THE LIBRARY

OF

THE UNIVERSITY
OF CALIFORNIA

LOS ANGELES

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

1899

Authorized Edition.

TO

PROFESSOR ASA GRAY

THIS VOLUME IS DEDICATED BY THE AUTHOR
AS A SMALL TRIBUTE OF EESPECT AND AFFECTION.

2033582

PREFACE TO THE REPRINT OF 1884.

THE text of the second edition has been left un-
touched, and I have merely given an account (which
does not pretend to be complete) of the progress of the
subject since 1880.

HETEROSTYLED PLANTS.

C. E. Bessey ('American Naturalist/ June, 1880,
p. 417) made careful measurements of the corolla, sta-
mens, and style in a number of flowers of Lithospermum
longiflorum. He shows that the length of corolla, and
especially the length of the style, is very variable. An
appearance of dimorphism is thus produced; but meas-
urements of the pollen show that there is no real hetero-
stylism.

C. B. Clarke (' Journ. Linn. Soc./ xvii. p. 159) has
made the curious observation that in Adenosacme longi-
folia the difference between the long- and short-styled
forms amounts to what would usually be called a char-
acter of first-rate systematic importance. In the short-
styled flowers, the stamens are on the corolla; in the
long-styled, they are at its very base, almost free from
it. In this form the corolla separates and leaves the
stamens standing on the ovary.

Ti PREFACE TO THE REPRINT OF 1884.

He also describes two forms of Randia uliginosa,
(i.) having large sessile flowers with separate stigmas
and producing a large fruit; (ii.) small pedunculated
flowers with clavate stigmas, and producing smaller
fruit.

C. B. Clarke ('Journ. Linn. Soc.,' xviii. p. 524)
shows that Macrotomia is dimorphic like Arnebia. Mr.
Clarke mentions as one of the earliest good notices of
heterostylism that Fischer and Meyer ('Enum. PI.
Schrenk.,' p. 34, published in 1841) speak of Macro-
tomia as having spccimina longistyla and brevistyla.

Breitenbach ('Botanische Zeitung/ 1880, p. 577)
believes that the ancestor of the heterostyled Primula
was homostyled. He grounds his belief on the ex-
amination of a large number of plants of P. elatior,
Jacq., and on some facts connected with the ontogene-
sis of the flowers. This opinion has been adversely
criticised by W. Behrens (' Botanisches Centralblatt,'
1880, p. 1082) and by Hermann Muller (' Bot. Zeitung,'

1880, p. 733).

A. Ernst (Caracas) (' Nature,' xxi., 1880, p. 217)
shows by measurement and experiment that Melochia
parviflora is heterostyled (dimorphic).

According to J. Todd (' American Naturalist,' xv.,

1881, p. 997), Black mustard (B. nigra) has two forms
of flower, differing in the length of the pistil ; the sta-
mens being of approximately the same length in the
two forms.

Trelease ('American Naturalist,' xvi., 1882, p. 13)
describes two forms of Oxalis violacea, which appear
to be long- and short-styled forms of a trimorphic
species. No mid-styled flowers could be found, and
Trelease is inclined to believe that the species is di-
morphic.

Ig. Urban (' Sitz. Bot. Verein, Prov. Brandenburg,'

PEEFACE TO THE REPRINT OF 1884. vii

xxiv., 1882) states that the Turneraceae contain a large
proportion of dimorphic plants. His monograph on this
family I know only from the abstract in the * Botan.
Centralblatt,' p. 207. He has made the following in-
teresting observations : — " In the Turneracese the dimor-
phic species tend to be perennials, with conspicuous flow-
ers, while the monomorphic species have smaller flowers,
and are chiefly annuals." He states that a tendency
to dimorphism in the monomorphic species expresses
itself only in elongation of the style.

In the subjects kindred to those considered in Chap-
ter VII, rather more work has been done.

F. Ludwig ('Zeitschrift f. d. gesam. Naturwiss.,'
1879, p. 44) describes three plant-forms in Plantago
lanceolata.

1. Hermaphrodites with white anthers.

2. Semi-females, with small shrivelled yellow an-
thers, containing a small quantity of pollen, of which
many grains are bad.

3. Purely female form.

Ludwig has noticed the tendency described by Del-
pino to entomophily in Plantago, the flowers being often
fairly conspicuous, and are visited by insects.

Ludwig draws some interesting general conclusions
on Gynodioecious plants.

1. They are all more or less dichogamic.

2. In the protandrous forms the females are more
numerous at the beginning of the season. In the pro-
togynous forms the reverse is the case.

3. Abortive anthers often degrade into perianth seg-
ments.

4. He confirms the received opinion that female flow-
ers are smaller than* hermaphrodites.

He discusses the origin of dioeciousness, assigning

viii PREFACE TO THE REPRINT OF 1884.

the first rank in the chain of causes to dichogamy. Simi-
lar views are given in the present edition, p. 283, in
connection with observations by Hildebrand.

In a subsequent paper ('Botan. Centralblatt/ 1880,
iv. p. 829) he describes a similar gynodioecious condi-
tion in some Stellarias and Cerastiums. Here there
are pure female, semi-female, and hermaphrodite plants,
the flowers of the female form being smaller than those
of the others. This distribution of sex he calls " gyno-
dimorphism," a condition which he describes ('Bot.
Centralblatt,' 1880, p. 1021) as occurring in Arenaria
ciliata and Alsine verna.

F. Ludwig ('Kosmos/* 1880-81, viii, 357) de-
scribes two forms of Erodium cicutarium. The first,
which is distinguished by having nectar-guides, is pro-
tandrous, and adapted for fertilisation by insects. The
second form is weakly protogynous and autogamic.
This form has no nectar-guides, and the petals are usu-
ally shed during the day on which the flowers open. It
resembles E. moschatum, which is homogamic (or weak-
ly protogynous). The first form is more like E. macro-
denum, which is markedly protandrous, and where auto-
gamy is impossible.

Hermann Miiller ('Nature/ xxiii. p. 337, 1881)
has shown that Syringa persica is gynomonrecious, hav-
ing on the same inflorescence a majority of hermaphro-
dite flowers of large size, and a minority of small-sized
females.

Stellaria glauca and Sherardia arvensis are gyno-
dicecious.

H. Miiller has also written an important paper on
Centaurea jacea ('Kosmos/ x., and 'Nature,' xxv.) in
which he publishes his change of opinion as to the origin

•See also 'Irmischia,' 1881, No. 1, and 'Bot. Centralblatt,' xii. p.
83, and viii. p. 87.

PREFACE TO THE REPRINT OF 1884. ix

of gynodiceciousness. Three different forms occur, but
on any given plant the flowers are of one kind. There
is a normal hermaphrodite form, and two divergent
forms which are practically male and female, and which
are distinguished from the hermaphrodite form by hav-
ing conspicuous sexless ray-florets ; of the two, the male
flowers are the more conspicuous. The female florets
have shrunken anthers devoid of pollen ; the male florets
have pistils which do not open, and are therefore func-
tionless. Numerous gradational forms exist which ren-
der the whole case especially instructive, and it was a
study of these gradations which induced Miiller to give
up his theory of gynodicecious plants. Miiller formerly
explained the origin of gynodireciousness by supposing
that those flowers which are smaller and less conspicu-
ous than the average tend to be visited last by insects,
so that their pollen is useless. In Centaurea the reduc-
tion of anthers is found beginning in flower-heads which
are not less conspicuous than the average. Miiller there-
fore gives up his former theory and agrees with the view
proposed by my father.*

Potonie (' Sitzb. d. Ges. Naturforsch. Freunde zu
Berlin,' 1880, p. 85, quoted in the ' Bot. Zeitung,' 1880,
p. 749) believes that in the gynodirecious Salvia praten-
sis the existence of a female form serves to ensure fer-
tilisation by a distinct plant.

But H. Miiller ('Bot. Zeitung/ 1880, p. 749) shows
that in the hermaphrodites, bees commonly visit the
lower and temporarily female flowers before passing on
to the upper male flowers, and that this ensures cross-
fertilisation between different plants.

Solms-Laubach ('Abhand. K. Gesell. Wiss. Gb't-
tingen,' xxviii., and 'Kosmos,' 1881) has given in his

* A short paper by H. Muller on gynodiceciousness in the genua
Dianthus, appeared in 'Nature,' 1881, xxiv.

x PBEFACE TO THE EEPRINT OP 1884.

valuable work on caprification an account of the relation
of the sexes in the cultivated fig and the caprificus.

HETERANTHY.

The existence of different kinds of anthers in
homostyled flowers is of interest as bearing on hetero-
stylism.

F. Ludwig (<Bot. Centralblatt/ 1880, pp. 246 and
1210) gives an account of the heteranthy of Plantago
major, of which two forms exist, one with brown, the
other with yellow anthers; the latter plants are much
rarer than the brown-anthered form. In another com-
munication to the same journal (1880, p. 861), he de-
scribes the heteranthy of Poterium sanguisorba, and
of a number of grasses, e. g. Lolium dactylis, Festuca,
Air a.

F. Miiller ('Nature,' xxiv., 1881, p. 307) has made
the curious observation that in the Melastomaceous
Heeria, sp., there are two sets of anthers: (1) yellow
ones serving as plunder to bees; (2) red ones so placed
as to subserve cross-fertilisation.

H. Miiller (' Nature/ 1882, p. 30) showed that in
Tinnantia undat (Commelynacese), as in Heeria, two
sets of anthers exist ; one set which attract pollen-seek-
ing insects, the other which cover the insect with pollen.
The upper stamens have yellow tufts of hair, which
(as in Tradescantia) serve as supports for visiting in-
sects. The pollen-grains are smaller in the upper sta-
mens. In Commclyna coslestis and communis there is
somewhat similar arrangement.

In a species of Melastoma, which has also two sets
of stamens, H. 0. Forbes ('Nature/ 1882, p. 386) saw
bees going straight to the yellow stamens, i. e. to those
which serve as an attraction. The yellow anthers have
the smaller pollen-grains, but those from the other set

PREFACE TO THE REPRINT OF 1884. xi

of anthers were the only ones seen to exsert tubes in
the stigmas.

J. E. Todd ('American Naturalist/ xvi., 1882, p.
281) gives a curious account of Solanum rostratum,
in which the pollen for fertilisation is the product of
a single long-curved anther; while the four other an-
thers are small, and serve to supply pollen to the bees
visiting the flower. The stigma is so placed that it
receives pollen from the part of the bee dusted by the
long anther.

CLEISTOGAMIC FLOWERS.

According to P. Ascherson (' Bulletin Soc. Linn, de
Paris/ 1880, p. 250),* Helianthemum salicifolium was
shown by LinnaBus to produce ripe seed from closed
flowers. Ascherson describes the cleistogamic flowers
of H. Kaliiricum and H. Lippii y. micranihum, Boiss.
Schweinfurth is given as authority for the existence of
cleistogamic flowers in Salvia lanigera. The following
species are said to be " often cleistogamic " : Lamium
amplexicaule, Juncus bufonius, Ajuga Iva, Campanula
dimorphantha.

In a second paper (' Sitz. d. Gesch. Naturf. Freunde
zu Berlin/ 1880, p. 97, quoted in the <Bot. Centralblatt')
Ascherson gives a further account of the cleistogamy
of Helianthemum Kahiricum. The flowers are open
in the early morning, so that cross-fertilisation is possi-
ble; the petals fall off in the course of the day, and
the sepals closely embrace the stamens and pistils, and
thus convert the flower into a cleistogamic one.

Baron E. Eggers (<Bot. Centralblatt/ 1881, viii. p.
57) states that Sinapis arvensis, when grown in the
West Indies, produces cleistogamic flowers.

* As abstracted in the ' Bot. Centralblatt.'

xii PREFACE TO THE REPRINT OF 1884.

The following Acanthacese have cleistogamic flow-
ers: Stenandrium rupestre, Didipetra assurgens, Ste-
monacanthus coccineus, Dianthera sessilis, Blechum
Brownei.

Among other families: Erithalis fruticosa (Eubia-
cece), Polystacliya luteola, are also cleistogamic.

The curious flowers of Pavonia hastata are described
by E. Heckel (' Comptes rendus/ Ixxxix. p. 609). This
species has cleistogamic flowers, which chiefly differ
in appearance from the perfect flowers, in having no
nectar-guides; there are, as usual, no nectaries. The
pollen is entomophilous in character, and it is said
that the tubes are protruded while the pollen is in the
anthers.

F. Ludwig (<Bot. Centralblatt/ 1880, p. 861) men-
tions Plantago virginica as producing under cultivation
only cleistogamic flowers.

F. Miiller (' Nature,' xix., 1879, p. 463) shows that
the curious submerged Podostomaceae of Brazil produce
flowers which are probably cleistogamic.

Solms-Laubach ('Gb'ttingen Nachrichten/ June,
1882) has written an interesting paper on Heteranthera,
a plant belonging to the Pontedereacea?. He describes
the cleistogamy of some species of the genus, and points
out that the form and distribution of the cleistogamic
flowers serve as a specific character, without which H.
callafolia could not be distinguished from H. Kotsch-
yana.

FRANCIS DARWIN.

Jan., 1884.

PKEFACE TO THE SECOND EDITION.

SINCE the publication of the first edition of this
book in 1877, several articles have appeared on the sub-
jects therein discussed, and many letters have been re-
ceived by me. I will here briefly state their nature,
as an aid to any one who may afterwards pursue the
same subjects. The text has been left as it originally
appeared, excepting that a few errors have been cor-
rected.

Dr. A. Ernst has proved in the clearest manner
'(' Nature/ Jan. 1, 1880, p. 217) that Melochia parvi-
folia, which is a common plant near Caracas, is hetero-
styled. The pollen-grains differ in the usual manner
in size in the two forms, as do the papillae on their stig-
mas. The illegitimate unions, especially when pollen
from the same flower was employed, were much less fer-
tile than the legitimate ones. A new family, the Bytt-
neriaceae, is thus added to those including heterostyled
plants.

Errara and Gevaert have published a paper on the
heterostylism of Primula elatior, in ' Bull. Soc. E. Bot.
Belg.,' torn, xvii., 1879.

I have quoted (p. 100) Dr. Alefeld's statement that
none of the American species of Linum are heterostyled.
This statement was disputed by Kuhn ('Bot. Zeit./
1866, p. 201), but has since been confirmed by Dr. Ign.

xiii

^ PREFACE.

Urban/ in ' Linnsea/ B. vii. p. 621. Mr. Meehan (' Bull.
Torrey Bot. Club/ vol. vi. p. 189) has endeavoured to
throw doubts on my observations on the sterility of the
forms of L. perenne when fertilised with their own-form
pollen, because a plant from Colorado yielded seed when
growing by itself ; but as might have been expected, and
as is sufficiently clear from the remarks of a well-known
reviewer in the ' American Journal of Science/ Mr.
Meehan mistook L. Lewisil, which is not heterostyled,
for L. perenne.

In the Boragineae, Lithospermum canescens differs,
according to Mr. Erwin F. Smith (' Bot. Gazette/
United States, vol. iv., 1879, p. 168), from the hetero-
styled species of the same genus by occasionally present-
ing a mid-styled form, which has a short pistil like that
of the short-styled, and short stamens like those of the
long-styled form. All the forms seem variable, and the
whole case requires further investigation.

Mr. Alex. S. Wilson informs me that on comparing
the pollen-grains from a long-styled plant of Erytlircea
centaurium with those from some short-styled plants
from the island of Arran, they differed in size and
shape, as in the case of the undoubtedly heterostyled
Menyanthcs trifoliata, a member of the same family of
the Gentianeae. I had myself formerly observed that
the flowers on different plants differed much in struc-
ture, but could not make out that they presented two
distinct forms.

The Rubiacese contain many more heterostyled
plants than any other family, and several additional
cases can now be added. Mr. C. B. Clarke has been

kind as to send me sketches made in India of two

extremely distinct forms of Adenosacme longifolia.

e remarks "that the peculiarity of the case is not

the difference in the length of the style and stamens

PREFACE. XV

in the two forms, but the extreme difference in the
point of insertion of the stamens." A mid-styled form
exists having a short pistil and short stamens seated on
the same level, only a little way up the tube of the
corolla. Mr. Clarke adds that heterostylism is quite
common in the Coffee tribe. Mr. Hiern, in his obser-
vations on the Eubiaceae of tropical Africa (' Journal
Linn. Soc. Bot./ vol. xvi., 1877, p. 252), remarks that
dimorphism occurs commonly, or at least in some spe-
cies, in four or five genera in the tribe of Hedyotideae.
Mr. M. S. Evans states (' Nature,' Sept. 19, 1878, p.
543) that in Natal there is a heterostyled Eubiaceous
plant, which occasionally, though rarely, presents a
third form, and in this the pistil and stamens are of
equal length and both are exserted from the mouth of
the corolla. He adds that he has found four other
heterostyled dimorphic plants, and one of these is a
monocotyledon.

Lastly, I have given (p. 135) Bouvardia leiantha as
doubtfully heterostyled; Mr. Bailey has now sent
me dried specimens, and as far as the lengths of the
pistil and stamens are concerned the species is clearly
heterostyled; but no difference could be detected in
the size of the pollen-grains; so the case must remain
doubtful.

With respect to trimorphic heterostyled plants, Dr.
Koehne, who has described the Lythraceae of Brazil,
has, with great kindness, sent me a long account of
them. He knows twenty-one species which are hetero-
styled, and 340 which are homostyled. He informs
me that Lythrum thymifolia is not heterostyled, and
that I must have received some other species under
this name. There are many dimorphic species in
America. Pemphis acidula is distinctly dimorphic, so
are some species of Eotala and Nesaea; thus two new

xvj PREFACE.

heterostyled genera are added to the family. Dr. Koehne
does not believe that any species of Lagerstrcemia is, or
has been, heterostyled and trimorphic. He has also
sent me an outline of an important view, well worth fol-
lowing out, namely, that heterostylism has arisen
through the modification of plants which were tend-
ing to become polygamous or dioecious.

It is stated at p. 187 that Mr. Leggett felt some
doubt whether Pontederia cordata was trimorphic and
heterostyled; but he has since written to me that his
doubts are removed : see also to this effect, in ' Bull.
Torrey Bot. Club/ vol. vi., 1877, p. 170. All three
forms of this Pontederia appear to be highly variable.
He informs me that humble-bees are the fertilisers.

With respect to the origin of the dioecious state,
which is discussed in the beginning of the seventh
chapter, Hermann Miiller has given some interesting
remarks in * Kosmos,' 1877, p. 290. The same author
shows (Ibid., p. 130) that Valeriana dioica exists under
four forms closely allied to the four presented by
Khamnus, as described in this same chapter. It is
much to be desired that some one should experimentise
on these forms and make out their meaning. Bernet
has published ('Bull. Soc. Bot. France,' torn, xxv.,
1878) a paper entitled, 'Disjunction des sexes dans
VEuonymus Europceus,' which may be compared with
my observations on the same plant. I have stated
at p. 297 that I could never find an hermaphrodite
plant of the common holly, but according to Mr.
Hibberd (' Gard. Chron.,' 1877, pp. 39 and 776) such
occur among the many cultivated varieties. The evi-
dence, however, is far from conclusive, for it does not
appear that Mr. Hibberd ever observed under the mi-
croscope pollen taken from a plant known to produce
berries. Trees of Juglans cinerea in the U. States are

PREFACE. xvii

monoecious, and like those of J. regia consist of two
sets, one being proterandrous and the other proterogy-
nous (Mr. C. G. Pringle, in ' Bot. Gazette,' vol. iv., 1879,
p. 237) ; and thus the cross-fertilisation of distinct trees
is insured. Mr. Alex. S. Wilson informs me that Silene
inftata is polygamous on Ben Lawers, as he found her-
maphrodite, male and female plants. The case is here
mentioned because the flowers on the females are small
like those on the females in the gyno-dioecious sub-class.
In an article in the ' Bull. Torrey Bot. Club,' July, 1871,
this Silene is, however, said to be gyno-direcious. As-
paragus officinalis is also polygamous, and the female
flowers are about half the size of the male ones; see
'Gard. Chron.,' May 25, 1878; also Breitenbach, in 'Bot.
Zeitung,' 1878, p. 163.

Several cases can now be added to my list of gyno-
dicecious plants, or those which exist as hermaphrodite
and female individuals; namely, according to Mr.
Whitelegge ('Nature,' Oct. 3, 1878, p. 588), Stachys
germanica, Ranunculus, acris, repens, and bulbosus.
H. Miiller found on the Alps ('Nature,' 1878, p. 516)
Geranium sylvaticum and Dianthus superbus in this
state, and the female flowers of the former were of
small size. So it is with Salvia pratensis, as he informs
me in a letter. I have received an additional account
of Plantago lanceolata being gyno-dioscious in England ;
and Dr. F. Ludwig of Greiz has sent me a description
of no less than five forms of this plant which graduate
into one another; the intermediate forms being com-
paratively rare, whilst the hermaphrodite form is the
commonest. With respect to the steps by which a gyno-
dicecious condition has been gained, H. Miiller main-
tains by many able arguments ('Kosmos,' 1877, pp. 23,
128, and 290) the view which he has propounded; and
several botanists think it more probable than the one

xviii

PREFACE.

advanced by me; see, for instance, 'Journal of Botany,'
Dec. 1877, p. 376.

I have stated (p. 13) that after inquiring from sev-
eral botanists I could hear of no instance, except a doubt-
ful one, of plants in an andro-dioecious condition, or ex-
isting as hermaphrodite and male individuals. But II.
Miiller ('Nature,' Sept. 12, 1878, p. 159) has found on
the Alps Veratrum album, Dryas octopetala, and Geum
reptans in this condition. It is an interesting fact that
the corollas of the male flowers are not diminished in
size like those of the females of gyno-dioecious plants.
Asa Gray has also reason to suspect that Diospyros vir-
giniana may be andro-dioecious.

The eighth chapter is devoted to cleistogamic flowers,
and I have struck out of the list there inserted four
genera, owing to information given me by Mr. Bentham
and Asa Gray. On the other hand, fifteen genera have
been added. Mr. Bentham informs me that the S.
American Trifolium polymorphism produces true cleis-
togamic flowers. Dalibarda, Milium, and Yilfa have
been added to the list on the authority of A. Gray in a
review of this book in the ' American Journal of Sci-
ence.' The cleistogamic flowers of Danthonia are de-
scribed by Pringle, in the ' American Naturalist,' 1878,
p. 248, and those of another Gramineous genus, Di-
plachne, by Ascherson, in ' Sitzungsb. der Gesell. Natur.
Freunde, Berlin,' Dec. 21, 1869. Krascheninikovia has
been added from some remarks made in ' Journal of
Botany,' 1877, p. 377. Batalin has published an essay
('Act. Hort. Petropol/ torn. v. fasc. 2, 1878), 'Kleisto-
gamische Bliithen der Caryophylleen,' namely, on Ceras-
tium and Polycarpon. F. Ludwig has described the cleis-
togamic flowers of Collomia grandiflora in ' Sitzb. Bot.
Vereins. Brandenburg.' Aug. 25, 1876 : see also on same
subject Scharlok, in 'Bot. Zeitung,' 1878, p. 641. A.

PREFACE. xix

Grisebach has discussed fully (' Nachrichten k. Gesell.
der Wissen. zu Gottingen/ June 1, 1878) the cleisto-
gamic flowers produced by Cardamine chenopodifolia,
which bury themselves in the ground. See also on same
subject Drude, in ' Sitzb. der Versamml. d. Naturf . in
Cassel,' 1878. From a note received from Dr. Koehne,
it is clear that Ammannia latifolia bears cleistogamic
flowers. According to Mr. Bessey (the ' American
Naturalist/ 1878, p. 69) this is likewise the case with
Lithospermum longiflorum. Three genera of Orchidea?
have been added to the list, from information given me
by Mr. Spencer Moore and from some remarks in
' Journal of Botany,' 1877, p. 377. Lastly, Mr. Bennett
has published (' Journ. Linn. Soc. Bot.,' No. 101, 1879)
some additional " notes on cleistogamic flowers," chiefly
on those of Viola and Impatiens.

With respect to the statement (p. 328) on the author-
ity of Mr. Wallis, that Drosera rotundifolia opens its
flowers only early in the morning, Mr. Conybeare in-
forms me that he once saw in Cornwall, at 2 p. M., the
ground " starred over with the fully-expanded flowers
of this plant." He had previously long endeavoured to
find a plant with open flowers.

The number of species in which pods produced by
cleistogamic flowers bury themselves in the ground is
remarkable. I have attributed (p. 337) this action to
the advantage gained by their protection from various
enemies, and much may be said in favour of this view;
but Mr. W. Thiselton Dyer in an interesting article
('Nature,' April 4, 1878, p. 446) has called attention
to some observations made long ago by Mr. Bentham
(' Catalogues des Plantes indig. des Pyrenees,' 1826, p.
85) on the fruiting of Helianthemum prostratum. He
believes, as does Mr. Dyer, that the capsules of this
Helianthemum and some other plants (for instance, of

xx PREFACE.

Cyclamen) are kept cool and moist by being laid on the
ground ; they thus mature more slowly, and are enabled
to grow to a larger size. In this simple action we prob-
ably see the first step to the further development of the
process, and to the capsules burying themselves beneath
the surface. In some cases the difference between the
subaerial and subterranean pods on the same plant and
both produced by cleistogamic flowers is extraordinary:
Mr. Meehan sent me three subterranean pods of Amplii-
carpcea monoica, each containing a single large seed ; and
my own plants produced several subaerial pods, each
containing from one to three small seeds. These latter
weighed on an average only -fa of the subterranean seeds !
This difference, however, is not quite accurate, as the
coats of the subterranean pods adhered so firmly to the
seeds that they were not removed and were weighed
with them; but from their thinness and lightness they
could not have much affected the result.

CONTENTS.

PREFACE TO REPRINT OF 1884 Page v

PREFACE xiii

INTRODUCTION . . .... 1-13

CHAPTER I.
HETEROSTYLED DIMORPHIC PLANTS : PRIMULACE^E.

Primula veris or the Cowslip— Differences in structure between the
two forms — Their degrees of fertility when legitimately and
illegitimately 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 Page 14-54

CHAPTER II.

HYBRID 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 Ox-
lips 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 — Sup-
plementary note on spontaneously produced hybrids in the
genus Yerbascurn 55-80

xxi; CONTENTS.

CHAPTER III.

HETEEOSTYLED DIMORPHIC PLANTS— continued.

Linum grandiflorum, long-styled form utterly sterile with own-
form pollen— Linura perenne, torsion of the pistils in the
long-styled formal one— Homostyled species of Liuum— Pul-
monaria officinalis, singular difference in self -fertility between
the English and German long-styled plants— Pulinonaria
angustifolia shown to be a distinct species, long-styled form
completely self-sterile— Polygon um fagopyrum— Various other
heterostyled genera— Rubiaceae— Mitchella repens, fertility of
the flowers in pairs— Houstonia— Faramea, remarkable differ-
ence 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 Rubi-
aceous genera not due to descent in common . Page 81-136

CHAPTER IV.

HETEEOSTYLED TEIMORPHIC PLANTS.

Lythrum salicaria — Description of the three forms — Their power
and complex manner of fertilising one another — Eighteen dif-
ferent unions possible — Mid-styled form eminently feminine
in nature — Lythrum Graefferi likewise trimorphic — L. thymi-
folia dimorphic — L. hyssopifolia homostyled — Nesaea verti-
cillata trimorphic— Lagerstrcemia, nature doubtful— Oxalis,
trimorphic species of— 0. Valdiviana— 0. Regnelli, the illegiti-
mate unions quite barren — 0. speciosa — 0. sensitiva — Homo-
styled species of Oxalis— Pontederia, the one monocotyledonous
genus known to include heterostyled species . . 137-187

CHAPTER V.

ILLEGITIMATE OFFSPRING OF HETEEOSTYLED PLANTS.

Illegitimate offspring from all three forms of Lythrum salicaria—
Their dwarfed stature and sterility, some utterly barren, some

CONTENTS. sxiii

fertile— Oxalis, transmission of form to the legitimate and
illegitimate seedlings — Primula Sinensis, illegitimate offspring
in some degree dwarfed and infertile — Equal-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 genera-
tions, their dwarfed stature and sterility — Equal-styled varie-
ties of P. veris — Transmission of form by Pulmonaria and
Polygonum — Concluding remarks — Close parallelism between
illegitimate fertilisation and hybridism . . Page 188-244

CHAPTER VI,

CONCLUDING REMARKS ON HETEROSTYLED 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 an-
thers 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 become heterostyled — Transmission of form
— Equal-styled varieties of heterostyled plants — Final re-
marks . . 245-277

CHAPTER VII.

POLYGAMOUS, DICECIOUS, AND GYNO-DICECIOUS PLANTS.

The conversion in various ways of hermaphrodite into dioecious
plants — Heterostyled plants rendered dioecious — Rubiaceae —
Verbenaceae — Polygamous and sub-dioecious plants — Euo-
nymus — Fragaria — The two sub-forms of both sexes of Rham-
nus and Epigtea — Ilex— Gyno-dicecious plants— Thymus, dif-
ference in fertility of the hermaphrodite and female individuals
— Satureia — Manner in which the two forms probably origi-
nated— Scabiosa and other gyno-dio3cious plants — Difference in
the size of the corolla in the forms of polygamous, dioecious,
and gyno-dioecious plants 278-308

CONTENTS.

CHAPTER VIII.

CLEISTOQAMIC 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 per-
fect flowers— Oxalis acetosella— 0. sensitiva, three forms of
cleistogamic flowers — Vandellia — Ononis — Impatiens — Dro-
sera — Miscellaneous observations on various other cleistogamic
plants— Anemophilous species producing cleistogamic flowers
— Leersia, perfect flowers rarely developed — Summary and con-
cluding remarks on the origin of cleistogamic flowers — The
chief conclusions which may be drawn from the observations in
this volume Page 309-344

INDEX 345-351

THE

DIFFERENT FORMS OF FLOWERS

ON

PLANTS OF THE SAME SPECIES.

INTKODUCTION.

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 botan-
ist, to which distinction I can lay no claim. As far as
the sexual relations of flowers are concerned, Linnaeus,
long ago divided them into hermaphrodite, monoecious,
dioecious, and polygamous species. This fundamental
distinction, with the aid of several subdivisions in each
of the four classes, will serve my purpose; but the classi-
fication is artificial, and the groups often pass into one
another.

The hermaphrodite class contains two interesting
sub-groups, namely, heterostyled and cleistogamic
plants; but here are several other less important
subdivisions, presently to be given, in which flowers
differing in various ways from one another are produced
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 Eelations." ' Journal

1

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 a 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 an-
other 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 ap-
pearance 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
pistil continues growing for a long time, so that if old
and young flowers are compared they might be thought

of the Proceedings of the Linnean P. elatior, Jacq. ; and on the

Society,' vol. vi. 1862, p. 77. Hybrid Nature of the Common

"On the Existence of Two Oxlip. With Supplementary Re-

Forms, and on their Reciprocal marks on Naturally Produced Hy-

Sexual Relation, in Several Species hrids in the Genus Verbascum."

of the Genus Linum." Ibid. vol. Ibid. vol. x. 1868, p. 437.
vii 1863, p. 6fl. * The term " heterostyled " does

On the Sexual Relations of not express all the differences be-

the Three Forms of Lythrum sali- tween the forms ; but this is a

caria." Ibid. vol. iii. 1864. p. 169. failure common in many cases.

On the Character and Hybrid- As the term has been adopted by

like Nature of the Offspring from writers in various countries, I am

the Illegitimate Unions of Dimor- unwilling to change it for that of

phic and Tnmorphic Plants." lieterogone or heteroqonous, though

" AV «*' 1C868' & 393' this has been Pr°P°sed by so high

s bpecinc Differences an authority as Prof. Asa Gray •

between Primula verts, Brit. Fl. see the 'American Naturalist,'

( var. offinnalM, Linn.), P. vnlgari*, Jan. 1877, p. 42.
Brit. Fl. (var. acaulis, Linn.), and

INTRODUCTION. 3

to be heterostyled. Again, a species tending to become
dioacious, 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 in-
dividuals, 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
will be described in the last chapter of this volume.
They are manifestly adapted for self -fertilisation, which

* 'Botanische Zeitung,' 1867, partakes of the nature of a mon-

p. 65. Several plants are known strosity. All the flowers on the

occasionally to produce flowers same plant are commonly affected

destitute of a corolla ; but they in the same manner. Such cases,

belong to a different class of though they have sometimes been

cases from cleistogamic flowers, ranked as cleistogamic, do not

This deficiency seems to result come within our present scope :

from the conditions to which the see Dr. Maxwell Masters, ' Vege-

plants have been subjected, and table Teratology,' 1869, p. 403.

4 INTRODUCTION.

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. Some few
plants produce subterranean flowers, as well as ordinary
ones; and these might have been formed into a small
separate subdivision.

Another interesting subdivision consists of certain
plants, discovered by H. Miiller, 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, Rhinan-
thus crista-galli, 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 concerned, namely, the assured propagation of the
species, they approach in nature cleistogamic flowers;
but they differ from them by the two kinds being pro-
duced on distinct plants.

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-
sion to refer to plants of this kind in the following
chapters, I will here give a few details respecting them.

der

INTRODUCTION. 5

It is familiar to every one that the ray-florets of the
Composites often differ remarkably from the others; and
so it is with the outer flowers of many Umbelliferag,
some Cruciferae, and a few other families. Several
species of Hydrangea and Viburnum offer striking
instances of the same fact. The Eubiaceous genus
Mussasnda 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
Acantaceous 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 bractere,
&c., and from what H. Miiller has observed f on the
frequency of the visits of insects to the flower-heads of
the Umbelliferse and Composites 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 J 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,
however, are of service in another and very different
manner, namely, by folding inwards at night and dur-

* J. Scott, ' Journal of Botany,' J See his interesting memoir,

London, new series, vol. i. 1872, ' Ueber die Geschlechtsverhiilt-

pp. 161-164. nisse bei den Compositen,' 1869,

t ' Die Befrucbtung der Blu- p. 92.
men,' pp. 108, 412.

6 INTRODUCTION.

ing 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, f

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
Compositae; or the male organs alone are aborted, as
in many Compositae. Between the sexless, female, and
hermaphrodite states of these latter flowers, the finest
gradations may be traced, as Hildebrand has shown.J
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
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,

* Kerner clearly shows that this and thus the organs of fructifica-
is the case : ' Die Schutzmittel des tion are protected. My grand-
Pollens,' 1873, p. 28. father, in 1790 ('Loves of the

t ' Gardener's Chronicle,' 1861, Plants,' canto iii. note to lines 184,

p. 1067. Lindley, 'Vegetable 188), remarks that "The flowers

Kingdom.' on Chrysanthemum, or petals of plants are perhaps in

1853, p. 706. Kerner in his inter- general more acrid than their

esting essay ( ' Die Schutzmittel leaves ; hence they are much sel-

der Bliithen gegen unherufene domer eaten hy insects."

Gaste,' 1875, p. 19) insists that the | 'TJeber die Geschlechtsver-

petals of most plants contain mat- haltnisse hei den Compositen,'

ter which is offensive to insects, 1869, pp. 78-91.
BO that they are seldom gnawed,

INTRODUCTION. ?

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 dioecious 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 dioecious 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 affected,
as seems to me the more probable view, or the reproduc-
tive organs first failed, their states of development are
now firmly correlated. We see this well illustrated 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.

There is a closely analogous subdivision of plants,
including the genus Muscari (or Feather Hyacinth)
and the allied Bellevalia, which bear both perfect

* I have discussed this subject in xviii. 2nd edit. vol. ii. pp. 152,
my 'Variation of Animals and 156.
Plants under Domestication,' chap.

g INTRODUCTION.

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 Labiatse, 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 TJmbelliferaB, 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 central
flowers are said * to be neuter or sterile, but I ob-
tained 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 Vaucher f " cette
singuliere degeneration s'etend quelquefois a I'ombelle
entiere." 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
condition of the species, when one flower alone, the
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

•'The English Flora,' by Sir rope,' 1841, torn. ii. p. 614. On the
J. E Smith, 1824, vol. ii. p. 39. Echinophora, p. 627.
t ' Hist. Phys. des Plantes d'Eu-

INTRODUCTION. 9

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 the normal condition (for in-
stance, the common Eue 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 Umbelliferse 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 monoecious
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
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

* This whole subject, including mesti cation,' chap. xxvi. 2nd edit,
pelorism, has been discussed, and vol. ii. p. 338.
references given, in my ' Variation f ' Bot. Zeitung,' 1867, p. 67.
of Animals and Plants under Do-
3

10

INTRODUCTION.

largely on many of the species in this, as well as in
the next or dioecious 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 monoecious 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). According to H. Miiller, the individual
plants of a few hermaphrodite species differ in a like
manner; some being proterandrous and others pro-
terogynous. f On cultivated trees of the Walnut and
Mulberry, the male flowers have been observed to abort
on certain individuals,^ which have thus been converted
into females; but whether there are any species in a
state of nature which co-exist as monoecious and female
individuals, I do not know.

The third Class consists of dioscious species, and the
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 inex-

* Delpino, 'Studi sopra uno xi. p. 507, and 1875, p. 26. On

iKiiaggio Anemofilo,' Firenze, proterandrous and proterogynous
hermaphrodite individuals of the

t Delpino, Ult. Osservazioni same species, see H. Miiller, ' Die

Bul1* ^P"1,?/ part- iL fasc- "• Befruchtunu,' &c., pp. 285, 339.

&-n n Wotterhan and H. J ' Gardener's Chron.,' 1847, pp.

Muller on Corylus, ' Nature,' vol. 541 558

INTRODUCTION. 11

plicable fact that with some dioecious plants, of which
the Eestiaceae of Australia and the Cape of Good Hope
offer the most striking instance, the differentiation 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 specimens of the same spe-
cies. In my seventh chapter some observations will be
given on the gradual conversion of heterostyled and of
ordinary hermaphrodite plants into dioecious or sub-
dio2eious species.

The fourth and last Class consists of the plants which
were called polygamous by Linmeus; but it appears to
me that it would be convenient to confine this term to
the species which co-exist as hermaprodites, 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 (Fraxinus 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 fe-
male trees, whilst the third produced none, so that it
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

12 INTRODUCTION.

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 monoecious 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 dioecious, 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 spe-
cies, for instance several kinds of Atriplex, bear on the
same plant hermaphrodite and female flowers; and these
might be called gyno-moncecious, if a name were desira-
ble for them.

Again there are plants which produce hermaphro-
dite and male flowers on the same individual, for in-
stance, some species of Galium, Veratrum, &c.; and
these might be called andro-moncecious. If there
exist plants, the individuals of which consist of herma-
phrodites and males, these might be distinguished
as andro-dicecious. But, after making inquiries from
several botanists, I can hear of no such cases. Lecoq,
however, states, f but without entering into full details,

* ' Geographic Botanique,' torn. v. p. 367. f Ibid. torn. iv. p. 488.

INTRODUCTION. 13

that some plants of Caltha 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
dioecious 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 cer-
tain dioecious, sub-dioscious, 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 information
and other assistance. Professor Asa Gray, also, has uni-
formly aided me in many ways. To Fritz Miiller of St.
Catharina, in Brazil, I am indebted for many dried
flowers of heterostyled plants, often accompanied with
valuable notes.

14 HETEROSTYLED DIMORPHIC PLANTS. CHAT. I.

CHAPTER I.
HETEBOSTYLED DIMOEPHIC PLANTS: PKIMULACILE.

Primula veris or the Cowslip — Differences in structure between the
two forms — Their degrees of fertility when legitimately and illegit-
imately united — P. elatior, vulgaris, Sinensis, auricula, &c. — Sum-
mary 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 com-
mon 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/' f 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 that some weaver who cultivated

Mohl( Bot. Zeitung,'1863,p.326), the polyanthus invented this

was first observed by Persoon in name, from being struck with

the year 1794. some degree of resemblance be-

Tln Johnson's Dictionary, tween the cluster of anthers in the

thrum is said to be the ends of mouth of the coroUa and the ends

weavers' threads ; and I suppose of his threads.

CHAP. I. PEIMULA VERIS. 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.

Long-styled form. Short-styled form.
PRIMULA VEEIS.

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. CHAP. I.

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 it is somewhat variable in shape, one differ-
ence is persistent, namely, 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.
(4rTiV of an incn) in diameter, whilst those from the
long-styled were about .0254 mm. (T15Vjr 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 oblong 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

CHAP. I. PRIMULA VERIS. 1Y

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 Professor Oliver,* that the
ovules in the unexpanded and unimpregnated flowers of
the latter are considerably larger 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 more space and nourishment for rapid de-
velopment.

To sum up the difference: — 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 ob-
long 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 sta-
mens 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. CHAP. 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 dioecious
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 to be given, of Primula veris.

CHAP. 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 of
Umbels
produced.

Number of
Capsules
produced.

Weight of
Seed
In grains.

9

33

199

83

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.

—

Number
of
Plants.

Weight
of Sled
Ingrains.

Number
of
Umbel..

Seed.

Number

tar

"pail;11

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
manner. A number of wild plants had been trans-

HETEROSTYLED DIMORPHIC PLANTS. CHAP. I.

planted during the previous autumn into a large bed
in my garden, and all were treated alike; the result
was: —

TABLE 3.

—

Number
of

Pliints.

Number
of
Umbels.

Weight
of Seed in
(trains.

Short-styled cowslips . .

47

173

745

Long-styled cowslips . .

58

208

692

These figures give us the following proportions: —
TABLE 4.

—

Number
of
Plants.

Te^f
grain..

Number
UmbeH.

Weight
of Seed in
grain..

Short-styled cowslips
Long-styled cowslips

100
100

1585
1093

100
100

430
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-styled 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 in
the former case, nearly as four to three.

Looking to these trials made during two successive
years on a large number of plants, we may safely con-
clude that the short-styled form is more productive
than the long-styled form, and the same result holds
good with some other species of Primula. Consequently

CHAP. I.

PRIMULA VERIS.

21

my anticipation that the plants *vith 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 cov-
ered by a net, did not produce any seed, though other
umbels on the same plants, artificially fertilised, pro-
duced an abundance of seed; and this fact shows that
the mere covering in itself was not injurious. Accord-
ingly, in 1861, several plants were similarly covered
just before they expanded their flowers; these turned
out as follows: —

TABLE 5.

—

Number
of

Plants.

Number of
Umbeh
produced.

Product of Seed.

Short-styled ....

6

24

f 1.3 grain weight of seed, or
1 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 evi-
dence, but I may add that ten pots of polyanthuses and
cowslips of both forms, protected from insects in my
greenhouse, did not set one pod, though artificially fer-

22 HETEROSTYLED DIMORPHIC PLANTS. CHAP. I.

tilised 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. hortorum and mus-
corum, 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
pollen being deposited on it. It follows from the
position of the organs that if the proboscis of a

* H- Mullor has also seen Antho- sucking the flowers 'Nature'
phora pilipes and a Bombylius Dec. 10th, 1874, p. 111.

CHAP. I. PEIMULA VERIS. 23

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 objects in 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
likewise be apt to cause the self -fertilisation of both
forms.

24 HETEROSTYLED DIMORPHIC PLANTS. CHAP. I.

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 oiher 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 illegitimate
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 union 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
many subsequent trials I followed the more accurate
plan of counting the seeds. Some of the capsules con-

CHAP. I.

PRIMULA VERIS.

25

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.

Total

Calculated

Nature of the Union.

Number of
fertilised.

Number
of
Capsules
produced.

Number of
good
Capsules.

Weight of
Seed in
grains.

Weight of
SecdLfrorn
100 good
Capsulei.

Long-styled by pollen"!
of short-styled. Le- >•

22

15

14

8.8

62

gitimate union. . . J

Long-styled by own- ]

form pollen. Illegiti- >

20

8

5

2.1

42

mate union . . . . J

Short-styled by pollen ]
of long-styled. Le- >

13

12

11

4.9

44

gitimate union . . J

Short-styled by own- ]

form pollen. Illegiti- >

15

8

6

1.8

33

mate union . . . . J

SUMMAEY :

The two legitimate )
unions J

35

27

25

13.7

54

The ^ two illegitimate )

35

16

11

3.9

35

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.

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

4

26

HETEROSTYLED DIMORPHIC PLANTS. CHAP. I.

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
represented in Fig. 2.

TABLE 7.

Nature of th*
Union.

Number
of Flow-

"l£"-

Tf

SSL

Number
of good

SSL

Weight
of Sled
in
grain..

Number
of

at

Weight
of i&d
In
grain..

Number

'£

Weight
of S«d
in
grains.

The two le- )
gitimate V
unions . . J

100

77

71

39

100

50

100

54

Thetwoille-)
gitimate [•
unions . . J

100

45

31

11

100

24

100

35

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.
Eeturning 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

CHAP. I.

PRIMULA VERIS.

27

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 poor
capsules are rejected, of which many were produced
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

Fig. 2.

Legitimate union.
Complete fertility.

Q

Illegitimate

union.

Incomplete

fertility.

/
!

Legitimate union.
Complete fertility.

Illegitimate
i union.
; Incomplete
J fertility.

ig-styled
form.

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
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-

28 HETEROSTYLED DIMORPHIC PLANTS. CHAP. I.

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 mod-
erately 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 39 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 ani-
mal 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,
so here we have two bodies, approximately equal in
numbei, 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

CHAP. I. PRIMULA VERIS. 29

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
individual 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 union, we shall best
appreciate their degree of lessened fertility by the
following facts. Gartner estimated the sterility of the
unions between distinct species,* in a manner which
allows of a strict comparison with the results of the
legitimate and illegitimate unions of Primula. With
P. veris, for every 100 seeds yielded by the two
legitimate 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,

* ' Versuche iibcr die Bastarderzeugung,' 1849, p. 216.

30 HETEROSTYLED DIMORPHIC PLANTS. CHAP. I.

the proportion was nearly the same — namely, as 100
to 62. Now Gartner has shown that, on the calcula-
tion of Verbascum lynchnitis yielding with its own pol-
len 100 seeds, it yielded when fertilised by the pollen of
V. Phceniceum 90 seeds; by the pollen of V. nigrum,
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 num-
ber of seeds than did P. auricula when fertilised illegiti-
mately 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, f 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
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

f'Jonrn. Linn. Soc. Bot.,' vol. fertilisation' how greatly the off-

vm., 1864, p. 93. spring from intercrossed plants

T I have shown in my work on profit in height, vigour, and fer-

the 'Effects of Cross and Self- tility.

CHAP. I. PRIMULA VERIS. 31

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 obligate 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
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

32 HETEROSTYLED DIMORPHIC PLANTS. CHAP. I.

seeds than the long-styled, when both forms are fer-
tilised, either naturally or artificially, in a legitimate
manner.

In the future chapter, when I treat of the offspring
from heterostyled dimorphic and trimorphic plants
illegitmately 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 officinalis), and the Primrose (P. vulgaris, vel acau-
lis) 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.

The results of my trials on the relative fertility of
the two forms, when legitimately and illegitimately
fertilised, are given in the table on the next page.

If we compare the fertilty of the two legitimate
unions taken together with that of the two illegitimate

* ' Die Befruchtuug der Blumen,' p. 347.

CHAP. I.

PRIMULA ELATIOR.

33

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

TABLE 8.
Primula elatior.

Number

Number of

Minimum

Nature of Union.

of
Flowers
fertilised.

priced*.

of Seed!

of Seeds
in any one

Capsule.

NumbeTof
Seeds per
Cap.ni;.

Long-styled form, by 1

pollen of short-styled. >
Legitimate union . . J

10

6

62

34

46.5

Long-styled form, by ]

own-form pollen. 11- >

20

4

49*

2

27.7

legitimate union . . j

Short-styled form, by ]
pollen of long-styled. >
Legitimate union . . J

10

8

61

37

47.7

Short-styled form, by )
own-form pollen. 11- V

17

3

19

9

12.1

legitimate union . . J

The two legitimate 1
unions together . . j

20

14

62

37

47.1

The two illegitimate )
unions together . . j

37

7

49*

2

35.5

* These seeds were so poor and small that they could hardly have
germinated.

capsule, the ratio is as 100 to 75. But this latter
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

34: HETEROSTYLED DIMORPHIC PLANTS. CHAP. I.

spontaneously 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 Khine),
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
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-

CHAP. I. PRIMULA VULGARIS. 35

styled, in which latter it is depressed on the summit;
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

Fig. 3.

Outlines of pollen-grains of Primula vulgaris, distended with water,
much 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.

as 100 to 93. The anthers do not differ in size in the
two forms. The pollen-grains from the short-styled
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 oi flowers from
the two forms were compared, and 12 of the finest

HETEKOSTYLED DIMORPHIC PLANTS. CHAP.!.

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
collected 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 illegiti-
mately fertilised, are given in the following table : —

TABLE 9.
Primula vulgaris.

Number

Maximum

Minimum

Nature of Union.

of
Flowers

good Cap-
sules pro-

Number of
Seeds in any

Number of
Seeds in any

Numbefof
Seeds per

fertilised.

duced.

oneCapsule.

oneCapsule.

Cap.uk

Long-styledform,bypol- 1
len from short-styled. >
Legitimate union . . J

12

11

77

47

66.9

Long-styled form, by )
own-form pollen. 11- >•

21

14

66

30

52.2

legitimate union . . J

Short-styled form, by 1

pollen from long- I
styled. Legitimate |

8

7

75

48

65.0

union J

Short-styled form, by)
own-form pollen. 11- >

18

7

43

5

18.8*

legitimate union . . J

The two legitimate I
unions together . . J

20

18

77

47

66.0

The two illegitimate \
unions together . . J

39

21

66

5

35.5*

* This average is perhaps rather too low.

We may infer from this table that the fertility of
the two illegitimate unions taken together, is to that of

CHAP. I. PRIMULA VULGARIS. 37

the two illegitimate unions taken together, as judged by
the proportional 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.
It is 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
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
6.2 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-
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.

38 HETEROSTYLED DIMORPHIC PLANTS. CHAP. I.

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 trimorphic 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 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 forms differs in shape, in the same manner
as in P. veris. The long-styled plants tend to flower

* After the appearance of my greatly about the size of the pol-

paper this author published some len-grains in the two forms. I

excellent observations on the pre- suppose that by mistake I meas-

sent species ('Bot. Zeitnng,' Jan. 1, ured twice over pollen-grains

1864), and he shows that I erred from the same form.

CHAP. I.

PRIMULA SINENSIS.

39

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.

Nature of Union.

Number

nSL.

fertilised.

Number
of good

pCrX£.

Average
Weight of
Seed, per
Capsule.

Average Number

of Seeds per
Capsule, as

ascertained on a
'^equcnt

Long-styled form, by pollen )
of short-styled. Legiti- >
mate union J

24

16

0.58

50

Long-styled form, by own- ]
form pollen. Illegitimate \
union J

20

13

0.45

35

Short-styled form, by pollen ]
of long-styled. Legitimate >•

8

8

0.76

64

Short-styled form, by own- ]
form pollen. Illegitimate /•
union J

•

4

0.23

25

The two legitimate unions )

32

24

0.64

57

The two illegitimate unions \
together j

27

17

0.40

30

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

40 HETEROSTYLED DIMORPHIC PLANTS. CHAP. I.

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 here 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; and
these are shown in a condensed form in the accompany-
ing table : —

TABLE 11.
Primula Sinensis (from Hildebrand).

Nature of Union.

Number

FC'er,
fertilised.

Number
of good
Capsules
produced.

Average
Number of

OfJET

Long-styled form, by pollen of short- j
styled. Legitimate union j

14

14

41

Long-styled form, by own-form pollen, ~)
from a distinct plant. Illegitimate !•
union J

26

26

18

Long-styled form, by pollen from same )
flower. Illegitimate union j

27

21

17

Short-styled form, by pollen of long- )
styled. Legitimate union j

14

14

44

Short-styled form, by own-form pollen, )
from a distinct plant. Illegitimate union j

16

16

20

Short-styled, by pollen from the same )
flower. Illegitimate union j

21

11

8

The two legitimate unions together .

28

28

43

The two illegitimate unions together 1
(own-form pollen) . . {

42

42

18

The two illegitimate unions together (pol- )
len from the same flower) . . . . . }

48

32

13

Besides using for the illegitimate unions pollen
from a distinct plant of the same form, as was always

CHAP. I. PRIMULA SINENSIS. 41

done by me, he tried, in addition, the effects of the
plant's own pellen. 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
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 be 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
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
produced 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

42 HETEROSTYLED DIMORPHIC PLANTS. CHAP. I.

spontaneously self-fertile, live 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; but
this explanation seems to me doubtful; his 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.

CHAP. I. PRIMULA AURICULA. 43

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 inequality 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 it is 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 differ-
ence 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
•BW& of an inch in diameter, whereas those from the long
stamens of the short-styled plants were barely roW, show-
ing a relative difference of about 71 to 100. The smaller
grains of the long-styled plants are also much more trans-
parent, and before distension with water more triangular
in outline than those of the other form. Mr. Scott f com-
pared ten plants of both forms growing under similar con-
ditions, and found that, although the long-styled plants
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 access of insects, and they did not produce a single seed.
Mr. Scott protected six plants of both forms, and found
them excessively 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,

* According to Kerner, our gar- and the short- styled 98 seeds per

den auriculas are descended from capsule: see his "Geschichte der

P. pubescens, Jacq., which is a hy- Aurikel," 'Zeitschr. des Deutsch-

brid between the true P. auricula en undOest. Alpen-Vereins,' Band

and hirsuta. This hybrid has now vi. p. 52. Also ' Die Primulaceen-

been propagated for about 300 Bastarten,' 'Oest. Bot. Zeitschrift,'

years, and produces, when legiti- 1835, Nos. 3, 4, and 5.

mately fertilised, a large number t ' Journ. Linn. Soc. Bot.,' vol.

of seeds ; the long-styled forms viii., 1864, p. 86.
yielding an average number of 73,

44 HETEROSTYLED DIMORPHIC PLANTS. CHAP. L

and he does not doubt that these had imperfectly ferti-
lised it.

I tried a few experiments by reciprocally fertilising the
two forms in the same manner as before, but my plants
were unhealthy, 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 fer-
tility of the two legitimate unions, taken together, is com-
pared with that of the two illegitimate unions together,
by the same two standards as before, namely, by the pro-
portional number of flowers which produced good capsules,
and by the average number of seeds per capsule. The fer-
tility of the legitimate unions is always taken at 100.

By the first standard, 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.

PRIMULA 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 ire 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 31.

PRIMULA 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 papillae. The pollen-grains
of the short-styled form are, as usual, " larger, less trans-
parent, and more bluntly triangular than those from the
long-styled plants." The fertility of the two legitimate
unions to that of the two illegitimate unions is by the first

CHAP. I. SUMMARY ON PRIMULA. 45

standard as 100 to 74, and by the second standard as 100
to 66.

PRIMULA INVOLUCRATA.

The pistil 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 papilla, whilst that of the
short-styled is smooth and depressed on the apex. The
pollen-grains of the two forms differ in size and trans-
parency 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
Primula. — 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 stand-
ards, namely, by that of the proportional number of
flowers which yielded capsules, and by that of the aver-
age number of seeds per capsule. But for full accu-
racy many more observations, under varied conditions,
would be requisite.

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

46 HETEROSTYLED DIMORPHIC PLANTS. CHAP. I.

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

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.

Name of Specie*

Illegitimate Unions.

Judged of by th«
Proportional Number
of Flowers which,
produced Capsule..

Judged of by the Average
Number (or V/cigM In
some CMOS) of Seed,
per Capsule.

Primula veris

27

60
84
?
10
80
95
74
72
71

„. f (Probably
' 1 too high.)
M ( (Probably
54 1 too low.)
63

53
42
15
31
66
48
44

P elatior . . .

P vulgaris

P. Sinensis

(second trial) . .
" (after Hildebrand ) .
P. auricula (Scott)

P. Sikkimensis (Scott) . . .
P. cortusoides (Scott) . . .
P. involucrata (Scott) . . .
P. farinosa (Scott) . . . .

Average of the nine species .

88.4

61.8

proportion of the flowers in both lots would fail to
produce capsules from various accidental causes; and
the ratio of %$ to fa or as 100 to 56 (in whole
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

CHAP. I. SUMMARY ON PRIMULA. 47

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, ac-
cording to the two standards, the difference of fertility
between the legitimate and illegitimate unions. Thus
all the flowers of P. Sinensis which were illegitimately
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
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

48 HETEROSTYLED DIMORPHIC PLANTS. CHAP. I.

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 Mr. 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

P. elatior .

P. vulgaris
P. Sinensis

. 44

(Probably
too low. )
(Perhaps
too low.)

Primula auricula .... 119
P. Sikkimensis .... 57

P. cortusoidcs 93

P. involucrata 74

P. farinosa . . 63

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 il-
legitimately 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
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

CHAP. I. HOMOSTYLED PRIMULAS. 49

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. Sinensis 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. — It 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.
Scoiica, verticillata, a variety of Sibirica, elata, mollis,
and longiflora,\ are truly homostyled ; and to these many

* H. Miiller has given in ' Na- f Koch was aware that this spe-

ture,' Dec. 10, 1874, p. 110, a draw- cies was homostyled: see "Tre-

ing of one of these species, viz. the viranus iiher Dichogamie nach

Alpine P. rillosa, and shows that it Sprengel und Darwin," 'Bot. Zei-

is fertilised exclusively by Lepi- tung,' Jan. 2, 1863, p. 4.
doptera.

50 HETEROSTYLED DIMORPHIC PLANTS. CHAP. I.

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 dis-
tinct individual than with its own pollen, is common
to very many species, as I have shown in my work " On
the Effects of Cross and Self-fertilisation."

HOTTONIA PALUSTRIS.

This aquatic member of the Primulaceae 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 forwards, the pistil being
enclosed. This difference between the two forms has
attracted the attention of various botanists, and that
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

* 'Das entdecke Geheiinniss der Natur,' p. 103.

CHAP. I. HOTTONIA PALUSTRIS. 51

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. Miiller *
gives figures of the stigmatic papillae of the two forms,
and those of the long-styled are seen to be more than
double the length, and much thicker than the papillae
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. Miiller 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-ferti-
lised, according to Miiller, chiefly by Diptera.

Mr. Scott f 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-
lication of his paper H. Miiller has made much fuller
experiments, and I give his results in the follow-
ing table, drawn up in accordance with my usual
plan : —

*'Die Befruchtung,' &c., page t 'Journ. Linn. Soc. Bot.,' vol.
350. viii., 1864, p. 79.

52 HETEKOSTYLED DIMORPHIC PLANTS. CHAP. I.

TABLE 13.
Hottonia palustris (from H. Mutter).

Nature of Union.

Number
of Capsulei
examined.

Average
Numb.? of
Seeds per
fapiuie.

Long-styled form, by pollen of short-styled. Le- )

34

91.4

Long-styled form, by own-form pollen, from a dis- 1
tinct plant. Illegitimate union j

18

77.5

Short-styled form, by pollen of long-styled. Le- 1

30

66.2

Short-styled form, by own-form pollen, from a dis- )
tinct plant. Illegitimate union j

19

18.7

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 illegitimately
fertilised long-styled flowers, relatively in both cases to
the product of the legitimately fertilised flowers.* The
two legitimate unions compared with the two il-
legitimate together yield seeds in the ratio of 100
to 61.

H. Miiller 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

*H. 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 all the cap-
sules produced by the two methods
of fertilisation, as given by him,

I arrive at the results shown 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

CHAP. I. ANDROSACE. 53

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 general Primula and Hottonia, Andro-
sace (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 Miiller sent me from South Brazil
dried flowers of a Statice which he believed to be heter-
ostyled. In the one form the pistil was considerably
longer and the stamens slightly shorter than the corre-
sponding organs in the other form. But as in the
shorter-styled form the stigmas reached up to the
anthers 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 state-

* See also " Treviranus " in 'Bot. Zeitung,' 1863, p. 6, on this plant
being dimorphic.

54 HETEROSTYLED DIMORPHIC PLANTS. CHAP. I.

ments made by Vaucher I was led to think that Solda-
nella 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 probable that Pyrola might be heterostyled,
but H. Miiller examined for me two species in North
Germany, and found this not to be the case.

CHAP. II. HYBRID PRIMULAS. 55

CHAPTER II.
HYBRID PBIMULAS.

The Oxlip a hybrid naturally produced between Primula veris and
vulgaris— The differences in structure and function between tho
two parent-species — Effects of crossing long-styled and shortrstyled
Oxlips with one another and with the two forms of both parent-
species — Character of the offspring from Oxlips artificially self-fer-
tilised 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 Alps.* 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. veris, vel officinalis) and
the primrose (P. vulgaris, vel acaulis) — is frequently
found, and it occurs occasionally almost everywhere.

*"DiePrimulaceen-Bastarten," 'Bull. Soc. Bot.de France,' torn.

'Oesterr. Bot. Zeitschrift,' Jahr x., 1853, p. 178. Also in 'Revue

1875, Nos. 3, 4, and 5. See also des Sciences Nat.,' 1875, p. 331.
Godron on hybrid Primulas in

56 HYBRID PRIMULAS. CHAP. II.

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.
Linnaeus 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 fur-
ther 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 is 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.
has pointed out certain differences Hist.,' 2nd series, vol. ii., 1848, p.
in the form of the capsules and 164.

CHAP. II. THE COMMON OXLIP. 57

the primrose, when legitimately and naturally ferti-
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 num-
ber 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,
earlier in the spring 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, f

The cowslip and primrose, when intercrossed, be-

* 'Phytologist.' vol. iii., p. 694. la France,' 1840, torn. ii. p. 376.

t H. Lecoq, ' Geograph. Bot. de With respect to the rarity of P.

1'Europe,' torn, viii., 1858, pp. 141, veria in western Scotland, see

144. See also ' Ann. and Mag. of H. C. Watson, ' Cybele Britan-

Nat. Hist,,' ix., 1842, pp. 156, 515. nica,' ii. p. 293.
Also Boreau, ' Flore du centre de
6

58 HYBRID PRIMULAS. CHAP. II.

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
19 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 (i. e. 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
13 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, f To show how sterile these hybrid unions

* 'Bastarderzeugung,' 1849, p. ciently numerous. The degree of

721- infertility of a cross is liable to

TMr. Scott has discussed the much fluctuation. Pollen from
nature of the polyanthus CProc. the cowslip at first appears rather
Linn. Soc. Bot.,' viii., 1864, p. more efficient on the primrose than
103), and arrives at a different that of the polyanthus; for 12
conclusion ; but I do not think flowers of both forms of the prim-
that his experiments were sum- rose, fertilised legitimately and

CHAP. 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 3.55 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 22.6 seeds. On the other hand,
cowslip gave five capsules, contain- the seeds produced by the poly-
ing on an average 32.4 seeds ; anthus-pollen were much the fin-
whilst 18 flowers similarly ferti- est of the whole lot, and were the
lised by polyanthus-pollen yielded only ones which germinated,
only five capsules, containing only

60 HYBRID PRIMULAS. CHAP. II.

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 the 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 t)f an isolated cowslip, or of
several cowslips if consisting of the same form, being
crossed by a neighbouring primrose and producing ox-
lips, as of one sex of a dioecious 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,! namely, " that seeds of the 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- tained an abundance of seed,
tologist' (vol. iii. p. 703) that he which is simply impossible,
covered with bell-glasses some cow- Hence there must have been
slips, primroses, &c., on which he some strange error in these ex-
experimented. He specifies all periments. which may be passed
the details of his experiment, but over as valueless,
does not say that he artificially f 'Phytologist,' ii. pp. 217, 852;
fertilised his plants ; yet he ob- iii. p. 43.

CHAP. II. THE COMMON OXLIP. 61

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 grada-
tions, 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 adami. 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 f raised, from the seeds of
a highly cultivated red cowslip, cowslips, oxlips of
various kinds, and a primrose. This case, if accurately

* London's 'Mag. of Nat. Hist.,' t 'Transact. Hort. Soc.,' iv. p.
iii. 1830, p. 409. 19.

62 HYBRID PRIMULAS. CHAP. H.

recorded, which I must 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 cation,' ch. xv. 2nd edit. vol. ii.
work 'On the Varintion of Ani- p. 69.
mals and Plants under Domesti-

CHAP. II. THE COMMON OXLIP. 63

natural treatment; but not one of them presented the
least variations 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 umbrels 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. CHAP. 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 char-
acter, 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.

For the sake of ascertaining the two latter points,
I 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 parent-species. In this instance 256 flowers

CHAP. 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
Oxlip.

Illegitimate union.

Legitimate union.

Illegitimate union.

Legitimate union.

Short-styled ox-
lip, by pollen of
short-styled ox-
lip: 20 flowers fer-

Short-styled ox-
lip, by pollen of
long-styled oxlip:
10 flowers ferti-

Long-styled ox-
lip, by its own
pollen : 24 flowers
fertilised, pro-

Long-styled ox-
lip, by pollen of
short-styled ox-
lip: 10 flowers

tilised, did not

lised, did not pro-

duced five cap-

fertilised, did not

produce one cap-

duce one capsule.

sules, containing

produce one cap-

sule.

6, 10, 20, 8, and 14

sule.

seeds. Average

11.6.

TABLE 15.

Both forms of the Oxlip crossed with Pollen of both
forms of the Cowslip, P. veris.

Illegitimate union.

Legitimate union.

Illegitimate union.

Legitimate union.

Short-styled ox-
lip, by pollen of

Short-styled ox-
lip, by pollen of

Long-styled ox-
lip, by pollen of

Long-styled ox-
lip, by pollen of

short-styled cow-

long-styled cow-

long-styled cow-

short-styled cow-

slip : 18 flowers

slip: ISflowcrsfer-

slip : 11 flowers

slip: 5 flowers fer-

fertilised, did not

tilised, produced

fertilised, pro-

tilised, produced

produce one cap-
sule.

three capsules,
containing 7, 3,

duced one cap-
sule, containing

two capsules, con-
taining 21 and 28

and 3 wretched

ISwretched seeds.

very fine seeds.

seeds, apparently

incapable of ger-

mination.

66

HYBRID PRIMULAS.

CHAP. II.

TABLE 16.

Both forms of the Oxlip crossed with Pollen of both
forms of the Primrose, P. vulgaris.

Illegitimate union.

Legitimate union.

Illegitimate union-

Legitimate union.

Short-styled ox-
lip, by pollen of
s h o r t - s t y 1 e d

Short-styled ox-
lip, by pollen of
long-styled prim-

Long-styled ox-
lip, by pollen of
long-styled prim-

Long-styled ox-
lip, by pollen of
short-styled

primrose: 34 flow-

rose : 26 flowers

rose : 11 flowers

primrose: 5 flow-

ers fertilised, pro-

fertilised, pro-

fertilised, pro-

ers fertilised, pro-

duced two cap-

duced six cap-

duced four cap-

duced five cap-

sules, containing
5 and 12 seeds.

sules, containing
16, 20, 5, 10, 19,
and 24 seeds. Av-

sules, containing
10, 7, 5, and 6
wretched seeds.

sules, containing
26, 32, 23, 28, and
34 seeds. Average

erage 15.7. Many

Average 7.0.

28.6.

of the seeds very

poor, some good.

TABLE 17.

Both forms of the Cowslip crossed with Pollen of

both forms of the Oxlip.

Illegitimate union.

Legitimate union.

Illegitimate union.

Legitimate union.

Short-styled
cowslip, by pol-
len of short-styled
oxlip: 8 flowers
fertilised, pro-

Long- styled
cowslip, by pol-
len of short-styled
oxlip: 8 flowers
fertilised, pro-

Long- styled
cowslip, by pol-
len of long-styled
oxlip : 8 flowers
fertilised, pro-

Short- styled
cowslip, by pol-
len of long-styled
oxlip : 8 flowers
fertilised, pro-

duced not one

duced one cap-

duced three cap-

duced eight cap-

capsule.

sule, containing

sules, containing

sules, containing

26 seeds.

5, 6, and 14 seeds.

58, 38, 31, 44, 23,

Average 8.3.

26, 37, and 66

seeds. Average

40.4.

TABLE 18.

Both forms of the Primrose crossed with Pollen of
both forms of the Oxlip.

Illegitimate union.

Legitimate union.

Illegitimate union.

Legitimate union.

Short- styled

Long- styled

Long- styled

Short- styled

primrose, by pol-
len ofshort-styled
oxlip: 8 flowers

primrose, by pol-
len ofshort-styled
oxlip : 8 flowers

primrose, by pol-
len of long-styled
oxlip: 8 flowers

primrose, by pol-
len of long-styled
oxlip : 8 flowers

fertilised, pro-

fertilised, pro-

fertilised, pro-

fertilised, pro-

duced not one

duced two cap-

duced eight cap-

duced four cap-

capsule.

sules, containing

sules, containing

sules, containing

5 and 2 seeds.

15, 7, 12, 20, 22, 7,

52, 52, 42, and 49

16, and 13 seeds.

seeds, some good

Average 14.0.

and some bad.

Average 48.7.

CHAP. II. THE COMMON OXL1P. 67

"We see in these five tables the number of capsules
and of seeds produced, by crossing both forms of the
oxl ip 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 con-
dition. 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 ferti-
lised 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 rather better condition than the male
organs; for though the short-styled oxlips yielded no
seeds when fertilised by the long-styled oxlips, and
hardly any when illegitimately fertilised by pure
cowslips 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. CHAP. 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 moder-
ately 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 man-
ner 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 inter se, or with either parent-species,
so that in this particular case, but not as we shall pres-
ently 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

CHAP. II. 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; but it perished early. The second
plant also died in September; and the first plant,
though all three grew under very favourable condi-
tions, 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,

70 HYBRID PRIMULAS. CHAP. 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. FL), as has been surmised by several
botanists. It is probable that oxlips may be produced
either from the cowslip or the primrose and 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.

CHAP. II. THE COMMON OXLIP. ft

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 frequented
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.

Y2 THE BARDFIELD OXLIP. CHAP. 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
Table 8 and 12) in the smaller proportion of the illegi-
timately 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, see 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 Lecoq, ' Geograph. f Babington's ' Manual of Brit-

Botaniquede 1'Europe,' torn, viii., ish Botany,' 1851, p. 258.

CHAP. II. THE BARDFIELD OXLIP. 73

oxlip is a hybrid between the primrose and cowslip, it
is not surprising that eight long-styled flowers of the
primrose, 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,f
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 hybridi-
sation; 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 ' Gardener's Chronicle,' 1867, p. 435 ;
also Mr. W. Marshall, ibid., p. 462.

t 'Phytologist,' vol. i. p. 1001, and vol. iii. p. 695.

74 HYBRID PRIMULAS. CHAP. II.

crossing other heterostyled species of Primula.* I
have already alluded to his statement, that in four in-
stances (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 Kolreuter
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 legit-
imately and illegitimately with pollen from the two
forms of P. auricula, 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. hirsuta 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 seeds per

* ' Journ. Linn. Soc. Bot.,' vol. viii., 1864, p. 93 to end.

CHAP. II. HYBRID VERBASCUMS. 75

capsule. So that out of the eight possible unions be-
tween 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 re-
sults of my twenty different crosses (Tables 14 to 18),
between the two forms of the oxlip, primrose, and cow-
slip. 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 peculiarities 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 crossed 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. auricula and hirsuta
was more fertile, in the ratio of 56 to 42, than the
illegitimate cross, nevertheless it is very doubtful,
from the extreme irregularity 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 (i. e. when
opposite forms are united) than when crossed illegiti-
mately.

Supplementary Note on some wild hybrid Verbascums.

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. CHAP. II.

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,f 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, || as
Gartner remarks, verification. Hence the following
case is worth recording, more especially as the two
species in question, V. thapsus and lyclinitis, are per-
fectly fertile when insects are excluded, showing that
the stigma of each flower receives its own pollen. More-
over the flowers offer only pollen to insects, and have
not been rendered attractive to them by secreting
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, &c., der Weiden,' lish Flora,' by Sir J. E. Smith,

1865- 1824, vol. i. p. 307.

t ' Mem. de 1' Acad. des Sciences || See Gartner, ' Bastarderzeu-

de Toulouse,' 5« serie, torn. v. p. 28. gung,' 1849, p. 590.

t ' Annales des Sc. Nat.,' 3« serie,
Bot. torn, xviii. p. 6.

CHAP. II. 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. To 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. thap-
sus, but in height the latter species. In the shape of
their leaves they often closely approach 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-

Y8 HYBRID VERBASCUMS. CHAP. II.

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 tliapsus
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 circumstances 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. phceniceum the corolla is not

* 'Bastarderzeugung,' p. 307. Smith,' vol. ii. p. 210. I was

t This was first observed hy guided to these references hy the

Correa de Serra : see Sir J. E. Rev. W. A. Leighton, who ob-

Smith's 'English Flora,' 1824, vol. sorved this same phenomenon

i. p. 311 ; also ' Life of Sir J. E. with V. virgatum.

CHAP. II. HYBRID VERBASCUMS. 79

cast 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
collecting 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 cau-

* ' The Effects of Cross and Self- fertilisation,' 1876, p. 89.

80 HYBRID VEEBASCUMS. CHAP. II.

tious in referring 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.

CHAP. III. LINUM GRANDIFLORUM. 81

CHAPTER III.

HETEBOSTYLED DIMORPHIC 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 difference in self- fertility hetween the English and German
long-styled plants — Pulmonaria angustifolia shown to be a distinct
species, long-styled form completely self-sterile — Polygonum fago-
pyrum — Various other heterostyled genera — Kubiacese — 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-styled form alone ; development
not as yet perfect— The heterostyled structure in the several
Eubiaceous genera not due to descent in common.

IT 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 L. grandiflorum.
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 this inal paper, 'Bot. Zeitung,' 1863,
is the case in his review of my orig- p. 189.

82

HETEROSTYLED DIMORPHIC PLANTS. CHAP. III.

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,
and thus lie within the tube of the corolla. In the

Fig. 4.

Long-styled form. Short-styled form,
s s, stigmas.

LlNUM GBANDIFLOEUM.

long-styled form the elongated stigmas stand nearly up-
right, 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 papillae 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 papillae are more crowded
and darker-coloured than in those with the longer

CHAP. III. j 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 in a 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. CHAP. III.

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

CHAP. 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 are
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 mis-
take 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 acci-
dentally 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 7.6

8G HETEROSTYLED DIMORPHIC PLANTS. CHAP. III.

seeds, but of apparently good seed only 4.3 per cap-
sule. At three separate times nearly a hundred flowers
were fertilised illegitimately with their own-form pollen,
taken from separate plants; and numerous other
flowers were produced, many of which must have re-
ceived their own pollen. From all these flowers on
the seventeen short-styled plants only fifteen capsules
were produced, of which only eleven contained 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 transported 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 capsules 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 like-
wise 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 fertilising many flowers with
their own- form pollen; and these did not produce any

CHAP. III. LINUM GEANDIFLORUM. 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 dis-
sected, and only a single pollen-grain had emitted a tube,

* ' Bot. Zeitung,' Jan. 1, 1864, p. 2.

88 HETEROSTYLED DIMORPHIC PLANTS. CHAP. III.

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. Eepeated 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. Eepeated the experiment, with the same
result after twenty-four hours.

Fifthly. Eepeated 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: —

Sixthly. I placed own-form pollen on three of the
stigmas of the 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 man-
ner, with the same result.

Eighthly. 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 short-

CHAP. III. LINUM GRANDIFLORUM. 89

styled flower were penetrated by innumerable tubes,
which were as yet short, and the stigmas themselves were
not at all discoloured. The three stigmas covered with
their own-form pollen were not penetrated 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 pene-
trated 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.

TentUly. Eepeated 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 cne 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
their tubes, and these apparently never penetrate the

90 HETEROSTYLED DIMORPHIC PLANTS. CHAP. III.

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 papillae, 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 tAvo 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 hete-
rostyled, 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
papilla?. 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 I

CHAP. III. LINUM PERENNE. 91

shall presently return. Differently from what occurs in
L. 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 corolla, 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 3 good seeds; twelve other flowers were legiti-
mately fertilised with pollen from long-styled flowers,
and these produced nine capsules, but one was bad;

92 HETEROSTYLED DIMORPHIC PLANTS. CHAP. 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 un-
covered short-styled plant which grew close to the un-*
covered long-styled plant yielded twelve capsules.

From these facts we have some reason to believe, as
in the case of L. grandiflorum, 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

CHAP. III. 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 of 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 in-
terval of eighteen hours, the tubes penetrated the stig-
matic 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 properly
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 to-
gether ; they were covered by a rather coarse net, through
which the wind, when high, passed ; and such minute in-
sects as Thrips could not, of course, be excluded ; yet we
have seen that the utmost possible amount of accidental
fertilisation 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 ex-
cluded, 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

9 i HETEEOSTYLED DIMORPHIC PLANTS. CHAP. III.

one sex to the other, or from hermaphrodite to herma-
phrodite, we can recognise structure as manifestly
adapted to its action as to that of insects when these
are the carriers. We see adaptation to the wind in the
incoherence of the pollen, — in the inordinate quantity
produced (as in the Conifera, 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 Gramineae, 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 fertilisa-
tion (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 irregu-
lar 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 Linum 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

CHAP. 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. CHAP. 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 movement
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 L. 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 neces-
sarily leave pollen on the proper surface of the elon-
gated stigmas; and when they visit the short-styled
flowers, they will leave pollen on the upturned stig-
matic 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 in-
sect'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

CHAP. III.

LINUM PERENNE.

9T

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 (Fig. 5), but will strike against them, at nearly

Fig. 5.

Long-styled form of L. PEEEXXE, var. Austriacum, in its early condi-
tion before the stigmas have rotated. The petals and calyx have
been removed on the near side.*

right angles, with the backs of their head or thorax.
Now, in the long-styled flowers, if each stigma did
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
with papillas, with their heads already charged with

* I neglected to get drawings from published engravings. His

made from fresh flowers of the two 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. CHAP. III.

pollen from the stamens of corresponding height borne
by the flowers of the other form, and legitimate fertilisa-
tion 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
grandiflora 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 evi-
dence, states that in Linum 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. — The pistil of the long-styled form
of this species is nearly twice as long as that of

* 'Fertilisation of Orchids,' p.' t' Etudes <=nr la G6ogr. Bot.,'
108, 2nd edit. 1877, p. 84. H. Lecoq, 1856, torn. v. p. 325.

CHAP. III. LIXUM FLAVUM. 90

the short-styled; the stigmas are longer and the
papillae 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. Two 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.
Xo 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 short-
styled plants of the two previous species apparently

100 HETEROSTYLED DIMORPHIC PLANTS. CHAP. III.

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. corymbiferum is certainly heterostyled,
as is, according to Planchon,* L. salsoloidcs. 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, saysf 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. J 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-
cum. 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 may
be suspected that they are frequented during the night
by small moths for the sake of the five minute drops

* Hooker's 'London Journal of Journal of Botany,' 1848, vol. vii.

Botany,' 1848, vol. vii. p. 174. p. 525) to be provided with

t 'Bot. Zeitung,' Sept. 18,1863, staminibus cxsertis;" another

p. 281. with " stylis staminibus longiori-

I It is not improbable that the bus," and another has stamina 5,

allied genus, Hugonia, is hetero- majora. stylos longe superantia."

styled, for one species is said by \ ' Die Befruchtung der Blu-

Planchon (Hooker's 'London men,' &c., p. 168.

CHAP. III. PULMONARIA OFFICINALIS. 101

of nectar secreted. Lastly, L. Lewisii is said by Plan-
chon 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 (

Pulmonaria ofjlcinalis. — 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 (i.e. 64 per cent.) had set
fruit, yielding 1.88 seed per fruit. The ten short-
styled plants bore 373 flowers, of which 262 (i. e.
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

* 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, Jan. 13,

Asa Gray, in ' American Journal p. 13.

102 HETEROSTYLED DIMORPHIC PLANTS. CHAP. III.

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 follow-
ing table : —

TABLE 19.
Pulmonaria, officinalis (from Hildebrand).

Number

Number

Nature of Union.

of
Flowers

of
Fruits

Number of
Seeds per

fertilised.

produced.

Fruit.

Long-styled flowers, by pollen of short- 1
styled. Legitimate union J

14

10

1.30

Long-styled flowers, 14 by own pollen, ]

and 16 by pollen of other plant of same >

30

0

0

form. Illegitimate union J

Short-styled flowers, by pollen of long- )
styled. Legitimate union J

16

14

1.57

Short-styled flowers, 11 by own pollen, 14 ]

by pollen of other plant of same form. >

25

0

0

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 sur-
prise 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
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

CHAP. III. PULMONARIA OFFICINALIS. 103

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 or by some other cause. We shall see in a
future chapter that heterostyled plants illegitimately
fertilised during several successive generations some-
times become more self-f ertile ; and this may have been
the case with my stock of the present species of Pul-
monaria; but in this case we must assume that the
long-styled plants were at first sufficiently fertile to

104 HETEROSTYLED DIMORPHIC PLANTS. CHAP. III.

yield some seed, instead of being absolutely self-sterile
like the German plants.

Pulmonaria angustifolia. — Seedlings 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 cer-
tainly have yielded a considerable number, namely,
about nine, judging from the results given in the fol-
lowing table (20). Therefore P. officinalis and angus-
tifolia appear to be good and distinct species, in con-
formity with other important functional differences be-
tween 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

CHAP. III. PULMONAEIA ANGUSTIFOLIA. 105

accompanying figure a slight bulging of the corolla
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 tho corolla, though variable in size, was
generally larger in the long-styled flowers than in the

Fig. 6.

Long-styled form. Short-styled form.

PtJLMONABIA ANGUSTIFOLIA.

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 form 115 to 112. From an average of seven
measurements of each 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-

106 HETEROSTYLED DIMORPHIC PLANTS. CHAP. III.

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-
bility of all the organs in both forms, we may perhaps
suspect that the plant is undergoing a change, and
tending to become dioecious.

My son collected in the Isle of Wight on two occa-
sions 202 plants, of which 125 were long-styled and

CHAP. III. PULMONARIA ANGUSTIFOLIA.

107

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
100 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 : —

TABLE 20.
Pulmonaria angustifolia.

Nature of Union.

Number
of
Flowers

fertilised.

Number
of
Fruits
produced.

Average

Numbefof
Seeds per
Fruit.

Long-styled flowers, by pollen of short- I
styled. Legitimate union J

18

9

2.11

Long-styled flowers, by own-form pollen. 1

18

0

0

Short-styled flowers, by pollen of long- 1
styled. Legitimate union j

„

15

2.60

Short-styled flowers, by own-form pollen. )

12

7

1.86

We see in this table that the fertility of the two
legitimate unions to that of the two illegitimate to-
gether is as 100 to 35, 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

108 HETEROSTYLED DIMORPHIC PLANTS. CHAP. III.

flowers in the first line was probably accidental, and
if so, the difference in the proportion of legitimately
and illegitimately fertilised flowers which yield fruit
is really greater than that represented by the ratio of
100 to 35. 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 138 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 respect they
differ greatly from the long-styled English plants of
P. officinalis, which were found by me to be moderate-
ly self-f ertile ; 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
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

CHAP. III. PULMONARIA ANGUSTIPOLIA. 109

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 the net bore 28 flowers besides those which
had been artificially fertilised, and of all these only
two produced a fruit each including a single 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,
vthus 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 high-
est possible number of seeds, namely 4, and 31 included
3 seeds. So we see how highly fertile these short-
styled plants were when illegitimately fertilised 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
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; nevertheless this pollen was highly efficient

HO HETEROSTYLED DIMORPHIC PLANTS. CHAP. III.

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-fertilisation,
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 Amsinclcia
spectabilis, sent me by Professor Asa Gray, I formerly
thought that this plant, a member of the Boraginese, 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 con-
vinced that the whole case was one of mere variability. The
first-formed flowers are apt to have stamens somewhat ar-
rested in development with very little pollen in their an-
thers; 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

* 'Die Gesclilcchter-Vertheilung bei den Pflanzen,' 1867, p. 37.

CHAP. III. POLYGONUM FAGOPYRUM. HI

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 Echium vulgare were
heterostyled, but soon saw my error. From information
given me, I examined dried flowers of another member of
the Boraginese, Arnebia hispidissima, collected from sev-
eral sites, and though the corolla, together with the in-
cluded organs, differed much in length, there was no sign
of heterostylism.

POLYGONUM FAGOPYRUM ( POLYGON ACE.E).

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 in diameter. 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, fertilised. They
produced 22 seeds, or 11 per flower-head.

Three flower-heads on long-styled plants received
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

* ' Die Geschlechter-Vertheilung,' &c., 1867, p. 34.

112 HETEROSTYLED DIMORPHIC PLANTS. CHAP. III.

were thus legitimately fertilised. They produced 8
seeds, or 4 per flower-head.

Four heads on short-styled plants similarly received
pollen from other short-styled plants, and were thus

Fig. 7.

Upper figure, the long-styled form ; lower figure, the short-styled.
Some of the anthers have dehisced, others have not.

POLYGONUM FAGOPYEUM. (From H. Miiller.)

illegitimately fertilised. They produced 9 seeds, or 2.25
per flower-head.

The result from fertilising the flower-heads in the
above imperfect manner cannot be fully trusted; but
I may state that the four legitimately fertilised flower-
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

CHAP. III. POLYGONUM FAGOPYRTJM. H3

illegitimately fertilised flowers on the same plants, in
the ratio of 100 to 82, as shown by the weights of an
equal number.

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. Miiller,* 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 mistaken in supposing
that the long-styled flowers cannot spontaneously fer-
tilise 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. Miiller, in his interesting description of several
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

* 'Die Befruchtung,' &c., p. 175, and 'Nature,' January 1, 1874,
p. 166.

114: HETEROSTYLED DIMORPHIC PLANTS. CHAP. III.

visited by insects; these are adapted for self -fertilisa-
tion, though still capable of cross-fertilisation. Ac-
cording to Delpino, the Polygonaceae are generally
fertilised by the wind, instead of by insects as in the
present genus.

LEUCOSMIA BURNETTIANA (THYMELLE).

As Professor Asa Gray has expressed his belief * that
this species and L. acuminata, as well as some species in
the allied genus Drymispermum, are dimorphic or hetero-
styled, I procured from Kew, through the kindness of Dr.
Hooker, two dried flowers of the former species, an in-
habitant 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 threat
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 supported 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 con-
siderable 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
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-

* 'American Journal of Sci- 'Journal of Botany,' vol. iii.,
ence,' 1865, p. 101, and Seemann's 1865, p. 305.

CHAP. III. MENYANTHES TRIFOLIATA. H5

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 papil-
lose condition in the short-styled form, that the present spe-
cies is truly heterostyled. This case resembles that of
Linum grandiflorum, in which the sole difference between
the two forms consists in the length of the pistils and stig-
mas. From the great length of the tubular corolla of Leu-
cosmia, it is clear that the flowers are cross-fertilised by
large Lepidoptera or by honey-sucking birds, and the posi-
tion 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 (GENTIANEJE).

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 3 to 2. The stigma of the former, as
my son observed, is decidedly 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 cap-
sules, yet the seeds have never germinated; and this looks
as if the short-styled form was sterile with its own pollen.

LlMNANTHEMUM INDICUM (GENTIANS^).

This plant is mentioned by Mr. Thwaites, in his Enu-
meration of the Plants of Ceylon, as presenting two forms ;

116 HETEROSTYLED DIMORPHIC PLANTS. CHAP. III.

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 3 to 5. The folia-
ceous 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, according
to Mr. Thwaites, are equally numerous (viz. from 70 to
80) in the two forms.

VILLARSIA [SP.?] (GENTIANE.E).

Fritz Miiller sent me from South Brazil dried flowers
of this aquatic plant, which is closely allied to Limnanthe-
mum. 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 be-
neath 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 con-
spicuously longer than those of the shorter stamens in the
long-styled flowers. In the former the sub-triangular pol-
len-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 be-
ing about 100 to 75. Fritz Miiller 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 Lyth-
rum salicaria 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 Gentianea3. All the species, as far as at pres-

CHAP. III. CORDIA. H?

ent known, are heterostyled, and all inhabit aquatic or sub-
aquatic stations.

FORSYTHIA SUSPENSA (OLEACE^).

Professor Asa Gray states that the plants of this species
growing 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 divergent.
This last character, however, may be only a temporary
one. There seems to be no difference in the papillose con-
dition 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 long-
est. 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 hetero-
styled ; 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.

CORDIA [SP.?] (CORDIACE^E.)

Fritz Miiller 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

* ' The American Naturalist,' July, 1873, p. 422.

118 HETEROSTYLED DIMORPHIC PLANTS. CHAP. III.

differences are not well pronounced in the two forms.
Linum grandiflorum shows us that a plant may be hetero-
styled 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 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 whole pistil
is longer than that of the short-styled, in about the ratio
of 3 to 2.

The stigmas of the short-styled form are seated be-
neath 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.

GlLIA (IPOMOPSIS) PULCHELLA VEL AGGREGATA (PoLEMONI-
ACE.E).

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 por-
tions 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 pos-
sible to compare, except by calculation, the absolute length
of the organs from different plants. Moreover the rela-
tive 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 & of an inch. I sus-
pect 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

* 'Proc. American Acad. of Arts and Sciences,' June 14, 1870,
p. 275.

CHAP. III. GILIA MICRANTHA. 119

flowers the difference in length between the pistils of the
two forms was certainly greater, but they were not actu-
ally measured. In the short-styled flowers, whether large
or small, the stigma is seated low down within the tube of
the corolla. The papillae 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 unattached portion being alone measured; but this
ratio cannot be trusted, owing to the great variability of
the stamens. The mean diameter of eleven pollen-grainy
from long-styled flowers, and of twelve from the short-
styled, was exactly the same. It follows from these several
statements, that the difference in length and state of sur-
face of the stigmas in the flowers is the sole reliable evi-
dence that this species is heterostyled ; 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 alto-
gether 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, G. coronopifolia,
belonging to the same section of the genus, he can see no
sign of dimorphism.

GILIA (LEPTOSIPHON) MICRANTHA.

A few flowers sent me from Kew had been somewhat in-
jured, 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 papillae 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 dif-
ference, as well as that between the stigmas of the two
forms, there can be no doubt that this species is hetero-
styled. So probably is Gilia nudicaulis, which likewise be-
longs to the Leptosiphon section of the genus, for I hear
from Professor Asa Gray that in some individuals the

120 HETEROSTYLED DIMORPHIC PLANTS. CHAP. III.

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 (POLEMONIACE^:).

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 an-
thers are arranged one below the other, the uppermost just
protruding from the throat of the corolla. In Phlox subu-
lata alone he has " seen both long and short styles ; and
here the short-styled plant has (irrespective of this char-
acter) 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 froin 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 difference 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 diam-
eter to the latter as 100 to 93 ; and this difference accords
with the belief that the plant is heterostyled. 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

* ' Proc. American Acad. of Arts and Sciences,' June 14, 1870, p. 248.

CHAP. III. ERYTHROXYLUM. 121

as 100 to 75 : here, then, the grains from the short-styled
form were considerably 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 de-
gree, 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-styled than in the
long-styled flowers, looks as if the plant was heterostyled;
for we know that with some species — for instance, Leu-
cosmia and certain Eubiacese — the stigma is longer and
more papillose in the short-styled form, though the re-
verse 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 somewhat opposed to the present species
being heterostyled ; as is the great difference in the length
of the pistil in several short-styled flowers. But the ex-
traordinary 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 Phlox subulata
is heterostyled. Possibly this species was once heterostyled,
but is now becoming sub-difficious ; 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 varia-
bility of their pollen-grains, and are becoming more mas-
culine, I will not pretend to conjecture; they might re-
main as hermaphrodites, for the co-existence of herma-
phrodite and female plants of the same species is by no
means a rare event.

ERYTHROXYLUM [SP.?] (ERYTHROXYLID.E).

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. 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
10

122 HETEROSTYLED DIMORPHIC PLANTS. CHAP. III.

stigmas stand beneath the anthers. The stigmas in many,
but not in all the short-styled flowers, are 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-nf th of

Fig. 8.

Long-styled form. Short styled form.

From a sketch by Fritz Miiller, magnified five times.
EEYTHEOXYLON [sp. ?].

their own length than those of the long-styled. Conse-
quently the anthers of the latter do not stand on a level
with, but rather above the stigmas of the other form. Dif-
ferently 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.*

* 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 petals often
vary from 5 to 7 ; the stamens from
10 to 14, and the pistils from
3 to 4.

CHAP. III. CRATOXYLOX FORMOSUM. 123

SETHIA ACUMINATA (ERYTHROXYLIOE).

Mr, Thwaites pointed out several years ago * that this
plant exists under two forms, which he designated as
forma stylosa et staminea; and the flowers sent to me by
him are clearly heterostyled. 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 smaller than those
of the short-styled. All the stamens in the short-styled
flowers are of nearly equal length, whereas in the 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 oltusifolia is heterostyled like 8. acuminata.

CRATOXYLON FORMOSUM (HYPERICINE^E).

Mr. Thiselton Dyer remarks that this tree, an inhabit-
ant of Malacca and Borneo, appears to be heterostyled. f
He sent me dried flowers, and the difference between the
two forms is conspicuous. 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 numerous 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 meas-
ured, and those from the short-styled were to those from
the long-styled as 100 to 86 in diameter. This plant, there-

* ' Enumeratio Plantarum Zcy- t 'Journal of Botany,' London,
laniae, ' 1864, p. 54. 1872, p. 26.

124 HETEROSTYLED DIMORPHIC PLANTS. CHAP. III.

fore, is in all respects a well-characterised heterostyled
species.

^GIPHILA ELATA (VERBENACE^).

Mr. Bentham was so kind as to send me dried flowers
of this species and of 2E. mollis, both inhabitants of South
America. The two forms differ conspicuously, as the deep-
ly 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 papillae. 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 other
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 about the ratio of 100 to 62. The two forms
of 2E. mollis present a like difference in the length of
their pistils and stamens.

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 an-
thers 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,

CHAP. III. MITCHELLA REPENS. 125

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 short-
ened, 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 hav-
ing suffered from hypertrophy, and is probably incapable
of fertilisation. If this be so the plant is dioecious, and,
judging from the two species previously described, it proba-
bly was once heterostyled, and has since been rendered
dioecious 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
Labiatse, in which females and hermaphrodites regularly
coexist. 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 dioecious than that
it consists of hermaphrodites and females; for if any one
of the isolated plants had been an hermaphrodite, it would
probably have produced some fruit.

This great natural family contains a much larger
number of heterostyled genera than any other one as
yet known.

Mitchella repens. — Professor Asa Gray sent me sev-
eral living plants collected when out of flower, and near-
ly 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

* A. Gray, ' Manual of the Bot. of the N. United States,' 1856, p. 172.

126 HETEROSTYLED DIMORPHIC PLANTS. CHAP. III.

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 calculating
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 Table 21.

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, ac-
cording to the proportion of flowers which yielded ber-
ries, 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

CHAP. III.

BORRERIA.

12T

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

TABLE 21.
Mitchella repens.

Nature of Union.

Number of
Pairs of
Flowers fer-
tilised dur-
ing the sec-
ond Season.

Number

2STC

ing the sec-
ond Season.

Average
Number of
good Seeds
per Drupe
in all the
Drupes dur-

i.±r

Long-styled flowers, by pollen of short- !
styled. Legitimate union j

9

8

4.6

Long-styled flowers, by own-form pollen. I
Illegitimate union j

8

3

2.2

Short-styled flowers, by pollen of long- 1
styled. Legitimate union j

8

7

4.1

Short-styled flowers, by own-form pollen. )
Illegitimate union j

9

0

2.0

The two legitimate unions together . . .

17

15 '

4.4

The two illegitimate unions together . . .

17

3

2.1

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 (KUBIACE^;).

Fritz Miiller 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-

128 HETEROSTYLED DIMORPHIC PLANTS. CHAP. III.

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 Miiller 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
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 Professor Kerner's view * their chief
use probably is to prevent the copious nectar being
stolen by small crawling insects, which could not render
any services 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,

* ' Die Schutzmittel der Bliithen gegen unberufene Gaste,' 1876,

CHAP. III. FARAMEA. 129

0

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. ?] (KUBIACE^E).

Fritz Miiller has fully described the two forms of
this remarkable plant, an inhabitant of South Brazil.*
In 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
instance is known; those from the short-styled flowers
being covered with sharp points; the smaller ones
from the long-styled being quite smooth. Fritz Miiller
remarks that this difference between the pollen-grains
of the two forms is evidently of service to the plant;

* 'Bot. Zeitung,' Sept. 10, 1869, p. 606.

130 HETEROSTYLED DIMORPHIC PLANTS. CHAP. III.

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

Fig. 9.

Short-styled f

Long-Btyled form.

Outlines of flowers from dried specimens. Pollen-grains, magnified
180 times, by Fritz Miiller.

FABAMEA [sp. ?].

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

CHAP. III. FARAMEA. 131

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 Miiller 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
rule with the Kubiacea?; and this is the best position
for the adherence of the pollen-grains to the proboscis
of an entering insect. Fritz Miiller therefore infers
that as the plant became heterostyled, and as the
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 use-
less, namely, that from the anthers which do not rotate
properly. It thus appears that the development of the
plant has not as yet been completed; the stamens have
indeed acquired their proper length, but not their full
and perfect power of rotation.*

e Fritz Muller gives another in- with the nocturnal habits of these

stance of the want of absolute per- insects, most of the flowers open

faction in the flowers of another only during the night; but some

member of the Kubiacese, namely, open in the day, and the pollen

Posoqueria frafirans, which is of such flowers is robbed, as Fritz

adapted in a most wonderful man- Muller has often seen, by humble-

ner for cross-fertilisation by the bees and other insects, without

agency of moths. (See 'Bot. Zeit- any benefit being thus conferred

ung,' 1866, No. 17.) In accordance on the plant.

132 HETEROSTYLED DIMORPHIC PLANTS. CHAP. III.

The several points of difference in structure between
the two forms of Faramea are highly remarkable.
Until within the 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)
(RUBIACE.E).

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, which latter are enclosed within the tube, but
only a short way down. In the short-styled form the an-
thers 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 Rubiaceae. Nevertheless there
is a considerable difference in the size of the pollen-grains
in the two forms; for, as Fritz Miiller informs me, those
of the short-styled are to those of the long-styled as 100
to 75 in diameter.

HOUSTONIA COZRULEA (RUBIACE^E).

Professor 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 stig-
mas 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 an-

CHAP. III. BUBIACILE. 133

thers 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 un-
favourable conditions, for some long-styled plants in a
state of nature yielded an average of 21.5 seeds per cap-
sule. 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 pre-
viously visited long-styled plants, produced capsules, eleven
of which were wholly sterile, but one contained 4, and an-
other 8 seeds. So that the short-styled form seems to be
very sterile with, its own pollen. Professor Asa Gray in-
forms me that the other North American species of this
genus are likewise heterostyled.

OLDEXLANDIA [SP.?] (KUBIACE.E).

Mr. J. Scott sent me from India dried flowers of a
heterostyled species of this genus, which is closely allied to
the last. The pistil in the long-styled flowers is longer by
about a quarter of its length, and the stamens shorter in
about the some proportion, than the corresponding organs
in the short-styled flowers. In the latter the anthers are
longer, and the divergent stigmas decidedly longer and
apparently thinner than in the 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.

HEDYOTIS [SP.?] (RUBIACE.E).

Fritz Miiller sent me from St. Catharina, in Brazil,
dried flowers of a small delicate species, which grows on
wet sand near the edges of fresh-water pools. In the long-
styled form the stigma projects above the corolla, and
stands on a level with the projecting anthers of the short-

134 HETEROSTYLED DIMORPHIC PLANTS. CHAP. III.

styled form ; but in the latter the stigmas stand rather be-
neath 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
39 ; and the papillae 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 spe-
cies, which is likewise heterostyled.

COCCOCYPSELUM [SP.?] (KUBIACE.E).

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 ex-
serted anthers of the short-styled form; and the enclosed
stigma of the latter also stand 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 di-
vergent, and more curled. Fritz Miiller informs 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.

LIPOSTOMA [SP.?] (BUBIACE.E).

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 correspondence in height between the stig-
mas 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

CHAP. III. RUBIACE^E. 135

are as 100 to 80 in diameter, compared with those from the
long-styled form.

CINCHONA MICRANTHA (EUSTACES).

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 38 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 considerably 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-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 can-
not be accounted for by unequal distension with water.

Besides the several Rubiaceous genera already men-
tioned, Fritz Miiller informs me that two or three species
of Psychotria and Rudgea eriantha, natives of St. Catha-
rina, 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 hot-
house, 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 con-
vinced that this is the case with Diodia and Spermacoce

* My attention was called to this given by Mr. Markham in his
plant by a drawing copied from 'Travels in Peru,' p. 539.
Howard's 'Quinologia,' Tab. 3,

136 HETEROSTYLED DIMORPHIC PLANTS. CHAP. III.

in the United States. Lastly, from Mr. W. W. Bailey's
description,* it appears that the Mexican Bouvardia le-
iantha is heterostyled.

Altogether we now know of 17 heterostyled genera
in the great family of the Bubiaceae; 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
Bubiaceae 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 some one or
even two or three progenitors in common. It further
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 char-
acter, which is not even of specific value in the hetero-
styled species, is often of generic value in other mem-
bers of the family.

* 'Bull, of the Torrey Bot. Club,' 1876, p. 106.

CHAP. IV. LYTHRUM SALICARIA. 137

CHAPTER IV.

HETEEOSTYLED TEIMOEPHIC 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 Grsefferi likewise trimorphic — L. thymifolia dimorphic —
L. hyssopifolia homostyled — Nessea verticillata trimorphic— Lager-
strosmia, nature doubtful — Oxalis, trimorphic species of— O. Valdi-
viana — O. Regnelli, the illegitimate unions quite barren — O. spe-
ciosa — 0. sensitiva — Homostyled species of Oxalis— Pontederia,
the one monocotyledonous genus known to include heterostyled
species.

IN" 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 Nesaea, 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

138 HETEROSTYLED TRIMORPHIC PLANTS. CHAP. IV.

are considered, there are five 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
complex 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 are of un-
equal length, 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 subse-
quently more carefully by Wirtgen ; but these botanists,
not being guided by any theory or even suspicion of
their functional 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.
d'Europe,' torn, ii., 1841, p. 371. des naturlmt. Vereins fur preuss.
Wirtgen, "UeberLy/Arwmsah'caria Rheinl.,' 5. Jahrgang, 1848, S. 7.

CHAP. IV. LYTHRUM SALICAEIA.

Fig. 10.

139

Micl-
Btyled

Short-
styled.

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 to each stigma to ensure full fertility.

140 HETEROSTYLED TRIMORPHIC PLANTS. CHAP. 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 papillae 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. Miiller* 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 g-^ mm. The grains, distended
with water, from the mid-length stamens are 7-7f,
and those from the shortest stamens 6-6^ 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 be presently explained. As these seeds,
when cleaned, seemed larger than those from the mid-

* ' Die Befruchtung der Blumen,' 1873, p. 193.

CHAP. IV. LYTERUM 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 con-
siderably 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-
len-grains of the longest stamens are 9-10 in di-
ameter, 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 per-
haps, as we shall see, this is rather too high an aver-
age. 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. CHAP. IV.

thers. The end of the pistil is generally bent upwards
at right angles. The six longest stamens, with their
pink filaments and green pollen, resemble the corre-
sponding stamens of the mid-styled form. But accord-
ing to H. Miiller, their pollen-grains are a little larger,
viz. 9^-1 0|, 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. Each
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

CHAP. IV. LYTHRUM SALICARIA. 143

both sets of stamens in all three forms, is copied from
H. Miiller; they are arranged in the order of their

size : —

Pollen-grains from longest stamens of short-styled form 9J to 10J

mid-styled

mid-length stamens of long-styled
short-styled

shortest stamens of long-styled
" " mid-styled

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

HETEROSTYLED TRIMORPHIC PLANTS. CHAP. IV.

same number as in the finest wild capsule which I
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 sepa-
rate plants growing near one another, and classified
them. My son did the same in Hampshire, and here
is the result: —

TABLE 22.

—

Long-styled.

Mid «tyled.

Short-styled.

Total.

North Wales
Hampshire

95
53

97
38

72

38

264

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

CHAP. IV. LYTHRTJM 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, ex-
cepting 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,
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

* H. Muller gives a list of the one bee, the Cilissa melannra, al-
species, 'Die Befruchtung der most confines its visits to this
Blumen,' p. 196. It appears that plant.

146 HETEROSTYLED TRIMORPHIC PLANTS. CHAP. IV.

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 Dictam-
nus frqxinella 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-
nacese, 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
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-

CHAP. IV. LYTHRUM SALICARIA. 147

ing from one nectary to the other. In Scrophularia
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, I
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
capsules) was accidentally left during several days
pressing against the net, and bees were seen inserting
their proboscides through the meshes, and in conse-

148 HETEEOSTYLED TRIMORPHIC PLANTS. CHAP. IV.

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 bees
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 car-
riers 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 bractese,
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
longer papillae 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

* 'Verhand. des naturhist. Vereins, fur Pr. Bheinl.,' 5. Jahrgang,
1848, pp. 11, 13.

CHAP. IV. LYTHRUM SALICARIA. 149

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
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 plants which I observed and he appears to have found the
grew in my garden, and probably stigmatic papillae differing con-
varied rather more than those stantly in length and structure in
growing in a state of nature. H. the three forms, being longest in
Miiller has described the stigmas the long-styled form,
of all three forms with great care,

150 HETEROSTYLED TRIMORPHIC PLANTS. CHAP. IV.

the mid- or the 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, i. e. on an average I fertilised above a dozen
flowers in the eighteen different methods. Each 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 stig-
ma was examined with a lens to see that there was suffi-
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-
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

CIIAP. IV. LYTHRUM SALICARIA. 151

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 con-
tained no good seed. In some part of each row of fig-
ures 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 ob-
tained during two successive years ; but more especially
because 1863 was a very hot and dry season, and the
plants had occasionally, to be watered. This did not
prevent the full complement of seeds being produced
from the more fertile unions; but it rendered the less
fertile 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.

152 HETEROSTYLED TRIMORPHIC PLANTS. CHAP. IV.

TABLE 23. — Long-styled Form.

Legitimate union.
13 flowers fertilised bythelongest
stamens of the mid-styled. These
stamens equal in strength the pistil
of the long-styled.
Product of good seed in each

capsule.

36 53

81 0

0 0

0 0

0 0

0
45
41

38 per cent, of these flowers
yielded capsules. Each capsule
contained, on an average, 51.2

II.

Legitimate union.
13 flowers fertilised bythelongest
stamens of the short-styled. These
stamens equal in length the pistil
of the long-styled.
Product of good seed in each

capsule.
159
43

96 poor seed.
103
0
0

104
119

131
118

114

84 per cent, of these flowers
yielded capsules. Each capsule
contained, on an average, 107.3
seeds.

III.

Illegitimate union.
14 flowers fertilised by the short-
est stamens of the mid-styled.
3 0

0 0

0 0

0 0

0 0

0

0 0

0
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.

V.

Illegitimate union.
15 flowers fertilised by own-form
mid-length stamens.

2 —

10 0

23 0

0 0

0 0

0 0

0 0

0 0

Too sterile for any average.

VI.

Illegitimate union.
15 flowers fertilised by own-form
shortest stamens.

4 —

8 0

4 0

0 0

0 0

0 0

0 0

0 0

Too sterile for any average.

CHAP. IV. LYTHRUM SALICAKIA. 153

Besides the above experiments, I fertilised a con-
siderable 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
experiment: 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 num-
ber as follows: —

20 20 35 21 19

26 24 12 23 10

7 30 27 29 13

20 12 29 19 35

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 seeds. I have spoken as if the plant had
received 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.
12

154 HETEROSTYLED TRIMORPHIC PLANTS. CHAP. IV.

TABLE 24.— Mid-styled Form.

I.

II.

Legitimate union.

Legitimate union.

12 flowers fertilised by the mid-

12 flowers fertilised by the mid-

length stamens of the long-styled.

length stamens of the short-styled.

These stamens equal in length the

These stamens equal in length the

pistil of the mid-styled.

pistil of the mid-styled.

Product of good seed in each

Product of good seed in each

capsule.

capsule.

138 122

112 109

149 50

130 143

147 151

143 124

109 119

100 145

133 138

33 12

144 0

141

104

92 per cent, of the flowers (pro-

100 per cent, of the flowers

bably 100 per cent.) yielded cap-

yielded capsules. Each capsule

sules. Each capsule contained, on

contained, on an average, 108.0

an average, 127.3 seeds.

seeds ; or, excluding capsules with

less than 20 seeds, the average is

116.7 seeds.

III.

IV.

Illegitimate union.

Illegitimate union.

13 flowers fertilised by the short-

15 flowers fertilised by the long-

est stamens of the long-styled.

est stamens of the short-styled.

83 12

130 86

0 19

115 113

r seeds small

14 29

0 851 and poor.

6 17

0

2 113

44 0

9 79

44 0

128

45 0

132 0

54 per cent, of the flowers

93 per cent, of the flowers

yielded capsules. Each capsule

yielded capsules. Each capsule

contained, on an average, 47.4

contained, on an average, 69.5

seeds; or, excluding capsules with

seeds ; or, excluding capsules with

less than 20 seeds, the average is

less than 20 seeds, the average is

60.2 seeds.

102.8.

CHAP. IV.

LYTHRUM SALICARIA.

155

TABLE 24. — Mid-styled Form — continued.

V.

VI.

Illegitimate union.

Illegitimate union.

12 flowers fertilised by own-form
longest stamens.

12 flowers fertilised by own-form
shortest stamens.

92 0

0 0

9 0

0 0

63 0

0 0

0

— • 0

136?* 0

0 0

0 0

0 0

0

0

Excluding the capsule with 136
seeds, 25 per cent, of the flowers

Not one flower yielded a capsule.

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.

Besides the experiments in the above table, I fer-
tilised 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.

* I 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 fertil-
ised in the latter manner would
have yielded about 136 seeds, and
it may be observed that one such
pod is 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 yield-
ed 92 seeds, in the same column
with that which yielded 136, I do
not know what to think. I en-

deavoured to prevent pollen drop-
ping from an upper to a lower
flower, and I tried to remember to
wipe the pincers carefully after
each fertilisation ; but in making
eighteen different 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 sec-
onds' time they might have done
irreparable mischief. It was also
extremely difficult to exclude
minute Diptera from the net. In
1862 I made the great mistake of
placing a mid-styled and a long-
styled under the same huge net :
in 1863 I avoided this error.

156 HETEROSTYLED TRIMORPHIC PLANTS. CHAP. IV.

TABLE 25. — Short-styled Form.

I.

II.

Legitimate union.

Legitimate union.

12 flowers fertilised by the short-

13 flowers fertilised by the short-

est stamens of the long-styled.

est stamens of the mid-styled.

These stamens equal in length the
pistil of the short-styled.

These stamens equal in length the
pistil of the short-styled.

69 56

93 69

61 88

77 69

88 112

48 53

66 111

43 9

0 62

0 0

0 100

0 0

—

— 0

83 per cent, of the flowers

61 per cent, of the flowers

yielded capsules. Each capsule
contained, on an average, 81.3

yielded capsules. Each capsule
contained, on an average, 64.6

seeds.

seeds.

III.

IV.

Illegitimate union.

Illegitimate union.

10 flowers fertilised by the mid-
length stamens of the long-styled.

10 flowers fertilised by the long-
est stamens of the mid-styled.

0 14

0 0

0 0

0 0

0 0

0 0

0 0

0 0

0

0

23

0

Too sterile for any average.

Too sterile for any average.

V.

VI.

Illegitimate union.

Illegitimate union.

10 flowers fertilised by own-form
longest stamens.

10 flowers fertilised by own-form
mid-length stamens.

0 0

64?* 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.

* I suspect that by mistake I to be thus fertilised were marked

fertilised this flower in compart- with black silk ; those with pollen

ment VI. with pollen from the from the mid-length stamens of

shortest stamens of the long-styled the short-styled with black thread ;

form, and it would then have and thus probably the mistake

yielded about 64 seeds. Flowers arose.

CHAP. IV. LYTHRUM SALICARIA. 15?

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
legitimately 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
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.

158 HETEROSTYLED TRIMORPHIC PLANTS. CHAP. IV.

Twelve mid-styled flowers fertilised illegitimately
by their own- form longest stamens yielded 25 per cent,
of capsules, which (excluding one with 9 seeds) con-
tained 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 nine 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
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.

Katun

of Union.

Number
of
Flowers
fertilised.

Number
of
Capsule,
produced.

Average
Number of
Seeds per
Capsu.e.

Averaee Num-
ber of Seeds
per Flower
fertilised.

The six

legitimate )

75

56

96.29

71.89

'

The twelve
unions .

illegitimate )
j

146

36

44.72

11.03

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.

CHAP. IV. LYTHRUM SALICARIA. 15£

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
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 at Tables 23, 24 and 25, and
to the diagram Fig. 10, p. 139. 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

160 HETEROSTYLED TRIMORPHIC PLANTS. CHAP. IV.

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
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,

CHAP. IV. LYTHRUM SALICAEIA. 161

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 cer-
tain characters fitted to ensure the legitimate fertilisa-
tion of the three forms.

Another conclusion which may be drawn from
Tables 23, 24, and 25, even from a glance at them,
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

162 HETEROSTYLED TRIMORPHIC PLANTS. CHAP. IV.

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
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. Miiller, 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 9£ to 10£ 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 6£ in diameter.

CHAP. IV. LYTHRUM SALICAEIA. 163

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
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

164 HETEROSTYLED TRIMORPHIC PLANTS. CHAP. IV.

the pollen from a single anther is far more than suffi-
cient to fertilise fully a stigma; since, 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 pre-
viously.

Finally, it has now been shown that Lythrum sali-
caria presents the extraordinary case of the same
species bearing three females, different in structure and
function, and three or even five sets (if minor differ-
ences are considered) of males; each set consisting of
half-a-dozen, which likewise differ from one another in
structure and function.

Lythrum Grcefferi. — I have examined numerous dried
flowers of this species, each from a separate plant, sent me
from Kew. Like L. salicaria, it is trimorphic, and the
three forms apparently 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 long-

CHAP. IV. LYTHRUM HYSSOPIFOLIA. 165

est 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 be-
tween this species and L. salicaria, but with some differ-
ences 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 di-
ameter 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 be-
tween the pollen-grains of the mid-length and shortest sta-
mens 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 Vauch-
er,* is dimorphic, like Primula, and therefore presents only
two forms. I received two dried flowers from Kew, which
consisted of the two forms; in one 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 form. There are only
six stamens ; these are somewhat graduated 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 sta-
mens alternate with the petals, and therefore correspond
homologically with the longest stamens of L. salicaria
and L. Grcefferi.

Lythrum hyssopifolia. — This species is said by Vauch-
er, 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. Wat-
son, 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

* ' Hist. Phys. des Plantes d' Europe,' torn. ii. (1841), pp. 369, 371.

166 HETEEOSTYLED TEIMOEPHIC PLANTS. CHAP. IV.

long, the stamens are likewise generally long; in the bud
the stamens are short; and Vaucher was perhaps thus de-
ceived. 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. thy mif olia. The stigma is included within the calyx,
and stands in the midst of the anthers, and would gen-
erally be fertilised by them ; but as the stigma and anthers
are upturned, and as, according to Vaucher, there is a pas-
sage 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. sali-
caria, 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 heterostyled, as such plants cannot habitually live
isolated any better than one sex of a dioecious species.

We thus see that within this genus some species are
heterostyled and trimorphic; one apparently heterostyled
and dimorphic, and one homostyled.

Nescea 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 pro-
portional lengths of their organs of fructification and in
all respects, in very nearly the same way as the three forms
of Lythrum Grcefferi. The green-pollen grains from the
longest stamens, measured along their longer axis and not
distended with water, were T^f? of an inch in length ; those
from the mid-length stamens rinsir, and those from the
shortest stamens -ri'-jnr of an inch. So that the largest pol-
len-grains are to the smallest in diameter as 100 to 65.
This plant inhabits swampy ground in the United States.
According to Fritz Miiller, f a species of this genus in St.
Catharina, in Southern Brazil, is homostyled.

* 'Geograph. Bot. de 1'Europe,' torn, vi., 1857, p. 157.
t 'Bot. Zeitung,' 1868, p. 112.

CHAP. IV. LAGERSTRCEMIA INDICA. 16?

Lagerstrcemia Indica. — This plant, a member of the
Lythracese, 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 sta-
mens with yellow pollen, which correspond in position
with the shortest stamens of Ly thrum; and from one to
five (the latter number being the commonest) very long
stamens, with thick flesh-coloured filaments and green
pollen, corresponding in position with the longest stamens
of Lythrum. In one flower, two of the long stamens pro-
duced 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 fer-
tilised with green pollen, and six with yellow pollen, but
not one set fruit. This latter fact by no means proves that
the plant is heterostyled, 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 sterile with its own pollen ; whilst
a long-styled plant of L, regince, 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 L. Indica in having eight long stamens with
thick filaments, and a crowd of shorter stamens. Thus the
evidence whether L. Indica is heterostyled is curiously con-
flicting; the unequal number of the short and long sta-
mens, their extreme variability, and especially the fact of
their pollen-grains not differing in size, are strongly op-
posed 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

168 HETEROSTYLED TRIMORPHIC PLANTS. CHAP. IV.

above-described anther of the Lagerstroemia ; we may there-
fore 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 Lagerstroemia, that in
Lythrum hyssopifolia, which is a homostyled species, some
of the shorter stamens vary in being either present or
absent, and that these stamens are altogether absent in
L. thymifolia. In another genus of the Lythracese, namely
Cuphea, three species raised by me from seed 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 pol-
len-grains ; so that they thus far resembled the stamens of
Lagerstrcemia. I found that Cuphea purpurea was highly
fertile with its own pollen when artificially aided, but
sterile when insects were excluded.*

OXALIS (GEBANIACE.E).

In 1863 Mr. Eoland 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-

* Mr. Spence informs me that some specimens of Mollia lepidota

in several species of the genus and speciosa from Kew, but could

Mollia (Tiliacese) which he col- not make out that their pistils

lected in South America, the differed in length in different

stamens of the five outer cohorts plants ; and in all those which

have purplish filaments and green I examined the stigma stood

pollen, whilst the stamens of the close beneath the uppermost

five inner cohorts have yellow anthers. The numerous stamens

pollen. He therefore suspected are graduated in length, and the

that these species might prove to pollen-grains from the longest and

be heterostyled and trimorphic : shortest ones did not present any

but he did not notice the length of marked difference in diameter,

the pistils. In the allied Luhea Therefore these species do not ap-

the outer purplish stamens are pear to be heterostyled.
destitute of anthers. I procured

CHAP. IV. OXALIS. 1C9

styled. In 1866 Professor Hildebrand proved,* by an
examination 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

Fig. 11.

Long-styled. Mid-styled. Short-styled.

OXALIS SPKCIOSA (with the petals removed).

B S S, stigmas. The dotted lines with arrows show which pollen must
be carried to the stigmas for legitimate fertilisation.

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 paperf 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 sali-
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

* ' Monatsber. der Akad. der forms at p. 42 of his ' Geschlechter-

Wiss. Berlin,' 1866, pp. 352, 372. VertheilunR.' &c., 1867.

He gives drawings of the three f 'Bot.Zeitung' 1871, pp. 416, 432.
13

170 HETEROSTYLED TRIMORPHIC PLANTS. CHAP. IV.

stamens in the two other forms. In the mid-styled
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-styled
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 : —

From the longest stamens of short-styled 8 to 9

mid-length " " 7 " 8

longest stamens of mid-styled 8

shortest " " 6

mid-length stamens of long-styled .... 7

shortest " 6

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.

CHAP. IV.

OXALIS VALDIVIANA.

171

TABLE 27.
Oxalis Valdiviana (from Hildebrand).

Cspsulei
produced.

Long-styled form, by pollen of longest)
stamens of short-styled. Legitimate f 28 28

union ,

Long-styled form, by pollen of longest)
stamens of mid-styled. Legitimate \ 21 21

union _

Long-styled form, by pollen of own and
own-form mid-length stamens. Illegiti- ^ 40
mate union ^

Long-styled form, by pollen of own and )
own-form shortest stamens. Illegiti- > 26 0

mate union J

Long-styled form, by pollen of shortest )
stamens of short-styled. Illegitimate > 16 1

union J

Long-styled form, by pollen of shortest)
stamens of mid-styled. Illegitimate > 9 0

union J

Mid-styled form, by pollen of mid-length
stamens of long-styled. Legitimate
union

Mid-styled form, by pollen of mid-length )
stamens of short-styled. Legitimate > 23 23

union J

Mid-styled form, by pollen of own and
own-form longest stamens. Illegitimate )• 52 0

union ,

Mid-styled form, by pollen of own and)
own-form shortest stamens. Illegitimate f 30 1

union

Mid-styled form, by pollen of shortest'
stamens of long-styled. Illegitimate }• 16 0

union . .

Mid-styled form, by pollen of longest sta-
mens of short-styled. Illegitimate
union

10

172 HETEROSTYLED TEIMORPHIC PLANTS. CHAP. TV.

TABLE 27 — continued.
Oxalis Valdiviana (from Hildebrand).

Number

Number

Number

Nature of Union.

Flowers
fertilised.

of
Capsules
produced.

of
Seeds per
Cap.uL

Short-styled form, by pollen of shortest]
stamens of long - styled. Legitimate >

18

18

11.0

union J

Short-styled form, by pollen of shortest]
stamens of mid - styled. Legitimate >

10

10

11.3

union J

Short-styled form, by pollen of own and ]
own-form longest stamens. Illegitimate >

21

0

0

Short-styled form, by pollen of own and]

own-form mid-length stamens. Illegiti- >

22

0

0

mate union J

Short-styled form, by pollen of longest]
stamens of mid - styled. Illegitimate >

4

0

0

union J

Short-styled form, by pollen of mid-length ]
stamens of long-styled. Illegitimate >•
union . . j

3

0

0

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 nets did not spon-
taneously 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 uncov-

CHAP. IV. OXALIS EEGNELLI. 173

ered 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,
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 papilla on its sur-
face included) is twice as large as that of the short-
styled, and that of the mid-styled intermediate in size.

174 HETEROSTYLED TRIMORPHIC PLANTS. CHAP. IV.

TABLE 28.
Oxalis JRegnelli (from Hildebrand).

Number

Number

Aver

N»ture of Union.

Flowers
fertilised.

of
Capsules
proceed.

Numbefof
S.>eds per
C»psule.

Long-styled form, by pollen of longest sta- 1
mens of short-styled. Legitimate union j

6

6

10.1

Long-styled form, by pollen of longest sta- I
mens of mid-styled. Legitimate union, j

5

5

10.6

Long-styled form, by pollen of own mid- }
length stamens. Illegitimate union . j

4

0

0

Long-styled form, by pollen of own short- )
est stamen. Illegitimate union . . . j

1

0

0

Mid-styled form, by pollen of mid-length ]

stamens of short-styled. Legitimate >

9

9

10.4

union J

Mid-styled form, by pollen of mid-length ]

stamens of long-styled. Legitimate >

10

10

10.1

Mid-styled form, by pollen of own longest )

stamens. Illegitimate union . . . . J

Mid-styled form, by pollen of own shortest I
stamens. Illegitimate union . . . . j

2

0

0

Mid-styled form, by pollen of longest sta- )
mens of short-styled. Illegitimate union j

1

0

0

Short-styled form, by pollen of shortest]
stamens of mid - styled. Legitimate >

9

9

10.6

Short-styled form, by pollen of shortest]
stamens of long - styled. Legitimate >

2

2

9.5

Short-styled form, by pollen of own mid- )
length stamens. Illegitimate union . j

12

0

0

Short-styled form, by pollen of own long- 1
est stamens. Illegitimate union . . . J

9

0

0

Short-styled form, by pollen of mid-length ]
stamens of long-styled. Illegitimate >

1

0

0

CHAP. IV.

OXALIS SPECIOSA.

175

The pollen-grains from the stamens in the three forms
are in their longer diameters as follows : —

Divisions of the

From the longest stamens of short-styled .
" mid-length "
" longest stamens of mid-styled .
" shortest " , .

" mid-length stamens of long-styled
" shortest " "

15 to 16
12 " 13

16
11 to 12

14

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.

TABLE 29.
Oxalis speciosa.

Number

Nnmber

Average

Nature of Union.

of

of

Number of

fertilised.

produced.

CapX

Long-styled form, by pollen of longest )
stamens of short-styled. Legitimate >

19

15

57.4

union J

Long-styled form, by pollen of longest)
stamens of mid-styled. Legitimate >

4

3

59.0

union J

Long-styled form, by pollen of own-form )
mid-length stamens. Illegitimate union )

9

2

42.5

Long-styled form, by pollen of own-form I
shortest stamens. Illegitimate union . j

11

0

0

Long-styled form, by pollen of shortest)

stamens of mid-styled. Illegitimate >

4

0

0

union . J

Long-styled form, by pollen of mid-length ~)
stamens of short-styled. Illegitimate >

12

5

30.0

union J

176 HETEROSTYLED TRIMORPH1C PLANTS. CHAP. IV.

TABLE 29 — continued.
Oxalis speciosa.

Nature of Union.

Number

JEss.

Number
of
Capsules
produced.

Average
Number of
Seeds per
CapsuTo.

Mid-styled form, by pollen of mid-length )
stamens of long-styled. Legitimate >

3

3

63.6

Mid-styled form, by pollen of mid-length )
stamens of short-styled. Legitimate >
union J

4

4

56.3

Mid-styled form, by mixed pollen from]
both own-form longest and shortest sta- >
mens. Illegitimate union j

9

2

19

Mid-styled form, by pollen of longest)
stamens of short-styled. Illegitimate >

12

1

8

Short-styled form, by pollen of shortest)
stamens of mid-styled. Legitimate >•

3

2

67

Short-styled form, by pollen of shortest)
stamens of long-styled. Legitimate >
union J

3

3

54.3

Short-styled form, by pollen of own-form )
longest stamens. Illegitimate union . J

5

1

8

Short-styled form, by pollen of own-form I
mid-length stamens. Illegitimate union j

3

0

0

Short-styled form, by both pollens mixed )
together, of own-form longest and mid- >
length stamens. Illegitimate union . J

13

0

0

Short-styled form, by pollen of longest)
stamens of mid-styled. Illegitimate >

7

0

0

Short-styled form, by pollen of mid-length )
stamens of long-styled. Illegitimate >
union J

10

1

54

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

CHAP. IV. OXALIS ROSEA. 177

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
many more seeds, and the illegitimately fertilised flow-
ers 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.
He has further shown that there is an analogous dif-
ference between the grains from the two sets of an-
thers 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 than 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

* ' Monatsber. der Akad. der Wiss. Berlin,' 1866, p. 372.

178 HETEROSTYLED TEIMORPHIC PLANTS. CHAP. IV.

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 0. 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,
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-fertilisation,
this is checked by the union being rendered more ster-
ile; 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 spontaneously a
few capsules, though extremely few compared 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 0. compressa with pollen from
their own two sets of stamens (the pollen-grains of
which differ in diameter as 100 to 83), and not one
produced a capsule. I formerly cultivated during
several years the short-styled form of a species pur-

CHAP. IV. OXALIS, OTHER SPECIES OF. 179

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, Hil-
debrand says that the short-styled form of 0. Deppei,
growing by itself, yields plenty of seed; but it is not
positively known that this species is heterostyled; and
the pollen-grains from the two sets of anthers do not
differ in diameter.

Some facts communicated to me by Fritz Miiller
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 Miiller 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

180 HETEROSTYLED TRIMORPHIC PLANTS. CHAP. IV.

any fruit on this species. The stamens in some of
the flowers are partially converted into petals. Fritz
Miiller, 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
form of some trimorphic species, perhaps accidentally
introduced into the district, which has since been
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 difference 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 pro-
ducing long-styled, mid-styled, and short-styled cleisto-
gamic flowers.

CHAP. IV. OXALIS, HOMOSTYLED SPECIES. 181

Homostyled Species of Oxalis. — Although the ma-
jority 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 0. aceto-
sella, and according to Hildebrand two other widely
distributed European species, 0. stricta and corniculata.
Fritz Miiller also informs me that a similarly consti-
tuted species is found in St. Catharina, and that it ia
quite fertile with its own pollen when insects are ex-
cluded. The stigmas of 0. stricta and of another homo-
styled species, viz. 0. tropceoloides, commonly stand on
a level with the upper anthers, and both these species
are likewise quite fertile when insects are excluded.

With respect to 0. 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 0. 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-

182 HETEROSTYLED TRIMORPHIC PLANTS. CHAP. IV.

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 plac-
ing pollen on the stigma, increases the fertility of the
flowers; and I found that this applied especially to
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 dioecious 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.

PONTEDEKIA [SP. ?] (PONTEDERIACE^) .

Fritz Miiller found this aquatic plant, which is al-
lied to the Liliaceae, 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 consid-
erably above the upper anthers of the same flower, and

* "Ueberden Trimorphisirms der Pontcderien," 'Jenaische Zeit-
schrift,' &c., Band 6, 1871, p. 74.

CHAP. IV. PONTEDERIA. 183

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 an-
thers 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 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 Miiller, 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

184: HETEROSTYLED TRIMORPHIC PLANTS. CHAP. IV.

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
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 Miiller, 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 Miiller 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

CHAP. IV. PONTEDEEIA. 185

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
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 : —

Long-styled form, from the mid-length stamens . . 13.2

(Average of 20 measurements.)
" " from the shortest stamens ... 9.0

(10 measurements.)
Mid-styled form, from the longest stamens .... 16.4

(15 measurements.)
" " from the shortest stamens ... 9.1

(20 measurements.)
Short-styled form, from the longest stamens .... 14.6

(20 measurements. )

" " 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;
14

186 HETEROSTYLED TRIMORPHIC PLANTS. CHAP. IV.

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
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 hve a case parallel
with that of the mid-styled form of Lytlirum 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 pre-
tend 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

* ' Bull, of the Torrey Botanical Club,' 1875, vol. vi. p. 62.

CHAP. IV. PONTEDERIA. 187

ones." On the other hand, he says that in all the
mature flowers, " the style was as long at least as
the longer stamens ; " " whilst in the young flowers it
was intermediate in length between the two sets of sta-
mens;" and if this be so, the species can hardly be
heterostyled.

188 ILLEGITIMATE OFFSPRING OF CHAP. V.

CHAPTER V.
ILLEGITIMATE OFFSPEINQ OF HETEKOSTYLED PLANTS.

Illegitimate 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 varieties 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 — Transmission 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 flow-
ers 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 fer-
tilised 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

CHAP. V. HETEROSTYLED TRIMORPHIC PLANTS. 189

short-styled form; so that the long-styled can be fer-
tilised 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 off-
spring.

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
illegitimate 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 fer-
tilised 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

190 ILLEGITIMATE OFFSPRING OF CHAP. V.

tried in 1863. The summer of 1864 was too hot and
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 pro-
duced by legitimate plants legitimately fertilised. 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 under-
stood that the extremes are so closely connected by
intermediate figures that the average is a fair one.
Large capsules were always selected for counting, in
order to avoid over-estimating the infertility of the sev-
eral 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

CHAP. V. HETEROSTYLED TRIMORPHIC PLANTS. 191

and naturally fertilised by other illegitimate plants,
contained on an average 44.2 seeds; whereas the
capsules on legitimate long-styled plants, legitimately
and naturally fertilised by other legitimate plants, con-
tained on an average 93 seeds. Therefore this illegiti-
mate plant yielded only 47 per cent, of the full and nor-
mal complement of seeds.

Standard Number of Seeds produced by Legitimate
Plants of the three Forms, when legitimately fer-
tilised.

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, 130;
maximum number observed out of thirty-one capsules,
151.

Short-styled form: average number of seeds, 83.5;
but we may, for the sake of brevity, say 83 ; maximum
number observed out of twenty-five capsules, 112.

CLASSES I. and II. Illegitimate Plants 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-
duct of the latter. These eight plants were much more
dwarfed, and much more sterile than those in the other

192 ILLEGITIMATE OFFSPRING OF CHAP. V.

two lots. The latter were raised from a long-styled
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 legiti-
mately 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
being 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

* Hildebrand first called atten- Primula Rinensis : but his results
tion ('Bot. Zeitimg.' Jan. 1, 1864, were not nearly so uniform as
p. 5) to this fact in the case of mine.

CHAP. V. HETEROSTYLED TRIMORPHIC PLANTS. 193

shrivelled or contained brown and tough, or pulpy
matter, without any good pollen-grains, and they never
shed their contents; they were in 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 the pollen-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 pro-
duct 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 re-
mote place close to a brother long-styled plant No. 2, so
that it must have been freely though illegitimately fertil-
ised; 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 in-
sects with its own pollen, yielded an immense number of
capsules, which contained on an average 21.5 seeds.

Plant 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 Xo. 1, by which it will have been illegit-
imately fertilised, it yielded in 1866 not a single capsule,
but in 1865 it yielded twenty-two capsules: the best of

* 'Beitriige zur Kenntniss der Befruchtung,' 1844, p. 116.

194 ILLEGITIMATE OFFSPRING OF CHAP. V.

these, fifteen in number, were examined; eight contained
no seed, and the remaining seven contained on an average
only three seeds, and these seeds were so small and shriv-
elled that I doubt whether they would have germinated.

Plants 3 and 4' These two long-styled plants, after be-
ing freely and legitimately fertilised during 1863 by the
game illegitimate 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. Dur-
ing 1864, 1865, and 1866, it was surrounded either by ille-
gitimate or legitimate plants of the other two forms; but
it did not yield a single capsule. It was a superfluous ex-
periment, but I likewise artificially fertilised in a legiti-
mate manner twelve flowers; but not one of these pro-
duced 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 sur-
rounded by illegitimate plants of various parentage, many
of which were highly fertile, and must thus have been legiti-
mately 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
39 per cent, of the full number of seeds. During 1864 it
was surrounded by legitimate and illegitimate plants of the
other two forms; and nine capsules (one poor one being re-
jected) 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 de-
scended from the long-styled form, almost certainly fer-
tilised with pollen from its own mid-length stamens,

CHAP. V. HETEROSTYLED TRIMORPHIC PLANTS. 195

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.

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 produced only 44 per cent, of the full comple-
ment of seeds.

Plant 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 86 and a minimum of 23. Hence the plant yielded 68
per cent, of the full complement 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 and a 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

196 ILLEGITIMATE OFFSPRING OF CHAP. V.

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 capsules was only 35.9 seeds, with a maximum of 60
and a 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 flow-
ered profusely, yet produced very few capsules; but these
contained numerous seeds. Ten capsules yielded an aver-
age of 71.9 seeds, with a maximum of 95 and a minimum of
29. Considering that this plant was illegitimate and ille-
gitimately fertilised by its brother long-styled seedlings,
the average and the maximum are so remarkably high that
I cannot at all understand the case. We should remember
that the average for a legitimate plant legitimately fertil-

CLASS III. Illegitimate Plants raised from a Short-
styled Parent fertilised with pollen from own-form
mid-length stamens.

I raised from this union nine plants, of which eight
were short-styled and one long-styled; so that there
seems to he 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 le-
gitimate 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 descended 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

CHAP. V. HETEROSTYLED TRIMORPHIC PLANTS. 197

this plant produced only 33 per cent, of the proper number
of seeds. The seeds themselves were small and irregular
in shape. Although so sterile on the female side, none
of the anthers were contabescent.

Plant 15. This short-styled plant, treated like the last
during the same year, yielded an average, from fifteen cap-
sules, of 27 seeds, with a maximum of 49 and a minimum
of 7. But two poor capsules may be rejected, and then the
average rises to 32.6, with the same maximum of 49 and
a minimum of 20; so that this plant attained 38 per cent,
of the normal standard of fertility, and was rather more
fertile than the last, yet many of the anthers were con-
tabescent.

Plant 16. This short-styled plant, treated like the two
last, yielded from ten capsules an average of 77.8 seeds,
with a maximum of 97 and a minimum of 60 ; so that this
plant produced 94 per cent, of the full number of seeds.

Plant 17. This, the one long-styled plant of the same
parentage as the last three plants, when freely and legiti-
mately fertilised 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 legiti-
mately fertilised with pollen from a legitimate short-styled
plant ; and nine capsules yielded an average of 82.5 seeds,
with a maximum of 98 and a 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.

CLASS 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

198 ILLEGITIMATE OFFSPRING OF CHAP. V.

full and normal height; the long-styled plant had sev-
eral of its anthers contabescent.

Plant 18. This mid-styled plant, when freely and legiti-
mately fertilised during 1865 by illegitimate plants de-
scended from self-fertilised long-, short-, and mid-styled
plants, yielded an average from ten capsules of 102.6 seeds,
with a maximum of 131 and a minimum of 63. Hence this
plant did not produce quite 80 per cent, of the normal num-
ber of seeds. Twelve flowers were artificially and legiti-
mately 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 fer-
tility, 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 aver-
age from ten capsules of 73.4 seeds, with a maximum of
87 and a minimum 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 cap-
sules with an average of 95.6 seeds ; so that the application
of pollen from a legitimate plant added, as in the two pre-
vious cases, to the fertility, but did not bring it up to the
proper standard.

Plant 20. This long-styled plant, of the same parent-
age with the two last mid-styled plants, and freely fer-
tilised in the same manner, yielded an average from ten
capsules of 69.6 seeds, with a maximum of 83 and a mini-
mum of 52. Hence this plant produced 75 per cent, of the
full number of seeds.

CLASS V. Illegitimate Plants raised from a Short-styled
Parent fertilised with pollen from the mid-length
stamens of the long-styled form. t

In the four previous classes, plarfts raised from the
three forms fertilised with pollen from either the longer
or shorter stamens of the same form, but generally not

CHAP. V. HETEROSTYLED TRIMORPHIC PLANTS. 199

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. From one of them, forming the pres-
ent Class V., twelve plants were raised; these con-
sisted of eight short-styled and four long-styled plants,
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 conta^-
bescent, 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; butt 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 legiti-
mately fertilised during 1865 by illegitimate plants, de-
scended from self-fertilised long-, mid-, and short-styled
parents, yielded an average from ten capsules of 43 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

200 ILLEGITIMATE OFFSPRING OF CHAP. V.

1866 it was freely and legitimately fertilised by other ille-
gitimate 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 seeds, with a maximum of 123 and a
minimum of 86 ; so that it produced 121 per cent, of seeds
in comparison with the normal standard. During 1864 it
was allowed to be freely and legitimately fertilised 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 cent, of seeds. In this
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 1864 been very hot and certainly unfa-
vourable to some of the plants of Lythrum.

Plant 28. 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 experiment, 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
legitmately 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 minimum of 24, thus attaining 59 per cent, of
the normal fertility. This low degree of fertility, I pre-
sume, was owing to the unfavourable 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.

Plant 25. The pollen of this long-styled plant contained
a moderate number of poor and shrivelled grains ; and this
is a surprising circumstance, as it yielded an extraordinary
number of seeds. During 1866 it was freely and legiti-

CHAP. V. HETEROSTYLED TRIMORPHIC PLANTS. 201

mately 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, pro-
ducing no less than 131 per cent, of seeds.

CLASS VI. Illegitimate Plants raised from Mid-styled
Parents fertilised with pollen from the shortest sta-
mens of the long-styled form.

I raised from this union twenty-five plants, which
proved to be seventeen long-styled and eight mid-
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 ap-
peared to be in this state. I counted the seeds in five
plants (Nos. 26 to 30), of which two were moderately
sterile and three fully fertile.

Plant 26. This mid-styled plant was freely and legiti-
mately fertilised, during the rather unfavourable year
1864, by numerous surrounding legitimate and illegitimate
plants. It yielded an average, from ten capsules of 83.5
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 mini-
mum 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.
15

202 ILLEGITIMATE OFFSPRING OF CHAP. V.

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 and a
minimum of 53, thus attaining to 76 per cent, of the normal
fertility. If the season had been more favourable, its fer-
tility would probably have been somewhat greater, but,
judging from the last experiment, only in a slight de-
gree.

Plant 28. This mid-styled plant, when legitimately fer-
tilised 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 mini-
mum of 69, thus producing 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.

Plant 29. This long-styled plant was legitimately fer-
tilised, 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 capsules (one poor
capsule having been excluded), of 100 seeds, with a maxi-
mum of 121 and a minimum of 77. This plant thus ex-
ceeded 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 SO. This long-styled plant was legitimately fer-
tilised during 1866 in the manner described under No. 26,
and yielded an average, from eight capsules, of 94 seeds,
with a maximum of 106 and a minimum of 66; so that it
exceeded the normal standard, yielding 101 per cent, of

Plant 31. Some flowers on this long-styled plant were
artificially and legitimately fertilised by one of its brother
illegitimate mid-styled plants ; and five capsules yielded an
average of 90.6 seeds, with a maximum of 97 and a mini-
mum of 79. Hence, as far as can be judged from so few
capsules, this plant attained, under these favourable cir-
cumstances, 98 per cent, of the normal standard.

CHAP. V. HETEROSTYLED TRIMORPHIC PLANTS. 203

CLASS VII. Illegitimate Plants raised from Mid-styled
Parents fertilised with pollen from the longest sta-
mens 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.
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 legiti-
mately fertilised, during the unfavourable year of 1864,
by numerous surrounding legitimate and illegitimate
plants. Eight capsules yielded an average of 127.2 seeds,
with a maximum of 144 and a minimum of 96; so that
this plant attained 98 per cent, of the normal standard.

Plant S3. 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
137 and a minimum of 90. Hence this plant produced no
less than 137 per cent, of seeds in comparison with the
normal standard.

Concluding Remarfcs 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-

204 ILLEGITIMATE OFFSPRING OF CHAP. V.

suits 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, as 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 (Classes 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-
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 VII.), 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

CHAP. V. HETEROSTYLED TRIMORPHIC PLANTS. 205

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 off-
spring, whether both, or one, or neither of the parents
are long-styled.

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 fertil-
ised, 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 following
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

* ' The Effects of Cross and Self-fertilisation in the Vegetable King-
dom,' 1876.

206

ILLEGITIMATE OFFSPRING OF CHAP. V.

TABLE 30.

Tabulated results of the fertility of the foregoing- illegiti-
mate plants, when legitimately fertilised, generally by
illegitimate plants, as described under each experiment.
Plants 11, 12, and 13 are excluded, as they were illegiti-
mately fertilised.

Normal Standard of Fertility of the three forms, when
legitimately and naturally fertilised.

Maximum

Form.

Number of
Seeds per
Capsule.

Number in
any one
Capsule.

Minimum Number in any one
Capsule.

Long-styled ....

93

159

-) No record was kept, as

Mid-styled ....

130

151

> all very poor capsules

Short-styled. . . .

83.5

112

J were rejected.

CLASSES I. and II. — Illegitimate Plants raised from
Long-styled Parents fertilised with pollen from own-
form mid-length or shortest stamens.

Number of Plant.

Form.

Average

Maximum

Minimum

Average Num-
ber of Seeds,
expressed as
the percentage
of the Normal
Standard.

Seeds per
Capsule.

any one
Capsule.

any one
Capsule.

ant 1

Long-styled

0

0

0

0

2

4.5

?

0

5

3

4.5

?

0

5

4

4.5

?

0

5

5

Oorl

2

0

Oorl

6

0

0

0

0

7

36.1

47

22

39

8

41.1

73

11

44

9

57.1

86

23

61

10

44.2

69

25

47

CLASS III. — Illegitimate Plants raised from Short-styled
Parents fertilised with pollen from own-form shortest
stamens.

Plant 14 .

Short-styled

28.3

51

11

33

" 15. ..

"

32.6

49

20

38

" 16 ...

M

77.8

97

60

94

' 17. ..

Long-styled

76.3

88

57

82 .

CHAP. V. HETEROSTYLED TRIMORPEIC PLANTS. 207

TABLE 30— continued.

CLASS IV. — Illegitimate Plants raised from Mid-styled
Parents fertilised with pollen from own-form longest
stamens.

Maximum

Minimum

Average Nnm-
ber cl Seeds,

Number of Plant

Form.

NumbeJof
Seeds ]>cr
Cap»ulo.

Number ia
SSS

Number in
any ena
Capiule.

ezprased a»
the j.crcen'ag«
oft_eNomiil

Plant 18 ...

Mid-styled.

102.6

131

63

80

" 19 ...

44

73.4

87

64

56

' 20 ...

Long-styled.

69.6

83

52

75

CLASS V. — Illegitimate Plants raised from Short-styled
Parents fertilised with pollen from the mid-length
stamens of the long-styled form.

Plant 21 ...

Short-styled

43.0

63

26

52

" 22 ...

"

100.5

123

86

121

" 23 ...

11

113.5

123

93

136

" 24. ..

Long-styled

82.0

120

67

88

" 25 ...

122.5

149

84

131

CLASS VI. — Illegitimate Plants raised from Mid-styled
Parents fertilised with pollen from the shortest sta-
mens of the long-styled form.

Plant 26

Mid-styled

86.0

109

61

66

' 27

"

99.4

122

53

76

' 28

"

89.0

119

69

68

' 29

Long-styled

100.0

121

11

107

' 30

"

94.0

106

66

101

' 31 ...

"

90.6

97

79

98

CLASS VII. — Illegitimate Plants raised from Mid-styled
Parents fertilised with pollen from the longest sta-
mens of the short-styled form.

Plant 32 .
" 33. ..

Mid-styled .
Short-styled

127.2
113.9

144
137

96
90

98
137

208 ILLEGITIMATE OFFSPRING OF CHAP. V.

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 Classes I. and II. were the offspring
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 Classes I.
and II. were almost certainly the product of pollen
from the mid-length stamens, and although very ster-
ile, 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, 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
included 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

CHAP. V; HETEROSTYLED TRIMORPHIC PLANTS. 209

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
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

210 ILLEGITIMATE OFFSPRING OF CHAP. V.

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
case 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
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 par-
ents 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,

CHAP. V. HETEROSTYLED TRIMORPHIC PLANTS. 211

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
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 sev-
eral foregoing conclusions will be apparent at the close
of this chapter, when the illegitimate unions between
the forms of the same species and their illegitimate off-
spring, are compared with the hybrid unions of dis-
tinct species and their hybrid offspring.

212 ILLEGITIMATE OFFSPRING OF CHAP. V.

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 an
illegitimate union resembles a hybrid one between
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
Oxalis Valdiviana. Hildebrand raised, as described in the
paper just referred to, 211 seedlings from all six legiti-
mate unions, and the three forms appeared among the off-
spring 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 con-
sisted 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 seed-
lings, 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 0. Regnelli, the result, as observed
by Hildebrand, was nearly the same, but more striking;
all the offspring from four of the legitimate unions con-
sisted of the two parent-forms, whilst amongst the seed-
lings from the other two legitimate unions the third form
appeared. Thus, of the 35 seedlings from the six legiti-
mate unions, 35 belonged to the same two forms as their
parents, and only 8 to the third form. Fritz Miiller also
raised in Brazil seedlings from long-styled plants of 0.
Regnelli legitimately fertilised with pollen from the long-
est stamens of the mid-styled form, and all these belonged
to the two parent-forms, f Lastly, seedlings were raised
by me from long-styled plants of 0. speciosa legitimately

*'Bot. Zeitung,' 1871, p. 433, t '.Tenaische Zeitsclirift ' &c.,
footnote. Band vi., 1871, p. 75.

CHAP.V. HETEROSTYLED DIMORPHIC PLANTS. 213

fertilised by the short-styled form, and from the latter
reciprocally fertilised by the long-styled; and these con-
sisted of 33 long-styled and 26 short-styled plants with not
one mid-styled form. There can, therefore, 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 occasion-
ally make their appearence; and this latter fact, as Hilde-
brand remarks, may be attributed to atavism, as some of
their progenitors will almost certainly have belonged to the
third form.

When, however, any form of Oxalis is fertilised illegiti-
mately with pollen from the same form, the seedlings ap-
pear to belong invariably to this form. Thus Hildebrand
states * that long-styled plants of 0. rosea growing by
themselves have been 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
0. hedysaroides growing by themselves, and these were all
mid-styled. So that the forms of Oxalis, when illegiti-
mately fertilised with their own pollen, behave like the
long-styled form of Lythrum salicaria, which when thus
fertilised 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-

* ' Ueber den Trimorphismus in Berlin.' 21st June, 1866, p. 373;
der Gattung Oxalis: Monats- and 'Bot. Zeitung,' 1871, p. 435.
berichte der Akad. der Wissen. zu

214 ILLEGITIMATE OFFSPRING OF CHAP. V.

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 re-
sults differ much during successive years, and the
seeds vary so greatly in size that it is hard to 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 gener-
ations 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 3?ellow
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

CHAP. V. HETEROSTYLED DIMORPHIC PLANTS. 215

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-
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,
I 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 possi-
ble maximum of 74 seeds; so that these illegitimate
plants were sterile when legitimately crossed.

I succeeded in raising from the above seven short-

216 ILLEGITIMATE OFFSPRING OF CHAP. V.

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
lived and flowered were short-styled; and twelve 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 nor-
mal average for legitimate short-styled plants legiti-
mately 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

CHAP. V. HETEROSTYLED DIMORPHIC PLANTS. 217

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, Constitu-
tion, and Fertility of the Illegitimate Offspring of Pri-
mula Sinensis. — In regard to the long-styled plants,
their 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

* Dr. Hildebrand, who first short-styled. From a short-styled

called attention to this suhject plant illegitimately fertilised with

(' Bot. Zeitung,' 1864, p. 5), raised its own pollon he raised fourteen

from a similar illegitimate union plants, of which eleven were short-

seventeen plants, of which four- styled and three long-styled,
teen were long-styled and three
16

218 ILLEGITIMATE OFFSPRING OF CHAP. V.

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 Sincnsis, the children of such
incestuous marriages, if they continued to marry in-
cestuously, would have their sterility only slightly in-
creased; 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 vari-
ation 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 observing, in 1862, a long-styled plant, de-
scended from a self -fertilised long-styled plant, 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 stig-
mas 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 be-
tween 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 average 43 seeds ; and
this number shows that the flowers had become abnormally
fertile in comparison with those of ordinary long-styled

CHAP. V. HETEROSTYLED DIMORPHIC PLANTS. 219

TABLE 31.
Primula Sinensis.

Name of Owner or Place.

Lolled

Short-styled
Form.

•vasr

Mr Horwood

o

o

17

Mr Duck

20

o

9

Baston

30

18

15

12

g

2

Holwood

42

12

0

High Elms

16

0

0

1

5

o

My own plants from purchased seeds

13

7

0

Total

134

51

43

plants when self -fertilised. I was thus led to examine 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 I infer
from the analogy of the other heterostyled species of
Primula, and from having raised the two forms of the pres-
ent species in exactly the same number from flowers which
had been legitimately 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 gardeners gener-
ally 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 gen-
erally reproduce long-styled offspring. From the con-
sideration of this table, it occurred to me in the year 1862,
that almost all the plants of the Chinese primrose culti-
vated in England would sooner 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-char-
acterised equal-styled plants, but with not one short-styled.

With respect to the equal-styled plants in the table,

220 ILLEGITIMATE OFFSPRING OF CHAP. V.

Mr. Horwood raised from purchased seeds four plants,
which he remembered 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 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-styled plants at Southampton; and
in both of them the grains differed extremely in size in
the same anthers, a large number being small and shriv-
elled, whilst many were fully as large as those of the short-
style 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 mon-
strosity; 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 pro-
jected most, the grains were in diameter to those in the
other plant, in which the stigma projected less, as 100 to
88; whereas the difference between the grains from per-
fectly characterised long-styled and short-styled plants is
as 100 to 57. So that these two plants were in an inter-
mediate condition. To return to the 17 plants in the first
line of Table 31 : from the relative position of their stig-
mas and anthers, they could hardly fail to fertilise them-
selves : and accordingly 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

CHAP. V. HETEROSTYLED DIMORPHIC PLANTS. 221

thirty other capsules, taken by hazard, of which twenty-
seven contained good seeds, averaging 35.5, with a maxi-
mum of 70; but if six poor capsules, each with less than
13 seeds, be excluded, the average rises to 42.5. These are
higher numbers than could be expected from either well-
characterised form if self-f ertilised ; and this high degree
of fertility accords with the view that the male organs be-
longed to one form, and the female organs partially 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 self -fertilised
equal-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 be-
lieved 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 astonishing 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 fertility
— unless, indeed, their high fertility may be accounted for
by the stigmas receiving pollen from the circumjacent an-
thers 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 ob-
served, and this produced nine equal-styled and twenty
long-styled plants. The equal-styled resembled in all re-
spects those previously described; and eight of their cap-
sules spontaneously self -fertilised contained on an average
44.4 seeds, with a maximum of 61 and a minimum of 23.

222 ILLEGITIMATE OFFSPRING OF CHAP. V.

In regard to the twenty long-styled plants, the pistil in
some of the flowers did not project quite so high as in ordi-
nary long-styled flowers ; and the stigmas, though properly
elongated, were smooth, so that we have here a slight ap-
proach 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 produced 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, con-
tained 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 be-
longing 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 de-
scended from two distinct stocks. The latter were derived
from a single plant, which the gardener is positive was
not long-styled ; hence probably it was equal-styled. In all
these fifteen plants the anthers occupying the same posi-
tion as in the long-styled form, closely surrounded the stig-
ma, which in one instance alone was slightly elongated.
Notwithstanding this position of the stigma, the flowers,
as the gardener assured me, did not yield many seeds ; and
this difference from the foregoing cases may perhaps have
been caused by the pollen being bad, as in some of the
Southampton 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 Ly thrum
and Oxalis, is clear ; for we have seen its first appearance

CHAP. V. HETEROSTYLED DIMORPHIC PLANTS. 223

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-
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 sur-
rounded 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 in-
creased length of the stamens, instead of, as with 'P. Sinen-
sis, 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

* ' Journal Proc. Linn. Soc.,' viii. (1864), p. 91.

224: ILLEGITIMATE OFFSPRING OF CHAP. V.

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 Scotland, 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 re-
produce the same form in so large a proportion as in the
case of P. Sinensis, We may further infer 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 ac-
cordance with this view, they yield less 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 occasion-
ally found on this species whilst growing in a state of

' Journal Proc. Linn. Soc.,' viii. (1864), p. 115.

CHAP. V. HETEROSTYLED DIMORPHIC PLANTS. 225

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. acaulls of Linn, and P. acaulis of Jacq.

Var. rubra. — Mr. Scott states * that this variety,
which grew in the Botanic Garden in Edinburgh, was
quite sterile when fertilised with pollen from the com-
mon primrose, as well as from a white variety of the
same species, but that some of the plants, when arti-
ficially fertilised with their own pollen, yielded a moder-
ate 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 two 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

* 'Journal Proc. Linn. Soc.,' viii. (1864), p.

226 ILLEGITIMATE OFFSPRING OF CHAP. V.

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.
In this last case we have an instance of reversion in
colour, without the possibility of any cross, to the grand-
parents or more distinct 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 opposite
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

CHAP. V. HETEROSTYLED DIMORPHIC PLANTS. 227

TABLE 32.
Primula vulgaris.

4

J

1|

Li

if

Nature of Plant experimented on, and
kind of Union.

If

tf

fc"f

|l!

w

12 f

t!

3

<!

1 =

1 *

Purple- and yellow-flowered ille-1

gitimate long-styled plants, ille- 1
gltimately fertilised with pollen |

72

11

11.5

26

5

from the same plant . . . . J

Purple- and yellow-flowered ille-

gitimate long-styled plants, ille-
gitimately fertilised Avith pollen

72

39

31.4

62

3

from the common long-styled

Or, if the ten poorest capsules, '
including less than 15 seeds, be

72

29

40.6

62

18

rejected, we get

Purple- and yellow-flowered ille-

gitimate long-styled plants, le-
gitimately fertilised with pollen
from the common short-styled

26

18

36.4

60

9

primrose

Or, if the two poorest capsules,

including less than 15 seeds, be

26

16

41.2

60

15

rejected, we get

The long-styled form of the com-

mon primrose, illegitimately ferti-
lised with pollen from the long-
styled illegitimate purple- and

20

14

15.4

46

1

yellow-flowered plants ....

Or. if the three poorest capsules

20

11

18 9

46

8

be rejected, we get

The short-stvled form of the com-

mon primrose, legitimately ferti-
lised with pollen from the long-

10

6

30.5

61

6

styled illegitimate purple- and

yellow-flowered plants .....

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.

228 ILLEGITIMATE OFFSPRING OF CHAP. V.

When these plants were illegitimately and legiti-
mately fertilised with pollen from the common prim-
rose, the average numbers were increased, but Avere 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 in a 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
primrose produces a considerable number of capsules.
There can, therefore, be no doubt that the fertility of
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
illegitimately fertilised with the same pollen. ISTow 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.

CHAP. V. HETEKOSTYLED DIMORPHIC PLANTS. 229

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,
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 heing 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 illegiti-
mately fertilised long-styled cowslips, and these con-
sisted 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 fertility

230 ILLEGITIMATE OFFSPRING OF CHAP. V.

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 ille-
gitimately, the number varied so greatly during suc-
cessive 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 num-
ber of fertilised flowers which produce capsules con-
taining any seed.

First, for the one illegitimate short-styled plant.
In the course of three seasons 27 flowers were illegiti-
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

CHAP. V. HETEROSTYLED DIMORPHIC PLANTS. 231

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, con-
taining 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
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-

232 ILLEGITIMATE OFFSPRING OF CHAP. V.

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
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 legitimately fer-
tilised with pollen from a legitimate plant, and this in-
creased 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,

CHAP.V. HETEROSTYLED DIMORPHIC PLANTS. 233

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-
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 produced
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
17

234 ILLEGITIMATE OFFSPRING OF CHAP. V.

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
row of these plants of the fourth illegitimate genera-
tion, thus freely exposed and legitimately fertilised, pro-
duced 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 un-
healthy, whilst 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

* For full details of this experiment, see my ' Effects of Cross and
Self-fertilisation,' 1876, p. 220.

CHAP. V. HETEROSTYLED DIMORPHIC PLANTS. 235

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 capsules,
compared with those produced by the surrounding legiti-
mate plants, in the ratio only of 5 to 100 ! It is there-
fore certain that illegitimate fertilisation, continued
during successive generations, affects the powers of
growth and fertility of P. veris to an extraordinary de-
gree; more especially when the plants are exposed to
ordinary conditions of life, instead of being protected in
a greenhouse.

Equal-styled red variety of P. veris. — Mr. Scott has
described* a plant of this kind growing in the Botanic Gar-
den of Edinburgh. He states that it was highly self -fertile,
although insects 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 resembles 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 fur-
ther states that this variety yielded very few seeds when
fertilised by either the long- or short-styled common cow-
slip, and, again, that both forms of the latter, when fer-
tilised 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 com-
mon 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

'Proc. Linn. Soc.' vol. viii. (1864), p. 105.

236 ILLEGITIMATE OFFSPRING OF CHAP. V.

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
function. 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 appar-
ently short-styled seedlings were similarly treated, nearly
all produced a great abundance of capsules, containing
numerous seeds, which germinated remarkably 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 with a few shrivelled grains. In function
this pollen was identical with that of the short-styled cow-
slip; for ten long-styled flowers of the common cowslip,
legitimately fertilised with pollen from a true equal-styled
variety, produced six capsules, containing on an average
34.4 seeds; whilst seven capsules on a short-styled cowslip
illegitimately 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 maxi-
mum 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

CHAP. V. HETEROSTYLED DIMORPHIC PLANTS. £37

than might have been expected. Secondly, nine capsules
from another equal-styled plant, which had not been pro-
tected from insects, but probably was self -fertilised, gave
an average of 45.2 seeds, with a maximum of 58. Thirdly,
another plant which had a very short pistil in 1865, pro-
duced spontaneously many capsules, six of which con-
tained 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 resem-
bled that of the long-styled form. In this condition it pro-
duced 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 aver-
age as before, viz. 35.1 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 cowslip (this being an illegitimate union), and pro-
duced seven capsules containing an average of 24.4 seeds,
with a maximum of 32. 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 30. Sixteen flowers were ferti-
lised with pollen from a long-styled cowslip, and produced
12 capsules, 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, con-
taining 18 and 23 seeds. Hence this plant, in function and
partially in structure, was in an almost exactly intenne-

238 ILLEGITIMATE OFFSPRING OF CHAP. V.

diate 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 spon-
taneously self -fertilised.

The foregoing five plants thus differ much from one an-
other 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, legiti-
mately fertilised, I once obtained from plants cultivated
in the greenhouse 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 self-ferti-
lised, gave averages of 44 and 45 seeds; but this high fer-
tility may perhaps be in part attributed to the stigma re-
ceiving 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 an almost exactly intermediate
condition in its female organs between the long- and short-
styled forms, and consequently, when self-fertilised,
yielded a lower 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 ex-
actly the same number as the parent-plant yielded in Edin-
burgh. Thirty-four flowers, fertilised with pollen from
the short-styled cowslip (and this is an analogous union),
produced 17 capsules, containing an average of 33.8 seeds.
It is a rather singular circumstance, for which I cannot
account, that 20 flowers, artificially fertilised on one occa-

CHAP.V. HETEROSTYLED DIMORPHIC PLANTS. 239

sion 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
seedlings were raised from one of the red-flowered, strictly
equal-styled, self -fertilised plants descended from the simi-
larly characterised Edinburgh plant. These 72 plants were
therefore 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. officinalis from a garden where the long-styled form
alone grew, 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 belong-
ing 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

' Bot. Zeitung,' 1865, p. 13.

24:0 ILLEGITIMATE OFFSPRING OF CHAP. V.

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.
officinalis, were fertile with their own pollen in a quite re-
markable degree for a heterostyled plant. From seeds care-
fully self-fertilised I raised 18 plants, of which 13 proved
short-styled and 5 long-styled.

POLYGONUM FAGOPYRUM.

From flowers on long-styled plants fertilised illegiti-
mately 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 consisted of 20 short-styled and 13
long-styled. So that the usual rule of illegitimately fer-
tilised 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 pro-
duct of a cross between distinct plants.

Concluding Remarks on the Illegitimate Offspring of
Heterostyled Trimorphic and Dimorphic Plants.

It is remarkable how closely and in how many points
illegitimate unions between the two or three forms of the
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

CHAP.V. HETEROSTYLED PLANTS. 241

slightly1 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 inter se or by another ille-
gitimate plant. When two species are crossed and
they produced numerous seeds, we expect as a general
rule that their hybrid offspring will be moderately
fertile; but if the parent species produced extremely
few seeds, we expect that the hybrids will be very
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

* This has been remarked by chapter a striking illustration in

many experimentalists in effect- the case of Primula veri*.

ing crosses between distinct spe- f ' Die Bastard befruchtung im

cies ; and in regard to illegitimate Pflanzenreich,' 1865.
unions I have given in the first

242 ILLEGITIMATE OFFSPRING OF CHAP. V.

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 an-
other plant of the same form, and twenty-four hours
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 seedlings
thus raised bore flowers more or less red, showing plainly

CHAP. V. HETEROSTYLED PLANTS. 243

how prepotent the legitimate pollen from a short-styled
plant was over the illegitimate poilen 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 that
of their illegitimate offspring, must depend exclusively
on the nature of the sexual elements and on their in-
compatibility for uniting in a particular 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

244 ILLEGITIMATE OFFSPRING. CHAP. V.

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 detecting any
differences sufficient to account for certain species cross-
ing 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 conclusion 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 ele-
ments, 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 con-
clusion is independently and strongly fortified by the
consideration of the illegitimate unions of trimorphic
and dimorphic heterostyled plants. In so complex and
obscure a subject as hybridism it is no slight gain to
arrive at a definite conclusion, namely, that we must
look exclusively to functional differences in the sexual
elements, as the cause of the sterility of species when first
crossed and of their hybrid offspring. It was this con-
sideration which led me to make the many observations
recorded in this chapter, and which in my opinion make
them worthy of publication.

CHAP. VI. REMARKS ON HETEROSTYLED PLANTS. 245

CHAPTER VI.
CONCLUDING EEMAEKS ON HETEROSTYLED PLANTS.

The essential character of heterostyled plants— Summary of the differ-
ences 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 in-
clude 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.

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, &c. ;
and so it is with many hermaphrodite animals, for
instance, land-snails or earth-worms; but in all these
cases any one individual can fully fertilise or be ferti-

* Asa Gray, 'American Journ. elsewhere as already referred to.
of Science,' 1865, p. 101; and Kuhn, 'Bot. Zeitung,' 1867. p. 67.

246 CONCLUDING REMARKS CHAP. VI.

lised by any other individual of the same species. This
is not so with heterostyled plants; a long-styled, mid-
styled or short-styled plant cannot fully fertilise or
be fertilised by any 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 dioecious
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 ab-
solutely 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 com-
plete 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 (33) 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

CHAP. VI. ON HETEROSTYLED PLANTS.

247

TABLE 33.

Fertility of the Legitimate Unions taken together, com-
pared with that of the Illegitimate Unions together.
The fertility of the Legitimate Unions, as judged by
both standards, is taken as 100.

of Species.

Illegitimate Unions.

Primula veris

P. elatior

P. vulgaris

P. Sinensis

P. Sinensis (second trial)

P. Sinensis (Hildebrand)

P. auricula (Scott)

P. Sikkhnensis "

P. cortusoides "

P. involuerata "

P. farinosa

Average of the nine species of Primula . .

Hottonia palustris (H. Muller)

Linum grandiflorum (the difference probably I

is much greater) J

L. perenne

L. perenne (Hildebrand)

Pulmonaria officinalis (German stock, Hilde- I

brand) J

Pulmonaria angustifolia

Mitchella repens

Borreria, Brazilian sp

Polygonum fagopyrum

Lythrum salicaria

Oxalis Valdiviana (Hildebrand)

O. Kegnelli

O. speciosa

27

60
84
0

100
80
95
74
72
71
88.4

the two sexes of dioecious plants. NOT 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
the corolla, and in Pontederia in its colour. In the re-

248 CONCLUDING REMARKS CHAP. VI.

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 smooth.

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 papillae; 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
seeds produced by the two or three forms often differ

CHAP. VI. ON HETEROSTYLED PLANTS. 249

in number, and sometimes in size and weight; thus,
five seeds from the long-styled form of Lytlirum 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 flow-
ers, and these set a larger proportional number of fruit,
which however yield a lower average number of seed,
than the long-styled plants. With heterostyled plants
we thus see in how many and in what important char-
acters the forms of the same undoubted species often
differ from one another — characters which with ordinary
plants would be amply sufficient to distinguish 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-five 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, when-
ever there is any difference between them. The diam-
eter 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,
and we should bear in mind that in the case of
18

250

CONCLUDING REMARKS

CHAP. VI.

TABLE 34.

Relative Diameter of the Pollen-grains from the forms
of the same Heterostyled Species; those from the
short-styled form being represented by 100.

Dimorphic Species.

Primula veris 67

" vulgaris .... 71
" Sinensis (Hilde-
brand) .... 57
" auricula .... 71
Hottonia palustris (H. Miil-
ler) 61

Hottonia palustris (self) . 64

J .i ii u in grandiflorum . . . 100

" perenne (diameter i

variable) . . j 100(?)

" flavum 100

Pulmonaria offlcinalis . . 78

" angustifolia . 91

Polygonum fagopyrum . . 82

Leucosmia Burnettiana . 99

JEgiphila elata 62

Menyanthes trifoliata . . 84
Limnanthemum Indicum . 100
Villarsia (sp. ?) .... 75

From the Long*-
ttyled form.

Forsythia suspensa ... 94

Cordia(sp. ?) 100

Gilia pulchella 100

" micrantha 81

Sethia acuminata .... 83

Erythroxyluin (sp. ?) . . . 93

Cratoxylon forrnosum . . 86
Mitehella repens, pollen-
grains of the long-styled a
little smaller.

Borreria (sp. ?) 92

Faramea (sp. ?) 67

Sutcria (sp. ?) (Fritz Miiller) 75

Houstonia ccerulca .... 72

Oldenlandia (sp. ?) . ... 78

Hedyotis (sp. ?) 88

Coccocypselum (sp. ?) (F. >

Miiller) } 1(

Lipostoma (sp. ?).... 80

Cinchona micrantha ... 91

Trimorphic Species.

Ratio eTTrewiinjr the extreme differences In diame-
ter of the pollen-brains from the two sets of
anthers in the three formi.

Lythrum salicaria .... 60

Nessea verticillata .... 65

OxalisValdiviana(Hildebrand) 71

" Eegnelli 78

' speciosa 69

" sensitiva 84

Pontederia (sp. ?) 55

Ratio between the diameters of the pollen-
prams of the two sets of anthers in the same
form.

Oxalis rosea, long-styled form )

(Hildebrand) . . . J 83
' compressa, short-styled i

form I

Pontederia (sp. ?) short-styled j

form | 87

" other sp., mid-styled i
form .

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,

CHAP. VI. ON HETEEOSTYLED PLANTS. 251

there is no exception to the rule that those from the
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 class 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 deter-
mined by the length of the pistil, down which the
tubes have to grow. That with plants in general there
is no close relationship between the size of the pollen-

* 'Sull' Opera, la Distribuzione dei Sessi nelle Piante,' &c., 1867,
p. 17.

252 CONCLUDING REMARKS CHAP. VI.

grains and the length of the pistil is manifest; for
instance, I found that the distended 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 Polygonum fagopyrum
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.

Notwithstanding 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. It is hardly possible to doubt that this
must occur in such cases as that of the Datura, in
which the tubes have to grow down the whole length
of the pistil, and therefore to a length equalling 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 spe-
cies from matter yielded by the pistil, we can see that
in the former case it would be necessary that the grains

CHAP. VI. ON HETEROSTYLED PLANTS. 253

of the two forms should differ in size relatively tq 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 expla-
nation can be considered satisfactory 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 Lvmnan-
themum Indicum 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 an-
gustifolia they vary much in size, but from an aver-
age of seven measurements of each kind the ratio
is as 100 to 91. In six genera of the Eubiaceae 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 difference
in the length of the stamens in the two forms of
Forsythia suspensa and of Unum flavum; but in these
two cases the anthers of the short-styled flowers are
shorter than those of the long-styled. The relative
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

254 CONCLUDING REMARKS CHAP. VI.

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 on a 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-styled form
are likewise somewhat longer and narrower; and in
the three forms of Oxalis 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
papilla? on the stigma of the long-styled form are longer

CHAP. VI. ON HETEROSTYLED PLANTS. 255

and often thicker than those on that of the short-
styled. For instance, the papillae 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 Houstonia ccerulea, in which the
stigmas are much shorter and stouter in the long-
styled than in the short-styled form, for the papillae
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 Linum grandiflorum varies
much, and the stigmatic papillae vary in a corre-
sponding manner. From this fact I inferred at first
that in all cases the difference in length between the
stigmatic papillaB 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 papillae.
It is a more probable view that the papilla?, which ren-
der the stigma of the long-styled form of various species
rough, serve to entangle effectually the large-sized pol-
len-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 papillaa 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 distributed,
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 di-
vided by Bentham and Hooker.

256

CONCLUDING REMARKS

CHAP. VI.

TABLE 35.
List of Genera including Heterostyled Species.

DlCOT

FLEDONS.

DICOTYLEDONS.

Cratoxylon.

Hypericinese.

Mitchella. Eubiacese.

Erythroxylum.

Erytnroxylese.

Diodia.

Sethia.

"

Borreria.

Linum.

Geraniacese.

Spermacoce.

Oxalis.

"

Primula. Primulacese.

Lythrum.

Lythracero.

Hottonia.

Nessea.

"

Androsace.

Cinchona.

Rubiaceae.

Forsythia. Oleaceae.

Bouvardia.

1

Menyanthes. Gentianacese.

Manettia.

'

Limnantlicmiiin. "

Hedyotis.

1

Villarsia.

Oldenlandia.

1

Gilia. Polemoniacea

Houstonia.

'

Cordia. Cordieae.

Coccocypselum.

1

Pulmonaria. Boragineae.

Lipostoma.

1

^Egiphila. Verbenaceae.

Knoxia.

4

Polygonum. Polygonese.

Faramea.

1

Thynielea. Tkymelese.

Psychotria.
Eudgea.

.

MONOCOTYLEDONS.

Suteria.

"

Pontederia. Pontederiaces

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 spe-
cies 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 Menyanthese and the several trimorphic species of
Oxalis must have inherited their structure from a

CHAP. VI. ON HETEROSTYLED PLANTS. 257

common 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
spread from a single centre to such widely remote and
separated areas. The family of the Rubiaceae contains
not far short of as many heterostyled genera as all the
other thirteen families together ; and hereafter no doubt
other Eubiaceous genera will be found to be hetero-
styled, although a large majority are homostyled. Sev-
eral 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 het-
erostyled 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 Boraginese and Verbenaceae, 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 charac-
terised. We may suspect that it has become hetero-
styled 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 yield-
ing a considerable number of spontaneously self-ferti-
lised seeds. Polygonum in possessing only a single het-
erostyled species is an extreme case; but every other
genus of considerable size which includes some such
species likewise contains homostyled species. Lyth-
rum includes trimorphic, dimorphic, and homostyled
species.

258 CONCLUDING REMARKS CHAP. VI.

Trees, bushes, and herbaceous plants, both large
and small, bearing single flowers or flowers in dense
spikes or heads, have been rendered heterostyled. 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 dioecious ; but I was soon forced
to relinquish 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 evident-
ly come under the same category with dimorphic, and
the former cannot be looked at as tending to become
dioecious. 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. This is shown by the large

* Out of the 38 genera known contain species inhabiting the
to include heterostyled species, just-specified stations. So that 43
about eight, or 21 per cent., are per cent, of those British plants
more or less aquatic in their which have their sexes separated
habits. I was at first struck with are more or less aquatic in their
this fact, for I was not then aware habits, whereas only 21 per cent,
how large a proportion of ordinary of heterostyled plants have such
plants inhabit such stations. Het- habits. I may add that the her-
erostyled plants may be said in maphrodite classes, from Monan-
one sense to have their sexes sepa- dria to Gynandria inclusive, con-
rated, as the forms must mutually tain 447 genera, of which 113 are
fertilise one another. Therefore aquatic in the above sense, or only
it seemed worth while to ascertain 25 per cent. It thus appears, as
what proportion of the genera in far as can be judged from such
the Linnean classes Monoecia, imperfect data, that there is some
Dicecia and Polygamia, contained connection between the separation
species which live "in water, of the sexes in plants and the
marshes, bogs or watery places." watery nature of the sites which
In Sir W. J. Hooker's ' British they inhabit ; but that this does
Flora ' (4th edit. 1838") these three not hold good with heterostyled
Linnean classes include 40 genera, species.
17 of which (i.e. 43 per cent.)

CHAP. VI. ON HETEROSTYLED PLANTS. 259

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 cor-
responding 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 dioecious, 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 had passed, and on
the more or less complete inheritance of the successive
adaptations of each part to the surrounding conditions.
Plants which are already well adapted by the structure

260 CONCLUDING REMARKS CHAP. VI.

of their flowers for cross-fertilisation by the aid of in-
sects 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 Leguminosse, Labiatse, Scrophulariaceas, Orchideae,
&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 large
number of seeds, and this obviously is a very common
case, heterostyled will have an advantage over dioecious
plants, as all the individuals of the former, whilst

* ' The Effects of Cross and Self-fertilisation,' 1876, p. 441.

CHAP. VI. ON HETEROSTYLED PLANTS. 261

only half of the latter, that is the females, yield
seeds. On the other hand, heterostyled plants seem to
have no advantage, as far as cross-fertilisation is con-
cerned, over those which are sterile with their own pol-
len. 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 he the case with heterostyled di-
morphic plants, unless they chance to belong to opposite
forms.

It may be added that species which are trimorphic
have 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 vigor-
ous 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 belonging to the
same form; and in this case they will legitimately fer-
tilise one another, and yield the full complement of vig-
orous 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
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
Rubiaceae they are dispersed in eight of the tribes. "We
may therefore conclude that this structure has been ac-

262 CONCLUDING REMARKS CHAP. VI.

quired 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 specta-
~bilis 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 Oxalis acetosella and various other plants.
I have also noticed an extraordinary amount of differ-
ence in the length of the pistil in cultivated 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 might 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 thus varied, it would never
have been rendered heterostyled, as this state would
then have been superfluous. But the parent-species of
our several existing heterostyled plants may have been,
and probably were (judging from their present consti-
tution) in some degree self-sterile ; and this would have
made regular cross-fertilisation still more desirable.

CHAP. VI. ON HETEROSTYLED PLANTS. 263

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 balancement (which
is admitted by many botanists) would tend to cause the
pistil to be reduced in those individuals in which the
stamens were greatly developed and to be increased in
length in those which had their stamens but little de-
veloped.

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

264 CONCLUDING REMARKS CHAP. VI.

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 originated.
A completely self-sterile plant or a dichogamous 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 can-
not fully fertilise or be fertilised by an individual of
the same form, but only by one belonging to another
form.

H. Miiller 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
manner will be nearly or completely lost. He was led
to this view by observing that Diptera frequently car-
ried pollen from the long-styled flowers of Hottonia to
the stigma of the same form, and that this illegitimate
union was not nearly so sterile as the corresponding
union in other heterostyled species. But this conclu-
sion 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

* ' Die Befruchtung der Blumen,' p. 352.

CHAP. VI. OX HETEROSTYLED PLANTS. 265

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 different. 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
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 acquire-
ment, 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
19

266 CONCLUDING REMARKS CHAP. VI.

the short-styled; but this is hardly ever the case. On
the contrary, there is sometimes the widest differ-
ence in this respect, as between the two illegitimate
unions of Pulmonaria angustifolia and of Hottonia pa-
lustris.

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
acquired, and must be the incidental result of differ-
ences in their vegetative systems. But how the sex-
ual elements of heterostyled plants came to differ from
what they were whilst the species was homostyled,
and how they became co-adapted in two sets of indi-
viduals, 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, the anthers
in size, and the pollen-grains in diameter. It ap-
pears, 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 sta-
mens of the trimorphic species of Lythrum and Oxalis,
the products of which are united for reproduction, by
so much the greater is the infertility of the union.
The same rule applies to the two illegitimate unions

CHAP. VI. ON HETEROSTYLED PLANTS. 267

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 diffi-
culty of understanding the nature and origin of the
co-adaptation between the reproductive organs of the
two forms of heterostyled plants, by considering 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 inorganic 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, Am-
sinckia 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 ex-
traordinary degree in the length of their pistils during
successive seasons; nevertheless they yielded during
these seasons exactly 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 appar-

268 CONCLUDING REMARKS CHAP. VI.

ently 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
the irreproductive 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. I have
elsewhere shown f that the sterility of species when
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 heterostyled plants and
of crossing distinct species. The great difference in the
degree of sterility between the various heterostyled spe-

* Gartner, ' Bastarderzeugung act on the reproductive system of

im Pflanzenreich,' 1849, p. 165. most organisms, it is probable that

t ' Origin of Species,' 6th edit, the close adaptation of the male to
p. 247 ; ' Variation of Animals and the female elements in the two
Plants under Domestication.' 2nd forms of the same heterostyled
edit. vol. ii. p. 169 ; ' The Effects species, or in all the individuals
of Cross- and Self-fertilisation,' p. of the same ordinary species, could
463. It may be well here to re- be acquired only under long-con-
mark that, judging from the re- tinued nearly uniform conditions
markable power with which ab- of life,
ruptly changed conditions of life

CHAP. VI. ON HETEROSTYLED PLANTS. £69

cies when illegitimately fertilised, and between the two
forms of the same species when similarly fertilised, har-
monises well with the view that the result is an inci-
dental one which follows from changes gradually effected
in their reproductive systems, in order that the sexual
elements of the distinct forms should act perfectly on
one another.

Transmission of the Two Forms by Heterostyled
'Plants. — The transmission of the two forms by hetero-
styled plants, with respect to which many facts were
given in the last chapter, may perhaps be found here-
after to throw some light on their manner of develop-
ment. 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 follow-
ing tables (3G and 37).

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 trimorphic Lythrum
salicaria, and with numerous seedlings from the long-
styled form of Oxalis 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

270

CONCLUDING REMARKS

CHAP. VI.

TABLE 36.

Nature of the Offspring from Illegitimately fertilised
Dimorphic Plants.

Numberl Number
of LOUR- of Short-

«tyle.l i styled
Offspring Offering

Primula veris . , .

Primula vulgaris

Primula auricula . .

Primula Sinensis .

Long-styled form, fertilised by
own-form pollen during five
successive generations, pro-
duced

'Short-styled form, fertilised)
by own-form pollen, pro- \
duced J

Long-styled form, fertilised by 1
own-form pollen during two I
successive generations, pro- (
duced J

Short-styled form, fertilised
by own-form pollen, is said
to produce during successive
generations offspring in
about the following propor-
tions . .

Pulmonaria officinalis
Polygonum fagopyrum

Long-styled form, fertilised by "]
own-form pollen during two I
successive generations, pro- [
duced J

f Long-styled form, fertilised by )
•< own-form pollen (Hilde- f
(. brand), produced . . . . J

f Short-styled form, fertilised)
« by own form pollen, pro- >
( duced J

f Long-styled form, fertilised by )
{ own-form pollen, produced . j

f Long-styled form, fertilised by )
1 own-form pollen, produced . J

(Short-styled form, fertilised)
-j by own-form pollen, pro- >
< duced J

CHAP. VI. ON HETEEOSTYLED PLANTS.

271

TABLE 37.

Nature of the Offspring from Illegitimately fertilised
Trimorphic Plants.

—

Number

°»
Oflspring

Numbei
of Mid-

<3£

Number
|of Short-
j 8tyled
Offspring

f Long-styled form, fertilised )
Lythrumsalicaria. 1 by own-form pollen, pro- \
( duced J

f Short-styled form, fertilised )
•j by own-form pollen, pro- V
( duced J

56
1

0
0

0

8

{Short-styled form, fertilised 1
by pollen from mid-length 1
stamens of long -styled |
form, produced . . . . J '

("Mid-styled form, fertilised)
< by own-form pollen, pro- >
(_ duced J

4
1

0
3

8
0

f Mid-styled form, fertilised]
« .< I by pollen from shortest i
1 stamens of long-styled [
[ form, produced . . . J

f Mid-styled form, fertilised]
« <t I by pollen from longest 1
1 stamens of short-styled f
[ form, produced . . . . J

f Long-styled form, fertilised
during several genera-
Oxalis rosea . . . i tions by own-form pollen,
produced offspring in the
[ ratio of

17
14

100

8
8

0

0

18

0

(Mid-styled form, fertilised)
" hedysaroides < by own-form pollen, pro- >
( duced J

0

17

0

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

272 CONCLUDING REMARKS CHAP. VI.

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 Miiller, 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 veris, from which
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 progenitor.
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 rendered still
more strange in the particular instance of P. veris, 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

* It may be suspected that this Scott, 'Journal Linn. Soc. Bot.,'

was the case with Primula, judg- vol. viii., 1864, p. 85). HerrBreit-

ing from the length of the pistil in enbach found many specimens of

geveral allied genera (see Mr. J. Primula elatior growing in a state

CHAP. VI. ON HETEROSTYLED PLANTS. 373

of nature any single plant of a trimorphic species no
doubt produces all three forms ; and this may be ac-
counted for either by its several flowers being sepa-
rately 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
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 case 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

of nature with some flowers on the greatly preponderated in number;

same plant long-styled, others there being 61 of this form to 9

short-styled and others equal- of the short-styled and 15 of the

styled ; and the long-styled form equal-styled.

274 CONCLUDING REMARKS CHAP. VL

flowers legitimately fertilised. With P. auricula 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-
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 varia-
tion 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 induce reversion, and
it is chiefly the cultivated species of Primula which be-
come equal-styled. Illegitimate fertilisation, which is
an abnormal process, is likewise an exciting cause; and
with illegitimately descended long-styled plants of P.
Sinensis, I have observed the first appearance and sub-
sequent stages of this variation. With some other plants
of P. Sinensis of similar parentage the flowers ap-
peared to have reverted to their original wild con-
dition. 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

CHAP. VI. ON HETEROSTYLED PLANTS. 275

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 sometimes 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 hermaphro-
dites amongst animals which properly have their sexes
separated; for the two sexes are combined in a mon-
strous hermaphrodite 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 Miiller has shown, both winged and wingless
males and females, besides the workers. But in none

276 CONCLUDIDG REMARKS CHAP. VI.

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
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

CHAP. VI. ON HETEROSTYLED PLANTS. 277

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 nature, 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 — the greater or
less power of fertilising and being fertilised — may char-
acterise 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 CHAP. VII.

CHAPTER VII.
POLYGAMOUS, DICECIOUS, AND GYKO-DICECIOUS PLANTS.

The conversion in various ways of hermaphrodite into dioecious plants
— Heterostyled plants rendered dioecious — Rubiacese — Verbenaceae
— Polygamous and sub-dioecious plants — Euonymus — Fragaria —
The two sub-forms of both sexes of Khamnus and Epigsea — 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 gyno-dice-
cious plants — Difference in the size of the corolla in the forms of
polygamous, dioecious, and gyno-dicecious plants.

THERE are several groups of plants in which all the
species are dioecious, 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 organized 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 exhib-
iting in the female flowers plain rudiments of male
organs, and conversely in the male flowers rudiments
of female organs, we may feel sure are descended from
plants which formerly had the two sexes combined 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

CHAP. VII. POLYGAMOUS PLANTS. 279

be left existing, of which many instances occur; and if
the female organs of the hermaphrodite were afterwards
to abort, the result would be a dioecious plant. Con-
versely, if we imagine the female organs alone to abort
in some individuals, males and hermaphrodites would
be left; and the hermaphrodites might afterwards be
converted into females.

In other cases, as in that of the common Ash-tree
mentioned in the Introduction, the stamens are rudimen-
tary in some individuals, the pistils in others, others
again remaining as hermaphrodites. Here the modifi-
cation 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 sup-
planted by the individuals having separated sexes, and
if these latter were equalised in number, a strictly dioe-
cious species would be formed.

There is much difficulty in understanding why her-
maphrodite plants should ever have been rendered
dioecious. 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 dioecious 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.

280 DKECIOUS AND CHAP. VII.

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 dioecious 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 manner. 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 pro-
duction 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 increase.
But in accordance with the law of compensation we
might expect that the individuals which produced such
seeds would, if living under severe conditions, tend
to produce less and less pollen, so that their anthers
would be reduced in size and might ultimately become
rudimentary. This view occurred to me owing to
a statement by Sir J. E. Smith f 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
recall the case of the mid-styled form of Lythrum sali-
caria, which produces a larger number of seeds than the

*See the facts given in 'The t' Trans. Linn. Soc.,' vol. xiii.
Effects of Cross and Self-fertilisa- p. 600.
tion,' p. 353.

CHAP. VII. POLYGAMOUS PLANTS. 281

other forms, and has somewhat smaller pollen-grains
which have less fertilising power than those of the cor-
responding 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 vice versa, I know
not. As soon as the anthers in a certain number of
individuals became reduced in size in the manner
just suggested or from any other cause, the other in-
dividuals would have to produce a larger supply of pol-
len; and such increased development would tend to
reduce the female organs through the law of compen-
sation, so as ultimately to leave them in a rudimen-
tary condition; and the species would then become
dioecious.

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 in-
sects which visited the flowers, or in their becoming more
anemophilous, for such plants require an enormous quan-
tity of pollen. The increased action of the male organs
would tend to affect through compensation the female
organs of the same flower ; and the final result would be
that the species would consist of males and hermaphro-
dites. But it is of no use considering this case and
other analogous ones, for, as stated in the Introduction,
the co-existence of male and hermaphrodite plants is ex-
cessively 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 be-
come or are becoming dioecious by many and excessively
small steps. In the case of polygamous species which

282 DIOECIOUS AND CHAP. VII.

exist as males, females and hermaphrodites, the latter
would have to be supplanted before the species could be-
come strictly dioecious; but the extinction of the her-
maphrodite 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 unknown laws which
govern the suppression of the male or female organs
in hermaphrodite plants, quite independently of any
tendency in them to become monoecious, dioecious, 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. Eobert Brown remarks * that
" the order of reduction or abortion of the stamina in
any natural family may with some confidence be pre-
dicted," by observing in other members of the family,
in which their number is complete, the order of the
dehiscence of the anthers; for the lesser permanence of
an organ is generally connected with its lesser perfec-
tion, and he judges of perfection by priority of develop-
ment. He also states that whenever there is a separation
of the sexes in an hermaphrodite 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 ex-
plain.

Plants under cultivation or changed conditions of

* 'Trans. Linn. Soc.,' vol. xii. p. 98. Or 'Miscellaneous Works,'
vol. ii. pp. 278-81.

CHAP. VII. POLYGAMOUS PLANTS. 283

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 sta-
mens 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 generations if they
failed altogether to perform their proper functions. Ac-
cording to Gartner,* if the anthers on a plant are con-
tabescent (and when this occurs it is always at a very
early period of growth) the female organs are some-
times precociously developed. I mention this case as
it appears to be one of compensation. So again is the
well-known fact, that plants which increase largely by
stolons or other such means are often utterly barren,
with a large proportion of their pollen-grains in a worth-
less 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 even to the
whole plant ; and in this latter case the species becomes
dioecious. In those rare instances mentioned in the

* 'Beitrage znir Kenntniss,' &c., chap, xviii.— 2nd edit. vol. ii.

p. 117 et seq. The whole subject pp. 146-56.

of the sterility of plants from va- t ' Ueber die Geschlechtsver-

rious causes has been discussed in haltnisse bei den Compositen,'
my 'Variation of Animals and
Plants under Domestication,'

284: DIOECIOUS AND CHAP. VII.

Introduction, in which some of the individuals of both
monoecious and hermaphrodite plants are proterand-
rous, others being proterogynous, their conversion into
a dioecious condition would probably be much facili-
tated, as they already consist of two bodies of individ-
uals, differing to a certain extent in their reproductive
functions.

Dimorphic heterostyled plants offer still more
strongly marked facilities for becoming dioecious; 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 or-
gans. Thus the great difficulty before alluded to is much
lessened in understanding how any cause whatever could
lead to the simultaneous reduction and ultimate sup-
pression 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
Rubiacea? contained more heterostyled genera than any
other family, and from their wide distribution we may
infer that many of them became heterostyled at a re-

CHAP. VII. POLYGAMOUS PLANTS. 285

mote period, so that there will have been ample time
for some of the species to have been since rendered dioe-
cious. Asa Gray informs me that Coprosma is dioecious,
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 Kubia-
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 dioecious in some
districts; for he says that one form has small sessile
anthers without a trace of pollen, the pistil being per-
fect ; 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 dioecious in
another.

Asperula is likewise a Eubiaceous 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 dioecious.
The male flowers have large anthers and a very small
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

* 'Proc. Acad. of Sciences of Philadelphia,' July 28, 1868, p. 183.

286 DKECIOUS AND CHAP. VII.

apparently quite destitute of pollen. Considering how
many Eubiaceous 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 Eubiaceous plant becoming dioecious.
Moreover, in an allied plant, Galium cruciatum, the fe-
male organs have been suppressed in most of the lower
flowers, whilst the upper ones remain hermaphrodite;
and here we have a modification of the sexual organs
without any connection with heterostylism.

Mr. Thwaites informs me that in Ceylon various
Eubiaceous plants are heterostyled; but in the case of
Discospermum one of the two forms is always barren,
the ovar}r 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 dioecious.

Most of the species of the South American genus
^Egiphila, a member of the Yerbenaceae, apparently are
heterostyled; and both Fritz Miiller and myself thought
that this was this the case with JE. 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 destitute of pol-
len 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 stigmas are reduced to half
their proper length, having also an abnormal appear-
ance ; whilst the stamens are perfect. This plant there-
fore is dioecious; and we may, I think, conclude that
a short-styled progenitor, bearing long stamens exserted
beyond the corolla, has been converted into the male;
and a long-styled progenitor with fully developed stig-
mas into the female.

CHAP. VII. POLYGAMOUS PLANTS. 287

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 mascu-
line. Certain appearances countenance the belief that
the reproductive system of Phlox subulala 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 dioe-
cious. 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 dioecious spe-
cies which owe their origin to the transformation 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 dioecious or sub-dioecious
plants, which are worth describing, chiefly as they show
by what fine gradations hermaphrodites may pass into
polygamous or difficious species.

Polygamous, Dioecious and Sub-dioecious Plants*
Euonymus Europceus (Celastrinese). — 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
those in the allied genus Celastrus are said to be
" polygamo-dioecious." 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 ap-

288

DIOECIOUS AND

CHAP. VII.

pearance well-developed. The other half have a perfect
pistil, with the stamens short, bearing rudimentary an-
thers destitute of pollen; so that these bushes are fe-
males. All the flowers on the same plant present the
same structure. The female corolla is smaller than that
on the polleniferous bushes. The two forms are shown
in the accompanying drawings.

Hermaphrodite or male. Female.

EUONYMUS EUROP.EUS.

I did not at first doubt that this species existed under
an hermaphrodite and female form; but we shall pres-
ently see that some of the bushes which appear to be
hermaphrodites never produce fruit, and these are in
fact males. The species, therefore, is polygamous in the
sense in which I use the term, and trioicous. The flow-
ers 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; neverthe-
less the other insects sufficed to fertilise effectually fe-
male bushes growing at a distance 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 prop-
erly, but I could never find in them a single grain
of pollen. It is somewhat difficult to compare the

CHAP. VII. POLYGAMOUS PLANTS. 289

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 of 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 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

290 DKECIOUS AND CHAP. VII.

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 fer-
tilisation 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
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

CHAP. VII. POLYGAMOUS PLANTS. 291

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 pollen-
iferous 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 pro-
duce 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 grada-
tion from the female bush, B, which in 1865 was covered
with " innumerable rniit," — 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 pro-
duced only 20 poor fruit, — to the three bushes, E, F,
and G, which did not this year, or during the two pre-
vious 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 dioecious
in function as any plant in the world. This case appears
to me very interesting, as showing how gradually an her-
maphrodite plant may be converted into a dioecious one.*

* According to Fritz Miiller Southern Brazil is in nearly the
("Bot. Zeitung.' 1870. p. 151), a same state as our Euonymus. The
Chamissoa (Amaranthacese) in ovules are equally developed in

292 DICECIOUS AND CHAP. VII.

Seeing how general it is for organs which are
almost 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 had
been originally short-styled, with the pistil in its pres-
ent 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 Eubiaceous genera and ^Egiphila; 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
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. (Eosa-
ceee). — 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

the two forms. In the female, the These latter plants do not com-

pistil is perfect, whilst the anthers monly yield any fruit, and are

are entirely destitute of pollen, therefore in function males. Nev-

In the polleniferous form, the pis- ertheless, on one occasion Fritz

til is short and the stigmas never Miiller found flowers of this kind

separate from one another, so that, in which the stigmas had sepa-

although their surfaces are cov- rated, and they produced some

ered with fairly well-developed pa- fruit,
pillae, they cannot be fertilised.

CHAP. VII. POLYGAMOUS PLANTS. 293

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 (F. elatior), is more strictly dioe-
cious; but Lindley made by selection an hermaphrodite
stock, f

Rhamnus catharticus (Rhamnene). — This plant is
well known to be dioecious. 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. Each 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 stig-
ma; in others the pistil is much more developed, with
the papillae on the stigmatic surfaces moderately large.
The ovules in both kinds of males are in an aborted con-
dition. On my mentioning this case to Professor Cas-

* Mr. Leonard Wray in ' Gard. formation on this subject, see
Chron,' 1861, p. 716. 'Variation under Domestication,'

t For references and further in- chap. x. 2nd edit. vol. i. p. 375.

294: DICECIOUS AND CHAP. VII.

pary, he examined several male plants in the botanic
gardens at Konigsberg, where there were no females, and
sent me the accompanying drawings.

Fig. 13.

Long-styled male. Short-styled male.

EHAMNUS CATHABTTCUS. (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 moder-
ately well developed bore slightly 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
the pistils in the males. The pistil varies consid-
erably in length in the female plants, so that they
may be divided into two sub-forms according to the
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-

CHAP. VII. POLYGAMOUS PLANTS. 295

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 lanceolatus 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

Fig. 14.

Long-styled
female.

RHAMNUS CATHAKTICUS.

son compared the pollen-grains from the two form.?,
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 ap-
pearing to produce less pollen, and from the grains

296 DIOECIOUS AND CHAP. VII.

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 dioecious, 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 of the incipient female flowers have been
reduced. The long-styled form of R. lanceolatus seems
to correspond with the males of E. catharlicus 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
Ehamnus are said to be dioecious * or sub dioecious. On
the other hand, R. frangula is an ordinary hermaphro-
dite, for my son found a large number of bushes all bear-
ing an equal profusion of fruit.

Epigcea repens (Ericaceae). — This plant appears to
be in nearly the same state as Rhamnus catharticus.
It is described by Asa Gray f 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

*Lecoq, 'Ge"ogr. Bot.' torn. v. July, 1876. Also, 'The American
1856, pp. 420-26. Naturalist,' 1876, p. 490.

t ' American Journal of Science,'

CHAP. VIL POLYGAMOUS PLANTS. 397

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.
(3) 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 stig-
ma, 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 dioscious. 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.

Ilex aquifolium (Aquifoliaceae). — In the several
works which I have consulted, one author alone f says
that the holly is direcious. During several years I have
examined many plants, but have never found one that
was really hermaphrodite. I mention this genus because
the stamens in the female flowers, although quite des-
titute of pollen, are but slightly arjd 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

* "Variations in Epicjxa re wns," t Vanch*r, 'Hist. Phys. des

' Proc. Acid. Nat. Soc. of Phila- Plantes d'Europe,' 1841, torn. ii.

delphia,' May 1868, p. 153. p. 11.
21

298 DICECIOUS AND CHAP. VII.

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, accord-
ing 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 dioecious, 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 dioecious, 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
Labiatae (as has long been noticed by botanists) than
in any other group. Such cases have been noticed by
myself in Tliymus serpyllum and vulgaris, Satureia
liortensis, Origanum vulgare, and Mentha hirsuta; and
by others in Nepeta glechoma, Mentha vulgaris and
aquatica, and Prunella vulgaris. In these two latter
species the female form, according to H. Miiller, is in-
frequent. To these must be added Dracocephalum
Moldavicum, Melissa officinalis and clinipodium, and
Hyssopus officinalis.* In the two last-named plants the

*H. Miiller, 'Die Befrnchtung and Lecoq were mistaken in think-

der Blumen,' 1873; and 'Nature,' ing that several of the plants

1873, p. 161. Vaucher, ' Plantes named in the text are dioecious.

d'Europe,' torn. iii. p. 611. For They appear to have assumed that

Dracocephalum, Schimper, as the hermaphrodite form was a

quoted by Braun, ' Annals and male ; perhaps they were deceived

Mag. of Nat. Hist.' 2nd series, vol. by the pistil not becoming fully

xviii. 1856, p. 380. Lecoq, 'Geo- developed and of proper length

graphic Bot. del'Europe,' tom.viii. until some time after the anthers

pp. 33, 38, 44, &c. Both Vaucher have dehisced.

CHAP. VII. GYNO-DICECIOUS PLANTS. 299

female form likewise appears to be rare, for I raised
many seedlings from 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 extreme-
ly 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 Labiatae. 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
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 an-
thers contained a very few full-sized grains, together
with a multitude of minute empty ones. In some fe-
males 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 Brit-
ain, Germany, and near Mentone, are in the state just

300 GYNO-DICECIOUS PLANTS. CHAP. VII.

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 hermaphro-
dites.

I 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, I
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 a distance
of half a mile it appeared of a pink colour, I could
not discover a single female. Therefore the her-
maphrodites must greatly exceed in number the fe-
males, 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 Labiatae 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 1873 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, f " It would, however, be a mistake to
suppose that the nature of the conditions determines

* ' Sull' Opera la Distribuzione H. Miillor, ' Die Befruchtung,
del Sessi nello Piante. &c.,' 1867, &c.,' r>. 327.
p. 7. With respect to Germany, f ' Nature,' June 1873, p. 162.

CHAP. VII. GYXO-DIGECIOUS PLANTS. 301

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 (T.
citriodorus, a var. of T. serpyllum}, which I was in-
formed 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 fe-
male plant numbered 160, and their seeds weighed 8.7
grains; whilst those from the hermaphrodite plant num-
bered 200, and their seeds weighed only 4.9 grains; so
that the seeds from the female plant were to those from
the hermaphrodite as 100 to 56 in weight. If the rela-
tive 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 T. 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 ac-
companying sketches, the anthers of the female, though
small, were well formed, but they contained very little
pollen, and not a single sound grain could be de-

302

GYNO-DKECIOUS PLANTS.

CHAP. VII.

tected. Eighteen 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

Fig. 15.

Hermaphrodite. Females.

THYMCS VULGAKIS (magnified).

doubt every female flower was fertilised; for on plac-
ing under the microscope* a large number of stigmas
from female plants, 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 hermaphrodites 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 lots of seeds were sown separately in two ad-
joining beds, and the seedlings from both the her-
maphrodite and female parent-plants consisted of both
forms.

Satureia Jiortcnsis. — Eleven 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 conditions
to which they had been subjected caused the great ex-

CHAP. VII. GYNO-DKECIOUS PLANTS. 3Q3

cess 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 col-
ourless anthers destitute of pollen. The windows of the
green-house were left open, and the flowers were inces-
santly 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, there-
fore, 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.

We may now consider the probable means by which
so many of the Labiatse 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

* ' Die Befruchtung der Blumen,' pp. 319, 326.

304: GYNO-DICECIOUS PLANTS. CHAP. VII.

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. From the data above given it follows
that ten plants of Tliymus 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 tendency to the increased production of
seed were steadily favoured, the result would be the
complete abortion of the male organs. I shall pres-
ently 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

* ' Befruchtnng der Blumen,' males co-exist; it is, however,

&c., p. 368. The two forms occur possible that he may have been

not only in Germany, but in deceived by the flowers being so

England and France. Lecoq strongly proterandrous. From

('Geographic Bot.' 1857, torn. vi. what Lecoq says, 8. succisa likewise

pp. 473, 477) says that male plants appears to occur under two forms

as well as hermaphrodites and fe- in France.

CHAP. VII. GYNO-DKECIOUS PLANTS. 3Q5

hermaphrodite flowers are strongly proterandrous, 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 ren-
dered 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 Labiatae. I have also observed
the existence of two forms in our endemic 8. succisa, and
in the exotic 8. atro-purpurea. In the latter plant, dif-
ferently to what occurs in 8. arvensis, the female flowers,
especially the larger circumferential ones, are smaller than
those of the hermaphrodite form. According to Lecoq,
the female flower-heads of 8. succisa are likewise smaller
than those of what he calls the male plants, but which are
probably hermaphrodites.

Echium vulgar -e (Boraginese). — The ordinary herma-
phrodite form appears to be proterandrous, and nothing
more need be said about it. The female differs in having
a much smaller corolla and shorter pistil, but a well-de-
veloped stigma. The stamens 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 perfect an-
thers, 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 fungoid growth, I exam-
ined 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 locali-
ties, exactly half of which were hermaphrodites, fourteen
were females, and two in an intermediate condition. 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

306 GYNO-DICECIOUS PLANTS. CHAP. VIL

the abortion of the stamens can hardly be due to the dry-
ness of the sites where the plants grew, as I at one time
thought probable. 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 unusu-
ally 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 gradu-
ate from an anemophilous into an entomophilous condi-
tion. 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 hermaphro-
dites. But I have found in two localities in England fe-
male and hermaphrodite forms existing together; and the
same fact has been noticed by others.f 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 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,t that such is the case with four
of the North American species. The corolla does not prop-
erly expand in the short-stamened form of these plants.

Cnicus Serratula Eriophorum. — In the Composite,
Cnicus palustris and acaulis are said by Sir J. E. Smith
to exist as hermaphrodites and females, the former being
the more frequent. With Serratula tinctoria a regular
gradation may be followed from the hermaphrodite to the

* ' Die Befruchtunjr,' &c., p. 342. N. United States,' 2nd edit. 1856,
t Mr. C. W. Crocker in ' The p. 269. See also ' American Jour-
Gardener's Chronicle,' 1864, p. 294. nal of Science,' Nov. 1862, p. 419,
Mr. W. Marshall writes to me to and ' Proc. American Academy of
the same effect from Ely. Science,' Oct. 14, 1862, p. 53.
t ' Manual of the Botany of the

CHAP. VII. SIZE OF THE COROLLA. 307

female form ; in one of the latter plants the stamens were
so tall that the anthers embraced the style as in the herma-
phrodites, but they contained only a few grains of pollen,
and these in an aborted condition; in another 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 (Cyperaceae) hermaphrodite
and female forms exist in Scotland and the Arctic regions
both of which yield seed.*

It is a curious fact that in all the foregoing po-
lygamous, dioacious, and gyno-dioecious 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,
Ilex, Fragaria, all or at least most of the before-named
Labiatse, Scdbiosa atro-purpurea, and Echium vulgare.
So it is, according to Von Mohl, with Cardamine
amara, Geranium 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.f 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

*Sir J. E. Smith, 'Transac- of the Lirnisean Society of Botany,'
tionsof the Linnsean Society,' vol. vol. ix. 1865. p. 161.
xiii. p. 599. Dr. Dickie, 'Journal f ' Bot. Zeitung,' 1863, p. 326.

308 SIZE OF THE COROLLA. CHAP. VII.

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 ETiamnus catliarticus 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. Miil-
ler's belief, the advantage derived from the polleniferous
flowers being visited first by insects has been sufficient
to lead to a gradual reduction of the corolla of the fe-
male. We should bear in mind that as the hermaphro-
dite is the normal form, its corolla has 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 occurred, had not the expenditure
saved by the abortion of the stamens been directed to the
female reproductive organs, so as to give to this form
increased fertility.

* It does not appear to me that serves to protect their pollen from

Kerner's view (' Die Schutzmittel rain. In the genus Thymus, for

des Pollens,' 1873, p. 56) can be instance, the aborted anthers of

accepted in the present roses, the female are much better pro-

naniely, that the larger corolla in tected than the perfect ones of the

the hermaphrodites and males hermaphrodite.

CHAP. VIII. CLEISTOGAMIC FLOWERS. 309

CHAPTER VIII.

CLEISTOGAMIC FLOWEBS.

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 several species, their
fertility compared with that of the perfect flowers — Oxalis acetosella
— O. sensitiva, three forms of cleistogamic flowers — Vandellia —
Ononis — Impatiens— Drosera — Miscellaneous observations on various
other cleistogamic plants — Anemophilous species producing cleisto-
gamic 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.

IT was known even before the time of Linnaeus that
certain plants produced two kinds of flowers, ordi-
nary open and minute closed ones; and this fact for-
merly gave rise to warm controversies about the sexu-
ality of plants. These closed flowers have been appro-
priately named cleistogamic by Dr. Kuhn.* They are
remarkable from their small size and from never open-
ing, so that they resemble buds; their petals are rudi-
mentary or quite aborted; their stamens are often re-
duced 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
same cases hardly at all developed. These flowers do
not secrete nectar or emit any odour; from their small

* ' Bot. Zeitung,' 1867, p. 65.

310 CLEISTOGAMIC FLOWERS. CHAP. VIII.

size, as well as from the corolla being rudimentary, they
are singularly inconspicuous. Consequently insects do
not visit them; nor if they did, could they find an en-
trance. Such flowers are therefore invariably self-fer-
tilised; yet they produce an abundance of seed. In sev-
eral 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 Euryale,*
remain closely shut as long as they are sub-

*Delpino, 'Sull' Opera, la Dis- Flora,' vol. iii. 1825. p. 157. For

tribuzione dei Sessi nelle Piante,' the behaviour of Menyanthos in

&c. 1867, p. 30. Subularia. how- Russia see GilHbert in 'Act. A cart,

ever, sometimes has its flowers St. Petersb.,' 1777. part ii. p. 45. —

fully expanded benenth the water. On Enrvale ' Gardener's Chroui-

see Sir J. E. Smith, 'English cle,' 1877, p. 280.

CHAP. VIII. CLEISTOGAMIC FLOWERS. 311

merged, and in this condition fertilise themselves.
They behave in this manner, apparently as a protec-
tion to their pollen, and produce open flowers when
exposed to the air; so that these cases seem rather
different from those of true cleistogamic flowers, and
have not been included in the list. Again, the flowers
of some plants which are produced very early or very
late in the season do not properly expand; and these
might perhaps be considered as incipiently cleisto-
gamic; but as they do not present any of the remark-
able peculiarities proper to the class, and as I have
not found any full record of such cases, they are not
entered in the list. When, however, it is believed on
fairly good evidence that the flowers on a plant in its
native country do not open at any hour of the day or
night, and yet set seeds capable of germination, these
may fairly be considered as cleistogamic, notwith-
standing that they present no peculiarities of struc-
ture. I will now give as complete a list of the genera
containing cleistogamic species as I have been able to
collect.

TABLE 38.

List of Genera including Cleistogamic Species (chiefly
after Kuhri).*

DICOTYLEDONS.

Eritrichium (Boraginete).

Cuscuta (Convolvulacese).

Scrophularia (Scrophularineae).

Linaria

Vandellia

Cryphiacanthus (Acanthacese).

Eranthemum "

DICOTYLEDONS.

Dsedalacanthus (Acanthacea?).

Dipteracanthus

,?Echmanthera

Euellia ,

Lamium (Labiatse).

Salvia

Oxybaphus (Nyctagineae).

* I have omitted Trifolium and appear to be properly cleistogamic.

Arachis from the list, because Von Correa de Mello ( Journal Linn

Mohl says ('Bot. Zeitung,' 1863, Soc. Bot.' vol xi 1870, p. 254)

p 312^ that the flower-stems observed plants of Arachis m

merely draw the flowers beneath Brazil, and could never find such

the ground and that these do not flowers. Plan tago has been omitted

312

CLEISTOGAMIC FLO WEES. CHAP. VIII.

TABLE S3— continued.

DICOTYLEDONS.

Nyctaginia (Nyctaginese).

Stapelia (Asclepiadse).

Specularia (Campanulacese).

Campanula

Hottonia (Primulacese).

Anandria (Composites).

Heterocarpsea ( Crucif erse ) .

Viola (Violacese).

Helianthemum (Cistinese).

Lechea

Pavonia (Malvacese).

Gaudichaudia (Malpighiacese).

Aspicarpa

Camarea

Janusia

Polygala (Polygalese).

Impatiens (Balsaminese).

Oxalis (Geraniaccse).

Ononis (Leguminosse).

Parochsetus

Chapmannia "

Stylosanthus "

DICOTYLEDONS.

Lespedeza (Leguminosse).

Vicia

Lathyrus

Martinsia vel 1 <i

Neurocarpum >

Amphicarpsea

Glycine

Galactia

Voandzeia

Drosera (Droseracese).

MONOCOTYLEDONS.

Juncus (Juncese).

Leersia (Graminese).

Hordeum

Cryptostachys "

Commelina (Commelineas).

Monochoria (Poutederacese).

Schomburgkia (Orchidse).

Cattleya

Epidendron

Thelymitra "

because as far as I can discover it
produces hermaphrodite and fe-
male flower-heads, but not cleis-
togamic flowers. Krascheninikowia
(vel Stellaria) has been omitted
because it seems very doubtful
from Maximowicz' description
whether the lower flowers which
have no petals or very small ones,
and barren stamens or none, are
cleistogamic ; the upper herma-
phrodite flowers are said never to
produce fruit, and therefore pro-
bably act as males. Moreover in
Stellaria graminea, as Babington
remarks ('British Botany,' 1851,
p. 51), " shorter and longer petals
accompany an imperfection of the
stamens or germen."

I have added to the list the fol-
lowing cases : Several Acanthacese,
for which see J. Scott in ' Journal
ofBot.' (London), new series, vol.
i., 1872, p. 161. With respect to
Salvia see Dr. Ascherson in ' Bot.
Zeitung,' 1871, p. 555. For Oxy-

baphus and Nyctaginia see Asa
Gray in ' American Naturalist,'
Nov. 1873, p. 692. From Dr.
Torrey's account of Hottonia in-
flata ('Bull, of Torrey Botan.
Club,' vol. ii. June, 1871) it is
manifest that this plant produces
true cleistogamic flowers. For
Pavonia see Bouch6 in ' Sitzungs-
berichte d. Gesellsch. Natur.
Frcunde,' Oct. 20, 1874, p. 90. I
have added Thelymitra, as from
the account given by Mr. Fitzger-
ald in his magnificent work on
' Australian Orchids ' it appears
that the flowers of this plant in its
native home never open, but they
do not appear to be reduced in
size. Nor is this the case with
the flowers of certain species of
Epidendron, Cattleya. &c. (see
second edition of my ' Fertilisation
of Orchids,' p. 147), which with-
out expanding produce capsules.
It is therefore doubtful whether
these Orchidese ought to have been

CHAP. VIII. VIOLA. 313

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 Leguminosae than in any other, and next
in order in that of the Acanthaceae and Malpighiaceaa.

A large number, but not all the species, of certain
genera, as of Oxalis and Viola, bear eleistogamic as well
as ordinary flowers. A second point which deserves no-
tice is that a considerable proportion of the genera pro-
duce 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 eleistogamic
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 eleistogamic 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. Miiller of
Upsala says that in the specimens which he observed
the petals were completely aborted, f 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

included in the list. From what *'Bot. Zeitung,' 1863, p. 30&-

France ' torn, x., 1863. p. 195, this contains the first full and satisfac-

plant appears to produce cleisto- tory account of any cleistogarmc

pamic flowers. The other additions flower.
to the list are noticed in my text.

314: CLEISTOGAMIC FLOWERS. CHAP. VIII.

cells or loculi remarkably distinct; they contain very
little pollen in comparison with those of the perfect
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 membra-
nous expansions flatter or not so hoodlike 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 $^ of an inch in diameter,
and therefore of smaller size than the ordinary pollen-
grains similarly treated, which have a diameter of
^FuS4 °f 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 an-
theriferous stamens. It is remarkable that there is an
open passage from the enlarged funnel-shaped extrem-
ity 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 considerably
from that of the perfect flower; for in the latter it is
much longer, and straight with the exception of the
rectangular bent stigma ; nor is it perforated by an open

CHAP. VIII. VIOLA. 315

The ordinary or perfect flowers have been said by
some authors never to produce capsules; but this is an
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 gener-
ally 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; I 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 hortorum for some time, and whenever it came
to a flower which did not stand in a convenient po-
sition 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

316 CLEISTOGAMIC FLOWERS. CHAP. VIII.

some cleistogamic flowers on the same plants; and the
result was that 14 capsules produced by the perfect
flowers contained on an average 9.85 seeds; and 17
capsules from the cleistogamic ones contained 9.6-1
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 in
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
specis of Viola. It is remarkable that this plant, ac-
cording to Delpino,f does not produce cleistogamic
flowers in one part of Liguria, whilst the perfect flow-
ers are there abundantly fertile; on the other hand,
cleistogamic flowers are produced by it near Turin.

* Vaucher says (' Hist. Phys. des See also Lecoq, 'Geograph. Bot.'

Plantes d'Europe,' torn. iii. 1844, torn. v. 1856, p. 180.

p. 309) that V. Jiirta and cottina f ' Bull' Opera, la Distribuzione

likewise bury their capsules.— del Sessi nelle Piante,' 1867, p. 30.

CHAP.VIli. VIOLA. 317

Another fact is worth giving as an instance of corre-
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 cleistogamic
flowers, many bud-like bodies which from their posi-
tion on the plant were certainly of a cleistogamic na-
ture. They consisted, as could be seen on bisecting
them, of a dense mass of minute scales closely folded
over one another, exactly like a cabbage-head in minia-
ture. 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 rendered 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 per-
fect flowers which I saw visited by hive- and humble-
bees, six were marked, but they produced only two cap-
sules, some of the others having been accidentally in-
jured. 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 Miiller, as I hear from his
brother, has found in the highlands of Southern 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. Hi*t. Review,' also Timhal-La grave in 'Bot. Zei-

July 1862, p. 238. With respect tung,' 1854, p. 772.

318 CLEISTOGAMIC FLOWERS. CHAP. VIII.

Viola nana. — Mr. 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 deli-
cate 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 sin-
gle cell of the larger rudimentary anther included 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 Roxburghiana. — This species bore in my hot-
house during two years a multitude of cleistogamic
flowers, which resembled in all respects those of the

CHAP. VIII. VIOLA. 319

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 cleistogamic
flowers.

Many other species, besides the five now described,
produce cleistogamic flowers; this is the case, accord-
ing to D. Miiller, Michalet, Von Mohl, and Hermann
Miiller, with V. elatior, lancifolia, sylvatica, palustris,
mirabilis, bicolor, ionodium, and biflora. But V. tri-
color 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 1'empeche pas de fruc-
tifier."

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 state-
ments by D. Miiller and Von Mohl that in V. mirabilis
the calyx does not remain quite closed; all five stamens
are provided with anthers, and some pollen-grains prob-
ably fall out of the cells on the stigma, instead of pro-
truding their tubes whilst still enclosed, as in the other
species. In V. hirta all five stamens are likewise an-
theriferous ; 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 sometimes one or even two of the others

320 CLEISTOGAMIC FLOWERS. CHAP. VIII.

are thus provided. Lastly, in V. canina never more
than two of the stamens, as far as I have seen, bear
anthers; the petals are much more reduced than in V.
hirta, and according to D. Miiller are sometimes quite
absent.

Oxalis 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 sometimes
quite aborted. In one case the tubes, which ended in
excessively fine points, were seen by me stretching up-
wards 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 with-
ered they produced not only cleistogamic but a few
minute open flowers, which were in an intermediate con-
dition between the two kinds. In one of these the pol-
len-tubes from the lower anthers had reached the stig-
mas, 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 down-
wards 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 number of seeds produced by these
flowers, I marked eight of them; two failed, one cast
its seed abroad, and the remaining five contained on an

* ' Bull. Soc. Bot. de France,' torn. vii. 1860, p. 465.

CHAP. VIII. OXALIS. 321

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 con-
siderably 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 ac-
cidental.

Hildebrand, whilst searching various Herbaria, ob-
served that many other species of Oxalis besides 0.
acetosella produce cleistogamic flowers ; * and I hear
from him that this is the case with the heterostyled tri-
morphic 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. I 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

1 Monatsbericlit der Akad. der Wiss. zu Berlin,' 1866, p. 369.

322 CLEISTOGAMIC FLOWERS. CHAP. VIII.

bases of the shorter stamens. Their stigmas are much
less papillose, and smaller in about the ratio of 13 to
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 cleiostogamic
flowers consisting of the three forms, through the prin-
ciple of correlated growth, by which the cleistogamic

CHAP. VIII. VANDELLIA. 323

flowers of the double violet have been rendered
double.

Vandellia nummularifolia. — Dr. Kuhn has col-
lected * all the notices with respect to cleistogamic
flowers in this genus, and has described from dried spe-
cimens those produced by an Abyssinian species. Mr.
Scott sent me from Calcutta seeds of the above com-
mon Indian weed, from which many plants were succes-
sively raised during several years. The cleistogamic
flowers are very small, being when fully mature under
sV of an inch (1.27 mm.) in length. The calyx does
not open, and within it the delicate transparent corolla
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 Tj-jj-g- 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 gener-
ally 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. Zcitung,' 1867, p. 65.

324 CLEISTOGAMIC FLOWERS. CHAP. VIII.

crowded yielded an average of only 48. Sixteen cap-
sules from perfect flowers artificially crossed with pol-
len 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-fer-
tilised.

Dr. Kuhn believes that the Abyssinian V. sessiflora
does not differ specifically from the foregoing species.
But its cleistogamic flowers apparently include four an-
thers 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. nummularifolia, 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 deformed.
These flowers may perhaps be ranked as cleistogamic,
as they are developed, and not merely drawn, beneath
the ground.

Ononis columns. — Plants were raised from seeds
sent me from Northern Italy. The sepals of the
cleistogamic flowers are elongated and closely pressed
together; the petals are much reduced in size', colour-
less, and folded over the interior organs. The fila-
ments of the ten stamens are united into a tube, and

* 'Bull. Soc. Bot. de France,' torn. vii. I860, p. 468.

CHAP. VIII. ONONIS. 325

this is not the case, according to Von Mohl, with the
cleistogamic flowers of other Leguminosse. 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 therefore differs
much from that of the perfect flower. During the year
1867 no perfect flowers were produced, but in the fol-
lowing 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 obtained
yielded on an average 3.66 seeds, with a maximum of
5 in one. Twelve perfect flowers were marked and al-
lowed to fertilise themselves spontaneously under a net,
and they yielded eight capsules, containing on an av-
erage 2.38 seeds, with a maximum of 3 in one. Fifty-
three capsules produced by the cleistogamic flowers con-
tained 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, 0. parviflora likewise bears
cleistogamic flowers ; and he informs me that these flow-
ers 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 co-
lumnce, bear a fresh crop of cleistogamic flowers in the
autumn.

Latliyrus nissolia apparently offers a case of the first

326 CLEISTOGAMIC FLOWERS. CHAP. VIII.

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 expan-
sion; 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
Mohl 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,
Amphicarpaea, and Voandzeia, the cleistogamic flowers
are produced on subterranean stems. The perfect flow-
ers 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 fulva. — Mr. A. W. Bennett has published
an excellent description, with figures, of this plant, f
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

* Cornea 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.' vol.

flowering and fruiting of this xiii. 1872, p. 147.

CHAP. VIII. IMPATIENS. 327

we should remember that this is a naturalised species.
The perfect flowers are usually barren in England ; but
Professor 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
importance 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 /. fulva. As in this latter species all five stamens
produce some pollen, though small in amount; a
single anther contains, according to Yon 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 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 /. balsamina are visited by
humble-bees,* and I am almost sure that this is the case
with the perfect flowers of I. noli-me-langere. 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
7. balsamina is proterandrous, so probably is the pres-
ent 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. Miiller, ' Die Befruchtung,' &c. p. 170.

328 CLEISTOGAMIC FLOWERS. CHAP. VIII.

were thrown up by some plants in my green-house
bore only cleistogamie 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 cleistogamie 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 case 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 cleis-
togamie.

A few miscellaneous observations may be added with
respect to some other species, as throwing light on our
subject. Mr. Scott states * that Eranthemum ambi-
guum bears three kinds of flowers, — large, conspicuous,
open ones, which are quite sterile — others of interme-
diate size, which are open and moderately fertile — and
lastly small closed or cleistogamie ones which are per-
fectly fertile. Ruellia tuberosa, likewise one of the
Acanthaceae, produces both open and cleistogamie flow-

* ' Journal of Botany,' London, new series, vol. i. 1872, pp. 161-4.

CHAP. VIII. CLEISTOGAMIC FLOWERS. 329

ers; 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 cleistogamie ones appear
only during the hot season. According to Torrey and
Gray, the North American species of Helianthemum,
when growing in poor soil, produce only cleistogamie
flowers. The cleistogamie flowers of Specularia per-
foliata are highly remarkable, as they are closed by a
tympanum formed by the rudimentary corolla, and with-
out any trace of an opening. 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. Sir J. Hooker and Dr. Thomson state f 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 produc-
ing a more globose ovary. The flowers are closed by
a tympanum 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 cleistogamie and per-
fect ones.

The solitary almost sessile cleistogamie 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, with-
out any opening or fissure." There is only a single

*Von Mohl, 'Bot. Zeitung,' of the perfect flower is mostly

1863, pp. 314 and 323. Dr. Brom- 5-cleft.

field rPhytologist,' vol. iii. p. f Journal Lmn. Soc.' vol. 11.

530) also remarks that the calyx 1857, p. 7. See also Professor

of the cleistogamie flowers is Oliver in 'Nat. Hist. Review,'

usually only 3-cleft, while that 1862, p. 240.
23

330 CLEISTOGAMIC FLOWERS. CHAP. VIII.

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-
pighiaceae seem to be more profoundly modified than
those in any of the foregoing genera. According to
A. de Jussieu f they are differently situated from the
perfect flowers; they contain only a single stamen, in-
stead 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." The
calyces of the perfect flowers are studded with glands,
and their absence on the cleistogamic flowers may prob-
ably be explained by an observation of Fritz Miiller,
who informs me that in the one species, Bunchosia
Oaudichaudiana, the fertilisation of which he has often
witnessed, the perfect flowers are regularly visited by
bees belonging to the genera Tetrapedia and Epicharis.
These bees sit down on the flowers, gnawing the
glands on the outside of the calyx, and in doing
so the under sides of their bodies are dusted with
pollen, by which afterwards other flowers are ferti-
lised. Such visits to the cleistogamic flowers would be
useless.

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

* Dr. Kirk, 'Jour. Linn. Soc.,' f 'Archives dn Museum.' trim.
vol. viii. 1864, p. 147. iii. 1843, pp. 35-38, 82-86, 589, 598.

CHAP. VIII. CLEISTOGAMIC FLOWERS. 331

capsules were produced in Mr. Farrer's hot-house; 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 papillae, 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 cleis-
togamic 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, 3| inches in length, which was sent me,
had likewise been developed from a single carpel. This
capsule contained an abundance of plumose seeds, many
of which appeared quite sound, but they did not ger-
minate when sown at Kew. Therefore the little
bud-like flower which produced this capsule prob-
ably was as destitute of pollen as were those which I
examined.

Juncus Ijufonius and Hordeum. — All the species
hitherto mentioned which produce cleistogamic flow-
ers are entomophilous ; but Juncus and seven genera
of Gramineae are anemophilous. Juncus lufonius is re-
markable * by bearing in parts of Kussia only cleisto-
gamic flowers, which contain three instead of the six
anthers found in the perfect flowers. In the genus

* See Dr. Ascherson's interesting paper in ' Bot. Zeitung,' 1871, p.
551. Also 1872, p. 697.

332 CLEISTOGAMIC FLOWERS. CHAP. VIII.

Hordeum it has been shown by Delpino * that the ma-
jority of the flowers are cleistogamic, some of the others
expanding and apparently allowing of cross-fertilisa-
tion. I hear from Fritz Miiller that there is a grass
in Southern Brazil, in which the sheath of the upper-
most 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 developing, and these plants afterwards produced
free or unenclosed panicles of small size, bearing per-
fect 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.f I pro-
cured plants from a stream near Eeigate, 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 ap-
pearance of the whole inside of the flower being thus
filled. The stigma is very small and the filaments ex-
tremely short; the anthers are less than -gV of an inch
in length, or about one-third of the length of those
in the perfect flowers. One of the three anthers de-
hisces before the two others. Can this have any rela-
tion with the fact that in some other species of Leersia

* ' Bollettini del Comizio agrario Hordeum, in ' Monatebericht d. K.

Parmense.' Marzo e Aprile, 1871. Akad. Berlin,' Oct. 1872, p. 7GO.

An abstract of this valuable paper f 'Bull. Bot. Soc. de France,'

is given in 'Bot. Zeitnng,' 1871. torn. x. 1863, p. 194.
p. 537. See also Hildebrand on

CHAP. VIII. LEERSIA. 333

only two stamens are fully developed ? * The anthers
shed their pollen on the stigma; at least in one in-
stance this was clearly the case, and by tearing open
the anthers under water the grains were easily detached.
Towards the apex of the anthers 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 in^nj- of an inch (.0181 mm.), whilst those of the
perfect flowers are about ^fa of an inch (.0254 mm.)
in diameter.

M. Duval-Jouv.e 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 fer-
tile. 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 stigmas and stamens
supported on long filaments with large anthers that
dehisced properly. If these florets had opened for a
short time unperecived by me and had then closed again,
the empty anthers would have been left dangling out-
side. Nevertheless they yielded on August 17th an
abundance of fine ripe seeds. Here then we have a near
approach to the single case as yet known f of this grass

* Asa Gray, ' Manual of Bot. of t Dr. Ascherson, ' Bot. Zcitung,'
United States,' 1856, p. 540. 1884, p. 350.

334 CONCLUDING REMARKS CHAP. VIII.

producing in a state of nature (in Germany) perfect
flowers which yielded a copious supply of fruit. Seeds
from the cleistogamic 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 sev-
eral exotic species, found that it apparently is the sole1
one which bears cleistogamic flowers. It ranges from
Persia to North America, and specimens from Pennsyl-
vania resembled the European ones in their concealed
manner of fructification. There can therefore be little
doubt that this plant generally propagates itself through-
out an immense area by cleistogamic 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 a sex-
ual 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 sta-
mens of 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 by no means
the case ; for various parts have been specially modified,

* T have collected several snch mestication.' ch. xviii. — 2nd edit,
cases in my ' Variation under Do- vol. ii. p. 153.

CHAP. VIII. ON CLEISTOGAMIC FLOWEKS. 335

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 Mono-
choria 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 Malpighiacese, 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 char-
acter becomes superfluous it tends sooner or later to
disappear.

Another peculiarity in these flowers is that the
pollen-grains generally emit their tubes whilst still

336 CONCLUDING REMARKS CHAP. VIIL

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 do"ubt 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 direction, lat-
erally 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 ab-
sence of any attraction to insects : and they thus
differ widely from the great majority of ordinary
flowers. Delpino believes f that cleistogamic flowers
have been developed in order to ensure the production
of seeds under climatic or other conditions which tend
to prevent the fertilisation of the perfect flowers. I do
not doubt that this holds good to a certain limited ex-
tent, but the production of a large supply of seeds with
little consumption of nutrient matter or expenditure of

* The case of Asclepias was de- emission of the tubes from the

scribed by E. Brown. Baillon as- pollen-masses while still within

serts ( ' Adansonia,' torn. ii. 1862, the anthers, in three widely dis-

p. 58) that with many plants the tinct Orchidean genera, namely

tubes are emitted from pollen- Aceras, Malaxis, and Neottia : see

grains which have not come into ' The Various Contrivances by

contact with the stigma ; and that which Orchids are Fertilised,' 2nd

they may be seen advancing hori- edit., p. 258.

zontally through the air towards t ' Sull' Opera la Distribuzione

the stigma. I have observed the dei Sessi nello Piante,' 18t>7, p. 30.

CHAP. VIII. ON CLEISTOGAMIC FLOWERS. 337

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 Oxalis 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 compared 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 Paeony.*
We thus see that cleistogamic 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
devoured by birds or other enemies. But this advan-
tage is accompanied by the loss of the power of wide
dissemination. !S!"o less than eight of the genera
in the list at the beginning of this chapter include
species which act in this manner, namely, several

* The an tli ori ties for these statements are given in my ' Effects of
Cross and Self-Fertilisation,' p. 376.

338 CONCLUDING REMARKS CHAP. VIII.

kinds of Viola, Oxalis, Vandellia, Linaria, Commelina,
and at least three genera of Leguminosae. 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 cu-
rious habit.

It has already been shown that in about 33 out of
the 67 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 eight 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
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

CHAP. VIII. ON CLEISTOGAMIC FLOWERS. 339

proportion of the plants bearing regular and irregular
flowers 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 ren-
dered 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 be-
haved 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 head of the
several species that this is not the case. The perfect
flowers of Viola are indeed sterile unless they are vis-
ited by bees; but when thus visited they yield the full
number of seeds. As far as I have been able to dis-
cover there is only one absolute exception to the rule
that the perfect flowers are fertile, namely, that of

* Dr. Ascherson, 'Bot. Zeit.,' 1871, p. 555.

3iO CONCLUDING REMARKS CHAP. VIII.

Voandzeia; and in this case we should remember that
cultivation often affects injuriously the reproductive or-
gans. Although the perfect flowers of Leersia some-
times yield seeds, yet this occurs so rarely, as far as
hitherto observed, that it practically forms a second ex-
ception to the rule.

As cleistogamic flowers are invariably fertilised, and
as they are produced in large numbers, they yield al-
together a much larger supply of seeds than do the per-
fect 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 seed-
lings of Ononis minutissima were put into competition
with two seedlings raised from cleistogamic flowers;
they were at first all of equal height; the crossed were
then slightly beaten; but on the following year they
showed the usual superiority of their class, and were to
the self-fertilised plants of cleistogamic 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
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,

CHAP. VIII. ON CLEISTOGAMIC FLOWERS. 341

but never expand (as with Thelymitra), and yet set
fruit, might easily be rendered eleistogamic. 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. Linnaeus
observed in 1753 that the flowers on several plants
brought from Spain and grown at TJpsala did not
show any corolla and yet produced seeds. Asa Gray
has seen flowers on exotic plants in the Northern United
States which never expanded and yet fruited. With
certain English plants, which bear flowers during near-
ly the whole year, Mr. Bennett found that those pro-
duced 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 Janu-
ary 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 an-
other in intermediate stations. Herr Bouche's obser-
vations 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 in-
creasing cold and darkness of the changing season, whilst
with others it is diminished by the increasing heat and
light.*

* For the statement by Linnseus, xxxix. 1865. p. 105. Bennett in

Bee Mohl in 'Bot. Zeitung,' 1863, 'Nature,' Nov. 1869, p. 11. The

S327 \sa Gray, ' American Rev. G. Henslow also says ( (jflr-

ournal of Science, '2nd series, vol. dener's Chronicle,' 1877, p. 271;

342 CONCLUDING REMARKS CHAP. VIII.

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 producing
their cleistogamic flowers under certain conditions, or,
on the other hand, producing them to the complete ex-
clusion 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 floAvers during
several successive years; and this is the case with Jun-
cus bufonius in its native land of Eussia. 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 development was due to cli-
mate; 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 indi-
rectly, 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 se-
lection might well complete the work and 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 completely closed
flower; also by the principle of correlated growth, and
by the tendency in all reduced organs finally to disap-

also 'Nature,' Oct. 19, 1876, p. ers are self-fertilised. On Lysima-

543) "that when the autumn rhia, H. Muller, 'Nature,' Sept.

draws on, and habitually in win- 1873, p. 433. Bouche, ' Sitzungrs-

ter for such of our wild flowers as hnricht der (resell. Naturforsch.

blossom at that season," the flow- Freunde,' Oct. 1874, p. 90.

CHAP. VIII. ON CLEISTOGAMIC FLOWERS. 343

pear. The result would be the production of cleisto-
gamic 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 wilt now sum up very briefly the chie'f 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 expenditure;
and we can hardly doubt that they have had their struc-
ture modified and degraded for this special purpose;
perfect flowers being still almost always produced so
as to allow of occasional cross-fertilisation. Herma-
phrodite plants have often been rendered monoecious,
dioecious or polygamous; but as the separation of the
sexes would have been injurious, had not pollen been al-
ready transported habitually by insects, or by the wind
from flower to flower, we may assume that the process
of separation did not commence 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 individual should not have its vital powers
taxed, under the struggle for life to which all organisms
are subjected, by producing both pollen and seeds.
With respect to the plants belonging to the gyno-dice-
cious sub-class, or those which co-exist as hermaphrodites
and females, it has been proved that they yield a much
larger supply of seeds than they would have done if
they had all remained hermaphrodites ; and we may feel
sure from the large number of seeds produced by many
plants that such production is often necessary or ad-

344 GENERAL CONCLUSIONS. CHAP. VIII.

vantageous. It is therefore probable that the two forms
in this sub-class have been separated 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 an-
other. If the sexual elements belonging to the same
form are united the union is an illegitimate one and
more or less sterile. With dimorphic species two ille-
gitimate unions, and with trimorphic species twelve
are possible. There is reason to believe that the ster-
ility of these unions has not been specially acquired,
but follows as an incidental result from the sexual ele-
ments 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 dis-
tinct species. Another and still more remarkable inci-
dental 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 dis-
tinct species.

INDEX.

ACANTHACE^.

COBYLXTS.

A.

Boragineie, 101.

Boreau on cowslip and primrose,

Acanthaceie, 312.

57.

Acer campestre, 12, 307.

Borreria, 127.

Adoxa, 9.

Bouch6 on Pavonia, 312 ; effect of

^giphila elata, 124.

temperature and light on corolla,

mollis, 124.

341.

obdurata, 124, 286.

Bouvardia leianiha, 135.

Alefeld, Dr., on Linum, 100.

Braun on Dracocephalum, 298.

Alisma natans, 310.

Breitenbach, W., on Primula ela*

Amphicarpsea, 326.

lior, 34, 272.

Amsinckia spectabilis, 110; varia-

Bromfield, Dr., on primrose and

bility in length of stamens and

cowslip, 57 ; Primula elatior, 73 ;

pistil, 262, 267.

Specularia perfoliata, 329.

Anchusa arvensis, 111.

Brown, Eobert, on sexual changes,

Androsace vitalliana, 53.
Anthers, size of, in different forms,

282.
Buckwheat, the common, 111.

253 ; contabescent, 283.

Arachis, 311.

Arnebia hispidissima, 111.

C.

Ascherson, Dr., on Salvia deisto-

gama, 312, 339 ; Juncus bufonins,

Cattha palustris, 13.

332 ; Leersia oryzoides, 333.

Campanula colorata, 329.

Asclepias, 336.

Cardamine amara, 307.

Ash, the common, 11.

Caspary, Prof., on Rhamnus cathar-

Asperula scoparia, 284.

ticus, 293.

Axell on Primula strieta, 50.

Cattleya, 312.

Chamissoa, 291.

Cinchona micrantha, 134.

B.

Cleistogamic flowers, 309; list of

genera, 311 ; on their origin,

Babington, Prof., on Primula ela-

342.

tior, 72 ; fitellaria graminea, 312.

Cnicus acaulis, 306.

Baillon, emission of the tubes from
pollen-grains, 336.

palustris, 306.
Coccocifpselurn, 133; pollen-grains

Belhomme, M., on ray-florets, 6.

of, 251.

Bennett, A. W., on Impatiens fulva,
326 ; flowers fertilised whilst in
the bud state, 341.

Coprosma, 285.
Cordia, 117 ; pistil of, 254.
Corolla, difference in size in the

Bentham, Mr., on the differentia-

sexes of the same species, 307,

tion of the sexes, 11.

308.

Bentham, Mr., on the cleistogamic

Corydalis, 146.

flowers of Ononis, 325.

Corylus avellana, 10.

24 345

346

INDEX.

COWSLIP.

GYNO-DKECIOUS.

Cowslip, the common, 14 ; short-

Euonymus Europseus, 287-292.

ana long-styled, 19-22, 56-71.

Euphrasia offieinalis, 4.

Cratoxylon formosum, 123.

Euryale, 310.

Crocker, C. W., on Plantago lanceo-

lata, 306.

F.

Cryptostachys, 312.

Ctiphea purpurea, 168.

Faramea, 129 ; pollen-grains, 129.

,

Fitzgerald, Mr., on Tlielymitra, 312.

Forsythia suspensa, 117 ; stamens,

D.

253.

viridissima, 117.

Darwin, Charles, on reproductive

Fragaria Chiloensis, 292.

organs under cultivation, 7 ; in-

elatior, 293.

tercrossed plants, 30 ; prepotency

vesca, 292.

of pollen, 62 ; insects fertilising,

Virginiana, 292.

flowers, 79 ; Cephalanthera gran-
diflora, 98 ; Epidendron and Cat-

Fraxinus excelsior, 11.

tleya, 313 ; number of pollen-

grains, 337.

G.

, W., on Pulmonaria angusti-

folia, 105, 107.

Galium cruciatum, 286.

Datura arborea, 252.

Gartner on the sterility of unions

Delpino, plants fertilised by the

between distinct species, 29 ;

wind, 10 ; on the walnut, 10 ;

Primula vulgaris and veris, 58,

Polygonacese, 114; pollen-grains,

59 ; hybrid Verbascums, 76, 77,

251 ; Thymus serpyllum, 299 ;

80 ; prepotency of pollen, 242 ;

closed or cleistogamic flowers,

variation in the sexual powers

310, 336 ; Viola odorata, 316.

of plants, 268 ; contabescent an-

Dianthus barbatiis, 30.

thers, 193, 283.

Dickie, Dr., on Eriophorum angus-

Gentianeie, 115.

tifolium, 307.

Geraniacese, 168.

Dictamnus fraxinetta, 146.
Diodia, 135.
Dioecious and sub-dioecious plants,

Geranium syhaticum, 307.
Gesneria pendulina, 262.
Gilia aggregata, 118.

287.

coronopifolia, 119.

Discospermum, 286.

micrantha, 119.

Doubleday, H., on Primula elatior,

nudicaulis, 119.

73.

pulchella, 118.

Dracocephalum Moldavicum, 298.
Drosera Anqlica, 328, 341.
rotundlfolia, 327.

Gillibert on Menyanthes, 310.
Gloriosa lily, the, 146.
Godron on hybrid Primulas, 55.

Duval-Jouve, M., on Cryptostachys,
313 ; Lcersia oryzoides, 332, 333.

Gray, Prof. Asa, proposes the term
heterogone or heterogonous, 2 ; on

Dyer, Thiselton, on Salma Hor-

Linum, 101 ; Leucosmia Burnetti-

minum, 8 ; Cratoxylon formosum,

ana and acuminata, 114; For-

123.

sythia suspensa, 117 ; Gilia pul-

chella, 118 ; G. coronopifolia, 119 ;

E.

Phlox subulata, 120 ; Mitchella

repens, 125 ; heterostyled plants,

Echium vulgare, 111, 305, 307.
Epidendron, 312.

245 ; Coprosma, 285 ; Euonymus,
287 ; Rhamnus lanceolatus, 295,

Epigssa repens, 296.

296 ; Epigtea repens, 296 ; Ilex

Equal-styled vars. of Primula, 273.

opaca, 298 ; Plantago media, 306 ;

Eranthemum ambiguum, 328.

Oxybaphus and Nyctaginia, 312 ;

Eriophorum angu'sti folium, 307.

impatiens fulva, 327 ; Leersia,

Erythroxylum, 121 ; pollen-grains
of, 251.

333 ; cleistofjamic flowers, 341.
Gyno-dicecious plants, 298.

INDEX.

34?

Hart, Mr., on Nepeta glechoma,
300.

Hautbois Strawberry, the, 293.

Hedyotis, 133.

Henslow, Eev. Prof., on hybrid
Primulse, 61.

Henslow, Ecv. G., on flowers self-
fertilised during the winter, 341.

Herbert, Dr., on hybrid Primulx,
61.

Heterostyled plants, illegitimate
offspring of, 188-244; essential
character of, 245; summary of
the differences of fertility be-
tween legitimately and illegiti-
mately fertilised plants, 247;
diameter of pollen-grains, 250 ;
size of anthers, structure of stig-
ma, 253 ; list of genera, 256 ; ad-
vantages derived from Hetero-
stylism, 259 ; means by which
plants became heterostyled, 261 ;
transmission of form, 269 ; equal-
styled varieties, 273 ; final re-
marks, 275.

• dimorphic plants, 14-54, 81-

138.

trimorphic plants, 137-187.

Hibiscus, pollen-grains, 337.

Hildebrand, Prof., introduces the
word " heterostyled," 2 ; on the
ray-florets of the Composite, 5, 6 ;
Primula Sinensis, 38, 40-42, 192,
217 ; Linum (trandiflorum, 86, 87 ;
L. perenne, 92 ; Pulmonaria offi-
cinalis, 101-103, 107, 239; P.
azurea, 110 ; Polygonum fagopy-
rum, 111 ; Oxalis, 169, 171-174,
177, 181, 212-213, 321 ; herma-
phrodite plants becoming uni-
sexual, 283 ; Hordeum, 332.

Homostyled species of Primula. 49.

Hooker, Dr., on Campanula, 329.

Hordeum, 331.

Hottonia inflata, 53, 312.

palustris, 50 ; relative fertility,

52 ; anthers of, 253 ; papillae on
stigma, 255.

Houstonia casrulea, 132, 255.

Hoy a carnosa, 330.

Hybrid Primulas, 55-71.

Hydrangea, 6, 7.

Hypericinese, 123.

Hyssopus officinalis, 298.

I.

Hex aguifolium, 297.

opaca, 298.

Illegitimate offspring of hetero-
styled plants, 188 ; Lythrum sali-
caria, dwarfed stature and ster-
ility, 192 ; Oxalis, transmission
of form to seedlings, 212 ; Pri-
mula sinensis, in some degree
dwarfed, 215 ; equal-styled va-
rieties, 218-223 ; Primula vul-
garis, 225 ; transmission of form
and colour, 225 ; seedlings, 227 ;
P. veris, 229 ; dwarfed stature
and sterility, 229-235; equal-
styled varieties, 235, 239 ; par-
allelism between illegitimate
fertilisation and hybridism, 243.

Tllecebrum, 310.

Impatiens, pollen-grains of, 337.

balsamina, 327.

fulva, 326.

noli-me-tangere, 327.

J.

Juglans refiia, 10.
Juncus bufonius, 331, 342.
Jussieu, A. de, on Malpighicese,

0«Jft

Kerner, Prof., on ray-florets, 6;
Auricula, 43 ; hybrid forms of
Primula, 55, 73 ; on use of hairs
within the corolla, 128; size of
corolla in male flowers, 308 ; use
of glands as a protection to
flowers, 330.

Kirk, Dr., on Monochoria vaginalis,
330.

Knoxia, 135.

Koch on Primula longiflora, 49.

KrascheniniTcowia, 312.

Kuhn, Dr., on cleistogamic flow-
ers, 3, 309, 310 ; list of plants pro-
ducing differently formed seeds,
9 ; heterostyled plants, 244 ; Van-
dellia nummularifolia, 323 ; V. ses-
siflora, 324.

348

INDEX.

L AGEBSTBCEMIA .

MULLEE.

Lythrum Grxfferi, 164.

L.

hyssopifolia, 165.

salicaria, 116, 137 ; power of

Lagerstrcemia Indica, 167.
parviflora, 167.

mutual fertilisation between the
three forms, 149-157; summary

regime, 167.
Lathyrus nissolia, 325, 341.

of results, 157-164; illegitimate
offspring from the three forms,

Lecoq, H., on the common maple,

191-203 ; concluding remarks on,

12; cowslips and primroses, 57;

203-211; mid-styled form, 241,

Primula elatior, 72 ; Linum Aus-

258, 259, 280 ; seeds, 249.

triacum, 98 ; Lythrum hyssopifolia,

thymifolia, 165.

166; Ehamnus, 296; gynodice-

cions plants, 298 ; Scabiosa suc-

cisa, 304 ; Viola odorata, 316.

M.

Lecrsia orysoides, 332-334; pollen-

grains of, 337.

Malpighiacex, 330.

Leggett, Mr., Pontederia cordata,

Manettia bicolor, 135.

186.

Maple, the common, 12.

Legitimate unions, summary on
the fertility of the two, com-

Marshall, W., on Primula elatior,
73 ; Plantago lanceolata, 306.

pared with that of the two ille-

Masters, Dr. Maxwell, on cleisto-

gitimate in Primula, 46-49 ; fer-

gamic flowers, 3.

tility of, compared with illegiti-

Maximowicz on Krascheninikowia,

mate, 247.

312.

Leighton, Eev. W. A., on the cow-

Meehan, Mr., on Mitchella, 285;

slip and primrose, 56 ; Verbascum
virgatum, 78.

Epigsea repens, 297.
Melissa clinipodium, 298.

Leontodon, pollen-grains, 337.

offidnalis, 298.

Leptosiphon, 119.

Mello, Correa de, on Arachis, 312;

Leucosmia acuminata, 114.

Voandzeia, 326.

Burnettiana, 114 ; stigma, 254.

Mentha aquatica, 398.

Lily, the Gloriosa, 146.

hirsuta, 298.

Limnanthemum Indicum, 115 ; pol-
len-grains, 251 ; anthers, 253.

vulgaris, 298.
Menyanthes, 310.

Linaria spuria, 324.

trifoliata, 115.

Lindley on Fragaria elatior, 293.
Linnaeus on Primula veris, vulgaris,

Michalet on Oxalis acetosella, 320 ;
Linaria spuria, 324.

and elatior, 56.

Mitchella, 285.

Linum angustifolium, 100.

repens, 125.

Austriacum, 97.

Mohl, H. von, on the common

catharticum, 100.

cowslip, 14 ; size of corolla in the

corymbiferum, 100.

sexes of the same species, 307 ;

flavum, 81, 98; stamens, 253.

Trifolium and Arachis, 311 ; cleis-

grandiflorum, 81 ; various ex-
periments, 87-89, 96 ; pistils and

togamic flower, 313, 341; Oxalis
acetosella, 320 ; Impatiens noli-

stamens, 254, 255; sterile with

me-tangere, 327 ; Specularia per-

its own-form pollen, 264, 266,

foliata, 329.

267.

Mollia lepidota, 168.

Lewisii, 101.

— — speciosa 168.

perenne, 90; torsion of the

Monnier, M., on Viola, 317.

styles, 95 ; long-styled form, 97 ;

Monochoria vaginalis, 329.

stigma, 248.

Mulberry, the, 10.

salsoloides, 100.
trigynum, 100.

Miiller, D., on Viola canina, 313.
Miiller, Fritz, on pollen of the Vil-

usitatissimum, 100.
Lipostoma, 134.
Lysimachia vulgaris, 4, 341.

larsia, 116; Faramea, 129-131;
Posoqueria fraqrans, 131 ; Nessea,
166 ; Oxalis, 179, 180 ; Pontederia,

INDEX.

349

MULLEB.

PRIMULA.

182-184; Oxalis Begnelli, 212;
Chamissoa, 291.

Oxalis speciosa, 168, 175, 212.
stricia. 181.

Miiller, H., on the frequency of

tropseoloides, 181.

visits by insects to the Umbelliferx
and Composites, 5 ; on dichogamy,
10 ; on Anthophora and Bombylius

Valdivmna, 170-172, 212.
Oxlip, the Bardfield, 32, 72.
, the common, 55 ; differences

sucking the cowslip, 22 ; Primula

in structure and function be-

elatior, 32 ; P. villosa, 49 ; Hottonia

tween the two parent species, 56 ;

palustris, 51 ; table of relative fer-
tility of, 52 ; Linum catharticum,
100; Polygonum fagopyrum, 112;

effects of crossing, 60 ; a hybrid
between the cowslip and prim-
rose, 70.

Lythrum salicaria, 145; on the

Oxybaphus, 312.

origin of heterostylism, 264 ; on

the Labiate, 298, 303; Thymus

serpyllum, 300 ; Scabiosa arvensis,

P.

304 ; Plantago lanceolata, 306 ; size

of corolla in the two sexes of the

Pseony, pollen-grains of, 337.

same species, 308 ; Impatiens bal-
samina, 327 ; Lysimachia, 342.

Parallelism between illegitimate
and hybrid fertilisation, 240.

Myosotis, 307.

Pavonia, 312.

Phlox Hentzii, 120.

nivalis, 120.

N.

subulata, 120, 287.

Planchon on Linum salsoloides, 100 ;

Nepeta glechoma, 300.

L. Lewisii, 101 ; on Hugonia, 100.

Nertera, 285.

Plantago lanceolata, 306.

Nessea verticillata, 166.

media, 306.

Nolana prostrata, variability in

Polemoniacese, 118.

length of stamens and pistil, 262.

Pollen-grains, relative diameter of,

Nydaginia, 312.

250.

Polyanthus, 18.

Polygonacex, 111.

0.

Polygonum bistorta, 113.

fagopyrum, 111, 240 ; pollen-

Oldenlandia, 132.

grains, 252.

Oleacese, 117.

Pontederia, 182 ; pollen-grains, 185 ;

Oliver, Prof., on ovules of Primula

size of anthers, 253.

veris, 17; Viola, 317; Campanula

cordata, 186.

colorata, 329.

Posoqueria fragrans, 131.

Ononis columnx, 324.

Primrose, the common, 34, 57-71.

minutissima, 325, 340.

Primula, the, heterostyled species

parviflora, 325.

of, 14 ; summary on, 45-49 ;

Origanum vulqare, 298.
Oxalis acetosella, 181; pistil of, 262;

homostyled species, 49.
auricula, 30, 43, 48, 74, 223.

cleistogamic flowers, 320 ; pollen-

equal-styled varieties, 273.

grains, 337.

cortusoides, 44.

Bowii, 179.

elata, 49.

compressa, 178.

elatior, Jacq., 32 ; relative fer-

corniculata, 181.

tility of the two forms, 32, 47 ;

Deppei, 179.

not a hybrid, 72, 73; equal-

hedysaroides, 213.
homostyled species, 181.

styled var. of, 224, 273.
farinosa, 45 ; equal-styled

incarnata, 321.

var., 224, 273.

Eegnelli, 173, 174, 212.

hirsuta, 74.

rosea, 177, 213.

involucrata, 45.

(Biophytum) sensitiva, 180, 321 ;
stigma, 254.

lonqiflora, 49.
moilis, 49, 50.

350

INDEX.

PBIMULA.

TEEVIRANUS.

Primula Scotica, 49, 50.

Salcia Horminum, 8.

Sibirica, 49.

Satureia hortensis, 302, 304.

Sikkimemis, 44, 47.

Scabiosa arvensis, 304.

Sinensit, 22, 29, 38 ; relative

atro-purpurea, 305, 307.

fertility, 39-43, 47, 48; long-

succisa, 305.

styled, 213 ; short-styled, 215 ;

Scott, J., on Primula auricula, 30,

transmission of form, constitu-

43, 223; P. vulgaris, 34; (var.

tion and fertility, 216 ; equal-

rubra), 225 ; P. Sikkimensis, 44 ;

styled variety, 218-223, 273, 274.
stricla, 50.

P. farinosa, 45, 224 ; homostyled
Primula;, 49, 50 : hybrids, 74, 75 ;

veris, 14 ; difference in struc-

length of pistil, 272; Hottonia

ture between the two forms, 15 ;

palustris, 51 ; Androsace vital-

degrees of fertility when legiti-

liana, 53; Polyanthus, 58; Mit-

mately or illegitimately united,
25-32 ; fertility possessed by ille-
gitimate plants, 228-235 ; equal-
styled red variety, 235-239 ;
long-styled, 242 ; length of pistil,

chella repens, 127 ; Acanthacete,
312 ; Eranthemum ambiquum bear-
ing three kinds of flowers, 328.
Scrophularia aquatica, 147.
Serratula tinctoria, 280, 306.

262, 266.

Sethia acuminata, 123.

verticillata, 49, 50.

Sethia obtusifolia, 123.

vttlosa, 49.

Smith, Sir J. E., on the carrot, 8 ;

vulgaris (var. acaulis Linn. ),

hybrid Verbascums, 76, 78; Ser-

34 ; pollen-grains, 35 ; relative

ratula tinctoria, 280 ; Onicus, 306 ;

fertility of the two forms, 36;

Subularia, 310.

length of pistil, 267.

Soldanella alpina, 54.

Primula vulgaris, var. rubra, 225-

Specularia perfoliata, 329.

228.

Spence, Mr., on Mollia, 168.

Prunella vulgaris, 298.

Spermacoce, 135.

Psyehotria, 135.

Sprengel on Hottonia palustris,

Pulmonaria angustifolia, 104, 240 ;

50.

anthers, 253, 287.
azurea, 110.

Stellaria graminea, 312.
Strawberry, the Hautbois, 293.

officinalis, 101, 239 ; number

Subularia, *310.

of flowers, 249 ; pistil, 251.

Suteria, 131.

E.

T.

Ranunculus aquatilis, 310.

Thelymitra, 312.

Ray-florets, their use, 5, 6.
Rhamnus catharticus, 293, 307 ; size

Thomson, Dr., on Campanula, 329.
Thrum-eyed, origin of term, 14.

of corolla, 308.

Thwaites, Mr., on ovules of Lim-

frangula, 296.

nanthemum Indicum, 115; Sethia

lanceolatus, 295.

acuminata, 123; Discospermum,

Rhinanthus crista-galli, 4.

286.

Rubiacese, 125, 131-136 ; size of an-

Thymelia, 114.

thers, 253 ; stigmas, 254 ; number

Thymus citriodorus, 301.

of heterostyled genera, 284-286.

serpyllum, 299, 301, 304.

Rudgea eriantha, 135.

vulgaris, 302.

Rue, the common, 9.

Timbal-Lagrave, M., on hybrids

Ruellia tuberosa, 328.

in genus Cistus, 76.

Torrey, Dr., on Hottonia inflata,

53, 312.

S.

Transmission of the two forms of

heterostyled plants, 269-270.

Salvia, 307.

Treviranus on Androsace vitalliana,

cleistogama, 339.

53 ; Linum, 81.

INDEX.

351

VANDELLIA.

V.

Vandellia nummulari folia, 323.

sessiflora, 324.

Vaucher on the carrot, 8 ; Solda-
nella^alpina, 54; Lythrum sali-
caria, 138, 144; L. thymifolia,
165 ; Ilex aquifolium, 297 ; on
Labiatie, 298; Viola hirta and
collina, 316.

Verbascum, wild hybrids of, 75-
80.

lychnitis, 30, 76-78.

phazniceum, 78.

thapsus, 76-79.

virgatum, 78.

Viburnum, 6, 7.

Vicia, 326.

Villarsia, 116 ; anthers, 252.

Kioto alba, 314, 319.

bicolor, 319.

biflora, 319.

conina, 313, 320.

collina, 316.

rfafior, 319.

hirta, 317, 319.

ionodittm, 319.

WKAY.

Fioto Zawci/oZia, 319.

mirabilis, 319.

nawa, 318, 319 ; pollen-grains

of, 337.

odorata, 316, 335.

palustris, 319.

Roxburghiana, 318.

Ruppii, 319.

sylvatica, 319.

tricolor, 319.

Foawdseio, 326.

W.

Walnut, the, 10.

Watson, H. C., on cowslips, prim-
roses, and oxlips, 57, 60, 63;
Primida elatior, 72, 73.

Weddell, Dr., on hybrids between
Aceras and Orchis, 76.

Wetterhan, Mr., on Corylus, 10.

Wichura, Max, on hybrid willows,
76 ; sterile hybrids, 241.

Wirtgen on Lythrum salicaria, 138,
144, 148.

Wooler, W., on Polyanthus, 18.

Wray, Leonard, on Fragaria, 293.

THE EXD.

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