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Full text of "The different forms of flowers on plants of the same species"


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New York: D, APPLETON & CO., Publishers. 



THE DIFFERENT FORMS OF 

FLOWERS ON PLANTS OF 

THE SAME SPECIES 



BY 



CHARLES DARWIN. M.A., F. R. S. 



WITH ILLUSTRA TIONS 



NEW YORK 
D. APPLETON AND COMPANY 
1903 



Authorized Edition. 



TO 

PKOFESSOR ASA GBAT 

THIS VOLUME IS DEDICATED BY THE AUTHOR 
AS A SMALL TRIBUTE OP RESPECT AND AFFECTION. 



PEEFACE TO THE EEPEINT 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. 

Heteeosttled 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. 



vi PREFACE TO THE REPRINT OF 1884. 

He also describes two forms of Bandia 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./ zviii. p. 524) 
shows that Maerotomia 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 Maero- 
tomia as having specimina longistyla and brevistyla. 

Breitenbach ('Botanische Zeitung,' 1880, p. 577) 
believes that the ancestor of the heterostyled Primulse 
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. 1083) and by Hermann Miiller (' 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. Frban (' Sitz. Bot. Verein, Prov. Brandenburg,' 



PREFACE TO THE REPRINT OF 1884. yii 

xxiv., 1883) states that the TurneraceBe 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 Turneraeese 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. 

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

1. Hermaphrodites with white anthers. 

3. 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 Gynodicecious plants. 

1. They are all more or less dichogamic. 

2. In the protaitdrous 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. 383, in 
connection with observations by Hildebrand. 

In a subsequent paper (' Botan. Centralblatt,' 1880, 
iv. p. 839) he describes a similar gynodicecious 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. 1031) 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 homogamie (or weak- 
ly protogynous) . The first form is more like E. macro- 
denum, which is markedly protandrous, and where auto- 
gamy is impossible. 

Hermann Mtiller ('Nature,' xxiii. p. 337, 1881) 
has shown that Syringa persica is gynomoncecious, 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 OP 1884. ix 

of gynodioeciousness. 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 fune- 
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 gynodioecious plants. Miiller formerly 
explained the origin of gynodioeciousness 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.* 

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

But H. MuUer ('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. Got- 
tingen,' xxviii., and 'Kosmos,' 1881) has given in his 

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



X PREFACE TO THE REPRINT 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 
1310) 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, 
Aira. 

F. Miiller (' ITature,' xxiv., 1881, p. 307) has made 
the curious observation that in the Melastomaceous 
lieeria, 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 Commelyna cwhstis 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 



PKEPACE TO THE REPRINT OP 1884. xi 

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

J. E. Todd ('American Katuralist/ xvi., 1883, p. 
381) gives a curious account of Solarium 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 Flov^tees. 

According to P. Ascherson ('Bulletin Soc. Linn, de 
Paris,' 1880, p. 350),* Helianthemum salicifolium was 
shown by Linneeus to produce ripe seed from closed 
flowers. Ascherson describes the cleistogamic flowers 
of H. Kahiricum and H. Lippiiy. micranthum, 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 
amplexibaule, Juncus bufonius, Ajuga Iva, Campanula 
dimorpliantha. 

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 PEBPACE TO THE REPRINT OP 1884. 

The following Aeanthaeeae have cleistogamic flow- 
ers: Stenandrium rupestre, DicUpetra assurgens, Ste- 
monacanthus coccinetis, Dianthera sessilis, Blechum 
Broivnei. 

Among other families: Erithalis fruticosa {Rubia- 
cea) , Polystachya 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. 

r. 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 Podostomaeese of Brazil produce 
flowers which are probably cleistogamic. 

Solms-Laubach (' Gottingen Naehrichten,' June, 
1883) has written an interesting paper on Heteranthera, 
a plant belonging to the Pontedereaeese. He describes 
the eleistogamy 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. 
callcefolia could not be distinguished from H. Kotsch- 
yana. 

Fkastcis Dakwin. 
Jan., 1S84, 



PKEFACE TO THE SECOND EDITIOK 



Since the publieatioii 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 
'('Fature,' Jan. 1, 1880, p. 317) 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- 
neriacese, 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.,' 
18C6, p. 201), but has since been confirmed by Dr. Ign, 

ziii 



xiv PKEPACE. 

Urban/ in ' Linnasa/ 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. Lewisii, 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. AVilson informs me that on comparing 
the pollen-grains from a long-styled plant of Erythrcea 
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 
Menyanthes trifoUata, a member of the same family of 
the Gentianeaa. 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 Rubiaeese contain many more heterostyled 
plants than any other family, and several additional 
cases can now be added. Mr. C. B. Clarke has been 
so kind as to send me sketches made in India of two 
extremely distinct forms of Adenosacme longifdlia. 
He remarks "that the peculiarity of the case is not 
.the difference in the length of the style and stamens 



PKEPAQB. XV 

in the two forms, but the extreme difEerence 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 Rubiaceae of tropical Africa ('Journal 
Linn. Soc. Bot.,' vol. xvi., 1877, p. 353), remarks that 
dimorphism occurs commonly, or at least in some spe- 
cies, in four or five genera in the tribe of Hedyotideee. 
Mr. M. S. Evans states (' Nature,' Sept. 19, 1878, p. 
543) that in Ifatal there is a heterostyied Eubiaeeous 
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 
heterostyied dimorphic plants, and one of these is a 
monocotyledon. 

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

With respect to trimorphic heterostyied 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- 
styied, and 340 which are homostyled. He informs 
me that Lyihrum thymifolia is not heterostyied, 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 N^esaea; thus two new 



xvi 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. 390. The same author 
shows (Ibid., p. 130) that Valeriana dioica exists under 
font 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,' tom. xxv., 
1878) a paper entitled, 'Disjonction des sexes dans 
VEuonymus Europceus,' which may be compared with 
my observations on the same plant. I have stated 
at p. 397 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 /. 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 
inflata 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-dicecious sub-class. 
In an article in the ' Bull. Torrey Bot. Club,' July, 1871, 
this Silene is, however, said to be gyno-dicecious. As-' 
■paragus officinalis is also polygamous, and the female 
flowers are about half the size of the male ones; see 
'Gard. Chron.,' May 35, 1878 ; also Breitenbach, in 'Bot. 
Zeitung,' 187«, 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 Dianfhus 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-dicecious in England ; 
and Dr. F. Ludwig of Greiz has sent me a description 
of no less than flve 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, 
128j and 290) the view which he has propounded; and 
several botanists think it more probsible 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-dicecious condition, or ex- 
isting as hermaphrodite and male individuals. But H. 
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-dicecious plants. 
Asa Gray has also reason to suspect that Diospyros vir- 
giniana may be andro-dicecious. 

The eighth chapter is devoted to cleistogamic flipwers, 
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 TrifoKum polymotphum produces true cleis- 
togamic flowers. Dalibarda, Milium, and Vilfa 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. 348, and those of another Gramineous genus, Di- 
plachne, by Aseherson, 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,' tom. v. fasC. 2, 1878), 'Kleisto- 
gamische Bliithen der Caryophylleen,' namely, on Ceras- 
tium and Polycarpon. F. Ludwig has described the cleis- 
togamic flowers of Gollomia 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 (' Naehrichten k. Gesell. 
der Wissen. zu Gottiiigen/ June 1, 1878) the cleisto- 
gaihic 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 
Natutalist,' 1878, p. G9) this is likewise the case with 
Lithospermum longiflorum. Three genera of Orchideas 
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. 338) 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 v. 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 Pyr^ndes,' 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 Amphi- 
carpwa 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 tjV 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 > i , . . Page t 

Preface , t , , , . xiii 

Introduction ..>•.<<<!. 1-13 



CHAPTER I, 

Heterostyled Dimorphic Plants : Primulace^. 

Primula veris or theCowsUp — Difleretlces 1ft structure between the 
two forms — Their degrees of fertility when legitimately and 
illegitimately united — P. elatiof, 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 Verbascum ........ 55-80 



xxii CONTENTS. 

CHAPTER III. 

Hetbrosttlkd Dimohphic Plants — continued, 

Linum grandiflorum, long-styled form utterly sterile with own- 
form pollen — Linum perenne, torsion of the pistils in the 
long-styled formal one — Homostyled species of Linum — Pul- 
monaria officinalis, singular difference in self-fertility between 
the English and German long-styled plants — Pulmonaria 
angustifolia shown to be a distinct species, long-styled form 
completely self-sterile — Polygonum f agopyrum — 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. 

Heterostyled Tbimobphic 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 Grsefferi likewise trimorphio — ^L. thymi- 
folia dimorphic — li, hyssopifolia homostyled — Nesaea verti- 
cillata trimorphic — Lagerstrcemia, nature doubtful — Oxalis, 
trimorphic species of — O. Valdiviana — 0. Regnelli, the illegiti- 
mate unions quite barren — 0. speciosa — O. sensitiva — ^Homo- 
styled species of Oxalis — Pontederia, the one monocotyledonous 
genus known to include heterostyled species - . . 137-187 

CHAPTER V. 

Illegitimate Offspring of Heterostyled Plants. 

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



CONTENTS. xxiii 

fertile — Oxalis, transmission of form to the legitimate and 
illegitimate seedlings — Primula Sinensis, illegitimate offspring 
in some degree dwarfed and infertile — Bqnal-styled varieties 
of P. Sinensis, auricula, farinosa, and elatior — P. Tulgaris, 
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. 

CoNCLuoiira Remakks on Heterosttled 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 — Pinal re- 
marks 245-277 



CHAPTER VII. 

POLTOAMOUS, DiCECIOUS, AND GyNO-DI<ECIOUS PIiANTS, 

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



XXiT CONTENTS. 

CHAPTER VIII. 

Cleistooauic Flowers. 

General character of cleistogamic flowers — List of the genera pro- 
ducing such flowers, and their distribution in the Tegetable 
series — ^Viola, description of the cleistogamic flowers in the 
several species ; their f ertilit 7 compared with that of the per- 
fect flowers — Ozalis acetosella — O. 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. 



IlfTRODUCTION. 

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, Linn^eua 
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 fiowers 
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 trimorphie, 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. 7,7. Hybrid Nature of . the Common 

"On the Existence of Two Oxiip. With Supplementary Ee- 

Forms, and on tlicir Boeiprocal marks on Naturally Produced Hy- 

SexualBelation, in Several Species hrids in the Grenus Verbascum." 

of th'e Qeiius Linum." Ibid. vol. Ibid. vol. x. 1868, p. 437. 
vii. 1863, p. 69. * The term "heterostyled" does 

" On the Sexual Belations of not express all the differences be- 

the Three Forms of I/jiOtrum aali- tween the fonqs ; but this is a 

carta." Ibid. vol. iii. 1864, p. 169. &ilure 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 Trimorphie Plants," hderogane or Aeteroj7onotM, though 

Ibid. vol. X. 1868, p. 893. this has been proposed by so high 

"On the Specific Differences an authority as Prof. Asa Gray: 

between PrimvXa dctm, Brit. Fl. see the 'American Natuialist, 

(var. ojjicmalit, Linn.), P. vuXgarit, Jan. 1877, p. 42, 
Srit. Fl. (vai. ocauJis, Linn.), and 



INTRODUCTION. 3 

to be heterostyled. Again, a species tending to become 
dioecious, witli 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 Zeitnng,' 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 aflected 

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

belong to a diflterent class of though they have sometimes been 

cases from cleistogamic flowers, ranked as cleistogamic, do not 

This deficien<y seems to result come within our present scope : 

from the conditions to which the see Dr. Maxwell Mastete, ' 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- 
fhus 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 towai-ds the outside of 
the iijflorescence 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. 



*H. MuUer, ' Nature,' Sept. 25, 'Die Befrnchtung der Blnmen,' 
1873 (vol. viii.), p. 433, and Nov. &c., 1873, p. 294. 
20, 1873 (vol. ix.), p. 44. Also 



INTRODUCTION. 5 

It is familiar to every one that the ray-florets of the 
Compositae, often differ remarkably from the others; and 
so it is with the outer flowers of many Umbelliferse, 
some CrucifersB, and a few other families. Several 
species of Hydrangea and Viburnum offer striking 
instances of the same fact. The Eubiaceous genus 
Mussaenda 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 bracteae, 
&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 Compositae 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 t that 
the ray-florets of the Compositae 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,' t See his interesting memoir, 

London, new series, vol. i. 1872, 'TJeber die Geschlechtsverhalt- 

pp. 161-164. nisse bei den Compositen,' 186B, 

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



6 INTRODUCTION. 

ing cold rainy weather, so as to protect the floret's 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 
Compositse; or the male organs alone are aborted, as 
in many Composits. Between the sexlessy 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. 



* Kemer clearly shows thilt 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, 'Vegetahle 188), remarks that "The flowers 

Kingdom,' on Chrysanthemnm, or petals of plants are perhaps in 

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

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

der Bliithen gegen unberufene domer eaten by insects." 

Gaste,' 1875, p. 19) insists that the t 'Ueber die Geschleohtsver- 

petals of most plants contain mat> haltnisse bei den Compositen,' 

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



INTRODUCTION. T 

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-dioecious — ^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 



. *Ihave discussed this subject in xviii. 2nd edit. vol. ii. pp. 152, 
my ' Variation of Animals and 156. 
Plants under Domestication,' chap. 
3 



8 INTR0DUCTI03J. 

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 Labiatas, 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 TJmbelliferse, 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 
unabel at all more eonspieuous 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 \ " 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, 1834, vol. ii. p. 39. Echinophora, p. 627. 

t 'Hist. Phys. desPlantesd'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 Compositse, 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 monceeious 
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 mestication,' chap. xzvi. 2nd edit, 

pelorism, has been discussed, and vol. ii. p. 338. 

references given, in my ' Variation f ' Bot. Zeitnng,' 1867, p. 67. 
of Animals and Plants under Do- 



10 INTROBUCTION. 

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 dioecious 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 

Lignaggio Anemofilo,' Firenze, proterandrous and proterogynous 

1871. hermaphrodite individuals of the 

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

suUa Dicogamia,' part. ii. fesc. ii. Befruchtung,' &c., pp. 285, 339 

p. 337. Mr. Wetterhan and H. % ' Gardener's Chron.,' 1847, pp. 

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



INTRODUCTION. H 

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- 
dicecious species. 

The fourth and last Class consists of the plants which 
were called polygamous by Linnoeus; but it appears to 
me that it would be convenient to coniine 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, hut 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 monoscious 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 Lccoq 
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-monoecious, 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-monoecious. If there 
exist plants, the individuals of which consist o! herma- 
phrodites and males, these might be distinguished 
as andro-dicecious. But, after making inquiries from 
several botanists, I can hear of no such casos. Lecoq, 
however, states,! but without entering into full details, 



• ' G^graphie Botaniquo,' torn. v. p. 367. t Ibid. torn. Iv. p. 488. 



INTRODUCTION. 13 

that some plants of CaltJia palustris produce only male 
flowers, and that these live mingled with the her- 
maphrodites. The rarity of such cases as this last one 
is remarkable, as the presence of hermaphrodite and 
male flowers on the same individual is not an un- 
usual occurrence; it would appear as if Nature did 
not think it worth while to devote a distinct indi- 
vidual to the production of pollen, excepting when 
this was indispensably necessary, as in the case of 
dicEcious species. 

I have now finished my brief sketch of the several 
cases, as far as known to me, in which flowers differing 
in structure or in function are produced by the same 
species of plant. Full details will be given in the fol- 
lowing chapters with respect to many of these plants. 
I will begin with the heterostyled, then pass on to cer- 
tain dioecious, sub-dioecious, 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 HETBEOSTYLED DIMORPHIC PLANTS. Chap. L 



CHAPTEE I. 

Heteeostyled Dimoephic Plants: PEuruLACEa!. 

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 
YitaUiana. 

It has long been known to botanists that the com- 
mon Cowslip {Primula veris, Brit. Mora, 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 struct with 

the year 1794. some degree of resemblance be- 

f In Johnson' s Dictionary, tween the cluster of anthers in the 

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

weavers' threads ; and I suppose of his threads. 



Chap. I. 



PKIMULA VEEIS. 



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. 
Peimttla vekis. 



pe 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 HETBROSTYLED 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. 
(tSt?!? 0^ ^^ inch) in diameter, whilst those from the 
long-styled were about .0254 mm. (tj^ 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. lY 

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 obr 
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. Eeview,' 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 381 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, aiid 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 Ptimula veris. 



Chap. I. 



PRIMULA VBRIS. 



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. 










Numlrar 

of 
Plants. 


Nninber of 
Umbali 
producfid. 


Namber of 
Capsnlei 
produced. 


"^S"' 




Ingrains. 


Short-styled cowslips ..... 
Long-styled cowslips 


9 
13 


33 

51 


199 
261 


83 
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 
Planta. 


Weight 
of Seed 
in grains. 


Namber 

of 
Vmbeli. 


Wejp.. 

Seed. 


Nnmber 
of Cftp- 
snlea. 


Weight 
of Seed in 
groins. 


Short-styled cowslips . . 
Long-styled cowslips . . . 


10 
10 


93 
70 


100 
100 


251 

178 


100 
100 


41 
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- 



20 HETBROSTYLBD 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. 







Nomber 

of 
Flanta. 


Nnmber 

«f 
Umbala. 


Walglit 

cfSe^in 

grains. 


is:-^ 




Short-styled cowslips . . 
Long-styled cowslips . • 


47 
58 


173 

208 


745 
692 


These figures give us the following proportior 
Table 4 




Nambflr 

of 
Flmita. 


grains. 


NiunUr 

at 
Vmtell. 


Weight 

ofSesdln 

gralu. 


Short-stvled cowsHds . . . ■ • 


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- 
elude 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 VEEIS, 



21 



my anticipation that the plants with longer pistils, 
rougher stigmas, shorter stamens, and smaller pollen- 
grains, would prove to be more feminine in nature, is 
exactly the reverse of the truth. 

In 1860 a few umbels on some plants of both the 
long-styled and short-styled form, which had been 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 i 
just before they expanded their flowers; these turned 
out as follows: — 

Table 5. 



KmnlMr of 
UmbeU 
produced. 



Frodact of Seed. 



Short-styled . 
Long-styled . 



6. 

18 



S4 

74 



f 1.3 grain weight of seed, or 
I about 50 in number. 

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 93 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 HBTBROSTYLBD 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 verhasei 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. Miiller has also seen Anfho- sucking the flowers. ' Nature,' 
phora pilipes and a Bomhylius Dec. 10th, 1874, p. 111. 



Chap. I. PKIMULA 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 proboseides 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. N"evertheless 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. L 

The several foregoing facts led me to try the effects 
of the two kinds of pollen on the stigmas of the 
two forms. Four essentially different unions are pos- 
sible ; namely, the fertilisation of the stigma of the long- 
styled form by its own-form pollen, and by that of 
the short-styled; and the stigma of the short-styled 
form by its own-form pollen, and by that of the long- 
styled. The fertilisation of either form with pollen from 
the other formi 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 " homomorphie " 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-- 
elude. 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. 



Natan of the Umoo. 


Namber of 
Flowers 
ferlilluid. 


Total 
Number 

of 
Capsule, 
produced. 


Number of 

good 
CspsDlea. 


Welglt of 
Seed In 
grains. 


Calculated 
Weight of 
Seed from 
100 good 
Capsules. 


Long-styled by pollen") 
of short-styled. Le- > 
gitimate union. . . ■) 


22 


15 


14 


8.8 


62 


Long-styled by own- ] 
form pollen. Illegiti- > 
mate union .... J 


20 


8 


5 


2.1 


42 


Short-styled by pollen 
of long-styled. Le- 
gitimate union . . J 


13 


12 


11 


4.9 


44 


Short-styled by own- 1 
form pollen. Illegiti- [ 
mate union .... J 


15 


8 


6 


1.8 


30 


Summary : 

The two legitimate ) 
unions J 


35 


27 


25 


13.7 


54 


The two illegitimate 
unions J 


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 



26 HETEEOSTTLED DIMORPHIC PLANTS. Chap. L 

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. 



Katun orOie 
Union. 


Nnmber 
ot Flow- 
ers ferU- 
lisad. 


Nnmlier 
of 

Cap- 
Boles. 


Number 

°'cir 

soles. 


Weight 
of Seed 

In 
grains. 


Number 

of 

Cap- 

sales. 


Weight 
of Seed 

In 
grains. 


Nomber 
of good 
Cap- 
sules. 


Weight 
of Seed 

In 
grains. 


The two le-] 
gitimate > 
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 a,s 100 to 44. Again, if we take an equal number of 



Chap. I. 



PRIMULA VBRIS. 



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. 




Legitimate union. 
Complete fertility. 




1 Illegitimate 
t union, 
j Incomplete 
/ fertility. 



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 HETEEOSTYLED DIMORPHIC PLANTS. Chap. 1 

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. ■yen's, 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. 



'Verguche uber die Bastarderzeugnng,' 1849, p. 216. 



30 HETEROSTYLBD DIMORPHIC PLANTS. Chap. I. 

the proportion was nearly the same — namely, as 100 
to 63. 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. Phomiceum 90 seeds; by the pollen of V. nigrum, 
63 seeds; by that of V. hlattaria, 63 seeds. So again, 
Dianthus barbatits fertilised by the pollen of D. superbus 
yielded 81 seeds and by the pollen of D. Japonicus 
I 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 illusti;ation of the same fact: he 
crossed Primula auricula with pollen of four other 
species (P. Palinuri, viscosa, hirsuta, and veriicillata) , 
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. 3 ; 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 



* 'Jounj. titm. Soo. Bot.,' vol. fertilisation' how greatly the off- 

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

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

the 'Effects of Cross arid Self- tUity. 



Chap. I. PRIMULA VBEIS, 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 HETEEOSTYLED 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. 
Bwrdfield Oxlip of English Authors. 

This plant, as well as the last or Cowslip {P. verts, 
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. MtLUer * 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 taten together with that of. the two illegitimate 



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



Chap. I. 



PRIMULA ELATIOK. 



83 



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. 



Nature of Union. 


Number 

of 
Flowers 
fertUised. 


Numter of 

good 

CapBulea 

pr<Muced. 


Maximum 
of Seed! 

in any one 
Capsule, 


Minimum 
of Seeds 

In any one 
Capsule. 


Average 
Number of 
Seeds per 
Capsule. 


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


10 


6 


68 


34 


46.5 


Long-styled form, by ] 
own-form pollen. 11- > 
legitimate union . . j 


80 


4 


49* 


8 


87.7 


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- > 
legitimate union . . J 


17 


3 


19 


9 


18.1 


The two legitimate 1 
unions together . . J 


80 


14 


68 


37 


47,1 


The two illegitimate 1 
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 Hot to have been counted. 
•Several long^styled and short^styled plants were pro- 
itected 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 Rhine), 
894 flowers produced by 198 plants of this species ; and 
he found 467 of these flowers to be long-styled, 411 
short-styled, and 16 equal-styled. I have heard of no 
other instance with heterostyled plants of equal-styled 
flowers appearing in a state of nature, though far from 
rare with plants which have been long cultivated. It 
is still more remarkable that in eighteen cases the 
same plant produced both long-styled and short-styled, 
or long-styled and equal-styled flowers; and in two 
out of the eighteen cases, long-styled, short-styled, and 
equal-styled flowers. The long-styled flowers greatly 
preponderated on these eighteen plants, — 61 consisting 
of this form, 15 of equal-styled, and 9 of the short- 
styled form. 

Pkimula 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 afld much more papillose than in the short- 



Chap. I. PRIMULA VULOARIS, 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 of flowers from 
the two forms were compared, and 13 of the finest 



36 HETEROSTYLED DIMORPHIC PLANTS. Chap. I. 

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. 



Nature of Union. 


Number 

of 
Flowers 
fertilised. 


Namber of 
good Cap- 
sules pro- 
duced. 


Mazlinnm 
Number of 
Seeds In any 
oneCapsale. 


MinlmiHQ 
Number of 
Seeds In any 
oneCapflule. 


Aversge 
NuTDber of 
Seeds per 
Capsule. 


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


12 


11 


77 


47 


66.9 


Long-styled form, by") 
own-form pollen. H- > 
legitimate union . . j 


21 


14 


66 


30 


52.2 


Short-styled form, by] 
pollen from long- 1 
styled. Legitimate f 
union 


8 


7 


75 


48 


65.0 


Short-styled form, by 
own-form pollen. D- 
legitimate union . . . 


18 


7 


43 


5 


18.8* 


The two legitimate 1 
unions together . . J 


20 


18 


77 


47 


66.0 


The two illegitimate 
unions together . . 


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 VUXGAEIS. 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 thua 
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 
6.3 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 HETEEOSTYLED DIMORPHIC PLANTS. Chap. I. 



Pkimdla 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 gome len-grains in the two forms. I 

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

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

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



Chap. I. 



PEIMtJLA 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 13.3 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. 



NstiinofUidoii. 


Number 

of 
Flowers 
feitUlsed. 


Nnmber 
of good 
CapBoIes 

PTOuUCfidi 


Average 
■Weight of 
Seeds per 

Capaule. 


Average Number 
ofSeedeper 

aacont^ned on a 
sabseqiient 
occasion. 


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


24 


16 


0.5S 


50 


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


20 


13 


0.45 


35 


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


8 


8 


0.76 


64 


Short-styled form, by own- 1 
form pollen. Illegitimate f 
union J 


7 


4 


0.23 


25 


The two legitimate unions 1 
together J 


32 


24 


0.64 


57 


The two illegitimate unions 1 
together. J 


87 


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 
5 



40 HETEROSTYLED DIMORPHIC PLANTS. Chap. L 

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. 


Nnmler 

of 
Flowers 
fertiUwi 


Number 
otEQoA 

pro°Ju^°. 


ATernge 

Seeds per 
CapRDle. 


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


14 


14 


41 


Long-styled form, by own-form • pollen, l 
from a distinct plant. Illegitimate > 


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 


U 


14 


44 


Short-styled form, by own-form pollen, 1 
from a distinct plant. Illegitimate union J 


16 


16 


20 


Short-styled, by pollen from the same 1 
flower. Illegitimate union J 


21 


11 


8 


The two legitimate unions together . . 


28 


28 


43 


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


42 


42 


18 


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


48 


33 


13 



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



Chap. I, PEIMULA SINENSIS, ' 41 

done by me, he tried, in addition, the effects of the 
plant's own pollen. He counted the seeds. 

It is remarkable that here all the flowers which 
were fertilised legitimately, as well as those fertilised 
illegitimately with pollen from a distinct plant be- 
longing to the same form, yielded capsules; and from 
this fact it might be inferred that the two forms were 
reciprocally much more fertile in his case than in 
mine. But his illegitimately fertilised capsules from 
both forms contained fewer seeds relatively to the 
legitimately fertilised capsules than in my experi- 
ments; for the ratio in his case is as 43 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 73 to 100. 

In order to ascertain how far the present species was 



42 HETEROSTYLED DIMORPHIC PLANTS. Chap. I. 

spontaneously self-fertile, five long-styled plants were 
protected by me from insects; and they bore up to a 
given period 147 flowers which set 63 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 35.9 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 
34 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 AUKICULA. 43 



Primula aukicula.* 

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 
Tg^TSTS of an inch in diameter, whereas those froni the long 
stamens of the short-styled plants were barely tbVt, 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 t 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 Kemer, our gar- and the short- styled 98 seeds per 

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

P. puiescens, Jacq., which is a hy- Aurikel," 'Zeitschr. desDeutsch- 

brid between the true P. aurictUa en und Oest. Alpen-Vereins,' Band 

and hirsuta. This hybrid has now vi. p. 62. Also ' Die Frimnlaceen- 

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 Joum. Linn. Soc. Bot.,' vol. 

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



44 HETBKOSTYLED DIMORPHIC PLANTS. Chap. 1. 

and lie 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 s re 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 papillae, 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. Chat. I. 

possible, in all the previous cases, by the manner in 
which the calculations have been made. Supposing, 
for instance, that 30 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 Speelu 



nlegicimate UnloDB. 



JadD^d of by the 

Proportional Number 

01 Flowers Trhlcb 

piodoced Capialea. 



Jndged of by the Average 

Namber (or Weight Id 

Bome cases) of Seeds 

per Capsule. 



Primula veris 
P. elatior . . 



P. vulgaris 

F. Sinensis 

" (second trial) 

" (after Hildebrand) 

P. auricula (Scott) . . 

P. Sikkimensis (Scott) 

P. cortusoides (Scott) 

P. involuciata (Scott) 

P. fa.rinosa (Scott) 

Aveiage of the nine species 




88.4 



65 

„, f (Probably 

^^1 too high.) 

„ f (Probably 

^jtKjblow.) 

63 

53 

4S 

15 

31 

66 

48 

44 



61.8 



proportion of the flowers in both lots would fail to 
produce capsules from various accidental causes; and 
the ratio of ^ to ^, 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 PEIMULA. 47 

of Table 13, 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 35 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 43 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 37 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 HETEROSTTLED 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 yens . 


71 




Primula auricula . . 


. . 119 


P. elatior . . 


44 


(Probably 
too low.) 


P. Sikkimensis . . 
P. cortusoides . . . 


. . 57 
. . 93 


P. vulgaris . 


36 


(Perhaps 
too low.) 


P. involucrata . . . 
P. farinosa .... 


. . 74 
. . 63 


P. Sinensis . 


71 









We thus see that, with the exception of P. auricula, the 
long-styled flowers of all nine species are more fertile 
than the short-styled flowers, when both forms are 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. Ifow, 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 flrst 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 37 other 
species * which are heterostyled; and to these probably 
others will be hereafter added. Nevertheless, some 
species are homostyled; that is, they exist only under 
a single form; but much caution is necessary on this 
head, as several species when cultivated are apt to 
become equal-styled. Mr. Scott believes that P. 
Scotica, verticillata, a variety of Sibirica, elata, mollis, 
and longif,ora,\ are truly homostyled; and 'to these many 



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

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

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

Alpine P. viUosa, and shows that it Sprengel und Dkrwin," ' Bot. Zei- 

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



60 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 Eifects 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 diflCeren'ee 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 Geheimniss der Natur,' p. 103. 



Chap. I. HOTTONIA PALUSTBIS. 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 stigmatie papillae of the two forms, 
and those of the long-styled are seen to he 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 t 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 Befruohtung,' &c., page t ' Joum. Linn. Soc. Eot.,' vol. 
850. viU., 1864, p. 79. 



62 HETEROSTYLED BIMOKPHIO PLANTS. Chap. I. 

Table 13. 
Hottonia palustris (from H. Miiller). 



Nature of Union. 


Nnmber 
ofCaiwulcB 


Average 
IT amber of 
Seeds per 
CapioiQ. 


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


34 


91.4 


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


18 


77.5 


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


30 


66.2 


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


19 


18.7 


The two legitimate unions together 


64 


78.8 


The two illegitimate unions together 


37 


48.1 



The most remarkable point in this table is the small 
average number of seeds from the short-styled flowers 
when illegitimately fertilised, and the unusually large 
average number of seeds yielded by the 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. ANDROSACB. 63 

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 31 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 "Treyiranus" in 'Bot. Zeituag,' 1863, p. 6, on this plant 
being dimorphic. 



si HETEROSTYLBD DIMOBPHIO PLANTS. Chap. I. 

ments made by Vaucher I was led to think that Solda- 
nella alpina was heterostyled, but it is impossible that 
Kemer, 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. li. HYBRID PRIMULAS. 55 



CHAPTER II. 

Hybbid Fbiuulab. 

The Oxlip a hybrid naturally produced between Primula veris and 
vulgaris — ^The differences in structure and function between the 
two parent-species — Effects of crossing long-styled and short-styled 
Oxlips with one another and with the two forms of both parent- 
species — Character of the offspring from Oxlips artificially self-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. 



*"DiePrimulacecn-Eastarten," 'Bull. Soc. Bnt.de France,' tom. 
'Oesterr. Bot. Zeitschrift,' Jahr x., 1853, p. 178. Also in 'Eevue 
1875, Nos. 3, 4, and 5. See also dcs Sciences Nat.,' 1875, p. 331. 
Godron on hybrid Primulas in 
6 



56 HYBRID PRIMULAS. Chap. U. 

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. Bornbus mv^corum and hortorum), and at night 
by moths, as I have seen in the case of Gucullia. 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 Eev. W. A. Leighton seed, in ' Ann. and Mag. of Nat. 
has pointed out certain differences Hist.,' 2nd series, vol. 11., 1848, p. 
in the form of the capsules and 164. 



Chap. II. THE COMMON OXLIP. 67 

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 N'orway, 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, ' Olograph. Bot. de With respect to the rarity of P. 

I'Europe,' torn. Tiii., 1858, pp. 141, veris In western Scotland, see 

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

Nat. Hist.,' ix., 1842, pp. 156, 515. nica.'li. p. 893. 
Also Boreau, ' Flore du centre de 



68 HYBRID PRIMULAS, Chap. IL 

have like distinct species, for they are far from 
being mutually fertile. Gartner * crossed 27 flowers 
of P. vulgaris with pollen of P. veris, and obtained 
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, t To show how sterile these hybrid unions 



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

721. infertility of a cross is liable to 

t Mr. Scott has discussed the much fluctuation. Pollen from 
nature of the polyanthus (' Proc. the cowslip at first appears rather 
Linn. Soo. Bot.,' viii., 1864, p. more efficient on the primrose than 
103), and arrives at a different that of the polyanthus; for 18 
conclusion ; but I do not think flowers of both forms of the prim- 
that his experiments were suffi- rose, fertilised legitimately and 



Chap. II. THE COMMON OXLIP. 69, 

were, I may remind the reader that 90 per cent, of the 
flowers of the primrose fertilised legitimately with 
primros.e-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-poUen 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. IL 

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 of 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, primioses, &c., on which he some strange error in these ex- 

expenmented. He specifies all periments, which may be passed 

■the-details of his experiment, but over as valueless, 

does not say that he artificially t '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 J 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 Eev. Prof. Henslow * raised from seeds of a 
cowslip growing in Ms 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 



* Loudon's 'Mag. of Nat. Hist.,' f "Transact. Hort. Soc.,' iv. p. 
iii. 1830, p. 409. 19. 



62 HYBRID PRIMULAS. Chap. II. 

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, &e., 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"'Vfti'iation of Ani- p. 69. 
mals and Plants under Doniesti- 



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 cp,ses 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 favbtir of the cowslip and primrose 
being varieties, and^- becomes, iii fact, an argurdent 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 exceUent ai-ticle on in the ' Phytologist,' vol. iii. p. 
this subject by Mt, 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; hut the 
P. elatior of Jacq., which, as we shall presently see, 
constitutes a distinct species, must not he 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 356 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 trimorphio 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. 

Short-styled ox- 
lip, by pollen of 
short-styled ox- 
lip: 20 flowers fer- 
tilised, did not 
produce one cap- 
sule. 



Legititnate union. 

Short-styled ox- 
lip, by pollen of 
loug-styledoxlip : 
10 flowers ferti- 
lised, did not pro- 
duce one capsule. 



Illegitimate union. 

Long-styled ox- 
lip, by itB own 
pollen : 24 flowers 
fertilised, pro- 
duced Ave cap- 
sules, containing 
6, 10, 20, 8, and 14 
seeds. Average 
11.6. 



Legitimate union. 

Long-styled ox- 
lip, by pollen of 
short-styled ox- 
lip: 10 flowers 
fertilised, did not 
produce one cap- 
sule. 



Table 15. 

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



Illegitimate union. 

Short-styled ox- 
lip, by pollen of 
short-styled cow- 
slip : 18 flowers 
fertilised, did not 
produce one cap- 
sule. 



Short-styled ox- 
lip, by pollen: of 
long-:Styled cow- 
slip: iSflowersfer- 
tilised, producfed 
three capsules, 
containing 7, ,3, 
and 3 wretched 
seeds, apparently 
incapable of ger- 
mination. 



Long-styled ox- 
lip, by pollen of 
long-styled cow- 
slip : 11 flowers 
fertilised, pro- 
duced one cap- 
sule, containing 
13 wretched seeds. 



Legitim/xte union. 

Long-styled ox- 
lip, by pollen of 
short-styled cow- 
slip: 5 flowers fer- 
tilised, produced 
two capsules, con- 
taining 21 and 28 
very fine seeds. 



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. lUegititnate union- Legitimate union. 



Short-styled ox- 
lip, by pollen of 
short-styled 
primrose: 34 flow- 
ers fertilised, pro- 
duced two cap- 
sules, containing 
S and 12 seeds. 



Short-styled ox- 
lip, by pollen of 
loug-styled prim- 
rose : 26 flowers 
fertilised, pro- 
duced six cap- 
sules, containing 
16, 20, 5, 10, 19, 
and 24 seeds. Av- 
erage 15.7. Many 
of the seeds very 
poor, some good. 



Long-styled ox- 
lip, by pollen of 
long-styled prim- 
rose : 11 flowers 
fertilised, pro- 
duced four cap- 
sules, containing 
10, 7, 5, and 6 
wretched seeds. 
Average 7.0. 



Loug-styled ox- 
lip, by pollen of 
short-styled 
primrose: 5 flow- 
ers fertilised, pro- 
duced five cap- 
sules, containing 
26, 32, 23, 28, and 
34 seeds. Average 
28.6. 



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- 
lenof short-styled 
oxlip: 8 flowers 
fertilised, pro- 
duced not one 
capsule. 



Long- styled 
cowslip, hy pol- 
lenofdiortityled 
oxlip: 8 flowers 
fertilised, ' pro- 
duced one cap- 
sule, containing 
26 seeds. 



Long- styled 
cowslip, by pol- 
len of long-styled 
oxlip : 8 flowers 
fertilised, pro- 
duced three cap- 
sules, containing 
5, 6, and 14 seeds. 
Average 8.3. 



Short-styled 
cowslip, by pol- 
len of long-styled 
oxlip: 8 flowers 
fertilised, ^rp- 
dnced eight :.^ratp- 
sules, containing 
58, 38, 31, 44, 23, 
26, 37, and 66 
seeds. Average 
40.4. 



Table 18. 

Both forms of the Primrose crossed with Pollen of 

both forms of the Oxlip. 



Illegitimate union. Legitimate union. Illegitimate union. Legitimate- union. 



■ Short-styled 
primrose, by pol- 
len of short-styled 
oxlip: 8 flowers 
fertilised, pro- 
duced not one 
capsule. 



Long- styled 
primrose, by pol- 
lenofshorfcstyled 
oxlip : 8 flowers 
fertilised, pro- 
duced two cap- 
sules, containing 
5 and 2 seeds. 



Long- styled 
primrose, by pol- 
len of Ion g-styled 
oxlip: 8 flowers 
fertilised, pro- 
duced eight cap- 
sules, containing 

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

16, and 13 seeds. 
Average 14.0. 



Short -styled; 
primrose, by pol- 
len of long-styled 
oxlip: 8 flowers 
fertilised, pro- 
duced four cap- 
sules, containing 
52, 52, 42, and 49 
seeds, some good 
and some bad. 
Average 48.7. 



Chap. II. THE COMMON OXLIP. 67 

"We see in these five tables the number of capsules 
and of seeds produced, by crossing both forms of the 
oxlip in a legitimate and illegitimate manner with one 
another, and with the two forms of the primrose and 
cowslip. I may premise that the pollen of two of the 
short-styled oxlips consisted of nothing but minute 
aborted whitish cells ; but in the third short-styled plant 
about one fifth of the grains appeared in a sound 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 
37.4 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 
tjie 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 eases, 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. n. 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. 



YO H.YBRID PEIMULAS. Cuap. 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 

*8ee also on this head Hardwicke'a 'Science-Gossip,' 1867, pp. 
il4, 137. 



Chap. II, THE COMMON OXLIP. VI 

hereafter see good reason to believe. The ease 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 
(Sause of the rare appearance of the oxlip in certain 
districts may be the rarity of some moth, which in 
dther districts habitually visits both the primrose and 
cowslip. 

Finally, as the cowslip and primrose differ in the 
various characters above specified, — as they are in a 
high degree sterile when intercrossed, — as there is no 
trustworthy evidence that either species, when un- 
crossed, has ever given birth to the other species or 
to any intermediate form, — and as the intermediate 
forms which are often found in a state of nature have 
been shown to be more or less sterile hybrids of the 
first or second generation, — ^we must for the future 
look at the cowslip and primrose as good and true 
species. 



72 THE BARDPIELD OXLIP. Chap. It 

Primula elatior, Jacq., or the Bardiield 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 13) 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 Britannlca,' vol. 'Ann. and Mae. Nat. Hist.,' vol. 

ji.. 1849, p. 292. For the Con- ix., 1842, pp. 156 and 515. 

tiiient, see Lecoq, 'G&>graph. t Babington's 'Mannal of Brit- 

Botaniqucde I'Europe,' torn, viii., ish Botany,' 1851, p. 258. 



Chap. II, THE BARDPIBLD 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. verts 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 la the ' Gaidenei's Chronicle,' 1867, p. 435 ; 
also Mr. W. Marshall, ibid., p. 462. 

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



74 HYBRID PRIMULAS. Chap. II, 

crossing other heterostyled species of Primula.* I 
Jiave 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 



» ' Jonrn. Linn. Soe. Bot.,' vol. viii,, 1S84, p. 93 to end. 



Chap. II. HYBEID VERBASCUMS. Y3 

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 43, 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 Verhascums. 

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,! and many hybrids between an 
Aceras and Orchis have been observed by Dr. Weddell. X 
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. thapsiis and lychnitis, 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 Wiohnra, ' Die Bastard- ? See, for instance, the ' Eng- 

hefruchtnng, &c., der Weiden,' lish Flora,' by Sir J. E. Smith, 

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

t ' M^m. de I'Acad. des Sciences || See Gartner, ' Bastarderzen- 

de Toulouse,' 5» s6rie, torn. v. p. 28. gung,' 1849, p. 590. 

t ' Annales des So. Nat.,' 3» s^rie, 
Bot. torn, xviii. p. 6. 



Chap. II. HYBEID VBRBASCUMS. Y7 

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 Y. 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 fiat 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- 



T8 HYBRID VERBASCUMS. Chap. IL 

mediate tint, but either pure white or pure yellow 
flowers, generally of the latter colour.* 

My observations were made in the autumn; so that 
I was able to collect some half-matured capsules from 
twenty of the thirty-three intermediate plants, and 
likewise capsules of the pure V. lychnitis and thapsus 
growing in the same field. All the latter were filled 
with perfect but immature seeds, whilst the capsules 
of the twenty intermediate plants did not contain one 
single perfect seed. These plants, consequently, were 
absolutely barren. From this fact, — from the one plant 
which was transplanted into my garden yielding when 
artificially fertilised with pollen from V. lychnitis and 
thapsus some seeds, though extremely few in number, — 
from the 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 Verbaseum, when 
the stem is jarred or struck by a stick, east ofiE 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 Terbascum lych- 
nitis and, as I believe, V. phcmiceum the corolla is not 



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

t This waa first observed by guided to these references by the 

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

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

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



Chap. II. HYBRID VERBASCUMS. 79 

east 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 foimd 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 flrst 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. 

tioTis in referring the specific identity of two forms 
from the presence of intermediate gradations; nor 
would it be easy in the many tases 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 oiler 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 GRANDIPLORUM. 81 



CHAPTER III. 

Heteeostyied Dimorphic 'Planub— continued. 

Linum grandifloium, 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 between 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 — Eubiacese— 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 
Bubiaceous 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 j)aper, '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. 
8 s, stigmas. 

LiNUM 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, 
ifevertheless, 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. . LINUM GRANDIPLORUM. 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 fiowers 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 ease was different 



84 HETEROSTYLED DxMORPHIC 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 1863 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 GKANDIFLORUM, 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 



80 HETEROSTYLED DIMOEPHIC PLANTS, Chap. IlL 

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 ease 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 difl;erence 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- 
■v^ise 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. in. LINUM GRANDIPLORUM. 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. ZeitUDg,' Jan. 1, 1864, p. 2. 



88 HETEROSTYLED DIMORPHIC PLANTS. Chap. IIL 

and this was a very short one. To make sure that the 
pollen was good, I took in this ease, 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 G2ANDIFL0EUM. 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. 

Tenthly. 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 one stigma, 
which was deeply penetrated by a multitude of tubes 
from the short-styled pollen, presented a conspicuous 
difference in being much curled, half-shrivelled, and 
discoloured, in comparison with the other four straight 
and bright pink stigmas. 

I could add other experiments: but those now 
given amply suffice to show that the pollen-grains of 
a short-styled flower placed on the stigma of a long- 
styled flower emit a multitude of tubes after an in- 
terval of from flve 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. IIL' 

stigmatic tissue deeply, and the stigmas themselves do- 
not soon become discoloured and twisted. 

This seems to me a remarkable physiological fact. 
The pollen-grains of the two forms are undistinguish- 
able under the microscope; the stigmas differ only in 
length, degree of divergence, and in the size, shade of 
colour, and approximation of their 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 two stigmas mutually 
recognise each other by some means. Taking fertility 
as the criterion of distinctness, it is no exaggeration to 
say that the pollen of the long-styled Linum grandi- 
florum (and conversely that of the other form) has been 
brought to a degree of differentiation, with respect to 
its action on the stigma of the same form, correspond- 
ing with that existing between the pollen and stigma 
of species belonging to distinct genera. 

Linum perenne. — This species is conspicuously hete- 
rostyled, as has been Tioticed 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 
papillae. 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. HI, LINUM PBRENNB. 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 difllerence 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 HETEKOSTYLBD DIMOKPflIC PLANTS. Chap. IIL 

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 30. 

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 PERBNNE. - 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.,o;f 
carrying pollen from plant to plant. I allude to this 
fact because botanists, in speaking of the fertilisation 
of various flowers, often refer to the wind or to insects 
as if the alternative, were indifferent. This view,/ ac- 
cording to my experience, is entirely, erroneous. When 
the wind is the agent in carrying pollen, either from 



94 HETBROSTYLBD DIMORPHIC PLANTS. Chap. IIL 

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 Coniferaj, 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 Graminea3, 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. LINtTM PBEENNB. 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. fiavum, 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 



B 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 tkey 
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- 
matie 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- 
eect'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 idi the' legitimate . fertilisa- 
tion of both forms.' The cotalla,' otL: perenne is' more 



Chap. III. 



LINUM PBEENNE. 



«7 



e;cpanded 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. peeenne, var. Austriamm, in its early condi- 
tion before the stigmas have rotated. The petals and calyz 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 papillae, with their heads already charged with 



* I neglected to get drawings 
made from fresh flowers of the two 
forms. But Mr. Fitch" 'has^made 
the »b<}Ve 'sketeh -of a long-styled 
flower fromi dried specifiiens and 



from published engriavibgs. His 
well-known_skill ensures accuracy 
in the prgpprtional size of the 
parts. ■■ -■■• - • ", ■ 



98 HETEROSTYLED DIMORPHIC PLANTS. Chaf. 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 Geplidlanthera 
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 Planchctn 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, liow 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 snr la G^gr. Bot.,' 
108, 2iid edit. 1877, p. 84. H. Lecoq, 1856, torn. v. p. 385. 



Chap. Ill, LINUM FLAVUM. 99 

the short-styled; the stigmas are longer and the 
papillse coarser. In the short-styled form the stigmas 
diverge and pass out between the filaments, as in the 
previous species. The stamens in the tw^o 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. 
No other capsules were produced by this plant. Three 
flowers on the short-styled plant were legitimately 
fertilised with pollen from the long-styled, and all 
three produced capsules, containing respectively no 
less than 8, 9, and 10 seeds. Three other flowers on 
this plant, which had not been artificially fertilised, 
produced capsules containing 5, 1, and 5 seeds; and 
it is quite possible that pollen may have been 
brought to them by insects from the long-styled plant 
growing in the same garden. Nevertheless as they 
did not yield half the number of seeds compared with 
the other flowers on the same plant which had been 
artificially and legitimately fertilised, and as the short- 
styled plants of the two previous species apparently 



100 HETEROSTYLED DIMOKPHIC 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. salsoloides. This 
botanist is the only one who seems to have inferred 
that heterostylism might have some important func- 
tional bearing. Dr. Alefeld, who has made a special 
study of the genus, says \ that about half of the sixty- 
five species known to him are heterostyled. This is 
the case with L. trigynum, which differs so much from 
the other species that it has been formed by him into 
a distinct genus. 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, angustifoKum, 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 minutfe 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 exsertls ; " another 

p 381. with " stylis staminibus lougiori- 

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

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

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

FlanchoD. (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 tbe same plant flowers with stamens 
and pistils of the same height, and others with the pistils 
either longer or shorter than the stamens. This ease 
formerly appeared to me an extraordinary one; but I 
am now inclined to believe that it is one merely of 
great variability.* 

PULMONAHIA (BORAGINE^e). 

Pulmoiiaria officinalis. — Hildebrand has published f 
a full account of this heterostyled plant. The pistil 
of the long-styled form is twice as long as that of the 
short-styled ; and the stamens difiEer 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 diifer 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 diiference 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. Thejformer bore 
389 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 363 (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. xzxvi., Sept., 1863, 

don Journal of Botany,' 1848, vol. p. 284. 

vii. p. 175. See on this subject f ' Bot. Zeitung,' 1885, Jan. 13, 

..Vsa Gray, in 'American Journal p. 13. 



102 HETEEOSTYLED DIMORPHIC PLANTS. Chap. IIL) 

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). 



Katnra of Union. 


Nrnnbar 

of 
Flo Men 
fertlUud. 


Nnmbot 

of 

Fnilto 

producod. 


fLvemgt 

Noinbrr of 

Seed! p« 

lYuli. 


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


14 


10 


1.30 


Long-styled floweis, 14 by own pollen, 1 
and 16 by pollen of other plant of same 
form. lUegitimate union J 


30 








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


16 


14 


1.57 


Short-styled floweis, 11 by own pollen, 14 1 
by pollen of other plant of same form. > 
Illegitimate union ) 


35 









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 eases. 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. PULMONAEIA 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, arlthough 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 -fertile; 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 
9 



104 HETBROSTYLED 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. officirialis (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 (30). 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. PULMONARIA 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 the corolla, though variable in size, was 
generally larger in the long-styled flowers than in the 

Fig. 6. 




Long-styled form. Short-stj'led form. 

PULMONAEIA 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 113. 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 
35 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 37 per cent.; wMlgt 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 ANGUSTIPOLIA. 



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. 



N>tiin of Union. 


Knmbor 

of 
Flowera 
fertUIud. 


°3 " 

Frnlta 
prodoced. 


Avenn 
Numlxlof 
Seeds por 


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


18 


9 


2.11 


Long-styled floweis, by own-fonn pollen. 
Illegitimate union 


18 








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


18 


15 


2.60 


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


18 


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 33, judged 
by the average number of seeds per fruit. But the 
small number of fruit yielded by the 18 long-styled 



108 HETEROSTYLBD DIMOEPHIC 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 -fertile ; but they agree in their behaviour with 
the German plants of P- officinalis experimented on by 
Hildebrand. 

Eighteen short-styled flowers legitimately fertilised 
yielded, as may be seen in Table 30, 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 
13 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. PULMONAEIA ANQUSTIFOLIA. 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 38 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, 
thus illegitimately fertilised set fruit. I judge of this 
proportion partly from estimation and partly from 
having examined three large branches, which had borne 
31 flowers, and these produced 16 fruits. Of the fruits 
produced 333 were collected (many being left un- 
gathered), and these included on an average 1.83 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 



no 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 angusUf cilia, 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. 

PulmoTuma azurea, according to Hildebrand, is not 
heterostyled.* 

From an examination of dried flowers of Amsinciia 
spectabilis, sent me by Professor Asa Gray, I formerly 
thought that this plant, a member of the BoraginesB, was 
heterostyled. The pistilvaries 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 Qeschlecliter-VerUieilung bei den Pflanzon,' 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 Boragineae, Arnehia 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 fagoptkum (PoLTGONACE.ffi). 

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 32 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,' &o., 1867, p. 34. 



112 HETEROSTYLBD 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. MuUer.) 

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



Ghap. III. POLYGONUM FAGOPYEUM. 113 

illegitimately fertilised flowers on the same plants, in 
the ratio of 100 to 83, 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 



1 * 'Die Eefruchtung,' &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 Polygonacese are generally 
fertilised by the wind, instead of by insects as in the 
present genus. 

Leucosmia Burnettiana (Thymelije). 

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 diflFers 
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 poUen- 



• 'American .Tournal of Sci- 'Journal of Botany,' vol. iii., 
ence,' 1865, p. 101, and Seemaim'g 1865, p. 305. 



Chap. III. MENYANTHES TRIFOLIATA. 115 

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 serres to smear the 
inserted organ thoroughly with pollen. 

Menyanthes tkifoliata (Gentiane^e). 

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. 

Limnanthemum Indicdm (Gentiane.«). 

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



116 HBTEROSTYLED DIMORPHIC PLANTS. Chap. Ill, 

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. 

ViLIiAESIA [SP.?] (GeNTIANE^). 

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 GentianesE. All the species, as far as at pres- 



Chap. III. COKDIA. 117 

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

FORSTTHIA 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-stjrled. 
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, TI. S., 
the published figures of this species belong to the short- 
styled form. 

Cordia [sp.?] (Oordiace^.) 

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. 

GiLiA (Ipomopsis) pulchella vel aggkegata (Polemoni- 

ACE^). 

Professor Asa Gray remarks with respect to this plant : 
" The tendency to dimorphism, of which there are traces, 
or perhaps rather incipient manifestations in various por- 
tions of the genus, is most marked in G. aggregata." * He 
sent me some dried flowers, and I procured others from 
Kew. Th«y 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-grains 
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 ; ^nd 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 papillse 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 Oilia nudicaulis, which likewise be- 
longs to the Leptosiphon section of the genus, for I hear 
from Professor Asa Gray that in some individuals the 
10 



120 HETBROSTYLED 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 (PoLEMONiACEiE). 

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 loi^g-stjrled P. subulata rarely Shows more than 
one." * Some dried flowers of both forms were sent me by 
him, and I received others from Kew, but I have failed 
to make out whether the species is heterostyled. In two 
flowers of nearly equal size, the pistil of the long-styled 
form was twice as long as that of the short-styled ; but in 
other cases the 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 



* ' Profc. American Acad, of Arts and Sciences,' Jnne 14, 1870, p. 848. 



Chap. III. BEYTHROXYLTJM. 121 

as 100 to Y5 : 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 thq belief that Phlox subulata 
is heterostyled. Possibly this species was once heterostyled, 
but is how becoming sub-dioecious ; 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 polleri-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^). 

Fritz Miiller sent me from South Brazil dried flowers 
of this tree, together with the accompanying drawings, 
which show the two forrns, 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 



122 HETEROSTYLED DIMORPHIC PLANTS. Chap, IIL 

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-fifth of 

Kg. 8. 





Long-styled form. Short-Btyled fonn. 

From a sketch by Fritz MuUer, magnified five times. 
Eeythboxylon [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 Ms let- 
ter to me that the floweis, 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. CRATOXYLON FORMOSUM. 123 

Sethi A acuminata (Erythroxylid^). 

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 ohtusifolia is heterostyled like S. acuminata. 

CeATOXYLON FORMOSUM (HYPERICINEiE). 

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 f onp 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- 



* ' EnnmeTatio FlantaTum Zey- t 'Jonmalof Botany,' London, 
laniae,' 1864, p. 54. 1872, p. 26. 



124 HETEBOSTTLED DIMORPHIC PLANTS. Chap. III. 

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

uSgIPHILA ELATA (VERBENACEiE). 

Mr. Bentham was so kind as to send me dried flowers 
of this species and of IE. 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 ^. mollis present a like difference in the length of 
their pistils and stamens. 

^GIPHILA OBDUEATA. 

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. HI. MITCHELLA KEPENS. 125 

■what is much more important, they were in a rudimentary 
condition in the two flowers examined by me, and did not 
contain a sitigle 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 dicecious, and, 
judging from the two species previously described, it proba- 
bly was once heterostyled, and has since been rendered 
dicBcious 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 
Labiatffi, 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 dicecious 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. 

EUBIACEiE. 

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. 173. 



126 HETEROSTYLED DIMOKPHIC 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. 



BOREERIA. 



327 



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. 



Natnra of Union. 


Nnmlwr of 

rain of 
Flowari fer- 
tUlieil dnr- 


Number 
of 
Drapes pro- 
duced dar- 
ing the aec- 
oiM Seuon. 


Aversfn 
Number of 
good Seede 
per Drupe 
In ell Ihe 
Drupea dur- 
ing the two 


Long-Styled flowers, by pollen of short- 1 
styled. Legitimate anion j 


9 


8 


4.6 


Long-styled flowers, by own-form pollen, j 
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. 1 
Illegitimate union J 


9 





8.0 


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. 

BOEEERIA, NOV. SP. NEAR VALEErANOIDES (KUBIACE^). 

Fritz Muller 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 Kemer'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 Oaste,' 1876. 
p. 37. 



Chap. III. FARAMEA. 129 

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. 

Faeamea [sp.?] (Eubiacb^). 

Fritz Miiller has fjiUy 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 almbst 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 diiler 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 j 



• 'Bot. Zeitung,' Sept. 10, 1889, 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-Btyled form. Long-Btyled form. 

Ontlinea of flowers from dried specimens. PoUen-giains, magnified 
180 times, by Fritz Miiller. 

Faeauea. [sp. ?]. 



the flowers. On the other handj 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. PAEAMBA. 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 Eubiaeeae; 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.* 



* Fritz Miiller gives another in- with the nocturnal habits of these 

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

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

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

Pumqueria fraprana, which is of such flowers is robbed, as Fritz 

adapted in a most wonderful man- Miiller has often seen, by hnmble- 

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

aptcney 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) 
(Eubiace.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 Bubiacese. 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 CCERULEA (EuBIACE^). 

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 nun. in length. In the short-styled form the an- 



Ghap. III. KUBIACB^. 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. 

OlDENLANDIA [SP.?] (EuBIACEiE). 

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 papillas 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.?] (EuBIACE^ffi). 

Fritz Miiller sent me from St. Oatharina, 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. IIL 

styled form; but in the latter the stigmas stand rather be- 
neath the level of the anthers in the other or loBg-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 papillse 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 t.o 88 in 
diameter. Fritz Miiller sent me a second, small-sized spe- 
cies, which is likewise heterostyled. 

COCCOCYPSELUM [SP.?] (RUBIACEiE). 

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.?] (EuBIACEiE). 

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. RUBIACB^. 136 

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

Cinchona micrantha (KuBiACEiE). 

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 diflference in shape in the two sets of grains can- 
not be accounted for by unequal distension with water. 

Besides the several Kubiaceous genera already men- 
tioned, Fritz Miiller informs me that two or three species 
of Psychotria and Budgea eriantha, natives of St. Catha- 
rina, in Brazil, are heterostyled, as is Manetiia bicolor. I 
may add that I forijierly 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 Amott'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 hy Mr. Markham in hia 
plant by a drawing copied flrom TraTrnla in Pom ' r, krq 
Howard's ' Quinologia,' Tab. 3, 
11 



136 HETEKOSTYLED DIMORPHIC PLANTS. Chap. UI. 

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 Rubiacess; 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 Pentham and Hooker, the 
Rubiacese 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 isj, they 
have not inherited this structure from some oj:e 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. dub,' 1876, p. 106. 



Chap. IV. LYTHEUM SALICABIA. 137 



CHAPTEE IV. 
Hetebostyled Tsimobphic Plants. 

Lythrum salicaria — ^Description of the three forms — ^Their power and 
complex manner of fertilising one another — ^Eighteen different 
unions possible — ^Mid-styled form eminently feminine in nature — 
Lythrum Greefferi likewise trimorphio — L. thymifolia dimorphic — 
L. hyssopifolia homostyled — Nessea verticillata trimorphic — Lager- 
strcemia, nature doubtful — Oralis, trimorphic species of — O. Yaldi- 
viana — O. Begnelli, the illegitimate unions quite barren — O. spe- 
ciosa — O. 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 Nessea, 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 mlicaria. — 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 TEIMORPHIC 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 distipct 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 natuThist. Vereins fur pieuss. 
Wirtgen, TJeberijrtftrwmsoKcorio Bheinl.,' 5. Jahrgang, 1848, 8. 7. 



Chap. IV. 



LYTHRUM SALICAEIA. 



139 



Fig. 10. 



Long- 
Btjled. 




Diagiam of the flowers of the three forms of lA/thrum talicaria, 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 he carried to each stigma to ensure full fertility. 



140 HETEROSTYLED TEIMORPHIC 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 j^-^ mm. The grains, distended 
with water, from the mid-length stamens are 7-7^, 
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. LYTHEUM 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 
143 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. 9J-10i, 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 difEerenee 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. LTTHRUM SALICAEIA. 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 9i to lOJ 



" " " " mid-styled " 


9 " 10 


" " mid-length stamens of long-styled " 


7 " 7i 


" " " short-styled " 


7 " 7i 


" shortest stamens of long-styled " 


6 " 6i 


mid-styled " 


6 " 6 



We here see that the largest pollen-grains come from 
the longest stamens and the least from the shortest; 
the extreme difference in diameter between them being 
as 100 to 60. 

The average number of seeds in the three forms was 
ascertained by counting them in eight fine selected 
capsules taken from plants growing wild, and the 
result was, as we have seen, for the long-styled (neg- 
lecting decimals) 93, mid-styled 130, and short-styled 
83. I should not have trusted in these ratios had I 
not possessed a number of plants in my garden which, 
owing to their youth, did not yield the full comple- 
ment of seed, but were of the same age and grew 
under the same conditions, and were freely visited by 
bees. I took six fine capsules from each, and found 
the average to be for the long-styled 80, for the mid- 
styled 97, and for the short-styled 61. Lastly, legiti- 
mate unions effected by me between the three forms 
gave, as may be seen in the following tables, for the 
long-styled an average of 90 seeds, for the mid-styled 
117, and for the short-styled 71. So that we have 
good concurrent evidence of a difference in the average 
production of seed by the three forms. To show that 
the unions effected by me often produced their full 
effect and may be trusted, I may state that one mid- 
styled capsule yielded 151 good seeds, which is the 



144 HETEROSTYLED TKIMORPHIC 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. !N'evertheless 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 N"orth 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-staled. 


MMatyled. 


Short-fllyled. 


Total. 


North Wales 

Hampshire 


S5 

53 


97 
38 


73 
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 



Ch4P. IV. LYTHRUM SALICAKIA. 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 proboseides 
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. MiiUer gives a list of the one bee, the OUissa melanura. al- 
snecies, 'Die Befruchtung der most confines its visits to this 
Blumen,' p. 196. It appears that plant. 



146 HETEROSTYLED TKIMORPHIC 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 fraxinella and others, by a temporary movement, 
which occurs in the ease 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 CorydaUs. 
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- 
naceae, and others. The rule consequently is, that 
when the pistils and stamens are curved or bent, the 
stigma and anthers are thiis 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 coronii, 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 difiicult 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 ptoboscides through the meshes, and in conse- 



148 HETEROSTYLBD TUIMORPHIC 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 bracteae, 
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 
heii^g 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 natarhist. Vereina, fur Pr. Bheinl.,' 5. Jahrgang, 
1848, pp. 11, 13. 



Chap. IV, LYTHRUM SALICAEIA. 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 tl^at state 
in which natural selection might readily do much for 
its modification. 

On the Power of Mutual Fertilisation tetween 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 papillse differing con- 
varied rather more than those stantly in length and strupture in 
growing in a state of natdre. H. the three forms, being longest in 
Miillsr has described the stigmas the long-styled form, 
of all three forms with great care. 



160 HETBROSTYLED TEIMORPHIC 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 323 
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- 
si][les 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 



Chap. 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. Sujch iinions are of a legitimate 
nature. The two next lovyer compartments show the 
result of the application of pollen from the two sets of 
stamens not eorresporiding 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. 
13 



152 HETEROSTYLED TRi:.IORPHIC PLANTS. Chap. IV. 



Table 23. — Long-styled Form. 



I. 


n. 


Legitimate union. 


LegUimate union. 


13 flowers fertilised by thelongest 


13 flowers fertilised by thelongest 


Btamena of the mid-styled. These 


stamens of the short-styled. These 


stamens equal iiL strength the pistil 


stamens equal in length the pistil 


of the long-stjrled. 


of the long-styled. 


Product of good seed in each 


Product of good seed in each 


capsule. 


capsule. 


36 53 


159 104 


81 


43 119 





96 poor seed. 98 





103 99 





131 


— 


116 


45 





41 


114 


38 per cent, of these flowers 


84 per cent, of these flowers 


yielded capsules. Each capsule 


yielded capsules. Each capsule 


contained, on an average, 51.2 


contained, on an average, 107.3 


seeds. 


seeds. 


in. 


IV. 


Illegitimate union. 


Illegitimate union. 


14 flowers fertilised by the short- 


12 flowers fertilised by the mid- 


est stamens of the mid-styled. 


length stamens of the short-styled. 


3 


20 























— 


— 












Too sterile for any average. 


Too sterile for any average. 


V. 


VI. 


Ulegitimate union. 


Illegitimate union. 


15 flowers fertilised by own-form 


15 flowers fertilised by own-form 


mid-length stamens. 


shortest stamens. 


2 — 


4 — 


10 


8 


23 


4 
































Too sterile for any average. 


Too sterile for any average. 



Chap. IV. LYTHRUM SALICARIA. 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 30 capsules, and these contained seeds in num- 
ber as follows: — 



so 


20 


35 


21 


19 


26 


24 


12 


23 


10 


7 


30 


27 


89 


13 


SO 


IS 


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 33, is the more fertile of the two 
self-unions. 



154 HETEEOSTYLED TRIMOEPHIC PLANTS. Chap. IV. 



Table 2L— Mid-styled Form. 



I. 


II. 


Legitimate union. 


Legitimate union. 


12 flowers fertilised by the mid- 


12 flowers fertilised by the mid- 


length Btamcns 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 


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, 103.0 


an average, 127.3 seeds. 


seeds ; or, excluding capsules with 




less than 20 seeds, the average is 




116.7 seeds. 


ni. 


IV. 


Illegitimate union. 


IlXegitimate 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 88 


19 


115 113 


t seeds small 
1 and poor. 


14 29 


6 17 


— 


2 113 


44 


9 79 


44 


128 


45 


132 


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. 



165 



Table 24. — Mid-styled Form — continued. 



V. 


VI. 


lUegitimate union. 
12 flowers fertilised by own-form 
longest stamens. 


12 flowers fertilised by own-form 
shortest stamens. 


92 

9 

63 



136?* 




ooo 1 oco 
oooooo 


Excluding the capsnle with 136 
seeds, 25 per cent., of the flowers 
yielded capsules, and each capsule 
contained, on an average, 54.6 
seeds ; or, excluding capsules with 
lees than 20 seeds, the average is 
77.5. 


Not one flower yielded a capsule. 



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 Imrdly 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 whfch yield- 
ed 92 seeds, in the same column 
with that which gelded 136, 1 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 
1863 1 made the great mistake of 
placing » mid-st^ed and a long- 
staled under the same huge net : 
in 1863 1 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 


These stamens equal in length the 


pistil of the shoit-styled. 


pistil of the short-styled. 


69 56 


03 69 


61 88 


77 69 


88 112 


48 53 


66 111 


43 9 


62 





100 







— 


83 per cent, of the flowers 


61 per cent, of the flowers 


yielded capsules. Each capsule 


yielded capsnles. Each capsule 


contained, on an averaga, 81.3 


contained, on an average, 64.6 


seeds. 


seeds. 


III. 


IV. 


Illegitimate union. 


Illegitimate union. 


10 flowers fertilised by the mid- 


10 flowers fertilised by the long- 


length stamens of the long-styled. 


est stamens of the mid-styled. 


14 























— 


— 


23 





Too sterile for any average. 


Too sterile for any average. 


V. 


VI. 


Ittegitimate union. 


Illegitimate union. 


10 flowers fertilised by own-form 


10 flowers fertilised by own-form 


longest stamens. 


mid-length stamens. 





64?» 














— 


— 





21 





9 


Too sterile for any average. 


Too sterile for any average. 



* I suspect that . hy mistake I 
fertilised this flower in compart- 
ment VI. with pollen from the 
shortest stamens of the long-styled 
form, and • it would then have 
yielded abbiit' 64 seeds. Flowers 



to be thus fertilised were marked 
with black silk ; those with pollen 
from the mid-length stamens of 
the short-styled with black thread; 
and thus probably the mistake 
arose. 



Chap. IV. LYTHRUM SALICARIA. 157 

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 31.5 



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 30 seeds) contained on an average 
103.8 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. 



168 HBTEROSTYLED TRIMOBPHIC 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 73 
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. 






Nalim of Union. 


KnmbflT 

of 
Flowen 
fertmied. 


NnmtieT 
of 

producM. 


ATflrago 

Number of 

Seeds per 

C'a)}ta;e. 


Average Nam. 

ber of Seeds 

per Fliwer 

fertili«!d. 


The six legitimate 1 
unions J 


75 


56 


96.39 


71.89 


Tlie twelve illegitimate 
unions 


146 


36 


44.73 


11.03 



Therefore the fertility of the legitimate unions to that 
of the illegitiftiate, 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. LYTHEUM SALICARIA. 159 

From this summarj' 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 33, 34 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 cohtain fewer seeds 
than those produced by the pollen from the mid- 
length stamens. The same result follows with the 



160 HETEEOSTYLED TRIMOKPHIC 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 apd 
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 difr 
ferenee 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 SALICARIA. 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 difEerent. In both these 
cases. the difEerence 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 1863 and 1863 than that from 
the shortest stamens of the long-styled form. Again, 
if we look to Table 33, 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 J 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 6J in diameter. 



Chap. IV. LYTHRUM SALICARIA. 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 ease. 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 RETEEOSTYLED 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 fei-tilisation 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 ease 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. LTTHRUM 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 ihymifolia. — 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 cal3^; 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. Qrcefferi. 

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 O. 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 HETEROSTYLED TRIMORPHIC PLANTS. Chap. IV, 

long, the stamens are likewise generally long; in the bud 
the stamens are short; and Yaucher 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. ihymifolia. 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. hyssopifoUa 
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 vertieillata. — ^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 Orcefferi. The green-polten grains from the 
longest stamens, measured along their longer axis and not 
distended with water, were T^fy of an inch in length ; those 
from the mid-length stamens -fiSir, and those from the 
shortest stamens tItJ-s- 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, t a species of this genus in St. 
Catharina, in Southern Brazil, is homostyled. 



* 'Geograph. Bot. de I'EuTope,' torn, vi., 1857, p. 157. 
t 'Bot. Zeitung,' 1868, p. 113. 



Chap. IV. LAGEESTRCEMIA INDICA. 16Y 

Lagerstrcetnia Indica. — This plant, a member of the 
Lythraceae, 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 Lythrum; 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 
Qardens 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. reginw, 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 
13 



168 HETEROSTYLED TRIMOEPHIC 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 
Lagerstroemia. I found that Cuphea purpurea was highly 
fertile with its own pollen when artificially aided, but 
sterile when insects were excluded.* 



OXALIS (GrERANIACE-aE). 

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, 13 mid-styled, and 31 
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 MoTlia lepidota 

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

MoUia (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 

he heterostyled and trimorphic : shortest ones did not present any 

huthe 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. 169 

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. u. 




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

OXA.UB SPECIOSA (with the petals removed). 

S8S, 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- 
Wias. Berlin,' 1866, pp. 352, 872. Vertheihmg,' &c., 1867. 
He gives drawings of the three t 'BotZeitung' 1871, pp.416, 432. 



170 HETEROSTYLKD TRIMOEPHIC 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 theistigmas 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 : — 

Dlvlitoiu of lilt 

Micrometer. 

From the longest stamens of short-styled 8 to 

" mid-length " " 7 " 8 

" longest stamens of mid-styled 8 

" shortest " " 6 

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

" shortest " " 6 

Therefore the extreme diiference 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. 



in 



Table 27. 
Oxalis Valdiviana (from Hildehrarid). 



Nslnra of Union. 


Nnmbei 

•f 

Flowers 
ferUllMd. 


ITiunbti 

of 
Csniilei 
prodncod. 


NomlHT 

01 

Seed! per 
Cepedle. 


Long-Styled fonn, by pollen of longest] 
stamens of short-styled. Legitimate > 


28 


28 


11.9 






Long-styled form, by pollen of longest] 
stamens of mid-styled. Legitimate > 
union > • J 


21 


21 


12.0 






Long-styled form, by pollen of own and ] 
own-form mid-length stamens. lUegiti- > 


40 


2 


5.5 






Long-styled form, by pollen of own and ] 
own-form shortest, stamens. lUegiti- > 
mate union J 


26 








Long-styled form, by pollen of shortest] 
stamens of short-styled. Illegitimate \ 


16 


1 


1 






Long-styled form, by pollen of shortest] 
stamens of mid-styled. Illegitimate > 


9 













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

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

Mid-styled form, by pollen of own and] 
own-foijn longest sta/mens. Illegitimate > 
union ,' J 

Mid-styled form, by pollen of own and] 
own-form shortest stamens. Illegitimate > 
union J 

Mid-styled fbrm, by pollen of shortest] 
stamens of long-styled. Illegitimate j- 
union ) 

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



38 



38 



11.3 



2a 



52 



10.4 



30 



16 



16 



2.5 



172 HETEROSTYLBD TRIMORPHIC PLANTS. Chap. IV. 

Table ZT— continued. 
Oxalia Valdiviana (from Hildebrand).. 



NituaofUilw. 


NmnUr 

of 
Flowen 
tetUlnd. 


Nombar 

of 
C>pmdM 
rnaand. 


Kumbor 
of 

CapnlT 


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


18 


18 


11.0 


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


10 


10 


11.3 


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


21 












Short-styled form, by pollen of own and I 
own-form mid-length stamens. lUegiti- > 
mate union J 


S2 








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


4 












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


3 









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 ^.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 3, 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 REGNBLLI. 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 38 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 speciosu. — 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 papillaB 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 HETBEOSTYLED TEIMORPHIC PLANTS. Chap. IV. 



Table 28. 
Oxalis Regnelli {from Hildehrand). 



Natore of Union. 


Nnmbet 

of 
Flowers 
fertillMd. 


Number 

of 
Cnjifulei 
produced. 


Avengo 

Number of 
Seed! per 
Cupiine. 


Long-Styled form, by pollen of longest sta- \ 
mens of short-styled. Legitimate union J 


6 


6 


10.1 


Long-styled form, by pollen of longest sta- 1 
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 








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


1 








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


9 


9 


10.4 






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


10 


10 


10.1 






Mid-styled form, by pollen of own longest 1 
stamens. Illegitimate union .... J 


9 








Mid-styled form, by pollen of own shortest 1 
stamens. Illegitimate union .... J 


2 








Mid-styled form, by pollen of longest sta- 1 
mens of short-styled. Illegitimate union J 


1 








Short-styled form, by pollen of shortest "I 
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 . . 


12 








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


9 








Short-styled form, by pollen of mid-length 1 
stamens of long-styled. Illegitimate > 


1 













Chap. IV. 



OXALIS SPECIOSA. 



1Y5 



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





DiviBloiuofth* 




Micrometer. 


From the longest stamens of short-styled . . 


. 15 to 16 


" mid-length " " . . 


. 12 " 13 


" longest stamens of mid-styled . . 


16 


" shortest " " 


. 11 to 13 


" mid-length stamens of long-styled . 


14 


" shortest 


12 



Therefore the extreme difEerence 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. 



Neture of UnloB, 


Number 

of 
Flowers 
fertllJeed. 


Nomber 

of 
Capenlee 
proanced. 


Average 
ff umber of 
Seeds per 
Copeule. 


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


19 


." 15 


'57:4 






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


4 


3 


59.0 






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


9 


2 


42.5 


Long-styled form, by pollen of own-form 1 
shortest stamens. Illegitimate union . J 


11 








Long-styled form, by pollen of shortest' 
stamens of mid-styled. Illegitimate 
union 


4 












Long-styled form, by pollen of mid-length ' 
stamens of short-styled. Illegitimate 


12 


5 


30.0 







176 HETEROSTYLBD TEIMORPHIC PLANTS. Chap. IVc 



Table 29— continued. 
Oxalis speciosa. 






Stbae of VnSm. 


N-omber 

of 
Flowen 
fettUlHil. 


Nnmba 

6«pBule« 
prodtiecd. 


ATorago 
Number of 
Seed! per 

CftpiDleL 


Mid-styled form, by pollen of mid-length I 
'Stamens of long-styled. Legitimate > 
union ) 


3 


3 


esjR 






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


4 


4 


56.3 






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


9 


S 


19 


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


12 


1 


8 






Sliort-styled form, by pollen of shortest 1 
stamens of mid-styled. Legitimate > 
union J 


3 


2 


67 


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


3 


3 


54.3 






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


5 


1 


8 


Short-styled form, by pollen of own-fohn ) 
„9iid-length stamens, niegitimate Union J 


3 








together, of own-form longest and mid- > 
length stamens. Illegitimate union . J 


13 








Short-styled form, by pollen of longest 1 
stamens of mid-styled. Illegitimate |- 
union 


7 












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


10 


1 


54 







We here see that thirty-six flowers on the three 
forms legitimately fertilised yielded 30 capsules, these 
containing on an average 58.35 seeds. Kinety-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 



* 'Mouatsbe^. der Akad. der Wiss. Berlin,' 1866, p. 372. 



178 HETEROSTYLBD TRIMORPHIC 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, qr, 
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, 
tliis 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 ^he 
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 compa"red 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 
39 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 OP. 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 
Gxalis, 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. FV. 

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 trimorphie 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 trimorphie. 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. Taldiviana and 
Begnelli. 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 

Ilomostyled 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 is 
quite fertile with its own pollen when insects are ex- 
eluded. 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 23 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 distin,ct 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, 9.3. 
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 dicecious condition, as Zuccarini 
and Lindley inferred from the differences in the re- 
productive organs of the three forms, the meaning of 
which they did not understand. 

PONTEDEEIA [SP. ?] (PoNTEDEEIACEJE) . 

Fritz Miiller found this aquatic plant, which is al- 
lied to the Liliaeese, 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 33, 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 



* " Ueber den Trimorphismiis der Pontederien," 'Jenaische Zeit- 
Schrift,' &c., Band 6, 1871, p. 74. 



Ghap. IV. PONTBDBRIA. 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 
tlje 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 
14 



184 HETEROSTYLED TRHUQRPHIC 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,' thjs would probably follow if only two forms 
had been originally introduced there; for, as we shall 
hereafter see from the observations of Hil;debrand,: 
Fritz MiiUer, 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 thifd 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^tyled as 100 to 16. Its summit is 
rectangularly bent .upwards, ^ aiid the stigma is rather 
broader tjian that of the mid-styled, and broader in 
about the ratio of 7 to 4 than that of the short-styled. 
In the mjd-styMd form, the stigma is plated rather 



Chap. IV. PONTEDBRIA. 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- 
Btyled 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 : — 



DlvliloDB of tha 
MicroiDeteT. 



Long-styled form, from the mid-length stamens . 
(Average of 20 measarements. 
" " from the shortest stamens . . 

(10 |aeasuremeuts.) 
Mid-styled form, from the longest stamens . . . 
(15 measurements.) 
" " from the shortest stamens . . 

(20 measurements.) 
Short-styled form, from the longest stamens . . . 
(20 measurements. ) 
" " from the mid-length stamens . 

(20 measarements.) 



13.2 
9.0 

16.4 
9.1 

14.6 

12.3 



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 tq 9.0, or as 100 to 55; 



186 HETEROSTYLED TEIMORPHIC 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 sh(^rt-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 Lythrum salicaria. 
In this latter plant the pollen-grains of the mid-styled 
forms are of smaller size and have less fertilising power 
than the corresponding ones in the other two forms; 
whilst the ovarium, however fertilised, yields a greater 
number of seeds; so that the mid-styled form is alto- 
gether- more feminine in nature than the other two 
forms. In the case of Pontederia, the ovarium in- 
cludes only a single ovule, and what the meaning of 
the difference in size between the pollen-gi-ains 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 Qub,' 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 ; " " wliilst 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 OP Chap. V. 



CHAPTEE V. 

Illegitimate Offspeino op Hetebostyled 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— I^mula 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 — CJoncluding 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. HETEKOSTYLED TRIMORPniC 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 
30,000 seeds of Lythrum salicaria — ^but chiefly because 
light is thus indirectly thrown on the important sub- 
ject of hybridism. 

Ltthhum 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 OPESPRING 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 maxiinum 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 (ITo. 10), which was legitimately 



Chap. V, HBTEEOSTYLED TEIMORPHIC 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 hy 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, 113. 

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 legitir 
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, 39, 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 SinensiK ; but his results 
tion ('Bot. Zeitung,' Jan. 1, 1864, were not nearly so unifoTm as 
V. 5) to this &ct in the case of mine. 



Chap. V. HETEROSTYLED TEIMOEPHIC 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 'So. 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 No. 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 



'Beitrage zur Kenntuiss der Befruchtuug,' 1S44, p. 116. 



194 ILLEGITIMATE OPPSPRING OP 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 
same 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 ijroduced 
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 TKIMORPHIC 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 OFPSPBING 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- 
ised is 93 seeds. 

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 be a strong tendency in this form to repro- 
duce, when self -fertilised, the parent-form; but the 
tendency is not so strong as with the long-styled. 
These nine plants never attained the full height of le- 
gitimate plants growing close to them. The anthers 
were contahescent in many of the flowers on several 
plants. 

Plant H. 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 ia minimum of 11. Hence 



Chap. V. HETEROSTYLBD TEIMOEPHIC 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 popr 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-farm 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 noTmal 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 
66 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 SO. 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. 

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



Chap. V. HETBROSTYLED TEIMORPHIC 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 (N"os. 21 to 
25) were observed; one yielded scarcely more than 
half the normal number; a second was slightly infer- 
tile; but the three others actually produced a larger 
average number of seeds, with a higher maximum, than 
the standard. In my concluding remarks I shall recur 
to this fact, which at first appears inexplicable. 

Plant SI. This short-styled plant, freely and legiti- 
mately fertilised during 1865 by illegitimate plants, de- 
scended from selfrfertilised 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 28. This short-styled plant produced perfectly 
sound pollen, as viewed under the microscope. During 
15 



200 ILLEGITIMATE OPPSPKING OP 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 jdelded 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 23. This short-styled plant produced perfectly 
sound pollen. During 1866 it was freely and legitimately 
fertilised by the other illegitimate plants specified under 
the last 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 2^. 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, HETBROSTYLED 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 S6. 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. 



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 nominal 
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, fi-om eight 
capsules, of 89 seeds, with a maximum of 119 and a mini- 
mum of 6P, 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. 

Plani 29. This long-styled plant was legitimately fer- 
tilised, during the unfavourable season pf 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 oent. 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. HBTEEOSTYLED TEIMORPHIC PLANTS. 203 

Class VII. Illegitimate Plants raised from Mid-styled 
Parents fertilised with pollen from the longest sta- 
mens of the shott-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 103.8 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 eases. 

Plant S2. 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 33. This short-styled plant was fertilised in the 
same manner and at the same time with the last ; and ten 
capsules yielded an average of 113.9, with a maximum of 
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 Bemarhs 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 OFFSPKINa OP Chap. V". 

Bults 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. HETEEOSTYLED TKIMOKPHIC 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 frllowing 
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, 13, and 13 are excluded, as they were illegiti- 
mately fertilised. 

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



r^ 


ATtnga 
Nmnbor of 
Saedapsr 

Capsole. 


Maximum 

Number In 

Buy one 

Cftpanlfl. 


Ulnlmnm XnmlMr In any one 
CapiBle. 


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


93 
130 
83.5 


159 
151 
112 


1 No record was kept, as 
> all very poor capsules 
i were rejected. 



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













Average Nnm- 
bero?Seed>, 






ATorago 


Aiarimm 


MinJmam 


Nombar of Plant. 


Foim. 


Nnmber of 
Seeda ihst 
Capanle. 


Komber in 
any one 


Nnmbar In 
any one 


ezpresied oe 
tho percentage 






Capanla. 


Capiule. 


of tho Ifonnal 












Standard. 


Plant 1 . . . 


Long-styled 














" 2 . . . 




4.5 


? 





5 


" 3 . . . 




4.5 


? 





5 


" 4 . . . 




4.5 


? 





5 


" 5 . . . 




Oorl 


2 





Oorl 


" 6 . . . 
















" 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 ShoH-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. . . 




77.8 


97 


60 


94 


" 17. . . 


Long-styled 


76.3 


88 


57 


82 



Chap. V. HETEROSTYLBD TKIMOKPHIC PLANTS. 207 



Table SO— continued. 

Class IV. — Illegitimate Plants raised from Mid-styled 
Parents fertilised with pollen from own-form longest 
stam,ens. 



ITnmliar of FUnt. 


Fonn. 


Ayernga 

Kumber of 
Saoda tier 
Cftpanla. 


Mnxlinuni 

Number lu 
any one 
Cftpiulo. 


Minim Bin 

anv ono 
Capinla. 


Averaee Num- 
ber ofSenla, 
expnoiod u 

tlie perceutun 

SUndwd. 


Plant 18. . . 
" 19. . . 
" 20. . . 


Mid-stjp-led. 
Long-styled. 


102.6 
73.4 
69.6 


131 

87 
83 


63 

64 
52 


80 
56 
75 



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



Plant 81. . . 


Short-Styled 


43.0 


63 


26 


52 


" 28. . . 




100.5 


123 


86 


121 


" 23. . . 


*' 


113.5 


123 


93 


136 


" 24. . . 


Long-styled 


82.0 


120 


67 


8S 


" 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 . 






27. 






28. 
29. 
30. 






31. 





Mid-styled 

(I 
Long-styled 



86.0 


109 


61 


99.4 


122 


53 


89.0 


119 


69 


100.0 


121 


77 


94.0 


106 


66 


90.6 


97 


79 



66 
78 
68 
107 
101 
98 



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



Plant 38 . 
" 33. 



Mid-styled . 
Short-styled 



127.2 
113.9 



144 
137 



96 
90 



137 



208 ILLEGITIMATE OFFSPRING GF 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 pdllen 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-forni 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 tha:t 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. T. HETEROSTYLED TEIMOKPHIC PLAKTS. 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 ILLIQITIMATB 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 ease 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 
dasses, some of the plants are moderately sterile. 



Chap. V. HETEROSTYLBD 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 OPPSPKING OP 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 ofi- 
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 ^^ll seed- 
lings, 1Y3 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. Begnelli, 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. 
Begnelli 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 Zeitschrift,' &c., 
footnote. Band vi., 1871, p, 75. 



Chap. V. HBTEROSTYLBD 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. The?e were 
all long-styled. They proved fully fertile or even 
fertile in excess ; fpr 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- 



* 'UeberdenTrimorphismnsin Berlin.' 21st .Tune, 1866, p. 373; 
der Gattung Oxalis : Monats- and ' Bot. Zeitang,' 1871, p. 435. 
boriohte 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 seedlin'?s, yielded seven 
capsules with an average of 53 seeds, with a maximum 
of 73. I must here state that I have found some 
difiBculty 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 ^iyOut highly ornamental plants; but when they 
flowered, they seemed, as my gardener remarked, to 
have gone back to the wild state; for the petals were 
pale-coloured, narrow, sometimes not touching each 
other, flat, generally deeply notched in the middle, 
but not flexuous on the margin, and with the yellow 
eye or centre conspicuous. Altogether these flowers 
were strikingly different from those of their pro- 
genitors; and this, I think, can only be accounted 
for on the principle of reversion. Most of the anthers 
on one plant were contabescent. Seventeen flowers 
on the grandchildren were illegitimately fertilised 
with pollen taken from other seedlings of the same 



Chap. V. HETEEOSTYLED DIMORPHIC PLANTS. 215 

lot, and produced fourteen capsules, containing on an 
average 39.3 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. 

Wg will now turn to the short-styled form: from a 
plant of this kind, fertilised with its own-form pollen, 
I raised, during February, 1863, 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- 
1;ainirig on an average 33.6 seeds, with a maximum 
of 39; 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 35 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- 
16 



216 ILLEGITIMATE OFFSPRING OP 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 38.2 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. Pour flowers on the same two grandchildren 
were legitimately fertilised by a long-styled illegiti- 
mate plant, and produced four capsules, containing only 
32.3 seedp 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 pojlen one long-styled and seven short-styled 
illegitimE^te seedlings. These seedlings were legiti- 
mately intercrossed, and from their seed fifteen plants 
were raifed, grandchildren of the first illegitimate 
union, ajid to my surprise all proved short-styled. 
Twelve ^hort-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. HETEEOSTYLED 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, GonsUtu- 
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 shorf^styled 

called attention to this sub;iei!t plant illegitimately fertilised with 

r Bot. Zeitung,' 1864. p. 5), raised its own pollen he raised fourteen 

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

spvpTitflen plants, of which four- styled and three long-styled, 
teen were long styled anrl three 



218 ILLEGITIMATE OPPSPEING OP 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 Sinensis, 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, neveiiheless 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 1863, 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 theformer, 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. 



Nsmfl of Owner or Place. 


Low-otylod 
Form. 


Short-styled 
Fon£. 


Eqosl-ityled 


Mr. Horwood ......... 

Mr. Duck 

Baston 

Chichester. 

Holwood 

High Elms 




20 
30 
12 
42 
16 
1 
13 





18 
9 

12 

5 
7 


17 
9 

15 
2 




Westerham 

My own plants from purchased seeds 







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 ofi, 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 OPTSPKING 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 1873, 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. HBTEEOSTTLED 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 OP 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. 
Ifotwithstanding 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 Lythrum 
and Oxalis, is clear; for we have seen its first appearance 



Chap. V, HBTBEOSTYLBD 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 
ofispring 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. Soo.,' viii. (1864), p. 91. 



224 ILLEGITIMATE OFFSPRING OP 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 heen 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 Proo, Linn. 800.,' viii. (1864), p. 115. 



Chap. V. HETEROSTYLBD 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. PL 
Var. acaulis of Linn, and P. acaulis of Jaeq. 

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. 

Pirst, in regard to the transmission of form and 
colour. The parent-plant was long-styled, and of a 
rich purple colour. Prom 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 



• ' Jonmal Proc. Linn. Soo.,' viii. (1864), p. I 



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 stainens 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 flrst 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 flrst 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. HETEKOSTYLED DIMORPHIC PLANTS. 227 



Table 32. 
Primula vulgaris. 



Nature of Fliist npertmented on, snl 
kind oj UDion. 


1 




is 






Purple- and yoUow-flowered ille- 
gitimate long-styled pbnts, iUe- 
gitmately fertilised with pollen 
from the same plant .... 


78 


11 


11.5 


26 


S 


Purple- and yellow-flowered ille- 
gitimate long-styled plants, iUe- 
ijitimately fertilised with pollen 
from the common long-styled 


72 
72 


30 
29 


31.4 
40.6 


6p 
62 


3 


Or, if the ten poorest capsules, 
including less than 15 seeds, he 
reiieoted, we get 


18 


Purple- and yellow-flowered ille- 
gitimate long-styledi plants, le- 
gitimately lertilised with pollen 
from the common short-styled 
primrose 


26 
26 


18 
16 


36.4 
41.2 


60 
60 


9 


Or, if the two poorest ■vcapsules, ' 
including less than 15'^eeds, be 
r^ected, wo get ...... 


15 


The long-styled form of the com- 
mon primrose, illegitimately ferti- 
lised with pollen from the long- 
styled illegitimate purple- and 
yellow-flowered plants ..... 

Or, if the three poorest (capsules 
be rcsjected, we get . . ' . . . 


20 
20 


14 
11 


15.4 
18.9 


46 
46 


1 

8 


The short-styled form of the com- 
mon primrose, legitimately ferti- 
lised with pollen from the long- 
styled illegitimate purple- and 
yellow-flowered plants ..... 


10 


6 


30.5 


61 


6 



sterile. For instance, 73 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 52.3 seeds, instead of only 11.5 seeds. 



228 ILLEGITIMATE OPFSPEING 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 were far 
from attaining the normal standards. So it was when 
both forms of the common primrose were fertilised 
with pollen from these illegitimate plants; and this 
shows that their male as well as their female organs 
were 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 oflEspring, 
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. Now we 
know that it is eminently characteristic of the illegiti- 
mate offspring of Primula Sinensis that they yield but 
few more seeds when legitimately fertilised than when 
fertilised with their own-form pollen. 



Chap. V. HETEEOSTYLBD DIMORPHIC PLANTS. 229 

Primula vekis, 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 being counted as the first 
generation. Their appearance may be attributed to 
atavism. From two other long-styled plants, fertilised 
with their own-form pollen, 72 plants were raised, 
■ffhich consisted of G8 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 anj;^ S3.tisf actory 
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, 33. As a standard of comparison 
I may state that during the same three seasons 44 
flowers borpe 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 flve 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- 
17 



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 flve 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. HETEROSTTLED DIMORPHIC PLANTS. 233 

and especially by the long endurance of the flowers. 
For instance, I fertilised many flowers on these plants, 
and flfteen 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 flrst 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 



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 33 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 flill details of this experiment, see my ' Effects of Cross and 
Self-feTtilisation,' 1876, p. gSO. 



Chap. V. HETBROSTYLED DIMOEPHIC PLANTS. 235 

out of doors, they became during the two following 
years much more dwarfed in stature and produced very 
few flowec-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 
deseribed* 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 



* ' Proe. 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, whichs-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 casesj 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. HBTEROSTYLED DIMORPHIC PLANTS. 237 

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 30.3 
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 interme- 



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. HETEROSTVLBD 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 Itow dbwn in 
the corolla in the proper position ; the remauiing 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 loag-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. 



240 ILLEGITIMATE OFFSPRING OP Chap. V. 

of seed when self -fertilised. Plants of the long-styled form 
of Pulmonaria angustifolia were, lik6 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 6 long-styled. 

Polygonum fagopyhum. 

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 
poUen, 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. HETBROSTYLED PLANTS. 241 

slightly lessened fertility to absolute barrenness, when 
not even a single seed-capsule is produced. In both 
cases the facility of effecting the first union is much 
influenced by the conditions to which the plants are 
exposed.* Both with hybrids and illegitimate plants 
the innate degree of sterility is highly variable in 
plants raised from the same mother-plant. In both 
cases the male organs are more plainly affected than 
the female; and we often find contabescent anthers 
enclosing shrivelled and utterly powerless pollen- 
grains. The more sterile hybrids, as Max Wichura 
has well shown, f are sometimes much dwarfed in 
stature, and have so weak a constitution that they are 
liable to premature death; and we have seen exactly 
parallel cases with the illegitimate seedlings of Lythrum 
and Primula. Many hybrids are the most persistent 
and profuse flowerers, as are some illegitimate plants. 
When a hybrid is crossed by either pure parent-form, 
it is notoriously much more fertile than when crossed 
inter se or by another hybrid; so when an illegitimate 
plant is fertilised by a legitimate plant, it is more 
fertile than when fertilised 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 ezperimentalistfl in effect- the case of Primvla veris. 

ing crosses between distinct spe- t 'Die Bastardbefruchtung im 

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



242 ILLEGITIMATE OPPSPEING OP 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 desti-oyed. Exactly the same 
thing occurs with the two forms of a heterostyled 
species. Thus several long-styled flowers of Primula 
verts 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. verts; 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 pollen from a long-styled 
plant. 

In all the several foregoing points the parallelism is 
wonderfully close between the effects of illegitimate 
and hybrid fertilisation. It is hardly an exaggeration 
to assert that seedlings from an illegitimately fer- 
tilised heterostyled plant are hybrids formed within 
the limits of one and the same species. This conclu- 
sion is important, for we thus learn that the difficulty 
in sexually uniting two organic forms and the sterility 
of their offspring, afford no sure criterion of so-called 
specific distinctness. If any one were to cross two 
varieties of the same form of Lythrum or Primula for 
the sake of ascertaining whether they were specifically 
distinct, and he found that they could be united only 
with some difficulty, that their offspring were extremely 
sterile, and that the parents and their offspring re- 
sembled in a whole series of relations crossed species 
and their hybrid offspring, he might maintain that his 
varieties had been proved to be good and true species; 
but he would be completely deceived. In the second 
place, as the forms of the same trimorphic or dimorphic 
heterostyled species are obviously identical in general 
structure, with the exception of the reproductive 
organs, and as they are identical in general constitu- 
tion (for they live under precisely the same condi- 
tions) the sterility of their illegitimate unions and 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 



CHAPTEE VI. 

CONCLUSINQ SeMABKS ON HETEBOSTYLED 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 alreadv referred to. 
of Science,' 1865, p. 101; and Kuhn, 'Bot. Zeitung,' 1867, p. 67. 



246 CONCLUDING REMARKS Chap, VI. 

Used 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- 
solij:tely 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 HETBEOSTTLED 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. 



Name of Spaclei . 



Ill«gltiiDatfl Unions, 



Proportional 
Number of 

Flowers 
wblch pro- 
duced 
Capsules. 



Seeds per 
Capsule. 



Primula veris 

P. elatior 

P. vulgaris 

P. Sinensis 

P. Sinensis (second trial) 

P. Sinensis (Hildebrand) 

P. auricula (Scott) 

P. Sikkimensis " 

P. cortusoides " 

P. involucrata " 

P. farinosa " 

Average of the nine species of Primula . . 

Hottonia palustria (H. Miiller) 

Linum grandiflorum (the difference probably I 

is much greater) J 

L. perenne 

L. perenne (Hildebrand) 

Pulmonaria officinalis (German stock, HUde- I 

brand) J 

Pulmonaria angustifolia 

Mitchella repens 

Borreria, Brazilian sp 

Polygonum fagopyrum 

Lythrum salicaria 

Oxalis Valdiviana (Hildebrand) 

O. EegnelU " 

O. speciosa " 



65 
75 
54 
63 
53 
42 
15 
31 
66 
48 
44 
69 
61 



20 




32 
47 


46 
46 
34 


49 



the two sexes of dioecious plants. Nor does the calyx 
differ, hut 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- 
18 



248 CONCLUDING EEMARKS 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 Ly thrum sali- 
caria equal in weight six from the mid-styled and seven 
from the short-styled form. Lastly, short-styled plants 
of Pulmonaria offlcinalis 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 onl}"^ 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 



250 



CONCLUDING EBMARKS 



Chap. VI. 



Table 34. 

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



Dimorph 


ic Species. 




Trom the Long- 




■trledfonn. 


■tyled form. 


Primula yens 67 


Foisytbia suspensa . . 


94 


" vulgaris .... 71 


Cordia (sp. ?) 


100 


" Sinensis (Hilde- 


Gilia pulchella .... 


100 


brand) .... 57 


" miciantha. . . . 


81 


" auricula .... 71 


Sethia acuminata . . . 


83 


Hottonia palustris (H. Miil- 


Erythroxylum (sp. ?) . . 


93 


ler) 61 


Cratoxylon formosum . 


86 


Hottonia palustris (self) . 64 


Mitchella repens, pollen 




Linum grandiflorum . . . 100 


grains of the long-styled a 


" perenne (diameter 

variable) . . .^""('^ 


little smaller. 




Borreria (sp. ?).... 


92 


" flavum 100 


Faramea (sp. ?).... 


67 


Fulmonaxia officinalis . . 78 


Suteria (sp. ?) (Fritz Miiller 


75 


" angustifolia . SI 


Houstonia coerulea . . . 


72 


Polygonum fagopyrum . . 82 


Oldenlandia (sp. ?) . . . 


78 


Leucosmia Bumettiana . 99 


Hedyotis (sp. ?) . . . . 


88 


JEgiphila elata 63 


Coococypselum (sp. ?) (P. 
Mffller) 




Menyanthes trifoliata . . 84 




Limnanthemum Indlcum . 100 


Lipostoma (sp. ?) . . . 


80 


ViUarsia (sp. ?) .... 75 


Cinchona micrantha . . 


91 



Trimorphic Species. 



Rfitio ezpreulnp the ertrflme dtffiireiicee In dtstne- 
trr of tbe Tiollea-gTAini from the two lets of 
nnthera In the three fonni. 

Lythrum salicaria .... 60 

Nesjea verticillata .... 65 

Ozalis Valdiviana (Hildebrand) 71 

" Eegnelli 78 

" speciosa 69 

" sensitiva 84 

Pontederia (sp. 7) 55 



Batio between the diameters of tbe polIcD- 
prslne of the two setu of anthen In the same 

Oxalis rosea, long-styled form i 

(Hildebrand) . . . J ®^ 



compressa, short-styled > 



form 



Pontederia (sp. ?) short-styled i 



form 



other sp., mid-styled i 



form 



83 



87 



86 



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 HETERQSTYLED 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 poUen- 



* 'SuU' Opera, la Distribuzioue dei Sessi aelle Piante,' &o., 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 iii 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 heterostjded 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-r 
cies from matter yielded by the -pistil, we can see that 
in the former case it would be necessary that the grains 



CHAP.Vr. ON BETBROSTTLBD PLANTS. 25S 

of the two forms should differ in size relatively to the 
length of the pistil which the tubes have to penetrate, 
but that in the latter case it would not be necessary 
that the grains should thus differ. Whether this 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 
paltistris in the ratio of 100 to 83. With Limnan- 
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 Linum flavumj 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 
jthe case with those of the common primrose- and 
sowslip. 

The pistil differs in length in the two forms of every 



264 CONCLUDING EEMAEKS Chap. VI, 

heterostyled plant, and although a similar difEerence 
is very general with the stamens, y6t 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 
papillae on the stigma of the long-styled form are longer 



Chap. VI. ON HBTEROSTYLBD PLANTS. 255 

and often thicker than those on that of the short- 
styled. For instance, the papillae on the long-styled 
stigma of Hottonia paltistris are more than twice the 
length of those in the . other form. This holds good 
even in the case of Houstonia coerulea, 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 papillae 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 papillae, 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 papillae 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 bejong to nine of the several great 
Series, into which phanerogamic plants have been di- 
vided by Bentham and Hooker. 



256 


CONCLUDING REMARKS 
Table 35. 


Chap, VI. 


List of Genera including Heterostyled Species. 


Dicotyledons. 


Dicotyledons. 


, Cratoxylon. 


HyperioinejB. 


J Mitehella. 


Bubiacese. 


, Erythroxylum. 


ErythroxylesB. 


i.Diodia. 


n 


Sethia. 


" 


Borreria. 


II 


Tiinum. 


Gteianiacete. 


; Spermacoce. 


*' 


Oxalis. 


" 


Primula. 


Frimulaceffi. 


Lythrum. 


Lythiaceffi. 


Hottonia. 


II 


Nesaea. 


(1 


Androsace. 


II 


' Cinchona. 


BubiacesB. 


. Forsythia. 


Oleacese. 


• Bouvardia. 


" 


v/Menyanthes. 


GentianacecB. 


> Manetda. 


" 


V Limnanthemum. " 


, Hedyotis. 


" 


« Villarsia. 


II 


* Oldenlandia. 


" 


>/Gilia. 


PolemoniacesB. 


VHoustonia. 


(1 


< Cordia. 


Cordieffi. 


, Coooocypselum. 


•■ 


' Pulmonaria. 


BoraginesB. 


• LipoBtoma. 


" 


• jEgiphila. 


VerbenacesB. 


• Knoxia. 


i( 


sj Polygonum. 


Polygoneae. 


• Faiamea. 


tt 


' Thymelea. 


ThymelesB. 


- Psyohotria. 


tt 


Monocotyledons. 


> Budgea. 








• Suteria. 


It 


. y Pontederia. 


PontederiacesB. 



In some of these families the heterostyled condition 
niiist have heen 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 Menyantheae .aiiid the several, trimorphic species of 
Oxalis must have inherited their structure ■ from a 



Chap. VI. ON HETEROSTYLBD PLANTS. 26-7 

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 Eubiaceae contains 
not far short of as many heterostyled genera as all the 
other thirteen families together ; and hereafter no doubt 
other Kubiaceous 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 Boragineae 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 i|; 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..' .IJytfrr 
.iim-includes trimorphic, dimorphic, and fiqnibstyle.d 
species. .. L "X '.;'.. ....'•■:-.■' 



258 CONCLUDING REMARKS Chap. VL 

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 inhabitins 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 waa 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- 
erost^led 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 &r as can be judged from such 
the Iiinnean classes Moncecia, imperfect data, that there is some 
DioBciaand 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. ISSS') these three not hold good with heterostyled 
Linnean classes include 40 genera, species. 
1? 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 Ly thrum salicaria 
would then consist of two heterostyled hermaphrodites 
and a female. ~So 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 ofEer 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 s.ame 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 LeguminosEB, Labiatae, Scrophulariaceae, 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 profltable 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. 411. 



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 be 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 teen 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 
Eubiaceae they are dispersed in eight of the tribes. We 
may therefore conclude that this structure has been acr 



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 diflSculty — 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 Amsinchia specta- 
hilis and Nolana prostraia 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 diehogamous 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 superfiuous. 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 HETEEOSTYLED 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 
diffieulty 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 
19 



264 CONCLUDING KEMABKS 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. ON HETEROSTTLED 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 ease 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 



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 iirst 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.vl on hbteeostyled 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 spectdbilis, 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 verts 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. VL 

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 ^^reproductive powers became modified in such a 
manner that the sexual elements in one set were 
adapted to act on the sexual elements of another set; 
and consequently that these elements in the same set 
or form incidentally became ill-adapted for mutual 
interaction, as in the case of distinct species. 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, ' Bastarderzeiigung act on the reproductive system of 

im Fflanzenreich,' 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 raajr be well here to re- be acquired only under long-con^ 

mark that, judging from the re- tinned nearly uniform conditions 

markable power with which ab- of life, 
mptly changed conditions of life 



Chap. VI. ON HETEROSTYLBD PLANTS. 269 

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 163 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 trimorphie Ly thrum 
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 trimorphie 
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. 



Nnmberj Nnmlrer 
of LODK- of Short- 

Htyled I Btyled 
Offiprmg O&pring 



Frimnla veriB . 



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



Frimnla vnlgaris . 



Primula auricula . 



Primula Sinensis 



{Short-styled form, fertilised 1 
by own-form pollen, pro- > 
duced j 

C Long-styled form, fertilised by 

I own-form pollen during two 

' I successive generations, pro- 

[ duced 

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

f Long-styled form, fertilised by 

J own-foi-m pollen during two 

■ I successive generations, pro- 

[ duced 

f Long-styled form, fertilised by ) 

" " i own-form pollen (Hilde- }■ 

( brand), produced .... J 

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

Pulmonaria officinalis f Long-s^led form, fertilised by t 
( own-form pollen, produced . j 



Polygonum fagopyrum ( Long-a^led form, fertilised by 
' I own-form pollen, produced . 



{Short-styled form, fertilised ] 
by own-form pollen, pro- > 
duced J 



156 



25 



52 



U 



11 
45 

13 



75 



24 


4 

20 



Chap. VI, ON HETEROSTYLED PLANTS. 



271 



Table 37. 

Nature of the Offspring from Illegitimately fertilised 
Trimxtrphic Plants. 



Nambtr 

of Long- 

Btyled 

Offspring 



Number }f umber 

of Mid- of eiiorl- 

etylod" Btyled 

Offtprldg Offiipring 



{Long-styled form, fertilised ' 
by own-form pollen, pro- 



duced 



{Short-styled form, fertilised 1 
by own-form pollen, pro- 
duced , J 

{Short-styled form, fertilised 
by pollen frommid-length 
stamens of long -styled 
form, produced .... 

Mid-styled form, fertilised] 
by own-form pollen, pro- , 
duced I 



cm 



Ozalis rosea. 



("Mid-styled form, fertilised 
I by pollen from shortest 
I stamens of long-styled 
[ form, produced . . . 

Mid-styled form, fertilised 
by pollen from longest 
stamens of short-styled 
form, produced , , . , 

r Long-styled form, fertilised 
during several genera- 
tions by own-form pollen, 
produced offspring in the 

I ratio of 



{Mid-styled form, fertilised! 
by own-form pollen, pro- >■ 
duced J 



56 



17 



14 



100 



17 



18 



not in so marked a manner as in the case of the long- 
styled form. There are three eases 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 



572 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 163 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). HeirBreit- 
ing from the length of the pistil in enbach found many specimens of 
several allied genera (see Mr. J. Primula datior growing in a state 



Chap. VI. ON HBTBROSTYLBD PLANTS. 273 

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 arid 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 natare with some flowers on the greatly preponderated in numher ; 

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

short-styled and others eqti^l- of the short-styled and 15 of the 

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



274 CONCLUDING RBMAKKS 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 somevrhat 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-styjed 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 KEMAEKS Chap. VE 

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 {he 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 ona 



Chap. VI., ON HBTEEOSTYLED 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 DItECIOUS AND Chap. VII. 



CHAPTER VII. 

Polygamous, Dkecious, and Gyno-di<ecious Plants. 

The conversion in various ways of hemmplirodite into dicecious plants 
— Heterostyled plants rendered dioecious — Bubiaceffi — Verbenaccae 
— Polygamous and sub-dioecious plants — Euonymus — ^Fragaria — 
The two sub-forms of both sexes of Bhamnus and Epigsea — Ilex — 
Gyno-dioecious 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, dicecious, and gyno-dioecious plants. 

There are several groups of plants in which all the 
species are dicecious, and these exhibit no rudiments 
in the one sex of the organs proper to the other. 
About the origin of such plants nothing is known. It 
is possible that they may be descended from ancient 
lowly 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 
20 



280 DKECIOUS AND Chap. VIL 

This, however, would he efEected 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. Soo.,' vol. xiii. 
EfTectn of Cross and Self-fertilisa- p. 600. 
tlon,' 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 fiower ; 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 DICECIOUS AND Chap. VIL 

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 e£Eectual 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. Soo.,' vol. xil. 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 Compositae,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 



* 'Beitragezur Kenntniss,' &o., chap, xviii. — 8nd 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 bet den Compositen,' 

ray ' Variation of Animals and 1869, p. 89. 
Plants under Domestication,' 



284: DICECIOUS 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 
diiler 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 
Eubiaceae 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. Vir. 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 iiowers 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 Eubia- 
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 Eubiaeeous 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, 1S6S, p. 183. 



286 DKECIOUS AND Chap.VIL 

apparently quite destitute of pollen. Considering how 
many Kubiaceous 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 Kubiaceous 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 
Kubiaceous plants are heterostyled; but in the case of 
Discospermum one of the two forms is always barren, 
the ovary containing about two aborted ovules in each 
loculus; whilst in the other form each loculus contains 
several perfect ovules; so that the species appears to 
be strictly dioecious. 

Most of the species of the South American genus 
.iEgiphila, a member of the Verbenaceae, apparently are 
heterostyled; and both Fritz Miiller and myself thought 
that this was this the case with 2E. 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 th6 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 suhulata 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 dicecious 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 dicecious or sub-dioecious 
plants, which are worth describing, chiefly as they show 
by what fine gradations hermaphrodites may pass into 
polygamous or dicecious species. 

Tolygamous, Dicecious and Sub-dioecious Plants. 

Euonymus Europceus (Celastrines). — 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 DKECIOUS 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 poUeniferous bushes. The two forms are shown 
in the accompanying drawings. 

Fig. 12. 




Hermaphrodite or male. Female. 

EUONYMCS EUBOP.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 poUeniferous 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. POLYGAMOPS 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 rudimsefttary 
ones were of a pink colour and not at all shrivelled. 
These two sets of pistils did not difEer 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 DICBCIOUS AND Chap. VH. 

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 diilerence 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 poUeniferous 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 poUeniferous 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 poUeniferous 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 poUeniferous 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 93 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 3.86 
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 pror 
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 fruit," — through the female A, 
which produced during the same year 97, — ^through the 
polleniferous bush C, which produced this year 93 fruits, 
these, however, containing a very low average number of 
seeds of small size, — through the bush D, which pro- 
duced only 30 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.* 



* Acooiding to Fritz Miiller Southern Brazil is in nearly the 
('Bot. Zeitung,' 1870, p. 1.51), a same state as onr Enonymns. The 
Chamissoa (AmarantbacesB) in ovules are equally devoloped 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 poUeniferous 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 -^giphila; 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 poUeniferous flowers 
being sometimes longer than those in the female 
flowers. 

Fragaria vesca, Virgtniana, Chiloensis, &c. (Eosa- 
ceae). — 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 fmit, and are 

are entirely destitute of pollen, therefore in function males. Nev- 

Iii the poUeniferous form, the pis- ertheless, on one occasion IVitz 

til is short and the stigmas never Miiller found flowers of this kind 

separate from one another, so that, in which the stigmas had sei>a- 

althongh their sui-faces are cov- rated, and they produced some 

ered with fairly well-developed pa- fruit, 
pillffi, 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 tliree 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 poUeni- 
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, t 

Bhamnus catharticus (Ehamnese). — 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 ' Oktrd. formation on this subject, see 
Chron,' 1861, p. 716. 'Variation under Domestication,' 

t For references and faitlier in- chap. x. 2ud 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. 

Bhamnus cathaeticub. (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 matiire. 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. 

Bhamnus 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 ilowers 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 




Long-styled 
female. female 

Bhamnub cathabticus. 

son compared the pollen-grains from the two forms, 
and those from the long-styled flowers were to those 
from the short-styled, on an average from ten measure- 
ments, as 10 to 9 in diameter; so that the two her- 
maphrodite forms of this species resemble in this 
respect the two male forms of B. cathartictis. 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 
21 



296 DKECIOUS AND Chap, VH. 

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 B. lanceolatus seems 
to correspond with the males of B. cathariictis 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 a,scertained. 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. 

JEpigwa repens (Ericaceae). — This plant appears to 
be in nearly the same state as Rhamnits catharticus. 
It is described by Asa Gray f as existing under four 
forms. (1) With long style, perfect stigma, and short 
abortive stamens. (3) Shorter style, but with stigma 
equally perfect, short abortive stamens. These two 



*Lecoq. 'G^ogr. Bot.' torn. v. July, 1876. Also, 'The American 
IfSfi. pp. 420-26. Naturalist,' 1876, p. 490. 

t ' American Journal of Science,' 



Chap. VIL POLYGAMOUS PLANTS. 297 

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 dioecious. 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 dioecious. 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 and sometimes not at 
all shorter than the perfect stamens in the male flowers. 
In the latter the ovary is small and the pistil is almost 
aborted. The filaments of the perfect stamens adhere 
for a greater length to the petals than in the female 
flowers. The corolla of the latter is rather smaller 
than that of the male. The male trees produce a 
greater number of flowers than the females. Asa Gray 



* "Variations in EpijrasorepejM," tVaucher, 'Hist. Phys. des 
' Proc. Acad. Nat. Soc. of Phila- Plantes d'Europe,' 1841, torn. ii. 
delphia,' May 1868, p. 153. p. 11. 



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-diacious 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 othpr group. Such cases have beem noticed by 
myself in Thymus serpyllum and vulgaris, Satureia 
lioriensis, Origanum vulgare, and Mentha hirsuta; and 
by others in Nepeta glechoma, Mentha vulgaris and 
aquatica, apd Prunella vulgaris. In these two latter 
species the female form, according to H. Miiller, is in- 
frequent. To these must be added ' Dracocephdlum 
Moldavicurn, Melissa offlcinalis and clinipodium, and 
Tlyssopus officinalis.* In the two last-named plants the 



*H. MuUer, 'Die Befhichtung and Lecoq were mistaken in think- 

der Blumen,' 1873; and 'Nature,' ing that seveial of the plants 

1873, p. 161. Vancher, ' Flantes named in the text are dioecious. 

d'Europe,' tom. 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 

rviji. 1856, p. 380. Lecoq, G^ developed and of prope* length 

graphieBot. del'Europe,' tom.viii. until some time after the antheis 

pp. 33, 38, 44, &c. Both Vancher have dehisced. 



Chap. VII. GTNO-DICECIOUS PLANTS. 290 

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 Labiatse. 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-DIOECIOUS PLANTS. Chap. VIL 

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.! It would, however, be a mistake to 
suppose that the nature of the conditions determines 



* ' Sull' Opera la Distribnzione H. MiilleT, ' Die Befinichtung, 
dei Sessi nelle Piante. &c.,' 1867, &c.,' p. 327. 
p. 7. With respect to Germany, t ' Nature,' June 1873, p. 162. 



Chap. VII. GYNO-DICECIOUS 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 tile 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-DICECIOPS PLANTS. 



Chap. VIl. 



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 




Bennaphrodlte. Females. 

Thymus vuLaABis (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. 

Saiureia Tiortensis. — Eleven seedlings were raised in 
separate pots in a hothed 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. 303 

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 33.3 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 Labiatae 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 Befraohtung der Blamen,' pp. 319,. SS6. 



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 Thymus serpi/llum, 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. 

Scdbiosa arvensis (Dipsacese). — ^It has been shown by 
H. Mtiller 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 



* ' Befruehtiing der Bluraen,' males co-exist ; it is, however, 

&o., 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 proteiandrous. From 

(!&6ogra.phie Bot.' 1857, torn. vi. what Lecoq says, R jhccmo likowiso 

pp. 473, 477) says that male plants appears to occur under two forms 

as wpll as hermaphrodites and fe- in Fiance. 



chap.vil gyno-dicecious plants. 305 

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 Labiatse. I have also observed 
the existence of two forms in our endemic S. succisa, and 
in the exotic S. 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 inyoelium. In 1862 many female plants were 
found ; and in 1864, 33 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 GrNO-DI(ECIOUS PLANTS. Chap. VH 

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,^ 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. 

Cnicua Serratula Eriophorum. — ^In the Gompositse, 
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 Befrnchtung,' &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. MaiBhall writes to me to and ' Proc. American Academy oi 
the same effect from Ely. Science,' Oct. 14, 1862, p. 53. 
t ' Manual of the Botany of the 



Chap. VII. SIZE OP 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 oAly a few grains of pollen, 
and ihese 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 (Cyperacese) 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, dioecious, 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 
Labiatffi, Scabiosa 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 3. E. Smith, 'Transao- of theLinnseanSocietyofBotany,' 
tionsof the LlnnsBan Society,' vol. vol. ix. 1865. p. 161. 
ziii. p. 599. Dr. Dickie, 'Journal f ' Bot. Zeitung,' 1863, p. 326. 



308 SIZE OP 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 Bhamnus catharticus not 
only the petals but the green and inconspicuous sepals 
of the female have been reduced in size; and in the 
strawberry the flowers are largest in the males, mid- 
sized in the hermaphrodites, and smallest in the fe- 
males. These latter cases, — the variability in the size 
of the corolla in some of the above species, for instance 
in the common thyme, — ^together with the fact that it 
never differs greatly in size in the two forms — make 
me doubt much whether natural selection has come 
into play; — that is whether, in accordance with H. 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 

Kemer's view ( ' Die Schutzmittel rain. In the genns Thymus, for 

des Pollens,' 1873, p. 56) can be instance, the aborted anthers of 

accepted in the present cases, the female are much better pro- 

namely, that the larger corolla in tected than the perfect ones of the 

the hermaphrodites and males hermaphrodite. 



Chap.YIII. CLBISTOGAMIC flowers. 309 



CHAPTER VIII. 

GliMSTOOAMIC FLOWEBS. 

General character of cleistogamic flowers — List of the genera prodncing 
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 — Osalis acetosella 
— O. sensitiva, three forms of cleistogamic flowers — Vandellla — 
Ononis — Impatiens — Drosera — Miscellaneous observations on various 
other cleistogamic plants — Anemophilous species prodncing 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 Linnsens 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 
some 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. 

Bize, 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 he 
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 
inforins me that in the South of France some of the 
flow«rs 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 Ranuncultis aquatilis, Alisma natans, 
Subularia, lUecebrum, Menyanthes, and Euryale,* 
remain closely shut as long as they are sub- 

•Delpino, 'Snll' Opera, la Dis- Flora,' vol. Hi. 1885. p. 157. For 

tribuzlone del Sessi nelle Piante,' the behaviour of Menyanthes in 

&c. 1867, p. 30. Subularia, how- Buasia see Gillibert in Act. Acad, 

ever, sometimes has its flowers St. Petersb.,' 1777, part ii. p. 45. — 

fully expanded beneath the water. On Enryale ' Gardener's CSironi- 

see Sir J. E. Smith, 'English cle,' 1877, p. 380. 



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 eases 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 sedson 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 Kuhn).* 

DICOTYLEDONS. 

DeedalacanthuB (Acanthacese). 
DipteTacanthus " 

JGchmanthera " 

Buellia " 

Lamium (Labiatse). 
Salvia " 

Oxybaphus (NyctagincBB). 



DICOTYLEDONS. 

Eritrlchlum (Boiagineffi). 
Cuscuta (Convolvnlacete). 
ScTophulaiia (ScrophularineEB). 
Linaria " 

Vandelll* " 

Cryphiaoanthus (Acanthacese). 
Eranthemum " 



* I have omitted Trifolium and appear to be properly cleistogamic. 

Aiachis from the list, because Von Correa de Mello ( ' Journal Linn. 

Mohl says ('Bot. Zeitung,' 1863, Soc. Hot.' vol. xi. 1870, p. 254) 

p. 312) that the flower-stems observed plants of Arachis in 

merely draw the flowers beneath Brazil, and could never find such 

the ground, and that these do not flowers. Plantago bus been omitted 

?3 



312 



CLEISTOGAMIC FLOWERS. 



Chap. VIIL 



Table 38 — continued. 



DICOTYLEDONS. 

Nyoiaginia (Nyctagineffi). 
Stapelia (Asclepiadse). 
Specularia (Campanulacese). 
Campanula " 

Hottonia (Frimulacece). 
Anandria (Gompositce). 
HeterocarpsBa (Cruciferse). 
Viola (Violacete). 
Helianthemum (dstineffi). 
Lechea 

Pavonla (Malvaceae). 
Gaudichandia (Malpighiaceee). 
Aspicaipa 
Oamarea 

Janusia " 

Polygala (Polygalete). 
Impatiens (Balsamineffi). 
Oxalls (Gerania<!esB). 
Ononis (Leguminosse). 
Parochsetus " 
Chapmannia " 
Stylosanthus " 



DICOTYLEDONS. 
Lespedeza (Leguminosffi). 
Vicia 
Lathyrus 

Martinsia vel] •■ 
Neurocarpum i 
Amphlcatpsea 
Glycine 

Galactia " 

Voandzeia " 

Drosera (Droseiacese). 

Monocotyledons. 

Juncus (Jnncese). 
Leersia (Giamineffi). 
Hordeum ". 

Cryptostachys " 
Commelina (Commclinese). 
Monochoria (Pontederaceffi). 
Schomburgkia (Orchids). 
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 therefor^ 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 Acanthaceie, 
for which see J. Scott in ' .Toumal 
of Bot.' (London), new series, vol. 
1., 187S, p. 161. With respect to 
Salvia see Dr. Ascherson in ' Bot. 
Zeitung,' 1871, p. 555. EorOxy- 



baphus and Xyctaginia see Asa 
Gray in 'American Naturalist,' 
Nov. 1873, p. 698. 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 Bouch€ in ' Sitzungs- 
berichte d. Gesellsch. Natur. 
Preunde,' Oct. 20, 1874, p. 90. I 
have added Thelymitra, as from 
the account given by Mr. Fitzger- 
ald in his magniflcent 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 Orchidcffi 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 Acanthacese and Malpighiacese. 

A large number, but not all the species, of certain 
genera, as of Oxalis and Viola, bear cleistogamic as well 
as ordinary flowers. A second point which 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 cleistogamic 
flowers, but only a few of them are worth giving, since 
the appearance of an admirable paper by Hugo von 
Mohl,* whose examination was in some respects much 
more complete than mine. His paper includes also an 
interesting history of our knowledge on the subject. 

Viola canina. — The calyx of the cleistogamic flowers 
differs in no respect from that pf 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. 309- 

Duval-Jouve says about Ciyptos- 328. 

tachys in 'Bull. Soc. Bot. de t Ibid. 1857, p. 730. This paper 

France,' torn, x., 1863, p. 195, this contains the first full and satisfac- 

plant appears to produce cleisto- tory account of any cleistogamic 

gamic flowers. The other additions flower. 

to the list are noticed in my test. 



S14 CLBISTOGAMIC PLOWEES. Chap. VIII. 

cells or locTili 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 -f^^ of an inch in diameter, 
and therefore of smaller size than the ordinary pollen- 
grains similarly treated, which have a diameter of 
^?W of ^11 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 
passage. 



Chap. YIII. 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 eases 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 mairked 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. Kot 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 Bomhus 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 cleistogamie 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 cleistogamie ones contained 9.64 
seeds, — an amount of difference of no significance. It 
is remarkable how much more quickly the capsules 
from the cleistogamie 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 cleistogamie 
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 bo 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 cleistogamie 
flowers in one part of Liguria, whilst the perfect flow- 
ers are there abundantly fertile; on the other hand, 
cleistogamie flowers are produced by it near Turin. 



* Vanoher says ('Hist. Phys.des See also Lecoq, 'G^ograph. Bot.' 

Plantes d'Europe,' torn. Hi. 1844, torn. v. 1856, p. 180. 

p. 309) that V. hirfa and r/iUirm t ' Snll' Opera, la Distrihnzione 

likewise bury their capsules. — dei Sessi nelle Piante,' 1867, p. 30. 



€hap. VIII. 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 etaternents are taken to the supposed sterility of the 

from Professor OUvrt's excellent perfect flowers in this eenns see 

article in the 'Nat. Hist. Review,' also Timbal-Laprave 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 35 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 F. canina. It is slightly bent towards the two 
fertile anthers. 

Viola Boxburghiana. — 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 eleistogamic 
flowers. 

Many other species, besides the five now described, 
produce eleistogamic flowers; this is the case, accord- 
ing to D. Miiller, Michalet, Von Mohl, and Hermann 
Miiller, with V. elatior, lancifolia, sylvatica, palustris, 
tnirabilis, 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 eleistogamic 
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 eleistogamic ones. According to M. Boisduval, an 
Italian species, V. Buppii, never bears in Prance " des 
fleurs bien apparentes, ce qui ne I'empeche pas de fruc- 
tifier." 

It is interesting to observe the gradation in the 
abortion of the parts in the eleistogamic 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- 
therif erous ; 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 CLBISTOGAMIC 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 T below the stigmas, so that 
their tubes had to traveL some way upwards. Ac- 
cording to Michalet iiiese 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 Fiance,' torn. vii. 1860, p. 468. 



Chai'. VIII. OXALIS. 321 

average 10.0 seeds per capsule. This is rather above 
the average 9.3, 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 



• ' Monatsberioht der Akad. der Wias, 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 flovrers. The styles are furrowed longitudinally, 
and are clothed with simple as well as glandular hairs, 
but only in the eleistogamic 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 eleistogamic flowers are produced by 
the long-styled plants, and mid-styled as well as 
short-styled eleistogamic flowers by the other two 
forms; so that there are three kinds of eleistogamic 
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 eleisto- 
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 eleistogamic 



Chap. VIII. VANDELLIA. 323 

flowers of the double violet have been rendered 
double. 

VandelUa 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 
^ 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 TTSTT 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, ani 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 oil and carried upwards 
in the shape of a little cap. The perfect flowers gener- 
ally appear befofe 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 thiey 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. Zeitnng,' 1867, p. 65. 



32 i CLBISTOGAMIC 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 Y. 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 j^he 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 columnw. — 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 Fiance,' torn. vil. 1860, 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 3.38 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. 

Lathyrus nissolia apparently offers a case of the flrst 



326 CLEISTOGAMIC FLO WEES. Chap. VIII. 

stage in the production of cleistogamic flowers, for on 
plants growing in a state of nature, many fif 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, 
Amphicarpsea, and Voandzeia, the cleistogamic flowers 
are produced on subterraneaii 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 lias 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 30 to 1; but 



* Correa de Mello ( ' Journal African plant, which is sometimes 

Linn. Soc. Bot.' vol. xi, 1870, p. cultivated in Brazil. 

254) particularly attended to the t 'Journal Linn. Soc. Bot.' vol. 

flowering and fruiting of this xiii. 1873, 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 ease 
with /. fulva. As in this latter species all five stamens 
produce some pollen, though small in amount; a 
single anther contains, according to Von Mohl, not 
more than 50 grains, and these emit their tubes 
while still enclosed within it. The pollen-grains of 
the perfect flowers are tied together by threads, but 
not, so 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 7. balsamina are visited by 
humble-bees,* and I am almost sure that this is the case 
with the perfect flowers of I. noli-me-iangere. 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 3, 2, and 1 seed. As 
I. 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 flrst flower-stems which 



* H. MuUer, ' Die Befruchtnng,' &c. p. 170. 
23 



328 CLEISTOGAMIC FLOWERS. Chip. 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 ilowers 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 oiir 
subject. Mr. Scott states * that Eranthemum ambi- 
guutn 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 
Aeanthacese, produces both open and cleistogamie flow- 



* ' Joamal of Botany,' London, new series, vol. i. 1872, pp. 161-4. 



Chap. VIII. CLBISTOGAMIC 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 cleistogamic 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 cleistogamic 
flowers. The cleistogamic 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 cleistogamic and per- 
fect ones. 

The solitary almost sessile cleistogamic flowers pro- 
duced by Monochoria vaginalis are differently protected 
from those in any of the previous cases, namely within 
" a short sack formed of the membranous spathe, with- 
out any opening or fissure." There is only a single 



*VoTi MoM, 'Bot. Zeitnng,' of the perfect flower is mostly 

1863, pp. 314 and 333. Dr. Brom- 5-cleft. 

field ( Phytologist.' vol. iii. p. t ' Journal Linn. Soc.' vol. ii. 

530) also remarks that the calyx 1857, p. 7. See also Professor 

of the cleistogamic flowers is Oliver in 'Nat. Hist. Review,' 

usually only 3-cleft, while that 1868, p. 840. 



330 CLEISTOGAMI€ 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- 
pighiaeese 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 
Gaudichaudiana, 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, 'Jonr. Linn, Soc.,' t 'Archives dn Miis#niti.' torn, 
vol. viil. 1864, p. 147. iii. 1843, pp. 35-38, 88-86, 589, 598.> 



Chap.VIII. CLBISTOGAMIC flowers. 331 

capsules were produced in Mr. Ferrer'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 hufonius and Hordeum. — All the species 
hitherto mentioned which produce cleistogamitf^ flow- 
ers are entomophilous ; but Juncus and seven genera 
of Graminese are anemophilous. Juncus hufonius is re- 
markable * by bearing in parts of Eussia only cleisto- 
gamic flowers, which contain three instead of the six 
anthers found in the perfect flowers. In the genus 



* See Dr. Asclierson's interesting paper in ' Bot. Zeitnng,' 1871, p. 
551. Also 1878, p. 697. 



332 CLBISTOGAMIC 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 Reigate, and cultivated 
them for several years in my green-house. The cleis- 
togamic flowers are very small, and usually mature their 
seeds within the sheaths of the leaves. These flowers 
are said by Duval-Jouve to be filled by slightly viscid 
fluid; but this was not the case with several that I 
opened; but there was a thin film of fluid between the 
coats of the glumes, and when these were pressed the 
fluid moved about, giving a singularly deceptive ap- 
pearance of the whole inside of the flower being thus 
filled. The stigma is very small and tji6 filaments ex- 
tremely short; the anthers are less than -jV 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 



• ' Bollettdni del Comizio agnirio Hordenm, in ' Monatshericht d . K. 

Parmense.' Marzo e Aprile, 1871. Akad. Berlin,' Oct. 1872, p. 760. 

An abstract of this valuable paper t'Bull. Bot. Soc. de France,' 

is given in 'Bot. Zeitung,' 1871, torn. x. 1863, p. 194. 
p. 537. See also Hildebiand 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 TT^ of an inch (.0181 mm.), whilst those of the 
perfect flowers are about tt^ of an inch (.0354 mm.) 
in diameter. 

M. Duval-Jouve states that the panicles very rarely 
protrude from their sheaths, but that when this does 
happen the flowers expand and exhibit well-developed 
ovaries and stigmas, together with full-sized anthers 
containing apparently sound pollen; nevertheless such 
flowers are invariably quite sterile. Schreiber had pre- 
viously observed that if a panicle is only half protruded, 
this half is sterile, whilst the still included half is 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, thdugh 
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. Ascheison, ' Bot. Zeitung,' 
United States,' 1856, p. 540. 1864, p. 350. 



334 CONCLUDING REMAKES 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 sole 
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. 



*I have collected several snch meatication,' ch. xviii. — 2nd edit, 
cases in my ' Variation nnder Do- vol. ii. p. 153. 



Chap. VIII. ON CLEISTOGAMIC FLOWERS, 336 

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. Moreoyer 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 Malpighiaceae, 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 EBMAEKS Chap. VIH. 

enclosed within the anthers; but this is not so re- 
markable a fact as was formerly thought, when the 
case of Asclepias was alone known.* It is, however, 
a wonderful sight to behold the tubes directing them- 
selves in a straight line to the stigma, when this 
is at some little distance from the anthers. As soon 
as they reach the stigma or the open passage leading 
into the ovarium, no doubt they penetrate it, guided 
by the same means, whatever these may be, as in the 
case of ordinary flowers. I thought that they might 
be guided by the avoidance of light : some pollen-grains 
of a willow were therefore immersed in an extremely 
weak solution of honey, and the vessel was placed 
so that the light entered only in one 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 B. Brown. Baillon as- pollen-masses while still within 

serts-CAdansonia,' torn. ii. 1863, 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' Xeottia : see 

grains which have not come into ' The Various ContnTances 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 ' SuU' Opera la Distribuzione 

the stigma. I have observed the dei Sessi nelle Piante,' 1867, p. 30. 



Chap. VIII. ON CLBIST06AMIC FLOWERS. 33Y 

vital force is probably a far more efBeient 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 350; with 
Leersia at 310 ; 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 Pffiony.* 
We thus see that cleistogamic flowers produce seeds with 
a wonderfully small expenditure of pollen; and they 
produce as a general rule qirite 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 oi 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. !N'o less than eight of the genera 
in the list at the beginning of this chapt-er include 
species which act in this manner, namely, several 



* The anthoritiea for these stn^ments are given in my ' Effects of 
Cross and Self-Fertilisation,' p. 376. 



338 CONCLUDING REMARKS Chap. VIIL 

kinds of Viola, Oxalis, Vandellia, Linaria, Commelina, 
and at least three genera of Leguminosse. 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, nameh', 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 PLOWEES. 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 eases 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. Aaoherson, 'Bot. Zeit.,' 1871, p. BBS.. 



340 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, &e. 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 CLEISTOQAMIC FLOWERS. 341 

but never expand (as with Thelymitra), and yet set 
fruit, might easily be rendered cleistogamic. Lathyrus 
nissolia seems to be in an incipient transitional state, 
as does Drosera Anglica, the flowers of which are not 
perfectly closed. There is good evidence that flowers 
sometimes fail to expand and are somewhat reduced 
in size, owing to exposure to unfavourable conditions, 
but still retain their fertility unimpaired. Linnaeus 
observed in 1753 that the flowers on several plants 
brought from Spain and grown at Upsala did not 
show any corolla and yet produced seeds. Asa Gray 
has seen flowers on exotic plants in the 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 afEect 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 hyLinn8ena, xxxix. 1865. p. 105. Bennett in 

see Mohl in 'Bot. Zeitung,' 1863, 'Nature,' Nov. 1869, p, 11. The 

p. 327. Asa Gray, 'American Rev. G. Henslow also says (' Gb r- 

Joumalof Science, 'Sndsoriea, vol, dener'a Chronicle,' 1877, p, S71; 



342 CONCLUDING EEMARKS 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 flowers during 
several successive years; and this is the case with Jun- 
cus bufonius in its native land of Kussia. 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- 



nlso 'Nature,' Oct. 19, 1876, p. eis are Relf-fertilised. On Lysima- 

543) "that when the antumn chia, H. Mnller, 'Nature.' Sept. 

draws on, and hahitnally in win- 1873, p. 433. Bonch£,' ' Sitzunps- 

ti>T for such of OUT wild flowers as hericht der Gesell. Naturforsch. 

blossom at that season," the flow- Freunde,' Oct. 1874, p. 00. 



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 will 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-dioe- 
cious sub-class, or those which co-exist as hermaphrodites 
and females, it has been proved that they jaeld 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- 
24 



344 GENERAL CONCLUSIONS. Chap. VIIL 

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 efEeeted 
in order that cross-fertilisation should be assured. For 
the full and legitimate fertilisabion 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. 



ACANTHACEiE. 



A. 



Acanthacese, 313. 

Acer campeatre, 12, 307. 

Adoxa, 9. 

.^ipMla elata, 134. 

monis, 184. 

obdurata, 134, 286. 

Alefeld, Dr., on Linum, 100. 

Aliema nutans, 310. 

Amphicarpsea, 328. 

Amsinckia epectabilis, 110 ; varia- 
bility in length of stamens and 
pistil, 363, 367. 

Anchusa arvensis, 111. 

Androsace vitaMiana, 53. 

Anthers, size of, in different forms, 
353 ; contabescent, 383. 

Arachis, 311. 

Arnebia hispidisshna, 111. 

Ascherson, Dr., on Salvia dewto- 
gama, 313, 339 ; Junaua hufonias, 
333 ; Leersia oryeoidea, 333. 

Asclepias, 336. 

Ash, the common, 11. 

Asperula scoparia, 284. 

Axell on Primula striefa, 50, 



B. 

Babington, Prof., on Primula elttr 
tior, 72 ; Stdlaria graminea, 312. 

Baillon, emission of the tubes from 
pollen-grains, 336. 

Belhomme, M., on ray-florets, 6. 

Bennett, A. W., on Impatiena fulva, 
336 ; flowers fertilised whilst in 
the bud state, 341. 

Bentham, Mr., on the differentia- 
tion of the sexes, 11. 

Bentham, Mr., on the oleistogamic 
flowers of Ononis, 325. 



COEYHIS. 

Bora^ineK, 101. 

Boreau on cowslip and primrose, 

57. 
Borreria, 127. 
Bouohfi on Pavonia, 312 ; effect of 

temperature and light on coroUa, 

341. 
Bowvardia leiantha, 135. 
Braun on Dracocephalum, 298. 
Breitenbach, W., on Primula ela- 

tior, 34, 273. 
Bromfleld, Dr., on primrose and 

cowslip, 57 ; Primvia datior, 73 ; 

Speeularia perfoliata, 329. 
Brown, Bobert, on sexual changes, 

282. 
Buckwheat, the common. 111, 



CcUtha paZttstris, 13. 
Campanula colorata, 329. 
Cardamine amara, 307. 
Caspary, Prof., on Bhamnua cathar- 

ticua, 293. 
Cattleya, 312. 
Chamissoa, 291. 
Cinchona micrarUha, 134. 
Clelstogamic flowers, 309; list of 

genera, 311 ; on their origin, 

342. 
Cnicua acaiiUa, 306. 

paluatria, 306. 

Coccocypadum, 133 ; pollen-grains 

of, 851. 
Coproama, 385. 
Cordia, 117 ; pistil of, 354. 
Corolla, difference in size in the 

sexes of the same species, 307, 

308. 
CorydalU, 146. 
Corylua aveUana, 10. 

345 



346 



INDEX. 



Cowslip, the common, 14 ; short- 
and long-styled, 19-22, 56-71. 

Cratoxylon formosum, 183. 

Crocker, C. W., on Ftantago lanceo- 
lata, 306. 

Cryptostachys, 312. 

Cuphea purpurea, 168. 

D. 

Darwin, Charles, on reproductive 
organs under cultivation, 7 ; in- 
tercrossed plants, 30 ; prepotency 
of pollen, 62 ; insects fertilising, 
flowers, 79 ; Cephalanthera gran- 
diflora, 98 ; Epidendron and Cat- 
tleya, 313 ; number of pollen- 
grains, 337. 

, W., on Pttlmonaria anguati- 

folia, 105, 107. 

Datura arhorea, 252. 

Delpino, plants fertilised by the 
wind, 10 ; on the walnut, 10 ; 
Polygonaeex, 114; pollen-grains, 
251 ; Thymus aerpyllum, 299 ; 
closed or cleistogamio flowers, 
310, 336 ; Viola odarata, 316. 

Dianthua barbatua, 30. 

Dickie, Dr., on Eriophorum angua- 
tifolium, 307. 

Didamnua fraxi/ndla, 146. 

Diodia, 135. 

Dioecious and sub-dioecious plants, 
287. 

Diacoapermum, 286. 

Doubleday, H., on Primula elatior, 
73. 

Dracoeephalum Moldamcum, 298. 

Droaera Anglica, 328, 341. 

rotundifolia, 327. 

Duval-Jouve, M., on Oryptoslachya, 
313 ; Leeraia oryzoidea, 332, 333. 

Dyer, Thiselton, on Salvia Hor- 
minum, 8 ; Cratoxylon farmoaum, 
123. 

E. 

Eehium vulgare. 111, 305, 307. 
Epidendron, 312. 
Epigaea repena, 296. 
Equal-atyled vara, of Primula, 273. 
Eramthemum ambiguwm, 328. 
Eriophorum angustifoliwm, 307. 
Erythroxylum, 121; pollen-grains 
of, 251. 



GYNO-DICECIOUS. 

Euonymua Europseua, 287-292. 
Euphrasia offimialia, 4. 
Euryale, 310. 



Faramea, 129 ; pollen-grains, 129. 
Fitzgerald, Mr. . on Tlielymiira, 312. 
Foraythia auapenaa, 117 ; stamens, 
253. 

viridiasima, 117. 

Fragaria ChUoenaia, 292. 

elatior, 293. 

veaca, 292. 

Virginiaiia, 292. 

Fraxinua excelsior, 11. 



G. 

Galium crucialum, 286. 

Gartner on the sterility of unions 
between distinct species, 29; 
Primula vulgaris t(nd veria, 58, 
59 ; hybrid Verbaacums, 76, 77, 
80 ; prepotency of pollen, 242 ; 
variation in the sexual powers 
of plants, 268 ; contabesceut an- 
thers, 193, 283. 

Gentianese, 115. 

Geraniacese, 168. 

Geranium aylvatieam, 307. 

Geaneria pendulima, 262. 

Gili.a aggregata, 118. 

coronopifolia, 119. 

mierantha, 119. 

nudieamlia, 119. 

pulchella, 118. 

Gillibert on Mmywnthes, 310. 

Gloriosa lily, the, 146. 

Godron on hybrid Primulas, 55. 

Gray, Prof. Asa, proposes the term 
heterogone or heterogonoue, 2 ; on 
lAnum, 101 ; Lencoamia Bu/melii- 
ana and acuminata, 114 j For- 
syfhia suapema, 117 ; Gilia pul- 
chella, 118 ; G. coronopifolia, 119 ; 
Phlox aubulata, 120; Mitehdla 
repena, 125 ; heterostyled plants, 
245 ; Coprosma, 285 ; Euonymua, 
287 ; SiMmnua laiiceolatua, 295, 
290 ; Epigiea repena, 296 ; Hex 
opaca, 298 ; Flantago media, 306 ; 
Oxybaphua and Nyctaginia, 312 ; 
impatiens fulva, 327; icemo, 
333 ; cleistogamic flowers, 341. 

Gyno-dicecious plants, 298. 



INDEX. 



347 



Hart, Mr., on JTcpeto glechoma, 
300. 

Hautbois Strawberry, the, 293. 

Medyotis, 133. 

Henslow, Eev. Prof., on hybrid 
Primvlm, 61. 

Henslow, Eev. 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- 

136. 

trimorphic plants, 137-^187. 

Hibiscus, pollen-grains, 337. 

Hildebrand, Prof., introduces the 
word "heterostyled," 2 ; on the 
ray-florets of the Compositie, 5, 6 ; 
Primula Sinensis, 38, 40-42, 192, 
217 ; Linum grandifiorum, 86, 87 ; 
X, perenne, 92 ; Pulmonaria offi- 
mnalis, 101-103, 107, 239; P. 
asurea, 110 ; Polygonum fagopy- 
rum, 111; Oxalis, 169, 171-174, 
177, 181, 212-213, 321; herma- 
phrodite plants becoming uni- 
sexual, 283 ; Sordeum, 332. 

Homostyled species of Primtda, 49. 

Hooker, Dr., on Campmmla, 329. 

Hordeum, 331. 

Hottonia inflata, 53, 812. 

pcdustris, 50 ; relative fertility, 

52 ; anthers of, 253 ; papillje on 
stigma, 255. 

Houstonia ccerulea, 132, 255. 

Hoya carnosa, 330. 

Hybrid Primulas, 55-71. 

Hydrangea, 6, 7. 

Hyperimnese, 123. 

Hyssopua officinalis, S98. 



I. 

Ilex aquifolium, 297. 

opaca, 298. 

Illegitimate offspring of hetero- 
styled plants, 188 ; l/ythmm sali- 
caria, dwarfed stature and ster- 
ility, 192 ; Oxalis, transmission 
of form to seedlings, 212 ; Pri- 
mula shwrms, 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 j par- 
allelism between illegitimate 
fertilisation and hybridism, 243. 

nieeebrum, 310. 

Impaiiens, i)ollen-giains of, 337. 

baJ-samina, 327. 

fidva, 326. 

nolirme-tangere, 327. 



J. 

Juglans regia, 10. 
Juncas iufonius, 331, 342. 
Jussieu, A. de, on Malpighicese, 
330. 



Kemer, 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 longifiora, 49. 

Krascheninihowia, 312. 

Kuhn, Dr., on cleistogamic flow- 
ers, 3, 309, 310 ; list of plants pro- 
ducing differently formed seeds, 
9 ; heterostyled plants, 244 ; Van- 
dettia nummularifolia, 323 ; V. ses- 
sijlora, 324. 



348 



INDEX. 



LAGEBSTECEMIA. 



L. 

Lagerstrcemia Indica,167. 

7 parrifiora, 167. 

reginse, 167. 

Lathyrus nissolia, 325, 341. 

Lecoq, H., on the common maple, 
12 ; cowslips and primroses, 57 ; 
Primula elatior, 72 ; Linum Ans- 
triacnm. 98 ; Lythrum hyssopifoUa, 
166 ; Ehammis, 296 ; gynodioe- 
cious plants, 398; Scabiosa mc- 
dsa, 304 ; Viola odorata, 318. 

Lecrsia orysoides, 332-334; pollen- 
grains of, 337. 

Leggett, Mr., Pontederia cordata, 
186. 

Legitimate unions, summary on 
the fertility of the two, com- 
pared with that of the two ille- 
gitimate in Primula, 46-49 ; fer- 
tility of, compared with illegiti- 
mate, 247. 

Leighton, Eev. W. A., on the cow- 
slip and primrose, 56 ; Verbasmm 
vvrgatum, 78. 

Leoritodon, pollen-grains, 337. 

Leptasiphon, 119. 

Leucosmia acuminata, 114. 

Bumettiana, 114 ; stigma, 254. 

Lily, the Gloriosa, 146. 

Limnanthemum Indicum, 115; pol- 
len-grains, 251 ; anthers, 253. 

JJ/naria spuria, 324. 

Lindley on Fraqaria eJaiior, 293. 

LinnaBUs on Primula veria, vulgaris, 
and elatior, 56. 

Linum angustifolium, 100. 

Austriacum, 97. 

catharticum, 100. 

eorymbiferum, 100. 

flavum, 81, 98; stamens, 253. 

grandiflorum, 81 ; various ex- 
periments, 87-89, 96; pistils and 
stamens, 254, 255; sterile with 
its own-form pollen, 264, 266, 
267. 

Lewisii, 101. 

perenne, 90; torsion of the 

styles, 95 ; long-styled form, 97 ; 
stigma, 248. 

salsoloides, 100. 

trigynum, 100. 

unitatissimum, 100. 

lApostoTna, 134. 

Lysimachia imlga/ris, 4, 341. 



Lythrum Grsefferi, 164. 

hyssopifoUa, 165. 

salicarm, 116, 137; power of 

mutual fertilisation between the 
three forms, 149-157; summary 
of results, 157-164; Illegitimate 
offspring from the three forms, 
191-203 ; concluding remarks on, 
203-211; mid-styled form, 241, 
258, 259, 280 ; seeds, 249. 

thymifolia, 165. 



M. 

Malpighiacex, 330. 
Manettia bicolor, 135. 
Maple, the common, 12. 
Mai-shall, W., on Primula elatior, 

73 ; Plantago lanoeolata, 306. 
Masters, Dr. Maxwell, on cleisto- 

gamio ilowers, 3. 
Maximowicz on Krascheninilcowia, 

312. 
Meehan, Mr., on Mitcliella, 285; 

Epigiea repens, 297. 
Melissa dinipodium, 298. 

officinalis, 298. 

Mello, Correa de, on Aracliis, 312; 

Voandeeia, 326. 
Mentha aquatica, 398. 

hirsvta, 298. 

vulgaris, 298. 

Menyanthes, 310. 

trifoliata, 115. 

Michalet on Oxalis acetosella, 320 ; 

Linaria spuria, 324. 
Mitchella, 285. 

repens, 125. 

Mohl, H. von, on the common 

cowslip, 14 ; size of corolla in the 

sexes of the same species, 307; 

Trifolimn, and Araehis, 311 ; cleis- 

togamic flower, 313, 341: Oxalis 

acetosella, 320 ; Impatiens noli- 

me-tangere, 327 ; Specularia per- 

foliata, 329. 
Mollia lepidota, 168. 

speeiosa, 168. 

Monnier, M., on Viola, 317. 
Monochoria vaginalis, 329. 
Mulberry, the, 10. 
MuUer, D., on Viola eanina, 313. 
Miiller, Fritz, on pollen of the ViU 

larsia, 116; Faramsa, 129-131; 

Posoqueria franrans, 131; Nessea, 

166; Oxalia, 179,180; Pontederia, 



INDEX. 



349 



MiJLLEK. 


PEIMULA. 


182-184; Oxalh BcgnelU, 212; 


Oxalis spedosa, 168, 175, 212. 


Chamisaoa, 291. 


stricUi. 181. 


MuUer, H., on the frequency of 


tropssoloides, 181. 


visits byinsects to the Vmhelliferee 


Vaidiviana, 170-172, 212. 


and Compositee, 5 ; on dichogamy, 


Oxlip, the Bardfield, 32, 72. 


10 ; on Anthophora and BomlyyliuB 


, the common, 55 ; differences 


sucking the cowslip, 22 ; PrittmLa 


in structure and function be- 


datior, 32 ; P. vUlosa, 49 ; Sottonia 


tween the two parent species, 56 ; 


palnstris, 51 ; table of relative fer- 


effects of crossing, 60 ; a hybrid 


tility of, 52 ; Linim catharticmn, 


between the cowslip and prim- 


100; Poiygomtm fagopyrum, 112; 


rose, 70. 


LyOiram, salicaria, 145 ; on the 


Oxybaphus, 312. 


origin of heteroslylism, 264 ; on 




the Labiate, 298, 303; Thymus 




aerpyllum, 300 ; ScaUoaa arvensis, 


P. 


304; Plantago lanceolata, 306 ; size 




of corolla in the two sexes of the 


Pseony, pollen-grains of, 337. 


same species, 308 ; Impatiens baU 


Parallelism between illegitimate 


aamhia, 327 ; Lysimachia, 343. 


and hybrid fertilisation, 240. 


Myosotis, 307. 


Pavonia, 312. 




Phlox Hentfiii, 120. 




niralis, 120. 


N. 


subrJata, 120, 287. 




Planchon on Linum salsoloides, 100 ; 


Nepeta gleehoma, 300. 


L. Lewisii, 101 ; on Bugouia, 100. 


Nertera, 285. 


Plantago lanceolata, 306. 


Nesxa vertieillata, 166. 


media, 306. 


Nolana prostrata, variability in 


Polemoniaceai, 118. 


length of stamens and pistil, 262. 


Pollen-grains, relative diameter of, 


Nyctaginia, 312. 


250. 




Polyanthus, 18. 




Polygonacese, 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 columnse, 324. 


Primrose, the common, 34, 57-71. 


minnUssima, 325, 340. 


Primula, the, heterostyled species 


parvifiora, 325. 


of, 14 ; summary on, 45-49 ; 


Origanum mZgare, 298. 


homostyled species, 49. 


Oxalis acetosella, 181 ; pistil of, 262 ; 


awiada, 30, 43, 48, 74, 223. 


cleistogamio flowers, 320 ; pollen- 


equal-styled varieties, 273. 


grains, 337. 


eortusoid£S, 4A. 


Bowii, 179. 


elata, 49. 


compressa, 178. 


elatior, Jacq., 32 ; relative fer- 


corniculafa, 181. 


tility of the two forms, 32, 47 ; 


Deppei, 179. 

hedysaroides, 213. 


not a hybrid, 72, 73 ; equal- 


styled var. of, 224, 273. 


homostyled species, 181. 


farinosa, 45 ; equal-styled 


incamata, 321. 


var., 224, 273. 


Regnelli, 173, 174, 212. 


hirsuta, 74. 


rosea, 177, 213. 


involucrata, 45. 


(Biophytnm) semitiva, 180, 321 ; 


longiflora, 49. 


stigma, 254. 


mollis, 49, 50. 



350 



INDEX. 



Frimula Scotica, 49, 50. 

Sitirica, 49. 

Sikkimensis, 44, 47. 

Sinensia, 22, 29, 38 ; relative 

fertility, 39-43, 47, 48; long- 
styled, 213 ; short-styled, 215 ; 
tiunsmission of form, constitu- 
tion and fertility, 216 ; equal- 
styled variety, 218-823, 273, 274. 

stricta, 50. 

veris, 14 ; difference in sti'uc- 

ture between the two forms, 15 ; 
degrees of fertility when legiti- 
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, 
262, 266. 

vertidUata, 49, 50. 

villosa, 49. 

vulgaris ( var. acatdis Linn. ), 

34 ; pollen-grains, 35 ; relative 
fertility of the two forms, 36; 
length of pistil, 267. 

Frimula vulgaris, var. rubra, 225- 
228. 

Prunella vulgaris, 298. 

Psychotria, 135. 

Pulmonaria angustifolia, 104, 240 ; 
anthers, 253, 287. 

asurea, 110. 

officinalis, 101, 239 ; number 

of flowers, 249 ; pistil, 851. 



E. 

Bammcttlus aquatilis, 310. 

Eay-florets, their use, 5, 6. 

Shamnus catharticus, 893, 307; size 
of corolla, 308. 

frangvla, 296. 

lanceolatus, 295. 

Mhinanthus crista-galli, 4. 

Subiacese, 125, 131-136 ; size of an- 
thers, 253 ; stigmas, 254 ; number 
of heterostyled genera, 284-886. 

Pudgea eriantha, 135. 

Eue, the common, 9. 

Pudlia tuberosa, 388. 



Salvia, 307. 

deistogama, 339. 



TEEVIBANUS. 

Salvia Horminum, 8. 

Satureia hortensis, 302, 304. 

Scabiosa arvensis, 304. 

atro-vurpurea, 305, 307. 

sucasa, 305. 

Scott, J., on Primula auricula, 80, 
43, 223; P. vulgaris, 34; (var. 
ruhra), 225 ; P. Sikkimensis, 4A ; 
P. farinosa, 45, 224 ; homostyled 
Primvlse, 49, 50 : hybrids, 74, 75 ; 
length of pistil, 272; Hottmia 
palustris, 51 ; Androsaee vital- 
liana, 53 ; Polyanthus, 58 ; Mit- 
chella repens, 127 ; Acanthaeeie, 
312 ; EranOwmum amhiguum bear- 
ing three kinds of flowers, 328. 

Scrophularia aquatiea, 147. 

Serratvila tindoria, 280, 306. 

Sethia acuminata, 123. 

Sethia obttisifolia, 133. 

Smith, Sir J. £., on the carrot, 8 ; 
hybrid Verbascums, 76, 78; Ser- 
ratvla tinetoria, 280 ; (}nicii,s, 306 ; 
Sabularia, 310. 

Soldanella (dpina, 54. 

^eciUaria perfoliata, 329. 

Spence, Mr., on Mollia, 168. 

^ermacoce, 135. 

Sprengel on Hottonia palustris, 
50. 

Stellaria graminea, 312. 

Strawberry, the Eautbois, 893. 

Subularia, 310. 

Suteria, 131, 



T. 

Thdymitra, 312. 

Thomson, Dr., on Campanula, 389. 
Thrum-eyed, origin of term, 14. 
Thwaites, Mr., on ovules of Lim- 

nanthemum Indicum, 115; Sethia 

acuminata, 183; Disco^ermum, 

886. 
Thymelia, 114. 
Thymus citriodorus, 301. 

serpyllum, 299, 301, 304. 

vulgaris, 302. 

Timbal-Lagrave, M., on hybrids 

in genus Oistas, 76. 
Torrey, Dr., on Hothmia infiala, 

53, 312. 
Transmission of the two forms of 

heterostyled plants, 269-270. 
Treviranus on Androsaee vUolliana, 

53 ; Linum, 81. 



INDEX. 



351 



VANDELLIA. 




WEAY. 
FJoia lancifoUa, 319. 


. V. 




mirabilis, 319. 

nana, 318, 319 ; pollen-grains 


Vandellia numnmlarifolia, 3S3. 




of, 337. 


aessifiora, 324. 




odorata, 316, 335. 


Vaucher on the carrot, 8 ; Solda- 


paluatris, 319. 


ndla^ alpina, 54 ; Lythrwn. 


soJi- 


Eoxburghiana, 318. 


caria, 138, 144; L. thymifolia, 


Suppii, 319. 


165 ; Ilex aquifolivm, 297 


on 


sylvatica, 319. 


LaMatse, 298; Viola hwta 


and 


tricoJor, 319. 


collina, 316. 




Voandseia, 326. 


Verbasmm, wild hybrids of, 

80. 
lychnitw, 30, 76-78. 


75- 






W. 


ph(eniceum, 78. 






thapsus, 76-79. 




Walnut, the, 10. 


virgatum, 78. 




Watson, H. C, on cowslips, prim- 


Viburnum, 6, 7. 




roses, and oxlips, 57, 60, 63; 


Vida, 326. 




Primula elatior, 72, 73. 


VUlarsia, 116 ; anthers, 252. 




Weddell, Dr., on hybrids between 


FioJa aJ6o, 314, 319. 




Aceras and Ordtis, 76. 


bieolor, 319. 




Wetterhan, Mr., on Corylus, 10. 


biflora, 319. 




Wichura, Max, on hybrid willows, 


canina, 313, 320. 




76 ; sterile hybrids, 241. 


coUina, 316. 




Wirtgen on Lythrum salicaria, 138, 


elatior, 319. 




144, 148. 


ftirta, 317, 319. 




Wooler, W., on Polyanthus, 18. 


ionodram, 319. 




Wray, Leonard, on Fragaria, 293. 



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biography." — London Standard. 

" His letters are a self-reveladon of the man, his work, his 
ambitions, his trials, his views of religion, his philosophy, his 
public activity and domestic happiness. . . . Whoso reads these 
volumes will feel that he knows better a man worth knowing, 
and the number who will read them will be great." — London 
Telegraph. 

" Huxley's career makes a wonderfiJ story." — London 
Mail. 

" Mr. Leonard Huxley has given the world many extremely 
valuable and interesting letters, all characteristic, and he has con- 
nected them by a well-written consecutive narrative which i« 
sufficient to weave them together." — London News. 

D. APPLETON AND COMPANY, NEW YORK. 



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