus fer-
tilised always produced with me long-styled offspring.
PRIMULA.
PRIMULA SINENSIS.
I raised during February 1862, from some long-
styled plants illegitimately fertilised with pollen from
the same form, twenty-seven seedlings. These were
all long-styled. They proved fully fertile or even
fertile in excess; for ten flowers, fertilised with pollen
from other plants of the same lot, yielded nine cap-
sules, containing on an average 39°75 seeds, with a
maximum in one capsule of 66 seeds. Four other
flowers legitimately crossed with pollen from a legiti-
mate plant, and four flowers on the latter crossed with
pollen from the illegitimate seedlings, yielded seven
capsules with an average of 53 seeds, with a maximum
of 72. I must here state that I have found some
difficulty in estimating the normal standard of fer-
tility for the several unions of this species, as the
results differ much during successive years, and
the seeds vary so greatly in size that it is hard to
* (‘Ucber den Trimorphismus zu Berlin,’ 21st June 1866, p, 373;
in der Gattung Oxalis: Monats- and ‘ Bot. Zeitung, 1871, p. 435,
perichte der Akad. der Wissen.
214 ILLEGITIMATE OFFSPRING OF Cuap. V
decide which ought to be considered good. In order
to avoid over-estimating the infertility of the several
illegitimate unions, I have taken the normal standard
as low as possible.
From the foregoing twenty-seven illegitimate plants,
fertilised with their own-form pollen, twenty-five seed-
ling grandchildren were raised; and these were all
long-styled ; so that from the two illegitimate gene-
rations fifty-two plants were raised, and all without
exception proved long-styled. These grandchildren
grew vigorously, and soon exceeded in height two
other lots of illegitimate seedlings of different parent-
age and one lot of equal-styled seedlings presently to
be described. Hence I expected that they would have
turned out highly ornamental plants; but when they
flowered, they seemed, as my gardener remarked, to
have gone back to the wild state; for the petals were
pale-coloured, narrow, sometimes not touching each
other, flat, generally deeply notched in the middle,
but not flexuous on the margin, and with the yellow
eye or centre conspicuous. Altogether these flowers
were strikingly different from those of their pro-
genitors; and this, I think, can only be accounted
for on the principle of reversion. Most of the anthers
on one plant were contabescent. Seventeen flowers
on the grandchildren were illegitimately fertilised
with pollen taken from other seedlings of the same
lot, and produced fourteen capsules, containing on an
average 29°2 seeds; but they ought to have con-
tained about 35 seeds. Fifteen flowers legitimately
fertilised with pollen from an illegitimate short-styled
plant (belonging to the lot next to be described) pro-
duced fourteen capsules, containing an average of 46
seeds; they ought to have contained at least 50 seeds.
Hence these grandchildren of illegitimate descent ap-
Cuar. V. HETEROSTYLED DIMORPHIC PLANTS. 215
pear to have lost, though only in a very slight degree,
their full fertility.
We will now turn to the short-styled form: from a
plant of this kind, fertilised with its own-form pollen,
T raised, during February 1862, eight seedlings, seven
of which were short-styled and one long-styled. They
grew slowly, and never attained to the full stature of
ordinary plants; some of them flowered precociously,
and others late in the season. Four flowers on these
short-styled seedlings and four on the one long-styled
seedling were illegitimately fertilised with their own-
form pollen and produced only three capsules, con-
taining on an average 23°6 seeds, with a maximum
of 29; but we cannot judge of their fertility from so
few capsules; and I have greater doubts about the
normal standard for this union than about any other ;
but I believe that rather above 25 seeds would be a
fair estimate. Eight flowers on these same short-styled
plants, and the one long-styled illegitimate plant
were reciprocally and legitimately crossed; they pro-
duced five capsules, which contained an average of
28°6 seeds, with a maximum of 36. A reciprocal
cross between legitimate plants of the two forms
would have yielded an average of at least 57 seeds,
with a possible maximum of 74 seeds; so that these
illegitimate plants were sterile when legitimately
crossed.
I succeeded in raising from the above seven short-
styled illegitimate plants, fertilised with their own-
form pollen, only six plants—grandchildren of the
first union. These, like their parents, were of low
stature, and had so poor a constitution that four died
before flowering. With ordinary plants it has been
a rare event with me to have more than a single plant
die out of a large lot. The two grandchildren which
15
216 ILLEGITIMATE OFFSPRING OF Cua. V.
lived and flowered were short-styled; and tweive of
their flowers were fertilised with their own-form pollen
and produced twelve capsules containing an average
of 28:2 seeds; so that these two plants, though be-
longing to so weakly a set, were rather more fertile
than their parents, and perhaps not in any degree
sterile. Four flowers on the same two grandchildren
were legitimately fertilised by a long-styled illegiti-
mate plant, and produced four capsules, containing
only 32:2 seeds instead of about 64 seeds, which is
the normal average for legitimate short-styled plants
legitimately crossed.
By looking back, it will be seen that I raised at
first from a short-styled plant fertilised with its own-
form pollen one long-styled and seven short-styled
illegitimate seedlings. These seedlings were legiti-
mately intercrossed, and from their seed fifteen plants
were raised, grandchildren of the first illegitimate
union, and to my surprise all proved short-styled.
Twelve short-styled flowers borne by these grand-
children were illegitimately fertilised with pollen
taken from other plants of the same lot, and produced
eight capsules which contained an average of 21:8
seeds, with a maximum of 35. These figures are
rather below the normal standard for such a union.
Six flowers were also legitimately fertilised with pollen
from an illegitimate long-styled plant and produced
only three capsules, containing on an average 23°6
seeds, with a maximum of 35. Such a union in the
case of a legitimate plant ought to have yielded an
average of 64 seeds, with a possible maximum of 73
seeds.
Summary on the Transmission of Form, Constitution,
and Fertility of the Illegitimate Offspring of Primula
Sinensis—In regard to the long-styled plants, their
Cuar. V. HETEROSTYLED DIMORPHIC PLANTS. 217
illegitimate offspring, of which fifty-two were raised in
the course of two generations, were all long-styled.*
These plants grew vigorously ; but the flowers in one
instance were small, appearing as if they had reverted
to the wild state. In the first illegitimate generation
they were perfectly fertile, and in the second their
fertility was only very slightly impaired. With
respect to the short-styled plants, twenty-four out of
twenty-five of their illegitimate offspring were short-
styled. They were dwarfed in stature, and one lot of
grandchildren had so poor a constitution that four out
of six plants perished before flowering. The two sur-
vivors, when illegitimately fertilised with their own-
form pollen, were rather less fertile than they ought
to have been; but their loss of fertility was clearly
shown in a special and unexpected manner, namely,
when legitimately fertilised by other illegitimate
plants: thus altogether eighteen flowers were fertilised
in this manner, and yielded twelve capsules, which
included on an average only 28°5 seeds, with a
maximum of 45. Now a legitimate short-styled plant
would have yielded, when legitimately fertilised, an
average of 64 seeds, with a possible maximum of 74,
This particular kind of infertility will perhaps be best
appreciated by a simile: we may assume that with
mankind six children would be born on an average from
an ordinary marriage; but that only three would be
born from an incestuous marriage. According to the
analogy of Primula Sinensis, the children of such
* Dr. Hildebrand, who first short-styled. From a short-styled
ealled attention to this subject
(‘ Bot. Zeitung’ 18U4, p. 5), raised
from a similar illegitimate union
seventeen plants, of whicb four-
teen were long styled and three
plant illegitimately fertilised with
its own pollen he raised fourteen
plants, of which eleven were short-
styled aad three long-styled.
218 ILLEGITIMATE OFFSPRING OF Cuapr. V.
mcestuous marriages, if they continued to marry in-
cestuous!y, would have their sterility only slightly
increased ; but their fertility would not be restored by
a proper marriage; for if two children, both of in-
cestuous origin, but in no degree related to each
other, were to marry, the marriage would of course be
strictly legitimate, nevertheless they would not give
birth to more than half the full and proper number
of children.
Equal-styled variety of Primula Sinensis——As any variation in
the structure of the reproductive organs, combined with changed
function, is a rare event, the following cases are worth giving
in detail. My attention was first called to the subject by ob-
serving, in 1862, a long-styled plant, descended from a self-
fertilised long-styled parent, which had some of its flowers in an
anomalous state, namely, with the stamens placed low down in
the corolla as in the ordinary long-styled form, but with the
pistils so short that the stigmas stood on a level with the anthers.
These stigmas were nearly as globular and as smooth as in the
short-styled form, instead of being elongated and rough as in
the long-styled form. Here, then, we have combined in the
same flower, the short stamens of the long-styled form with a
pistil closely resembling that of the short-styled form. But
the structure varied much even on the same umbel: for in two
flowers the pistil was intermediate in length between that of
the long and that of the short-styled form, with the stigma
elongated as in the former, and smooth as in the latter; and in
three other flowers the structure was in all respects like that of
the long-styled form. These modifications appeared to me so
remarkable that I fertilised eight of the flowers with their own
pollen, and obtained five capsules, which contained on an aver-
age 43 seeds; and this number shows that the flowers had
become abnormally fertile in comparison with those of ordinary
long-styled plants when self-fertilised. I was thus led to ex-
amine the plants in several small collections, and the result
showed that the equal-styled variety was not rare.
In a state of nature the long and short-styled forms would no
doubt occur in nearly equal numbers, as J infer from the analogy
of tho other heterostyled species of Primula, and from having
Cuar. V. HETEROSTYLED DIMORPHIC PLANTS. 219
TasBieE 31,
Primula Sinensis.
Name of Owner or Place, Mane led er eo
Myr. Horwood . . 1. . . o 0 17
Mr.Duck . . 2. . 1 20 0 9
BastODe oot in Se, Ae 30 18 15
Chichester . 2. 1. 1 6 oe 12 9 2
Holwood) we ey ye 42 12 0
High Elms... ww we 16 0 0
Westerham. . . . ew 6 1 5 0
My own plants from purchased seeds 13 7 0
Total a ewe wt 8 134 51 43
raised the two forms of the present species in exactly the same
number from flowers which had been leyitimately crossed. The
preponderance in the above table of the long-styled form over
the short-styled (in the proportion of 134 to 51) results from gar-
deners generally collecting seed from self-fertilised flowers; and
the long-styled flowers produce spontaneously much more seed
(as shown in the first chapter) than the short-styled, owing to the
anthers of the long-styled form being placed low down in the
corolla, so that, when the flowers fall off, the anthers are dragged
over the stigma; and we now also know that long-styled plants,
when self-fertilised, very generally reproduce long-styled off-
spring. From the consideration of this table, it occurred to
me in the year 1862, that almost all the plants of the Chinese
primrose cultivated in England would sodner or later become
long-styled or equal-styled; and now, at the close of 1876, I
have had five small collections of plants examined, and almost
all consisted of long-styled, with some more or less well-cha-
racterised equal-styled plants, but with not one short-styled.
With respect to the equal-styled plants in the table, Mr. Hor-
wood raised from purchased seeds four plants, which he re-
membered were certainly not long-styled, but either short or
equal-styled, probably the latter. These four plants were kept
separate and allowed to fertilise themselves; from their seed the
seventeen plants in the table were raised, all of which proved
equal-styled. The stamens stood low down in the corolla as in
the long-styled form ; and the stigmas, which were globular and
220 ILLEGITIMATE OFFSPRING OF Cuar. V.
smooth, were either completely surrounded by the anthers, or
stood close above them. My son William made drawings for
me, by the aid of the camera, of the pollen of one of the above
equal-styled plants; and, in accordance with the position of the
stamens, the grains resembled in their small size those of the
long-styled form. He also examined pollen from two equal-style l
plants at Southampton; and in both of them the grains dif-
fered extremely in size in the same anthers, a large numbcr
being small and shrivelled, whilst many were fully as large as
those of the short-styled form and rather more globular. It is
probable that the large size of these grains was due, not to their
having assumed the character of the short-styled form, but to
monstrosity; for Max Wichura has observed pollen-grains of
monstrous size in certain hybrids. The vast number of the
small shrivelled grains in the above two cases explains the fact
that, though equal-styled plants are generally fertile in a high
degree, yet some of them yield few seeds. I may add that my
son compared, in 1875, the grains from two white-flowered
plants, in both of which the pistil projected above the anthers,
but neither were properly long-styled or equal-styled; and in
the one in which the stigma projected most, the grains were
in diameter to those in the other plant, in which the stigma pro-
jected less, as 100 to 88; whereas the difference between the
grains from perfectly characterised long-styled and short-styled
plants is as 100 to 57. So that these two plants were in an
intermediate condition. To return to the 17 plants in the first
line of Table 31: from the relative position of their stigmas and
anthers, they could hardly fail to fertilise themselves; and ac-
cordingly four of them spontaneously yielded no less than 180
capsules; of these Mr. Horwood selected eight fine capsules for
sowing; and they included on an average 54°8 seeds, with a
maximum of 72. He gave me thirty other capsules, taken
by hazard, of which twenty-seven contained good seeds, aver-
aging 85°5, with a maximum of 70; but if six poor cap-
sules, each with less than 13 seeds, be excluded, the average
rises to 42°5. These are higher numbers than could be ex-
pected from either well-characterised form if self-fertilised ; and
this high degree of fertility accords with the view that the
male organs belonged to one form, and the female organs par-
tially to the other form; so that a self-union in the case of the
equal-styled variety is in fact a legitimate union.
The seed saved from the above seventeen sclf-fortilised equal
Cuar. V. HETEROSTYLED DIMORPHIC PLANTS. 221
styled plants produced sixteen plants, which all proved equal-
styled, and resembled their parents in all the above-specified
respects. The stamens, however, in one plant were seated higher
up the tube of the corolla than in the true long-styled form;
in another plant almost all the anthers were contabescent. These
sixteen plants were the grandchildren of the four original plants,
which it is believed were equal-styled; so that this abnormal
condition was faithfully transmitted, probably through three,
and certainly through two generations. The fertility of one of
these grandchildren was carefully observed: six flowers were
fertilised with pollen from the same flower, and produced six
capsules, containing on an average 68 seeds, with a maximum
of 82; and a minimum of 40. Thirteen capsules spontaneously
self-fertilised yielded an average of 53°2 seeds, with the astonish-
ing maximum in one of 97 seeds. In no legitimate union has
so high an average as 68 seeds been observed by me, or nearly
so high a maximum as 82 and 97. These plants, therefore, not
only have lost their proper heterostyled structure and peculiar
functional powers, but have acquired an abnormal grade of fer-
tility—unless, indeed, their high fertility may be accounted for
by the stigmas receiving pollen from the circumjacent anthers
at exactly the most favourable period.
With respect to Mr. Duck’s lot in Table 31, seed was saved
from a single plant, of which the form was not observed,
and this produced nine equal-styled and twenty long-styled
plants. The equal-styled resembled in all respects those pre-
viously described; and eight of their capsules spontaneously
self-fertilised contained on an average 44°4 seeds, with a
maximum of 61 and a minimum of 23. In regard to the
twenty long-styled plants, the pistil in some of the flowers did
not project quite so high as in ordinary long-styled flowers;
and the stigmas, though properly elongated, were smooth; so
that we have here a slight approach in structure to the pistil of
the short-styled form. Some of these long-styled plants also
approached the equal-styled in function; for one of them pro-
duced no less than fifteen spontaneously self-fertilised capsules,
and of these eight contained, on an average, 31°7 seeds, with
a maximum of 61. This average would be rather low for a
long-styled plant artificially fertilised with its own pollen, but
is high for one spontaneously self-fertilised. For instance,
thirty-four capsules produced by the illegitimate grandchildren
of a long-styled plant, spontaneously self-fertilised, contained
222 ILLEGITIMATE OFFSPRING OF Cuar. V,
on an average only 9'1 seeds, with a maximum of 46. Some
seeds indiscriminately saved from the foregoing twenty-nine
equal-styled and long-styled plants produced sixteen seedlings,
grandchildren of the original plant belonging to Mr. Duck; and
these consisted of fourteen equal-styled and two long-styled
plants ; and I mention this fact as an additional instance of the
transmission of the equal-styled variety.
The third lot in the table, namely the Baston plants, are the
last which need be mentioned. The long and short-styled plants,
and the fifteen equal-styled plants, were descended from two
distinct stocks. The latter were derived from a single plant,
which the gardener is positive was not long-styled; hence, pro-
bably, it was equal-styled. In all these fifteen plants the anthers,
occupying the same position as in the long-styled form, closely
surrounded the stigma, which in onc instance alene was slightly
elongated. Notwithstanding this position of the stigma, the
flowers, as the gardener ussured me, did not yield many seeds ;
and this ditference from the foregoing cases may perhaps have
been caused by the pollen being bad, as in some of the South-
ampton equal-styled plants.
Conclusions with respect to the equal-styled variety of
P. Sinensis.—That this is a variation, and not a third or
distinct form, as in the trimorphic genera Lythrum and
Oxalis, is clear; for we have seen its first appearance
in one out of a lot of illegitimate long-styled plants ;
and in the case of Mr. Duck’s seedlings, long-styled
plants, only slightly deviating from the normal state,
as well as equal-styled plants were produced from the
same self-fertilised parent. The position of the sta-
mens in their proper place low down in the tube of the
corolla, together with the small size of the pollen-
grains, show, firstly, that the equal-styled variety is a
modification of the long-styled form, and, secondly, that
the pistil is the part which has varied most, as indeed
was Obvious in many of the plants. This variation is
of frequent occurrence, and is strongly inherited when
it has once appeared. It would, however, have pos-
Cnar. V. HETEROSTYLED DIMORPHIC PLANTS. 223
sessed little interest if it had consisted of a mere
change of structure; but this is accompanied by modi-
fied fertility. Its occurrence apparently stands in
close relation with the illegitimate birth of the parent
plant; but to this whole subject I shall hereafter
recur.
PRIMULA AURICULA.
Although I made no experiments on the illegitimate offspring
of this species, I refer to it for two reasons :—First, because
I have observed two equal-styled plants in which the pistil
resembled in all respects that of the long-styled form, whilst
the stamens had become elongated as in the short-styled form,
so that the stigma was almost surrounded by the anthers. The
pollen-grains, however, of the elongated stamens resembled in
their small size those of the shorter stamens proper to the long-
styled form. Hence these plants have become equal-styled by
the increased length of the stamens, instead of, as with P.
Sinensis, by the diminished length of the pistil. Mr. J. Scott
observed five other plants in the same state, and he shows * that
one of them, when self-fertilised, yielded more seed than an
ordinary long- or short-styled form would have done when
similarly fertilised, but that it was far inferior in fertility to
either form when legitimately crossed. Hence it appears that
the male and female organs of this equal-styled variety have
been modified in some special manner, not only in structure
but in functional powers. This, moreover, is shown by the
singular fact that both the long-styled and short-styled plants,
fertilised with pollen from the equal-styled variety, yield a
lower average of seed than when these two forms are fertilised
with their own pollen.
The second point which deserves notice is that florists always
throw away the long-styled plants, and save seed exclusively
from the short-styled form. Nevertheless, as Mr. Scott was
informed by a man who raises this species extensively in Scot-
land, about one-fourth’ of the seedlings appear long-styled; so
that the short-styled form of the Auricula, when fertilised by
its own pollen, does not reproduce the same form in so large a
proportion as in the case of P. Sinensis. We may further infer
* ‘Journal Proc. Linn. Soc.’ viii. (1864) p. 91.
224 ILLEGITIMATE OFFSPRING OF Cuar. V
that the short-styled form is not rendered quite sterile by a
long course of fertilisation with pollen of the same form: but as
there would always be some liability to an occasional cross with
the other form, we cannot tell how long self-fertilisation has
been continued.
PRIMULA FARINOSA,
Mr. Scott says * that it is not at all uncommon to find equal-
styled plants of this heterostyled species. Judging from the
size of the pollen-grains, these plants owe their structure, as in
the case of P. auricula, to the abnormal elongation of the
stamens of the long-styled form. In accordance with this view,
they yield Jess seed when crossed with the long-styled form
than with the short-styled. But they differ in an anomalous
manner from the equal-styled plants of P. auricula in being
extremely sterile with their own pollen.
PRIMULA ELATIOR.
It was shown in the first chapter, on the authority of
Herr Breitenbach, that equal-styled flowers are occasionally
found on this species whilst growing in a state of nature; and
this is the only instance of such an occurrence known to me,
with the exception of some wild plants of the Oxlip—a hybrid
between P. veris and vulgaris—which were equal-styled. Herr
Breitenbach’s case is remarkable in another way; for equal-
styled flowers were found in two instances on plants which bore
both long-styled and short-styled flowers. In every other
instance these two forms and the equal-styled variety have been
produced by distinct plants.
PRIMULA VULGARIS, Brit. Fl.
Var. acaulis of Linn. and P. acaulis of Jacq.
Var. rubra.—Mr. Scott statest that this variety, which
grew in the Botanic Garden in Edinburgh, was quite
sterile when fertilised with pollen from the common
ptimrose, as well as from a white variety of the same
* ‘Journal Proc. Linn. Soe.’ viii. (1864), p. 115.
+ Ibid. p. 98.
Cuar. V. HETEROSTYLED DIMORPHIC PLANTS. 225
species, but that some of the plants, when artificially
fertilised with their own pollen, yielded a moderate
supply of seed. He was so kind as to send me some
of these self-fertilised seeds, from which I raised the
plants immediately to be described. I may premise
that the results of my experiments on the seedlings,
made on a large scale, do not accord with those by
Mr. Scott on the parent-plant.
First, in regard to the transmission of form and
colour. The parent-plant was long-styled, and of a
rich purple colour. From the self-fertilised seed 23
plants were raised; of these 18 were purple of dif-
ferent shades, with 2 of them a little streaked and
freckled with yellow, thus showing a tendency to
reversion; and 5 were yellow, but generally with a
brighter orange centre than in the wild flower. All
the plants were profuse flowerers. All were long-
styled; but the pistil varied a good deal in length
even on the same plant, being rather shorter, or con-
siderably longer, than in the normal long-styled form ;
and the stigmas likewise varied in shape. It is,
therefore, probable that an equal-styled variety of the
primrose might be found on careful search; and I
have received two accounts of plants apparently in this
condition. The stamens always occupied their proper
position low down in the corolla; and the pollen-
grains were of the small size proper to the long-styled
form, but were. mingled with many minute and
shrivelled grains. The yellow-flowered and the purple-
flowered plants of this first generation were fertilised
under a net with their own pollen, and the seed sepa-
rately sown. From the former, 22 plants were raised,
and all were yellow and long-styled. From the latter
or the purple-flowered plants, 24 long-styled plants
were raised, of which 17 were purple and 7 yellow.
226 ILLEGITIMATE OFFSPRING OF Cuap, V.
In this last case we have an instance of reversion in
colour, without the possibility of any cross, to the grand-
parents or more distant progenitors of the plants in
question. Altogether 23 plants in the first generation
and 46 in the second generation were raised ; and the
whole of these 69 illegitimate plants were long-styled !
Eight purple-flowered and two yellow-flowered plants
of the first illegitimate generation were fertilised in
various ways with their own pollen and with that of
the common primrose; and the seeds were separately
counted, but as I could detect no difference in fertility
between the purple and yellow varieties, the results
are run together in the following table.. (See next
page.)
If we compare the figures in this table with those
given in the first chapter, showing the normal fertility
of the common primrose, we shall see that the illegiti-
mate purple- and yellow-flowered varieties are very
sterile. For instance, 72 flowers were fertilised with
their own pollen and produced only 11 good capsules ;
but by the standard they ought to have produced 48
capsules ; and each of these ought to have contained
on an average 52:2 seeds, instead of only 11°5 seeds.
When these plants were illegitimately and _ legiti-
mately fertilised with pollen from the common prim-
rose, the average numbers were increased, but were far
from attaining the normal standards. So it was when
both forms of the common primrose were fertilised
with pollen from these illegitimate plants; and this
shows that their male as well as their female organs
were ina deteriorated condition. The sterility of these
plants was shown in another way, namely, by their not
producing any capsules when the access of all insects
(except such minute ones as Thrips) was prevented ;
for under these circumstances the common long-styled
Caar. V. HETEROSTYLED DIMORPHIC PLANTS. 227
TABLE 32.
Primula vulgaris.
5 te cei eas ;
#/ 2/2, |2.4|44
se | 32 /88,! 222) g22
3 5a
Nature of Plant experimented on, 85 So 1/2445 /438| 425
and kind of Union. ae | #2 | as8| Ese) 82a
oe | ag | bso | sc] Ese
Az a | 9s Bob Bob
&/| 8@{4 |8 4/2 4
Purple- and yellow-flowered illegi-
timate long-styled plants, il/egi-
timately fertilised with pollen
from the same plant . .
72 11 | 1175 | 26 5
Purple- and yellow-flowered illegi-
timate long-styled plants, elegi-
timately tertilised with pollen} 72 39 | 31°4] 62 3
from the common long-styled
primrose.
Or, if the ten poorest capsules,
including less than 15 seeds, be}| 72 29 | 40°6 | 62 18
rejected, we get. oer ar]
Purple- and yellow-flowered illegi-)
timate long-styled plants, deyi-|
timately fertilised with pollen 26 18 | 36°4) 60 9
trom the common short-styled
primrose.
Or, if the two poorest capsules,
including less than 15 seeds, be
rejected, we get. . . |
26 16 | 4r*2 | 60 15
Thelong-styled form of the common)
primrose, il/e.jitnately tertilised |
with pollen from the long-styled}| 20 14 | 15°4) 46 1
illegitimate purple- and yellow-
flowered plants. . .
Or, if the three poorest spe
be rejected, we get. . . ao Ir | 18°9 | 46 8
The short-styled form of the common)
primrose, legitimately fertilised
with pollen trom the long-styled >| 10 6 | 30°35 | 61 6
illegitimate purple- and yellow-
flowered plants, . . .
primrose produces. a considerable number of capsules.
There can, therefore, be no doubt that the fertility of
228 ILLEGITIMATE OFFSPRING OF Cuap. V,
these plants was greatly impaired. The loss is not
correlated with the colour of the flower ; and it was to
ascertain this point that I made so many experiments.
As the parent-plant growing in Edinburgh was found
by Mr. Scott to be in a high degree sterile, it may
have transmitted a similar tendency to its offspring,
independently of their illegitimate birth. I am, how-
ever, inclined to attribute some weight to the illegiti-
macy of their descent, both from the analogy of other
cases, and more especially from the fact that when the
plants were legitimately fertilised with pollen of the
common primrose they yielded an average, as may be
seen in the table, of only 5 more seeds than when
tllegitimately fertilised with the same pollen. Now we
know that it is eminently characteristic of the illegiti-
mate offspring of Primula Sinensis that they yield but
few more seeds when legitimately fertilised than when
fertilised with their own-form pollen.
PRIMULA VERIS, Brit. Fl.
Var. officinalis of Linn., P. officinalis of Jacq.
Seeds from the short-styled form of the cowslip
fertilised with pollen from the same form germinate
so badly that I raised from three successive sowings
only fourteen plants, which consisted of nine short-
styled and five long-styled plants Hence the short-
styled form of the cowslip, when self-fertilised, does not
transmit the same form nearly so truly as does that
of P. Sinensis. From the long-styled form, always
fertilised with its own-form pollen, I raised in the
first generation three long-styled plants,—from their
seed 53 long-styled grandchildren,—from their seed
4 long-styled great-grandchildren,—from their seed
20 long-styled great-great-grandchildren,—and lastly,
Cnar. V. HETEROSTYLED DIMORPHiC PLANTS. 229
from their seed 8 long-styled and 2 short-styled great-
great-great-grandchildren. In this last generation
short-styled plants appeared for the first time in the
course of the six generations,—the parent long-styled
plant which was fertilised with pollen from another
plant of the same form being counted as the first
generation. Their appearance may be attributed to
atavism. From two other long-styled plants, fertilised
with their own-form pollen, 72 plants were raised,
which consisted of 68 long-styled and 4 short-styled.
So that altogether 162 plants were raised from ille-
gitimately fertilised long-styled cowslips, and these
consisted of 156 long-styled and 6 short-styled plants.
We will now turn to the fertility and powers of
growth possessed by the illegitimate plants. From
a short-styled plant, fertilised with its own-form
pollen, one short-styled and two long-styled plants,
and from a long-styled plant similarly fertilised three
long-styled plants were at first raised. The fertiléty
of these six illegitimate plants was carefully observed ;
but I must premise that I cannot give any satisfactory
standard of comparison as far as the number of the
seeds is concerned ; for though I counted the seeds
of many legitimate plants fertilised legitimately and
illegitimately, the number varied so greatly during
successive seasons that no one standard will serve well
‘for illegitimate unions made during different seasons.
Moreover the seeds in the same capsule frequently
differ so much in size that it is scarcely possible
to decide which ought to be counted as good seed.
There remains as the best standard of comparison the
proportional number of fertilised flowers which pro-
duce capsules containing any seed.
First, for the one illegitimate short-styled plant.
In the course of three seasons 27 flowers were illegiti-
230 ILLEGITIMATE OFFSPRING OF Cuar, V.
mately fertilised with pollen from the same plant, and
they yielded only a single capsule, which, however, con-
tained a rather large number of seeds for a union of
this nature, namely, 23. As a standard of comparison
I may state that during the same three seasons 44
flowers borne by legitimate short-styled plants were
self-fertilised, and yielded 26, capsules; so that the
fact of the 27 flowers on the illegitimate plant having
produced only one capsule proves how sterile it was.
To show that the conditions of life were favourable,
I will add that numerous plants of this and other
species of Primula all produced an abundance of
capsules whilst growing close by in the same soil with
the present and following plants. The sterility of the
above illegitimate short-styled plant depended on
both the male and female organs being in a deterio-
rated condition. This was manifestly the case with
the pollen; for many of the anthers were shrivelled
or contabescent. Nevertheless some of the anthers
contained pollen, with which I succeeded in fertilising
some flowers on the illegitimate long-styled plants
immediately to be described. Four flowers on this
same short-styled plant were likewise legitimately fer-
tilised with pollen from one of the following long-
styled plants; but only one capsule was produced,
containing 26 seeds; and this is a very low number
for a legitimate union.
With respect to the five illegitimate long-styled
plants of the first generation, derived from the above
self-fertilised short-styled and long-styled parents,
their fertility was observed during the same three
years. These five plants, when self-fertilised, differed
considerably from one another in their degree of
fertility, as was the case with the illegitimate long-
styled plants of Lythrum salicaria; and their fertility
Cuar. V. HETEROSTYLED DIMORPHIC PLANTS. 231
varied much according to the season. I may premise,
as a standard of comparison, that during the same
years 56 flowers on legitimate long-styled plants of
the same age and grown in the same soil, were fer-
tilised with their own pollen, and yielded 27 capsules ;
that is, 48 per cent. On one of the five illegitimate
long-styled plants 36 flowers were self-fertilised in
the course of the three years, but they did not produce
a single capsule. Many of the anthers on this plant
were contabescent; but some seemed to contain
sound pollen. Nor were the female organs quite
‘impotent; for I obtained from a legitimate cross one
capsule with good seed. On a second illegitimate
long-styled plant 44 flowers were fertilised during the
same years with their own pollen, but they produced
only a single capsule. The third and fourth plants
were in a very slight degree more productive. The
fifth and last plant was decidedly more fertile; for
42 self-fertilised flowers yielded 11 capsules. Alto-
gether, in the course of the three years, no less than
160 flowers on ‘these five illegitimate long-styled
plants were fertilised with their own pollen, but they
yielded only 22 capsules. According to the standard
above given, they ought to have yielded 80 capsules.
These 22 capsules contained on an average 15:1 seeds.
I believe, subject to the doubts before specified, that
with legitimate plants the average number from a
union of this nature would have been above 20 seeds.
Twenty-four flowers on these same five illegitimate
long-styled plants were legitimately fertilised with
pollen from the above-described illegitimate short-
styled plant, and produced only 9 capsules, which is
an extremely small number for a legitimate union.
These 9 capsules, however, contained an average of 38
apparently good seeds, which is as large a number as
16
232 ILLEGITIMATE OFFSPRING OF Cuap. V.
legitimate plants sometimes yield. But this high aver-
age was almost certainly false; and I mention the case
for the sake of showing the difficulty of arriving at a
fair result; for this average mainly depended on two
capsules containing the extraordinary numbers of 75
and 56 seeds; these seeds, however, though I felt
bound to count them, were so poor that, judging from
trials made in other cases, I do not suppose that one
would have germinated ; and therefore they ought not
to have been included. Lastly, 20 flowers were legiti-
mately fertilised with pollen from a legitimate plant,
and this increased their fertility; for they produced
10 capsules. Yet this is but a very small proportion
for a legitimate union.
There can, therefore, be no doubt that these five
long-styled plants and the one short-styled plant of
the first illegitimate generation were extremely sterile.
Their sterility was shown, as in the case of hybrids,
in another way, namely, by their flowering profusely,
and especially by the long endurance of the flowers.
For instance, I fertilised many flowers on these plants,
and fifteen days afterwards (viz. on March 22nd) I
fertilised numerous long-styled and short-styled flowers
on common cowslips growing close by. These latter
flowers, on April 8th, were withered, whilst most of the
‘illegitimate flowers remained quite fresh for several
days subsequently ; so that some of these illegitimate
plants, after being fertilised, remained in full bloom
for above a month.
We will now turn to the fertility of the 53 illegiti-
mate long-styled grandchildren, descended from the
long-styled plant which was first fertilised with its
own pollen, The pollen in two of these plants included
a multitude of small and shrivelled grains. Never-
theless they were not very sterile; for 25 flowers, fer-
Cuar. V. HETEROSTYLED DIMORPHIC PLANTS. 233
tilised with their own pollen, produced 15 capsules,
containing an average of 16°3 seeds. As already
stated, the probable average with legitimate plants
for a union of this nature is rather above 20 seeds.
These plants were remarkably healthy and vigorous,
as long as they were kept under highly favourable
conditions in pots in the greenhouse ; and such treat-
ment greatly increases the fertility of the cowslip.
When these same plants were planted during the next
year (which, however, was an unfavourable one), out
of doors in good soil, 20 self-fertilised flowers pro-
duced only 5 capsules, containing extremely few and
wretched seeds.
Four long-styled great-grandchildren were raised
from the self-fertilised grandchildren, and were kept
under the same highly favourable conditions in the
greenhouse; 10 of their flowers were fertilised with
own-form pollen and yielded the large proportion of 6
capsules, containing on an average 18-7 seeds. From
these seeds 20 long-styled great-great-grandchildren
were raised, which were likewise kept in the greenhouse.
Thirty of their flowers were fertilised with their own
pollen and yielded 17 capsules, containing on an aver-
age no less than 32, mostly fine seeds. It appears,
therefore, that the fertility of these plants of the fourth
illegitimate generation, as long as they were kept
under highly favourable conditions, had not decreased,
but had rather increased. The result, however, was
widely different when they were planted out of doors
in good soil, where other cowslips grew vigorously and
were completely fertile ; for these illegitimate plants
now became much dwarfed in stature and extremely
sterile, notwithstanding that they were exposed to the
visits of insects, and must have been legitimately fer-
tilised by the surrounding legitimate plants. A whole
234 ILLEGITIMATE OFFSPRING: OF Cuse. V
row of these plants of the fourth illegitimate genera-
tion, thus freely exposed and legitimately fertilised,
produced only 3 capsules, containing on an average
only 17 seeds. During the ensuing winter almost all
these plants died, and the few survivors were miserably
unhealthy, wiilst the surrounding legitimate plants
were not in the least injured.
The seeds from the great-great-grandchildren were
sown, and 8 long-styled and 2 short-styled plants of
the fifth illegitimate generation raised. These whilst
still in the greenhouse produced smaller leaves and
shorter flower-stalks than some legitimate plants with
which they grew in competition ; but it should be ob-
served that the latter were the product of a cross with
a fresh stock,—a circumstance which by itself would
have added much to their vigour.* When these ille-
gitimate plants were transferred to fairly good soil
out of doors, they became during the two following
years much more dwarfed in stature and produced very
few flower-stems ; and although they must have been
legitimately fertilised by insects, they yielded cap-
sules, compared with those produced by the surround-
ing legitimate plants, in the ratio only of 5 to 100!
It is therefore certain that illegitimate fertilisation,
continued during successive generations, affects the
powers of growth and fertility of P. veris to an extra-
ordinary degree ; more especially when the plants are
exposed to ordinary conditions of life, instead of being
protected in a greenhouse.
Equat-styled red variety of P. veris—My. Scott has described +
a plant of this kind growing in the Botanic Garden of Edin-
burgh. He states that it was highly self-fertile, although insects
* For full details of this ex- t ‘Proc. Linn. Soc.’ vol. viii
periment, see my ‘ Effects of Cross (1864), p. 105.
and Self-fertilisation,’ 1876, p. 220. .
Cuar. V. HETEROSTYLED DIMORPHIC PLANTS. 235
were excluded; and he explains this fact by showing, first, that
the anthers and stigma are in close apposition, and that the
stamens in length, position and size of their pollen-grains
resemble those of the short-styled form, whilst the pistil re-
sembles that of the long-styled form both in length and in the
structure of the stigma. Hence the self-union of this variety is,
in fact, a legitimate union, and consequently is highly fertile.
Mr. Scott further states that this variety yielded very few seeds
when fertilised by either the long- or short-styled common
cowslip, and, again, that both forms of the latter, when fertilised
by the equal-styled variety, likewise produced very few seeds.
But his experiments with the cowslip were few, and my results
do not confirm his in any uniform manner.
I raised twenty plants from self-fertilised seed sent me by Mr.
Scott; and they all produced red flowers, varying slightly in
tint. Of these, two were strictly long-styled both in structure
and in function; for their reproductive powers were tested by
crosses with both forms of the common cowslip. Six plants
were equal-styled; but on the same plant the pistil varied a
good deal in length during different seasons. This was likewise
the case, according to Mr. Scott, with the parent-plant. Lastly,
twelve plants were in appearance short-styled; but they varied
-much more in the length of their pistils than ordinary short-
styled cowslips, and they differed widely from the latter in
their powers of reproduction. Their pistils had become short-
styled in structure, whilst remaining long-styled in functten.
Short-styled cowslips, when insects are excluded, are extremely
barren: for instance, on one occasion six fine plants produced
only about 50 seeds (that is, less than the product of two good
capsules), and on another occasion not a single capsule. Now,
when the above twelve apparently short-styled seedlings were
similarly treated, nearly all produced a great abundance of
capsules, containing numerous seeds, which germinated re~-
markably well. Moreover three of these plants, which during
the first year were furnished with quite short pistils, on the
following year produced pistils of extraordinary length. The
greater number, therefore, of these short-styled plants could not
be distinguished in function from the equal-styled variety. The
anthers in the six equal-styled and in the apparently twelve
short-styled plants were seated high up in the corolla, as in the
true short-styled cowslip; and the pollen-grains resembled
those of the same form in their large size, but were mingled
236 ILLEGITIMATE OFFSPRING OF Cuap. V
with a few shrivelled grains. In function this pollen was
identical with that of the short-styled cowslip; for ten long-
styled flowers of the common cowslip, legitimately fertilised
with pollen from a true equal-styled variety, produced six cap-
sules, containing on an average 34°4 seeds; whilst seven cap-
sules on a short-styled cowslip iHegitimately fertilised with
pollen from the equal-styled variety, yielded an average of only
14:5 seeds.
As the equal-styled plants differ from one another in their
powers of reproduction, and as this is an important subject,
I will give a few details with respect to five of them. First, an
equal-styled plant, protected from insects (as was done in all
the following cases, with one stated exception), spontaneously
produced numerous capsules, five of which gave an average of
44°8 seeds, with a maximum in one capsule of 57. But six
capsules, the product of fertilisation with pollen from a short-
styled cowslip (and this is a legitimate union), gave an average
of 28°5 seeds, with a maximum of 49; and this is a much lower
average than might have been expected. Secondly, nine cap-
sules from another equal-styled plant, which had not been
protected from insects, but probably was self-fertilised, gave an
average of 45:2 seeds, with a maximum of 58. Thirdly, another
piant which had a very short pistil in 1865, produced spon-
taneously many capsules, six of which contained an average of
33°9 seeds, with a maximum of 38. In 1866 this same plant
had a pistil of wonderful length; for it projected quite above
the anthers, and the stigma resembled that of the long-styled
form. In this condition it produced spontaneously a vast
number of fine capsules, six of which contained almost exactly
the same average number as before, viz. 34°3, with a maximum
of 38. Four flowers on this plant, legitimately fertilised with
pollen from a short-styled cowslip, yielded capsules with an
-average of 30°2 seeds. Fourthly another short-styled plant
spontaneously produced in 1865 an abundance of capsules, ten
of which contained an average of 35:6 seeds, with a maximum
of 54. In 1866 this same plant had become in all respects long-
styled, and ten capsules gave almost exactly the same average
as before, viz. 85'1 seeds, with a maximum of 47. Eight
flowers on this plant, legitimately fertilised with pollen from
a short-styled cowslip, produced six capsules, with the high
average of 53 seeds, and the high maximum of 67. Eight
flowers were also fertilised with pollen from a long-styled cow-
Cuar. V. HETEROSTYLED DIMORPHIC PLANTS. 237
slip (this being an illegitimate union), and produced seven
capsules, containing an average of 24°4 seeds, with a maximum
of 82. The fifth and last plant remained in the same condition
during both years: it had a pistil rather longer than that of the
true short-styled form, with the stigma smooth, as it ought to
be in this form, but abnormal in shape, like a much-elongated
inverted cone. It produced spontaneously many capsules, five
of which, in 1865, gave an average of only 15:6 seeds; and in
1866 ten capsules still gave an average only a little higher, viz.
of 22°1, with a maximum of 80. Sixteen flowers were. fertilised
with pollen from a long-styled cowslip, and produced 12 cap-
sules, with an average of 24°9 seeds, and a maximum of 42.
Eight flowers were fertilised with pollen from a short-styled
cowslip, but yielded only two capsules, containing 18 and 23
seeds. Hence this plant, in function and partially in structure,
was in an almost exactly intermediate state between the long-
styled and short-styled form, but inclining towards the short-
styled; and this accounts for the low average of seeds which it
produced when spontaneously self-fertilised.
The foregoing five plants thus differ much from one another in
the nature of their fertility. In two individuals a great difference
in the length of the pistil during two succeeding years made no
difference in the number of seeds produced. As all five plants
possessed the male organs of the short-styled form in a perfect
state, and the female organs of the long-styled form in a more
or less complete state, they spontaneously produced a surprising
number of capsules, which generally contained a large average
of remarkably fine seeds. With ordinary cowslips, legitimately
fertilised, I once obtained from plants cultivated in the green-
house the high average, from seven capsules, of 58°7 seeds, with
a maximum in one capsule of 87 seeds; but from plants grown
out of doors I never obtained a higher average than 41 seeds.
Now two of the equal-styled plants, grown out of doors and
spontaneously s¢if-fertilised, gave averages of 44 and 45 seeds;
but this high fertility may perhaps be in part attributed to the
stigma receiving pollen from the surrounding anthers at exactly
the right period. Two of these plants, fertilised with pollen
from a short-styled cowslip (and this in fact is a legitimate
union), gave a lower average than when self-fertilised. On the
other hand, another plant, when similarly fertilised by a cowslip,
yielded the unusually high average of 53 seeds, with a maximum
of 67. Lastly, as we have just seen, one of these plants was in
238 ILLEGITIMATE OFFSPRING OF Cuar. V.
an almost exactly intermediate condition in its female organs
between the long- and short-styled forms, and consequently,
when self-fertilised, yielded a low average of seed. If we add
together all the experiments which I made on the equal-styled
plants, 41 spontaneously self-fertilised capsules (insects having
been excluded) gave an average of 34 seeds, which is exactly the
same number as the parent-plant yielded in Edinburgh. Thirty-
four flowers, fertilised with pollen from the short-styled cowslip
(and this is an analogous union), produced 17 capsules, contain-
ing an average of 83°8 seeds. It is a rather singular circum-
stance, for which I cannot account, that 20 flowers, artificially fer-
tilised on one occasion with pollen from the same plants yielded
only ten capsules, containing the low average of 26°7 seeds.
As bearing on inheritance, it may be added that 72 seed-
lings were raised from one of the red-flowered, strictly equal-
styled, self-fertilised plants descended from the similarly cha-
racterised Edinburgh plant. These 72 plants were there-
fore grandchildren of the Edinburgh plant, and they all bore,
as in the first generation, red flowers, with the exception of
one plant, which reverted in colour to the common cowslip.
In regard to structure, nine plants were truly long-styled
and had their stamens seated low down in the corolla in the
proper position; the remaining 63 plants were equal-styled,
though the stigma in about a dozen of them stood a little below
the anthers. We thus see that the anomalous combination in the
same flower, of the male and female sexual organs which properly
exist in the two distinct forms, was inherited with much force,
Thirty-six seedlings were also raised from long and short-styled
common, cowslips, crossed with pollen from the equal-styled
variety. Of these plants one alone was equal-styled, 20 were
short-styled, but with the pistil in three of them rather too
long, and the remaining 15 were long-styled. In this case we
have an illustration of the difference between simple inheritance
and prepotency of transmission; for the equal-styled variety,
when self-fertilised, transmits its character, as we have just
seen, with much force, but when crossed with the common
cowslip cannot withstand the greater power of transmission
of the latter.
PuLMonaRIA.
I have little to say on this genus. I obtained seeds of P. offi
stzalis from a garden where the long-styled form alono grew,
Cuar. V. HETEROSTYLED PLANTS. 239
and raised 11 seedlings, which were all long-styled. These
plants were named for me by Dr. Hooker. They differed, as has
been shown, from the plants belonging to this species which in
Germany were experimented on by Hildebrand;* for he found that
the long-styled form was absolutely sterile with its own pollen,
whilst my long-styled seedlings and the parent-plants yielded a
fair supply of seed when self-fertilised. Plants of the long-
styled form of Pulmonaria angustifolia were, like Hildebrand’s
plants, absolutely sterile with their own pollen, so that I could
never procure a single seed. On the other hand, the short-
styled plants of this species, differently from those of P. off-
cinulis, were fertile with their own pollen in a quite remarkable
degree for a heterostyled plant. From seeds carefully self-fer-
tilised I raised 18 plants, of which 13 proved short-styled and
5 long-styled.
PoLtyconum FAGOPYRUM.
From flowers on long-styled plants fertilised illegitimately
with pollen from the same plant, 49 seedlings were raised, and
these consisted of 45 long-styled and 4 short-styled. From
flowers on short-styled plants illegitimately fertilised with pollen
from the same plant 33 seedlings were raised, and these con-
sisted of 20 short-styled and 13 long-styled. So that the usual
rule of illegitimately fertilised long-styled plants tending much
more strongly than short-styled plants to reproduce their own
form here holds good. The illegitimate plants derived from
both forms flowered later than the legitimate, and were to the
latter in height as 69 to 100. But as these illegitimate plants
were descended from parents fertilised with their own pollen,
whilst the legitimate plants were descended from parents crossed
with pollen from a distinct individual, it is impossible to know
how much of their difference in height and period of flowering,
is due to the illegitimate birth of the one set, and how much
to the other set being the product of a cross between distinct
plants.
Concluding Remarks on the Illegitimate Offspring of
Heterostyled Trimorphic and Dimorphic Plants.
{4 is remarkable how closely and in how many points
illegitimate unions between the two or three forms of the
* Bot. Zeitung,’ 1865, p. 13.
240 ILLEGITIMATE OFFSPRING OF Cuar. V,
same heterostyled species, together with their illegiti-
mate offspring, resemble hybrid unions between distinct
species together with their hybrid offspring. In both
‘cases we meet with every degree of sterility, from very
slightly lessened fertility to absolute barrenness, when
not even a single seed-capsule is produced. In both
cases the facility of effecting the first union is much
influenced by the conditions to which the plants are
exposed.* Both with hybrids and illegitimate plants
the innate degree of sterility is highly variable in
plants raised from the same mother-plant. In both
cases the male organs are more plainly affected than
the female; and we often find contabescent anthers
enclosing shrivelled and utterly powerless pollen-
grains. ‘The more sterile hybrids, as Max Wichura
has well shown,f are sometimes much dwarfed in
stature, and have so weak a constitution that they are
liable to premature death; and we have seen exactly
parallel cases with the illegitimate seedlings of Lythrum
and Primula. Many hybrids are the most persistent
and profuse flowerers, as are some illegitimate plants.
When a hybrid is crossed by either pure parent-form,
it is notoriously much more fertile than when crossed
inter se or by another hybrid ; so when an illegitimate
plant is fertilised by a legitimate plant, it is more
fertile than when fertilised cnter se or by another ille-
gitimate plant. When two species are crossed and
they produce numerous seeds, we expect as a general
rule that their hybrid offspring will be moderately
fertile; but if the parent species produce extremely
few seeds, we expect that the hybrids will be very
* This has been remarked by chapter a striking illustration in
many expcrimentalistsin effecting the case of Primula veris.
crosses hetween distinct species; + ‘Die Bastardbefruchtung im
and in regard to illegitimate Pflanzenreich,’ 1865.
unions I have given in the first
Cuar. V. HETEROSTYLED PLANTS. 241
sterile. But there are marked exceptions, as shown
by Gartner, to these rules. So it is with illegitimate
unions and illegitimate offspring. Thus the mid-
styled form of Lythrum salicaria, when illegitimately
fertilised with pollen from the longest stamens of
the short-styled form, produced an unusual number
of seeds; and their illegitimate offspring were not at
all, or hardly at all, sterile. On the other hand, the
illegitimate offspring from the long-styled form, ferti-
lised with pollen from the shortest stamens of the same
form, yielded few seeds, and the illegitimate offspring
thus produced were very sterile; but they were more
sterile than might have been expected relatively to the
difficulty of effecting the union of the parent sexual
elements. No point is more remarkable in regard to
the crossing of species than their unequal reciprocity.
Thus species A will fertilise B with the greatest ease ;
but B will not fertilise A after hundreds of trials. We
have exactly the same case with illegitimate unions;
for the mid-styled Lythrum salicaria was easily ferti-
lised by pollen from the longest stamens of the short-
styled form, and yielded many seeds; but the latter
form did not yield a single seed when fertilised by the
longest stamens of the mid-styled form.
Another important point is prepotency. Gartner
-has shown that when a species is fertilised with pollen
‘from another species, if it be afterwards fertilised with
its own pollen, or with that of the same species, this
is so prepotent over the foreign pollen that the effect
‘of the latter, though placed on the stigma some time
‘previously, is entirely destroyed. Exactly the same
thing occurs with the two forms of a heterostyled
species. Thus several long-styled flowers of Primula
veris were fertilised illegitimately with pollen from
another plant of the same form, and twenty-four hours
242 ILLEGITIMATE OFFSPRING OF Cap. V.
afterwards legitimately with pollen from a short-styled
dark-red polyanthus which is a variety of P. veris ;
and the result was that every one of the thirty seed-
lings thus raised bore flowers more or less red, show-
ing plainly how prepotent the legitimate pollen from
a short-styled plant was over the legitimate pollen
from a long-styled plant.
In all the several foregoing points the parallelism is
wonderfully close between the effects of illegitimate
and hybrid fertilisation. It is hardly an exaggeration
to assert that seedlings from an illegitimately fer-
tilised heterostyled plant are hybrids formed within
-the limits of one and the same species. This conclu-
sion is important, for we thus learn that the difficulty
in sexually uniting two organic forms and the sterility
of their offspring, afford no sure criterion of so-called
specific distinctness. If any one were to cross two
varieties of the same form of Lythrum or Primula for
the sake of ascertaining whether they were specifically
distinct, and he found that they could be united only
with some difficulty, that their offspring were extremely
sterile, and that the parents and their offspring re-
sembled in a whole series of relations crossed species
and their hybrid offspring, he might maintain that his
varieties had been proved to be good and true species ;
but he would be completely deceived. In the second
place, as the forms of the same trimorphic or dimorphic
heterostyled species are obviously identical in general
structure, with the exception of the reproductive
organs, and as they are identical in general constitu-
tion (for they live under precisely the same condi-
tions), the sterility of their illegitimate unions and
tLat of their illegitimate offspring, must depend ex-
clusively on the nature of the sexual elements and
on their incompatibility for uniting in a particular
Cuar. V HETEROSTYLED PLANTS. 248
manner. And as we have just seen that distinct species
when crossed resemble in a whole series of relations the
forms of the same species when illegitimately united,
we are led to conclude that the sterility of the former
must likewise depend exclusively on the incompatible
nature of their sexual elements, and not on any general
difference in constitution or structure. We are, indeed,
led to this same conclusion by the impossibility of de-
tecting any differences sufficient to account for certain
species crossing with the greatest ease, whilst other
closely allied species cannot be crossed, or can be crossed
only with extreme difficulty. We are led to this con-
clusion still more forcibly by considering the great
difference which often exists in the facility of crossing
reciprocally the same two species; for it is manifest in
this case that the result must depend on the nature of
the sexual elements, the male element of the one
species acting freely on the female element of the
other, but not so in a reversed direction. And now we
see that this same conclusion is independently and
strongly fortified by the consideration of the illegiti-
mate unions of trimorphic and dimorphic heterostyled
plants. In so complex and obscure a subject as hybrid-
ism it is no slight gain to arrive at a definite conclu-
sion, namely, that we must look exclusively to func-
tional differences in the sexual elements, as the cause
of the sterility of species when first crossed and of
their hybrid offspring. It was this consideration which
led me to make the many observations recorded in this
chapter, and which in my opinion make them worthy
of publication.
244 CONCLUDING REMARKS Cuap. VL
CHAPTER VI.
Conciupine Remarks oN HeEtTgErosTyLep PLANTs,
The essential character of heterostyled plants—Summary of the
differences in fertility between legitimately and illegitimately fer-
tilised plants—Diameter of the pvllen-grains, size of anthers and
structure of stigma in the different forms—Affinities of the genera
which include heterostyled species—-Nature of the advantages
derived from heterostylism—The means by which plants became
heterostyled—Transmission of form—Kqual-styled varieties of
hetcrostyled plants—Final remarks,
in the foregoing chapters all the heterostyled plants
known to me have been more or less fully described.
Several other cases have been indicated, especially by
Professor Asa Gray and Kuhn,* in which the indi-
viduals of the same species differ in the length of
their stamens and pistils; but as I have been often de-
ceived by this character taken alone, it seems to me
the more prudent course not to rank any species as
heterostyled, unless we have evidence of more impor-
tant differences between the forms, as in the diameter
of the pollen-grains, or in the structure of the stigma.
The individuals of many ordinary hermaphrodite plants
habitually fertilise one another, owing to their male
and female organs being mature at different periods,
or to the structure of the parts, or to self-sterility, &.;
and so it is with many hermaphrodite animals, for
instance, land-snails or earth-worms ; but in all these
eases any one individual can fully fertilise or be ferti-
* Asa Gray, ‘American Journ. elsewhere as already referred to,
af Science,’ 1865, p. 101; and Kuhn, ‘ Bot. Zeitung,’ 1867, p. 67.
Cuar. VI. ON HETEROSTYLED PLANTS. 245
lised by any other individual of the same species. This
is-not so with heterostyled plants: a long-styled, mid-
styled or short-sty.ed plant cannot fully fertilise or
be fertilised by a_y other individual, but only by
one belonging to another form. Thus the essen-
tial character of plants belonging to the heterostyled
class is that the individuals are divided into two or
three bodies, like the males and females of dicecious
plants or of the higher animals, which exist in approxi-
mately equal numbers and are adapted for reciprocal
fertilisation. The existence, therefore, of two or three
bodies of individuals, differing from one another in the
above more important characteristics, offers by itself
good evidence that the species is heterostyled. But
absolutely conclusive evidence can be derived only
from experiments, and by finding that pollen must be
applied from the one form to the other in order to
ensure complete fertility.
In order to show how much more fertile each form
is when legitimately fertilised with pollen from the
other form (or in the case of trimorphic species, with
the proper pollen from one of the two other forms)
than when illegitimately fertilised with its own-form
pollen, I will append a Table (83) giving a summary
of the results in all the cases hitherto ascertained.
The fertility of the unions may be judged by two
standards, namely, by the proportion of flowers which,
when fertilised in the two methods, yield capsules, and
by the average number of seeds per capsule. When
there is a dash in the left-hand column opposite to
the name of the species, the proportion of the flowers
which yielded capsules was not recorded.
The two or three forms of the same heterostyled
species do not differ from one another in general habit
or foliage, as sometimes, though rarely, happens with
246 CONCLUDING REMARKS Cuap, VL
TaBLe 383.
Fertility of the Legitimate Unions taken together, compared with
that of the Illegitimate Unions together. The fertility of the
Legitimate Unions, as judged by both standards, is taken as 100,
Illegitimate Uniuns,
Proportional
Name of Species. Number of Average
Flowers Number of
which pro. Seeds per
ducec Capsule,
Capsules.
Primula veris 2. 1 1. ew ee ee 69 65
Poelations 2 2 2 @ @ % 2 % & 27 15
Povulgaris « 2 . s © © + 60 54
P.Sinensis . . ee hogs 25) le gph tg 84 63
P. Sinensis (second trial) 3. 16D He Sp ts 0 53
P. Sinensis(Hildebrand) . . . . . 100 42
P. auricala (Scott)... wo ctete fi 80 15
P. BibRimensig a, 4 cc we oe Ra ee 95 31
P. cortusoides , . . Mace, he 74 66
PivOuugae ew Rw 72 48
P. farinosa >. ‘ 71 44
Average of the nine species of Primula | 88°4 69
Hottonia palustris (H. Muller). . — 61
Linum grandiflorum ee difference pacer = 69
is much greater) .
L, perenne . _ 20
L. perenne (Hildebrand) 0 0
Pulmonaria officinalis (German stock, aie 0 0
brand). . . . ' a a
Pulmonaria angustifolia 35 82
Mitchella repens, 20 47
Borreria, Brazilian sp. _ 0
Polygonum fagopyrum . _ 46
Lythrum salicaria. 33 46
Oxalis Valdiviana (Hildebrand). 2 34
O. Regnelli ys 0 0
O. speciosa acs 15 49
—
the two sexes of dicecious plants. Nor does the calyx
differ, but the corolla sometimes differs slightly in shape,
owing to the different position of the anthers. In Bor-
reria the hairs within the tube of the corolla are differ-
ently situated in the long-styled-and short-styled forms.
In Pulmonaria there is a slight difference in the size of
Cuap. VI. ON HETEROSTYLED PLANTS. 247
the corolla, and in Pontederia in its colour. In the re-
productive organs the differences are much greater and
more important. In the one form the stamens may be
all of the same length, and in the other graduated in
length, or alternately longer and shorter. The fila-
ments may differ in colour and thickness, and are
sometimes nearly thrice as long in the one form as in the
other. They adhere also for very different proportional
lengths to the corolla. The anthers sometimes differ
much in size in the two forms. Owing to the rotation
of the filaments, the anthers, when mature, dehisce to-
wards the circumference of the flower in one form of
Faramea, and towards the centre in the other form. The
pollen-grains sometimes differ conspicuously in colour,
and often to an extraordinary degree in diameter.
They differ also somewhat in shape, and apparently in
their contents, as they are unequally opaque. In the
short-styled form of Faramea the pollen-grains are
covered with sharp points, so as to cohere readily to-
gether or to an insect; whilst the smaller grains of the
long-styled form are quite gmooth.
With respect to the pistil, the style may be almost
thrice as long in the one form as in the other. In
Oxalis it sometimes differs in hairiness in the three
forms. In Linum the pistils either diverge and pass
out between the filaments, or stand nearly upright and
parallel to them. The stigmas in the two forms often
differ much in size and shape, and more especially in
the length and thickness of their papille; so that
the surface may be rough or quite smooth. Owing to
the rotation of the styles, the papillose surface of
the stigma is turned outwards in one form of Linum
perenne, and inwards in the other form. In flowers of
the same age of Primula veris the ovules are larger in
the long-styled than in the short-styled form. The
17
248 CONCLUDING REMARKS Cuar. VI
seeds produced by the two or three forms often differ
in number, and sometimes in size and weight; thus,
five seeds from the long-styled form of Lythrum sali-
caria equal in weight six from the mid-styled and
seven from the short-styled form. Lastly, short-styled
plants of Pulmonaria officinalis bear a larger number
of flowers, and these set a larger proportional number
of fruit, which however yield a lower average number
of seed, than the long-styled plants. With hetero-
styled plants we thus see in how many and in what
important characters the forms of the same undoubted
species often differ from one another—characters which
with ordinary plants would be amply sufficient to dis-
tinguish species of the same genus.
As the pollen-grains of ordinary species belonging
to the same genus generally resemble one another
closely in all respects, it is worth while to show, in the
following table (34), the difference in diameter be-
tween the grains from the two or three forms of the
same heterostyled species in the forty-three cases in
which this was ascertained. But it should be observed
that some of the following measurements are only
approximately accurate, as only a few grains were
measured. In several cases, also, the grains had been
dried and were then soaked in water. Whenever they
were of an elongated shape their longer diameters
were measured. The grains from the short-styled
plants are invariably larger than those from the long-
styled, whenever there is any difference between them.
The diameter of the former is represented in the table
by the number 100.
We here see that, with seven or eight exceptions
out of the forty-three cases, the pollen-grains from one
form are larger than those from the other form of the
same species. The extreme difference is as 100 to 55;
Cuap. VI. ON HETEROSTYLED PLANTS. 249
Tabue 34.
Relative Diameter of the Pollen-grains from the forms of the sume
Heterostyled Species; those from the shori-styled form being
represented by 100.
Dimorphice Species.
From the Long- From tbe Longs
styled form styled form.
Primulaveris . . . . 67 Cordia(sp.?) . . . . 100
» vulgaris . 71 Gilia pulchella . . . . 100
- Sinensis( Hildebrand) 57 » Micrantha, . . . 81
» auricula .. 71 Sethia acuminata . . . 83
Hottonia palustris (H. Miller) 61 Erythroxylum (sp.?) . . 93
» (elf) . 64 Cratoxylon formosum . . 86
Linum grandiflorum . . 100 Mitchella repens, pollen-
» perenne(diameter va- rains of the long-styled
riable). . “}100 ® 4 little smaller. are
» flavum. . . . 100 Borreria (sp. os ook: Sep 92
Pulmonaria officinalis . . 78 Faramea (sp. 67
angustifolia . 91 Suteria (sp. 5) (Fritz Muller) 75
Polygonum fagopyrum. , 82 Houstonia cerulea . . 72
Leucosmia Burnettiana . 99 Oldenlandia (sp.?) . . . 78
#giphilaelata. . . . 62 Hedyotis (sp.?). 88
Menyanthes trifoliata . . 84 Coccocypselum (sp. a @ 100
Limnanthemum Indicum . 100 Muller) . .
Villarsia (sp.?). 6 0. 75 Lipostoma (sp.?) . . . 80
Worsythia suspensa. . . 94 Cinchona micrantha . . 91
Trimorphic Species.
Ratio expressing the extreme differences | Ratio between the diameters of the pollen-
- in diameter of the pollen-grains from the grains of the two sets of anthers in the
two sets of anthers in the three forms. same form.
Lythrum salicaria. . . . 60 | Oxalis rosea, long-styled form 83
Nesza verticillata. . 65 (Hildebrand) .
Oxalis Valdiviana (Hildebrand) 71 9 compressa, short-styled
7 83
a Regnelli. S Gas . 78 form .
» Speciosa . . . « 69 | Pontederia (sp. ?) abated) 87
» sensitiva . . . . 84 form. . . .
Pontederia (sp.?) . . . 55 ” other maa | 86
form. . 2 »
and we should bear in mind that in the case of
spheres differing to this degree in diameter, their
contents differ in the ratio of six to one. With all
the species in which the grains differ in diameter,
there is no exception to the rule. that those from the
250 CONCLUDING REMARKS Cuar. VL
anthers of the short-styled form, the tubes of which
have to penetrate the longer pistil of the long-styled
form, are larger than the grains from the other form.
This curious relation led Delpino* (as it formerly did
me) to believe that the larger size of the grains in
the short-styled flowers is connected with the greater
supply of matter needed for the development of their
longer tubes. But the case of Linum, in which
the grains of the two forms are of equal size, whilst
the pistil of the one is about twice as long as that
of the other, made me from the first feel very
doubtful with respect to this view. My doubts have
since been strengthened by the cases of Limnanthe-
mum and Coccocypselum, in which the grains are of
equal size in the two forms; whilst in the former
genus the pistil is nearly thrice and in the latter
twice as long as in the other form. In those species
in which the grains are of unequal size in the two
forms, there is no close relationship between the de-
gree of their inequality and that of their pistils.
Thus in Pulmonaria officinalis and in Erythroxy-
lum the pistil in the long-styled form is about
twice the length of that in the other form, whilst in
the former species the pollen-grains are as 100 to
78, and in the latter as 100 to 93 in diameter. In
the two forms of Suteria the pistil differs but little
in length, whilst the pollen - grains are as 100 to
75 in diameter. These cases seem to prove that the
difference in size between the grains in the two
forms is not determined by the length of the pistil,
down which the tubes have to grow. That with
plants in general there is no close relationship between
a Sull’ Opera, la D’stribuzione dei Sessi nelle Piunte,’ &e. 1867,
Pp id.
Cnar. VI. ON HETEROSTYLED PLANTS. 251
the size of the pollen-grains and the length of the
pistil is manifest: for instance, I found that the dis-
tended grains of Datura arborea were ‘00243 of an
inch in diameter, and the pistil no less than 9°25
inches in length ; now the pistil in the small flowers
of Polygonwm JSagopyrum is very short, yet the larger
pollen-grains from the short-styled plants had exactly
the same diameter as those from the Datura, with its
enormously elongated pistil.
Ni otwithstanding these several considerations, it is
difficult quite to give up the belief that the pollen-grains
from the longer stamens of heterostyled plants have
become larger in order to allow of the development of
longer tubes; and the foregoing opposing facts may
possibly be reconciled in the following manner. The
tubes are at first developed from matter contained
within the grains, for they are sometimes exserted
to a considerable length, before the grains have
touched the stigma; but botanists believe that they
afterwards draw nourishment from’ the conducting
tissue of the pistil. Jt is hardly possible to doubt
that this must occur in such cases as that of the Da-
tura, in which the tubes have to grow down the whole
length of the pistil, and therefore to a length equal-
ling 3,806 times the diameter of the grains (namely,
°00243 of an inch) from which they are protruded.
I may here remark that I have seen the pollen-grains
of a willow, immersed in a very weak solution of honey,
protrude their tubes, in the course of twelve hours, to
a length thirteen times as great as the diameter of the
grains. Now if we suppose that the tubes in some
heterostyled species are developed wholly or almost
wholly from matter contained within the grains, while
in other species from matter yielded by the pistil, we
can see that in the former case it would be necessary
252 CONCLUDING REMARKS Cuar. VIL
that the grains of the two forms should differ in size
relatively to the length of the pistil which the tubes
have to penetrate, but that in the latter case it would
not be necessary that the grains should thus differ.
Whether this explanation can be considered satisfac-
tory must remain at present doubtful.
There is another remarkable difference between the
forms of several heterostyled species, namely in the
anthers of the short-styled flowers, which contain the
larger pollen-grains, being longer than those of the
long-styled flowers. This is the case with Hottonia
palustris in the ratio of 100 to 83. With Limnan-
themum Indicwm the ratio is as 100 to 70. With the
allied Menyanthes the anthers of the short-styled form
are a little and with Villarsia conspicuously larger
than those of the long-styled. With Pulmonaria
angustifolia they vary much in size, but from an
average of seven measurements of each kind the ratio
isas 100 to 91. In six genera of the Rubiacez there
is a similar difference, either slightly or well marked.
Lastly, in the trimorphic Pontederia the ratio is 100
to 88; the anthers from the longest stamens in the
short-styled form being compared with those from the
shortest stamens in the long-styled form. On the
other hand, there is a similar and well-marked differ-
ence in the length of the stamens in the two forms
of Forsythia suspensa and of Linwm flavum ; but in
these two cases the anthers of the short-styled flowers
are shorter than those of the long-styled. The rela-
tive size of the anthers was not particularly attended
to in the two forms of the other heterostyled plants,
but I believe that they are generally equal, as is
certainly the case with those of the common primrose
and cowslip.
The pistil differs in length in the two forms of every
Cuar. V1. ON HETEROSTYLED PLANTS. 253
heterostyled plant, and although a similar difference
is very general with the stamens, yet in the two
forms of Linum grandiflorum and of Cordia they are
equal. There can hardly be a doubt that the rela-
tive length of these organs is an adaptation for the
safe transportal by insects of the pollen from the one
form to the other. The exceptional cases in which
these organs do not stand exactly ona level in the two
forms may probably be explained by the manner in
which the flowers are visited. With most of the
species, if there is any difference in the size of the
stigma in the two forms, that of the long-styled, what-
ever its shape may be, is larger than that of the short-
styled. But here again there are some exceptions to
the rule, for in the short-styled form of Leucosmia
Burnettiana the stigmas are longer and much narrower
than those of the long-styled ; the ratio between the
lengths of the stigmas in the two forms being 100 to 60.
In the three Rubiaceous genera, Faramea, Houstonia
and Oldenlandia, the stigmas of the short-styied form
are likewise somewhat longer and narrower; and in
the three forms of Owalis sensitiva the difference is
strongly marked, for if the length of the two stigmas
of the long-styled pistil be taken as 100, it will be
represented in the mid- and short-styled forms by
the numbers 141 and 164. As in all these cases the
stigmas of the short-styled pistil are seated low down
within a more or less tubular corolla, it is probable
that they are better fitted by being long and narrow
for brushing the pollen off the inserted proboscis of
an insect.
With many heterostyled plants the stigma differs
in roughness in the two forms, and when this is the
case there is no known exception to the rule that the
papille on the stigma of the long-styled form are longer
254 CONCLUDING REMARKS Cuar. VL
and often thicker than those on that of the short-
styled. For instance, the papille on the long-styled
stigma of Hottonia palustris are more than twice the
length of those in the other form. This holds good
even in the case of Houstonta coerulea, in which the
stigmas are much shorter and stouter in the long-
styled than in the short-styled form, for the papille
on the former compared with those on the latter are
as 100 to 58 in length. The length of the pistil
in the long-styled form of Linwm grandiflorum varies
much, and the stigmatic papille vary in a corre-
sponding manner. From this fact I inferred at first
that in all cases the difference in length between the
stigmatic papille in the two forms was one merely of
correlated growth; but this can hardly be the true or
general explanation, as the shorter stigmas of the
long-styled form of Houstonia have the longer papille.
It is a more probable view that the papille, which
render the stigma of the long-styled form of various
species rough, serve to entangle effectually the large-
sized pollen-grains brought by insects from the short-
styled form, thus ensuring its legitimate fertilisation.
This view is supported by the fact that the pollen-
grains from the two forms of eight species in Table
34 hardly differ in diameter, and the papillz on their
stigmas do not differ in length.
The species which are at present positively or
almost positively known to be heterostyled belong, as
shown in the following table, to 38 genera, widely dis-
tributed throughout the world. These genera are
included in fourteen Families, most of which are very
distinct from one another, for they belong to nine of
the several great Series, into which phanerogamic
plants have been divided by Bentham and Hooker.
Cuar. VI. ON HETEROSTYLED PLANTS. 255
Taye 35.
List of Genera including Heterostyled Species.
DicoTYLEpons, DICOTYLEDONS.
Cratoxylon. Hypericinez. Mitchella. Rubiacee.
Erythroxylum. Erythroxylez. Diodia. ”
Sethia. E Borreria, ”
Linum, Geraniacezx. Spermacoce. ”
Oxalis. ‘i Primula. Primulacez.
Lythrum. Lythraces. Hottonia. ”
Nesea. 0 Androsace, -
Cinchona. Rubiacez. Forsythia. Oleaceze
Bouvardia, ‘4 Menyanthes. Gentianacex.
Manettia. 3 Limnanthemum. ‘5
Hedyotis. es Villarsia. 3
Oldenlandia. * Gilia. Polemoniacea,
Houstonia. vs Cordia. Cordiex.
Coccocypseluin. 55 Pulmonaria. Boraginee.
Lipostoma, 5) AXgiphila. Verbenacez.
Knoxia. 5 Polygonum. Polygonez.
Faramea. Thymelea. Thymelee.
Psychotria. sity
Rudgea, at MonocoTyLEDons,
Suteria. - Pontederia. Pontederiacee.
In some of these families the heterostyled condition
must have been acquired at a very remote period.
Thus the three closely allied genera, Menyanthes,
Limnanthemum, and Villarsia, inhabit respectively
Europe, India, and South America. Heterostyled
species of Hedyotis are found in the temperate regions
of North and the tropical regions of South America.
Trimorphic species of Oxalis live on both sides of
the Cordillera in South America and at the Cape of
Good Hope. In these and some other cases it is not
probable that each species acquired its heterostyled
structure independently of its close allies. If they
did not do so, the three closely connected genera of
the Menyanthee and the several trimorphic species of
Oxalis must have inherited their structure from a
tommon progenitor. But an immense lapse of time
will have been necessary in all such cases for the
modified descendants of a common progenitor to have
256 CONCLUDING REMARKS Cuar. VL
spread from a single centre to such widely remote and
separated areas. Ihe family of the Rubiacez contains
not far short of as many heterostyled genera as all
the other thirteen families together; and hereafter
ne doubt other Rubiaceous genera will be found to
be heterostyled, although a large majority are homo-
styled. Several closely allied genera in this family
probably owe their heterostyled structure to descent
in common; but as the genera thus characterised are
distributed in no less than eight of the tribes into
which this family has been divided by Bentham and
Hooker, it is almost certain that several of them
must have become heterostyled independently of
one another. What there is in the constitution or
structure of the members of this family which favours
their becoming heterostyled, I cannot conjecture.
Some families of considerable size, such as the Bo-
ragineze and Verbenaces, include, as far as is at
present known, only a single heterostyled genus,
Polygonum also is the sole heterostyled genus in its
family; and though it is a very large genus, no other
species except P. fagopyrum is thus characterised. We
may suspect that it has become heterostyled within
a comparatively recent period, as it seems to be less
strongly so in function than the species in any other
genus, for both forms are capable of yielding a con-
siderable number of spontaneously self-fertilised seeds.
Polygonum in possessing only a single heterostyled
species is an extreme case; but every other genus of
considerable size which includes some such species
likewise contains homostyled species. Lythrum in-
cludes trimorphic, dimorphic, and homostyled species.
Trees, bushes, and herbaceous plants, both large
and small, bearing single flowers or flowers in dense
spikes or heads, have been rendered heterostyled.
Cuap. VI. ON HETEROSTYLED PLANTS. 257
So have plants which inhabit alpine and lowland sites,
dry land, marshes and water.*
When I first began to experimentise on hetero-
styled plants it was under the impression that they
were tending to become dicecious ; but I was soon forced
to reliuquish this notion, as the long-styled plants of
Primula which, from possessing a longer pistil, larger
stigma, shorter stamens with smaller pollen-grains,
seemed to be the more feminine of the two forms,
yielded fewer seeds than the short-styled plants which
appeared to be in the above respects the more mascu-
line of the two. Moreover, trimorphic plants evidently
come under the same category with dimorphic, and
the former cannot be looked at as tending to become
dicecious. With Lythrum salicaria, however, we have
the curious and unique case of the mid-styled form
being more feminine or less masculine in nature than
the other two forms.
* Out of the 38 genera known
to include heterostyled species,
about eizht, or 21 per cent., are
more or less aquatic in their
habits. I was at first struck with
this fact, for I was not then aware
how large a proportion of or-
dinary plants inhabit such sta-
tions. Heterostyled plants may
be said in one sense to have their
sexes separated, as the forms must
mutually fertilise one another.
Therefore it seemed worth while
to ascertain what proportion of
the genera in the Linnean classes,
Moneecia, Diccia and Poly-
gamia, contained species which
live “‘in water, marshes, bogs or,
watery places.” In Sir W. J.
Hooker’s ‘British Flora’ (4th
edit. 1838) these three Linnean
slasses include £0 genera, 17 of
This is shown by the large
which (ie. 43 per cent.) contain
species inhabiting the just-speci-
fied stations. So that 43 per cent,
of those British plants which
have their sexes separated are
more or less aquatic in their
habits, whereas only 21 per cent.
of heterostyled plants have such
habits. I may add that the her-
maplhrodite classes, from Monan-
dria to Gynandria inelusive, cons
tain 447 genera, of which 113 are
aquatic in the above sense, or only
25 per cent. It thus appears, as
far ag can be judged from such
imperfvct data, that there is some
connection betwecn the separation
of the sexes in plants and the
watery nature of the sites which
they inhabit; but that this does
not hold good with heterostyled
species,
258 CONCLUDING REMARKS Cuar. VL
number of seeds which it yields in whatever manner
it may be fertilised, and by its pollen (the grains of
which are of smaller size than those from the corre-
sponding stamens in' the other two forms) when
applied to the stigma of any form producing fewer
seeds than the normal number. If we suppose the
process of deterioration of the male organs in the mid-
styled form to continue, the final result would be the
production of a female plant; and Lythrum salicaria
would then consist of two heterostyled hermaphrodites
and a female. No such case is known to exist, but it
is a possible one, as hermaphrodite and female forms
of the same species are by no means rare. Although
there is no reason ‘to believe that heterostyled plants
are regularly becoming diccious, yet they offer sin-
gular facilities, as will hereafter be shown, for such
conversion; and this appears occasionally to have been
effected.
We may feel sure that plants have been rendered
heterostyled to ensure cross-fertilisation, for we now
know that a cross between the distinct individuals of
the same species is highly important for the vigour and
fertility of the offspring. The same end is gained by
dichogamy or the maturation of the reproductive ele-
ments of the same flower at different periods,—by
diceciousness—self-sterility—the prepotency of pollen
from another individual over a plant’s own pollen,—and
lastly, by the structure of the flower in relation to the
visits of insects. The wonderful diversity of the means
for gaining the same end in this case, and in many
others, depends on the nature of all the previous
changes through which the species has passed, and on
the more or less complete inheritance of the successive
adaptations of each part to the surrounding conditions,
Ouap. VI. ON HETEROSTYLED PLANTS. 259
Plants which are already well adapted by the structure
of their flowers for cross-fertilisation by the aid of
insects often possess an irregular corolla, which has
been modelled in relation to their visits; and it would
have been of little or no use to such plants to have
become heterostyled. We can thus understand why
it is that not a single species is heterostyled in such
great families as the Leguminose, Labiate, Scrophu-
lariaceze, Orchidez, &c., all of which have irregular
flowers. Every known heterostyled plant, however,
depends on insects for its fertilisation, and not on the
wind ; so that it is a rather surprising fact that only
one genus, Pontederia, has a plainly irregular corolla.
Why some species are adapted for cross-fertilisation,
whilst others within the same genus are not so, or
if they once were, have since lost such adaptation
and in consequence are now usually self-fertilised, I
have endeavoured elsewhere to explain to a certain
limited extent.* If it be further asked why some
species have been adapted for this end by being made
heterostyled, rather than by any of the above specified
means, the answer probably lies in the manner in
which heterostylism originated,—a subject immedi-
ately to be discussed. Heterostyled species, however,
have an advantage over dichogamous species, as all
the flowers on the same heterostyled plant belong to
the same form, so that when fertilised legitimately by
insects two distinct individuals are sure to intercross,
On the other hand, with dichogamous plants, early or
late flowers on the same individual may intercross ;
and a cross of this kind does hardly any or no good.
Whenever it is profitable to a species to produce a
* ‘Tho Effects of Cross and Self-fertilisation,’ 1876, p. 441.
260 CONCLUDING REMARKS Cuar. VI
large number of seeds and this obviously is a very
common case, heterostyled will have an advantage
over dicecious plants, as all the individuals of the
former, whilst only half of the latter, that is the
females, yield seeds. On the other hand, hetero-
styled plants seem to have no advantage, as far as
cross-fertilisation is concerned, over those which are
sterile with their own pollen. They lie indeed under
a slight disadvantage, for if two self-sterile plants
grow near together and far removed from all other
plants of the same species, they will mutually and
perfectly fertilise one another, whilst this will not be
the case with heterostyled dimorphic plants, unless
they chance to belong to opposite forms.
It may be added that species which are trimorphic
nave one slight advantage over the dimorphic; for if
only two individuals of a dimorphic species happen
to grow near together in an isolated spot, the chances
are even that both will belong to the same form, and
in this case they will not produce the full number of
vigorous and fertile seedlings; all these, moreover,
will tend strongly to belong to the same form as their
parents. On the other hand, if two plants of the same
trimorphic species happen to grow in an isolated spot,
the chances are two to one‘in favour of their not be-
longing to the same form; and in this case they will
legitimately fertilise one another, and yield the full
complement of vigorous offspring.
The Means by which Plants may have been rendered
Heterostyled.
This is a very obscure subject, on which I can throw
little light, but which is worthy of discussion. It has
Cuap. VI. ON HETEROSTYLED PLANTS. 261
been shown that heterostyled plants occur in fourteen
natural families, dispersed throughout the whole vege-
table kingdom, and that even within the family of the
Rubiacee they are dispersed in eight of the tribes. We
may therefore conclude that this structure has been
acquired by various plants independently of inheritance
from a common progenitor, and that it can be acquired
without any great difficulty—that is, without any very
unusual combination of circumstances.
It is probable that the first step towards a species
becoming heterostyled is great variability in the length
of the pistil and stamens, or of the pistil alone. Such
variations are not very rare: with Amsinckia spectabilis
and Nolana prostrata these organs differ so much in
length in different individuals that, until experiment-
ing on them, I thought both species heterostyled.
The stigma of Gesneria pendulina sometimes protrudes
far beyond, and is sometimes seated beneath the
anthers; so it is with Ozalis acetosella and various
other plants. I have also noticed an extraordinary
amount of difference in the length of the pistil in cul-
tivated varieties of Primula veris and vulgaris.
As most plants are at least occasionally cross-fer-
tilised by the aid of insects, we may assume that this
was the case with our supposed varying plant; but
that it would have been beneficial to it to have been
more regularly cross-fertilised. We should bear in
mind how important an advantage it has been
proved to be to many plants, though in different
degrees and ways, to be cross-fertilised. It migh.
well happen that our supposed species did not vary
in function in the right manner, so as to become
either dichogamous or completely self-sterile, or in
structure so as to ensure cross-fertilisation. If it had
262 CONCLUDING REMARKS Cuar. VI.
. thus varied, it would never have been rendered hetero-
styled, as this state would then have been superfluous.
But the parent-species of our several existing hetero-
styled plants may have been, and probably were (judg-
ing from their present constitution) in some degree
self-sterile ; and this would have made regular cross-
fertilisation still more desirable.
Now let us take a highly varying species with most
or all of the anthers exserted in some individuals, and
in others seated low down in the corolla; with the
stigma also varying in position in like manner. Insects
which visited such flowers would have different parts
of their bodies dusted with pollen, and it would be a
mere chance whether this were left on the stigma of
the next flower which was visited. If all the anthers
could have been placed on the same level in all the
plants, then abundant pollen would have adhered to
the same part of the body of the insects which fre-
quented the flowers, and would afterwards have been
deposited without loss on the stigma, if it likewise
stood on the same unvarying level in all the flowers.
But as the stamens and pistils are supposed to have
already varied much in length and to be still varying,
it might well happen that they could be reduced much
more easily through natural selection into two sets of
different lengths in different individuals, than all to
the same length and level in all the individuals. We
know from innumerable instances, in which the two
sexes and the young of the same species differ, that
there is no difficulty in two or more sets of individuals
being formed which inherit different characters. In
our particular case the law of compensation or balance-
ment (which is admitted by many botanists) would
tend to cause the pistil to be reduced in those indli-
Cxap. V1. ON HETEROSTYLED PLANTS. 263
viduals in which the stamens were greatly developed,
and to be increased in length in those which had their
stamens but little developed.
Now if in our varying species the longer stamens
were to be nearly equalised in length in a considerable
body of individuals, with the pistil more or less reduced ;
and in another body, the shorter stamens to be simi-
larly equalised, with the pistil more or less increased in
length, cross-fertilisation would be secured with little
loss of pollen; and this change would be so highly
beneficial to the species, that there is no difficulty in be-
lieving that it could be effected through natural selec-
tion. Our plant would then make a close approach in
structure to a heterostyled dimorphic species ; or to a
trimorphic species, if the stamens were reduced to two
lengths in the same flower in correspondence with that
of the pistils in the other two forms. But we have not
as yet even touched on the chief difficulty in under-
standing how heterostyled species could have origi-
nated. A completely self-sterile plant or a dicho-
gamous one can fertilise and be fertilised by any
other individual of the same species; whereas the
essential character of a heterostyled plant is that an
individual of one form cannot fully fertilise or be fer-
tilised by an individual of the same form, but only
by one belonging to another form.
H. Miller has suggested* that ordinary or homo-
styled plants may have been rendered heterostyled
merely through the effects of habit. Whenever pollen
from one set of anthers is habitually applied to a pistil
of particular length in a varying species, he believes
that at last the possibility of fertilisation in any other
* ' Die Befruchtung der Blumen,’ p. 352.
18
264 CONCLUDING REMARKS Cuap. VI.
manner will be nearly or completely lost. He was
led to this view by observing that Diptera frequently
carried poilen from the long-styled flowers of Hottonia
to the stigma of the same form, and that this ille-
gitimate union was not nearly so sterile as the corre-
sponding union in other heterostyled species. But
this conclusion is directly opposed by some other
cases, for instance by that of Linum grandiflorum ;
for here the long-styled form is utterly barren with
its own-form pollen, although from the position
of the anthers this pollen is invariably applied to
the stigma. It is obvious that with heterostyled
dimorphic plants the two female and the two male
organs differ in power; for if the same kind of pollen
be placed on the stigmas of the two forms, and again
if the two kinds of pollen be placed on the stigmas of
the same form, the results are in each case widely dif-
ferent. Nor can we see how this differentiation of the
two female and two male organs could have been
effected merely through each kind of pollen being
habitually placed on one of the two stigmas.
Another view seems at first sight probable, namely,
that an incapacity to be fertilised in certain ways has
been specially acquired by heterostyled plants. We
may suppose that our varying species was somewhat
sterile (as is often the case) with pollen from its own
stamens, whether these were long or short; and that
such sterility was transferred to all the individuals
with pistils and stamens of the same length, so that
these became incapable of intercrossing freely ; but
that such sterility was eliminated in the case of the
individuals which differed in the length of their pistils
and stamens. It is, however, incredible that so peculiar
a form of mutual infertility should have been specially
Cap. VI. ON HETEROSTYLED PLANTS. 265
acquired unless it were highly beneficial to the species ;
and although it may be beneficial to an individual
plant to be sterile with its own pollen, cross-fertilisa-
tion being thus ensured, how can it be any advan-
tage to a plant to be sterile with half its brethren,
that is, with all the individuals belonging to the
same form? Moreover, if the sterility of the unions
between plants of the same form had been a special
acquirement, we might have expected that the long-
styled form fertilised by the long-styled would have
been sterile in the same degree as the short-styled
fertilised by the short-styled; but this is hardly ever
the case. On the contrary, there is sometimes the
widest difference in this respect, as between the two
illegitimate unions of Pulmonaria angustifolia and of
Hottonia palustris.
It is a more probable view that the male and female
organs in two sets of individuals have been by some
means specially adapted for reciprocal action; and
that the sterility between the individuals of the same
set or form is an incidental and purposeless result.
The meaning of the term “incidental” may be illus-
trated by the greater or less difficulty in grafting or
budding together two plants belonging to distinct
species; for as this capacity is quite immaterial to the
welfare of either, it cannot have been specially ac-
quired, and must be the incidental result of differ-
ences in their vegetative systems. But how the
sexual elements of heterostyled plants came to differ
from what they were whilst the species was homo-
styled, and how they became co-adapted in two sets of
individuals, are very obscure points. We know that
in the two forms of our existing heterostyled plants
the pistil always differs, and the stamens generally
differ in length; so does the stigma in structure,
266 CONCLUDING REMARKS Cuap. VI.
the anthers in size, and the pollen-grains in diameter,
It appears, therefore, at first sight probable that
organs which differ in such important respects could
act on one another only in some manner for which
they had been specially adapted. The probability of
this view is supported by the curious rule that the
greater the difference in length between the pistils
and stamens of the trimorphic species of Lythrum and
Oxalis, the products of which are united for reproduc-
tion, by so much the greater is the infertility of the
union. The same rule applies to the two illegitimate
unions of some dimorphic species, namely, Primula
vulgaris and Pulmonaria angustifolia ; but it entirely
fails in other cases, as with Hottonia palustris and
Linum grandiflorum. We shall, however, best perceive
the difficulty of understanding the nature and origin
of the co-adaptation between the reproductive organs
of the two forms of heterostyled plants, by consider-
ing the case of Linum grandiflorum: the two forms of
this plant differ exclusively, as far as we can see, in
the length of their pistils; in the long-styled form,
the stamens equal the pistil in length, but their
pollen has no more effect on it than so much in-
organic dust; whilst this pollen fully fertilises the
short pistil of the other form. Now, it is scarcely
credible that a mere difference in the length of the
pistil can make a wide difference in its capacity for
being fertilised. We can believe this the less because
with some plants, for instance, Amsinckia spectabilis,
the pistil varies greatly in length without affecting
the fertility of the individuals which are intercrossed.
So again I observed that the same plants of Primula
veris and vulgaris differed to an extraordinary degree
in the length of their pistils during successive seasons ;
nevertheless they yielded during these seasons exactly
Cur. VI. ON HETEROSTYLED PLANTS. 267
the same average number of seeds when left to fertilise
themselves spontaneously under a net.
We must therefore look to the appearance of inner
or hidden constitutional differences between the indi-
viduals of a varying species, of such a nature that the
male element of one set is enabled to act efficiently
only on the female element of another set. We need
not doubt about the possibility of variations in the
constitution of the reproductive system of a plant, for
we know that some species vary so as to be completely
self-sterile or completely self-fertile, either in an appa-
rently spontaneous manner or from slightly changed
conditions of life. Gartner also has shown* that the in-
dividual plants of the same species vary in their sexual
powers in such a manner that one will unite with a
distinct species much more readily than another. But
what the nature of the inner constitutional differences
may be between the sets or forms of the same varying
species, or between distinct species, is quite unknown.
It seems therefore probable that the species which
have become heterostyled at first varied so that two
or three sets of individuals were formed differing in
the length of their pistils and stamens and in other
co-adapted characters, and that almost simultaneously
their reproductive powers became modified in such a
manner that the sexual elements in one set were
adapted to act on the sexual elements of another set ;
and consequently that these elements in the same set
or form incidentally became ill-adapted for mutual
interaction, as in the case of distinct species. 1 have
elsewhere shown { that the sterility of species when
* Gartner, ‘Bastarderzeugung Plants under Domestication,’ 2nd
im Ptlanzenreich,’ 1849, p. 165. edit. vol. ii. p. 169 ; ‘ The Eifects of
+ ‘Origin of Species, 6th edit. Crossand Self-fertilisation,’ p. 463.
p. 247; ‘ Variation of Animalsand It may bo well here to remark
268 CONCLUDING REMARKS Cuar, VI.
first crossed and of their hybrid offspring must also
be looked at as merely an incidental result, following
from the special co-adaptation of the sexual elements
of the same species. We can thus understand the
striking parallelism, which has been shown to exist
between the effects of illegitimately uniting hetero-
styled plants and of crossing distinct species. The
great difference in the degree of sterility between the
various heterostyled species when illegitimately fer-
tilised, and between the two forms of the same species
when similarly fertilised, harmonises well with the
view that the result is an incidental one which follows
from changes gradually effected in their reproductive
systems, in order that the sexual elements of the dis-
tinct forms should act perfectly on one another.
Transmission of the Two Forms by Heterostyled Plants.
—The transmission of the two forms by heterostyled
plants, with respect to which many facts were given in
the last chapter, may perhaps be found hereafter to
throw some light on their manner of development.
Hildebrand observed that seedlings from the long-
styled form of Primula Sinensis when fertilised with
pollen from the same form were mostly long-styled,
and many analogous cases have since been observed
by me. All the known cases are given in the two
following tables.
that, judging from the remark-
able power with which abruptly
changed conditions of life act on
the reproductive system of most
organisms, it is probable that the
close adaptation of the male to the
female elements in the two forms uf
the same heterostyled species, or
in all the individuals of the same
ordinary species, could be acquired
only under long-continued nearly
uniform conditions of life.
Cir. VI.
ON HETEROSTYLED PLANTS.
269
TaBie 36.
Nature of the Offspring from Illegitimutely fertilised Dimorphic
Plants.
Number | Number
of Loung- | of Snorts
styled styled
Offspring.}Offspring.
Long-styled form, fertilised by
, A own-form pollen during five
Prtomala vents successive ues ae 156 S
duced. .
Short-styled form, fertilised by 5 9
bid *\ own-form pollen, produced .
Long-styled form, fertilised by
e A own-form pollen during two
Primula vulgaris) successive aoeeain, ae st 9
duced.
(Short-styled form, fertilised by
own-form pollen, is said to
Primula auricula .4 produce during successive 25 75
generations offspring in about
the following proportions
Long-styled form, fertilised by
5 Be own-form pollen during two
Primula Sinensis . successive ani Las a 0
duced, . .
Bay ee form, fertilised by
is own-form pollen aan 14 3
brand), produced, .
Short-styled form, fertilised by 1 24
m8 a own-form pollen, produced .
* . 4. (Long-styled form, fertilised by
Pulmonaria offcinalis{ own-form poll sh, produced 11 0
.. f{Long-styled form, fertilised by =
Polygonum fagopy: um{ own-form pollen, produced . * |
Short-styled form, fertilised by
e { own-form pollen, produced "} 18 #0
270 CONCLUDING REMARKS
Cuar. VL
TaBe 37.
Nature of the Offspring from Illegitimately fertilised Trimorphie
Plants.
Number | Number | Number
of Long- | of Mid- | of Short~
——s styled | styled | styled
Offspring. Offspring. Offspring.
Long-styled form, fertilised
Lythrum salicaria.{ by own-form peer ae 56 0 0
duced . .
Short-styled form, fertilised
” » «§ by own-form pellets ba 1 0 8
duced . .
Short-styled form, fertilised
by pollen from mid-length 4 0 8
id » *) stamens of long - aaa
form, produced
Mid-styled form, fertilised 2} 1 3 0
m, » "\ own-form pollen, saree
Mid-styled form, fertilised by
pollen from shortest sta 7 8 0
” » *) mens of a sis
produced .
Mid-styled form, fertilised by
pollen from longest sta-
” ” —*) mens of shor ae ie form, u z i
produced . .
Long-styled form, fertilised
during several generations
Oxalis rosea, «4 by own-form pollen, pro-}| 100 (0) 0)
duced offspring in the
vratioof . . . .
» redysaroides genes form, fertilised et 0 17 e
own-form pollen, produced
Cuar. VIL ON HETEROSTYLED PLANTS. 271
We see in these two tables that the offspring from
a form illegitimately fertilised with pollen from
another plant of the same form belong, with a few
exceptions, to the same form as their parents. For
instance, out of 162 seedlings from long-styled plants
of Primula veris fertilised during five generations in
this manner, 156 were long-styled and only 6 short-
styled. Of 69 seedlings from P. vulgaris similarly
raised all were long-styled. So it was with 56 seedlings
from the long-styled form of the trimorpnic Lythrum
salicaria, and with numerous seedlings from the long-
styled form of Ozxalis rosea. The offspring from the
short-styled forms of dimorphic plants, and from both
the mid-styled and short-styled forms of trimorphic
plants, fertilised with their own-form pollen, likewise
tend to belong to the same form as their parents, but
not in so marked a manner as in the case of the long-
styled form. There are three cases in Table 37, in
which a form of Lythrum was fertilised illegitimately
with pollen from another form; and in two of these
cases all the offspring belonged to the same two forms
as their parents, whilst in the third case they belonged
to all three forms.
The cases hitherto given relate to illegitimate unions,
but Hildebrand, Fritz Miller, and myself found that
a very large proportion, or all of the offspring, from a
legitimate union between any two forms of the tri-
morphic species of Oxalis belonged to the same two
forms. A similar rule therefore holds good with unions
which are fully fertile, as with those of an illegiti-
mate nature which are more or less sterile. When
some of the seedlings from a heterostyled plant belong
to a different form from that of its parents, Hildebrand
accounts for the fact by reversion. For instance, the
long-styled parent-plant of Primula verts, from which
272 CONCLUDING REMARKS Cuar. VI,
the 162 illegitimate seedlings in Table 36 were derived
in the course of five generations, was itself no doubt
derived from the union of a long-styled and a short-
styled parent; and the 6 short-styled seedlings may be
attributed to reversion to their short-styled progeni-
tor. But it is a surprising fact in this case, and in
other similar. ones, that the number of the offspring
which thus reverted was not larger. The fact is ren-
dered still more strange in the particular instance of
P. verts, for there was no reversion until four or five
generations of long-styled plants had been raised. It
may be seen in both tables that the long-styled form
transmits its form much more faithfully than does the
short-styled, when both are fertilised with their own-
form pollen; and why this should be so it is difficult
to conjecture, unless it be that the aboriginal parent-
form of most heterostyled species possessed a pistil
which exceeded its own stamens considerably in
length.* I will only add that in a state of nature
any single plant of a trimorphic species no doubt pro-
duces all three forms; and this may be accounted for
either by its several flowers being separately fertilised
by both the other forms, as Hildebrand supposes; or
by pollen from both the other forms being deposited
by insects on the stigma of the same flower.
Equal-styled varieties—The tendency of the di-
morphic species of Primula to produce equal-styled
varieties deserves notice. Cases of this kind have
* It may be suspected that this
was the case with Primula, judg-
ing from the length of the pistil
in several allied genera (see
Mr. J. Scott, ‘Journal Linn. Soe.
Bot, vol. viii. 1864, p. 85). Herr
Breitenbach found many specimens
af Primula clatior growing in a
state of nature with some flowers
on the same plant long-styled,
others short-styled and others
equal-styled; and the long-styled
form greatly preponderated in
number; there being 61 of this
form to 9 of the short-styled and
15 of the equal-styled.
Crap. VI. ON HETEROSTYLED PLANTS. 273
been observed, as shown in the last chapter, in no less
than six species, namely, P. veris, vulgaris, Sinensis,
auricula, farinosa, and elatior. In the ease of P. veris,
the stamens resemble in length, position and size
of their pollen-grains the stamens of the short-styled
form; whilst the pistil closely resembles that'of the
long-styled, but as-it varies much in length, one proper
to the short-styled form appears to have been elongated
and to have assumed at the same time the functions
of a long-styled pistil. Consequently the flowers are
capable of spontaneous self-fertilisation of a legiti-
mate nature and yield a full complement of seed, or
even more than the number produced by ordinary
flowers legitimately fertilised. With P. Sinensis, on
the ‘other hand, the stamens resemble in all respects
the shorter ones proper to the long-styled form, whilst
the pistil makes a near approach to that of the short-
styled, but as it varies in length, it would appear as
if a long-styled pistil had been reduced in length and
modified in function. The flowers in this case as in
the last are capable of spontaneous legitimate ferti-
lisation, and are rather more productive than ordinary
flowers legitimately fertilised. With P. auricule and
farinosa the stamens resemble those of the short-styled
form in length, but those of the long-styled in the
size of their pollen-grains ; the pistil also resembles that
of the long-styled, so that although the stamens and
pistil are of nearly equal length, and consequently
pollen is spontaneously deposited on the stigma, yet
the flowers are not legitimately fertilised and yield
only a very moderate supply of seed. We thus see,
firstly, that equal-styled varieties have originated in
various ways, and, secondly, that the combination of
the two forms in the same flower differs in complete-
274 CONCLUDING REMARKS Cuap. Vi
ness. With P. elatior some of the flowers on the same
plant have become equal-styled, instead of all of
them as in the other species.
Mr. Scott has suggested that the equal-styled varie-
ties arise through reversion to the former homostyled
condition of the genus. This view is supported by
the remarkable fidelity with which the equal-styled
variation is transmitted after it has once appeared. I
have shown in Chapter XIII. of my ‘Variation of
Animals and Plants under Domestication,’ that any
cause which disturbs the constitution tends to in-
duce reversion, and it is chiefly the cultivated
species of Primula which become equal-styled. Tlle-
gitimate fertilisation, which is an abnormal process,
is likewise an exciting cause; and with illegitimately
descended long-styled plants of P. Stnensis, I have
observed the first appearance and subsequent stages
of this variation. With some other plants of P. St-
nensis of similar parentage the flowers appeared
to have reverted to their original wild condition.
Again, some hybrids between P. veris and vulgaris
were strictly equal-styled, and others made a near
approach to this structure. All these facts support
the view that this variation results, at least in part,
from reversion to the original state of the genus,
before the species had become heterostyled. On the
other hand, some considerations indicate, as previously
remarked, that the aboriginal parent-form of Primula
had a pistil which exceeded the stamens in length.
The fertility of the equal-styled varieties has been
somewhat modified, being sometimes greater and some-
times less than that of a legitimate union. Another
view, however, may be taken with respect to the origin
of the equal-styled varieties, and their appearance
may be compared with that of hermaphrodites amongst
Cuar. V1. ON HETEROSTYLED PLANTS. 275
animals which properly have their sexes separated ;
for the two sexes are combined in a monstrous her-
maphrodite in a somewhat similar manner as the
two sexual forms are combined in the same flower of
an equal-styled variety of a heterostyled species.
Final remarks.—The existence of plants which have
been rendered heterostyled is a highly remarkable
phenomenon, as the two or three forms of the same
undoubted species differ not only in important points
of structure, but in the nature of their reproductive
powers. As far as structure is concerned, the two
sexes of many animals and of some plants differ to an
extreme degree; and in both kingdoms the /same
species may consist of males, females, and hermaphro-
dites, Certain hermaphrodite cirripedes are aided in
their reproduction by a whole cluster of what I have
called complemental males, which differ wonderfully
from the ordinary hermaphrodite form. With ants
we have males and females, and two or three castes of
sterile females or workers. With Termites there are,
as Fritz Miller has shown, both winged and wingless
males and females, besides the workers. But in none
of these cases is there any reason to believe that the
several males or several females of the same species
differ in their sexual powers, except in the atrophied
condition of the reproductive organs in the workers of
social insects. Many hermaphrodite animals must
unite for reproduction, but the necessity of such
union apparently depends solely on their structure.
On the other hand, with heterostyled dimorphic
species there are two females and two sets of males,
and with trimorphic species three females and three
sets of males, which differ essentially in their sexual
276 CONCLUDING REMARKS Car. VI,
powers. We shall, perhaps, best perceive the complex
and extraordinary nature of the marriage arrangements
of a trimorphic plant by the following illustration.
Let us suppose that the individuals of the same species
of ant always lived in triple communities; and that
in one of these, a large-sized female (differing also in
other characters) lived with six middle-sized and six
small-sized males ; in the second community a middle-
sized female lived with six large- and six small-sized
males; and in the third, a small-sized female lived
with six large- and six middle-sized males. Each of
these three females, though enabled to unite with any
male, would be nearly sterile with her own two sets of
males, and likewise with two other sets of males of the
same size with her own which lived in the other two
communities; but she would be fully fertile when
paired with a male of her own size. Hence the thirty-
six males, distributed by half-dozens in the three com-
munities, would be divided into three sets of a dozen
each; and these sets, as well as the three females,
would differ from one another in their reproductive
powers in exactly the same manner as do the distinct
species of the same genus. But it is a still more
remarkable fact that young ants raised from any one
of the three female ants, illegitimately fertilised by a
male of a different size would resemble in a whole
series of relations the hybrid offspring from a cross
between two distinct species of ants. They would be
dwarfed in stature, and more or less, or even utterly
barren. Naturalists are so much accustomed to behold
great diversities of structure associated with the two
sexes, that they feel no surprise at almost any amount
of difference ; but differences in sexual nature have
been thought to be the very touchstone of specific
distinction. We now see that such sexual differences
Cuar. VI. ON HETEROSTYLED PLANTS. 277
—the greater or less power of fertilising and being
fertilised—may characterise the co-existing individuals
of the same species, in the same manner as they
characterise and have kept separate those groups of
individuals, produced during the lapse of ages, which
we rank and denominate as distinct species.
278 DICECIOUS AND Cuar VIE
CHAPTER VII.
Po.ycamous, Diactous, anp GyNo-piacrous PLaNTs.
The conversion in various ways of hermaphrodite into dicecious planta
—Heterostyled plants rendered dicecious—Rubiacex—Verbenacess
—Polygamous and sub-dicecious plants—Euonymus—Fragaria—
The two sub-forms of both sexes of Rhamnus and Epigea—Ilex—
Gyno-dicecious plants— Thymus, difference in fertility of the her-
maphrodite and female individuals—Satureia—Manner in which
the two forms probably originated—Scabiosa and other gyuo-
diceecious plants—Difference in the size of the corolla in the forms
of polygamous, dicecious, and gyno-dicecious plants.
THERE are several groups of plants in which all the
species are dicecious, and these exhibit no rudiments
in the one sex of the organs proper to the other.
About the origin of such plants nothing is known. It
is possible that they may be descended from ancient
lowly organised forms, which had from the first their
sexes separated ; so that they have never existed as
hermaphrodites. There are, however, many other
groups of species and single ones, which from being
allied on all sides to hermaphrodites, and from ex-
hibiting in the female flowers plain rudiments of
male organs, and conversely in the male flowers rudi-
ments of female organs, we may feel sure are descended
from plants which formerly had the two sexes com-
bined in the same flower. It is a curious and obscure
problem how and why such hermaphrodites have been
rendered bisexual.
If in some individuals of a species the stamens
alone were to abort, females and hermaphrodites would
Cuap. VIL. POLYGAMOUS PLANTS. 279
be left existing, of which many instances occur; and
if the female organs of the hermaphrodite were after-
wards to abort, the result would be a dicecious plant.
Conversely, if we imagine the female organs alone to
abort in some individuals, males and hermaphrodites
would be left; and the hermaphrodites might after-
wards be converted into females.
In other cases, as in that of the common Ash-tree
mentioned in the Introduction, the stamens are rudi-
mentary in some individuals, the pistils in others,
others again remaining as hermaphrodites. Here the
modification of the two sets.of organs appears to have
occurred simultaneously, as far as we can judge from
their equal state of abortion. If the hermaphrodites
were supplanted by the individuals having separated
sexes, and if these latter were equalised in number, a
strictly dicecious species would be formed.
There is much difficulty in understanding why her-
maphrodite plants should ever have been rendered
dicecious. There would be no such conversion, unless
pollen was already carried regularly by insects or by the
wind from one individual to the other; for otherwise
every step towards diceciousness would lead towards
sterility. As we must assume that cross-fertilisation
was assured before an hermaphrodite could be changed
into a dicecious plant, we may conclude that the con-
version has not been effected for the sake of gaining
the great benefits which follow from cross-fertilisa-
tion. We can, however, see that if a species were
subjected to unfavourable conditions from severe com-
petition with other plants, or from any other cause, the
production of the male and female elements and the
maturation of the ovules by the same individual, might
prove too great a strain on its powers, and the separa-
tion of the sexes would then be highly beneficial,
19
280 DICECIOUS AND Cuar. VIL
This, however, would be effected only under the con-
tingency of a reduced number of seeds, produced by
the females alone, being sufficient to keep up the
stock.
There is another way of looking at the subject which
partially removes a difficulty that appears at first sight
insuperable, namely, that during the conversion of an
hermaphrodite into a dicecious plant, the male organs
must abort in some individuals and the female organs
in others. Yet as all are exposed to the same con-
ditions, it might have been expected that those
which varied would tend to vary in the same man-
ner. As a general rule only a few individuals of a
species vary simultaneously in the same manner; and
there is no improbability in the assumption that
some few individuals might produce larger seeds
than the average, better stocked with nourishment. If
the production of such seeds were highly beneficial to
a species, and on this head there can be little doubt,*
the variety with the large seeds would tend -to in-
crease. But in accordance with the law of compensa-
tion we might expect that the individuals which pro-
duced such seeds would, if living under severe con-
ditions, tend to produce less and less pollen, so that
their anthers would be reduced in size and might ulti-
mately become rudimentary. This view occurred to
me owing to a statement by Sir J. E. Smitht that
there are female and hermaphrodite plants of Serratula
tinctoria, and that the seeds of the former are larger
than those of the hermaphrodite form. It may also
be worth while to rocall the case of the mid-styled
form of Lythrum salicaria, which produces a larger
* Sco the facts given in ‘The t ‘Trans, Linn, Soc., vol. xiii
Effects of Cross and Self-fertilisa- p. 600.
tion,’ p. 353,
FOLLOWING
PAGE IS
DAMAGED
BEST IMAGE
AVAILABLE
Cuar. VIL. POLYGAMOUS PLANTS 281
number of séeds than the other forms, and has some-
what smaller pollen-grains which have less fertilising
power than those of the corresponding stamens in the
other two forms; but whether the larger number of
seeds is the indirect cause of the diminished power
of the pollen, or wice versé, | know not. As soon
as the anthers in a certain number of individuals be-
came reduced in size in the manner just suggested or
from any other cause, the other individuals would have
to prodyes ager supply of pollen; and such in-
creased déve.e ce a a@guld tend to reduce the female
organs through the” ay af compensation, so as ulti-
mately to leave them ‘in’a rudimentary condition ;
and the species would then become dicecious.
Instead of the first change occurring in the female
organs we may suppose that the male ones first varied,
so that some individuals produced a larger supply of
pollen. This would be beneficial under certain cir-
cumstances, such as a change in the nature of the
insects which visited the flowers, or in their be-
coming more anemophilous, for such plants require an
enormous quantity of pollén. The increased action of
the male organs would tend to affect through compen-
sation the female organs of the same flower; and the
final result would be that the species would consist of
males and hermaphrodites. But it is of no use con-
sidering this case and other analogous ones, for, as
stated in the Introduction, the co-existence of male
and hermaphrodite plants is excessively rare.
It is no valid objection -to the foregoing views that
changes of such a nature would be effected with ex-
treme slowness, for we shall presently see good reason
to believe that various hermaphrodite plants have
become or are becoming dicecious by many and ex-
cessively small steps. In the case of polygamous
FOLLOWING
PAGE IS
DAMAGED
BEST IMAGE
AVAILABLE
282 DICECIOUS AND Cuap. Via.
species, which exist as males, females and hermaphro-
dites, the latter would have to be supplanted before
the species could become strictly dicecious; but the
extinction of the hermaphrodite form would probably
not be difficult, as a complete separation of the sexes
appears often to be in some way beneficial. The males
and females would also have to be equalised in
number, or produced in some fitting proportion for the
effectual fertilisation of the females.
There are, no doubt, many unl, ites which
govern the suppression of the ¢xpert#2 .cinale organs
in hermaphrodite planis, awe independently of any
tendency in them to become moneecious, dicecious, or
polygamous. We see this in those hermaphrodites
which from the rudiments still present manifestly
once possessed more stamens or pistils than they
now do,—even twice as many, as a whole verticil has
often been suppressed. Robert Brown “remarks* that
“the order of reduction or abortion of the stamina
in any natural family may with some confidence be
predicted,” by observing in. ‘other members of the
family, in wnich their number is complete, the order
of the dehiscence of the anthers; for the lesser per-
manence of an organ is generally connected with its
lesser perfection, and he judges of perfection by
priority of development. He also states that when-
ever there is a separation of the sexes in an her-
maphrodite plant, which bears flowers on a simple
spike, it is the females which expand first; and this
he likewise attributes to the female sex being the
more perfect of the two, but why the female should
be thus valued he does not explain.
* «Trans. Linn, Soe.’ vol. xii. p. 98. Or ‘ Miscellaneous Works,’ vol
ii. pp. 278-81.
Cuapr. VIL. POLYGAMOUS PLANTS. 283
Plants under cultivation or changed conditions of
life frequently become sterile; and the male organs
are much oftener affected than the female, though the
latter alone are sometimes affected. The sterility of
the stamens is generally accompanied by a reduction
in their size ; and we may feel sure, from a wide-spread
analogy, that both the male and female organs would
become rudimentary in the course of many genera-
tions if they failed altogether to perform their proper
functions. According to Gartner,* if the anthers on
a plant are contabescent (and when this occurs it is
always at a very early period of growth) the female
organs are sometimes precociously developed. I
mention this case as it appears to be one of com-
pensation. So again is the well-known fact, that
plants which increase largely by stolons or other such
means are oftgn utterly barren; with a large proportion
of their pollen-grains in a worthless condition.
Hildebrand has shown that with hermaphrodite
plants which are strongly proterandrous, the stamens
in the flowers which open first sometimes abort; and
this seems to follow from their being useless, as no
pistils are then ready to be fertilised. Conversely
the pistils in the flowers which open last sometimes
abort; as when they are ready for fertilisation all the
pollen has been shed. He further shows by means of
a series of gradations amongst the Composite, f that
a tendency from the causes just specified to produce
either male or female florets, sometimes spreads
to all the florets on the same head, and sometimes
* ‘Beitrige zur Kenntniss, &. chap. xviii—2nd edit. vol. ii.
p. 117 et seq. Thewhole subj.ct pp. 146-56.
of the sterility of plants from + ‘Ueber die Geschlechtsver.
various causes has been discussed hialtnisse bei den Compositen,’
in my ‘Variation of Animals 1869, p. 89.
and Plants under Domestication,’
284 DIGCIOUS AND Cuar. VIL
even to the whole plant; ard in this latter case the
species becomes dicecious. In those rare instances men-
tioned in the Introduction, in which some of the indi-
viduals of both moncecious and hermaphrodite plants
are proterandrous, others being proterogynous, their
conversion into a dicecious condition would probably be
much facilitated, as they already consist of two bodies
of individuals, differing to a certain extent in their
reproductive functions.
Dimorphic heterostyled plants offer still more
strongly marked facilities for becoming dicecious; for
they likewise consist of two bodies of individuals in
approximately equal numbers, and what probably is
more important, both the male and female organs
differ in the two forms, not only in structure but in
function, in nearly the same manner as do the repro-
ductive organs of two distinct species belonging to
the same genus. Now if two species are subjected to
changed conditions, though of the same nature, it is
notorious that they are often affected very differently ;
therefore the male organs, for instance, in one form of
a heterostyled plant might be affected by those un-
known causes which induce abortion, differently from
the homologous but functionally different organs in
the other form; and so conversely with the female
organs. Thus the great difficulty before alluded to is
much lessened in understanding how any cause what-
ever could lead to the simultaneous reduction and
ultimate suppression of the male organs in half the
individuals of a species, and of the female organs in
the other half, whilst all were subjected to exactly the
same conditions of life.
That such reduction or suppression has occurred
in some heterostyled plants is almost certain. The
Rubiacez contain more heterostyled genera than any
Suar. VIL POLYGAMOUS PLANTS. 285
other family, and from their wide distribution we may
infer that many of them became heterostyled at a re-
mote period, so that there will have been ample time for
some of the species to have been since rendered diw-
cious. Asa Gray informs me that Coprosma is dicecious,
and that it is closely allied through Nertera to Mitch-
ella, which as we know is a heterostyled dimorphic
species. In the male flowers of Coprosma the stamens
are exserted, and in the female flowers the stigmas ;
so that, judging from the affinities of the above three
genera, it seems probable that an ancient short-styled
form bearing long stamens with large anthers and
large pollen-grains (as in the case of several Rubia-
ceous genera) has been converted into the male Co-
prosma; and that an ancient long-styled form with short
stamens, small anthers and small pollen-grains has
been converted into the female form. But according
to Mr. Meehan,* Mitchella itself is dicecious in some
districts; for he says that one form has small sessile
anthers without a trace of pollen, the pistil being
perfect; while in another form the stamens are perfect
and the pistil rudimentary. He adds that plants
may be observed in the autumn bearing an abundant
crop of berries, and others without a single one.
Should these statements be confirmed, Mitchella will
be proved to be heterostyled in one district and
dicecious in another.
Asperula is likewise a Rubiaceous genus, and from
the published description of the two forms of A. sco-
paria, an inhabitant of Tasmania, I did not doubt that
it was heterostyled; but on examining some flowers
sent me by Dr. Hooker they proved to be dicecious.
The male flowers have large anthers and a very smal!
* Proc, Acad. of Sciences of Philadelphia, July 28, 1868, p. 182,
286 DIGCIOUS AND Czar. VIL.
ovarium, surmounted by a mere vestige of a stigma
without any style; whilst the female flowers possess
a large ovarium, the anthers being rudimentary and
apparently quite destitute of pollen. Considering
how many Rubiaceous genera are heterostyled, it is a
reasonable suspicion that this Asperula is descended
from a heterostyled progenitor; but we should be
cautious on this head, for there is no improbability in
a homostyled Rubiaceous plant becoming dicecious.
Moreover, in an allied plant, Galiwm ecruciatum, the
female organs have been suppressed in most of the
lower flowers, whilst the upper ones remain hermaph-
rodite; and here we have a modification of the sexual
organs without any connection with heterostylism.
Mr. Thwaites informs me that in Ceylon various
Rubiaceous plants are heterostyled ; but in the case
of Discospermum one of the two forms is always
barren, the ovary containing about two aborted ovules
in each loculus; whilst in the other form each loculus
contains several perfect ovules; so that the species
appears to be strictly dicecious.
Most of the species of the South American genus
ZEgiphila, a member of the Verbenacee, apparently
are heterostyled; and both Fritz Muller and myself
thought that this was the case with 4. obdurata, so
closely did its flowers resemble those of the heterostyled
species. But on examining the flowers, the anthers of
the long-styled form were found to be entirely desti-
tute of pollen and less than half the size of those in
the other form, the pistil being perfectly developed.
On the other hand, in the short-styled form the stig-
mas are reduced to half their proper length, having
also an abnormal appearance ; whilst the stamens are
perfect. This plart therefore is dicecious; and we
may, I think, conclude that a short-styled progenitor,
Crap. VIL. POLYGAMOUS PLANTS. 287
bearing long stamens exserted beyond the corolla,
has been converted into the male; and a long-styled
progenitor with fully developed stigmas into the fe-
male.
From the number of bad pollen-grains in the small
anthers of the short stamens of the long-styled form
of Pulmonaria angustifolia, we may suspect that this
form is tending to become female; but it does not
appear that the other or short-styled form is becoming
more masculine. Certain appearances countenance
the belief that the reproductive system of Phlow subu-
lata is likewise undergoing a change of some kind.
I have now given the few cases known to me in
which heterostyled plants appear with some consider-
able degree of probability to have been rendered
dicecious. Nor ought we to expect to find many such
cases, for the number of heterostyled species is by no
means large, at least in Europe, where they could
hardly have escaped notice. Therefore the number of
dicecious species which owe their origin to the trans-
formation of heterostyled plants is probably-not so
large as might have been anticipated from the facilities
which they offer for such conversion.
In searching for cases like the foregoing ones, I have
been led to examine some dicecious or sub-dicecious
plants, which are worth describing, chiefly as they
show by what fine gradations hermaphrodites may
pass into polygamous or dicecious species.
Polygamous, Diccious and Sub-dicecious Plants.
Euonymus Europeus (Celastrinez).—The spindle-tree
is described in all the botanical works which I have
consulted as an hermaphrodite. Asa Gray speaks of
the flowers of the American species as perfect, whilst
288 DIGCIOUS AND Cusar. VIL
those in the allied genus Celastrus are said to be
“polygamo-dicecious.” If a number of bushes of our
spindle-tree be examined, about half will be found to
have stamens equal in length to the pistil, with well-
developed anthers; the pistil being likewise to all
appearance well developed. The other half have a
perfect pistil, with the stamens short, bearing rudi-
mentary anthers destitute of pollen; so that these
bushes are females. All the flowers on the same plant
present the same structure. The female corolla is
smaller than that on the polleniterous bushes. The
two forms are shown in the accompanying drawings.
Hermaphrodite or male, Female,
Evonymus Evrop£vs,
1 did not at first doubt that this species existed
under an hermaphrodite and female form; but we shall
presently see that some of the bushes which appear
to be hermaphrodites never produce fruit, and these
are in fact males. The species, therefore, is poly-
gamous in the sense in which I use the term, and tri-
oicous. The flowers are frequented by many Diptera
and some small Hymenoptera for the sake of the
nectar secreted by the disc, but I did not see a single
bee at work; nevertheless the other insects sufficed to
‘Cuap. VII. POLYGAMOUS PLANTS. 289
fertilise effectually female bushes growing at a dis-
tance of even 30 yards from any polleniferous bush.
The small anthers borne by the short stamens of
the female flowers are well formed and dehisce pro-
perly, but I could never find in them a single grain
of pollen. It is somewhat difficult to compare the
length of the pistils in the two forms, as they vary .
somewhat in this respect and continue to grow after
the anthers are mature. The pistils, therefore, in old
flowers on a polleniferous plant are often of consider-
ably greater length than in young flowers on a female
plant. On this account the pistils from five flowers
from so many hermaphrodite or male bushes were
compared with those from five female bushes, before
the anthers had dehisced and whilst the rudimentary
ones were of a pink colour and not at all shrivelled.
These two sets of pistils did not differ in length, or if
there was any difference those of the polleniferous
flowers were rather the longest. In one hermaphrodite
plant, which produced during three years very few
and poor fruit, the pistil much exceeded in length
the stamens bearing perfect and as yet closed an-
thers; and I never saw such a case on any female
plant. It is a surprising fact that the pistil in the
male and in the semi-sterile hermaphrodite flowers
has not been reduced in length, seeing that it per-
forms very poorly or not at all its proper function.
The stigmas in the two forms are exactly alike; and
in some ef the polleniferous plants which never pro-
duced any fruit I found that the surface of the stigma
was viscid, so that pollen-grains adhered to it and had
exserted their tubes. The ovules are of equal size
in the two forms. Therefore the most acute botanist,
judging only by structure, would never have suspected
290 DIGECIOUS AND Cuar. VIL
that some of the bushes were in function exclusively
males.
Thirteen bushes growing near one another in a
hedge consisted of eight females quite destitute of
pollen and of five hermaphrodites with well-developed
anthers. In the autumn the eight females were well
covered with fruit, excepting one, which bore only a
moderate number. Of the five hermaphrodites, one
bore a dozen or two fruits, and the remaining four
bushes several dozen; but their number was as nothing
compared with those on the female bushes, for a single
branch, between two and three feet in length, from
one of the latter, yielded more than any one of the
hermaphrodite bushes. The difference in the amount
of fruit produced by the two sets of bushes is all the
more striking, as from the sketches above given it is
obvious that the stigmas of the polleniferous flowers
can hardly fail to receive their own pollen ; whilst the
fertilisation of the female flowers depends on pollen
being brought to them by flies and the smaller
Hymenoptera, which are far from being such efficient
carriers as bees.
I now determined to observe more carefully during
successive seasons some bushes growing in another
place about a mile distant. As the female bushes
were so highly productive, I marked only two of them
with the letters A and B, and five polleniferous bushes
with the letters C to G. I may premise that the
year 1865 was highly favourable for the fruiting of all
the bushes, especially for the polleniferous ones, some
of which were quite barren except under such favour-
able conditions. The season of 1864 was unfavourable,
In 1863 the female A produced “ some fruit ;” in 1864
only 9; and in 1865, 97 fruit. The female B in 1863
was “covered with fruit;” in 1864 it bore 28; and in
Cusp. VIL = POLYGAMOUS PLANTS. 291
1865 “innumerable very fine fruits.” I may add,
that three other female trees growing close by were
observed, but only during 1863, and they then bore
abundantly. With respect to the polleniferous bushes,
the one marked C did not bear a single fruit during
the years 1863 and 1864, but during 1865 it produced
no less than 92 fruit, which, however, were very poor.
I selected one of the finest branches with 15 fruit, and
these contained 20 seeds, or on an average 1°33 per
fruit. I then took by hazard 15 fruit from an adjoin-
ing female bush, and these contained 43 seeds; that
is, more than twice as many, or on an average 2°86
per fruit. Many of the fruits from the female bushes
included four seeds, and only one had a single seed ;
whereas not one fruit from the polleniferous bushes
contained four seeds. Moreover when the two lots of
seeds were compared, it was manifest that those from
the female bushes were the larger. The second
polleniferous bush, D, bore in 1863 about two dozen
fruit,—in 1864 only 3 very poor fruit, each containing
a single seed,—and in 1865, 20 equally poor fruit.
Lastly, the three polleniferous bushes, E, F, and G,
did not produce a single fruit during the three years
1863, 1864, and 1865.
We thus see that the female bushes differ somewhat
in their degree of fertility, and the polleniferous ones
in the most marked manner. We have a perfect
gradation from the female bush, B, which in 1865 was
covered with “innumerable fruits,’—through the
female A, which produced during the same year 97,—
through the polleniferous bush C, which produced
this year 92 fruits, these, however, containing a very
low average number of seeds of small size,—through
the bush D, which produced only 20 poor fruit,—to
the three bushes, EH, F, and G, which did not this
292 DICECIOUS AND Cuap. VIL.
year, or during the two previous years, produce a
single fruit. If these latter bushes and the more
fertile female ones were to supplant the others, the
spindle-tree would be as strictly dicecious in function
as any plant in the world. This case appears to me
very interesting, as showing how gradually an herma-
phrodite plant may be converted into a dicecious one.*
Seeing how general it is for organs which are
almost or quite functionless to be reduced in size, it is
remarkable that the pistils of the polleniferous plants
should equal or even exceed in length those of the
highly fertile female plants. This fact formerly led
me to suppose that the spindle-tree had once been
heterostyled ; the hermaphrodite and male plants hav-
ing been originally long-styled, with the pistils since
reduced in length, but with the stamens retaining
their former dimensions; whilst the female plant bad
been originally short-styled, with the pistil in its pre-
sent state, but with the stamens since greatly-reduced
and rendered rudimentary. A conversion of this kind
is at least possible, although it is the reverse of
that which appears actually to have occurred with
some Rubiaceous genera and Aigiphila; for with these
plants the short-styled form has become the male, and
the long-styled the female. It is, however, a more
simple view that sufficient time has not elapsed for the
* According to Fritz Miller
( Bot. Zeitung,’ 1870, p. 151), a
Chamissoa (Amaranthacee) in
Scuthern Brazil is in nearly the
same state as our Euonymus. The
ovules are equally developed in the
two forms. Inthe femule the pistil
is perfect, whilst the anthers are
entirely destitute of pollen, In
the polleniferous form, the pistil
ia short and the stigmas never
separate from one another, so
that, although their surfaces are
covered with fairly well-developed
papilla, they cannot be fertilised,
‘These latter plants do not come.
mouly yield any fruit, and are
therefore in function males. Never-
theless, on one oceasion Fritz
Miiller found flowers of this kind in
which the stigmas had separated,
and they produced some fruit.
~
Cuap. VIL. POLYGAMOUS PLANTS. 293
reduction of the pistil in the male and hermaphrodite
flowers of our Euonymus; though this view does not
account for the pistils in the polleniferous flowers
being sometimes longer than those in the female
flowers.
Fragaria vesca, Virginiana, Chiloensis, &c. (Rosacee).
—A tendency to the separation of the sexes in the
cultivated strawberry seems to be much more strongly
marked in the United States than in Europe; and
this appears to be the result of the direct action of
climate on the reproductive organs. In the best ac-
count which I have seen,* it is stated that many of the
varieties in the United States consist of three forms,
namely, females, which produce a heavy crop of fruit,—
of hermaphrodites, which “seldom produce other than
a very scanty crop of inferior and imperfect berries,”
—and of males, which produce none. The most skilful
cultivators plant “seven rows of female plants, then
one row of hermaphrodites, and so on throughout the
field.” The males bear large, the hermaphrodites
mid-sized, and the females small flowers. The latter
plants produce few runners, whilst the two other forms
produce many; consequently, as has been observed
both in England and in the United States, the polleni-
ferous forms increase rapidly and tend to supplant
the females. We may therefore infer that much more
vital force is expended in the production of ovules
and fruit than in the production of pollen. Another
species, the Hautbois strawberry (£’. elatior), is more
strictly dicwcious; but Lindley made by selection an
hermaphrodite stock.
Bhamnus catharticus (Rhamnew). —This plant is well
* Mr. Leonard Wray in‘Gard. information on this subject, sce
Chron.’ 1861, p. 716. ‘Variation under Domestication,’
+ For references and further chip. a. 2nd edit, vol. i, p. $75.
294. DICECIOUS AND Cuar. VIL
known to be dicecious. My son William found the
two sexes growing in about equal numbers in the Isle
of Wight, and sent me specimens, together with obser-
vations on them. ach sex consists of two sub-forms.
The two forms of the male differ in their pistils:
in some plants it is quite small, without any distinct
stigma; in others the pistil is much more developed,
with the papill on the stigmatic surfaces moderately
large. The ovules in both kinds of males are in an
aborted condition. On my mentioning this case to Pro-
fessor Caspary, he examined several male plants in
the botanic gardens at Konigsberg, where there were
no females, and sent me the accompanying drawings.
Fig. 13.
yf §
NI
Long-styled male, Short-styled male.
RHAMNUS CATHARTICUS, (From Caspary.)
In the English plants the petals are not so greatly
reduced as represented in this drawing. My son ob-
served that those males which had their pistils mode-
rately well developed bore slighly larger flowers, and,
what is very remarkable, their pollen-grains exceeded
by a little in diameter those of the males with greatly
reduced pistils. This fact is opposed to the belief that
the present species was once heterostyled; for in this
case it might have been expected that the shorter-
styled plants would have had larger pollen-grains.
In the female plants the stamens are in an ex-
tremely rudimentary condition, much more so than
Cuap. VII. POLYGAMOUS PLANTS. 295
the pistils in the males. The pistil varies consi-
derably in length in the female plants, so that they
may be divided into two sub-forms according to tle
Fig. 14,
Long-styled Short-styled
female, female.
RHAMNUS CATHARTICUS,
length of this organ. Both the petals and sepals are
decidedly smaller in the females than in the males;
and the sepals do not turn downwards, as do those of
the male flowers when mature. All the flowers on the
same male or same female bush, though subject to
some variability, belong to the same sub-form; and
as my son never experienced any difficulty in decid-
ing under which class a plant ought to be included,
he believes that the two sub-forms of the same sex
do not graduate into one another. I can form no
satisfactory theory how the four forms of this plant
originated.
Rhamnus lanceolatys exists in the United States,
as I am informed by Professor Asa Gray, under two
hermaphrodite forms. In the one, which may be called
the short-styled, the flowers are sub-solitary, and in-
clude a pistil about two-thirds or only half as long as
that in the other form; it has also shorter stigmas. The
stamens are of equal length in the two forms; but the
anthers of the short-styled contain rather less pollen,
as far as I could judge from a few dried flowers. My
20
296 DIGECIOUS AND Cuap. VIL
son compared the pollen-grains from the two forms,
and those from the long-styled flowers were to those
from the short-styled, on an average from ten measure-
ments, as 10 to 9 in diameter; so that the two her-
maphrodite forms of this species resemble in this
respect the two male forms of R. catharticus. The
long-styled form is not so common as the short-styled.
The latter is said by Asa Gray to be the more fruitful
of the two, as might have been expected from its
appearing to produce less pollen, and from the grains
being of smaller size; it is therefore the more highly
feminine of the two. The long-styled form produces
a greater number of flowers, which are clustered to-
gether instead of being sub-solitary; they yield some
fruit, but as just stated are less fruitful than the other
form, so that this form appears to be the more mas-
culine of the two. On the supposition that we have
here an hermaphrodite plant becoming dicecious, there
are two points deserving notice; firstly, the greater
length of the pistil in the incipient male form; and
we have met with a nearly similar case in the male
and hermaphrodite forms of Euonymus compared with
the females. Secondly, the larger size of the pollen-
grains in the more masculine flowers, which perhaps may
be attributed to their having retained their normal size ;
whilst those in the incipient female flowers have been
reduced. The long-styled form of R.lanceolatus seems
to correspond with the males of R. catharticus which
have a longer pistil and larger pollen-grains. Light
will perhaps be thrown on the nature of the forms
in this genus, as soon as the power of both kinds of
pollen on both stigmas is ascertained. Several other
species of Rhamnus are said to be dicecious* or sub-
* * Lecoq, ‘Géogr. Bot.’ tom. v. 1856, pp. 420-26.
Cua. VII. POLYGAMOUS PLANTS. 297
dicecious. On the other hand, R. frangula is an ordi-
nary hermaphrodite, for my son found a large number
of bushes all bearing an equal profusion of fruit.
Epigea repens (Kricacee).—This plant appears to
be in nearly the same state as Rhamnus catharticus.
It is described by Asa Gray* as existing under four
forms. (1) With long style, perfect stigma, and short
abortive stamens. (2) Shorter style, but with stigma
equally perfect, short abortive stamens. These two
female forms amounted to 20 per cent. of the speci-
mens received from one locality in Maine; but all
the fruiting specimens belonged to the first form.
(8) Style long, as in No. 1, but with stigma imperfect,
stamens perfect. (4) Style shorter than in the last,
stigma imperfect, stamens perfect. These two latter
forms are evidently males. Therefore, as Asa Gray
remarks, “the flowers may be classified into two kinds,
each with two modifications; the two main kinds
characterised by the nature and perfection of the
stigma, along with more or less abortion of the
stamens; their modifications, by the length of the
style.’ Mr. Meehan has described the extreme
variability of the corolla and calyx in this plant, and
shows that it is dicecious. It is much to be wished
that the pollen-grains in the two male forms should
be compared, and their fertilising power tried on the
two female forms.
Llex aquifolium (Aquifoliaceze).—In the several
works which I have consulted, one author alonet says
that the holly is dicecious. During several years I
*¢ American Journalof Science, delphia,’ May 1868, p. 153.
July 1876. Also'The American t Vaucher, ‘Hist. Phys. des
Naturalist,’ 1876, p. 490. Plantes d’Europe,’ 1841, tom. ii
+ “Variationsin Epigea repens,” p. 11.
Proc. Acad. Nat. Soc. of Phila-
298 GYNO-DICECIOUS PLANTS. Cuar. VIL
have examined many plants, but have never found
one that was really hermaphrodite. I mention this
genus because the stamens in the female flowers, al-
though quite destitute of pollen, are but slightly and
sometimes not at all shorter than the perfect stamens
in the male flowers. In the latter the ovary is small
and the pistil is almost aborted. The filaments of the
perfect stamens adhere for a greater length to the
petals than in the female flowers. The corolla of
the latter is rather smaller than that of the male.
The male trees produce a greater number of flowers
than the females. Asa Gray informs me that I. opaca,
which represents in the United States our common
holly, appears (judging from dried flowers) to be in a
similar state ; and so it is, according to Vaucher, with
several other but not with all the species of the genus.
Gyno-dicecious Plants.
The plants hitherto described either show a tendency
to become dicecious, or apparently have become so
within a recent period. But the species now to be
considered consist of hermaphrodites and females
without males, and rarely show any tendency to
be dicecious, as far as can be judged from their
present condition and from the absence of species
having separated sexes within the same groups.
Species belonging to the present class, which I have
called gyno-dicecious, are found in various widely
distinct families; but are much more common in the
Labiate (as has long been noticed by botanists) than
in any other group. Such cases have been noticed
by myself in Thymus serpyllum and vulgaris, Satureia
hortensis, Origanum vulgare, and Mentha hirsuta; and
by others in Nepeta glechoma, Mentha vulgaris and
Cuapr. VIL. GYNO-DIGECIOUS PLANTS. 299
aquatica, and Prunella vulgaris. In these two latter
species the female form, according to H. Miller, is
infrequent. To these must be added Dracocephalum
Moldavicum, Melissa officinalis and clinipodium, and
Hyssopus officinalis.* In the two last-named plants the
female form likewise appears to be rare, for I raised
many seedlings of both, and all were hermaphrodites.
It has already been remarked in the Introduction that
andro-dicecious species, as they may be called, or those
which consist of hermaphrodites and males, are ex-
tremely rare, or hardly exist.
Thymus serpyllum.—The hermaphrodite plants pre-
sent nothing particular in the state of their reproduc-
tive organs; and so it is in all the following cases. The
females of the present species produce rather fewer
flowers and have somewhat smaller corollas than the
hermaphrodites; so that near Torquay, where this
plant abounds, I could, after a little practice, distin-
guish the two forms whilst walking quickly past them.
According to Vaucher, the smaller size of the corolla
is common to the females of most or all of the above-
mentioned Labiate. The pistil of the female, though
somewhat variable in, length, is generally shorter,
with the margins of the stigma broader and formed
of more lax tissue, than that of the hermaphrodite.
The stamens in the female vary excessively in length ;
they are generally enclosed within the tube of the
* H. Miiler, ‘Die Befruchtung
jer Blumen,’ 1873; and ‘ Nature,’
1873, p. 161. Vaucher, ‘ Plantes
(’Kurope, tom. iii, p. 611. For
Dracocephalum, Schimper, as
quoted by Braun, ‘Annals and
Mag. of Nat. Hist.’ 2nd series, vol.
xviii. 1856, p. 380, Lecoq, ‘ Géo-
graphie Bot, de 1’Europe,’ tom. viii.
pp. 33, 38, 44, &e. Both Vaucher
and Lecoq were mistaken in think-
ing that several of the plants
named in the text are dicecious.
They appear to have assumed that
the hermaphrodite form was a
male; perhaps they were de-
ceived by the pistil not becoming
fully developed and of proper
length until some time after the
anthers have dehisccd.
300 GYNO-DIGECIOUS PLANTS. Cuar. VIL.
corolla, and their anthers do not contain any sound
pollen; but after long search I found a single plant
with: the stamens moderately exserted, and their
anthers contained a very few full-sized grains, together
with a multitude of minute empty ones. In some
females the stamens are extremely short, and their
minute anthers, though divided into the two normal
cells or loculi, contained not a trace of pollen: in
others again the anthers did not exceed in diameter
the filaments which supported them, and were not
divided into two loculi. Judging from what I have
myself seen and from the descriptions of others, all
the plants in Britain, Germany, and near Mentone,
are in the state just described; and I have never
found a single flower with an aborted pistil. It is,
therefore, remarkable that, according to Delpino,* this
plant near Florence is generally trimorphic, consisting
of males with aborted pistils, females with aborted
stamens, and hermaphrodites.
T found it very difficult to judge of the proportional
number of the two forms at Torquay. They often
grow mingled together, but with large patches con-
sisting of one form alone. At first I thought that the
two were nearly equal in number; but on examining
every plant which grew close to the edge of a little
overhanging dry cliff, about 200 yards in length, 1]
found only 12 females; all the rest, some hundreds
in number, being hermaphrodites. Again, on an
extensive gently sloping bank, which was so thickly
covered with this plant that, viewed from the distance
of half a mile it appeared of a pink colour, I could
not discover a single female. Therefore the her-
* ‘Sull’ Opera, la Distribuzione H. Miilier, ‘Die Befruchtung,
dei Sessi nelle Piante, &c.’ 1867, &c.,’ p. 227.
p. 7. With respect to Germany,
Cuar. VII. GYNO-DIGCIOUS PLANTS. 301
maphrodites must greatly exceed in number the
females, at least in the localities examined by me.
A very dry station apparently favours the presence
of the female form. With some of the other above-
named Labiate the nature of the soil or climate
likewise seems to determine the presence of one or
both forms; thus with Nepeta glechoma, Mr. Hart found
in 1878 that all the plants which he examined near
Kilkenny in Ireland were females; whilst all near
Bath were hermaphrodites, and near Hertford both
forms were present, but with a preponderance of her-
maphrodites.* It would, however, be a mistake to
suppose that the nature of the conditions determines
the form independently of inheritance; for I sowed
in the same small bed seeds of T. serpyllum, gathered
at Torquay from the female alone, and these produced
an abundance of both forms. There is every reason
to believe, from large patches consisting of the same
form, that the same individual plant, however much
it may spread, always retains the same form. In two
distant gardens I found masses of the lemon-thyme
(TL. ettriodorus, a var. of T. serpyllum), which I was
informed had grown there during many years, and
every flower was female.
With respect to the fertility of the two forms, I
marked at Torquay a large hermaphrodite and a large
female plant of nearly equal sizes, and when the seeds
were ripe I gathered all the heads. The two heaps
were of very nearly equal bulk; but the heads from
the female plant numbered 160, and their seeds
weighed 8'7 grains; whilst those from the _her-
maphrodite plant numbered 200, and their seeds
weighed only 4:9 grains; so that the seeds from the
* ‘Nature,’ June 1873, p. 162,
302 GYNO-DIG@CIOUS PLANTS. Cuapr. VII.
female plant were to those from the hermaphrodite
as 100 to 56 in weight. If the relative weight of
the seeds from an equal number of flower-heads from
the two forms be compared, the ratio is as 100 for the
female to 45 for the hermaphrodite form.
Thymus vulgaris—The common garden thyme re-
sembles in almost every respect TZ. serpyllum. The
same slight differences between the stigmas of the
two forms could be perceived. In the females the
stamens are not generally quite so much reduced as
in the same form of T. serpyllum. In some specimens
sent me from Mentone by Mr. Moggridge, together
with the accompanying sketches, the anthers of the
Fig. 15.
Hermaphrodite, Females.
THYMUS VULGARIS (magnified),
female, though small, were well formed, but they con-
tained very little pollen, and not a single sound grain
could be detected. Nighteen seedlings were raised
from purchased seed, sown in the same small bed;
and these consisted of seven hermaphrodites and
eleven females. They were left freely exposed to
the visits of bees, and no doubt every female flower
was fertilised; for on placing under the micro-
scope a large number of stigmas from female plants,
Cuap. VII GYNO-DIGCIOUS PLANTS. 303
not one could be found to which pollen-grains of
thyme did not adhere. The seeds were carefully
collected from the eleven female plants, and they
weighed 98-7 grains; and those from the seven her-
maphrodites 36°5 grains. This gives for an equal
number of plants the ratio of 100 to 58; and we
here see, as in the last case, how much more fertile
the females are than the hermaphrodites. These two
Jots of seeds were sown separately in two adjoining
beds, and the seedlings from both the hermaphro-
dite and female parent-plants consisted of both forms.
Satureia hortensis.—HKleven seedlings were raised in
separate pots in a hotbed and afterwards kept in the
green-house. They consisted of ten females and of
a single hermaphrodite. Whether or not the condi-
tions to which they had been subjected caused the great
excess of females I do not know. In the females the
pistil is rather longer than that of the hermaphrodite,
and the stamens are mere rudiments, with minute
colourless anthers destitute of pollen. The windows
of the green-house were left open, and the flcwers
were incessantly visited by humble and hive bees.
Although the ten females did not produce a single
grain of pollen, yet they were all thoroughly well
fertilised by the one hermaphrodite plant, and this
is an interesting fact. It should be added that no
other plant of this species grew in my garden. The
seeds were collected from the finest female plant,
and they weighed 78 grains; whilst those from the
hermaphrodite, which was a rather larger plant than
the female, weighed only 33:2 grains; that is, in the
ratio of 100 to 43. The female form, therefore, is very
much more fertile than the hermaphrodite, as in the two
last cases ; but the hermaphrodite was necessarily self:
fertilised, and this probably diminished its fertility.
3804 GYNO-DIGECIOUS PLANTS. Cuap. VIL
We may now consider the probable means by which
so many of the Labiate have been separated into two
forms, and the advantages thus gained. H. Miiller*
supposes that originally some individuals varied so as
to produce more conspicuous flowers; and that insects
habitually visited these first, and then dusted with
their pollen visited and fertilised the less conspicuous
flowers. The production of pollen by the latter plants
would thus be rendered superfluous, and it would be
advantageous to the species that their stamens should
abort, so as to save useless expenditure. They would
thus be converted into females. But another view may
be suggested: as the production of a large supply of
seeds evidently is of high importance to many plants,
and as we have seen in the three foregoing cases
that the females produce many more seeds than the
hermaphrodites, increased fertility seems to me the
more probable cause of the formation and separation of
the two forms. Fyrom the data above given it follows
that ten plants of Thymus serpyllum, if half consisted
of hermaphrodites and half of females, would yield
seeds compared with ten hermaphrodite plants in the
ratio of 100 to 72. Under similar circumstances the
ratio with Satureia hortensis (subject to the doubt from
the self-fertilisation of the hermaphrodite) would be as
100 to 60. Whether the two forms originated in cer-
tain individuals varying and producing more seed than
usual, and consequently producing less pollen; or in
the stamens of certain individuals tending from some
unknown cause to abort, and consequently producing
more seed, it is impossible to decide; but in either
case, if the tencency to the increased production of
seerl were steadily favoured, the result would be the
* ‘Dic Befruchtung der Blumen,’ pp. 319, 326.
Cuap. VII. GYNO-DIGECIOUS PLANTS. 305
complete abortion of the male organs. I shall pre
sently discuss the cause of the smaller size of the
female corolla.
Scabiosa arvensis (Dipsacese).—It has been shown by H. Miiller
that this species exists in Germany under an hermaphrodite and
female form.* In my neighbourhood (Kent) the female plants
do not nearly equal in number the hermaphrodites. The stamens
of the females vary much in their degree of abortion; in some
plants they are quite short and produce no pollen; in others
they reach to the mouth of the corolla, but their anthers are not
half the proper size, never dehisce, and contain but few pollen-
grains, these being colourless and of small diameter: ‘The her-
maphrodite flowers are strongly proterandous, and H. Miiller
shows that, whilst all the stigmas on the same flower-head are
mature at nearly the same time, the stamens dehisce one after
the other; so that there is a great excess of pollen, which serves
to fertilise the female plants. As the production of pollen by
one set of plants is thus rendered superfluous, their male organs
have become more or less completely aborted. Should it be
hereafter proved that the female plants yield, as is probable,
more seeds than the hermaphrodites, I should be inclined to
extend the same view to this plant as to the Labiate. I have
also observed the existence of two forms in our endemic 8.
succisa, and in the exotic S. atro-purpurea. In the latter plant,
differently to what occurs in S. arvensis, the female flowers,
especially the larger circumferential ones, are smaller than those
of the hermaphrodite form. According to Lecog, the female
flower-heads of S. swecisa are likewise smaller than those of
what he calls the male plants, but which are probably her-
maphrodites.
Echium vulgare (Buraginese).—The ordinary hermaphrodite
form appears to Le proterandrous, and nothing more need be said
about it. The female differs in having a much smaller corolla
The stamens
and shorter pistil, but a well-developed stigma.
* ‘Befruchtung der Blumen,’
&e., p. 368. The two forms occur
not only in Germany, but in
England and France. Lecogq,
(Géographie But.’ 1857, tom. vi.
pp. 473, 477) says that male
plants as well as hermaplirodites
and females co-exist; it is, how-
ever, possible that he may have
been deceived by the flowers being
so strongly proterandrous. From
what Lecoq says, S. succisa like-
wise uppears to oceur under two
forms in France.
306 GYNO-DICECIOUS PLANTS. Cuap. VII.
are short; the anthers do not contain any sound pollen-grains,
but in their place yellow incoherent cells which do not swell
in water. Some plants were in an intermediate condition; that
is, had one or two or three stamens of proper length with per-
fect anthers, the other stamens being rudimentary. In one such
plant half of one anther contained green perfect pollen-grains,
and the other half yellowish-green imperfect grains. Both forms
produced seed, but I neglected to observe whether in equal
numbers. As I thought that the state of the anthers might be
due to some fangoid growth, I examined them both in the bud
and mature state, but could find no trace of mycelium. In 1862
many female plants were found; and in 1864, 32 plants were
collected in two localities, exactly half of which were hermaphro-
dites, fourteen were females, and two in an intermediate con-
dition. In 1866, 15 plants were collected in another locality,
and these consisted of four hermaphrodites and eleven females.
I may add that this season was a wet one, which shows that the
abortion of the stamens can hardly be due to the dryness of the
sites where the plants grew, as I at one time thought pro-
bable. Seeds from an hermaphrodite were sown in my garden,
and of the 23 seedlings raised, one belonged to the intermediate
form, all the others being hermaphrodites, though two or three
of them had unusually short stamens. I have consulted several
botanical works, but have found no record of this plant varying
in the manner here described.
Plantago lanceolata (Plantaginese).—Delpino states that this
plant presents in Italy three forms, which graduate from an
anemophilous into an entomophilous condition. According to
H. Miiller,* there are only two forms in Germany, neither of
which show any special adaptation for insect fertilisation, and
both appear to be hermaphrodites. But Ihave found in twe
localities in England female and hermaphrodite forms existing
together; and the same fact has been noticed by others.t The
females are less frequent than the hermaphrodites; their stamens
are short, and their anthers, which are of a brighter green
whilst young than those of the other form, dehisce properly, yet
contain either no pollen, or a small amount of imperfect grains
of variable size. All the flower-heads on a plant belong to
* ‘Die Befruchtung,’ &., p. 342. Mr. W. Marshall writes to me to
+ Mr. C. W. Crocker in ‘The the same effect from Ely.
Gardener’s Chronicle,’ 1864, p. 294.
Cuap. VII. 307
the same form. It is well known that this species is strongly
proterogynous, and I found that the protruding stigmas of both
the hermaphrodite and female flowers were penetrated by pollen-
tubes, whilst their own anthers were immature and had not
escaped out of the bud. Plantago media does not present two
forms; but it appears from Asa Gray’s description,* that such
is the case with four of the North American species. The co-
rolla does not properly expand in the short-stamened form of
these plants.
Cnicus, Serratula, Eriophorum.—titn the Composite, Cnicus
palustris and acaulis are said by Sir J. E. Smith to exist as her-
maphrodites and females, the former being the more frequent.
With Serratula tinctoria a regular gradation may be followed
from the hermaphrodite to the female form; in one of the latter
plants the stamens were so tall that the anthers embraced the
style as in the hermaphrodites, but they contained only a few
grains of pollen, and these in an aborted condition; in an-
other female, on the other hand, the anthers were much more
reduced in size than is usual. Lastly, Dr. Dickie has shown
that with Eriophorum angustifolium (Cyperacee) hermaphro-
dite and female forms exist in Scotland and the Arctic regions,
both of which yield seed. +
SIZE OF THE COROLLA.
It is a curious fact that in all the foregoing poly-
gamous, dicecious, and gyno-diecious plants in which
any difference has been observed in the size of the
corolla in the two or three forms, it is rather larger in
the females, which have their stamens more or less or
quite rudimentary, than in the hermaphrodites or males,
This holds good with Euonymus, Rhamnus catharticus,
lex, Fragaria, all or at least most of the before-named
Labiate, Scabiosa atro-purpurea, and Echium vulgare.
So it is, according to Von Mohl, with Cardamine
* ‘Manual of the Botany of
the N. United States,’ 2nd edit.
1856, p. 269. See also ‘ American
Journal of Science,’ Nov. 1862,
p. 419, and ‘Proc. American
Academy of Science,’ Oct. 14,
1862, p. 53.
+ Sir J. E. Smith, ‘ Trans,
Linn. Soe.’ vol. xiii. p. 599,
Dr. Dickie, ‘ Journal Linn. Soc.
Bot.’ vol. ix. 1865, p. 161.
308 SIZE OF THE COROLLA. ~ Cuap. VIL.
amara, Geraniun sylvaticum, Myosotis, and Salvia.
On the other hand, as Von Mohl remarks, when a
plant produces hermaphrodite flowers and others
which are males owing to the more or less complete
abortion of the female organs, the corollas of the
males are not at all increased in size, or only excep-
tionally and in a slight degree, as in Acer.* It seems
therefore probable that the decreased size of the female
corollas in the foregoing cases is due to a tendency to
abortion spreading from the stamens to the petals. We
see how intimately these organs are related in double
flowers, in which the stamens are readily converted
into petals. Indeed some botanists believe that petals
do not consist of leaves directly metamorphosed, but of
metamorphosed stamens. That the lessened size of the
corolla in the above case is in some manner an indirect
result of the modification of the reproductive organs is
supported by the fact that in Rhamnus catharticus not
only the petals but the green and inconspicuous sepals
of the female have been reduced in size; and in the
strawberry the flowers are largest in the males, mid-
sized in the hermaphrodites, and smallest in the fe-
males. These latter cases,—the variability in the size
of the corolla in some of the above species, for instance
in the common thyme,—together with the fact that it
never differs greatly in size in the two forms—make
me doubt much whether natural selection has come
into play;—that is whether, in accordance with H.
Miller’s belief, the advantage derived from the pol-
leniferous flowers being visited first by insects has
been sufficient to lead to a gradual reduction of the
corolla of the female. We should bear in mind that as
the hermaphrodite is the normal form, its corolla has
* “Bit, Zeitung,’ 1863, p. 326,
Cuap. VII.
SIZE OF THE COROLLA.
309
probably retained its original size.* An objection to
the above view should not be passed over; namely, that
the abortion of the stamens in the females ought to
have added through the law of compensation to the
size of the corolla; and this perhaps would have oc-
curred, had not the expenditure saved by the abor-
tion of the stamens been directed to the female repro-
ductive organs, so as to give to this form increased
fertility.
* It does not appear to me
that Kerner’s view (‘ Die Schutz-
mittel des Pollens,’ 1873, p. 56)
can be accepted in the present
cases, namely that the larger
corolla in the hermaphrodites and
males serves to protect their pollen
from rain. In the genus Thymus,
for instance, the aborted anthers
of the female are much better
protected than the perfect ones of
the hermaphrodite.
310 CLEISTOGAMIO FLOWERS. Cuar. VIII
CHAPTER VIII.
CLEISTOGAMIo FLOWERS.
General character of cleistogamic flowers—List of the genera producing
such flowers, and their distribution in the vegetable series—Viola,
description of the cleistogamic flowers in the sever.l species, their
fertility compared with that of the perfect flowers—Oxalis
acetosella—O. sensitiva, three forms of cleistogamiv flowers—Vau-
dellia—Ononis—Impatiens—Drosera—Miscellaneous observations
or various other cleistogamic plants—Anemophilous species produc-
ing cleistogamic flowers—Leersia, perfect flowers rarely developed
--Summary and concluding remarks on the origin of cleistogamic
flowers—The chief conclusions which may be drawn from the
observations in this volume.
Ir was known even before the time of Linneus that
certain plants produced two kinds of flowers, ordi-
nary open, and minute closed ones; and this fact
formerly gave rise to warm controversies about the
sexuality of plants. These closed flowers have been
appropriately named cleistogamic by Dr. Kuhn.*
They are remarkable from their small size and from
never opening, so that they resemble buds; their petals
are rudimentary or quite aborted; their stamens are
often reduced in number, with the anthers of very
small size, containing few pollen-grains, which have
remarkably thin transparent coats, and generally emit
their tubes whilst still enclosed within the anther-
cells ; and, lastly, the pistil is much reduced in size,
with the stigma in some cases hardly at all developed.
These flowers do not secrete nectar or emit any odour;
from their small size, as well as from the corolla being
rudimentary, they are singularly inconspicuous. Con
* ‘Bot. Zeitung,’ 1867, p. 65.
Cuap. VIII. CLEISTOGAMIO FLOWERS. 31]
sequently insects do not visit them; nor if they did,
could they find an entrance. Such flowers are therefore
invariably self-fertilised ; yet they produce an abund-
ance of seed. In several cases the young capsules
bury themselves beneath the ground, and the seeds
are there matured. These flowers are developed before,
or after, or simultaneously with the perfect ones.
Their development seems to be largely governed by
the conditions to which the plants are exposed, for
during certain seasons or in certain localities only
cleistogamic or only perfect flowers are produced.
Dr. Kuhn, in the article above referred to, gives a
list of 44 genera including species which bear flowers
of this kind. To this list I have added some genera,
and the authorities are appended in a foot-note. I
have omitted three names, from reasons likewise given
in the foot-note. But it is by no means easy to de-
cide in all cases whether certain flowers ought to be
ranked as cleistogamic. For instance, Mr. Bentham
informs me that in the South of France some of the
flowers on the vine do not fully open and yet set
fruit; and I hear from two experienced gardeners that
this is the case with the vine in our hot-houses; but
as the flowers do not appear to be completely closed it
would be imprudent to consider them as cleistogamic.
The flowers of some aquatic and marsh plants, for
instance of Ranunculus aquatilis, Alisma natans,
Subularia, Illecebrum, Menyanthes, and LEuryale,*
remain closely shut as long as they are sub-
merged, and in this condition fertilise themselves.
* Delpino,‘ Sull’ Opera, laDistri- vol. iii. 1825, p. 157. For the
buzione de: Sessi nelle Piante,’ &c. behaviour of Menyanthes in Russia
1867, p. 30. Subularia, however, see Gillibert in ‘Act. Acad. St. Pe-
sometimes has its flowers fully _tersb.,’ 1777, part ii. p. 45.—On
expanded beneath the water, see Euryale, ‘Gaidener’s Chronicle.
Sir J. E. Smith, ‘English Flora, 1877, p. 280.
21
314 CLEISTOGAMIC FLOWERS. Cuap. VIIL
The first point that strikes us in considering this list
of 55 genera, is that they are very widely distributed
in the vegetable series. They are more common in the
family of the Leguminose than in any other, and next
in order in that of the Acanthacez and Malpighiacez.
A large number, but not all the species, of certain
genera, as of Oxalis and Viola, bear cleistogamic as
well as ordinary flowers. A second point which de-
serves notice is that a considerable proportion of the
genera produce more or less irregular flowers; this is
the case with about 32 out of the 55 genera, but to this
subject I shall recur.
I formerly made many observations on cleistogamic
flowers, but only a few of them are worth giving, since
the appearance of an admirable paper by Hugo von
Mohl,* whose examination was in some respects much
more complete than mine. His paper includes also an
interesting history of our knowledge on the subject.
Viola canina.—The calyx of the cleistogamic flowers
differs in no respect from that of the perfect ones. The
petals are reduced to five minute scales; the lower one,
which represents the lower lip, is considerably larger
than the others, but with no trace of the spur-like
nectary; its margins are smooth, whilst those of the
other four scale-like petals are papillose. D. Miller of
Upsala says that in the specimens which he observed
the petals were completely aborted.t The stamens are
very small, and only the two lower ones are provided
with anthers, which do not cohere together as in the
perfect flowers. The anthers are minute, with the two
cells or loculi remarkably distinct; they contain very
little pollen in comparison with those of the perfect
* ‘Bot, Zeitung,’ 1863, p.309- paper contains the first full and
satisfactory account of any cleisto-
28.
t Ibid. 1857, p. 730. This gamic flower.
Cuap. VIII. VIOLA. 815
flowers. The connective expands into a membranous
hood-like shield which projects above the anther-cells.
These two lower stamens have no vestige of the curious
appendages which secrete nectar in the perfect flowers.
The three other stamens are destitute of anthers and
have broader filaments, with their terminal membran-
ous expansions flatter or not so hood-like as those of
the two antheriferous stamens. The pollen-grains have
remarkably thin transparent coats; when exposed to
the air they shrivel up quickly ; when placed in water
they swell, and are then $539 of an inch in diameter,
and therefore of smaller size than the ordinary pollen-
grains similarly treated, which have a diameter of
iY of an inch. In the cleistogamic flowers, the
pollen-grains, as far as I could see, never naturally fall
out of the anther-cells, but emit their tubes through a
pore at the upper end. I was able to trace the tubes
from the grains some way down the stigma. The pistil
is very short, with the style hooked, so that its ex-
tremity, which is a little enlarged or funnel-shaped
and represents the stigma, is directed downwards,
being covered by the two membranous expansions of
the antheriferous stamens. It is remarkable that there
is an open passage from the enlarged funnel-shaped
extremity to within the ovarium ; this was evident, as
slight pressure caused a bubble of air, which had been
drawn in by some accident, to travel freely from one
end to the other: a similar passage was observed by
Michalet in V. alba. The pistil therefore differs con-
siderably from that of the perfect flower; for in the
latter it is much longer, and straight with the excep-
tion of the rectangularly bent stigma; nor is it per-
forated by an open passage.
The ordinary or perfect flowers have been said by
some authors never to produce capsules; but this is an
316 CLEISTOGAMIC FLOWERS. Cuap. VIIL
error, though only a small proportion of them do so.
This appears to depend in some cases on their anthers
not containing even a trace of pollen, but more gene-
rally on bees not visiting the flowers. I twice covered
with a net a group of flowers, and marked with threads
twelve of them which had not as yet expanded. This
precaution is necessary, for though as a general rule
the perfect flowers appear considerably before the
cleistogamic ones, yet occasionally some of the latter
are produced early in the season, and their capsules
might readily be mistaken for those produced by. the
perfect flowers. Not one of the twelve marked perfect
flowers yielded a capsule, whilst others under the net
which had been artificially fertilised produced five
capsules; and these contained exactly the same aver-
age number of seeds as some capsules from flowers
outside the net which had been fertilised by bees. I
have repeatedly seen Bombus hortorum, lapidarius, and
a third species, as well as hive-bees, sucking the
flowers of this violet: 1 marked six which were thus
visited, and four of them produced fine capsules; the
two others were gnawed off by some animal. I
watched Bombus hortorwm fdr some time, and when-
ever it came to a flower which did not stand in a con-
venient position to be sucked, it bit a hole through the
spur-like nectary. Such ill-placed flowers would not
yield any seed or leave descendants; and the plants
bearing them would thus tend to be eliminated through
natural selection.
The seeds produced by the cleistogamic and perfect
flowers do not differ in appearance or number. On
two occasions I fertilised several perfect flowers with
pollen from other individuals, and afterwards marked
some cleistogamic flowers on the same plants; and the
result was that 14 capsules produced by the perfect
Cuar, VIII. VIOLA. 317
flowers contained on an average 9°85 seeds; and 17
capsules from the cleistogamic ones contained 9°64
seeds,—an amount of difference of no significance. It
is remarkable how much more quickly the capsules
from the cleistogamic flowers are developed than those
from the perfect ones; for instance, several perfect
flowers were cross-fertilised on April 14th, 1863, and a
month afterwards (May 15th) eight young cleistogamic
flowers were marked with threads; and when the two
sets of capsules thus produced were compared on
June 3rd, there was scarcely any difference between
them in size.
Viola odorata (white-flowered, single, cultivated va-
riety).—The petals are represented by mere scales as
in the last species; but differently from in the last,
all five stamens are provided with diminutive anthers.
Small bundles of pollen-tubes were traced from the
five anthers into the somewhat distant stigma. The
capsules produced by these flowers bury themselves 1
the soil, if it be loose enough, and there mature them-
selves.* Lecoq says that it is only these latter cap-
sules which possess elastic valves; but I think this
must be a misprint, as such valves would obviously be
of no use to the buried capsules, but would serve to
scatter the seeds of the sub-aerial ones, as in the other
species of-Viola. It is remarkable that this plant, ac-
cording to Delpino,t does not produce cleistogamic
flowers in one part of Liguria, whilst the perfect flowers
are there abundantly fertile; on the other hand,
cleistogamic flowers are produced by it near Turin.
Another fact is worth giving as an instance of corre-
* Vaucher says (‘Hist. Phys.des tom. v. 1856, p. 180.
Plantes d’Europe. tom. iii. 1844, + ‘Sull’ Opera, Ja Distribuzione
p. 309) that V. hirta and ecollina dei Sessi nelle Piante,’ &c., 1867,
likewise bury their capsules.— pp. 30. ;
See also Lecoq, *Géograph. Bot.’
318 CLEISTOGAMIC FLOWERS. Cuap. Viil
lated development: I found on a purple variety,
after it had produced its perfect double flowers, and
whilst the white single variety was bearing its cleisto-
gamic flowers, many bud-like bodies which from their
position on the plant were certainly of a cleistogamic
nature. They consisted, as could be seen on bisecting
them, of a dense mass of minute scales closely folded
ever one another, exactly like a cabbage-head in
miniature. I could not detect any stamens, and in the
place of the ovarium there was a little central column.
The doubleness of the perfect flowers had thus spread
to the cleistogamic ones, which therefore were ren-
dered quite sterile.
Viola hirta.—The five stamens of the cleistogamic
flowers are provided, as in the last case, with small
anthers, from all of which pollen-tubes proceed to the
stigma. The petals are not quite so much reduced
as in V. canina, and the short pistil instead of being
hooked is merely bent into a rectangle. Of several
perfect flowers which I saw visited by hive- and humble-
bees, six were marked, but they produced only two
capsules, some of the others having been accidentally
injured. M. Monnier was therefore mistaken in this
case as in that of V. odorata, in supposing that the
perfect flowers always withered away and aborted. He
states that the peduncles of the cleistogamic flowers
curve downwards and bury the ovaries beneath the
soil.* I may here add that Fritz Miller, as I hear
from his brother, has found in the highlands of South-
ern Brazil a white-flowered species of violet which
bears subterranean cleistogamic flowers.
* These statements are taken to the supposed sterility of the
from Professor Oliver’s excellent perfect flowers in this genus see
article in the ‘ Nat. Hist. Review, also Timbal-Lagrave in ‘ Bot
July 1862, p. 238. With respect Zeitung,’ 1854, p. 772.
Cuar, VIIL VIOLA. 319
Viola nana..—My. Scott sent me seeds of this Indian
species from the Sikkim Terai, from which I raised
many plants, and from these other seedlings during
several successive generations. They produced an
abundance of cleistogamic flowers during the whole of
each summer, but never a perfect one. When Mr. Scott
wrote to me his plants in Calcutta were behaving simi-
larly, though his collector saw the species in flower in
its native site. This case is valuable as showing that
we ought not to infer, as has sometimes been done,
that a species does not bear perfect flowers when grow-
ing naturally, because it produces only cleistogamic
flowers under culture. The calyx of these flowers is
sometimes formed of only three sepals; two being
actually suppressed and not merely coherent with the
others; this occurred with five out of thirty flowers
which were examined for this purpose. The petals are
represented by extremely minute scales. Of the sta-
mens, two bear anthers which are in the same state as
in the previous species, but, as far as I could judge,
each of the two cells contained only from 20 to 25 de-
licate transparent pollen-grains. These emitted their
tubes in the usual manner. The three other stamens
bore very minute rudimentary anthers, one of which
was generally larger than the other two, but none of
them contained any pollen. In one instance, however,
a single cell of the larger rudimentary anther in-
cluded a little pollen. The style consists of a short
flattened tube, somewhat expanded at its upper end,
and this forms an open channel leading into the
ovarium, as described under V. canina, It is slightly
bent towards the two fertile anthers.
Viola Roaburghiana.—This species bore in my hot-
house during two years a multitude of cleistogamic
flowers, which resembled in all respects those of the
820 CLEISTOGAMIC FLOWERS. Cuav. VIII.
last species; but no perfect ones were produced. Mr.
Scott informs me that in India it bears perfect flowers
only during the cold season, and that these are quite
fertile. During the hot, and more especially during
the rainy season, it bears an abundance of cleisto-
gamic flowers.
Many other species, besides the five now described,
produce cleistogamic flowers ; this is the case, accord-
ing to D. Miller, Michalet, Von Mohl, and Hermann
Miller, with V. elatior, lancifolia, sylvatica, palustris,
mirabilis, bicolor, ionodium, and biflora. But V. tricolor
does not produce them.
Michalet asserts that V. palustris produces near
Paris only perfect flowers, which are quite fertile; but
that when the plant grows on mountains cleistogamic
flowers are produced; and so it is with V. biflora.
The same author states that he has seen in the case
of V. alba flowers intermediate in structure between
the perfect and cleistogamic ones. According to M.
Boisduval, an Italian species, V. Ruppii, never bears
in France “des fleurs bien apparentes, ce qui ne l’em-
péche pas de fructifier.”
It is interesting to observe the gradation in the
abortion of the parts in the cleistogamic flowers of
the several foregoing species. It appears from the
statements by D. Miller and Von Mohl that in V. mi-
rabilis the calyx does not remain quite closed ; all five
stamens are provided with anthers, and some pollen-
grains probably fall out of the cells on the stigma,
instead of protruding their tubes whilst still enclosed,
as in the other species. In V. hirta all five sta-
mens are likewise antheriferous; the petals are not
so much reduced and the pistil not so much modified
as in the following species. In V. nana and elatior
only two of the stamens properly bear anthers, but
Cuap. VIII. OXALIS. 321
sometimes one or even two of the others are thus pro-
vided. Lastly, in V. cantina never more than two of
the stamens, as far as I have seen, bear anthers; the
petals are much more reduced than in V. hérta, and
according to D. Miller are sometimes quite absent.
Owalis acetosella—The existence of cleistogamic
flowers on this plant was discovered by Michalet.*
They have been fully described by Von Mohl, and I
can add hardly anything to his description. In my
specimens the anthers of the five longer stamens were
nearly on a level with the stigmas; whilst the smaller
and less plainly bilobed anthers of the five shorter
stamens stood considerably below the stigmas, so that
their tubes had to travel some way upwards. Ac-
cording to Michalet these latter anthers are some-
times quite aborted. In one case the tubes, which
ended in excessively fine points, were seen by me
stretching upwards from the lower anthers towards
the stigmas, which they had not as yet reached. My
plants grew in pots, and long after the perfect flowers
had withered they produced not only cleistogamic but
a few minute open flowers, which were in an inter-
mediate condition between the two kinds. In one of
these the pollen-tubes from the lower anthers had
reached the stigmas, though the flower was open.
The footstalks of the cleistogamic flowers are much
shorter than those of the perfect flowers, and are so
much bowed downwards that they tend, according to
Von Mohl, to bury themselves in the moss and dead
leaves on the ground. Michalet also says that they
are often hypogean. In order to ascertain the num-
ber of seeds produced by these flowers, I marked eight
of them; two failed, one cast its seed abroad, and the
* ‘Bull. Soc. Bot. de France,’ tom. vii. 1860, p 465.
822 CLEISTOGAMIC FLOWERS. Cuap. VIIL.
remaining five contained on an average 10:0 seeds
per capsule. This is rather above the average 9:2,
which eleven capsules from perfect flowers fertilised
with their own pollen yielded, and considerably above
the average 7°9, from the capsules of perfect flowers
fertilised with pollen from another plant; but this
latter result must, I think, have been accidental.
Hildebrand, whilst searching various Herbaria, ob-
served that many other species of Oxalis besides O.
acetosella produce cleistogamic flowers;* and I hear
from him that this is the case with the heterostyled
trimerphic 0. incarnata from the Cape of Good Hope.
Oxalis (Biophytum) sensitiva.—This plant is ranked
by many botanists as a distinct genus, but as a sub-
genus by Bentham and Hooker. Many of the early
flowers on a mid-styled plant in my hot-house did not
open properly, and were in an intermediate condition
between cleistogamic and perfect. “Their petals varied
from a mere rudiment to about half their proper size ;
nevertheless they produced capsules. J attributed
their state to unfavourable conditions, for later in the
season fully expanded flowers of the proper size ap-
peared. But Mr. Thwaites afterwards sent me from
Ceylon a number of long-styled, mid-styled, and short-
styled flower-stalks preserved in spirits; and on the
same stalks with the perfect flowers, some of which were
fully expanded and others still in bud, there were
small bud-like bodies containing mature pollen, but
with their calyces closed. These cleistogamic flowers
do not differ much in structure from the perfect ones
of the corresponding form, with the exception that
their petals are reduced to extremely minute, barely
visible scales, which adhere firmly to the rounded
* *Monatsbericht der Akad. der Wiss. zu Berlin, 1866, p. 369.
Car. VIIL OXALIS. 323
bases of the shorter stamens. Their stigmas are much
less papillose, and smaller in about the ratio of 13 tu
20 divisions of the micrometer, as measured trans-
versely from apex to apex, than the stigmas of the
perfect flowers. The styles are furrowed longitudinally,
and are clothed with simple as well as glandular hairs,
but only in the cleistogamic flowers produced by the
long-styled and mid-styled forms. The anthers of the
longer stamens are a little smaller than the correspond-
ing ones of the perfect flowers, in about the ratio of
11 to 14. They dehisce properly, but do not appear
to contain much pollen. Many pollen-grains were
attached by short tubes to the stigmas; but many
others, still adhering to the anthers, had emitted
their tubes to a considerable length, without having
come in contact with the stigmas. Living plants
ought to be examined, as the stigmas, at least of the
long-styled form, project beyond the calyx, and if
visited by insects (which, however, is very improbable)
might be fertilised with pollen from a perfect flower.
The most singular fact about the present species is
that long-styled cleistogamic flowers are produced by
the long-styled plants, and mid-styled as well as
short-styled cleistogamic flowers by the other two
forms ; so that there are three kinds of cleistogamic
and three kinds of perfect flowers produced by this
one species! Most of the heterostyled species of
Oxalis are more or less sterile, many absolutely so, if
illegitimately fertilised with their own-form pollen.
It is therefore probable that the pollen of the cleisto-
gamic flowers has been modified in power, so as to act
on their own stigmas, for they yield an abundance of
seeds. We may perhaps account for the cleistogamic
flowers consisting of the three forms, through the prin-
ciple of correlated growth, by which the cleistogamio
824 CLEISTOGAMIC FLOWERS. Cuap. VIII
flowers of the double violet have been rendered
double.
Vandellia nummularifolia.—Dr. Kuhn has collected*
all the notices with respect to cleistogamic flowers in
this genus, and has described from dried specimens
those produced by an Abyssinian species. Mr. Scott
sent me from Calcutta seeds of the above common
Indian weed, from which many plants were success-
ively raised during several years. The cleistogamic
flowers are very small, being when fully mature under
gy of an inch (1:27 mm.) in length. ‘The calyx does
not open, and within it the delicate transparent <orolla
remains closely folded over the ovarium. There are
only two anthers instead of the normal number of four,
and their filaments adhere to the corolla. The cells of
the anthers diverge much at their lower ends and are
only 7%, of an inch (-181 mm.) in their longer diameter.
They contain but few pollen-grains, and these emit
their tubes whilst still within the anther. The pistil
is very short, and is surmounted by a bilobed stigma.
As the ovary grows the two anthers together with the
shrivelled corolla, all attached by the dried pollen-
tubes to the stigma, are torn off and carried upwards
in the shape of a little cap. The perfect flowers gene-
rally appear before the cleistogamic, but sometimes
simultaneously with them. During one season a large
number of plants produced no perfect flowers. It has
been asserted that the latter never yield capsules; but
this is a mistake, as they do so even when insects are
excluded. Fifteen capsules from cleistogamic flowers
on plants growing under favourable conditions con-
tained on an average 64:2 seeds, with a maximum of
87; whilst 20 capsules from plants growing much
* ‘Bot. Zeitung, 1867, p. 65,
Cuar. VIII. ONONIS. 3825
crowded yielded an average of only 48. Sixteen cap-
sules from perfect flowers artificially crossed with pollen
from another plant contained on an average 93 seeds,
with a maximum of 137. Thirteen capsules from self-
fertilised perfect flowers gave an average of 62 seeds,
with a maximum of 135. Therefore the capsules from
the cleistogamic flowers contained fewer seeds than
those from perfect flowers when cross-fertilised, and
slightly more than those from perfect flowers self-
fertilised.
Dr. Kuhn believes that the Abyssinian J. sessiflora
does not differ specifically from the foregoing species.
But its cleistogamic flowers apparently include four
anthers instead of two as above described. The plants,
moreover, of V. sessiflora produce subterranean runners
which yield capsules; and I never saw a trace of such
runners in V. nummilarifolia, although many plants
were cultivated.
Linaria spuria.—Michalet says* that short, thin,
twisted branches are developed from the buds in the
axils of the lower leaves, and that these bury them-
selves in the ground. They there produce flowers
not offering any peculiarity in structure, excepting
that their corollas, though properly coloured, are de-
formed. These flowers may be ranked as cleistogamic,
as they are developed, and not merely drawn, beneath
the ground.
Ononis columnz.—Plants were raised from seeds sent
me from Northern Italy. ‘The sepals of the cleisto-
gamic flowers are elongated and closely pressed to-
gether; the petals are much reduced in size, colour-
ess, and folded over the interior organs. The fila-
ments of the ten stamens are united into a tube, and
* ‘Bull. Soc. Bot. de France,’ tom. vii. 1860, p. 468.
326 CLEISTOGAMIC FLOWERS. Cnap. VITL
this is not the case, according to Von Mobhl, with the
cleistogamic flowers of other Leguminose. Five of
the stamens are destitute of anthers, and alternate with
the five thus provided. The two cells of the anthers
are minute, rounded and separated from one another
by connective tissue; they contain but few pollen-
grains, and these have extremely delicate coats. The
pistil is hook-shaped, with a plainly enlarged stigma,
which is curled down, towards the anthers; it there-
fore differs much from that of the perfect flower.
During the year 1867 no perfect flowers were pro-
duced, but in the following year there were both
perfect and cleistogamic ones.
Ononis minutissima.—My plants produced both per-
fect and cleistogamic flowers; but I did not examine
the latter. Some of the former were crossed with
pollen from a distinct plant, and six capsules thus ob-
tained yielded on an average 3°66 seeds, with a maxi-
mum of 5 in one. Twelve perfect flowers were marked
and allowed to fertilise themselves spontaneously under
a net, and they yielded eight capsules, containing on
an average 2°38 seeds, with a maximum of 8 in one.
Fifty-three capsules produced by the cleistogamic
flowers contained on an average 4°1 seeds, so that
these were the most productive of all; and the seeds
themselves looked finer even than those from the
crossed perfect flowers. According to Mr. Bentham
O. parviflora likewise bears cleistogamic flowers ; and
he informs me that these flowers are produced by all
three species early in the spring; whilst the perfect
ones appear afterwards, and therefore in a reversed
order compared with those of Viola and Oxalis. Some
of the species, for instance Ononis columne, bear a
fresh crop of cleistogamic flowers in the autumn.
Lathyrus nissolia apparently offers a case of the first
Cuar, VIII. IMPATIENS. 327
stage in the production of cleistogamic flowers, for on
plants growing in a state of nature, many of the flowers
never expand and yet produce fine pods. Some of
the buds are so large that they seem on the point of
expansion ; others are much smaller, but none so small
as the true cleistogamic flowers of the foregoing
species. As I marked these buds with thread and
examined them daily, there could be no mistake about
their producing fruit without having expanded.
Several other Leguminous genera produce cleisto-
gamic flowers, as may be seen in the previous list; but
much does not appear to be known about them. Von
Moh! says that their petals are commonly rudimentary,
that only a few of their anthers are developed, their
filaments are not united into a tube and their pistils
are hook-shaped. In three of the genera, namely Vicia,
Amphicarpea, and Voandzeia, the cleistogamic flowers
are produced on subterranean stems. The perfect
flowers of Voandzeia, which is a cultivated plant, are
said never to produce fruit ;* but we should remember
how often fertility is affected by cultivation.
Impatiens fuiva.—Mr. A. W. Bennett has published
an excellent description, with figures, of this plant.t
He shows that the cleistogamic and perfect flowers
differ in structure at a very early period of growth, so
that the existence of the former cannot be due merely
to the arrested development of the latter,—a conclusion
which indeed follows from most of the previous de-
scriptions. Mr. Bennett found on the banks of the Wey
that the plants which bore cleistogamic flowers alone
were to those bearing perfect flowers as 20 to 1; but
* Correa de Mello (‘Journal African plant, which is sometimes
Linn. Soc. Bot.’ vol. xi. 1870, p. cultivated in Brazil.
254) particularly attended to the t ‘Journal Linn. Soc. Bot.’ vob
flowering and fruiting of this xiii, 1872, p. 147.
22
328 CLEISTOGAMIC FLOWERS. Cuar. VIII.
we should remember that this is a naturalised species.
The perfect flowers are usually barren in England; but
Prof. Asa Gray writes to me that after midsummer in
the United States some or many of them produce
capsules.
Impatiens noli-me-tangere.—I can add nothing of im-
portance to Von Mohl’s description, excepting that
one of the rudimentary petals shows a vestige of a
nectary, as Mr. Bennett likewise found to be the case
with J. fulva. As in this latter species all five stamens
produce some pollen, though small in amount; a
single anther contains, according to Von Mohl, not
more than 50 grains, and these emit their tubes
while still enclosed within it. The pollen-grains of the
perfect flowers are tied together by threads, but not,
so as far as I could see, those of the cleistogamic
flowers ; and a provision of this kind would here have
been useless, as the grains can never be transported
by insects. The flowers of I. balsamina are visited by
humble-bees,* and I am almost sure that this is the
case with the perfect flowers of I. noli-me-tangere. From
the perfect flowers of this latter species covered with
a net eleven spontaneously self-fertilised capsules were
produced, and these yielded on an average 3°45 seeds.
Some perfect flowers with their anthers still containing
an abundance of pollen were fertilised with pollen from
a distinct plant; and the three capsules thus produced
contained, to my surprise, only 2,2,and 1 seed. As
I. balsamina is proterandrous, so probably is the pre-
sent species ; and if so, cross-fertilisation was effected
by me at too early a period, and this may account for
the capsules yielding so few seeds.
Drosera rotundifolia—The first flower-stems which
* H. Miller, ‘Dic Befruchtung,’ &e. p. 170
Uaae. VIII. CLEISTOGAMIC FLOWERS. 3829
were thrown up by some plants in my green-house
bore only cleistogamic flowers. The petals of small
size remained permanently closed over the repro-
ductive organs, but their white tips could just be
seen between the almost completely closed sepals.
The pollen, which was scanty in amount, but not so
scanty as in Viola or Oxalis, remained enclosed
within the anthers, whence the tubes proceeded and
penetrated the stigma. As the ovarium swelled the
little withered corolla was carried upwards in the
form of a cap. These cleistogamic flowers produced
an abundance of seed. Later in the season perfect
flowers appeared. With plants in a state of nature the
flowers open only in the early morning, as I have been
informed by Mr. Wallis, who particularly attended to
the time of their flowering. In the caso of D. Anglica,
the still folded petals on some plants in my green-
house opened just sufficiently to leave a minute
aperture; the anthers dehisced properly, but the
pollen-grains adhered in a mass to them, and thence
emitted their tubes, which penetrated the stigmas.
These flowers, therefore, were in an intermediate con-
dition, and could not be called either perfect or
cleistogamic.
A few miscellaneous observations may be added
with respect to some other species, as throwing light.
on our subject. Mr. Scott states* that Hranthemum
ambiguum bears three kinds of flowers,—large, con-
spicuous, open ones, which are quite sterile,—others
of intermediate size, which are open and moderately
fertile—and lastly small closed or cleistogamic ones,
which are perfectly fertile. Ruellia tuberosa, likewise
one of the Acanthacee, produces both open and cleis-
* ‘Journal of Botany,’ London, new series, vol. i. 1872, pp. 161-4.
330 Cuap. VIII.
togamic flowers; the latter yield from 18 to 24, whilst
the former only from 8 to 10 seeds ; these two kinds of
flowers are produced simultaneously, whereas in several
other members of the family the cleistogamic ones
appear only during the hot season. According to
Torrey and Gray, the North American species of He-
lianthemum, when growing in poor soil, produce only
cleistogamic flowers. The cleistogamic flowers of
Specularia perfoliata are highly remarkable, as they
are closed by a tympanum formed by the rudi-
mentary corolla, and without any trace of an open-
ing. The stamens vary from 3 to 5 in number,
as do the sepals.* The collecting hairs on the pistil,
which play so important a part in the fertilisation
of the perfect flowers, are here quite absent. Drs.
Hooker and Thomson statet that some of the Indian
species of Campanula produce two kinds of flowers ;
the smaller ones being borne on longer peduncles
with differently formed sepals, and producing a more
globose ovary. The flowers are closed by a tym-
panum like that in Specularia. Some of the plants
produce both kinds of flowers, others only one kind ;
both yield an abundance of seeds. Professor Oliver
adds that he has seen flowers on Campanula colorata
in an intermediate condition between cleistogamic and
perfect ones.
The solitary almost sessile cleistogamic flowers pro-
duced by Monochoria vaginalis are differently protected
from those in any of the previous cases, namely, within
“a short sack formed of the membranous spathe,
CLEISTOGAMIC FLOWERS.
* Von Mohl, ‘Bot. Zeitung,’
1863, pp. 3J4 and 323. Dr. Brom-
field (‘ Phytologist,’ vol. iii. p.
of the perfect flower is mostly
5-cleft.
+ ‘Journal Linn. Soe.’ vol. ii
530) also remarks that the calyx
of the cleistogamic flowers is
usually only 3-cleft, while that
1857, p. 7. See also Professor
Oliver in ‘Nat. Hist. Review,
1862, p. 240.
Cuap. VIII. CLEISTOGAMIC FLOWERS. 331
without any opening or fissure.” There is only a
single fertile stamen; the style is almost obsolete,
with the three stigmatic surfaces directed to one side.
Both the perfect and cleistogamic flowers produce
seeds.*
The cleistogamic flowers on some of the Mal-
pighiaceze seem to be more profoundly modified than
those in any of the foregoing genera. According to
A. de Jussieut they are differently situated from the
perfect flowers; they contain only a single stamen,
instead of 5 or 6; and it is a strange fact that this
particular stamen is not developed in the perfect
flowers of the same species. The style is absent or
rudimentary ; and there are only two ovaries instead
of three. Thus these degraded flowers, as Jussieu
remarks, “laugh at our classifications, for the greater
number of the characters proper to the species, to the
genus, to the family, to the class disappear.” I may
-add that their calyces are not glandular, and as,
according to Kerner,t the fluid secreted by such
glands generally serves to protect the flowers from
crawling insects, which steal the nectar without aiding
in their cross-fertilisation, the deficiency of the glands
in the cleistogamic flowers of these plants may perhaps
be accounted for by their not requiring any such
protection.
As the Asclepiadous genus Stapelia is said to pro-
duce cleistogamic flowers, the following case may be
worth giving. I have never heard of the perfect flowers
of Hoya carnosa setting seeds in this country, but some
capsules were produced in Mr. Farrer’s hot-house ;
* Dr. Kirk, ‘Journ. Linn. Soc. t ‘Die Schutzmittel der Bliithen
vol. viii. 1864, p. 147. gegen unberufene Giste,” 1876,
+ ‘Archives du Muséum,’ tom. p. 25.
iii. 1843, pp. 35-38, 82-86, 589, 598.
832 CLEISTOGAMIC FLOWERS. Cuap VIIL
and the gardener detected that they were the product
of minute bud-like bodies, three or four of which
could sometimes be found on the same umbel with the
perfect flowers. They were quite closed and hardly
thicker than their peduncles. The sepals presented
nothing particular, but internally and alternating
with them, there were five small flattened heart-shaped
papille, like rudiments of petals ; but the homological
nature of which appeared doubtful to Mr. Bentham
and Dr. Hooker. No trace of anthers or of stamens
could be detected ; and I knew from having examined
many cleistogamic flowers what to look for. There
were two ovaries, full of ovules, quite open at their
upper ends, with their edges festooned, but with no
trace of a proper stigma. In all these flowers one of
the two ovaries withered and blackened long before
the other. The one perfect capsule, 84 inches in
length, which was sent me, had likewise been de-
veloped from a single carpel. This capsule con-
tained an abundance of plumose seeds, many of which
appeared quite sound, but they did not germinate
when sown at Kew. Therefore the little bud-like
flower which produced this capsule probably was as
destitute of pollen as were those which I examined.
Juncus bufonius and Hordeum.—All the species
hitherto mentioned which produce cleistogamic
flowers are entomophilous; but four genera, Juncus,
Hordeum, Cryptostachys, and Leersia are anemophi-
lous. Juncus bufonius is remarkable* by bearing in
parts of Russia only cleistogamic flowers, which con-
tain three instead of the six anthers found in the
perfect flowers. In the genus Hordeum it has been
oe Dr. Ascherson’s interesting paper in ‘ Bot. Zeitung,’ 187],
p. 551
Cuar. VIII. LEERSIA. 333
shown by Delpino* that the majority of the flowers are
cleistogamic, some of the others expanding and ap-
parently allowing of cross-fertilisation. I hear from
Fritz Miller that there is a grass in Southern Brazil,
in which the sheath of the uppermost leaf, half a
metre in length, envelopes the whole panicle; and
this sheath never opens until the self-fertilised seeds
are ripe. On the roadside some plants had been cut
down, whilst the cleistogamic panicles were develop-
ing, and these plants afterwards produced free or un-
enclosed panicles of small size, bearing perfect flowers.
Leersia oryzoides—It has long been known that
this plant produces cleistogamic flowers, but these were
first described with care by M. Duval-Jouve.t I pro-
cured plants from a stream near Reigate, and cultivated
them for several years in my green-house. The cleis-
togamic flowers are very small, and usually mature
their seeds within the sheaths of the leaves. These
flowers are said by Duval-Jouve to be filled by slightly
viscid fluid; but this was not the case with several
that I opened; but there was a thin film of fluid
between the coats of the glumes, and when these were
pressed the fluid moved about, giving a singularly
deceptive ‘appearance of the whole inside of the flower
being thus filled. The stigma is very small and the
filaments extremely short; the anthers are less than
gy of an inch in length or about one-third of the
length of those in the perfect flowers. One of the
three anthers dehisces before the two others. Can
this have any relation with the fact that in some other
* ¢Bollettini del Comizio agra- on Hordeum, in ‘Monatsbericht d,
tio Parmense.’ Marzo e Aprile, K. Akad. Berlin,’ Oct. 1872, p. 760.
1871. An abstract of this valuable t ‘Bull. Bot. Soc. de France,
paper is given in ‘Bot. Zeitung,’ tom. x. 1863, p. 194,
1871, p.537. See also Hildebrand
834 CLEISTOGAMIC FLOWERS. Cap. VIIL
species of Leersia only two stamens are fully de-
veloped?* The anthers shed their pollen on the
stigma; at least in one instance this was clearly the
case, and by tearing open the anthers under water
the grains were easily detached. Towards the apex of
the anther the grains are arranged in a single row and
lower down in two or three rows, so that they could be
counted ; and there were about 35 in each cell, or 70
in the whole anther ; and this is an astonishingly small
number for an anemophilous plant. The grains have
very delicate coats, are spherical and about zgyq of
an inch (‘0181 mm.), whilst those of the perfect flowers
are about zy4g5 Of an inch (0254 mm.) in diameter.
M. Duval-Jouve states that the panicles very rarely
protrude from their sheaths, but that when this does
happen the flowers expand and exhibit well-developed
ovaries and stigmas, together with full-sized anthers
containing apparently sound pollen ; nevertheless such
flowers are invariably quite sterile. Schreiber had pre-
viously observed that if a panicle is only half protruded,
this half is sterile, whilst the still included half is
fertile. Some plants which grew in a large tub of
water in my green-house behaved on one occasion in a
very different manner. They protruded two very
large much-branched panicles; but the florets never
opened, though these included fully developed stig-
mas, and stamens supported on long filaments with
large anthers that dehisced properly. If these florets
had opened for a short time unperceived by me and
had then closed again, the empty anthers would
have been left dangling outside. Nevertheless they
yielded on August 17th an abundance of fine ripe
seeds. Here then we have a near approach to the
* Asa Gray, ‘Manual of Bot. of United States, 1856, p. 540.
Cua. VIII. LEERSIA. 335
single case as yet known* of this grass producing in a
state of nature (in Germany) perfect flowers which
yielded a copious supply of fruit. Seeds from the cleis-
togamic flowers were sent by me to Mr. Scott in
Calcutta, who there cultivated the plants in various
ways, but they never produced perfect flowers.
In Europe Leersia oryzoides is the sole representa-
tive of its genus, and Duval-Jouve, after examining
several exotic species, found that it apparently is the
sole one which bears cleistogamic flowers. It ranges
from Persia to North America, and specimens from
Pennsylvania resembled the European ones in their
concealed manner of fructification. There can there-
fore be little doubt that this plant generally propa-
gates itself throughout an immense area by cleisto-
gamic seeds, and that it can hardly ever be invigorated
by cross-fertilisation. It resembles in this respect
those plants which are now widely spread, though they
increase solely by asexual generation.
Concluding Remarks on Cleistogamic Flowers——That
these flowers owe their structure primarily to the
arrested development of perfect ones, we may infer
from such cases as that of the lower rudimentary petal
in Viola being larger than the others, like the lower
lip of the perfect flower,—from a vestige of a spur in
the cleistogamic flowers of Impatiens,—from the ten
stamens cf Ononis being united into a tube,—and
other such structures. The same inference may be
drawn from the occurrence, in some instances, on the
same plant of a series of gradations between the
cleistogamic and perfect flowers. But that the former
owe their origin wholly to arrested development is
* Dr. Ascherson, ‘ Bot. Zeitung,” cases in my ‘Variation under
1864, p 350. Domestication, ch. xviii—2nd
¢ Ihave collected several such edit, vol. ii. p. 153.
336 CONCLUDING REMARKS Caar. VII
by no means the case; for various parts have been
specially modified, so as to aid in the self-fertilisation
of the flowers, and as a protection to the pollen; for
instance, the hook-shaped pistil in Viola and in some
other genera, by which the stigma is brought close
to the fertile anthers,—the rudimentary corolla of
Specularia modified into a perfectly closed tympanum,
and the sheath of Monochoria modified into a closed
sack,—the excessively thin coats of the pollen-grains,
—the anthers not being all equally aborted, and other
such cases. Moreover Mr. Bennett has shown that
the buds of the cleistogamic and perfect flowers of
Impatiens differ at a very early period of growth.
The degree to which many of the most important
organs in these degraded flowers have been reduced
or even wholly obliterated, is one of their most re-
markable peculiarities, reminding us of many parasitic
animals. In some cases only a single anther is left,
and this contains but few pollen-grains of diminished
size; in other cases the stigma has disappeared,
leaving a simple open passage into the ovarium.: It
is also interesting to note the complete loss of trifling
points in the structure or functions of certain parts,
which though of service to the perfect flowers, are of
none to the cleistogamic; for instance the collecting
hairs on the pistil of Specularia, the glands on the
calyx of the Malpighiacee, the nectar-secreting ap-
pendages to the lower stamens of Viola, the secretion
of nectar by other parts, the emission of a sweet odour,
and apparently the elasticity of the valves in the
buried capsules of Viola odorata. We here see, as
throughout nature, that as soon as any part or
character becomes superfluous it tends sooner or later
to disappear.
Auother peculiarity in these flowers is that the
Cuar. VII] ON CLEISTOGAMIC FLOWERS. 337
pollen-grains generally emit their tubes whilst still
enclosed within the anthers; but this is not so re-
markable a fact as was formerly thought, when the
case of Asclepias was alone known.* It is, however,
a wonderful sight to behold the tubes directing them-
selves in a straight line to the stigma, when this
is at some little distance from the anthers. As
soon as they reach the stigma or the open passage
leading into the ovarium, no doubt they penetrate it,
guided by the same means, whatever these may be,
as in the case of ordinary flowers. I thought that
they might be guided by the avoidance of light: some
pollen-grains of a willow were therefore immersed in
an extremely weak solution of honey, and the vessel
was placed so that the light entered only in one di-
rection, laterally or from below or from above, but the
long tubes were in each case protruded in every
possible direction.
As cleistogamic flowers are completely closed they
are necessarily self-fertilised, not to mention the
absence of any attraction to insects; and they thus
differ widely from the great majority of ordinary
flowers. Delpino believes{ that cleistogamic flowers
have been developed in order to ensure the production
of seeds under climatic or other conditions which tend
* The case of Asclepias was de-
scribed by R. Brown. Baillon as-
serts (‘ Adansonia,’ tom. ii. 1862,
p. 58) that with many plants the
tubes are emitted from pollen-
grains which have not come into
contact with the stigma; and that
they may be seen advancing hori-
zoutally through the air towards
the stigma. I have observed the
emission of the tubes from the
pollen-masses whilst still within
the anthers, in three widely distinct
Orchidean genera namely Aceras,
Malaxis, and Neottia: see ‘The
Various Contrivances hy which
Orchids are Fertilised,” 2nd edit.
p. 258.
t ‘Sull’ Opera la Distribuzione
dei Sessi nelle Piante,’? 1867,
p. 30.
838 CONCLUDING REMARKS Cuar. VIIL
to prevent the fertilisation of the perfect flowers. I do
not doubt that this holds good to a certain limited extent,
but the production of a large supply of seeds with little
consumption of nutrient matter or expenditure of vital
force is probably a far more efficient motive power.
The whole flower is much reduced in size; but what
is much more important, an extremely small quantity
of pollen has to be formed, as none is lost through the
action of insects or the weather; and pollen contains
much nitrogen and phosphorus. Von Mohl estimated
that a single cleistogamic anther-cell of Oaalis aceto-
sella contained from one to two dozen pollen-grains ;
we will say 20, and if so the whole flower can have
produced at most 400 grains; with Impatiens the
whole number may be estimated in the same manner
at 250; with Leersia at 210; and with Viola nana at
only 100. These figures are wonderfully low com-
pared with the 243,600 pollen-grains produced by a
flower of Leontodon, the 4,863 by an Hibiscus, or the
3,654,000 by a Peony.* We thus see that cleisto-
gamic flowers produce seeds with a wonderfully small
expenditure of pollen; and they produce as a general
rule quite as many seeds as the perfect flowers.
That the production of a large number of seeds is
necessary or beneficial to many plants needs no evi-
dence. So of course is their preservation before they
are ready for germination ; and it is one of the many
remarkable peculiarities of the plants which bear
cleistogamic flowers, that an incomparably larger pro-
portion of them than of ordinary plants bury their
young ovaries in the ground ;—an action which it
may be presumed serves to protect them from being
* The authorities for these statements are given in my ‘ Effects of
Cross and Self-Fertilisation,’ p. 376.
Cnarp. VIII. ON CLEISTOGAMIC FLOWERS. 339
devoured by birds or other enemies. But this advan-
tage is accompanied by the loss of the power of wide
dissemination. No less than eight of the genera
in the list at the beginning of this chapter include
species which act in this manner, namely, several
kinds of Viola, Oxalis, Vandellia, Linaria, Commelina,
and at least three genera of Leguminose. The seeds
also of Leersia, though not buried, are concealed in
the most perfect manner within the sheaths of the
leaves. Cleistogamic flowers possess great facilities
for burying their young ovaries or capsules, owing to
their small size, pointed shape, closed condition and
the absence of a corolla; and we can thus understand
how it is that so many of them have acquired this
curious habit.
It has already been shown that in about 32 out of
the 55 genera in the list just referred to, the perfect
flowers are irregular; and this implies that they have
been specially adapted for fertilisation by insects.
Moreover three of the genera with regular flowers are
adapted by other means for the same end. Flowers
thus constructed are liable during certain seasons to
be imperfectly fertilised, namely, when the proper
insects are scarce; and it is difficult to avoid the
belief that the production of cleistogamic flowers,
which ensures under all circumstances a full supply
of seed, has been in part determined by the perfect
flowers being liable to fail in their fertilisation. But
if this determining cause be a real one, it must be of
subordinate importance, as four of the genera in the
list are fertilised by the wind; and there seems no
reason why their perfect flowers should fail to be
fertilised more frequently than those in any other
anemophilous genus: In contrast with what we here
see with respect to the large proportion of the perfect
840 CONCLUDING REMARKS Cuap. VIII.
flowers being irregular, one genus alone out of the 38
heterostyled genera described in the previous chapters
bears such flowers; yet all these genera are absolutely
dependent on insects for their legitimate fertilisation.
I know not how to account for this difference in the
proportion of the plants bearing regular and irregular
tlowers in the two classes, unless it be that the hetero-
styled flowers are already so well adapted for cross-fer-
tilisation, through the position of their stamens and
pistils and the difference in power of their two or
three kinds of pollen, that any additional adaptation,
namely, through the flowers being made irregular,
has been rendered superfluous.
Although cleistogamic flowers never fail to yield
a large number of seeds, yet the plants bearing them
usually produce perfect flowers, either simultaneously
or more commonly at a different period; and these
are adapted for or admit of cross-fertilisation. From
the cases given of the two Indian species of Viola,
which produced in this country during several years
only cleistogamic flowers, and of the numerous plants
of Vandellia and of some plants of Ononis which
behaved during one whole season in the same manner,
it appears rash to infer from such cases as that of
Salvia cleistogama not having produced perfect flowers
during five years in Germany,* and of an Aspicarpa
not having done so during several years in Paris, that
these plants would not bear perfect flowers in their
native homes. Von Mohl and several other botanists
have repeatedly insisted that as a general rule the
perfect flowers produced by cleistogamic plants are
sterile; but it has been shown under the had of the
several species that this is not the case. The perfect
* Dr. Ascherson, ‘ Bot. Zeit.’ 1871, p. 555.
Cuap. VIII. ON CLEISTOGAMIC FLOWERS. 341
flowers of Viola are indeed sterile unless they are
visited by bees; but when thus visited they yield the
fall number of seeds. As far as I have been able to
discover there is only one absolute exception to the
tule that the perfect flowers are fertile, namely, that
of Voandzeia; and in this case we should remember
that cultivation often affects injuriously the repro-
ductive organs. Although the perfect flowers of
Leersia sometimes yield seeds, yet this occurs so
rarely, as far as hitherto observed, that it practically
forms a second exception to the rule.
As cleistogamic flowers are invariably fertilised, and
as they are produced in large numbers, they yield
altogether a much larger supply of seeds than do
the perfect flowers on the same plant. But the latter
flowers will occasionally be cross-fertilised, and their
offspring will thus be invigorated, as we may infer
from a wide-spread analogy. But of such invigoration
I have only a small amount of direct evidence: two
crossed seedlings of Ononis minutissima were put into
competition with two seedlings raised from cleisto-
gamic flowers ; they were at first all of equal height ;
the crossed were then slightly beaten; but on the fol-
lowing year they showed the usual superiority of their
class, and were to the self-fertilised plants of cleisto-
gamic origin -as 100 to 88 in mean height. With
Vandellia twenty crossed plants exceeded in height
twenty plants raised from cleistogamic seeds only by
a little, namely, in the ratio of 100 to 94.
It is a natural inquiry how so many plants belong-
ing to various very distinct families first came to have
the development of their flowers arrested, so as ulti-
mately to become cleistogamic. That a passage from
the one state to the other is far from difficult is shown
by the many recorded cases of gradations between the
342 CONCLUDING REMARKS Cuap. VIII.
two states on the same plant, in Viola, Oxalis, Biophy-
tum, Campanula, &c. In the several species of Viola
the various parts of the flowers have also been modified
in very different degrees.. Those plants which in their
own country produce flowers of full or nearly full size,
but never expand (as with Thelymitra), and yet set
fruit, might easily be rendered cleistogamic, Lathyrus
nissolia seems to be in an incipient transitional state,
as does Drosera Anglica, the flowers of which are not
perfectly closed. There is good evidence that flowers
sometimes fail to expand and are somewhat reduced
in size, owing to exposure to unfavourable conditions,
but still retain their fertility unimpaired. Linneus
observed in 1753 that the flowers on several plants
brought from Spain and grown at Upsala did not
show any corolla and yet produced seeds. Asa
Gray has seen flowers on exotic plants in the North-
ern United States which never expanded and yet
fruited. With certain English plants, which bear
flowers during nearly the whole year, Mr. Bennett
found that those produced during the winter season
were fertilised in the bud; whilst with other species
having fixed times for flowering, but “which had
been tempted by a mild January to put forth a few
wretched flowers,” no pollen was discharged from the
anthers, and no seed was formed. The flowers of
Lysimachia vulgaris if fully exposed to the sun expand
properly, while those growing in shady ditches have
smaller corollas which open only slightly ; and these
two forms graduate into one another in intermediate
stations. Herr Bouché’s observations are of especial
interest, for he shows that both temperature and the
amount of light affect the size of the corolla; and he
gives measurements proving that with some plants
the corolla is diminished by the increasing cold and
Cuar. VIII. ON CLEISTOGAMIC FLOWERS. 343
darkness of the changing season, whilst with others
it is diminished by the increasing heat and light.*
The belief that the first step towards flowers being
rendered cleistogamic was due to the conditions to
which they were exposed, is supported by the fact
of various plants belonging to this class either not pro-
ducing their cleistogamic flowers under certain condi-
tions, or, on the other hand, producing them to the
complete exclusion of the perfect ones. Thus some
species of Viola do not bear cleistogamic flowers when
growing on the lowlands or in certain districts. Other
plants when cultivated have failed to produce perfect
flowers during several successive years; and this is
the case with Juncus bufonius in its native land of
Russia. Cleistogamic flowers are produced by some
species late and by others early in the season ; and this
agrees with the view that the first step towards their de-
velopment was due to climate; though the periods at
which the two sorts of flowers now appear must since
have become much more distinctly defined. We do not
know whether too low or too high a temperature or the
amount of light acts in a direct manner on the size of
the corolla, or indirectly through the male organs being
first affected. However this may be, if a plant were
prevented either early or late in the season from fully
expanding its corolla, with some reduction in its size,
but with no loss of the power of self-fertilisation, then
natural selection might well complete the work and
* For the statement by Linnezus,
see Mob] in ‘ Bot. Zeitung,’ 1863,
p. 327. Asa Gray, ‘ American
Journal of Science,’ 2nd _ series,
vol, xxxix. 1865, p.105. Bennett
in ‘Nature,’ Nov. 1869, p. 11.
The Rev. G. Henslow also says
(‘ Gardene’s Chronicle,’ 1877, p.
271: also ‘ Nature,’ Oct. 19, 1876,
23
p- 543) “that when the antumn
draws on, and habitually in winter
for such of our wild flowers as
blossom at that season,” the flowers
are self-fertilised. On Lysima-
chia, H. Miller, ‘ Nature,’ Sept,
1873, p. 433. Buuché, ‘ Sitzungs-
bericht der Gesell. Naturforscu,
Freunde’ Oct. 1874, p. 90.
344 GENERAL CONCLUSIONS. Cuar. VIIL
render it strictly cleistogamic. The various organs
would also, it is probable, be modified by the peculiar
conditions to which they are subjected within a com-
pletely closed flower; also by the principle of corre-
lated growth, and by the tendency in all reduced
organs finally to disappear. The result would be the
production of cleistogamic flowers such as we now
see them; and these are admirably fitted to yield a
copious supply of seed at a wonderfully small cost to
the plant.
I will now sum up very briefly the chief conclusions
which seem to follow from the observations given in
this volume. Cleistogamic flowers afford, as just
stated, an abundant supply of seeds with little ex-
penditure ; and we can hardly doubt that they have
had their structure modified and degraded for this
special purpose; perfect flowers being still almost al-
ways produced so as to allow of occasional cross-fertilisa-
tion. Hermaphrodite plants have often been rendered
moneecious, dicecious or polygamous; but as the sepa-
ration of the sexes would have been injurious, had not
pollen been already transported habitually by in-
sects or by the wind from flower to flower, we may
assume that the process of separation did not com-
mence and was not completed for the sake of the
advantages to be gained from cross-fertilisation. The
sole motive for the separation of the sexes which
occurs to me, is that the production of a great number
of seeds might become superfluous to a plant under
changed conditions of life; and it might then be highly
beneficial to it that the same flower or the same indi-
vidual should not have its vital powers taxed, under
the struggle for life to which all organisms are sub-
jected, by producing both pollen and seeds. With
Cuar. VIII. GENERAL CONCLUSIONS. 345
respect to the plants belonging to the gyno-dicecious
sub-class, or those which co-exist as hermaphrodites
and females, it has been proved that they yield a
much larger supply of seed than they would have
done if they had all remained hermaphrodites; and we
may feel sure from the large number of seeds pro-
duced by many plants that such production is often
necessary or advantageous. It is therefore probable
that the two forms in this sub-class have been sepa-
rated or developed for this special end.
Various hermaphrodite plants have become hetero-
styled, and now exist under two or three forms; and
we may confidently believe that this has been effected
in order that cross-fertilisation should be assured.
For the full and legitimate fertilisation of these plants
pollen from the one form must be applied to the
stigma of another. If the sexual elements belonging
to the same form are united the union is an illegiti-
mate one and more or less sterile. With dimorphic
species two illegitimate unions, and with trimorphic
species twelve are possible. There is reason to believe
that the sterility of these unions has not been specially
acquired, but follows as an incidental result from the
sexual elements of the two or three forms having been
adapted to act on one another in a particular manner,
so that any other kind of union is inefficient, like
that between distinct species. Another and still more
remarkable incidental result is that the seedlings
from an illegitimate union are often dwarfed and
more or less or completely barren, like hybrids from
the union of two widely distinct species.
( 346 )
INDEX.
AOANTHACEA,
A.
Acanthacex, 313
Acer campestre, 12, 308
Adoxa, 9
Agiphila elata, 123
— mollis, 123
obdurata, 124, 286
Alefeld, Dr., on Linum, 100
Alisma natans, 311
Amphicarpxa, 327
Amsinckia spectabilis, 110; varia-
bility in length of stamens and
pistil, 261, 266
Anchusa arvensis, 111
Androsace vitalliana, 53
Anthers, size of, in different forms,
252; contabescent, 283
Arachis, 312
Arnebia hispidissima, 111
Ascherson, Dr., on Salvia cleisto-
gama, 313, 340; Juncus bufonius,
332; Leersia oryzoides, 335
Asclepias, 337
Ash, the common, 11
Asperula scoparia, 285
Axell on Primula stricta, 50
B.
Babington, Prof.,on Primula elatior,
72; Stellaria graminea, 313
Baillon, emission of the tubes from
pollen-grains, 337
Belhomme, M., on ray-florets, 6
Bennett, A. W., on Impatiens fulva,
327; flowers fertilised whilst in
the bud state, 342
Bentham, Mr., on the differentiation
of the sexes, 11
COROLLA.
Bentham, Mr., on the clcistogamie
flowers of Ononis, 326
Boraginex, 101
Boreau on cowslip and primrose, 57
Borreria, 127
Bouché on Pavonia, 313; effect of
temperature and light on corolla,
342
Bouvardia leiantha, 135
Braun on Dracocephalum, 299
Breitenbach, W., on Primula elatior,
34, 272
Bromfield, Dr., on primrose and
cowslip, 57; Primula elatior, 73;
Specularia perfoliata, 330
Brown, Robert, on sexual changes,
- 282
: Buckwheat, the common, 111
C.
Caltha palustris, 13
Campanula colorata, 330
Cardamine amara, 307
Caspary, Prof., on Rhamnus cathar-
ticus, 294
Cattleya, 313
Chamissoa, 292
Cinchona micrantha, 134
Cleistogamic flowers, 310; list of
genera, 312; on their origin, 343
Cnicus acaulis, 307
— palustris, 307.
Coccocypselum, 133; pollen-grains
of, 250
Coprosma, 285
Cordia, 117; pistil of, 253
Corolla, difference in size in tho
sexes of the same species, 307
309
INDEX.
347.
CORYDALIS,
Corydalis, 146
Corylus avellana, 10
Cowslip, the common, 14; short-
and long-styled, 19-22, 56-71
‘Cratoxylon formosum, 123
Crocker, C. W., on Plantago lanceo-
lata, 306 :
Cryptostachys, 313, 332
Cuphea purpurea, 168
Dd
Darwin, Charles, on reproductive
organs under cultivation, 7; in-
tercrossed plants, 30; prepotency
of pollen, 62; insects fertilising
flowers, 79; Cephalanthera gran-
diflora, 98; Epidendron and Cat-
tleya, 313; number of pollen-
grains, 338
, W., on Pulmonaria angusté-
folia, 105, 107
Datura arborea, 251
Delpino, plants fertilised by the
wind, 10; on the walnut, 10;
Polygonacex, 114; pollen-grains,
250; Thymus serpyllum, 299;
elused or cleistugamic flowers,
311, 337; Véola odorata, 317
Dianthus barbatus, 30
Dickie, Dr., on Eriophorum angusti-
folium, 307
Dictamnus fraxinella, 146
Diodia, 135
Dicecious and sub-dicecious plants,
287
Discospermum, 286
Doubleday, H., on Primula elatior,
73
Dracocephalum Moldavicum, 299
Drosera Anglica, 329, 342
rotundifolia, 328
Duyal-Jouve, M., on Cryptustachys,
318; Leersia oryzoides, 333, 334
Dyer, Thiselton, on Salvia Hor-
minum, 8; Cratoxylon formosum,
123
E.
Echium vulgare, 111, 305, 307
Epidendron, 313
GRAY,
Epigeza repens, 297
Eranthemum ambiguum, 329
Eriophorum angustifolium, 307
Erythroxylum, 121; pollen-giains of,
250
Euonymus Europxus, 287-293
Euphrasia officinalis, 4
Euryale, 311
F.
Faramea, 128; pollen-grains of, 129
Fitzgerald, Mr., on Thelymitra, 313
Forsythia suspensa, 117; stamens,
252
viridissima, 117
Fragaria Chiloensis, 293
—— elatior, 293
—— vesca, 293
Virginiana, 293
Frazinus eacelsior, 11
G.
Galium cruciatum, 286
Gartner on the sterility of unions
between distinct species, 29; Pri-
mula vulgaris and veris, 58, 59;
hybrid Verbascums, 76, 77, 80;
prepotency of pollen, 241; varia-
tion in the sexual powers of
plants, 267; contabesceut anthers,
193, 283
Gentianezx, 115
Geraniacex, 169
Geranium sylvaticum, 308
Gesneria pendulina, 261
Gilia aggregata, 118
— coronopifolia, 119
— micrantha, 119
—— nudicaulis, 119
—— pulchella, 118
Gillibert on Menyanthes, 311
Gloriosa Lily, tie, 146
Godron on hybrid Primulas, 55
Gray, Prof. Asa, proposes the term
heterogone or heterogonous, 2; on
Linum, 101; Leucosmia Bur-
nettiana and acuminata, 114;
Forsythia suspensa, 117; Gilia
pulchella, 118; G. coronopifolia,
348
INDEX.
GYNO-DIGCIOUS.
119; Phlow subulata, 119; Mit-
chella repens, 125; heterostyled
plants, 244; Coprosma, 285; Eu-
onymus, 287; Rhamnus lanceo-
latus, 295, 296; Lpigea repens,
297; Ilex opaca, 298; Plantago
media, 307; Oxybaphus and Nycta-
ginia, 313; Impatiens fulva, 328 ;
Leersia, 334; cleistogamic flowers,
342
Gyno-dicecious plants, 298
H.
Hart, Mr., on Nepeta glechoma, 301
Hautbois Strawberry, the, 293
Hedyotis, 133
Henslow, Rev. Prof., on hybrid Pri-
mulx, 61
Henslow, Rev. G., on flowers self-
fertilised during the winter, 343
Herbert, Dr., on hybrid Primulz,
61
Heterostyled plants, illegitimate off-
spring of, 188-243; essential cha- _
racter of, 244; summary of the
differences of fertility between
legitimately and illegitimately fer-
tilised plants, 246; diameter of
pollen-grains, 249 ; size of anthers,
structure of stigma, 252; list of
genera, 255; advantages derived
from Heterostylism, 258; means
by which plants became hetero-
styled, 260 ; transmission of form,
268; equal-styled varieties, 272;
final remarks, 275
— dimorphic plants, 14-54, 81-
136
— trimorphic plants, 137-187
Hibiscus, pollen-grains, 338
Hildebrand, Prof., introduces the
word “ heterostyled,” 2; on the
ray-florets of the Composita, 5, 6;
Primula Sinensis, 38, 40-43, 192,
217; Linum grandiflorum, 86, 87;
L. perenne, 92; Pulmonaria offi-
cinalis, 101-103, 107, 239; P.
azurea, 110; Polygonum fagopy-
rum, 111; Owalis, 169, 171-174,
178 182, 211-213, 322; herma-
KERNER.
phrodite plants becoming uni-
sexual, 283; Hordeum, 333
Homostyled species of Primula, 49
Hooker, Dr., on Campanula, 330
Hordeum, 332
Hottonia inflata, 53, 3138
palustris, 50; relative fertility,
52; anthers of, 252; papille on
stigma, 254
Houstonia cerulea, 132, 254
Hoya carnosa, 331
Hybrid Primulas, 55-71
Hydrangea, 6, 7
Hypericinex, 123
Hyssopus officinalis, 299
L
Tlea aquifolium, 297
— opaca, 298
Illegitimate offspring of heterostyled
plants, 188; Lythrum salicaria,
dwarfed stature and sterility, 192 ;
Oxalis, transmission of form to
seedlings, 212; Primula Sinensis,
in some degree dwarfed, 215;
equal-styled varieties, 218-223;
Primula vulgaris, 224; trans-
mission of form and colour, 225;
seedlings, 227; P. veris, 228;
dwarfed stature and_ sterility,
229-234; equal-styled varieties,
234, 238; parallelism between
illegitimate fertilisation and hy-
bridism, 242
Illecebrum, 311
Impatiens, pollen-grains of, 338
— balsamina, 328
— fulva, 327
—— noli-me-tangere, 328
a
Juglans regia, 10
Juncus bufonius, 332, 343
Jussieu, A. de, on Malpighiacex.
331
K.
Kerner, Prof., on ray-florets, 6 ; Aurz
cula, 43 ; hybrid fornis of Primula,
55, 73; on use of hairs within
INDEX.
349
-,
KIRK,
the corolla, 128; size of corolla in
male flowers, 309; use of glands
as a protection to flowers, 331
Kirk, Dr., on Monochoria vaginalis,
331
Knozia, 135
Koch on Primula longiflora, 50
Krascheninikowia, 312
Kuhn, Dr., on cleistogamic flowers,
3, 310, 311; list of plants pro-
ducing differently formed seeds,
9; heterostyled plants, 244; Van-
dellia nummularifolia, 324; V.
sessiflora, 325
L,
Lagerstremia Indica, 167
— parviflora, 168
— regine, 168
Lathyrus nissolia, 326, 342
Lecoq, H., on the common maple,
12; cowslips and primroses, 57 ;
Primula elatior, 72; Linum Aus-
triacum, 98; Lythrum hyssopi-
folia, 166; Rhamnus, 296; gyno-
dicecious plants, 299; Scabiosa
succisa, 305 ; Viola odorata, 317
Leersia oryzoides, 333-335 ; pollen-
grains of, 338
Leggctt, Mr., Pontederta cordata,
187
Legitimate unions, summary on the
fertility of the two, compared with
that of the two illegitimate in Pri-
mula, 46-49; fertility of, com-
pared with illegitimate, 246
Leighton, Rey. W. A., on the cow-
slip and primrose, 56; Verbascum
virgatum, 78
Leontodon, pollen-grains, 338
Leptosiphon, 119
Leucosmia acuminata, 114
— Burnettiana, 114; stigma, 253
Lily, the Gloriosa, 146
Limnanthemum Indicum, 116; pol-
len-grains, 250; authers, 252
Linaria spuria, 325
Lindley on Fragaria elatior, 293
Linneus on Primula veris, vulgaris,
and elatior, 56
Linum angustijolium, 100
MENYANTHES,
Linum Austriacum, 97
catharticum, 100
corymbiferum, 100
flavum, 81, 98; stamens, 252
—— grandiflorum, 81; various ex-
periments, 87-89, 96; pistils and
stamens, 253, 254; sterile with its
own-form pollen, 264, 266
Lewisii, 101
— perenne, 90; torsion of the
styles, 95; long-styled form, 97;
stigma, 247
—— salsoloides, 100
—— trigynum, 100
usttatissimum, 100
Lipostoma, 134
Lysimachia vulgaris, 4, 342
Lythrum Greffert, 165
—— hyssopifolia, 166
—— salicaria, 116, 137; power of
mutual fertilisation between the
three forms, 149-157; summary
of results, 157-165; illegitimate
offspring from the three forms,
191-203 ; concluding remarks on,
203-211; mid-styled form, 241,
257, 258, 280; seeds, 248
—— thymifolia, 165 ‘
M.
Malpighiacezx, 331
Manettia bicolor, 135
Maple, the common, 12
Marshall, W., on Primula elatior,
73; Plantago lanceolata, 306
Masters, Dr. Maxwell, on clvisto-
gamic flowers, 3 ;
Maximowicez on Krascheninikowia,
312
Meehan, Mr, on Mitchella, 285;
Epigea repens, 297
Melissa clinipodium, 299
officinalis, 299
Mello, Correa de, on Arachis, 312
Voandzeia, 327
Mentha aquatica, 299
hirsuta, 298
—— vulgaris, 298
Menyanthes, 311
— trifoliatu, 115
350
INDEX.
MICHALET,
Michalet on Ozalis acetosella, 321 ;
Linaria spuria, 325
Mitchella, 285
repens, 125
Mohl, H. von, on the common
cowslip, 14; size of corolla in the
sexes of the same species, 307,
308; Trifolium and Arachis, 312;
cleistogamic flowers, 314, 342;
Oxalis acetosella, 321; Impatiens
noli-me-tangere, 320; Specularia
perfoliata, 330
Mollia lepidota, 168
speciosa, 168
Monnier, M., on Viola, 318
Monochoria vaginalis, 330
Mulberry, the, 10
Miiller, D., on Viola canina, 314
Miller, Fritz, on pollen of the Vil-
larsia, 116; Faramea, 128-130;
Posoqueria fragrans, 131; Neszxa,
167; Oxalis, 180, 181; Pontederia,
183-185; Oxalis Regnelli, 212;
Chamissoa, 292
Miiller, H., on the frequency of
visits by insects to the Umbelli-
fere and Composite, 5; on dicho-
gamy, 10; on Anthophora and
Bombylius sucking the cowslip,
22 ; Primula elatior, 32 ; P. villosa,
49; Hottonia palustris, 51; table
of relative fertility of, 52, 53;
Linum catharticum, 100; Poly-
gonum fagopyrum, 113; Lythrum
salicaria, 145; on the origin of
heterostylism, 263; on the La-
biate, 299, 304; Thymus serpyllum,
300; Scabiosa arvensis, 305: Plan-
tago lanceolata, 306; size of co-
rolla in the two sexes of the same
species, 308; Impatiens balsa-
mina, 828; Lysimachia, 343
Myosotis, 308
N,
Nepeta glechoma, 301
Nertera, 285
Nesea verticillata, 167
Nolana prostrata, variability in
length of stamens and pistil, 261
Nyctaginia, 313
POLEMONIACER,
0.
Oldenlandia, 132
Oleacex, 117
Oliver, Prof., on ovules of Primula
veris.17 Viola, 318; Campanula
colorata, 330
Ononis columnzx, 325
minutissima, 326, 341
parviflora, 326
Origanum vulgare, 298
Ozalis acetosella, 181, 182; pistil of,
261; cleistogamic flowers, 321;
pollen-grains, 338
—— Bowiti, 179
—— compressa, 179
—— corniculata, 181
—— Deppei, 179
—— hedysaroides, 213
— homostyled species, 181
incarnata, 322
—— Reqnelli, 173-175, 212
rosea, 178, 213
—— (Biophytum) _ sensitiva,
322; stigma, 253
— speciosa, 169, 175, 212
stricta, 181, 182
tropzxoloides, 182
—— Valdiviana, 170-172, 211, 212
Oxlip, the Bardwell, 32, 72
——, the common, 55; differences
in stractureand function between
the two parent-species, 56 ; effects
of crossing, 60; a hybrid between
the cowslip and primrose, 70
Oxybaphus, 313
181,
P,
Peony, pollen-grains of, 338
Parallelism between illegitimate and
hybrid fertilisation, 239
Pavonia, 313
Phlox Hentzii, 120
— nivalis, 120
—— subulata, 119, 287
Planchon on Linum salsoloides, 100;
L. Lewisti, 101; on Hugonia, 100
Plantago lanceolata, 306
media, 307
Polgmoniacee, 118
INDEX.
351
POLLEN-GRAINB,
Pollen-grains, relative diameter of,
249
Polyanthus, 18
Polygonacex, 111
Polygonum bistorta, 114
fagopyrum, 111, 239; pollen-
grains, 251
Pontederia, 183; pollen-grains, 186 ;
size of anthers, 252
cordata, 187
Posoqueria fragrans, 131
Primrose, the common, 34, 57-71
Primula, the, heterostyled species of,
14; summary on, 45-49; homo-
atyled species, 49
—— auricula, 30, 43, 48, 74, 223
—— equal-styled varieties, 273
—— cortusvides, 44
—— elata, 49
—— elutior, Jacq., 32; relative fer-
tility of the two forms, 33, 47;
not a hybrid, 72, 73; equal-styled
var. of, 224, 273
Farinosa, 45; equal-styled var.,
224, 273
— hirsuta, 74
—— involucrata, 45
— longiflora, 50
—— mollis, 49, 50
—— Scotica, 49, 50
— Sibirica, 49
—— Sikkimensis, 44, 47
— Sinensis, 22, 30, 38; relative
fertility, 39-43, 47, 49; long-
styled, 213; short-styled, 215;
transmission of form, constitution
and fertility, 216; equal-styled
variety, 218-223, 273, 274
— stricta, 50
—— veris, 14: difference in struc-
ture between the two forms, 15;
degrees of fertility when legiti-
mately or illegitimately united,
25-32; fertility possessed by ille-
gitimate plants, 228-234; equal-
styled red variety, 234-238 ; long-
styled, 241; length of pistil, 261,
266
—— verticilluta, 49, 50
villosa, 49
— vulgaris (var. acaulis Linn.),
34; pollen-grains, 35; relative fer-
SETHIA.
tility of the two forms, 37; length
of pistil, 266
Primula vulgaris,var. rubra, 224-228
Prunella vulgaris, 299
Psychotria, 135
Pulmonaria angustifolia, 104, 239;
anthers, 252, 287
—— azurea, 110
— officinalis, 101, 238 ; number ot
flowers, 248; pistil, 250
R.
Ranunculus aquatilis, 311
Ray-florets, their use, 5, 6
Rhamnus catharticus, 294, 307; size
of corolla, 308
—— frungula, 297
lanceolatus, 295
Rhinanthus crista-galli, 4
Rubiacez, 125, 181-186; size of
anthers, 252; stigmas, 253;
number of heterostyled gencra
Q84, 285
Rudgea eriantha, 135
Rue, the common, 9
Ruellia tuberosa, 329
Salvia, 308
—— cleistogama, 340
Horminum, 8
Satureia hortensts, 303, 304
Scabiosa arvensis, 305
—— atro-purpurea, 305, 307
—— succisa, 305
Scott, J..on Primula auricula, 30,
43, 223; P. vulgaris, 34; (var.
rubra), 224; P. Sikkimensis, 44;
P. farinosa, 45, 224; homostyled
Primulz, 49,50; hybrids, 74, 75;
length of pistil, 272; Hottonia
palustris, 51; Androsace vital-
liana, 53; Polyanthus, 58; Mit-
chella repens, 127; Acanthacezx,
313; Eranthemum ambiguum bear-
ing three kinds of flowers, 329
Scrophularia aquatica, 147
Serratula tinctoria, 280, 307
Sethin weuminata, 122
352
INDEX.
SETHIA.
Sethia obtusifolia, 122
Smith, Sir J. E., on the carrot, 8;
hybrid Verbascums, 76, 78; Ser-
ratula_ tinctoria, 280; Cnicus,
307; Subularia, 311
Soldanella alpina, 54
Specularia perfoliata, 330
Spence, Mr., on Mollia, 168
Spermacoce, 135
Sprengel on Hottonia palustris, 51
Stellaria graminea, 313
Strawberry, the Hautbois, 293
Subularia, 311
Suteria, 131
T,
Thelymitra, 313
Thomson, Dr., on Campanula, 330
Thrum-eyed, origin of term, 14
Thwaites, Mr., on ovules of Lim-
nanthemum Indicum, 116 ; Sethia
acuminata, 122; Discospermum,
286
Thymelia, 114
Thymus citriodorus, 301
—— serpyllum, 299, 301, 302, 304
— vulgaris, 302
Timbal-Lagrave, M., on hybrids in
genus Cistus, 76
Torrey, Dr., on Hottonia inflata,
53, 313
Transmission of the two forms of
heterostyled plants, 268-270
Treviranus on Androsace vital-
liana, 53; Linum, 81
Vv.
Vandellia nummularifolia, 324
— sessiflora, 325
Vaucher on the carrot, 8; Solda-
nella alpina, 54; Lythrum sali-
caria, 138, 144; L. thymiéfolia,
165; Ilex aquifolium, 297; on
WRAY.
Labiatz, 299; Viola hirta and
collina, 317
Verbascum, wild hybrids of, 75-80
— lychnitis, 30, 76-78
— pheniceum, 78
—— thapsus, 76-79
— virgatum, 78
Viburnum, 6, 7
Vicia, 327
Villarsia, 116; anthers, 252
- Viola alba, 315, 320
—— bicolor, 320
— biflora, 320
— canina, 314, 321
— collina, 317
—— elatior, 320
— hirta, 318, 320
—— tonodium, 320
—— lancifolia, 320
— mirabilis, 320
—— nana, 319, 320; pollen-graine
of, 338
— odorata, 317, 336
—— palustris, 320
—— Roxburghiana, $19
— Ruppii, 320
—— sylvatica, 320
tricolor, 4, 320
Voandzeia, 327
Ww.
Walnut, the, 10
Watson, H. C., on cowslips, prim-
roses, and oxlips, 57, 60, 63;
Primula eatior, 72, 73
Weddell, Dr., on hybrids between
Aceras and Orchis, 76
Wetterhan, Mr., on Corylus, 10
Wichura, Max, on hybrid willows,
76; sterile hybrids, 240
Wirtgen on Lythrum salicaria, 188,
144, 148
Wooler, W., on Polyanthus, 18
Wray, Leonard, on Fragaria, 293
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