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Full text of "The effects of cross and self fertilisation in the vegetable kingdom"

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Presented by 
Dr. Pearl Oliphant 



COLLEGE OF OSTEOPATHIC PHYSICIANS 
AND SURGEONS LOS ANGELES, CALIFORNIA 







r-w 




THE EFFECTS 



CROSS AND SELF FERTILISATION 



VEGETABLE KINGDOM. 



BY CHARLES DARWIN, LL.D., F.R.S. 



SECOND EDITION. 
FIFTH IMPKKSSION. 



LONDON: 
JOHN MURRAY, ALBEMABLE STREET. 

1900. 



UNIFORM EDITIONS. 

WORKS BY CHARLES DARWIN, F.R.S. 
?/C" 

' LIFE AND LETTERS OF CHARLES DARWIN. With 
an Autobiographical Chapter. Edited by FBAKCIS DABWIN. Portraits. 
3 vols. 36s. 
NATURALIST'S JOURNAL OF RESEARCHES INTO THE 

NATURAL HISTORY AND GEOLOGY OK COUNTRIES VISITED during a VOYAGE 
ROUND THE WORLD. With 1 00 Illustrations by PBITCHETT. 21. Popular 
Edition. Woodcuts. 3s. 6d. 

ORIGIN OF SPECIES BY MEANS OF NATURAL SELEC- 
TION ; or, THE PRESERVATION OF FAVOURED RACES IN THE STRUGGLE FOB 
LIFE. Large Type Edition, 2 vols. 12s. Popular Edition, 6*. 

VARIOUS CONTRIVANCES BY WHICH ORCHIDS ARE 
FERTILIZED BY INSKCTS. Woodcuts. 7s. 6d. 

VARIATION OF ANIMALS AND PLANTS UNDER DO- 
MESTICATION. Illustrations. 15s. 

DESCENT OF MAN, AND SELECTION IN RELATION TO 

SEX. Illustrations. Large Type Edition, 2 vols. 15*. Popular Edition, 
7*. 6d. 

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ANIMALS. Illustrations. 12s. 

INSECTIVOROUS PLANTS. Illustrations. 9. 
MOVEMENTS AND HABITS OF CLIMBING PLANTS, 

Woodcuts. 6s. 

EFFECTS OF CROSS AND SELF-FERTILIZATION IN 

THE VEGETABLE KINGDOM. Illustrations. 9s. 

DIFFERENT FORMS OF FLOWERS ON PLANTS OF 
THE SAME SPECIES. Illustrations. 7s. 6d. 

LIFE OF ERASMUS DARWIN. Portrait. It. 6d. 
POWER OF MOVEMENT IN PLANIS. 

FORMATION OF VEGETABLE MOULD THROUGH THE 
ACTION OF WORMS. Woodcuts. 6s. 

FACTS AND ARGUMENTS FOR DARWIN. By FRITZ 

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The above works are Pub'ished by JOHN MURRAY. 

STRUCTURE AND DISTRIBUTION OF CORAL REEFS. 

SMITH, ELDER, & Co. 

GEOLOGICAL OBSERVATIONS ON VOLCANIC ISLANDS 
AND PARTS OF SOUTH AMERICA. SMITH ELDEB & Co. 

MONOGRAPH OF THE CIllRIPEDIA. Illustrations. 2 vols. 
vo. RAY SOCIETY 

MONOGRAPH OF THE FOSSIL LEPADIDM, OR PEDUN- 
CULATED CIRRIPEDS OF GREAT BRITAIN. 

PALJEONT GRAPHICAL SOCIETY 

MONOGRAPH OF THE FOSSIL BALANIDJ2 AND VER- 
OF GREAT BRITAIN. PAL^OKTOGKAPHICAL SOCIETY. 

LONDON : PRINTED BY WILLIAM CLOWES AND SOXS, LIMITED, 
8TAMFOBD STREET ASD CHABING CBOSS. 



CONTENTS. 

CHAPTER I. 

INTRODUCTOKY KKMARKS. 

Various means which favour or determine the cross-fertilisation a 
plants Benefits derived from cross-fertilisation Self- fertilisa- 
tion favourable to the propagation of the species Brief history 
of the subject Object of tlie experiments, and the manner in 
which they were tried Statistical value of the measurements 
The experiments carried on during several successive genera- 
tions Nature of the relationship of the plants in the later 
generations Uniformity of the conditions to which the plants 
were subjected Some apparent and some real causes of error 
Amount of pollen employed Arrangement of the work 
Importance of the conclusions Page 1-27 

CHAPTER II. 

CONVOLVULACE.. 

Ipomoea purpurea, comparison of the height and fertility of the 
crossed and self- fertilised plants during ten successive genera- 
tions Greater constitutional vigour of the crossed plants 
The effects on the offspring of crossing different flowers on the 
same plant, instead of crossing distinct individuals The 
effects of a cross with a fresh stock The descendants of the 
self-fertilised plant named Hero Summary on the growth, 
vigour, and fertility of the successive crossed and self-fertilised 
generations Small amount of pollen in the anthers of the self- 



CONTENTS. 



fertilised plat is of the later generations, and the sterility of 
their first-pr )duced flowers Uniform colour of the flowers 
produced by the self-fertilised plants The advantage from a 
cross between two distinct plants depends on their differing in 
constitution Page 28-62 



CHAPTER III. 

SCBOPHUIARIACE^E, GESNEEIACE^, LABIAT2E, ETC. 

Mimulus luteus ; height, vigour, and fertility of the crossed and 
self-fertilised plants of the first four generations Appearance 
of a new, tall, and highly self-fertile variety Offspring from a 
cross between self-fertilised plants Effects of a cross with a 
fresh stock Effects of crossing flowers on the same plant 
Summary on Mimulus luteus Digitalis purpurea, superiority 
of the crossed plants Effects of crossing flowers on the same 
plant Calceolaria Linaria vulgaris Verbascum thapsus 
Vandellia nummularifolia Cleistogamic flowers Gesneria pen- 
dulina Salvia coccinea Origanum vulgare, great increase of 
the crossed plants by stolons Thunbergia alata .. 63-97 



CHAPTER IV. 

CBUCIFER^E, PAPAVERACEJE, RESEDACE.E, ETC. 

Brassica oleracea, crossed and self-fertilised plants Great effect of 
a cross with a fresh stock on the weight of the offspring Iberis 
umbellata Papaver vagum Eschscholtzia californica, seed- 
lings from a cross with a fresh stock not more vigorous, but 
more fertile than the self-fertilised seedlings Keseda lutea and 
odorata, many individuals sterile with their own pollen Viola 
tricolor, wonderful effects of a cross Adonis sestivalis 
Delphinium consolida Viscaria oculata, crossed plants hardly 
taller, but more fertile than the self-fertilised Dianthus 
caryophyllus, crossed and self-fertilised plants compared for four 
generations Great effects of a cross with a fresh stock 
Uniform colour of the flowers on the self-fertilised plants 
Hibiscus africamiB .. . 98-141 



CONTENTS. r 

CHAPTER V. 

GERANIACE.E, LEGUMINOS^E, ONAGRACE.S;, ETC. 

Pelargonium zonale, a cross between plants propagated by cuttings 
does no good Tiopseolura minus Lknnanthes douglasii 
Lupinus luteus and pilosus Phaseolus ruultiflorus and vul- 
garis. Lithyrus odoratus, varieties of, never naturally inter- 
cross' in England Pisum sativum, varieties of, rarely inter- 
cross, but a cross between them highly beneficial Sarothamnua 
scoparius, wonderful effects of a cross Ononis minutissima, 
cleistogamic flowers of Summary on the Leguminosae Clarkia 
elegans Bartonia aurea Passiflora gracilis Apium petrose- 
linum Scabiosa atropurpurea Lactuca sativa Specularia 
speculum Lobelia ramosa, advantages of a cross during two 
generations Lobelia fulgens Nemophila insignis, great ad- 
vantages of a cross Borago officinalis Nolana prostrata. 

Page 142-187 

CHAPTER VI. 

SOLANACE^, PBIMULACE^E, POLYGONE.E, ETC. 

Petunia violacea, crossed and self-fertilised plants compared for four 
generations Effects of a cross with a fresh stock Uniform 
colour of the flowers on the self-fertilised plants of the fourth 
generation Nicotiana tabacum, crossed and self-fertilised 
plants of equal height Great effects of a cross with a distinct 
sub-variety on the height, but not on the fertility, of the off- 
spring Cyclamen persicmn, crossed seedlings greatly superior 
to the self-fertilised Anagallis collina Primula veris 
Equal-styled variety of Primula veris, fertility of, greatly 
increased by a cross with a fresh stock Fagopynim esculentum 
Beta vulgaris Canna warscewiczi, crossed and self-fertilised 
plants of equal height Zea mays Phalaris canariensis. 

188-237 



CONTENTS. 



CHAPTEE VII. 

SUMMARY OF THE HEIGHTS AND WEIGHTS OF THE CROSSED 
AND SELF-FERTILISED PLANTS. 

Number of species and plants measured Tables given Pre- 
liminary remarks on the offspring of plants crossed by a fresh 
stock Thirteen cases specially considered The effects of 
crossing a self- fertilised plant eithe/ bj another self-fertilised 
plant or by an intercrossed plant of the old stock Summary 
of the results Preliminary remarks on the crossed and self- 
fertilised plants of the same stock The twenty-six exceptional 
cases considered, in which the crossed plants did not exceed 
greatly in height the self-fertilised Most of these cases shown 
not to be real exceptions to the rule that cross-fertilisation is 
beneficial Summary of results Relative weights of the 
crossed and self-fertilised plants Page 238-284 



CHAPTER VIII. 

DIFFERENCE BETWEEN CROSSED AND SELF-FERTILISED PLANTS IN 
CONSTITUTIONAL VIGOUR AND IN OTHER RESPECTS. 

Greater constitutional vigour of crossed plants The effects of great 
crowding Competition with other kinds of plants Self-fer- 
tilised plants more liable to premature death Crossed plants 
generally flower before the self-fertilised Negative effects of 
intercrossing flowers on the same plant Cases described 
Transmission of the good effects of a cross to later generations 
Effects of crossing plants of closely related parentage 
Uniform colour of the flowers on plants self-fertilised during 
several generations and cultivated under similar conditions. 

285-311 

CHAPTER IX. 

THE EFFECTS OF CROSS-FERTILISATION AND SELF-FERTILISATION 
ON THE PRODUCTION OF SEEDS. 

Fertility of plants of crossed and self-fertilised parentage, both lots- 
being fertilised in the same manner Fertility of the parent- 
plants when first crossed and self-fertilised, and of their crossed 



CONTENTS. Vil 

and self-fertilised offspring when again crossed and self-fertilised 

Comparison of the fertility of flowers fertilised with their 
own pollen and with that from other flowers on the same plant 

Self-sterile plants Causes of self-sterility The appearance 
of highly self-fertile varieties Self-fertilisation apparently in 
some respects beneficial, independently of the assured produc- 
tion of seeds Rektive weights and rates of germination of 
seeds from crossed and self-fertilised flowers .. Page 312-355 



CHAPTER X. 

MEANS OF FERTILISATION. 

Sterility and fertility of plants when insects are excluded The 
moans by which flowers are cross-fertilised Structures favour- 
able to self-fertilisation Relation between the structure and 
conspicnousuess of flowers, the visits of insects, and the advan- 
tages of cross-fertilisation The means by which flowers are 
fertilised with pollen from a distinct plant Greater fertilising 
power of such pollen Auemophilous species Conversion of 
anemophilous species into entomophilous Origin of nectar 
Anemophilous plants generally have their sexes separated 
Conversion of diclinous into hermaphrodite flowers Trees 
often have their sexes separated 356-417 



CHAPTER XI. 

THE HABITS OF INSECTS IN RELATION TO THE FERTILISATION 
OF FLOWERS. 

[usects visit the flowers of the same species as long as they can 
Cause of this habit Means by which bees recognise the 
flowers of the same species Sudden secretion of nectar 
Nectar of certain flowers unattractive to certain insects In- 
dustry of bees, and the number of flowers visited within a short 
time Perforation of the corolla by bees Skill shown in the 
operation Hive-bees profit by the holes made by humble-bees 
Effects of habit The motive for perforating flowers to save 
time Flowers growing in crowded masses chiefly perforated. 

418-438 



Till CONTENTS. 

CHAPTER XII. 

GENERAL RESULTS. 

Cross-fertilisation proved to be beneficial, and self-fertilisation in 
jurious Allied species differ greatly in the means by which 
cross-fertilisation is favoured and self-fertilisation avoided 
The benefits and evils of the two processes depend on the degree 
of differentiation in the sexual elements The evil effects not 
due to the combination of morbid tendencies in the parents 
Nature of the conditions to which plants are subjected when 
growing near together in a state of nature or under culture, and 
the effects of such conditions Theoretical considerations with 
respect to the interaction of differentiated sexual elements 
Practical lessons Genesis of the two sexes Close correspon- 
dence between the effects of cross-fertilisation and self-fertilisa- 
tion, and of the legitimate and illegitimate unions of hetero- 
styled plants, in comparison with hybrid unions Page 439-474 



Page 475-487 



THE 

EFFECTS 

^ OF 

CEOSS AND SELF-FEETILISATION. 



CHAPTEE I. 

INTRODUCTORY REMARKS. 

Various means which favour or determine the cross -fertilisation of 
plants Benefits derived from cross-fertilisation Self-fertilisation 
favourable to the propagation of the species Brief history of the 
subject Object of the experiments, and the manner in which they 
were tried Statistical value of the measurements The experi- 
ments carried on during several successive generations Nature 
of the relationship of the plants in the later generations Unifor- 
mity of the conditions to which the plants were subjected Some 
apparent and some real causes of error Amount of pollen em 
ployed Arrangement of the work Importance of the conclusions. 

THERE is weighty and abundant evidence that the 
flowers of most kinds of plants are constructed so as 
to be occasionally or habitually cross-fertilised by 
pollen from another flower, produced either by the 
same plant, or generally, as we shall hereafter see 
reason to believe, by a distinct plant. Cross-fertilisa- 
tion is sometimes ensured by the sexes being separated, 
and in a large number of cases by the pollen and 
stigma of the same flower being matured at different 
times. Such plants are called dichogamous, and have 
been divided into two sub-classes : proterandrous species. 



Si INTRODUCTORY REMARKS. CHAP.!. 

in which the pollen is mature before the stigma, and 
proterogynous species, in which the reverse occurs; 
this latter form of dichogamy not being nearly so 
common as the other. Cross-fertilisation is also en- 
sured, in many cases, by mechanical contrivances of 
wonderful beauty, preventing the impregnation of the 
flowers by their own pollen. There is a small class of 
plants, which I have called dimorphic and trimorphic, 
but to which Hildebrand has given the more appro- 
priate name of heterostyled ; this class consists of 
plants presenting two or three distinct forms, adapted 
for reciprocal fertilisation, so that, like plants with 
separate sexes, they can hardly fail to be intercrossed 
in each generation. The male and female organs of 
some flowers are irritable, and the insects which touch 
them get dusted with pollen, which is thus transported 
to other flowers. Again, there is a class, in which the 
ovules absolutely refuse to be fertilised by pollen from 
the same plant, but can be fertilised by pollen from 
any other individual of the same species. There are 
also very many species which are partially sterile with 
their own pollen. Lastly, there is a large class in 
which the flowers present no apparent obstacle of any 
kind to self-fertilisation, nevertheless these plants are 
frequently intercrossed, owing to the prepotency of 
pollen from another individual or variety over the 
plant's own pollen. 

As plants are adapted by such diversified and effec- 
tive means for cross-fertilisation, it might have been 
inferred from this fact alone that they derived some 
great advantage from the process ; and it is the object 
of the present work to show the nature and importance 
of the benefits thus derived. There are, however, some 
exceptions to the rule of plants being constructed so 
as to allow of or to favour cross-fertilisation, for some 



CHAP. I. INTRODUCTORY REMARKS 3 

few plants seeni to be invariably self-fertilised ; yet 
even these retain traces of having been formerly 
adapted for cross-fertilisation. These exceptions need 
not make us doubt the truth of the above rule, any 
more than the existence of some few plants which pro- 
duce flowers, and yet never set seed, should make us 
doubt that flowers are adapted for the production of 
seed and the propagation of the species. 

We should always keep in mind the obvious fact 
that the production of seed is the chief end of the 
act of fertilisation ; and that this end can be gained 
by hermaphrodite plants with incomparably greater 
certainty by self-fertilisation, than by the union of 
the sexual elements belonging to two distinct flowers 
or plants. Yet it is as unmistakably plain that innu- 
merable flowers are adapted for cross-fertilisation, as 
that the teeth and talons of a carnivorous animal are 
adapted for catching prey ; or that the plumes, wings, 
and hooks of a seed are adapted for its dissemination. 
Flowers, therefore, are constructed so as to gain two 
objects which are, to a certain extent, antagonistic, and 
this explains many apparent anomalies in their struc- 
ture. The close proximity of the anthers to the stigma 
in a multitude of species favours, and often leads, to 
self-fertilisation ; but this end could have been gained 
far more safely if the flowers had been completely 
closed, for then the pollen would not have been injured 
by the rain or devoured by insects, as often happens. 
Moreover, in this case, a very small quantity of pollen 
would have been sufficient for fertilisation, instead of 
millions of grains being produced. But the openness 
of the flower and the production of a great and ap- 
parently wasteful amount of pollen are necessary for 
cross -fertilisation. These remarks are well illustrated 
by the plants called cleistogamic, which bear on the 

B 2 



4 INTRODUCTORY REMARKS. CHAP. I. 

same stock two kinds of flowers. The flowers of the one 
kind are minute and completely closed, so that they 
cannot possibly be crossed ; but they are abundantly 
fertile, although producing an extremely small 
quantity of pollen. The flowers of the other kind 
produce much pollen and are open ; and these can be, 
and often are, cross-fertilised. Hermann Miiller has 
also made the remarkable discovery that there are 
some plants which exist under two forms; that is, 
produce on distinct stocks two kinds of hermaphrodite 
flowers. The one form bears small flowers constructed 
for self-fertilisation ; whilst the other bears larger and 
much more conspicuous flowers plainly constructed 
for cross-fertilisation by the aid of insects ; and without 
their aid these produce no seed. 

The adaptation of flowers for cross-fertilisation is a 
subject which has interested me for the last thirty- 
seven years, and I have collected a large mass of ob- 
servations, but these are now rendered superfluous by 
the many excellent works which have been lately pub- 
lished. In the year 1857 I wrote * a short paper on 
the fertilisation of the kidney bean ; and in 1862 my 
work ' On the Contrivances by which British and 
Foreign Orchids are Fertilised by Insects ' appeared. 
It seemed to me a better plan to work out one group 
of plants as carefully as I could, rather than to pub- 
lish many miscellaneous and imperfect observations. 
My present work is the complement of that on 
Orchids, in which it was shown how admirably these 
plants are constructed so as to permit of, or to favour, 
or to necessitate cross-fertilisation. The adaptations 



* 'Gardeners' Chronicle,' 1857, 'Annals and Mag. of Nat. Hist. 
p. 725, and 1858, p. 828. Also 3rd series, vol. ii. 18o8, p. 462. 



CHAP. I. INTRODUCTORY REMARKS. 5 

for cross-fertilisation are perhaps more obvious in the 
Orchideae than in any other group of plants, but it is 
an error to speak of them, as some authors have done, 
as an exceptional case. The lever-like action of the 
stamens of Salvia (described by Hildebrand, Dr. W. 
Ogle, and others), by which the anthers are depressed 
and rubbed on the backs of bees, shows as perfect a 
structure as can be found in any orchid. Papilion- 
aceous flowers, as described by various authors for 
instance, by Mr. T. H. Farrer offer innumerable 
curious adaptations for cross-fertilisation. The case of 
Posoqueria fragrans (one of the Rubiaceae), is as won- 
derful as that of the most wonderful orchid. The 
stamens, according to Fritz Miiller,* are irritable, so 
that as soon as a moth visits a flower, the anthers ex- 
plode and cover the insect with pollen ; one of the 
filaments which is broader than the others then moves 
and closes the flower for about twelve hours, after 
which time it resumes its original position. Thus the 
stigma cannot be fertilised by pollen from the same 
flower, but only by that brought by a moth from some 
other flower. Endless other beautiful contrivances for 
this same purpose could be specified. 

Long before I had attended to the fertilisation of 
flowers, a remarkable book appeared in 1793 in Ger- 
many, 'Das Entdeckte Geheimniss der Natur,' by 
C. K. Sprengel, in which he clearly proved by innumer- 
able observations, ho.w essential a part insects play in 
the fertilisation of many plants. But he was in ad- 
vance of his age, and his discoveries were for a long 
time neglected. Since the appearance of my book on 
Orchids, many excellent works on the fertilisation of 
flowers, such as those by Hildebrand, Delpino, Axell, 



'* 'Botanische Zeitung,' I860, p. 129. 



6 INTRODUCTORY REMARKS. CHAP. I 

and Hermann Miiller,* and numerous shorter papers, 
Have been published. A list would occupy several 
pages, and this is not the proper place to give their 
titles, as we are not here concerned with the means, 
but with the results of cross-fertilisation. No one 
who feels interest in the mechanism by which nature 
effects her ends, can read these books and memoirs 
without the most lively interest. 

From my own observations on plants, guided to a 
certain extent by the experience of the breeders of 
animals, I became convinced many years ago that it 
is a general law of nature that flowers are adapted to 
be crossed, at least occasionally, by pollen from a 
distinct plant. Sprengel at times foresaw this law, but 
only partially, for it does not appear that he was aware 
that there was any difference in power between pollen 
from the same plant and from a distinct plant. In the 
introduction to his book (p. 4) he says, as the sexes 
are separated in so many flowers, and as so many other 
flowers are dichogamous, " it appears that nature has 
not willed that any one flower should be fertilised by 
its own pollen." Nevertheless, he was far from keeping 
this conclusion always before his mind, or he did not 



* Sir John Lubbock has given known, visit the flowers of each 

an interesting summary of the species. He likewise enters on 

whole subject in his ' British Wild new ground, by showing not only 

Flowers considered in relation to that flowers are adapted for their 

Insects,' 1875. Hermann Miiller's own good to the visits of certain 

work ' Die Befruchtung der Blu- insects ; but that the insects 

men durch Insekten,' 1873, con- themselves are excellently adapted 

tains an immense number of for procuring nectar or pollen 

original observations and gene- from certain flowers. The value 

ralieations. It is, moreover, in- of H. Miiller's work can hardly be 

valuable as a repertory with re- over-estimated, and it is much to 

ferences to almost everything be desired that it should be trans- 

which has been published on the kted into English. Severin 

subject. His work differs from Axell's work is written in Swedish, 

that of all others in specifying so that I have not been able to 

what kinds of insects, as far as read it. 



CHAP. I. INTRODUCTORY REMARKS. 7 

see its full importance, as may be perceived by any- 
one who will read his observations carefully ; and he 
consequently mistook the meaning of various struc- 
tures. But his discoveries are so numerous and his 
work so excellent, that he can well afford to bear a 
small amount of blame. A most capable judge, H. 
Miiller, likewise says :* "It is remarkable in how very 
many, cases Sprengel rightly perceived that pollen is 
necessarily transported to the stigmas of other flowers 
of the same species by the insects which visit them, 
and yet did not imagine that this transportation was 
of any service to the plants themselves." 

Andrew Knight saw the truth much more clearly, 
for he remarks,! " Nature intended that a sexual in- 
tercourse should take place between neighbouring 
plants of the same species." After alluding to the 
various means by which pollen is transported from 
flower to flower, as far as was then imperfectly known, 
he adds, " Nature has something more in view than that 
its own proper males should fecundate each blossom." 
In 1811 Kolreuter plainly hinted at the same law, as 
did afterwards another famous hybridiser of plants, 
Herbert.* But none of these distinguished observers 
appear to have been sufficiently impressed with the 



* Die Befruchtung der Blu- J Kolreuter, Mem. de 1'Acad. 

men,' 1873, p. 4. His words are : de St. Pe'tersbourg,' torn. iii. 1809 

" Es 1st merkwiirdig, in \vie zahl- (published 1811), p. 197. After 

reichen Fallen Sprengel richtig showing how well the Malvaceae 

erkannte, dass durch die Besuch- are adapted for cross-fertilisation, 

enden Insekten der Bliithenataub he asks, " An id aliquid in recessu 

mit Nothwendigkeit auf die Nar- habeat, quod hujusoemodi flores 

ben nnderer Bliithen derselben nunquam proprio suo pulvere, sed 

Art iibertragen wird, ohne auf die semper eo aliarum suse specie! 

Vermuthung zu kpmmen, dass in impregnentur, merito quajritur ? 

dieser Wirkung der Nutzen des Certe natura nil facit frustra.** 

Insektenbesuches fur die Pflanzen Herbert, ' Amaryllidacew, with a 

eelbst gesucht werden miisse." Treatise on Cross-bred Vege 

t ' Philosophical Transactions,' tables,' 1837. 
1799, p. 202. 



8 INTRODUCTORY REMARKS. CHAP. L 

truth and generality of the law, so as to insist on it 
and impress their belief on others. 

In 1862 I summed up my observations on Orchids 
by saying that nature " abhors perpetual self-fertilisa- 
tion." If the word perpetual had been omitted, the 
aphorism would have been false. As it stands, I 
believe that it is true, though perhaps rather too 
strongly expressed; and I should have added the 
self-evident proposition that the propagation of the 
species, whether by self-fertilisation or by cross-fertili- 
sation, or asexually by buds, stolons, &c. is of paramount 
importance. Hermann Miiller has done excellent 
service by insisting repeatedly on this latter point. 

It often occurred to me that it would be advisable 
to try whether seedlings from cross-fertilised flowers 
were in any way superior to those from self-fertilised 
flowers. But as no instance was known with animals 
of any evil appearing in a single generation from the 
closest possible interbreeding, that is between brothers 
and sisters, I thought that the same rule would hold 
good with plants ; and that it would be necessary at 
the sacrifice of too much time to self-fertilise and inter- 
cross plants during several successive generations, in 
order to arrive at any result. I ought to have re- 
flected that such elaborate provisions favouring cross- 
fertilisation, as we see in innumerable plants, would 
not have been acquired for the sake of gaining a 
distant and slight advantage, or of avoiding a distant 
and slight evil. Moreover, the fertilisation of a flower 
by its own pollen corresponds to a closer form of inter- 
breeding than is possible with ordinary bi-sexual 
animals; so that an earlier result might have been 
expected. 

I was at last led to make the experiments recorded 
in the present volume from the following circumstance^ 



CHAP. L INTRODUCTORY REMARKS. 9 

For the sake of detei mining certain points with respect 
to inheritance, and without any thought of the effects 
of close interbreeding, I raised close together two 
large beds of self-fertilised and crossed seedlings from 
the same plant of Linaria vulgaris. To my surprise, 
the crossed plants when fully grown were plainly taller 
and more vigorous than the self-fertilised ones. Bees 
incessantly visit the flowers of this Linaria and carry 
pollen "from one to the other; and if insects are ex- 
cluded, the flowers produce extremely few seeds ; so 
that the wild plants from which my seedlings were 
raised must have been intercrossed during all previous 
generations. It seemed therefore quite incredible that 
the difference between the two beds of seedlings could 
have been due to a single act of self-fertilisation ; and 
I attributed the result to the self-fertilised seeds not 
having been well ripened, improbable as it was that 
all should have been in this state, or to some other 
accidental and inexplicable cause. During the next 
year, I raised for the same purpose as before two large 
beds close together of self-fertilised and crossed seed- 
lings from the carnation, Dianfhus caryophyllus. Thia 
plant, like the Linaria, is almost sterile if insects are 
excluded ; and we may draw the same inference as 
before, namely, that the parent-plants must have been 
intercrossed during every or almost every previous 
generation. Nevertheless, the self-fertilised seedlings 
were plainly inferior in height and vigour to the 
crossed. 

My attention was now thoroughly aroused, for I could 
hardly doubt that the difference between the two beds 
was due to the one set being the offspring of crossed, 
and the other of self-fertilised flowers. Accordingly I 
selected almost by hazard two other plants, which 
happened to be in flower in the greenhouse, namely, 



10 INTRODUCTORY REMARKS. CHAP. I 

Mimulus luteus and Ipomoea purpurea, both of which, 
unlike the Linaria and Dianthus, are highly self- 
fertile if insects are excluded. Some flowers on a 
single plant of both species were fertilised with their 
own pollen, and others were crossed with pollen from 
a distinct individual ; both plants being protected by a 
net from insects. The crossed and self-fertilised seeds 
thus produced were sown on opposite sides of the same 
pots, and treated in all respects alike ; and the plants 
when fully grown were measured and compared. With 
both species, as in the cases of the Linaria and 
Dianthus, the crossed seedlings were conspicuously 
superior in height and in other ways to the self- 
fertilised. I therefore determined to begin a long 
series of experiments with various plants, and these 
were continued for the following eleven years ; and we 
shall see that in a large majority of cases the crossed 
beat the self-fertilised plants. Several of the excep- 
tional cases, moreover, in which the crossed plants 
were not victorious, can be explained. 

It should be observed that I have spoken for the 
sake of brevity, and shall continue to do so, of crossed 
and self-fertilised seeds, seedlings, or plants ; these 
terms implying that they are the product of crossed or 
self-fertilised flowers. Cross-fertilisation always means 
a cross between distinct plants which were raised from 
seeds and not from cuttings or buds. Self-fertilisation 
always implies that the flowers in question were im- 
pregnated with their own pollen. 

My experiments w,ere tried in the following manner. 
A single plant, if it produced a sufficiency of flowers, or 
two or three plants were placed under a net stretched 
on a frame, and large enough to cover the plant 
(together with the pot, when one was used) without 
touching it. This latter point is important, for if 



CHAP. I. INTRODUCTOEY REMARKS. 11 

the flowers touch the net they may be cross-fertilised 
by bees, as I have known to happen ; and when the net 
is wet the pollen may be injured. I used at first 
" white cotton net," with very fine meshes, but after- 
wards a kind of net with meshes one-tenth of an 
inch in diameter; and this I found by experience 
effectually excluded all insects excepting Thrips, which 
no net. will exclude. On the plants thus protected 
several flowers were marked, and were fertilised with 
their own pollen ; and an equal number on the same 
plants, marked in a different manner, were at the same 
time crossed with pollen from a distinct plant. The 
2rossed flowers were never castrated, in order to make 
the experiments as like as possible to what occurs 
under nature with plants fertilised by the aid of 
insects. Therefore, some of the flowers which were 
crossed may have failed to be thus fertilised, and 
afterwards have been self-fertilised. But this and 
some other sources of error will presently be discussed. 
In some few cases of spontaneously self-fertile species, 
the flowers were allowed to fertilise themselves under 
the net ; and in still fewer cases uncovered plants were 
allowed to be freely crossed by the insects which in- 
cessantly visited them. There are some great advan- 
tages and some disadvantages in my having occasion- 
ally varied my method of proceeding ; but when there 
was any difference in the treatment, it is always so 
stated under the head of each species. 

Care was taken that the seeds were thoroughly 
ripened before being gathered. Afterwards the crossed 
and self-fertilised seeds were in most cases placed on 
damp sand on opposite sides of a glass tumbler covered 
by a glass plate, with a partition between the two lots ; 
and the glass was placed on the chimney-piece in a 
warm room. I could thus observe the germination of 



12 INTRODUCTORY REMARKS. CHAP. L 

the seeds. Sometimes a few would germinate on one 
side before any on the other, and these were thrown 
away. But as often as a pair germinated at the same 
time, they were planted on opposite sides of a pot, with 
a superficial partition between the two; and I thus 
proceeded until from half-a-dozen to a score or more 
seedlings of exactly the same age were planted on 
the opposite sides of several pots. If one of the young 
seedlings became sickly or was in any way injured, 
it was pulled up and thrown away, as well as its 
antagonist on the opposite side of the same pot. 

As a large number of seeds were placed on. the sand 
to germinate, many remained after the pairs had been 
selected, some of which were in a state of germination 
and others not so ; and these were sown crowded 
together on the opposite sides of one or two rather 
larger pots, or sometimes in two long rows out of doors. 
In these cases there was the most severe struggle for 
life among the crossed seedlings on one side of the 
pot, and the self-fertilised seedlings on the other side, 
and between the two lots which grew in competition 
in the same pot. A vast number soon perished, 
and the tallest of the survivors on both sides when 
fully grown were measured. Plants treated in this 
manner, were subjected to nearly the same conditions 
as those growing in a state of nature, which have to 
struggle to maturity in the midst of a host of 
competitors. 

On other occasions, from the want of time, the seeds, 
instead of being allowed to germinate on damp sand, 
were sown on the opposite sides of pots, and the fully 
grown plants measured. But this plan is less accurate, 
as the seeds sometimes germinated more quickly on 
one side than on the other. It was however necessary 
to act in this manner with some few species, as certain 



CHAP. I. INTRODUCTORY REMA.RKS. 13 

kinds of seeds would not germinate well when exposed 
to the light ; though the glasses containing them were 
kept on the chimney-piece on one side of a room, 
and some way from the two windows which faced 
the N.E.* 

The soil in the pots in which the seedlings were 
planted, or the seeds sown, was well mixed, so as to 
be uniform in composition. The plants on the two 
sides were always watered at the same time and as 
equally as possible ; and even if this had not been 
done, the water would have spread almost equally to 
both sides, as the pots were not large. The crossed 
and self-fertilised plants were separated by a super- 
ficial partition, which was always kept directed towards 
the chief source of the light, so that the plants on both 
sides were equally illuminated. I do not believe it 
possible that two sets of plants could have been sub- 
jected to more closely similar conditions, than were 
my crossed and self-fertilised seedlings, as grown in 
the above described manner. 

In comparing the two sets, the eye alone was never 
trusted. Generally the height of every plant on both 
sides was carefully measured, often more than once, 
viz., whilst young, sometimes again when older, and 
finally when fully or almost fully grown. But in 
some cases, which are always specified, owing to the 
want of time, only one or two of the tallest plants on 
each side were measured. This plan, which is not a 
good one, was never followed (except with the crowded 



* This occurred in the plainest species germinated on the bare 

manner with the seeds of Papaver sand, though left there for some 

vagum and Delphinium consolida, weeks ; but when these same seeds 

and less plainly with those of were placed on earth in pots, and 

Adonis sestivalits and Ononis minu- covered with a thin layer of sand, 

iistrima. Rarely more than one they germinated immediately in 

or two of the seeds of these four large numbers. 



14 INTRODUCTOBY REMARKS. CHAP. A. 

plants raised from the seeds remaining after the pairs 
had been planted) unless the tallest plants on each 
side seemed fairly to represent the average difference 
between those on both sides. It has, however, some 
great advantages, as sickly or accidentally injured 
plants, or the offspring of ill-ripened seeds, are thus 
eliminated. When the tallest plants alone on each side 
were measured, their average height of course exceeds 
that of all the plants on the same side taken togethes 
But in the case of the much crowded plants raised 
from the remaining seeds, the average height of the 
tallest plants was less than that of the plants in pairs, 
owing to the unfavourable conditions to which they 
were subjected from being greatly crowded. For our 
purpose, however, of the comparison of the crossed and 
self-fertilised plants, their absolute height signifies 
little. 

As the plants were measured by an ordinary English 
standard divided into inches and eighths of an inch, I 
have not thought it worth while to change the frac- 
tions into decimals. The average or mean heights 
were calculated in the ordinary rough method by 
adding up the measurements of all, and dividing the 
product by the number of plants measured ; the result 
being here given in inches and decimals. As the 
different species grow to various heights, I have always 
for the sake of easy comparison given in addition the 
average height of the crossed plants of each species 
taken as 100, and have calculated the average height 
of the self-fertilised plant in relation to this standard. 
With respect to the crowded plants raised from the 
seeds remaining after the pairs had been planted, 
and of which only some of the tallest on each side 
were measured, I have not thought it worth while to 
complicate the results by giving separate averages 



CHAP. I. INTRODUCTORY REMARKS. 15 

for them and for the pairs, but have added up all 
their heights, and thus obtained a single average. 

I long doubted whether it was worth while to give 
the measurements of each separate plant, but have 
decided to do so, in order that it may be seen that the 
superiority of the crossed plants over the self-fertilised, 
does not commonly depend on the presence of two or 
three extra fine plants on the one side, or of a few 
very poor plants on the other side. Although several 
observers have insisted in general terms on the off- 
spring from intercrossed varieties being superior to 
either parent-form, no precise measurements have been 
given ;* and I have met with no observations on 
the effects of crossing and self-fertilising the indi- 
viduals of the same variety. Moreover, experiments ol 
this kind require so much time mine having been 
continued during eleven years that they are not 
likely soon to be repeated. 

As only a moderate number of crossed and self- 
fertilised plants were measured, it was of great impor- 
tance to me to learn how far the averages "were trust- 
worthy. I therefore -asked Mr. Galton, who has had 
much experience in statistical researches, to examine 
some of my tables of measurements, seven in number, 
namely, those of Ipomo3a, Digitalis, Keseda lutea, 
Viola, Limnanthes, Petunia, and Zea. I may premise 
that if we took by chance a dozen or score of men 
belonging to two nations and measured them, it would 
I presume be very rash to form any judgment from 
such small numbers on their average heights. But 
the case is somewhat different with my crossed and 
self-fertilised plants, as they were of exactly the same 



* A summary of these state- and Plants under Domestication, 
ments, with references, may be chap, xvii., 2nd edit., 1875, voL 
fonnd in my ' Variation of Animals ii. p. 109. 



16 



INTRODUCTORY REMARKS, 



CHAP. I 



age, were subjected from first to last to the same 
conditions, and were descended from the same parents. 
When only from two to six pairs of plants were 
measured, the results are manifestly of little or no 
value, except in so far as they confirm and are con- 
firmed by experiments made on a larger scale with 
other species. I will now give the report on the seven 
tables of measurements, which Mr. Galton has had the 
great kindness to draw up for me. 

"I have examined the measurements of the plants with care, 
and by many statistical methods, to find out how far the means 
of the several sets represent constant realities, such as would 
come out the same so long as the general conditions of growth 
remained unaltered. The principal methods that were adopted 
are easily explained by selecting one of the shorter series 
of plants, say of Zea mays, for an example." 

Zed mays (young plants). 



As recorded 


ABEAKGED IN ORDEB OF MAGNITUDE. 




In Separate Pots. 


In a Single Series. 


Column I. 


II. 


III. 


IV. 


V. 


VI. 


VII. 


VIII. 




Crossed. 


Self-fert. 


Crossed. 


Self-fert. 


Crossed. 


Self-fert. 


Difference 




Inches. 


Inches. 


Inches. 


Inches. 


Inches. 


Inches. 


Inches. 


Pot I. 


23| 
12 


17 i 

202 


23 1 
21 


20 i 

20 


23 1 
23 1 


20 i 
20 


-*j 

-31 




21 


20 


12 




l?i 


23 


20 


-3 














22 \ 


18| 


-3J 




22 


20 


22 




20 


22 i 


181 




Pot II. 


19$ 


181 


21 




18| 


22 


18jj 






21 1 


1*1 


19 




18i 


21 1 


18 
















213 


18 


~3| 




22 1 


18| 


23 




18| 


21 


18 


-3 




203 


151 


22 




18 


21 


17 i 


-8| 


Pot III. 


18 


16 


21 




16| 


20 1 


lj 


-31 




21 I 


18 


20 




16 


19| 


16| 


-2? 


Pot IV. 


23 

21 
22J 


16 

18 
12| 


18 

23 

22J 


151 

18 
18 


18 
12 
12 


15 
15| 
18 


(M CO O 
1 + + 




23 


15 i 


21 




15| 










12 


18 


12 




til 









CHAP. I. 



INTRODUCTORY REMARKS. 



17 



" The observations as I received them are shown in columns IL 
and III., where they certainly have no primd facie appearance of 
regularity. But as soon as we arrange them in the order of 
their magnitudes, as in columns IV. and V., the case is materially 
altered. We now see, with few exceptions, that the largest 
plant on the crossed side in each pot exceeds the largest plant 
on the self-fertilised side, that the second exceeds the second, 
the third the third, and so on. Out of the fifteen cases in the 
table, there are only two exceptions to this rule. We may 
therefore' confidently affirm that a crossed series will always 
be found to exceed a self-fertilised series, within the range of 
the conditions under which the present experiment has been 
made.' 



Pot. 


Crossed. 


Self-fert. 


Difference. 


I. 


18? 


19 


+o 


II. 


20? 


19 


-13 


III. 


21 1 


161 


-*1 


IV. 


19| 


16 


~3| 



" Next as regards the numerical estimate of this excess. The 
mean values of the several groups are so discordant, as is shown 
in the table just given, that a fairly precise numerical estimate 
seems impossible. But the consideration arises, whether the 
difference between pot and pot may not be of much the same 
order of importance as that of the other conditions upon which 
the growth of the plants has been modified. If so, and only 
on that condition, it would follow that when all the measure- 
ments, either of the crossed or the self-fertilised plants, were 
combined into a single series, that series would be statistically 
regular. The experiment is tried in columns VII. and VEIL, 
where the regularity is abundantly clear, and justifies us in 
considering its mean as perfectly reliable. I have protracted 
these measurements, and revised them in the usual way, by 
drawing a curve through them with a free hand, but the re- 
vision barely modifies the means derived from the original 
observations. In the present, and in nearly all the other cases, 
the difference between the original and revised means is under 
2 per cent, of their value. It is a very remarkable coincidence 





18 INTRODUCTOEY EEMARKS. CHAP. I 

that in the seven kinds of plants, whose measurements I have 
examined, the ratio between the heights of the crossed and of 
the self-fertilised ranges in five cases within very narrow limits. 
In Zea mays it is as 100 to 84, and in the others it ranges 
between 100 to 76 and 100 to 86." 

" The determination of the variability (measured by what is 
technically called the ' probable error ') is a problem of more 
delicacy than that of determining the means, and I doubt, after 
making many trials, whether it is possible to derive useful 
conclusions from these few observations. We ought to have 
measurements of at least fifty plants in each case, in order to 
be in a position to deduce fair results. One fact, however, 
bearing on variability, is very evident in most cases, though not 
in Zea mays, viz., that the self-fertilised plants include the 
larger number of exceptionally small specimens, while the 
crossed are more generally full grown." 

"Those groups of cases in which measurements have been 
made of a few of the tallest plants that grew in rows, each of 
which contained a multitude of plants, show very clearly that 
the crossed plants exceed the self-fertilised in height, but they 
do not tell by inference anything about their respective mean 
values. If it should happen that a series is known to follow 
the law of error or any other law, and if the number of indi- 
viduals in the series is known, it would be always possible to 
reconstruct the whole series when a fragment of it has been 
given. But I find no such method to be applicable in the 
present case. The doubt as to the number of plants in each row 
is of minor importance ; the real difficulty lies in our ignorance 
of the precise law followed by the series. The experience of 
the plants in pots does not help us to determine that law, 
because the observations of such plants are too few to enable 
us to lay down more than the middle terms of the series to 
which they belong with any sort of accuracy, whereas the cases 
we are now considering refer to one of its extremities. There 
are other special difficulties which need not be gone into, as the 
one already mentioned is a complete bar." 

Mr. Galton sent me at the same time graphical 
representations which he had made of the measure- 
ments, and they evidently form fairly regular curves. 
He appends the words "very good " to those of Zea ana 



CHAP. I. INTRODUCTORY REMARKS. 19 

Limnanthes. He also calculated the average height 
of the crossed and self-fertilised plants in the seven 
tables by a more correct method than that followed 
by me, namely, by including the heights, as estimated 
in accordance with statistical rules, of a few plants 
which died before they were measured ; whereas I 
merely added up the heights of the survivors, and 
divided the sum by their number. The difference in 
our results is in one way highly satisfactory, for 
the average heights of the self-fertilised plants, as 
deduced by Mr. Galton, is less than mine in all the 
cases excepting one, in which our averages are 
the same ; and this shows that I have by no means 
exaggerated the superiority of the crossed over the 
self-fertilised plants. 

After the heights of the crossed and self-fertilised 
plants had been taken, they were sometimes cut down 
close to the ground, and an equal number of both 
weighed. This method of comparison gives very 
striking results, and I wish that it had been oftener 
followed. Finally a record was often kept of any 
marked difference in the rate of germination of the 
crossed and self-fertilised seeds, of the relative periods 
of flowering of the plants raised from them, and of 
their productiveness, that is, of the number of seed- 
capsules which they produced and of the average 
number of seeds which each capsule contained. 

When I began my experiments I did not intend to 
raise crossed and self-fertilised plants for more than a 
single generation ; but as soon as the plants of the 
first generation were in flower I thought that I would 
raise one more generation, and acted in the following 
manner. Several flowers on one or more of the self- 
fertilised plants were again self-fertilised ; and several 

c 2 



20 INTRODUCTORY REMARKS. CHAP. I. 

flowers on one or more of the crossed plants were ferti- 
lised with pollen from another crossed plant of the 
same lot. Having thus once begun, the same method 
was followed for as many as ten successive generations 
with some of the species. The seeds and seedlings were 
always treated in exactly the same manner as already 
described. The self-fertilised plants, whether originally 
descended from one or two mother-plants, were thus in 
each generation as closely interbred as was possible ; 
and I could not have improved on my plan. But 
instead of crossing one of the crossed plants with 
another crossed plant, I ought to have crossed the self- 
fertilised plants of each generation with pollen taken 
from a non-related plant that is, one belonging to a 
distinct family or stock of the same species and variety. 
This was done in several cases as an additional experi- 
ment, and gave very striking results. But the plan 
usually followed was to put into competition and 
compare intercrossed plants, which were almost always 
the offspring of more or less closely related plants, with 
the self-fertilised plants of each succeeding genera- 
tion ; all having been grown under closely similar 
conditions. I have, however, learnt more by this method 
of proceeding, which was begun by an oversight and 
then necessarily followed, than if I had always crossed 
the self-fertilised plants of each succeeding generation 
with pollen from a fresh stock. 

I have said that the crossed plants of the successive 
generations were almost always inter-related. When 
the flowers on an hermaphrodite plant are crossed 
with pollen taken from a distinct plant, the seedlings 
thus raised may be considered as hermaphrodite brothers 
or sisters ; those raised from the same capsule being as 
close as twins or animals of the same litter. But in 
one sense the flowers on the same plant are distinct 



OHAP. I. INTRODUCTORY REMARKS. 21 

individuals, and as several flowers on the mother-plant 
were crossed by pollen taken from several flowers on 
the father-plant, such seedlings would be in one sense 
half-brothers or sisters, but more closely related than 
are the half-brothers and sisters of ordinary animals. 
The flowers on the mother-plant were, however, com- 
monly crossed by pollen taken from two or more dis- 
tinct pjants ; and in these cases the seedlings might 
be called with more truth half-brothers or sisters. 
When two or three mother-plants were crossed, as often 
happened, by pollen taken from two or three father- 
plants (the seeds being all intermingled), some of the 
seedlings of the first generation would be in no way 
related, whilst many others would be whole or half- 
brothers and sisters. In the second generation a large 
number of the seedlings would be what may be called 
whole or half first-cousins, mingled with whole and 
half-brothers and sisters, and with some plants not at 
all related. So it would be in the succeeding genera- 
tions, but there would also be many cousins of the 
second and more remote degrees. The relationship will 
thus have become more and more inextricably complex 
in the later generations ; with most of the plants in 
some degree and many of them closely related. 

I have only one other point to notice, but this is one 
of the highest importance ; namely, that the crossed 
and self-fertilised plants were subjected in the same 
generation to as nearly similar and uniform conditions as 
was possible. In the successive generations they were 
exposed to slightly different conditions as the seasons 
varied, and they were raised at different periods. But 
in other respects all were treated alike, being grown 
in pots in the same artificially prepared soil, being 
watered at the same time, and kept close together 
in the same greenhouse or hothouse. They were 



22 INTRODUCTORY REMARKS. CHAP. I, 

therefore not exposed during successive years to such 
great vicissitudes of climate as are plants growing out 
of doors. 

On some apparent and real Causes of Error in my Ex- 
periments. It has been objected to such experiments 
as mine, that covering plants with a net, although only 
for a short time whilst in flower, may affect their health 
and fertility. I have seen no such effect except in one 
instance with a Myosotis, and the covering may not 
then have been the real cause of injury. But even if 
the net were slightly injurious, and certainly it was not 
so in any high degree, as I could judge by the appear- 
ance of the plants and by comparing their fertility with 
that of neighbouring uncovered plants, it would not 
have vitiated my experiments ; for in all the more im- 
portant cases the flowers were crossed as well as self- 
fertilised under a net, so that they were treated in this 
respect exactly alike. 

As it is impossible to exclude such minute pollen- 
carrying insects as Thrips, flowers which it was intended 
to fertilise with their own pollen may sometimes have 
been afterwards crossed with pollen brought by these 
insects from another flower on the same plant ; but as 
we shall hereafter see, a cross of this kind does not 
produce any effect, or at most only a slight one. When 
two or more plants were placed near one another 
under the same net, as was often done, there is some 
real though not great danger of the flowers which 
were believed to be self-fertilised being afterwards 
crossed with pollen brought by Thrips from a distinct 
plant. I have said that the danger is not great, 
because I have often found that plants which are 
pelf-sterile, unless aided by insects, remained sterile 
when several plants of the same species were placed 



CHAP. I. INTRODUCTORY REMARKS. 23 

under the same net. If, however, the flowers which 
had been presumably self-fertilised by me were in any 
case afterwards crossed by Thrips with pollen brought 
from a distinct plant, crossed seedlings would have 
been included amongst the self-fertilised ; but it should 
be especially observed that this occurrence would tend 
to diminish and not to increase any superiority in 
average height, fertility, &c., of the crossed over the 
self-fertilised plants. 

As the flowers which were crossed were never cas- 
trated, it is probable or even almost certain that I 
sometimes failed to cross-fertilise them effectually, and 
that they were afterwards spontaneously self-fertilised. 
This would have been most likely to occur with dicho- 
gamous species, for without much care it is not easy to 
perceive whether their stigmas are ready to be fer- 
tilised when the anthers open. But in all cases, 
as the flowers were protected from wind, rain, and the 
access of insects, any pollen placed by me on the 
stigmatic surface whilst it was immature, would gener- 
ally have remained there until the stigma was mature ; 
and the flowers would then have been crossed as was 
intended. Nevertheless, it is highly probable that 
self-fertilised seedlings have sometimes by this means 
got included amongst the crossed seedlings. The effect 
would be, as in the former case, not to exaggerate 
but to diminish any average superiority of the crossed 
over the self-fertilised plants. 

Errors arising from the two causes just named, and 
from others, such as some of the seeds not having 
been thoroughly ripened, though care was taken to 
avoid this error the sickness or unperceived injury of 
any of the plants, will have been to a large extent 
eliminated, in those cases in which many crossed and 
self-fertilised plants were measured and an average 



24 INTRODUCTORY REMARKS. CHAP. I. 

struck. Some of these causes of error will also have 
been eliminated by the seeds having been allowed to 
germinate on bare damp sand, and being planted in 
pairs ; for it is not likely that ill-matured and well- 
matured, or diseased and healthy seeds, would germi- 
nate at exactly the same time. The same result will 
have been gained in the several cases in which only a 
few of the tallest, finest, and healthiest plants on each 
side of the pots were measured. 

Kolreuter and Gartner* have proved that with some 
plants several, even as many as from fifty to sixty, 
pollen-grains are necessary for the fertilisation of all 
the ovules in the ovarium. Naudin also found in 
the case of Mirabilis that if only one or two of its 
very large pollen-grains -were placed on the stigma, 
the plants raised from such seeds were dwarfed. 
I was therefore careful to give an amply sufficient 
supply of pollen, and generally covered the stigma 
with it ; but I did not take any special pains to place 
exactly the same amount on the stigmas of the self- 
fertilised and crossed flowers. After having acted in 
this manner during two seasons, I remembered that 
Gartner thought, though without any direct evidence, 
that an excess of pollen was perhaps injurious ; and it 
has been proved by Spallanzani, Quatrefages, and 
Newport, f that with various animals an excess of the 
seminal fluid entirely prevents fertilisation. It was 
therefore necessary to ascertain whether the fertility of 
the flowers was affected by applying a rather small and 
an extremely large quantity of pollen to the stigma. 
Accordingly a very small mass of pollen-grains was 



* 'Kenntnias der Befruch- torn. i. p. 27. 

tung,' 1844, p. 345. Naudin, f 'Transactions Philosophical 
' Nouvelles Archives du Museum,' Soc.' 1853, pp. 253-258. 



CHAP. I. INTRODUCTORY REMARKS. 25 

placed on one side of the large stigma in sixty-four 
flowers of Ipomoea purpurea, and a great mass of pollen 
over the whole surface of the stigma in sixty-four other 
flowers. In order to vary the experiment, half the 
flowers of both lots were on plants produced from self- 
fertilised seeds, and the other half on plants from 
crossed seeds. The sixty -four flowers with an excess 
of pollen yielded sixty-one capsules; and excluding 
four capsules, each of which contained only a single 
poor seed, the remainder contained on an average 5 07 
seeds per capsule. The sixty-four flowers with only a 
little pollen placed on one side of the stigma yielded 
sixty-three capsules, and excluding one from the same 
cause as before, the remainder contained on an average 
5 '129 seeds. So that the flowers fertilised with little 
pollen yielded rather more capsules and seeds than did 
those fertilised with an excess ; but the difference is 
too slight to be of any significance. On the other 
hand, the seeds produced by the flowers with an excess 
of pollen were a little heavier of the two ; for 170 of 
them weighed 79 67 grains, whilst 170 seeds from the 
flowers with very little pollen weighed 79-20 grains. 
Both lots of seeds having been placed on damp sand 
presented no difference in their rate of germination. 
We may therefore conclude that my experiments were 
not affected by any slight difference in the amount of 
pollen used ; a sufficiency having been employed in 
all cases. 

The order in which our subject will be treated in 
the present volume is as follows. A long series of ex- 
periments will first be given in Chapters II. to VI. 
Tables will afterwards be appended, showing in a con- 
densed form the relative heights, weights, and fertility 
of the offspring of the various crossed and self-fertilised 



26 INTRODUCTORY REMARKS. CHAP. I. 

species. Another table exhibits the striking results 
from fertilising plants, which during several generations 
had either been self-fertilised or had been crossed 
with plants kept all the time under closely similar 
conditions, with pollen taken from plants of a distinct 
stock and which had been exposed to different con- 
ditions. In the concluding chapters various related 
points and questions of general interest will be 
discussed. 

Anyone not specially interested in the subject need 
not attempt to read all the details; though they 
possess, I think, some value, and cannot be all sum- 
marised. But I would suggest to the reader to take 
as an example the experiments on Ipomoea in Chapter 
II. ; to which may be added those on Digitalis, Origa- 
num, Viola, or the common cabbage, as in all these 
cases the crossed plants are superior to the self- 
fertilised in a marked degree, but not in quite the 
same manner. As instances of self-fertilised plants 
being equal or superior to the crossed, the experiments 
on Bartonia, Canna, and the common pea ought to be 
read; but in the last case, and probably in that of 
Canna, the want of any superiority in the crossed 
plants can be explained. 

Species were selected for experiment belonging to 
widely distinct families, inhabiting various countries. 
In some few cases several genera belonging to the 
same family were tried, and these are grouped toge- 
ther ; but the families themselves have been arranged 
not in any natural order, but in that which was the 
most convenient for my purpose. The experiments 
have been fully given, as the results appear to me of 
sufficient value to justify the details. Plants bearing 
hermaphrodite flowers can be interbred more closely 
than is possible with the higher animals, and are there- 



CHAP. I. INTRODUCTORY REMARKS. 27 

fore well-fitted to throw light on the nature and extent 
of the good effects of crossing, and on the evil effects 
of close interbreeding or self-fertilisation. The most 
important conclusion at which I have arrived is that 
the mere act of crossing by itself does no good. The 
good depends on the individuals which are crossed 
differing slightly in constitution, owing to their pro- 
genitor^ having been subjected during several genera- 
tions fo slightly different conditions, or to what we 
call in our ignorance spontaneous variation. This 
conclusion, as we shall hereafter see, is closely con- 
nected with various important physiological problems, 
such as the benefit derived from slight changes in the 
conditions of life, and this stands in the closest con- 
nection with life itself. It throws light on the origin of 
the two sexes and on their separation or union in the 
same individual, and lastly on the whole subject of 
hybridism, which is one of the greatest obstacles to the 
general acceptance and progress of the great principle 
of evolution. 

In order to avoid misapprehension, I beg leave to 
repeat that throughout this volume a crossed plant, 
seedling, or seed, means one of crossed parentage, that 
is, one derived from a flower fertilised with pollen 
from a distinct plant of the same species. And that 
a self-fertilised plant, seedling, or seed, means one 
of self-fertilised parentage, that is, one derived from 
a flower fertilised with pollen from the same flower, 
or sometimes, when thus stated, from another flower 
on the same plant. 



IPOMCEA PURPTJEEA. CHAP. II 



CHAPTER II. 

CONVOLVTLACE2E. 

Ipomoea purpurea, comparison of the height and fertility of th 
crossed and self-fertilised plants during ten successive generations 
Greater constitutional vigour of the crossed plants The effects 
on the offspring of crossing different flowers on the same plant, 
instead of crossing distinct individuals The effects of a cross with 
a fresh stock The descendants of the self-fertilised plant named 
Hero Summary on the growth, vigour, and fertility of the suc- 
cessive crossed and self-fertilised generations Small amount of 
pollen in the anthers of the self-fertilised plants of the later genera- 
tions, and the sterility of their first-produced flowers Uniform 
colour of the flowers produced by the self-fertilised plants The 
ad vantage from a cross between two distinct plants depends on their 
differing in constitution. 

A PLANT of Iponioea purpurea, or as it is often called in 
England the convolvulus major, a native of South 
America, grew in my greenhouse. Ten flowers on this 
plant were fertilised with pollen from the same flower ; 
and ten other flowers on the same plant were crossed 
with pollen from a distinct plant. The fertilisation of 
the flowers with their own pollen was superfluous, as 
this convolvulus is highly self-fertile ; but I acted in 
this manner to make the experiments correspond in all 
respects. Whilst the flowers are young the stigma 
projects beyond the anthers ; and it might have been 
thought that it could not be fertilised without the aid 
of humble-bees, which often visit the flowers ; but as 
the flower grows older the stamens increase in length, 
and their anthers brush against the stigma, which thus 



CHAP. II. CROSSED AND SELF-FERTILISED PLANTS. 



receives some pollen. The number of seeds produced 
by the crossed and self-fertilised flowers differed very 
little. 

Crossed and self-fertilised seeds obtained in the above 
manner were allowed to germinate on damp sand, and as often 
as pairs germinated at the same time they were planted in the 
manner described in the Introduction, on the opposite sides of 
two pots. Five pairs were thus planted ; and all the remaining 
seeds, -whether or not in a state of germination, were planted on 
the opposite sides of a third pot, so that the young plants on 
both sides were here greatly crowded and exposed to very 
severe competition. Rods of iron or wood of equal diameter 
were given to all the plants to twine up; and as soon as one of 
each pair reached the summit both were measured. A single 
rod was placed on each side of the crowded pot, No. TTT., and 
only the tallest plant on each side was measured. 

TABLE I. (First Generation.) 



No. of Pot. 


Seedlings from 
Crossed Plants. 


Seedlings from 
Self-fertilised Plants. 


I. 


Inches. 
87 1 
87 1 
89 


Inches. 
69 
66 
73 


II. 


88 
87 


68 1 
60j 


III. 

Plants crowded ; the 
tallest one mea- 
sured on each side. 


77 


57 


Total in inches. 


516 


394 



The average height of the six crossed plants is here 86 inches, 
whilst that of the six self-fertilised plants is only 65 '66 inches, 
so that the crossed plants are to the self-fertilised in height as 
100 to 76. It should be observed that this difference is not due 
to a few of the crossed plants being extremely tall, or to a few of 
the self-fertilised being extremely short, but to all the crossed 
plants attaining a greater height than their antagonists. The 
three pairs in Pot I. were measured at two earlier periods, and 
the difference was sometimes greater and sometimes less than that 



3C IPOMOEA PURPUREA CHAP. II 

at the final measuring. But it is an interesting fact, of which 1 
have seen several other instances, that one of the self-fertilised 
plants, when nearly a foot in height, was half an inch taller 
than the crossed plant ; and again, when two feet high, it wag 
1| inch taller, but during the ten subsequent days the crossed 
plant began to gain on its antagonist, and ever afterward asserted 
its supremacy, until it exceeded its self-fertilised opponent by 
16 inches. 

The five crossed plants in Pots I. and II. were covered with a 
net, and produced 121 capsules ; the five self-fertilised plants 
produced eighty-four capsules, so that the numbers of capsules 
were as 100 to 69. Of the 121 capsules on the crossed plants 
sixty-five were the product of flowers crossed with pollen from a 
distinct plant, and these contained on an average 5 23 seeds per 
capsule; the remaining fifty-six capsules were spontaneously 
self-fertilised. Of the eighty-four capsules on the self-fertilised 
plants, all the product of renewed self-fertilisation, fifty--five 
(which were alone examined) contained on an average 4 '85 
seeds per capsule. Therefore the cross-fertilised capsules, com- 
pared with the self-fertilised capsules, yielded seeds in the 
proportion of 100 to 93. The crossed seeds were relatively 
heavier than the self-fertilised seeds. Combining the above 
data (i.e., number of capsules and average number of contained 
seeds), the crossed plants, compared with the self-fertilised., 
yielded seeds in the ratio of 100 to 64. 

These crossed plants produced, as already stated, fifty-six 
spontaneously self-fertilised capsules, and the self-fertilised 
plants produced twenty-nine such capsules. The former con- 
tained on an average, in comparison with the latter, seeds 
in the proportion of 100 to 99. 

In Pot III., on the opposite sides of which a large number of 
crossed and self-fertilised seeds had been sown and the seed- 
lings allowed to struggle together, the crossed plants had at 
first no great advantage. At one time the tallest crossed was 
25i inches high, and the tallest self-fertilised plants 21|. But 
the difference afterwards became much greater. The plants on 
both sides, from being so crowded, were poor specimens. The 
flowers were allowed to fertilise themselves spontaneously under 
a net; the crossed plants produced thirty-seven capsules, the 
self-fertilised plants only eighteen, or as 100 to 47. The former 
contained on an average 3 -62 seeds per capsule; and the latter 
3 '38 seeds, or as 100 to 93. Combining these data (i.e., number 



CHAP. II. CROSSED AND SELF-FERTILISED PLANTS. 



31 



of capsules and average number of seeds), the crowded crossed 
plants produced seeds compared with the self-fertilised as 100 
to 45. These latter seeds, however, were decidedly heavier, a 
hundred weighing 41 64 grains, than those from the capsules 
on the crossed plants, of which a hundred weighed 36 79 grains ; 
and this probably was due to the fewer capsules borne by the 
self-fertilised plants having been better nourished. We thus see 
that the crossed plants in this the first generation, when grown 
under favourable conditions, and when grown under unfavour- 
able conditions from being much crowded, greatly exceeded in 
height, and in the number of capsules produced, and slightly 
in the number of seeds per capsule, the self-fertilised plants. 

Crossed and self-fertilised Plants of the Second Generation. 
Flowers on the crossed plants of the last generation (Table I.) 
were crossed by pollen from distinct plants of the same genera- 
tion ; and flowers on the self-fertilised plants were fertilised by 
pollen from the same flower. The seeds thus produced were 
treated in every respect as before, and we have in Table II. 
the result. 

TABLE II. (Second Generation.') 



No. of Pot. 


Crossed Plants. 


Self-fertilised Plants. 


I. 


Inches. 
87 


Inche*. 
67 1 




83 


80 1 


II. 


85 J 
89 
77| 


6! I 
79 
41 


Total inches. 


505 


398 



Here again every single crossed plant is taller than its anta- 
gonist. The self-fertilised plant in Pot I., which ultimately 
reached the unusual height of 80| inches, was for a long time 
taller than the opposed crossed plant, though at last beaten by 
it. The average height of the six crossed plants is 84* 16 inches, 
whilst that of the six self-fertilised plants is 66 '33 inches, or 
as 100 to 79. 

Crossed and self-fertilised Plants of the Third Generation. Seeds 
from the crossed plants of the last generation (Table II.) again 



32 



IPOMffiA PURPUEEA. 



CHAP. II. 



crossed, and from the self-fertilised plants again self-fertilised, 
were treated in all respects exactly as before, with the following 
result : 

TABLE HE. (Third Generation.) 



No. of Pot. Crossed Plants. 


Self-fertilised Plants. 


I. 


Inches. 
74 

72 
73 1 


Inches. 
56 1 

% 


II. 


82 
81 
82 


59 
30 
66 


Total inches. 


464-5 


317-0 



Again all the crossed plants are higher than their antagonists : 
their average height is 77 '41 inches, whereas that of the self- 
fertilised is 52-83 inches, or as 100 to 68. 

I attended closely to the fertility of the plants of this third 
generation. Thirty flowers on the crossed plants were crossed 
with pollen from other crossed plants of the same generation, 
and the twenty-six capsules thus produced contained, on an 
average, 4-73 seeds; whilst thirty flowers on the self-fertilised 
plants, fertilised with the pollen from the same flower, produced 
twenty-three capsules, each containing 4-43 seeds. Thus the 
average number of seeds in the crossed capsules was to that in 
the self-fertilised capsules as 100 to 94. A hundred of the 
crossed seeds weighed 43 27 grains, whilst a hundred of the self- 
fertilised seeds weighed only 37 63 grains . Many of these lighter 
self-fertilised seeds placed on damp sand germinated before the 
crossed ; thus thirty-six of the former germinated whilst only 
thirteen of the latter or crossed seeds germinated. In Pot I. 
the three crossed plants produced spontaneously under the net 
(besides the twenty-six artificially cross-fertilised capsules) 
seventy-seven self-fertilised capsules containing on an average 
4 '41 seeds; whilst the three self-fertilised plants produced 
spontaneously (besides the twenty-three artificially self-fertilised 
capsules) only twenty-nine self-fertilised capsules, containing OR 
an average 4 -14 seeds. Therefore the average number of seeds 
in the two lots of spontaneously self-fertilised capsules was as 



CIIAP. II. CROSSED AND SELF-FERTILISED PLANTS. 33 



100 to 94. Taking into consideration the number of capsules 
together with the average number of seeds, the crossed plants 
(spontaneously self-fertilised) produced seeds in comparison with 
the self-fertilised plants (spontaneously self-fertilised) in the 
proportion of 100 to 35. By whatever method the fertility of 
these plants is compared, the crossed are more fertile than the 
self-fertilised plants. 

I tried in several ways the comparative vigour and powers of 
growth of the crossed and self-fertilised plants of this third 
generation. Thus, four self-fertilised seeds which had just 
germinated were planted on one side of a pot, and after an in- 
terval of forty-eight hours, four crossed seeds in the same state 
of germination were planted on the opposite side ; and the pot 
was kept in the hothouse. I thought that the advantage thus 
given to the self-fertilised seedlings would have been so great 
that they would never have been beaten by the crossed ones. 
They were not beaten until all had grown to a height of 18 
inches; and the degree to which they were finally beaten is 
shown in the following table (No. IV.). We here see that the 
average height of the four crossed plants is 76 ' 62, and of the 
four self-fertilised plants 65 '87 inches, or as 100 to 86 ; there- 
fore less than when both sides started fair. 

TABLE IV. (Third Generation, the self-fertilised Plants having 
had a start of forty-eight hours.") 



No. of Pot. 


Crossed Plants. 


Self-fertilised Plants. 


III. 


Inches. 

781 

77 1 
73 


Inches. 
73| 
53 

75j 


Total inches. 


306-5 


263-5 



Crossed and self-fertilised seeds of the third generation were 
also sown out of doors late in the summer, and therefore under 
unfavourable conditions, and a single stick was given to each 
lot of plants to twine up. The two lots were sufficiently 
separate so as not to interfere with each other's growth, and the 
ground was clear of weeds. As soon as they were killed by the 
first frost (and there was no difference in their hardiness), the 
two tallest crossed plants were found to be 24 5 and 22 5 inches. 



34 



IPOMOEA PURPUEEA. 



CHAP. II 



whilst the two tallest self-fertilised plants were only 15 and 
12-5 inches in height, or as 100 to 59. 

I likewise sowed at the same time two lots of the same seeds 
in a part of the garden which was shady and covered with 
weeds. The crossed seedlings from the first looked the most 
hsalthy, but they twined up a stick only to a height of 7i inches ; 
whilst the self-fertilised were not able to twine at all ; and the 
tallest of them was only 3 inches in height. 

Lastly, two lots of the same seeds were sown in the midst of 
a bed of candy-tuft (Iberis) growing vigorously. The seedlings 
came up, but all the self-fertilised ones soon died excepting one, 
which never twined and grew to a height of only 4 inches. 
Many of the crossed seedlings, on the other hand, survived; 
and some twined up the stems of the Iberis to the height of 
11 inches. These cases prove that the crossed seedlings 
have an immense advantage over the self-fertilised, both when 
growing isolated under very unfavourable conditions, and when 
put into competition with each other or with other plants, as 
would happen in a state of nature. 

Crossed and self-ftrtilised Plants of the Fourth Generation. Seed- 
lings raised as before from the crossed and self-fertilised plants 
of the third generation in Table III., gave results as follows : 
TABLE V. (Fourth Generation.) 



No. of Pot 


Crossed Plants. 


Self-fertilised Plants. 


I. 


Inches. 
84 
47 


Inches. 
80 
44J 


IL 


83 
59 


73 J 
51* 


III. 


82 
65 i 
68 


56 J 
63 
52 


Total inches. 


488-5 


421-0 



Here the average height of the seven crossed plants is 69 -78 
inches, and that of the seven self-fertilised plants 60 ' 14 ; or as 
100 to 86. This smaller difference relatively to that in the 
former generations, may be attributed to the plants having been 
raised during the depth of winter, and consequently to their not 



CHAP. II. CKOSSED AND SELF-FERTILISED PLANTS. 35 



having grown vigorously, as was shown by their general ap- 
pearance and from several of them never reaching the summits 
of the rods. In Pot LT., one of the self-fertilised plants was for 
a long time taller by two inches than its opponent, but was 
ultimately beaten by it, so that all the crossed plants exceeded 
their opponents in height. Of twenty-eight capsules produced 
by the crossed plants fertilised by pollen from a distinct plant, 
each contained on an average 4 '75 seeds; of twenty-seven self- 
fertilised capsules on the self-fertilised plants, each contained 
on an average 4 -47 seeds ; so that the proportion of seeds in tht 
crossed and self-fertilised capsules was as 100 to 94. 

Some of the same seeds, from which the plants in the last 
Table V. had been raised, were planted, after they had germi- 
nated on damp sand, in a square tub, in which a large Brug- 
mansia had long been growing. The soil was extremely poor 
and full of roots ; six crossed seeds were planted in one corner, 
and six self-fertilised seeds in the opposite corner. All the 
seedlings from the latter soon died excepting one, and this grew 
to the height of only li inch. Of the crossed plants three 
survived, and they grew to the height of 2i inches, but were not 
able to twine round a stick ; nevertheless, to my surprise, they 
produced some small miserable flowers. The crossed plants 
thus had a decided advantage over the self-fertilised plants 
under this extremity of bad conditions. 

Crossed and self-fertilised Plants of the Fifth Genera tion These 
were raised in the same manner as before, and when measured 
gave the following results : 

TABLE VI. (Fifth Generation.") 



No. of Pot 


Crossed Plants. 


Self-fertilised Plants. 


I. 


Inches. 
96 
86 
69 


Inches. 
73 
78 
29 


II. 


84 
84 
76 1 


51 
84 
59 


Total inches. 


495-25 


374-00 



The average height of the six crossed plants is 82 -54 inches, 

D 2 



IPOM(EA PURPUEEA. 



CHAP. II. 



and that of the six self-fertilised plants 62 '33 inches, or as 100 
to 75. Every crossed plant exceeded its antagonist in height. 
In Pot I. the middle plant on the crossed side was slightly 
injured whilst young by a blow, and was for a time beaten by 
its opponent, but ultimately recovered the usual superiority. 
The crossed plants produced spontaneously a vast number more 
capsules than did the self-fertilised plants ; and the capsules of 
the former contained on an average 3 '37 seeds, whilst those of 
the latter contained only 3 per capsule, or as 100 to 89. But 
looking only to the artificially fertilised capsules, those on the 
crossed plants again crossed contained on an average 4 '46 
seeds, whilst those on the self-fertilised plants again self- 
fertilised contained 4 77 seeds ; so that the self-fertilised cap- 
sules were the more fertile of the two, and of this unusual fact 
I can offer no explanation. 

Crossed and self-fertilised Plants of the Sixth Generation. 
These were raised in the usual manner, with the following result. 
I should state that there were originally eight plants on each 
side; but as two of the self-fertilised became extremely un- 
healthy and never grew to near their full height, these as well 
as their opponents have been struck out of the list. If they had 
been retained, they would have made the average height of the 
crossed plants unfairly greater than that of the self-fertilised. 
I have acted in the same manner in a few other instances, when 
one of a pair plainly became very unhealthy. 

TABLE VII. (Sixth Generation.) 



No. of Pot. 


Crossed Plants. 


Self-fertilised Plants. 


I. 


Inches. 
93 
91 


Inches. 
50 i 
65 


II. 


79 
86 J 
88 


50 

87 
62 


III. 


87 J 


64 } 


Total inches. 


525 


379 



The average height of the six crossed plants is here 87 '5, and 
rf the six self-fertilised plan ts 63 16, or as 100 to 72. This large 
difference was chiefly due to most of the plants, especially the 



CHAP. II. CROSSED AND SELF-FERTILISED PLANTS. 37 



Belf-fertilised ones, having become unhealthy towards the close 
of their growth, and they were severely attacked by aphides. 
From this cause nothing can be inferred with respect to theii 
relative fertility. In this generation we have the first instance 
of a self-fertilised plant in Pot II. exceeding (though only by 
half an inch) its crossed opponent. This victory was fairly won 
after a long struggle. At first the self-fertilised plant was several 
inches taller than its opponent, but when the latter was 4a 
feet high it had grown equal ; it then grew a little taller than 
the self-fertilised plant, but was ultimately beaten by it to the 
extent of half an inch, as shown in the table. I was so much 
surprised at this case that I saved the self-fertilised seeds of 
this plant, which I will call the " Hero," and experimented on 
its descendants, as will hereafter be described. 

Besides the plants included in Table VII., nine crossed and 
nine self-fertilised plants of the same lot were raised in two 
other pots, IV. and V. These pots had been kept in the hot- 
house, but from want of room were, whilst the plants were 
young, suddenly moved during very cold weather into the 
coldest part of the greenhouse. They all suffered greatly, and 
never quite recovered. After a fortnight only two of the nine 
self-fertilised seedlings were alive, whilst seven of the crossed 
survived. The tallest of these latter plants when measured was 
47 inches in height, whilst the tallest of the two surviving self- 
fertilised plants was only 32 inches. Here again we see how much 
more vigorous the crossed plants are than the self-fertilised. 

Crossed and self -fertilised Plants of the Seventh Generation. 
These were raised as heretofore with the following result : 

TABLE VTTT. (Seventh Generation.) 



No. of Pot. 


Crossed Plants. 


Self-fertilised Plants. 


I. 


Inches. 
84 1 
84f 
761 


Inches. 

Si 1 

55 1 


II. 


8*1 

90 
82 


65 

51 i 

80 1 


III. 


83 
86 


67 i 
60 1 


IV. 


84 


75| 


Total inches. 


755-50 


G14-25 



38 IPOMCEA PURPTJKEA CHAP. IL 

Each of these nine crossed plants is higher than its opponent, 
though in one case only by three-quarters of an inch. Their 
average height is 83 -94 inches, and that of the self-fertilised 
plants 68-25, or as 100 to 81. These plants, after growing to 
their full height, became very unhealthy and infested with 
aphides, just when the seeds were setting, so that many of the 
capsules failed, and nothing can be said on their relative 
fertility. 

Crossed and self-fertilised Plants of the Eighth Generation. As 
just stated, the plants of the last generation, from which the 
present ones were raised, were very unhealthy and their seeds 
of unusually small size ; and this probably accounts, through 
abnormal premature growth, for the two lots behaving dif- 
ferently to what they did in any of the previous or succeeding 
generations. Many of the self- fertilised seeds germinated before 
the crossed ones, and these were of course rejected. When the 
crossed seedlings in Table IX. had grown to a height of between 
I and 2 feet, they were all, or almost all, shorter than their self- 
fertilised opponents, but were not then measured. When they 
had acquired an average height of 32'28 inches, that of the 
self-fertilised plants was 40 '68, or as 100 to 122. Moreover, 
every one of the self-fertilised plants, with a single exception, 
exceeded its crossed opponent. When, however, the crossed 
plants had grown to an average height of 77 - 56 inches, they 
just exceeded (viz., by 7 of an inch) the average height of the 
self-fertilised plants; but two of the latter were still taller than 
their crossed opponents. I was so much astonished at this whole 
case, that I tied string to the summits of the rods ; the plants 
being thus allowed to continue climbing upwards. When their 
growth was complete they were untwined, stretched straight, 
and measured. The crossed plants had now almost regained 
their accustomed superiority, as may be seen in Table IX. 

The average height of the eight crossed plants is here 113 25 
inches, and that of the self-fertilised plants 96 '65, or as 100 tc 
85. Nevertheless two of the self-fertilised plants, as may be seen 
in the table, were still higher than their crossed opponents. 
The latter manifestly had much thicker stems and many more 
lateral branches, and looked altogether more vigorous than the 
self-fertilised plants, and generally flowered before them. The 
earlier flowers produced by these self-fertilised plants did not 
set any capsules, and their anthers contained only a small 
amount of pollen ; but to this subject I shall return. Neverthe- 



CHAP. U. CROSSED AND SELF-FERTILISED PLANTS. 39 



less capsules produced by two other self-fertilised plants of the 
.same lot, not included in Table IX., which had been highly 
favoured by being grown in separate pots, contained the large 
average number of 5 1 seeds per capsule. 

TABLE IX. {Eighth Generation.') 



No. of Pot. 


Crossed Plants. 


Self-fertilised Plants. 


I. 


Inches, 
llli 
127 
130 J 


Inches. 
96 
54 
93 J 


II. 


97? 
89 j 


94 

125 {j 


III. 


103 f 

100 1 

147 3 


1151 
84] 

109| 


Total inches. 


908-25 


773-25 



Crossed and self-fertilised Plants of the Ninth Generation. 
The plants of this generation were raised in the same manner 
as before, with the result shown in Table X. 

The fourteen crossed plants average in height 81 '39 inches 
and the fourteen self-fertilised plants 64*07, or as 100 to 79. 
One self-fertilised plant in Pot III. exceeded, and one in Pot IV. 
equalled in height, its opponent. The self-fertilised plants 
showed no sign of inheriting the precocious growth of their 
parents; this having been due, as it would appear, to the 
abnormal state of the seeds from the unhealthiness of their 
parents. The fourteen self-fertilised plants yielded only forty 
spontaneously self-fertilised capsules, to which must be added 
seven, the product of ten flowers artificially self-fertilised. On 
the other hand, the fourteen crossed plants yielded 152 spon- 
taneously self-fertilised capsules ; but thirty-six flowers on these 
plants were crossed (yielding thirty-three capsules), and these 
flowers would probably have produced about thirty sponta- 
neously self-fertilised capsules. Therefore an equal number 
of the crossed and self-fertilised plants would have produced 
capsules in the proportion of about 182 to 47, or as 100 to 26. 
Another phenomenon was well pronounced in this generation, 
but I believe had occurred previously to a slight extent ; 



40 



IPOMCEA PUEPUKEA. 



CHAF. II. 



namely, that most of the flowers on the self-fertilised plants 
were somewhat monstrous. The monstrosity consisted in the 
corolla being irregularly split so that it did not open properly, 
with one or two of the stamens slightly foliaceous, coloured, 
and firmly coherent to the corolla. I observed this monstrosity 
in only one flower on the crossed plants. The self-fertilised 
plants, if well nourished, would almost certainly, in a few more 
generations, have produced double flowers, for they had already 
become in some degree sterile.* 

TABLE X. (Ninth Generation.) 



No. of Pot. 


Crossed Plants. 


Self-fertilised Plants. 


I. 


Inches. 
83 1 
gft] 

83 1 


Inches. 
57 
71 
48 


II, 


83 
* 64 
MJ 


45 
43 1 
38 1 


III. 


79 
88 J 
61 


63 
71 
89$ 


IV. 


82 | 

90 


82 1 
76 


V. 

Crowded plants. 


89 1 
92 1 

92J 


67 
741 

70 


Total inches. 


1139-5 


897-0 



Crossed and self -fertilised Plants of the Tenth Generation. Six 
plants were raised in the usual manner from the crossed plants 
of the last generation (Table X.) again intercrossed, and from 
the self-fertilised again self-fertilised. As one of the crossed 
plants in Pot I. in the following table became much diseased, 
having crumpled leaves, and producing hardly any capsules, it 
and its opponent have been struck out of the table. 



* See on this subject ' Variation 
of Animals and Plants under 



Domestication,' chap, xviii. 2nd 
edit vol. i/. p. 152. 



CHAP. II. FLOWERS ON SAME PLANT CROSSED. 
TABLE XI. (Tenth Generation.') 



41 



No. of Pot. 


Crossed Plants. 


Self-fertilised Plants. 


I. 


Inches. 
92 i 

94| 


Inches. 
47 i 
34 


II. 


87 
89 i 
105 


54 1 
49 
66 1 


Total inches. 


468-5 


252-0 



The five crossed plants average 93 '7 inches, and the five self- 
fertilised only 50-4, or as 100 to 54. This difference, however, 
is so great that it must be looked at as in part accidental. The 
six crossed plants (the diseased one here included) yielded spon- 
taneously 101 capsules, and the six self-fertilised plants 88, 
the latter being chiefly produced by one of the plants. But as 
the diseased plant, which yielded hardly any seed, is here included, 
the ratio of 101 to 88 does not fairly give the relative fertility 
of the two lots. The stems of the six crossed plants looked so 
much finer than those of the six self-fertilised plants, that after 
the capsules had been gathered and most of the leaves had fallen 
off, they were weighed. Those of the crossed plants weighed 
2,693 grains, whilst those of the self-fertilised plants weighed 
only 1,173 grains, or as 100 to 44; but as the diseased and 
dwarfed crossed plant is here included, the superiority of the 
former in weight was really greater. 

The Effects on the Offspring of crossing different Flowers 
on the same Plant, instead of crossing distinct Individuals. 
In all the foregoing experiments, seedlings from 
flowers crossed by pollen from a distinct plant (though 
in the later generations more or less closely related) 
were put into competition with, and almost invariably 
proved markedly superior in height to the offspring 
from self-fertilised flowers. I wished, therefore, to 
ascertain whether a cross between two flowers on the 
same plant would give to the offspring any superiority 



42 IPOMCEA PUKPUEEA. CHAP. II. 

over the offspring from flowers fertilised with their 
own pollen. I procured some fresh seed and raised 
two plants, which were covered with a net ; and several 
of their flowers were crossed with pollen from a dis- 
tinct flower on the same plant. Twenty-nine capsules 
thus produced contained on an average 4 -86 seeds per 
capsule ; and 100 of these seeds weighed 36 77 grains. 
Several other flowers were fertilised with their own 
pollen, and twenty-six capsules thus produced con- 
tained on an average 4 - 42 seeds per capsule; 100 of 
which weighed 42 61 grains. So that a cross of this 
kind appears to have increased slightly the number of 
seeds per capsule, in the ratio of 100 to 91 ; but these 
crossed seeds were lighter than the self-fertilised in the 
ratio of 86 to 100. I doubt, however, from other 
observations, whether these results are fully trust- 
worthy. The two lots of seeds, after germinating on 
sand, were planted in pairs on the opposite sides of 
nine pots, and were treated in every respect like the 
plants in the previous experiments. The remaining 
seeds, some in a state of germination and some not 
so, were sown on the opposite sides of a large pot 
(No. X.) ; and the four tallest plants on each side of 
this pot were measured. The result is shown in 
Table XII. 

The average height of the thirty-one crossed plants is 
73 23 inches, and that of the thirty-one self-fertilised 
plants 77-41 inches; or as 100 to 106. Looking to 
each pair, it may be seen that only thirteen of the 
crossed plants, whilst eighteen of the self-fertilised 
plants exceed their opponents. A record was kept with 
respect to the plant which flowered first in each pot ; 
and only two of the crossed flowered before one of the 
self-fertilised in the same pot ; whilst eight of the self- 
fertilised flowered first. It thus appears that the 



OHAP. II. FLOWERS ON SAME PLANT CROSSED. 



43 



TABLE XTL 



No. of Pot. 


Crossed Plants. 


Self-fertilised Plants. 




Inches. 


Inches. 


I. 


82 


77j 




75 


87 




65 


64 




76 


871 


II. 


78 3 


84 




43 


86 3 




65$ 


90 i 


in. 


61? 


86 




85 


69 | 




89 


87| 


IV. 


83 


803 




73 1 

67 


88 i 
8*3 


v. 


78 


663 




76 i 


77* 




57 


811 


VL 


703 


80 




79 


823 




79| 


553 


VII. 


76 


77 




84 1 
79 


?33 


VIII. 


73 


763 




67 


82 




83 


80, 


IX. 


73 1 

78 


783 
673 


X. 


34 


823 


Crowded plants. 


82 
84| 


36 f 
693 




71 


75 


Total inches. 


2270-25 


2399-75 



44 POMCEA PUEPUEEA. CHAP. II. 

crossed plants are slightly inferior in height and in 
earliness of flowering to the self-fertilised. But the 
inferiority in height is so small, namely as 100 to 106, 
that I should have felt very doubtful on this head, 
had I not cut down all the plants (except those 
in the crowded pot No. X.) close to the ground and 
weighed them. The twenty -seven crossed plants 
weighed 16 ounces, and the twenty-seven self-fer- 
tilised plants 20 ounces; and this gives a ratio of 
100 to 124. 

A self-fertilised plant of the same parentage as those 
in Table XII. had been raised in a separate pot for a 
distinct purpose ; and it proved partially sterile, the 
anthers containing very little pollen. Several flowers 
on this plant were crossed with the little pollen which 
could be obtained from the other flowers on the same 
plant ; and other flowers were self-fertilised. From the 
seeds thus produced four crossed and four self- fertilised 
plants were raised, which were planted in the usual 
manner on the ojfposite sides of two pots. All these 
four crossed plants were inferior in height to their 
opponents ; they averaged 78 18 inches, whilst the 
four self-fertilised plants averaged 84 '8 inches ; or as 
100 to 108.* This case, therefore, confirms the last. 
Taking all the evidence together, we must conclude 
that these strictly self-fertilised plants grew a little 
taller, were heavier, and generally flowered before 
those derived from a cross between two flowers on the 
same plant. These latter plants thus present a won- 
derful contrast with those derived from a cross between 
two distinct individuals. 



* From one of these self-ferti- an average only 3' 2 seeds per 

Used plants, spontaneously self- capsule; so that this plant had 

fertilised, I gathered twenty-four apparently inherited some of the 

capsules, and they contained on sterility of its parent. 



CHAP. II. CROSS WITH A FRESH STOCK. 45 

The Effects on the Offspring of a Cross with a distinct 
or fresh Stock belonging to the same Variety. From the 
two foregoing series of experiments we see, firstly, the 
good effects during several successive generations of 
a cross between distinct plants, although these were 
in some degree inter-related and had been grown 
under nearly the same conditions ; and, secondly, the 
absence, of all such good effects from a cross between 
flowers on the same plant ; the comparison in both 
cases being made with the offspring of flowers fertilised 
with their own pollen. The experiments now to be 
given show how powerfully and beneficially plants, 
which have been intercrossed during many successive 
generations, having been kept all the time under 
nearly uniform conditions, are affected by a cross with 
another plant belonging to the same variety, but to a 
distinct family or stock, which had grown under dif- 
ferent conditions. 

Several flowers on the crossed plants of the ninth generation 
in Table X., were crossed with pollen from another crossed plant 
of the same lot. The seedlings thus raised formed the tenth 
intercrossed generation, and I will call them the " intercrossed 
plants" Several other flowers on the same crossed plants ot 
the ninth generation were fertilised (not having been castrated) 
with pollen taken from plants of the same variety, but belonging 
to a distinct family, which had been grown in a distant garden 
at Colchester, and therefore under somewhat different conditions. 
The capsules produced by this cross contained, to my surprise, 
fewer and lighter seeds than did the capsules of the intercrossed 
plants ; but this, I think, must have been accidental. The seed- 
lings raised from them I will call the " Colchester-crossed." The 
two lots of seeds, after germinating on sand, were planted in 
the usual manner on the opposite sides of five pots, and the 
remaining seeds, whether or not in a state of germination, 
were thickly sown on the opposite sides of a very large pot, 
No. VI., in Table XIII. In three of the six pots, after the 
young plants had twined a short way up their sticks, one of the 



46 



IPOMOSA PUKPUEEA. 



CHAP. II. 



Colchester-crossed plants was much taller than any one of 
the intercrossed plants on the opposite side of the same pot ; 
and in the three other pots somewhat taller. I should state 
that two of the Colchester-crossed plants in Pot JV., when 
about two-thirds grown, became much diseased, and were, 
together with their intercrossed opponents, rejected. The 
remaining nineteen plants, when almost fully grown, were 
measured, with the following result : 



TABLE XIII. 



No. of Pot. 


Colchester-crossed 
Plants. 


Intercrossed Plants of 
the Tenth Generation. 


I. 


Inches. 
87 
87 3 
85| 


Inches. 
78 
68 1 
94| 


II. 


93 g 
85 1 
90| 


60 
87 
45| 


HI. 


84 
92 
85 


70J 

81| 
86 


IV. 


95f 


65$ 


V. 


90 1 

^ 


85 1 
63 
62f 


VI. 

Crowded plants in a 
very large pot. 


90 1 
75 
71 
83 . 
63 
65 


43 1 
39 i 
30 
86 
53 
48f 


Total inches. 


1596-50 


1249-75 



In sixteen out of these nineteen pairs, the Colchester-crossed 
plant exceeded in height its intercrossed opponent. The average 
height of the Colchester-crossed is 84 '03 inches, and that of 
the intercrossed 65 "78 inches; or as 100 to 78. With respect 



CHAP. II. DESCENDANTS OF HERO. 47 

to the fertility of the two lots, it was too troublesome to collect 
and count the capsules on all the plants ; so I selected two of 
the best pots, V. and VI., and in these the Colchester-crossed 
produced 269 mature and half-mature capsules, whilst an equal 
number of the intercrossed plants produced only 154 capsules ; 
or as 100 to 57. By weight the capsules from the Colchester- 
crossed plants were to those from the intercrossed plants as 
100 to 51 ; so that the former probably contained a somewhat 
larger average number of seeds. 



We learn from this important experiment that 
plants in some degree related, which had been inter- 
crossed during the nine previous generations, when they 
were fertilised with pollen from a fresh stock, yielded 
seedlings as superior to Jhe seedlings of the tenth 
intercrossed generation, as these latter were to the self- 
fertilised plants of the corresponding generation. For 
if we look to the plants of the ninth generation in 
Table X. (and these offer in most respects the fairest 
standard of comparison) we find that the intercrossed 
plants were in height to the self-fertilised as 100 to 79, 
and in fertility as 100 to 26 ; whilst the Colchester- 
crossed plants are in height to the intercrossed as 100 
to 78, and in fertility as 100 to 51. 



The Descendants of the self-fertilised Plant, named Hero, which 
appeared in the Sixth self-fertilised Generation. In the five genera 
tions before the sixth, the crossed plant of each pair was taller 
than its self-fertilised opponent; but in the sixth generation 
(Table VII., Pot II.) the Hero appeared, which after a long and 
dubious struggle conquered its crossed opponent, though by 
only half an inch. I was so much surprised at this fact, that 
I resolved to ascertain whether this plant would transmit 
its powers of growth to its seedlings. Several flowers on 
Hero were therefore fertilised with their own pollen, and the 
seedlings thus raised were put into competition with self-fer- 
tilised and intercrossed plants of the corresponding generation. 
The three lots of seedlings thus all belong to the seventh genera- 



48 IPOMCEA PURPUREA. CHAP. II, 

tion. Their relative heights are shown in the two following 
TABLE XIV. 



No. of Pot. 


Self-fertilised Plants 
of the Seventh Gene- 
ration, Children of 


Self-fertilised Plants 
of the Seventh Gene- 
ration. 


L 


Inches. 
74 
60 
55 


Inches. 
894 
61 
49 


II. 


92 
91 1 

74 


82 
56 
38 


Total inch*.. 


447-25 


375-50 



The average height of the six self-fertilised children of Hero 
is 74 54 inches, whilst that of the ordinary self-fertilised plants 
of the corresponding generation is only 62 -58 inches, or as 100 
to 84. 

TABLE XV. 



No. of Pot. 


Self-fertilised Plants 
of the Seventh Gene- 
ration, Children of 
Hero. 


Intercrossed Plants of 
the Seventh Gene- 
ration. 


III. 


Inches. 
92 


Inches. 
76 1 


IV. 


87 
87i 


89 
86 1 


Total inches. 


266-75 


252-50 



Here the average height of the three self-fertilised children of 
Hero is 88 '91 inches, whilst that of the intercrossed plants is 
84-16; or as 100 to 95. We thus see that the self-fertilised 
children of Hero certainly inherit the powers of growth of their 
parents; for they greatly exceed in height the self-fertilised 
offspring of the other self-fertilised plants, and even exceed 
by a trifle the intercrossed plants, all of the corresponding 
generation. 



ClIAP. II. 



DESCENDANTS OF HERO. 



Several flowers on the self-fertilised children of Hero in Table 
XIV. were fertilised with pollen from the same flower; and from 
the seeds thus produced, self-fertilised plants of the eighth 
generation (grand-children of Hero) were raised. Several other 
flowers on the same plants were crossed with pollen from the other 
children of Hero. The seedlings raised from this cross may be 
considered as the offspring of the union of brothers and sisters. 
Tho result of the competition between these two sets of seedlings 
(namely self-fertilised and the offspring of brothers and sisters) 
is given in the following table : 

TABLE XVI. 



No. of Pot. 


Self-fertilised Grand- 
children of Hero, 
from the Self-fertilised 
Children. Eighth 
Generation. 


Grandchildren from a 
cross between the self- 
fertilised Children of 
Hero. Eighth Gene- 
ration. 


I. 


Inches. 
86 1 
90| 


Inches. 
95 1 
95| 


II. 


96 

V7 


85 

93 


IIL 


73 
66 
84j 


86 
82 1 

70| 


rv. 


S 1 
5 1 


66? 

15 i 

38 

78i 


V. 


SI 


82 1 
83$ 


Total inches. 


1037-00 


973-13 



The average height of the thirteen self-fertilised grandchildren 
of Hero is 79 '76 inches, and that of the grandchildren from a 
cross between the self-fertilised children is 74 85 ; or as 100 to 94. 
But in Pot IV. one of the crossed plants grew only to a height of 
15i inches ; and if this plant and its opponent are struck out, as 
would be the fairest plan, the average height of the crossed 
plants exceeds, but only by a fraction of an inch, that of the self- 



50 IPOMCEA PURPUREA. CHAP. II. 

fertilised plants. It is therefore clear that a cross between the 
self-fertilised children of Hero did not produce any beneficial effect 
worth notice ; and it is very doubtful whether this negative result 
can be attributed merely to the fact of brothers and sisters having 
been united, for the ordinary intercrossed plants of the several 
successive generations must often have been derived from the 
union of brothers and sisters (as shown in Chap. I.), and yet all 
of them were greatly superior to the self-fertilised plants. We 
are therefore driven to the suspicion, which we shall soon see 
strengthened, that Hero transmitted to its offspring a peculiar 
constitution adapted for self-fertilisation. 

It would appear that the self-fertilised descendants of Hero 
have not only inherited from Hero a power of growth equal to 
that of the ordinary intercrossed plants, but have become more 
fertile when self-fertilised than is usual with the plants of the 
present species. The flowers on the self-fertilised grandchildren 
of Hero in Table XVI. (the eighth generation of self-fertilised 
plants) were fertilised with their own pollen and produced plenty 
of capsules, ten of which (though this is too few a number for a 
safe average) contained 5'2 seeds per capsule, a higher average 
than was observed in any other case with the self-fertilised plants. 
The anthers produced by these self-fertilised grandchildren were 
also as well developed and contained as much pollen as those on 
the intercrossed plants of the corresponding generation ; whereas 
this was not the case with the ordinary self-fertilised plants of 
the later generations. Nevertheless some few of the flowers 
produced by the grandchildren of Hero were slightly monstrous, 
like those of the ordinary self-fertilised plants of the later genera- 
tions. In order not to recur to the subject of fertility, I may add 
that twenty-one self-fertilised capsules, spontaneously produced 
by the great-grandchildren of Hero (forming the ninth generation 
of self-fertilised plants), contained on an average 4 47 seeds ; and 
this is as high an average as the self-fertilised flowers of any 
generation usually yielded. 

Several flowers on the self-fertilised grandchildren of Hero in 
Table XVI. were fertilised with pollen from the same flower ; and 
the seedlings raised from them (great-grandchildren of Hero) 
formed the ninth self-fertilised generation. Several other flowers 
were crossed with pollen from another grandchild, so that they 
may be considered as the offspring of brothers and sisters, and the 
seedlings thus raised may be called the intercrossed great-grand- 
children. And lastly, other flowers were fertilised with pollen 



CHAP. II. SUMMARY OF OBSERVATIONS. 51 

from a distinct stock, and the seedlings thus raised may be 
called the Colchester-crossed great-grandchildren. In my anxiety 
to see what the result would be, I unfortunately planted the 
three lots of seeds (after they had germinated on sand) in the 
hothouse in the middle of winter, and in consequence of this the 
seedlings (twenty in number of each kind) became very unhealthy, 
some growing only a few inches in height, and very few to their 
proper height. The result, therefore, cannot be fully trusted ; 
and it would be useless to give the measurements in detail. In 
order to Strike as fair an average as possible, I first excluded all 
the plants under 50 inches in height, thus rejecting all the most 
unhealthy plants. The six self-fertilised thus left were on an 
average 66 '86 inches high; the eight intercrossed plants 63 '2 
high; and the seven Colchester-crossed 65 '37 high; so that 
there was not much difference between the three sets, the self- 
fertilised plants having a slight advantage. Nor was there any 
great difference when only the plants under 36 inches in height 
were excluded. Nor again when all the plants, however much 
dwarfed and unhealthy, were included. In this latter case the 
Colchester-crossed gave the lowest average of all ; and if these 
plants had been in any marked manner superior to the other 
two lots, as from my former experience I fully expected they 
would have been, I cannot but think that some vestige of such 
superiority would have been evident, notwithstanding the very 
unhealthy condition of most of the plants. No advantage, as far 
as we can judge, was derived from intercrossing two of the 
grandchildren of Hero, any more than when two of the children ' 
were crossed. It appears therefore that Hero and its descendants 
have varied from the common type, not only in acquiring great 
power of growth, and increased fertility when subjected to self- 
fertilisation, but in not profiting from a cross with a distinct 
stock ; and this latter fact, if trustworthy, is a unique case, as 
far as I have observed in all my experiments. 

Summary on the Growth, Vigour, and Fertility of the 
successive Generations of the crossed and self-fertilised 
Plants of Ipomcea purpurea, together with some miscel- 
laneous Observations. 

In the followi ag table, No. XVII., we see the average 
or mean heights of the ten successive generations of 
the intercrossed and self-fertilised plants, grown in 

E 2 



52 



IPOMCEA PUEPUREA. 



CIIAP. Jl. 



competition with each other; and in the right-hand 
column we have the ratios of the one to the other, the 
height of the intercrossed plants being taken at 100. 
In the bottom line the mean height of the seventy- 
three intercrossed plants is shown to be 85 84 inches, 
and that of the seventy-three self-fertilised plants 
66-02 inches, or as 100 to 77. 

TABLE XVII. 

Jpomcea purpurea. Summary of Measurements (in Inches) of 
the Ten Generations. 



Number of the Generation. 


Number 
of 
Crossed 
Plants. 


Average 
Height 
of Crossed 
Plants. 


Number 
of Self- 
ferti- 
lised 
Plants. 


Average 
Height ol 
Self-ferti 
lised 
Plants. 


Ratio between 
Average 
Heights of 
Crossed and 
Self-fertilised 
Plants. 


First generation . 
Table I. 


6 


86-00 


6 


65-66 


as 100 to 76 


Second generation . 
Table II. 


6 


84-16 


6 


66-33 


as 100 to 79 


Third generation. . . 
Table III. 


6 


77-41 


6 


52-83 


is 100 to 68 


Fourth generation 
Table V. 


7 


69-78 


7 


60-14 


as 100 to 86 


Fifth generation . 
Table VI. 


6 


82-54 


6 


62-33 


as 100 to 75 


Sixth generation . 
Table VII. 


6 


87-50 


6 


63-16 


as 100 to 72 


Seventh generation . 
Table VIII. 


9 


83-94 


9 


68-25 


as 100 to 81 


Eighth generation 
Table IX. 


8 


113-25 


8 


96-65 


as 100 to 85 


Ninth generation . - - J 
Table X. 


14 


81-39 ! 


14 


64-07 


as 100 to 79 


Tenth generation 
Table XI. 


5 


93-70 


5 


50-40 


as 100 to 54 


All the ten generations'! 
taken together . ./ 


73 


85-84 


73 


66-02 


is 100 to 77 



CHAP. II. 



SUMMARY OF OBSERVATIONS. 



53 



The mean height of the self-fertilised plants in 
each of the ten generations is also shown in the 
accompanying diagram, that of the intercrossed plants 
being taken at 100 ; and on the right side we see 
the relative heights of the seventy-three intercrossed 
plants, and of the seventy-three self-fertilised plants. 
The difference in height between the crossed and 



Diagram showing the mean heights of the crossed and self-fertilised 
plants of Iponvxa purpurea in the ten generations ; the mean height of the 
crossed plants being taken as 100. On the right hand, the mean heights of 
the crossed and self-fertilised plants of all the generations taken together 
are shown. 

self-fertilised plants will perhaps be best appreciated 
by an illustration : If all the men in a country were 
on an average 6 feet high, and there were some families 
which had been long and closely interbred, these 
would be almost dwarfs, their average height during 
ten generations being only 4 feet 8 inches. 



54 IPOMCEA PUEPUEEA. CHAP. II 

It should be especially observed that the average dif- 
ference between the crossed and self-fertilised plants 
is not due to a few of the former having grown to an 
extraordinary height, or to a few of the self-fertilised 
being extremely short, but to all the crossed plants 
having surpassed their self-fertilised opponents, with 
the few following exceptions. The first occurred in 
the sixth generation, in which the plant named " Hero'" 
appeared ; two in the eighth generation, but the self- 
fertilised plants in this generation were in an anomalous 
condition, as they grew at first at an unusual rate and 
conquered for a time the opposed crossed plants ; and 
two exceptions in the ninth generation, though one 
of these plants only equalled its crossed opponent. 
Therefore, of the seventy-three crossed plants, sixty- 
eight grew to a greater height than the self-fertilised 
plants, to which they were opposed. 

In the right-hand column of figures, the difference 
in height between the crossed and self-fertilised plants 
in the successive generations is seen to fluctuate much, 
as might indeed have been expected from the small 
number of plants measured in each generation being 
insufficient to give a fair average. It should be 
remembered that the absolute height of the plants 
goes for nothing, as each pair was measured as 
soon as one of them had twined up to the summit 
of its rod. The great difference in the tenth genera- 
tion, viz., 100 to 54, no doubt was partly accidental, 
though, when these plants were weighed, the differ- 
ence was even greater, viz., 100 to 44. The smallest 
amount of difference occurred in the fourth and the 
eighth generations, and this was apparently due to 
both the crossed and self-fertilised plants having 
become unhealthy, which prevented the former attain- 
ing their usual degree of superiority. This was an 



CHAP. II. SUMMARY OF OBSERVATIONS. 55 

unfortunate circumstance, but my experiments were 
not thus vitiated, as both lots of plants were exposed 
to the same conditions, whether favourable or un- 
favourable. 

There is reason to believe that the flowers of this 
Ipomoaa, when growing out of doors, are habitually 
crossed by insects, so that the first seedlings which I 
raised /rom purchased seeds were probably the offspring 
of a cross. I infer that this is the case, firstly from 
humble-bees often visiting the flowers, and from the 
quantity of pollen left by them on the stigmas of su-ch 
flowers ; and, secondly, from the plants raised from the 
same lot of seed varying greatly in the colour of their 
flowers, for as we shall hereafter see, this indicates 
much intercrossing.* It is, therefore, remarkable 
that the plants raised by me from flowers which were, 
in all probability, self-fertilised for the first time after 
many generations of crossing, should have been so 
markedly inferior in height to the intercrossed plants 
as they were, namely, as 76 to 100. As the plants 
which were self-fertilised in each succeeding generation 
necessarily became much more closely interbred in 
the later than in the earlier generations, it might have 
been expected that the difference in height between 
them and the crossed plants would have gone on in- 
creasing ; but, so far is this from being the case, that 
the difference between the two sets of plants in the 
seventh, eighth, and ninth generations taken together 
is less than in the first and second generations together. 
When, however, we remember that the self-fertilised 
and crossed plants are all descended from the same 



* Verlot says (' Sur la Produo- color, cannot be kept pure unless 

tion des Vur^tes,' 1865, p. 66) grown at a distance from all otbei 

that certain varieties of a closely varieties, 
allied plant, the Convolvulus tri- 



56 IPOMGEA PURPUKEA. CHAP. IL 

mother-plant, that many of the crossed plants in each 
generation were related, often closely related, and that 
all were exposed to the same conditions, which, as we 
shall hereafter find, is a very important circumstance, it 
is not at all surprising that the difference between 
them should have somewhat decreased in the later 
generations. It is, on the contrary, an astonishing fact, 
that the crossed plants should have been victorious, 
even to a slight degree, over the self-fertilised plants 
of the later generations. 

The much greater constitutional vigour of the 
crossed than of the self-fertilised plants, was proved on 
five occasions in various ways ; namely, by exposing 
them, while young, to a low temperature or to a 
sudden change of temperature, or by growing them, 
under very unfavourable conditions, in competition 
with full-grown plants of other kinds. 

With respect to the productiveness of the crossed 
and self-fertilised plants of the successive generations, 
my observations unfortunately were not made on any 
uniform plan, partly from the want of time, and partly 
from not having at first intended to observe more than 
a single generation. A summary of the results is here 
given in a tabulated form, the fertility of the crossed 
plants being taken as 100. 

First Generation of crossed and self-fertilised Plants 
growing in competition with one another. Sixty-five 
capsules produced from flowers on five crossed plants 
fertilised by pollen from a distinct plant, and fifty-five 
capsules produced from flowers on five self-fertilised 
plants fertilised by their own pollen, contained seeds 
in the proportion of 100 to 93 

Fifty-six spontaneously self-fertilised capsules on 
the above five crossed plants, and twenty-five sponta- 
neously self-fertilised capsules on the above five self- 
fertilised plants, yielded seeds in the proportion of . 100 to 99 



CHAP. II. 



SUMMARY OF OBSERVATIONS. 



57 






Combining the total number of capsules produced 
by these plants, and the average number of seeds in 
each, the above crossed and self-fertilised plants 
yielded seeds in the proportion of . . . . 100 to 64 

Other plants of this first generation grown under 
unfavourable conditions and spontaneously self-ferti- 
lised, yielded seeds in the proportion of . . . 100 to 45 

TJiird Generation <f crossed and self-fertilised Plants. 
Crossed capsules compared with self-fertilised cap- 
sules contained seeds in the ratio of ... 100 to 94 

An equal number of crossed and self-fertilised 
plants, both spontaneously self-fertilised, produced 
capsules in the ratio of . . ... . . 100 to 38 

And these capsules contained seeds in the ratio of . 100 to 94 

Combining these data, the productiveness of the 
crossed to the self-fertilised plants, both spontane- 
ously self-fertilised, was as 100 to 35 

Fourth Generation of crossed and self -fertilised flants. 
Capsules from flowers on the crossed plants ferti- 
lised by pollen from another plant, and capsules from 
flowers on the self-fertilised plants fertilised with their 
own pollen, contained seeds in the proportion of . 100 to 94 

Fifth Veneration of crossed and self-fertilised Plants. 
The crossed plants produced spontaneously a vast 
number more pods (not actually counted) than the 
self-fertilised, and these contained seeds in the pro- 
portion of 100 to 89 

Ninth Generation of crossed and self-fertilised Plants. 
Fourteen crossed plants, spontaneously self-ferti- 
lised, and fourteen self-fertilised plants spontaneously 
self-fertilised, yielded capsules (the average number 
of seeds per capsule not having been ascertained) in 
the proportion of 100 to 26 

Plants derived from a cross with a fresh Stock com- 
pared with intercrossed Plants. The offspring of inter- 
crossed plants of the ninth generation, crossed by a 
fresh stock, compared with plants of the same stock 
intercrossed during ten generations, both sets of plants 
left uncovered and naturally fertilised, produced 
capsules by weight as 100 to 51 

We see in this table that the crossed plants are 



58 IPOMCEA PURPUREA. CIUP. II 

always in some degree more productive than the self- 
fertilised plants, by whatever standard they are com- 
pared. The degree differs greatly ; but this depends 
chiefly on whether an average was taken of the seeds 
alone, or of the capsules alone, or of both combined. 
The relative superiority of the crossed plants is chiefly 
due to their producing a much greater number of cap- 
sules, and not to each capsule containing a larger 
average number of seeds. For instance, in the third 
generation the crossed and self-fertilised plants pro- 
duced capsules in the ratio of 100 to 38, whilst the 
seeds in the capsules on the crossed plants were to 
those on the self-fertilised plants only as 100 to 94. 
In the eighth generation the capsules on two self- 
fertilised plants (not included in the above table), 
grown in separate pots and thus not subjected to any 
competition, yielded the large average of 5'1 seeds. 
The smaller number of capsules produced by the self- 
fertilised plants may be in part, but not altogether, 
attributed to their lessened size or height ; this being 
chiefly due to their lessened constitutional vigour, so 
that they were not able to compete with the crossed 
plants growing in the same pots. The seeds produced 
by the crossed flowers on the crossed plants were not 
always heavier than the self-fertilised seeds on the 
self-fertilised plants. The lighter seeds, whether pro- 
duced from crossed or self-fertilised flowers, generally 
germinated before the heavier seeds. I may add that 
the crossed plants, with very few exceptions, flowered 
before their self-fertilised opponents, as might have 
been expected from their greater height and vigour. 

The impaired fertility of the self-fertilised plants was 
shown in another way, namely, by their anthers being 
smaller than those in the flowers on the crossed plants. 
This was first observed in the seventh generation, but 



CHAP. II. SUMMARY OF OBSERVATIONS. 59 

may have occurred earlier. Several anthers from flowers 
on the crossed and self-fertilised plants of the eighth 
generation were compared under the microscope ; and 
those from the former were generally longer and plainly 
broader than the anthers of the self-fertilised plants. 
The quantity of pollen contained in one of the latter 
was, as far as could be judged by the eye, about half 
of that Contained in one from a crossed plant. The 
impaired fertility of the self-fertilised plants of the 
eighth generation was also shown in another manner, 
which may often be observed in hybrids namely, by the 
first-formed flowers being sterile. For instance, the 
fifteen first flowers on a self-fertilised plant of one of the 
later generations were carefully fertilised with their 
own pollen, and eight of them dropped off; at the same 
time fifteen flowers on a crossed plant growing in the 
same pot were self-fertilised, and only one dropped off. 
On two other crossed plants of the same generation, 
several of the earliest flowers were observed to fertilise 
themselves and to produce capsules. In the plants of 
the ninth, and I believe of some previous generations, 
very many of the flowers, as already stated, were 
slightly monstrous ; and this probably was connected 
with their lessened fertility. 

All the self-fertilised plants of the seventh genera- 
tion, and I believe of one or two previous generations, 
produced flowers of exactly the same tint, namely, of a 
rich dark purple. So did all the plants, without any 
exception, in the three succeeding generations of self- 
fertilised plants ; and very many were raised on account 
of other experiments in progress not here recorded. 
My attention was first called to this fact by my 
gardener remarking that there was no occasion to label 
the self-fertilised plants, as they could always be known 
by their colour. The flowers were as uniform in tint 



60 IPOMCEA PURPUREA. CHAP. IL 

as those of a wild species growing in a state of nature ; 
whether the same tint occurred, as is probable, in the 
earlier generations, neither my gardener nor self could 
recollect. The flowers on the plants which were first 
raised from purchased seed, as well as during the first 
few generations, varied much in the depth of the 
purple tint ; many were more or less pink, and occa- 
sionally a white variety appeared. The crossed plants 
continued to the tenth generation to vary in the same 
manner as before, but to a much less degree, owing, 
probably, to their having become more or less closely 
inter-related. We must therefore attribute the extra- 
ordinary uniformity of colour in the flowers on the 
plants of the seventh and succeeding self-fertilised 
generations, to inheritance not having been interfered 
with by crosses during several preceding generations, 
in combination with the conditions of life having been 
very uniform. 

A plant appeared in the sixth self-fertilised genera- 
tion, named the Hero, which exceeded by a little in 
height its crossed antagonist, and which transmitted 
its powers of growth and increased self-fertility to its 
children and grandchildren. A cross between the 
childien of Hero did not give to the grandchildren 
any advantage over the self-fertilised grandchildren 
raised from the self-fertilised children. And as far as 
my observations can be trusted, which were made on 
very unhealthy plants, the great-grandchildren raised 
from intercrossing the grandchildren had no advantage 
over the seedlings from the grandchildren the product 
of continued self-fertilisation ; and what is far more 
remarkable, the great-grandchildren raised by crossing 
the grandchildren with a fresh stock, had no advantage 
over either the intercrossed or self-fertilised great- 
grandchildren. It thus appears that Hero and ita 






CHAP. II. SUMMARY OF OBSERVATIONS. 61 

descendants differed in constitution in an extraordinary 
manner from ordinary plants of the present species. 

Although the plants raised during ten successive 
generations from crosses between distinct yet inter- 
related plants almost invariably exceeded in height, 
constitutional vigour, and fertility their self-fertilised 
opponents, it has been proved that seedlings raised 
by intercrossing flowers on the same plant are by no 
means superior, on the contrary are somewhat inferior 
in height and weight, to seedlings raised from flowers 
fertilised with their own pollen. This is a remarkable 
fact, which seems to indicate that self-fertilisation is 
in some manner more advantageous than crossing, 
unless the cross brings with it, as is generally the case, 
some decided and preponderant advantage ;Jbut to this 
subject I shall recur in a future chapter. 

The benefits which so generally follow from a 
cross between two plants apparently depend on the 
two differing somewhat in constitution or character. 
This is shown by the seedlings from the intercrossed 
plants of the ninth generation, when crossed with 
pollen from a fresh stock, being as superior in 
height and almost as superior in fertility to the again 
intercrossed plants, as these latter were to seedlings 
from self-fertilised plants of the corresponding gene- 
ration. We thus learn the important fact that the 
mere act of crossing two distinct plants, which are 
in some degree inter-related and which have been 
long subjected to nearly the same conditions, does 
little good as compared with that from a cross between 
plants belonging to different stocks or families, and 
which have been subjected to somewhat different con- 
ditions. We may attribute the good derived from 
the crossing of the intercrossed plants during the 
ten successive generations to their still differing some- 



62 IPOMCEA PUBPUEEA. CHAP. IL 

what in constitution or character, as was indeed proved 
by their flowers still differing somewhat in colour. 
But the several conclusions which may be deduced 
from the experiments on Ipomcea will be more fully 
considered in the final chapters, after all my other 
observations have been given. 



CHAP. III. MIMULUS LUTEUS. ' 63 



CHAPTEE III. 

S(#OPHULARIACEJI, GESNEBIACKffl, L.ABIATJS, ETC. 



Mimulus luteus ; height, vigour, and fertility of the crossed and self- 
fertilised plants of the first four generations Appearance of a 
new, tall, and highly self-fertile variety Offspring from a cross 
between self-fertilised plants Effects of a cross with a fresh stock 

Effects of crossing flowers on the same plant Summary on 
Mimulus luteus Digitalis purpurea, superiority of the crossed 
plants Effects of crossing flowers on the same plant Calceolaria 

Linaria vulgaris Verbascum thapsus Vandellia nummulari- 
folia Cleistogamic flowers Gesneria pendulina Salvia coccinea 
Origanum vulgare, great increase of the crossed plants by stolons 

Thunbergia alata. 

IN the family of the Scrophulariacese I experimented 
on species in the six following genera : Mimulus, 
Digitalis, Calceolaria, Linaria, Verbascum, and Van- 
dellia. 

II. SCEOPHULAEIACE^E. MIMULUS LUTEUS. 

The plants which I raised from purchased seed varied greatly 
in the colour of their flowers, so that hardly two individuals 
were quite alike ; the corolla being of all shades of yellow, 
with the most diversified blotches of purple, crimson, orange, 
and coppery brown. But these plants differed in no other 
respect.* The flowers are evidently well adapted for fertilisa- 
tion by the agency of insects ; and in the case of a closely allied 
species, M. roseus, I have watched bees entering the flowers, thus 
getting their backs well dusted with pollen; and when they 
entered another flower the pollen was licked off their backs by 



* I sent several specimens with The flowers with much red have 

variously coloured flowers to Kew, been named by horticulturists aa 

nnd Dr. Hooker informs me that var. Youngiana. 
they all consisted of Jf. luteus. 



64 MIMULUS LUTEUS. CHAP. III. 

the two-lipped stigma, the lips of which are irritable and close 
like a forceps on the pollen-grains. If no pollen is enclosed 
between the lips, these open again after a time. Mr. Kitchener 
has ingeniously explained * the use of these movements, namely, 
to prevent the self-fertilisation of the flower. If a bee with 
no pollen on its back enters a flower it touches the stigma, 
which quickly closes, and when the bee retires dusted with 
pollen, it can leave none on the stigma of the same flower. 
But as soon as it enters any other flower, plenty of pollen is 
left on the stigma, which will be thus cross-fertilised. Never- 
theless^ if insects are excluded, the flowers fertilise themselves 
perfectly and produce plenty of seed ; but I did not ascertain 
whether this is effected by the stamens increasing in length 
with advancing age, or by the bending down of the pistil. The 
chief interest in my experiments on the present species, lies in 
the appearance in the fourth self-fertilised generation of a 
variety which bore large peculiarly-coloured flowers, and grew 
to a greater height than the other varieties ; it likewise became 
more highly self-fertile, so that this variety resembles the 
plant named Hero, which appeared in the sixth self-fertilised 
generation of Ipomoea. 

Some flowers on one of the plants raised from the purchased 
seeds were fertilised with their own pollen ; and others on the 
same plant were crossed with pollen from a distinct plant. The 
seeds from twelve capsules thus produced were placed in 
separate watch-glasses for comparison ; and those from the six 
crossed capsules appeared to the eye hardly more numerous 
than those from the six self-fertilised capsules. But when the 
seeds were weighed, those from the crossed capsules amounted 
to 1'02 grain, whilst those from the self-fertilised capsules 
were only '81 grain; so that the former were either heavier or 
more numerous than the latter, in the ratio of 100 to 79. 

Crossed and self -fertilised Plants of the First Generation. Having 
ascertained, by leaving crossed and selMertilised seed on damp 
sand, that they germinated simultaneously, both kinds were 
thickly sown on opposite sides of a broad and rather shallow 
pan ; so that the two sets of seedlings, which came up at the 
same time, were subjected to the same unfavourable conditions. 
This was a bad method of treatment, but this species was one of 
the first on which I experimented. When the crossed seedlings 



' A Year's Botany,' 1874, p. 118. 



CHAP. III. CKOSSED AND SELF-FERTILIaED PLANTS. 65 

were on an average half an inch high, the self-fertilised ones 
were only a quarter of an inch high. When grown to their full 
height under the above unfavourable conditions, the four tallest 
crossed plants averaged 7 '62, and the four tallest self-fertilised 
5 87 inches in height ; or as 100 to 77. Ten flowers on the crossed 
plants were fully expanded before one on the self-fertilised 
plants. A few of these plants of both lots were transplanted 
into a large pot with plenty of good earth, and the self-fertilised 
plants, not now being subjected to severe competition, grew 
during the following year as tall as the crossed plants; but 
from a case which follows it is doubtful whether they would 
have long continued equal. Some flowers on the crossed plants 
were crossed with pollen from another plant, and the capsules 
thus produced contained a rather greater weight of seed than 
those on the self-fertilised plants again self-fertilised. 

Grossed and self -fertilised Plants of the Second Generation, Seeds 
from the foregoing plants, fertilised in the manner just stated, 
were sown on the opposite sides of a small pot (I.) and came up 
crowded. The four tallest crossed seedlings, at the time of 
flowering, averaged 8 inches in height, whilst the four tallest 
self-fertilised plants averaged only 4 inches. Crossed seeds 
were sown by themselves in a second small pot, and self- 
fertilised seeds were sown by themselves in a third small pot ; 
so that there was no competition whatever between these two 
lots. Nevertheless the crossed plants grew from 1 to 2 
inches higher on an average than the self-fertilised. Both lots 
looked equally vigorous, but the crossed plants flowered earlier 
and more profusely than the self-fertilised. In Pot L, in which 
the two lots competed with each other, the crossed plants flowered 
first and produced a large number of capsules, whilst the 
self-fertilised produced only nineteen. The contents of twelve 
capsules from the crossed flowers on the crossed plants, and 
of twelve capsules from self-fertilised flowers on the self-fertilised 
plants, were placed in separate watch-glasses for comparison 
and the crossed seeds seemed more numerous by half than the 
self-fertilised. 

The plants on both sides of Pot I., after they had seeded, 
were cut down and transplanted into a large pot with plenty of 
good earth, and in the following spring, when they had grown 
to a height of between 5 and 6 inches, the two lots were equal, 
as occurred in a similar experiment in the last generation. 
But after some weeks the crossed plants exceeded the self- 



66 MIMULUS LUTEUS. CHAI>. Ill 

fertilised ones on the opposite side of the same pot, though not 
nearly to so great a degree as before, when they were subjected 
to very severe competition. 

Crossed and self-fertilised Plants of the Third Generation. 
Crossed seeds from the crossed plants, and self-fertilised seeds 
from the self-fertilised plants of the last generation, were sown 
thickly on opposite sides of a small pot, No. I. The two tallest 
plants on each side were measured after they had flowered, and 
the two crossed ones were 12 and 7i inches, and the two self- 
fertilised ones 8 and 65 inches in height ; that is, in the ratio of 
100 to 69. Twenty flowers on the crossed plants were again 
crossed and produced twenty capsules ; ten of which contained 
1-33 grain weight of seeds. Thirty flowers on the self-fertilised 
plants were again self-fertilised and produced twenty-six 
capsules ; ten of the best of which (many being very poor) con- 
tained only -87 grain weight of seeds; that is, in the ratio of 
100 to 65 by weight. 

The superiority of the crossed over the self-fertilised plants 
was proved in various ways. Self-fertilised seeds were sown on 
one side of a pot, and two days afterwards crossed seeds on the 
opposite side. The two lots of seedlings were equal until they 
were above half an inch high ; but when fully grown the two 
tallest crossed plants attained a height of 12 and 8t inches, 
whilst the two tallest self-fertilised plants were only 8 and i 2 
inches high. 

In a third pot, crossed seeds were sown four days afte: the 
self-fertilised, and the seedlings from the latter had at first, as 
might have been expected, an advantage; but whe.i the two 
lots were between 5 and 6 inches in height, they were equal, 
and ultimately the three tallest crossed plants were 11, 10, and 
8 inches, whilst the three tallest self-fertilised were 12, 8i, and 
7z inches in height. So that there was not much difference 
between them, the crossed plants having an average advantage 
of only the third of an inch. The plants were cut down, and 
without being disturbed were transplanted into a larger pot. 
Thus the two lots started fair in the following spring, and now 
the crossed plants showed their inherent superiority, for the two 
tallest were 13 inches, whilst the two tallest self-fertilised plants 
were only 11 and 8 2 inches in height ; or as 100 to 75. The 
two lots were allowed to fertilise themselves spontaneously : the 
crossed plants produced a large number of capsules, whilst the 
nelf-fertilised produced very few and poor ones. The seeds 



CHAT. III. CROSSED AND SELF-FERTILISED PLANTS. 67 

from eight of the capsules on the crossed plants weighed 65 
grain, whilst those from eight of the capsules on the self-fer- 
tilised plants weighed only -22 grain; or as 100 to ?4. 

The crossed plants in the above three pots, as in almost all 
the previous experiments, flowered before the self-fertilised. 
This occurred even in the third pot in which the crossed seeds 
were sown four days after the self-fertilised seeds. 

Lastly, seeds of both lots were sown on opposite sides of a 
large pot in which a Fuchsia had long been growing, so that the 
earth was full of roots. Both lots grew miserably ; but the 
crossed seedlings had an advantage at all times, and ultimately 
attained to a height of 3i inches, whilst the self-fertilised seed- 
lings never exceeded 1 inch. The several foregoing experiments 
prove in a decisive manner the superiority in constitutional 
vigour of the crossed over the self-fertilised plants. 

In the three generations now described and taken together, the 
average height of the ten tallest crossed plants was 8*19 inches, 
and that of the ten tallest self-fertilised plants 5 -29 inches (the 
plants having been grown in small pots), or as 100 to 65. 

In the next or fourth self-fertilised generation, several plants 
of a new and tall variety appeared, which increased in the 
later self-fertilised generations, owing to its great self-fertility, 
to the complete exclusion of the original kinds. The same 
variety also appeared amongst the crossed plants, but as it was 
not at first regarded with any particular attention, I know 
not how far it was used for raising the intercrossed plants ; and 
in the later crossed generations it was rarely present. Owing to 
the appearance of this tall variety, the comparison of the crossed 
and self-fertilised plants of the fifth and succeeding generations 
was rendered unfair, as all the self-fertilised and only a few or 
none of the crossed plants consisted of it. Nevertheless, the 
results of the later experiments are in some respects well worth 
giving. 

Crossed and self-fertilised Plants of the Fourth Generation. Seed* 
of the two kinds, produced in the usual way from the two sets of 
plants of the third generation, were sown on opposite sides of 
two pots (I. and II.); but the seedlings were not thinned 
enough and did not grow well. Many of the self-fertilised 
plants, especially in one of the pots, consisted of the new and 
tall variety above referred to, which bore large and almost white 
flowers marked with crimson blotches. I will call it the 
White variety. I believe that it first appeared an ongst both the 

F 2 



68 MIMULUS LUTET/S. CHAP. III. 

crossed and self-fertilised plants of the last generation ; but 
neither my gardener nor myself could remember any such variety 
in the seedlings raised from the purchased seed. It must there- 
fore have arisen either through ordinary variation, or, judging 
from its appearance amongst both the crossed and self-fertilised 
plants, more probably through reversion to a formerly existing 
variety. 

In Pot I. the tallest crossed plant was 8i inches, and the 
tallest self-fertilised 5 inches in height. In Pot II. the tallest 
crossed plant was 6j inches, and the tallest self-fertilised plant, 
which consisted of the white variety, 7 inches in height ; and 
this was the first instance in my experiments on Mimulus in 
which the tallest self-fertilised plant exceeded the tallest crossed. 
Nevertheless, the two tallest crossed plants taken together were 
to the two tallest self-fertilised plants in height as 100 to 80. 
As yet the crossed plants were superior to the self-fertilised in 
fertility; for twelve flowers on the crossed plants were crossed 
and yielded ten capsules, the seeds of which weighed 1 '71 grain. 
Twenty flowers on the self-fertilised plants were self-fertilised, 
and produced fifteen capsules, all appearing poor ; and the seeds 
from ten of them weighed only '68 grain, so that from an 
equal number of capsules the crossed seeds were to the self- 
fertilised in weight as 100 to 40. 

Crossed and self-fertilised Plants of the Fifth Generation. Seeds 
from both lots of the fourth generation, fertilised in the usual 
manner, were sown on opposite sides of three pots. When the 
seedlings flowered, most of the self-fertilised plants were found 
to consist of the tall white variety. Several of the crossed plants 
in Pot I. likewise belonged to this variety, as did a very few in 
Pots II. and III. The tallest crossed plant in Pot I. was 7 inches, 
and the tallest self-fertilised plant on the opposite side 8 inches ; 
in Pots II. and III. the tallest crossed were 4 and 5i, and the 
tallest self-fertilised 7 and 6 inches in height; so that the 
average height of the tallest plants in the two lots was as 100 
for the crossed to 126 for the self-fertilised ; and thus we have 
a complete reversal of what occurred in the four previous gene- 
rations. Nevertheless, in all three pots the crossed plants 
retained their habit of flowering before the self-fertilised. The 
plants were unhealthy from being crowded and from the extreme 
heat of the season, and were in consequence more or less 
sterile ; but the crossed plants were somewhat less sterile than 
the self-fertilised plants. 



CHAP. III. CROSSED AND SELF-FERTILISED PLANTS. 69 



Crvssed and self -fertilised Plants of the Sixth Generation. 
from plants of the fifth generation crossed and self-fertilised in 
the usual manner were sown on opposite sides of several pots. 
On the self-fertilised side every single plant belonged to the tall 
white variety. On the crossed side some plants belonged to this 
variety, but the greater number approached in character to the 
old and shorter kinds with smaller yellowish flowers blotched 
with coppery brown. When the plants on both sides were from 
2 to 3 inches in height they were equal, but when fully grown 
the self- fertilised were decidedly the tallest and finest plants, but, 
from want of time, they were not actually measured. In half 
the pots the first plant which flowered was a self-fertilised one, 
and in the other half a crossed one. And now another remark- 
able change was clearly perceived, namely, that the self-fertilised 
plants had become more self-fertile than the crossed. The 
pots were all put under a net to exclude insects, and the crossed 
plants produced spontaneously only fifty-five capsules, whilst 
the self-fertilised plants produced eighty-one capsules, or as 100 
to 147. The seeds from nine capsules of both lots were placed 
in separate watch-glasses for comparison, and the self-fertilised 
appeared rather the more numerous. Besides these sponta- 
neously self-fertilised capsules, twenty flowers on the crossed 
plants again crossed yielded sixteen capsules; twenty-five 
flowers on the self-fertilised plants again self-fertilised yielded 
seventeen capsules, and this is a larger proportional number of 
capsules than was produced by the self-fertilised flowers on the 
self-fertilised plants in the previous generations. The contents 
of ten capsules of both these lots were compared in separate 
watch-glasses, and the seeds from the self-fertilised appeared 
decidedly more numerous than those from the crossed plants. 

Ciossed and self-fertilised Plants of the Seventh Generation. 
Crossed and self-fertilised seeds from the crossed and self-ferti- 
lised plants of the sixth generation were sown in the usual 
manner on opposite sides of three pots, and the seedlings were 
well and equally thinned. Every one of the self-fertilised plants 
(and many were raised) in this, as well as in the eighth and ninth 
generations, belonged to the tall white variety. Their uniformity 
of character, in comparison with the seedlings first raised from 
the purchased seed, was quite remarkable. On the other hand, 
the crossed plants differed much in the tints of their flowers, 
but not, I think, to so great a degree as those first raised. 
I determined this time to measure the plants on both sides 



70 MIMULUS LUTE US. CHAP. III. 

carefully. The self-fertilised seedlings came up rather before the 
crossed, but both bts were for a time of equal height. When first 
measured, the average height of the six tallest crossed plants in 
the three pots was 7 '02, and that of the six tallest self-fertilised 
plants 8'97 inches, or as 100 to 128. When fully grown the 
same plants were again measured, with the result shown in the 
following table : 

TABLE XVIII. (Seventh Generation.) 



No. of Pot. 


Crossed Plants. 


Self-fertilised Plants. 


I. 


Inches. 
"1 

HI 


Inches. 
19J 
18 


II. 


12 1 

ul 


Xj 


III. 


i 
1*1 


iJi 


Total inches. 


68-63 


93-88 



The average height of the six crossed is here 11 '43, and that 
of the six self-fertilised 15-64, or as 100 to 137. 

As it was now evident that the tall white variety transmitted 
its characters faithfully, and as the self-fertilised plants consisted 
exclusively of this variety, it was manifest that they would 
always exceed in height the crossed plants which belonged 
chiefly to the original shorter varieties. This line of experiment 
was therefore discontinued, and I tried whether intercrossing 
two self-fertilised plants of the sixth generation, growing in dis- 
tinct pots, would give their offspring any advantage over the 
offspring of flowers on one of the same plants fertilised with then- 
own pollen. These latter seedlings formed the seventh genera- 
tion of self-fertilised plants, like those in the right-hand column 
in Table XVIII. ; the crossed plants were the product of six 
previous self-fertilised generations with an intercross in the 
last generation. The seeds were allowed to germinate on sand, 
and were planted in pairs on opposite sides of four pots, all the 
remaining seeds being sown crowded on opposite sides of Pot 
V. in Table XIX. ; the three tallest on each side in this latter pot 
being alone measured. All the plants were twice measured the 
first time whilst young, and the average height of the crossed plants 



CHAP. III. CROSSED AND SELF-FERTILISED PLANTS. 71 



to that of the self-fertilised was then as 100 to 122. When fully 
grown they were again measured, as in the following table : 

TABLE XIX. 



No. of Pot. 


Intercrossed Plants 
from Self-fertilised ' 
Plants of the Sixth 
Generation. 


Self-fertilised Plants 
of the Seventh 
Generation. 


% I. 


Inches. 
12| 

10 I 
10 

Mj 


Inches 
15| 

!J ! 

11 


II. 


'?! 
'?! 


HI 

H3 
*l 

14| 


in. 


g| 


!?l 


IV. 


7J 

8 1 
7| 


H| 

8 


V. 

Crowded. 


S 1 

8 


ioi 

9 3 

9 


Total in inches. 


159-38 


175-50 



The average height of the sixteen intercrossed plants is here 
9 96 inches, and that of the sixteen self-fertilised plants 10 96, or 
as 100 to 110 ; so that the intercrossed plants, the progenitors of 
which had been self-fertilised for the six previous generations, 
and had been exposed during the whole time to remarkably uni- 
form conditions, were somewhat inferior in height to the plants 
of the seventh self-fertilised generation. But as we shall pre- 
sently see that a similar experiment made after two additional 
generations of self-fertilisation gave a different result, I know 
not how far to trust the present one. In three of the five 
pots in Table XIX. a self-fertilised plant flowered first, and in 
the other two a crossed plant. These self-fertilised plants were 
remarkably fertile, for twenty flowers fertilised with their own 
pollen produced no less than nineteen very fine capsules 1 



72 MIMULUS LUTEUS CHAP. III. 

The effects of a Cross with a distinct Stock. Some flowers on the 
self-fertilised plants in Pot IV. in Table XIX. were fertilised 
with their own pollen, and plants of the eighth self-fertilised 
generation were thus raised, merely to serve as parents in the fol- 
lowing experiment. Several flowers on these plants were allowed 
to fertilise themselves spontaneously (insects being of course 
excluded), and the plants raised from these seeds formed the 
ninth self-fertilised generation ; they consisted wholly of the tall 
white variety with crimson blotches. Other flowers on the 
same plants of the eighth self-fertilised generation were crossed 
with pollen taken from another plant of the same lot ; so that 
the seedlings thus raised were the offspring of eight previous 
generations of self-fertilisation with an intercross in the last 
generation ; these I will call the intercrossed plants. Lastly, 
other flowers on the same plants of the eighth self-fertilised 
generation were crossed with pollen taken from plants which had 
been raised from seed procured from a garden at Chelsea. The 
Chelsea plants bore yellow flowers blotched with red, but differed 
in no other respect. They had been grown out of doors, whilst 
mine had been cultivated in pots in the greenhouse for the 
last eight generations, and in a different kind of soil. The 
seedlings raised from this cross with a wholly different stock 
may be called the " Chelsea-crossed." The three lots of seeds 
thus obtained were allowed to germinate on bare sand; and 
whenever a seed in all three lots, or in only two, germinated at 
the same time, they were planted in pots superficially divided 
into three or two compartments. The remaining seeds, 
whether or not in a state of germination, were thickly sown in 
three divisions in a large pot, X., in Table XX. When the plants 
had grown to their full height they were measured, as shown in 
the following table ; but only the three tallest plants in each of 
the three divisions in Pot X. were measured. 

In this table the average height of the twenty-eight Chelsea- 
crossed plants is 21-62 inches; that of the twenty-seven inter- 
crossed plants 12 2 ; and that of the nineteen self-fertilised 10 44. 
But with respect to the latter it will be the fairest plan to strike out 
two dwarfed ones (only 4 inches in height), so as not to exaggerate 
the inferiority of the self-fertilised plants ; and this will raise the 
average height of the seventeen remaining self-fertilised plants 
to 11 '2 inches. Therefore the Chelsea-crossed are to the inter- 
crossed in height as 100 to 56 ; the Chelsea-crossed to the self- 
fertilised as 100 to 52 ; and the intercrossed to the self-fertilised 



CHAP. III. CROSS WITH A FRESH STOCK. 

TABLE XX. 



73 



No. of Pot. 


Plants from Self- 
fertilised Plants of 
the Eighth Genera- 
tion crossed by 
Chelsea Plants. 


Plants from an in- 
tercross between 
the Plants of the 
Eighth Self-ferti- 
lised Generation. 


Self-fertilised 
Plants of the Ninth 
Generation from 
Plants of the 
Eighth Self-ferti- 
lised Generation. 


I. 

Jk 


Inches. 
30 1 
28i 


Inches. 
14 
13g 
131 


Inches. 
93 

10J 

10 


II. 


20 
22| 


HI 

12 

9i 


llf 

12 


m. 




23 1 
24 1 
25 1 


12 


81 

111 
6| 


IV. 


22 1 
22 
17 


9 
8 8 


jj, 


V. 


22 
19f 
23| 


9 
11 



13j 


VI. 


28| 

22 


1 7 8S 
12 8 


12 
16| 


VII. 


12| 
24 1 
20 1 
26 1 


15 

12| 

HI 


- 


VIII. 


171 

22 1 
27 


SI 

1*1 





IX. 


22| 
6 
20 i 


ni 

17 

"1 


'' 


X. 

Crowded Plants. 


18i 
16 8 
17j 


n 

8 
10 


101 

8 1 
11 1 


Total inches. 


605-38 


329-50 


198-50 



74 MIMULUS LUTEUS. CHIP. Ill 

as 100 to 92. We thus see how immensely superior in height 
the Chelsea-crossed are to the intercrossed and to the self- 
fertilised plants. They began to show their superiority when 
only one inch high. They were also, when fully grown, much 
more branched with larger leaves and somewhat larger flowers 
than the plants of the other two lots, so that if they had been 
weighed, the ratio would certainly have been much higher than 
that of 100 to 56 and 52. 

The intercrossed plants are here to the self-fertilised in 
height as 100 to 92; whereas in the analogous experiment 
given in Table XIX. the intercrossed plants from the self- 
fertilised plants of the sixth generation were inferior in height 
to the self-fertilised plants in the ratio of 100 to 110. I 
doubt whether this discordance in the results of the two 
experiments can be explained by the self-fertilised plants in the 
present case having been raised from spontaneously Self- 
fertilised seeds, whereas in the former case they were raised 
from artificially self-fertilised seeds; nor by the present plants 
having been self-fertilised during two additional generations, 
though this is a more probable explanation. 

With respect to fertility, the twenty-eight Chelsea-crossed 
plants produced 272 capsules; the twenty-seven intercrossed 
plants produced 24 ; and the seventeen self-fertilised plants 17 
capsules. All the plants were left uncovered so as to be naturally 
fertilised, and empty capsules were rejected. 

Capsules. 

Therefore 20 Chelsea-crossed plants would have produced 194-29 
20 Intercrossed plants 17 '77 

20 Self-fertilised plants 20 'OC 

Grains, 
The seeds contained in 8 capsules from the Chelsea- ) j.^ 

crossed plants weighed | 

The seeds contained in 8 capsules from the Intercrossed ) Q.gj 

plants weighed ...,..} 

The seeds contained in 8 capsules from the Self-fertilised j. 0-33 

plants weighed ...... 5 

If we combine the number of capsules produced together with 
the average weight of contained seeds, we get the following 
extraordinary ratios : 

Weight of seed produced by the same number ) inn t 4 
of Chelsea-crossed and intercrossed plants . J 1UU TO 



CHAP. IIL FLOWERS ON SAME PLANT CEOSSED. 75 

Weight of seed produced by the same number ) ,, inn to 3 

of Chelsea-crossed and self-fertilised plants 
Weight of seeds produced by the same number ) , QQ ^ 

of intercrossed and self-fertilised plants . . f 

It is also a remarkable fact that the Chelsea-crossed plants 
exceeded the two other lots in hardiness, as greatly as they did 
in height, luxuriance, and fertility. In the early autumn most of 
the pots ..were bedded out in the open ground ; and this always 
injures plants which have been long kept in a warm greenhouse. 
All three lots consequently suffered greatly, but the Chelsea- 
crossed plants much less than the other two lots. On the 3rd of 
October the Chelsea-crossed plants began to flower again, and 
continued to do so for some time ; whilst not a single flower was 
produced by the plants of the other two lots, the stems of which 
were cut almost down to the ground and seemed half dead. 
Early in December there was a sharp frost, and the stems of 
Chelsea-crossed were now cut down ; but on the 23rd of December 
they began to shoot up again from the roots, whilst all the plants 
of the other two lots were quite dead. 

Although several of the self-fertilised seeds, from which the 
plants in the right-hand column in Table XX. were raised, germi- 
nated (and were of course rejected) before any of those of the 
other two lots, yet in only one of the ten pots did a self- 
fertilised plant flower before the Chelsea-crossed or the inter- 
crossed plants growing in the same pots. The plants of these 
two latter lots flowered at the same time, though the Chelsea- 
crossed grew so much taller and more vigorously than the 
intercrossed. 

As already stated, the flowers of the plants originally raised 
from the Chelsea seeds were yellow ; and it deserves notice that 
every one of the twenty-eight seedlings raised from the tall 
white variety fertilised, without being castrated, with pollen 
from the Chelsea plants, produced yellow flowers; and this 
shows how prepotent this colour, which is the natural one of 
the species, is over the white colour. 

The Effects on the Offspring of intercrossing Flowers on the 
same Plant, instead of crossing distinct Individuals. In all the 
foregoing experiments the crossed plants were the product of a 
cross between distinct plants. I now selected a very vigorous 
plant in Table XX., raised by fertilising a plant of the eighth 
self-fertilised generation with pollen from the Chelsea stock, 



76 



MIMULUS LUTEUS. 



CHAP. III. 



Several flowers on this plant were crossed with pollen from other 
flowers on the same plant, and several other flowers were 
fertilised with their own pollen. The seed thus produced was 
allowed to germinate on bare sand; and the seedlings were 
planted in the usual manner on the opposite sides of six 
pots. All the remaining seeds, whether or not in a state of 
germination, were sown thickly in Pot VII. ; the three tallest 
plants on each side of this latter pot being alone measured. As I 
was in a hurry to learn the result, some of these seeds were sown 
late in the autumn, but the plants grew so irregularly during 
the winter, that one crossed plant was 28J inches, and two 
others only 4, or less than 4 inches in height, as may be seen 
in Table XXI. Under such circumstances, as I have observed 
in many other cases, the result is not in the least trust- 
worthy ; nevertheless I feel bound to give the measurements. 

TABLE XXI. 



No. of Pot. 


Plants raised from a 
Cross between dif- 
ferent Flowers on the 
same Plant. 


Plants raised from 
Flowers fertilised 
with their own 
Pollen. 


I. 


Inches. 
17 
9 


Inches. 
17 
3J 


II. 


28 1 
16| 
13f 


I 1 

2 


III. 


4 
2 


IS' 


IV. 


23 1 
15| 


?! 


V. 


7 


133 


VI. 


g' 


M 

2 


VII. 
Crowded. 


21 
H| 
12* 


X* 

HI 


Total inches. 


210-88 


140-75 



CIIAP. III. FLOWERS ON SAME PLANT CROSSED. 



77 



The fifteen crossed plants here average 14*05, and the fifteen 
self-fertilised plants 9 '38 in height, or as 100 to 67. But if 
all the plants under ten inches in height are struck out, the ratio 
of the eleven crossed plants to the eight self-fertilised plants 
is as 100 to 82. 

On the following spring, some remaining seeds of the two 
lots were treated in exactly the same manner; and the measure- 
ments of the seedlings are given in the following table : 

TABLE XXII. 



No. of Pot. 


Plants raised from a 
Cross between diffe- 
rent Flowers on the 
same Plant. 


Plants raised from 
Flowers fertilised 
with their own Pollen. 


I. 


Inches. 
12 

104 


Inches. 
19 1 
20 1 
li| 


II. 


16 


H 

191 

17| 


IIL 


15 
181 


IP 


IV. 


in 


161 


V. 


25f 


22| 


VI. 


15 

20 ii 

27 1 


191 

Sj 


VIL 


ll 8 
13j 


7 8 

7 


VIII. 
Crowded. 


181 
181 
181 

18J 


SI 
| 


Total in inches. 


370-88 


353-63 



78 MIMULUS LUTEUS. CHAP. Ill 

Here the average height of the twenty-two crossed plants is 
16-85, and that of the twenty-two self-fertilised plants 16 "07 ; or 
as 100 to 95. But if four of the plants in Pot VII., which are 
much shorter than any of the others, are struck out (and this 
would be the fairest plan), the twenty-one crossed are to the 
nineteen self-fertilised plants in height as 100 to 100 '6 that is, 
are equal. All the plants, except the crowded ones in Pot VIII., 
after being measured were cut down, and the eighteen crossed 
plants weighed 10 oz., whilst the same number of self-fertilised 
plants weighed lOi oz., or as 100 to 102 '5 ; but if the dwarfed 
plants in Pot VII. had been excluded, the self-fertilised would 
have exceeded the crossed in weight in a higher ratio. In all 
the previous experiments in which seedlings were raised from a 
cross between distinct plants, and were put into competition 
with self-fertilised plants, the former generally flowered first ; 
but in the present case, in seven out of the eight pots a 
self-fertilised plant flowered before a crossed one on the 
opposite side. Considering all the evidence with respect to 
the plants in Table XXU., a cross between two flowers on the 
same plant seems to give no advantage to the offspring thus 
produced, the self-fertilised plants being in weight superior. But 
this conclusion cannot be absolutely trusted, owing to the 
measurements given in Table XXI., though, these latter, from 
the cause already assigned, are very much less trustworthy than 
the present ones. 

Summary of Observations on Mimulus luteus. In the 
three first generations of crossed and self-fertilised 
plants, the tallest plants alone on each side of the 
several pots were measured ; and the average height 
of the ten crossed to that of the ten self-fertilised 
plants was as 100 to 64. The crossed were also much 
more fertile than the self-fertilised, and so much 
more vigorous that they exceeded them in height, even 
when sown on the opposite side of the same pot after 
an interval of four days. The same superiority was 
likewise shown in a remarkable manner when both 
kinds of seeds were sown on the opposite sides of a pot 
with very poor earth full of the roots of another plant. 



CHAP. III. SUMMARY OF OBSERVATIONS. 79 

In one instance crossed and self-fertilised seedlings, 
grown in rich soil and not put into competition with 
each other, attained to an equal height. When we 
come to the fourth generation the two tallest crossed 
plants taken together exceeded by only a little the two 
tallest self-fertilised plants, and one of the latter beat 
its crossed opponent, a circumstance which had not 
occurred in the previous generations. This victorious 
self-fertilised plant consisted of a new white-flowered 
variety, which grew taller than the old yellowish 
varieties. From the first it seemed to be rather more 
fertile, when self-fertilised, than the old varieties, and 
in the succeeding self-fertilised generations became 
more and more self-fertile. In the sixth generation the 
self-fertilised plants of this variety compared with the 
crossed plants produced capsules in the proportion 
of 147 to 100, both lots being allowed to fertilise 
themselves spontaneously. In the seventh generation 
twenty flowers on one of these plants artificially 
self-fertilised yielded no less than nineteen very fine 
capsules ! 

This variety transmitted its characters so faithfully 
to all the succeeding self-fertilised generations, up to 
the last or ninth, that all the many plants which were 
raised presented a complete uniformity of character ; 
thus offering a remarkable contrast with the seedlings 
raised from the purchased seeds. Yet this variety 
retained to the last a latent tendency to produce 
yellow flowers ; for when a plant of the eighth self- 
fertilised generation was crossed with pollen from a 
yellow-flowered plant of the Chelsea stock, every 
single seedling bore yellow flowers. A similar variety, 
at least in the colour of its flowers, also appeared 
amongst the crossed plants of the third generation. 
No attention was at first paid to it, and I know not 



80 MIMULUS LUTEUS. CHAP. III. 

how far it was at first used either for crossing or self- 
fertilisation. In the fifth generation most of the 
self-fertilised plants, and in the sixth and all the 
succeeding generations every single plant consisted of 
this variety ; and this no doubt was partly due to its 
great and increasing self-fertility. On the other 
hand, it disappeared from amongst the crossed plants 
in the later generations ; and this was probably 
due to the continued intercrossing of the several 
plants. From the tallness of this variety, the self- 
fertilised plants exceeded the crossed plants in height 
in all the generations from the fifth to the seventh 
inclusive; and no doubt would have done so in the 
later generations, had they been grown in competition 
with one another. In the fifth generation the crossed 
plants were in height to the self-fertilised, as 100 to 
126 ; in the sixth, as 100 to 147 ; and in the seventh 
generation, as 100 to 137. This excess of height may 
be attributed not only to this variety naturally growing 
taller than the other plants, but to its possessing a 
peculiar constitution, so that it did not ^suffer from 
continued self-fertilisation. 

This variety presents a strikingly analogous case to 
that of the plant called the Hero, which appeared in 
the sixth self-fertilised generation of Ipomoea. If 
the seeds produced by Hero had been as greatly in 
excess of those produced by the other plants, as was the 
case with Mimulus, and if all the seeds had been 
mingled together, the offspring of Hero would have 
increased to the entire exclusion of the ordinary 
plants in the later self-fertilised generations, and from 
naturally growing taller would have exceeded the 
crossed plants in height in each succeeding generation. 

Some of the self-fertilised plants of the sixth gene- 
ration were intercrossed, as were some in the eighth 



CHAI.IH. DIGITALIS PUBPUREA. 81 

generation ; and the seedlings from these crosses were 
grown in competition with self-fertilised plants of the 
two corresponding generations. In the first trial the 
intercrossed plants were less fertile than the self- 
fertilised, and less tall in the ratio of 100 to 110. 
In the second trial, the intercrossed plants were more 
fertile than the self-fertilised in the ratio of 100 to 
73, and:- taller in the ratio of 100 to 92. Notwith- 
standing that the self-fertilised plants in the second 
trial were the product of two additional generations 
of self-fertilisation, I cannot understand this discor- 
dance in the results of the two analogous experiments. 

The most important of all the experiments on 
Mimulus are those in which flowers on plants of the 
eighth self-fertilised generation were again self-ferti- 
lised ; other flowers on distinct plants of the same lot 
were intercrossed ; and others were crossed with a new 
stock of plants from Chelsea. The Chelsea-crossed 
seedlings were to the intercrossed in height as 100 to 
56, and in fertility as 100 to 4 ; and they were to the 
self-fertilised plants, in height as 100 to 52, and in 
fertility as 100 to 3. These Chelsea-crossed plants 
were also much more hardy than the plants of the 
other two lots ; so that altogether the gain from the 
cross with a fresh stock was wonderfully great. 

Lastly, seedlings raised from a cross between flowers 
on the same plant were not superior to those from 
flowers fertilised with their own pollen ; but this result 
cannot be absolutely trusted, owing to some previous 
observations, which, however, were made under very 
unfavourable circumstances. 

DIGITALIS PURPUKEA. 

The flowers of the common Foxglove are proterandrous ; that 
is, the pollen is mature and mostly shed before the stigma of 
the same flower is ready for fertilisation. This is effected by 

G 



82 DIGITALIS PtUPUREA. CHAP. III. 

the larger humble-bees, which, whilst in search of nectar, carry 
pollen from flower to flower. The two upper and longer 
stamens shed their pollen before the two lower and shorter 
ones. The meaning of this fact probably is, as Dr. Ogle re- 
marks,* that the anthers of the longer stamens stand near to 
the stigma, so that they would be the most likely to fertilise it ; 
and as it is an advantage to avoid self-fertilisation, they shed 
their pollen first, thus lessening the chance. There is, however, 
but little danger of self-fertilisation until the bifid stigma 
opens ; for Hildebrand f found that pollen placed on the stigma 
before it had opened produced no effect. The anthers, which 
are large, stand at first transversely with respect to the tubular 
corolla, and if they were to dehisce in this position they would, 
as Dr. Ogle also remarks, smear with pollen the whole back and 
sides of an entering humble-bee in a useless manner ; but the 
anthers twist round and place themselves longitudinally before 
they dehisce. The lower and inner side of the mouth of the 
corolla is thickly clothed with hairs, and these collect so much 
of the fallen pollen that I have seen the under surface of a 
humble-bee thickly dusted with it ; but this can never be ap- 
plied to the stigma, as the bees in retreating do not turn their 
under surfaces upwards. I was therefore puzzled whether these 
. hairs were of any use ; but Mr. Belt has, I think, explained 
their use : the smaller kinds of bees are not fitted to fertilise 
the flowers, and if they were allowed to enter easily they would 
steal much nectar, and fewer large bees would haunt the 
flowers. Humble-bees can crawl into the dependent flowers 
with the greatest ease, using the "hairs as footholds while 
sucking the honey ; but the smaller bees are impeded by 
them, and when, having at length struggled through them, they 
reach the slippery precipice above, they are completely 
baffled." Mr. Belt says that he watched many flowers during 
a whole season in North Wales, and " only once saw a small 
bee reach the nectary, though many were seen trying in vain to 
doso."* 

I covered a plant growing in its native soil in North Wales 
with a net, and fertilised six flowers each with its own pollen, 



* 'Popular Science Review,' gua,' 1874, p. 132. But it appears 

Jan. 1870, p. 50. from H. Miiller (' Die Befruchtung 

t Geschlechter - Vertheilung der Blumen,' 1873, p. 285), that 

boi den Pflanzen,' 1867, p. 20. small insects sometimes succeed 

J ' The Naturalist in Nicara- in entering the flowers. 



CHAP. III. CROSSED AND SELF-FERTILISED PI ANTS. 83 

and six others with pollen from a distinct plant growing within 
the distance of a few feet. The covered plant was occasionally 
shaken with violence, so as to imitate the effects of a gale of 
wind, and thus to facilitate as far as possible self-fertilisation, 
It bore ninety-two flowers (besides the dozen artificially ferti- 
lised), and of these only twenty-four produced capsules ; whereas 
almost all the flowers on the surrounding uncovered plants were 
fruitful. Of the twenty-four spontaneously self-fertilised cap- 
sules, only two contained their full complement of seed; six 
contained a moderate supply; and the remaining sixteen ex- 
tremely few seeds. A little pollen adhering to the anthers after 
they had dehisced, and accidentally falling on the stigma when 
mature, must have been the means by which the above twenty- 
four flowers were partially self-fertilised ; for the margins of the 
corolla in withering do not curl inwards, nor do the flowers in 
dropping off turn round on their axes, so as to bring the pollen- 
covered hairs, with which the lower surface is clothed, into con- 
tact with the stigma by either of which means self- fertilisation 
might be effected. 

Seeds from the above crossed and self-fertilised capsules, after 
germinating on bare sand, were planted in pairs on the opposite 
sides of five moderately-sized pots, which were kept in the green- 
house. The plants after a time appeared starved, and were 
therefore, without being disturbed, turned out of their pots, and 
planted in the open ground in two close parallel rows. They 
were thus subjected to tolerably severe competition with one 
another ; but not nearly so severe as if they had been left in the 
pots. At the time when they were turned out, their leaves were 
between 5 and 8 inches in length, and the longest leaf on 
the finest plant on each side of each pot was measured, with the 
result that the leaves of the crossed plants exceeded, on an 
average, those of the self- fertilised plants by '4 of an inch. 

In the following summer the tallest flower-stem on each plant, 
when fully grown, was measured. There were seventeen crossed 
plants ; but one did not produce a flower- stem. There were also, 
originally, seventeen self-fertilised plants, but these had such 
poor constitutions that no less than nine died in the course of 
the winter and spring, leaving only eight to be measured, as in 
the following table : 



G 2 



84 



DIGITALIS PUKPUREA. 



CHAP. Ill 



TABLE XXIIL 

The tallest Flower-stem on each Plant measured : means that 
the Plant died before a Flower-stem was produced. 



No. of Pot. 


Crossed Plants. 


Self-fertilised Plants. 


I. 


Inches. 
53 1 
57 1 
57 1 
65 


Inches. 
27| 

". 




II. 


34 1 
52 1 

63 1 


39 
21 


III. 


57 1 
53 1 
50 1 
37 1 


53, 





IV. 


64j 

37 | 


23J 



y 


53 
47 1 
34f 







Total in inches. 


821-25 


287-00 



The average height of the flower-stems of the sixteen crossed 
plants is here 51 '33 inches; and that of the eight self-fertilised 
plants, 35-87 ; or as 100 to 70. But this difference in height does 
not give at all a fair idea of the vast superiority of the crossed 
plants. These latter produced altogether sixty-four flower-stems, 
each plant producing, on an average, exactly four flower-stems ; 
whereas the eight self-fertilised plants produced only fifteen 
flower-stems, each producing an average only of 1'87 stems, and 
these had a less luxuriant appearance. We may put the result in 
auother way : the number of flower-stems on the crossed plants was 
to those on an equal number of self-fertilised plants as 100 to 48. 

Three crossed seeds in a state of germination were also planted 
in three separate pots; and three self-fertilised seeds in the 
same state in three other pots. These plants were therefore 
at first exposed to no competition with one another, and when 



CHAP. III. CROSSED AND SELF-FERTILISED PLANTS. 85 

turned out of their pots into the open ground they were planted 
at a moderate distance apart, so that they were exposed to much 
less severe competition than in the last case. The longest leaves 
on the three crossed plants, when turned out, exceeded those on 
the self-fertilised plants by a mere trifle, viz., on an average by 
17 of an inch. When fully grown the three crossed plants 
produced twenty-six flower-stems ; the two tallest of which on 
each plant were on an average 54*04 inches in height. The 
three self-fertilised plants produced twenty-three flower-stems, 
the two tallest of which on each plant had an average height of 
46'18 inches. So that the difference between these two lots, 
which hardly competed together, is much less than in the last 
case when there was moderately severe competition, namely, as 
100 to 85, instead of as 100 to 70. 

The Effects on the Offspring of intercrossing different Flowers on 
the same Plant, instead of crossing distinct Individuals. A fine 
plant growing in my garden (one of the foregoing seedlings) was 
covered with a net, and six flowers were crossed with pollen from 
another flower on the same plant, and six others were fertilised 
with their own pollen. All produced good capsules. The seeds 
from each were placed in separate watch-glasses, and no difference 
could be perceived by the eye between the two lots of seeds ; 
and when they were weighed there was no difference of any sig- 
nificance, as the seeds from the self-fertilised capsules weighed 
7 '65 grains, whilst those from the crossed capsules weighed 
7' 7 grains. Therefore the sterility of the present species, when 
insects are excluded, is not due to the impotence of pollen 
on the stigma of the same flower. Both lots of seeds and seed- 
lings were treated in exactly the same manner as in the previous 
table (XXIII.), excepting that after the pairs of germinating seeds 
had been planted on the opposite sides of eight pots, all the 
remaining seeds were thickly sown on the opposite sides of Pots IX. 
and X. in Table XXIV. The young plants during the following 
spring were turned out of their pots, without being disturbed, 
and planted in the open ground in two rows, not very close 
together, so that they were subjected to only moderately severe 
competition with one another. Very differently to what occurred 
in the first experiment, when the plants were subjected to 
somewhat severe mutual competition, an equal number on each 
side either died or did not produce flower-stems. The tallest 
flower-stems on the surviving plants were measured, as shown in 
the following table : 



86 



FLOWERS ON SAME PLANT CROSSED. CHAP. IIL 



TABLE XXIV. 
N.B. signifies that the Plant died, or did not produce a Floiver- 



No. of Pot. 


Plants raised from a 
Cross between dif- 
ferent Flowers on the 
same Plant. 


Plants raised from 
Flowers fertilised 
with thtir own Pollen. 


I. 


Inches. 

46 1 
43 


Inches. 
45 1 
52 



II. 


881 

7 


Ml 

47 1 


III. 


54J 


46 1 


IV. 


32 J 

43 1 


41 1 
29 1 
37 1 


V. 


46| 
43 


42 

l| 


VI. 


48 
461 


Sj 


VII. 


48 J 
42 


25 
40| 


VIII. 


46| 


39J 


IX. 
Crowded Plants. 


49 

46 1 



8' 

361 
ft 


X. 

Crowded Plants. 


46 j 
35 j 
24 j 
41 i 
17 1 


4 o' J 

34 1 
40 i 
41 1 


Total inches. 


1078-00 


995-38 



CHAP. III. CALCEOLARIA. 87 

The average height of the flower-stems on the twenty-five 
crossed plants in all the pots taken together is 43 12 inches, and 
that of the twenty-five self-fertilised plants 39 '82, or as 100 to 
U2. In order to test this result, the plants planted in pairs in 
Pots I. to VIII. were considered by themselves, and the average 
height of the sixteen crossed plants is here 44 9, and that of the 
sixteen self-fertilised plants 42'03, or as 100 to 94. Again, the 
plants raised from the thickly sown seed in Pots XI. and X., 
which were subjected to very severe mutual competition, were 
taken by themselves, and the average height of the nine crossed 
plants is 39 86, and that of the nine self-fertilised plants 35 ' 88, or 
as 100 to 90. The plants in these two latter pots (IX. and X.), 
after being measured, were cut down close to the ground and 
weighed: the nine crossed plants weighed 57 '66 ounces, and 
the nine self-fertilised plants 45 '25 ounces, or as 100 to 78. On 
the whole we may conclude, especially from the evidence of 
weight, that seedlings from a cross between flowers on the same 
plant have a decided, though not great, advantage over those 
from flowers fertilised with their own pollen, more especially 
in the case of the plants subjected to severe mutual competition. 
But the advantage is much less than that exhibited by the 
crossed offspring of distinct plants, for these exceeded the self- 
fertilised plants in height as 100 to 70, and in the number of 
flower-stems as 100 to 48. Digitalis thus differs from Ipomcea, 
and almost -certainly from Mimulus, as with these two species 
a cross between flowers on the same plant did no good. 

CALCEOLARIA. 

A bushy greenhouse variety, with yettow flowers blotched with purple. 

The flowers in this genus are constructed so as to favour or 
almost ensure cross-fertilisation;* and Mr. Anderson remarks t 
that extreme care is necessary to exclude insects in order to 
preserve any kind true. He adds the interesting statement, that 
when the corolla is cut quite away, insects, as far as he has seen, 
never discover or visit the flowers. This plant is, however, self- 
fertile if insects are excluded. So few experiments were 
made by me, that they are hardly worth giving. Crossed and 
self-fertilised seeds were sown on opposite sides of a pot, and 



* Hildebrand, as quoted by t ' Gardeners' Chronicle,' 185H 

H. Miiller, ' Die Befruchtung p. 534. 
der Blumen,' 1873, p. 277. 



88 LIN ARIA VULGARIS. CHAP. III. 

after a time the crossed seedlings slightly exceeded the self- 
fertilised in height. When a little further grown, the longest 
leaves on the former were very nearly 3 inches in length, 
whilst those on the self-fertilised plants were only 2 inches. 
Owing to an accident, and to the pot being too small, only one 
plant on each side grew up and flowered ; the crossed plant was 
19s inches in height, and the self-fertilised one 15 inches; or as 
100 to 77. 

LlNARIA VULGARIS. 

It has been mentioned in the introductory chapter that two 
large beds of this plant were raised by me many years ago from 
crossed and self-fertilised seeds, and that there was a conspicu- 
ous difference in height and general appearance between the 
two lots. The trial was afterwards repeated with more care ; 
but as this was one of the first plants experimented on, my 
usual method was not followed. Seeds were taken from wild 
plants growing in this neighbourhood and sown in poor soil in 
my garden. Five plants were covered with a net, the others 
being left exposed to the bees, which incessantly visit the flowers 
of this species, and which, according to H. Miiller, are the 
exclusive fertilisers. This excellent observer remarks * that, as 
the stigma lies between the anthers and is mature at the same 
time with them, self-fertilisation is possible. But so few seeds 
are produced by protected plants, that the pollen and stigma of 
the same flower seem to have little power of mutual interaction. 
The exposed plants bore numerous capsules forming solid 
spikes. Five of these capsules were examined and appeared to 
contain an equal number of seeds; and these being counted in 
one capsule, were found to be 166. The five protected plants pro- 
duced altogether only twenty-five capsules, of which five were 
much finer than all the others, and these contained an average of 
23 6 seeds, with a maximum in one capsule of fifty-five. So that 
the number of seeds in the capsules on the exposed plants to 
the average number in the finest capsules on the protected 
plants was as 100 to 14. 

Some of the spontaneously self-fertilised seeds from under 
the net, and some seeds from the uncovered plants naturally 
fertilised and almost certainly intercrossed by the bees, were 
sown separately in two large pots of the same size ; so that the 



Die Befruohtung,' &c. p. 279. 



CHAP. IIL VEBBASCUM THAPSUS. 89 

two lots of seedlings were not subjected to any mutual competi- 
tion. Three of the crossed plants when in full flower were 
measured, but no care was taken to select the tallest plants ; 
their heights were 7f, 7|, and 6| inches; averaging 7 '08 in 
height. The three tallest of all the self-fertilised plants were 
then carefully selected, and their heights were 6|, 5f , and 5|, 
averaging 5 '75 in height. So that the naturally crossed plants 
were to the spontaneously self-fertilised plants in height, at 
least as much as 100 to 81. 

VEBBASCUM THAPSUS. 

The flowers of this plant are frequented by various insects, 
chiefly by bees, for the sake of the pollen. H. Miiller, however, 
has shown ('Die Befruchtung,' &c. p. 277) that F. nigrum 
secretes minute drops of nectar. The arrangement of the re- 
productive organs, though not at all complex, favours cross- 
fertilisation; and even distinct species are often crossed, for a 
greater number of naturally produced hybrids have been observed 
in this genus than in almost any other.* Nevertheless the 
present species is perfectly self -fertile, if insects are excluded ; 
for a plant protected by a net was as thickly loaded with fine 
capsules as the surrounding uncovered plants. V&rbascum 
lychnitis is rather less self-fertile, for some protected plants did 
net yield quite so many capsules as the adjoining uncovered 
plants. 

Plants of F. thapsus had been raised for a distinct purpose 
from self- fertilised seeds ; and some flowers on these plants were 
again self-fertilised, yielding seed of the second self-fertilised 
generation ; and other flowers were crossed with pollen from a 
distinct plant. The seeds thus produced were sown on the 
opposite sides of four large pots. They germinated, however, so 
irregularly (the crossed seedlings generally coming up first) 
that I was able to save only six pairs of equal age. These when 
in full flower were measured, as in the following table (XXV.). 

"We here see that two of the self-fertilised plants exceed in 
height their crossed opponents. Nevertheless the average height 
of the six crossed plants is 65 '34 inches, and that of the six 
self- fertilised plants 56 -5 inches ; or as 100 to 86. 



* I have given a striking case found growing wild : ' Journal of 
of a large number of such hybrids Linn. Soc. Bot.' vol. x. p. 451. 
between F. thapstu and lychnitis 



90 



VANDELLIA NUMMULAKIFOLIA. 
TABLE XXV. 



CHAP. IIL 



No. of Pot. 


Crossed Plants. 


Self-fertilised Plants 
of the Second Gene- 
ration. 


I. 


Inches. 
76 


Inches. 
53| 


II. 


54 


66 


III. 


62 
60 j 


75 
30 1 


IV. 


73 
66j 


62 
52 


Total in inches. 


392-13 


339-00 



VANDELLIA NTTMMULABIFOLIA. 

Seeds were sent to me by Mr. J. Scott from Calcutta of this 
small Indian weed, which bears perfect and cleistogamic * flowers. 
The latter are extremely small, imperfectly developed, and never 
expand, yet yield plenty of seeds. The perfect and open 
flowers are also small, of a white colour with purple marks ; they 
generally produce seed, although the contrary has been 
asserted ; and they do so even if protected from insects. They 
have a rather complicated structure, and appear to be adapted 
for cross-fertilisation, but were not carefully examined by me. 
They are not easy to fertilise artificially, and it is possible that 
some of the flowers which I thought that I had succeeded in 
crossing were afterwards spontaneously self-fertilised under the 
net. Sixteen capsules from the crossed perfect flowers contained 
on an average ninety-three seeds (with a maximum in one 
capsule of 137), and thirteen capsules from the self-fertilised 
perfect flowers contained sixty-two seeds (with a maximum in 
one capsule of 135) ; or as 100 to 67. But I suspect that this 
considerable excess was accidental, as on one occasion nine 
crossed capsules were compared with seven self-fertilised cap- 
sules (both included in the above number), and they contained 
almost exactly the same average number of seed. I may add 



* The convenient term of cleis- 
togamic was proposed by Kuhn in 



an article on the present genua in 
' Bot. Zeituug,' 1867, p. G5. 



OHAP. III. VANDELLIA NUMMULARIFOLIA. 9.1 

that fifteen capsules from self-fertilised cleistogamic flowers con- 
tained on an average sixty-four seeds, with a maximum in one 
of eighty-seven. 

Crossed and self-fertilised seeds from the perfect flowers, and 
other seeds from the self-fertilised cleistogamic flowers, were sown 
in five pots, each divided superficially into three compartments. 
The seedlings were thinned at an early age, so that twenty 
plants were left in each of the three divisions. The crossed plants 
when in full flower averaged 4'3 inches, and the self-fertilised 
plants from the perfect flowers 4 ' 27 inches in height ; or as 100 
to 99. The self-fertilised plants from the cleistogamic flowers 
averaged 4 '06 inches in height; so that the crossed were in 
height to these latter plants as 100 to 94. 

I determined to compare again the growth of plants raised 
from crossed and self-fertilised perfect flowers, and obtained two 
fresh lots of seeds. These were sown on opposite sides of five 
pots, but they were not sufficiently thinned, so that they grew 
rather crowded. When fully grown, all those above 2 inches 
in height were selected, all below this standard being rejected ; 
the former consisted of forty-seven crossed and forty-one self- 
fertilised plants ; thus a greater number of the crossed than of 
the self-fertilised plants grew to a height of above 2 inches. Of 
the crossed plants, the twenty-four tallest were on an average 
3' 6 inches in height; whilst the twenty- four tallest self- 
fertilised plants were 3 38 inches in average height ; or as 100 
to 94. All these plants were then cut down close to the ground, 
and the forty-seven crossed plants weighed 1090 '3 grains, and 
the forty-one self-fertilised plants weighed 887 4 grains. There- 
fore an equal number of crossed and self-fertilised would have 
been to each other in weight as 100 to 97. From these several 
facts we may conclude that the crossed plants had some real, 
though very slight, advantage in height and weight over the 
self-fertilised plants, when grown in competition with one 
another. 

The crossed plants were, however, inferior in fertility to the 
self-fertilised. Six of the finest plants were selected out of the 
forty-seven crossed plants, and six out of the forty-one self- 
fertilised plants ; and the former produced 598 capsules, whilst 
the latter or self-fertilised plants produced 752 capsules. All 
these capsules were the product of cleistogamic flowers, for the 
plants did not bear during the whole of this season any perfect 
flowers. The seeds were counted in ten cleistogamic capsules 



GESNEKIA PENDULINA, 



CHAP. I1L 



produced by the crossed plants, and their average number was 
46 4 per capsule ; whilst the number in ten cleistogamic capsules 
produced by the self-fertilised plants was 49 '4 ; or as 100 to 106 

m. GESNEEIACE^. GKSNEBIA PEKDULINA. 

In Gesneria the several parts of the flower are arranged on 
nearly the same plan as in Digitalis,* and most or all of the 
species are dichogamous. Plants were raised from seed sent me 
by Fritz Miiller from South Brazil. Seven flowers were crossed 
with pollen from a distinct plant, and produced seven capsules 
containing by weight 3*01 grains of seeds. Seven flowers on the 
same plants were fertilised with their own pollen, and theii 
seven capsules contained exactly the same weight of seeds 
Germinating seeds were planted on opposite sides of four pots 
and when fully grown measured to the tips of their leaves. 

TABLE XXVI. 



No. of Pot. 


Crossed Plants. 


Self-fertilised Plants. 


' 


Inches. 
42j 
24J 


Inches. 
39 
27f 


II. 


33 
27 


308 
1 


III. 


33 j 
29j 


31? 
28f 


IV. 


30 1 
36 


29{j 
26 1 


Total inches. 


256-50 


233-13 



The average height of the eight crossed plants is 32-06 inches, 
and that of the eight self-fertilised plants 29-14; or as 100 
to 90. 



* Dr. Ogle, ' Popular Science Review,' Jan 1870, p. 51. 



CHAP. III. 



SAL VI A COCCINEA. 



93 



IV. LABIATES. SAL vi A COCOINKA.* 

This specias, unlike most of the others in the same genus, 
yields a good many seeds when insects are excluded. I gathered 
ninety-eight capsules produced by flowers spontaneously self- 
fertilised under a net, and they contained on an average 1*45 
seeds, whilst flowers artificially fertilised with their own pollen, 
in which case the stigma will have received plenty of pollen, 
yielded on an average 3 '3 seeds, or more than twice as many. 
Twenty flowers were crossed with pollen from a distinct plant, 
and twenty-six were self-fertilised. There was no great difference 
in the proportional number of flowers which produced capsules 
by these two processes, or in the number of the contained seeds 
or in the weight of an equal number of seeds. 

Seeds of both kinds were sown rather thickly on opposite sides 
of three pots. When the seedlings were about 3 inches in 
height, the crossed showed a slight advantage over the self- 
fertilised. When two-thirds grown, the two tallest plants on 
each side of each pot were measured ; the crossed averaged 16 37 
inches, and the self-fertilised 11 '75 in height; or as 100 to 71. 
When the plants were fully grown and had done flowering, the 
two tallest plants on each side were again measured, with the 
results shown in the following table : 

TABLE XXVII. 



No. of Pot. 


Crossed Plants. 


Self-fertilised Plant* 


I. 


Inches. 
32 1 
20 


Inches. 
25 
18g 


II. 


32? 
M| 


20 1 
19* 


III. 


29 1 

28 


25 
18 


Total inches. 


167-13 


127-00 



* The admirable mechanical 
adaptations in this genus for 
favouring or ensuring cross-ferti- 
liation, have been fully described 



by Sprengel, Hildebrand, Delpino, 
H. Muller, Ogle, and others, in 
their several works. 



94 OK1GANUM VULGAUE. CHAP. Ill 

It may be here seen that each of the six tallest crossed plants 
exceeds in height its self-fertilised opponent; the former 
averaged 27 '85 inches, whilst the six tallest self-fertilised plants 
averaged 21 16 inches ; or as 100 to 76. In all three pots the 
first plant which flowered was a crossed one. All the crossed 
plants together produced 409 flowers, whilst all the self-fertilised 
together produced only 232 flowers ; or as 100 to 57. So that 
the crossed plants in this respect were far more productive than 
the self-fertilised. 

OBIGANUM VULQARE. 

This plant exists, according to H. Muller, under two forms ; 
one hermaphrodite and strongly proterandrous, so that it is 
almost certain to be fertilised by pollen from another flower ; 
the other form is exclusively female, has a smaller corolla, and 
must of course be fertilised by pollen from a distinct plant 
in order to yield any seeds. The plants on which I experi- 
mented were hermaphrodites ; they had been cultivated for a 
long period as a pot-herb in my kitchen garden, and were, like 
so many long-cultivated plants, extremely sterile. As I felt 
doubtful about the specific name I sent specimens to Kew, and 
was assured that the species was 0. vulgare. My plants formed 
one great clump, and had evidently spread from a single root 
by stolons. In a strict sense, therefore, they all belonged to the 
same individual. My object in experimenting on them was, 
firstly, to ascertain whether crossing flowers borne by plants 
having distinct roots, but all derived asexually from the same 
individual, would be in any respect more advantageous than 
self-fertilisation ; and, secondly, to raise for future trial seedlings 
which would constitute really distinct individuals. Several 
plants in the above clump were covered by a net, and about two 
dozen seeds (many of which, however, were small and withered) 
were obtained from the flowers thus spontaneously self-fertilised. 
The remainder of the plants were left uncovered and were in- 
cessantly visited by bees, so that they were doubtless crossed 
by them. These exposed plants yielded rather more and finer 
seed (but still very few) than did the covered plants. The two 
lots of seeds thus obtained were sown on opposite sides of two 
pots ; the seedlings were carefully observed from their first 
growth to maturity, but they did not differ at any period in 
height or in vigour, the importance of which latter observation 
we shall presently see. When fully grown, the tallest crossed 



CHAP. III. ORIGANUM VULGARK. 95 

plant in one pot was a very little taller than the tallest self- 
fertilised plant on the opposite side, and in the other pot 
exactly the reverse occurred. So that the two lots were in fact 
equal ; and a cross of this kind did no more good than crossing 
two flowers on the same plant of Ipomoea or Mimulus. 

The plants were turned out of the two pots without being 
disturbed and planted in the open ground, in order that they 
might grow more vigorously. In the following summer all the 
self-fertilised and some of the quasi-crossed plants were covered 
by a net. Many flowers on the latter were crossed by me with 
pollen from a distinct plant, and others were left to be crossed 
by the bees. These quasi-crossed plants produced rather more 
seed than did the original ones in the great clump when left 
to the action of the bees. Many flowers on the self-fertilised 
plants were artificially self-fertilised, and others were allowed 
to fertilise themselves spontaneously under the net, but they 
yielded altogether very few seeds. These two lots of seeds 
the product of a cross between distinct seedlings, instead of as 
in the last case between plants multiplied by stolons, and the 
product of self-fertilised flowers were allowed to germinate on 
bare sand, and several equal pairs were planted on opposite 
sides of two large pots. At a very early age the crossed 
plants showed some superiority over the self-fertilised, which 
was ever afterwards retained. When the plants were fully 
grown, the two tallest crossed and the two tallest self-fertilised 
plants in each pot were measured, as shown in the following 
table. I regret that from want of time I did not measure all 
the pairs ; but the tallest on each side seemed fairly to represent 
the average difference between the two lots. 

TABLE XXVIII. 



No. of Pot. 


Crossed Plants (two 
tallest in each pot). 


Self-fertilised Plants 
(two tallest in each 
pot). 


I 


Inch s. 
26 
21 


Inches. 
24 
21 


II. 


17 
16 


12 
i 


Total inches. 


80-0 


68-5 



96 THTJNBEEGIA ALATA. CHAP. III. 

The average height of the crossed plants is here 20 inches, and 
that of the self-fertilised 17'12 ; or as 100 to 86. But this excess 
of height by no means gives a fair idea of the vast superiority in 
vigour of the crossed over the self-fertilised plants. The crossed 
flowered first and produced thirty flower-stems, whilst the self- 
fertilised produced only fifteen, or half the number. The pots 
were then bedded out, and the roots probably came out of the 
holes at the bottom and thus aided their growth. Early in the 
following summer the superiority of the crossed plants, owing 
to their increase by stolons, over the self-fertilised plants was 
truly wonderful. In Pot I., and it should be remembered that 
very large pots had been used, the oval clump of crossed plants 
was 10 by 4i inches across, with the tallest stem, as yet young, 
5i inches in height ; whilst the clump of self-fertilised plants, 
on the opposite side of the same pot, was only 85 by 2 1 inches 
across, with the tallest young stem 4 inches in height. In Pot 
II., the clump of crossed plants was 18 by 9 inches across, with 
the tallest young stem 83 inches in height ; whilst the clump of 
self-fertilised plants on the opposite side of the same pot was 12 
by 4i inches across, with the tallest young stem 6 inches in 
height. The crossed plants during this season, as during the 
last, flowered first. Both the crossed and self-fertilised plants 
being left freely exposed to the visits of bees, manifestly produced 
much more seed than their grand-parents, the plants of the 
original clump still growing close by in the same garden, and 
equally left to the action of the bees 

V. ACANTHACE2E. THUNBERGIA ALATA. 

It appears from Hildebrand's description (' Bot. Zeitung,' 1867, 
p. 285) that the conspicuous flowers of this plant are adapted 
for cross-fertilisation. Seedlings were twice raised from pur- 
chased seed; but during the early summer, when first expe- 
rimented on, they were extremely sterile, many of the anthers 
containing hardly any pollen. Nevertheless, during the autumn 
these same plants spontaneously produced a good many seeds. 
Twenty-six flowers during the two years were crossed with 
pollen from a distinct plant, but they yielded only eleven 
capsules; and these contained very few seeds! Twenty-eight 
flowers were fertilised with pollen from the same flower, and 
these yielded only ten capsules, which, however, contained 
rather more seed than the crossed capsules. Eight pairs of 



CHAP. III. THUNBERGIA ALATA. 97 

germinating seeds were planted on opposite sides of five pots ; 
and exactly half the crossed and half the self-fertilised plants 
exceeded their opponents in height. Two of the self-fertilised 
plants died young, before they were measured, and their crossed 
opponents were thrown away. The six remaining pairs grew 
very unequally, some, both of the crossed and self-fertilised 
plants, being more than twice as tall as the others. The average 
height of the crossed plants was 60 inches, and that of the self- 
fertilised plants 65 inches, or as 100 to 108. A cross, therefore, 
between distinct individuals here appears to do no good ; but 
this result deduced from so few plants in a very sterile condition 
and growing very unequally, obviously cannot be trusted. 



98 BEASSICA OLEBAOEA. CHAP. IV. 



CHAPTEK IV. 

CBCCTFEBJE, PAPAVERACES:, EESEDACEJB, ETC. 

Brassiea Oleracea, crossed and self-fertilised plants Great effect of a 
cross with a fresh stock on the weight of the offspring Iberis 
umbellata Papaver vagum Eschscholtzia californiea, seedlings 
from a cross with a fresh stock not more vigorous, but more 
fertile than the self- fertilised seedlings Eesedalutca and odorata, 
many individuals sterile with their own pollen Viola tricolor, 
wonderful effects of a cross Adonis sestivalis Delphinium consolida 
Viscaria oculata, crossed plants hardly taller, but more fertile than 
the self-fertilised DJanthus caryophyllus, crossed and self-fertilised 
plants compared for four generations Great effects of a cross witk 
a fresh stock Uniform colour of the flowers on the self-fertilised 
plants Hibiscus africauus. 

VI. CKUCIFEK.ZE. BEASSICA OLERACEA. 
For. Cattell's Early Barnes Cabbage. 

THE flowers of the common cabbage are adapted, as shown by 
H. Miiller,* for cross-fertilisation, and should this fail, for self- 
fertilisation. It is well known that the varieties are crossed so 
largefy by insects, that it is impossible to raise pure kinds in the 
same garden, if more than one kind is in flower at the same time 
Cabbages, in one respect, were not well fitted for my experiments, 
as, after they had formed heads, they were often difficult to mea- 
sure. The flower-stems also differ much in height ; and a poor 
plant will sometimes throw up a higher stem than that of a fire 
plant. In the later experiments, the fully-grown plants were cut 
down and weighed, and then the immense advantage from a 
cross became manifest. 

A single plant of the above variety was covered with a net 
just before flowering, and was crossed with pollen from another 
plant of the same variety growing close by ; and the seven cap- 
sules thus produced contained on an average 16 '3 seeds, with a 



1 Die Befruchtung,' &c. p. 139. 



CHAP. IV. CROSSED AND SELF-FERTILISED PLANTS. 99 

maximum of twenty in one capsule. Some flowers were arti- 
ficially self-fertilised, but their capsules did not contain so many 
seeds as those from flowers spontaneously self- fertilised under 
the net, of which a considerable number were produced. Fourteen 
of these latter capsules contained on an average 4'1 seeds, with 
a maximum in one of ten seeds ; so that the seeds in the crossed 
capsules were in number to those in the self-fertilised capsules as 
100 to 25. The self-fertilised seeds, fifty-eight of which weighed 
3 '88 grains, were, however, a little finer than those from the 
crossed capsules, fifty-eight of which weighed 3 76 grains. When 
few seeds are produced, these seem often to be better nourished 
and to be heavier than when many are produced. 

The two lots of seeds in an equal state of germination were 
planted, some on opposite sides of a single pot, and some in the 
open ground. The young crossed plants in the ]K>t at first ex- 
ceeded by a little in height the self-fertilised ; then equalled them ; 
were then beaten ; and lastly were again victorious. The plants, 
without being disturbed, were turned out of the pot, and planted 
in the open ground; and after growing for some time, the 
crossed plants, which were all of nearly the same height, exceeded 
the self-fertilised ones by 2 inches. When they flowered, the 
flower-stems of the tallest crossed plant exceeded that of the 
tallest self-fertilised plant by 6 inches. The other seedlings 
which were planted in the open ground stood separate, so that 
they did not compete with one another ; nevertheless the crossed 
plants certainly grew to a rather greater height than the self-fer- 
tilised ; but no measurements were made. The crossed plants 
which had been raised in the pot, and those planted in the open 
ground, all flowered a little before the self-fertilised plants. 

Crossed and self -fertilised Plants of the Second Generation. Some 
flowers on the crossed plants of the last generation were again 
crossed with pollen from another crossed plant, and produced 
fine capsules. The flowers on the self-fertilised plants of the 
last generation were allowed to fertilise themselves spontaneously 
under a net, and they produced some remarkably fine capsules. 
The two lots of seeds thus produced germinated on sand, and 
eight pairs were planted on opposite sides of four pots. These 
plants were measured to the tips of their leaves* on the 
20th of October of the same year, and the eight crossed plants 
averaged in height 8 '4 inches, whilst the self-fertilised averaged 
8'53 inches, so that the crossed were a little inferior in height, 
as 100 to 101*5. By the 5th of June of the following year these 

H 2 



100 



BRASSICA OLEEACEA. 



CHAP. IV 



plants had grown much bulkier, and had begun to form 
heads. The crossed had now acquired a marked superiority 
in general appearance, and averaged 8 '02 inches in height, 
whilst the self-fertilised averaged 7 '31 inches; or as 100 to 91. 
The plants were then turned out of their pots and planted 
undisturbed in the open ground. By the 5th of August their 
heads were fully formed, but several had grown so crooked that 
their heights could hardly be measured with accuracy. The 
crossed plants, however, were on the whole considerably taller 
than the self-fertilised. In the following year they flowered ; the 
crossed plants flowering before the self-fertilised in three of the 
pots, and at the same time in Pot II. The flower-stems were 
now measured, as shown in Table XXIX. 

TABLE XXIX. 

Measured to tops of Flower-stems ; signifies that a Flower-stem 
was not formed. 



No. of Pot. 


Crossed Plants. 


Self-fertilised Plants. 


I. 


Inches. 
49 
39$ 


Inches. 
44 
41 


II. 


37 1 
33| 


38 
35 J 


HI. 


47 
40 
42 


511 

41 
l 


IV. 


43 S 

3Ji 


20 jj 

| 


Total in inches. 


369-75 


351-00 



The nine flower-stems on the crossed plants here average 41 -08 
inches, and the nine on the self-fertilised plants 39 inches in 
height, qr as 100 to 95. But this small difference, which, more- 
over, depended almost wholly on one of the self-fertilised plants 
being only 20 inches high, does not in the least show the vast 
superiority of the crossed over the self-fertilised plants. Both 
lots, including the two plants in Pot IV., which did not 
flower, were now cut down close to the ground and weighed, but 



CHAP. IV. 



CROSS WITH A FKESH STOCK. 



101 



those in Pot II. were excluded, for they had been accidentally 
injured by a fall during transplantation, and one was almost 
killed. The eight crossed plants weighed 219 ounces, whilst the 
eight self-fertilised plants weighed only 82 ounces, or as 100 to 37 ; 
so that the superiority of the former over the latter in weight was 
great 

The Effects of a Cross with a fresh Stock. Some flowers on a 
crossed plant of the last or second generation were fertilised, 
without being castrated, by pollen taken from a plant of the 
same variety, but not related to my plants, and brought from a 
nursery garden (whence my seeds originally came) having a dif- 
ferent soil and aspect. The flowers on the self-fertilised plants 
of the last or second generation (Table XXIX.) were allowed to 
fertilise themselves spontaneously under a net, and yielded 
plenty of seeds. These latter and the crossed seeds, after germi- 
nating on sand, were planted in pairs on the opposite sides 
of six large pots, which were kept at first in a cool greenhouse. 
Early in January their heights were measured to the tips of their 
leaves. The thirteen crossed plants averaged 13 16 inches in 
height, and the twelve (for one had died) self-fertilised plants 
averaged 13 '7 inches, or as 100 to 104; so that the self-fertilised 
plants exceeded by a little the crossed plants. 

TABLE XXX. 

Weight of Plants after they had formed Heads. 



No. of Pot. 


Crossed Plants from 
Pollen of fresh Stock. 


Self-fertilised Plants 
of the Third Gene- 
ration. 


I. 


Ounces. 
130 


Ounce*. 
18] 


II. 


74 


34? 


III. 


121 


17J 


IV. 


127 1 


14 


V. 


90 


11J 


VL 


106 1 


46 


Total in ounces. 


649-00 


142-25 



102 BRASSICA OLERACEA. CHAP. IV 

Early in the spring the plants were gradually hardened, and 
turned out of their pots into the open ground without being 
disturbed. By the end of August the greater number had 
formed fine heads, but several grew extremely crooked, from 
having been drawn up to the light whilst in the greenhouse. 
As it was scarcely possible to measure their heights, the finest 
plant on each side of each pot was cut down close to the ground 
and weighed. In the preceding table we have the result. 

The six finest crossed plants average 108*16 ounces, whilst 
the six finest self-fertilised plants average only 23 7 ounces, or 
as 100 to 22. This difference shows in the clearest manner the 
enormous benefit which these plants derived from a cross with 
another plant belonging to the same sub- variety, but to a fresh 
stock, and grown during at least the three previous generations 
under somewhat different conditions. 

The Offspring from a cut-leaved, curled, and variegated white 
green Cabbage crossed with a cut-leaved, curled, and variegated 
crimson-green Cabbage, compared with the self-fertilised Offspring 
from the two Varieties. These trials were made, not for the 
sake of comparing the growth of the crossed and self-fertilised 
seedlings, but because I had seen it stated that these varieties 
would not naturally intercross when growing uncovered and 
near one another. This statement proved quite erroneous ; but 
the white-green variety was in some degree sterile in my garden, 
producing little pollen and few seeds. It was therefore no 
wonder that seedlings raised from the self-fertilised flowers of this 
variety were greatly exceeded in height by seedlings from a cross 
between it and the more vigorous crimson-green variety ; and 
nothing more need be said about this experiment. 

The seedlings from the reciprocal cross, that is, from the crim- 
son-green variety fertilised with pollen from the white-green 
variety, offer a somewhat more curious case. A few of these 
crossed seedlings reverted to a pure green variety with their 
leaves less cut and curled, so that they were altogether in a much 
more natural state, and these plants grew more vigorously and 
taller than any of the others. Now it is a strange fact that a 
much larger number of the self-fertilised seedlings from the 
crimson-green variety than of the crossed seedlings thus reverted ; 
and as a consequence the self-fertilised seedlings grew taller by 
2i inches on an average than the crossed seedlings, with which 
they were put into competition. At first, however, the crossed 
seedlings exceeded the self-fertilised by an average of a quarter 



CHAP. IV. IBEEIS UMBELLATA. 103 

of an inch. We thus see that reversion to a more natural con- 
dition acted more powerfully in favouring the ultimate growth 
of these plants than did a cross ; but it should be remembered 
that the cross was with a semi-sterile variety having a feeble 
constitution. 

IBEEIS UMBELLATA. 
For. Eermesiana. 

This variety produced plenty of spontaneously self-fertilised 
seed under a net. Other plants in pots in the greenhouse were 
left uncovered, and as I saw small flies visiting the flowers, it 
seemed probable that they would be intercrossed. Consequently 
seeds supposed to have been thus crossed and spontaneously self- 
fertilised seeds were sown on opposite sides of a pot. The 
self-fertilised seedlings grew from the first quicker than the 
supposed crossed seedlings, and when both lots were in full 
flower the former were from 5 to 6 inches higher than the crossed ! 
I record in my notes that the self-fertilised seeds from which 
these self-fertilised plants were raised were not so well ripened 
as the crossed ; and this may possibly have caused, from pre- 
mature growth, the great difference in their height, in nearly 
the same manner as when self-fertilised seeds of other plants 
were sown a few days before the crossed in the same pot. 
We have seen a somewhat analogous case with the self-fertilised 
plants of the eighth generation of Ipomcea, raised from unhealthy 
parents. It is a curious circumstance, that two other lots of the 
above seeds were sown in pure sand mixed with burnt earth, 
and therefore without any organic matter ; and here the sup- 
posed crossed seedlings grew to double the height of the self- 
fertilised, before both lots died, as necessarily occurred at an 
early period. We shall hereafter meet with another case 
apparently analogous to this of Iberis in the third generation 
of Petunia. 

The above self*fertilised plants were allowed to fertilise them- 
selves again under a net, yielding self-fertilised plants of the 
second generation, and the supposed crossed plants were crossed 
by pollen of a distinct plant ; but from want of time this was done 
in a careless manner, namely, by smearing one head of expanded 
flowers over another. I should have thought that this would 
have succeeded, and perhaps it did so; but the fact of 108 
of the self-fertilised seeds weighing 4 '87 grains, whilst the same 
number of the supposed crossed seeds weighed only 3 "57 grains, 



J04 



IBERIS UMBELLATA. 



CHAP. 



does not look like it. Five seedlings from each lot of seeds were 
raised, and the self-fertilised plants, when fully grown, exceeded 
in average height by a trifle (viz. 4 of an inch) the five probably 
crossed plants. I have thought it right to give this case and the 
last, because had the supposed crossed plants proved superior 
to the self-fertilised in height, I should have assumed without 
doubt that the former had really been crossed. As it is, I do not 
know what to conclude. 

Being much surprised at the two foregoing trials, I deter- 
mined to make another, in which there should be no doubt about 
the crossing. I therefore fertilised with great care (but as 
usual without castration) twenty-four flowers on the supposed 
crossed plants of the last generation with pollen from distinct 
plants, and thus obtained twenty-one capsules. The self-fertilised 
plants of the last generation were allowed to fertilise themselves 
again under a net, and the seedlings reared from these seeds 
formed the third self-fertilised generation. Both lots of seeds, 
after germinating on bare sand, were planted in pairs on 
the opposite sides of two pots. All the remaining seeds were 
sown crowded on opposite sides of a third pot ; but as all the 
self-fertilised seedlings in this latter pot died before they grew 
to any considerable height, they were not measured. The 
plants in Pots I. and II. were measured when between 7 and 
8 inches in height, and the crossed exceeded the self-fertilised 
in average height by 1 57 inches. When fully grown they were 
again measured to the summits of their flower-heads, with the 
following result : 

TABLE XXXI. 



No. of Pot. 


Crossed Plants. 


Self-fertilised Plants 
of the Third Gene- 
ration. 


I. 


Incnes. 
18 
21 


Inches. 
19 
21 


II. 


19 
17f 


Ml 

.1! 

M| 


Total in inches. 


133-88 


114-75 



CHAP. IV. CROSS WITH A FBESH STOCK. 105 

The average height of the seven crossed plants is here 19 12 
inches, and that of the seven self-fertilised plants 16 '39, or as 
100 to 86. But as the plants on the self-fertilised side grew 
very unequally, this ratio cannot be fully trusted, and is probably 
too high. In both pots a crossed plant flowered before any one 
of the self-fertilised. These plants were left uncovered in the 
greenhouse; but from being too much crowded they were not 
very productive. The seeds from all seven plants of both lots 
were counted ; the crossed produced 206, and the self-fertilised 
154; or as 100 to 75. 

Cross by afresh Stock. From the doubts caused by the two 
first trials, in which it was not known with certainty that the 
plants had been crossed; and from the crossed plants in the 
last experiment having been put into competition with plants 
selMertilised for three generations, which moreover grew very 
unequally, I resolved to repeat the trial on a larger scale, and 
in a rather different manner. I obtained seeds of the same 
crimson variety of J. umbellata from another nursery garden, 
and raised plants from them. Some of these plants were allowed 
to fertilise themselves spontaneously under a net; others were 
crossed by pollen taken from plants raised from seed sent me by 
Dr. Durando from Algiers, where the parent-plants had been cul- 
tivated for some generations. These latter plants differed in hav- 
ing pale pink instead of crimson flowers, but in no other respect. 
That the cross had been effective (though the flowers on the crim- 
son mother-plant had not been castrated) was well shown when the 
thirty crossed seedlings flowered, for twenty -four of them produced 
pale pink flowers, exactly like those of their father ; the six others 
having crimson flowers exactly like those of their mother 
and like those of all the self-fertilised seedlings. This case 
offers a good instance of a result which not rarely follows 
from crossing varieties having differently coloured flowers; 
namely, that the colours do not blend, but resemble perfectly those 
either of the father or mother plant. The seeds of both lots, 
after germinating on sand, were planted on opposite sides of 
eight pots. When fully grown, the plants were measured to 
the summits of the flower-heads, as shown in the following 
table : 



106 



IBEBIS UMBELLATA. 



CHAP. IV 



TABLE XXXII. 

Iberis umbellata : signifies that the Plant died. 



No. of Pot. 


Plants from a Cross 
with a fresh Stock. 


Plants from Spon- 
taneously Self-ferti- 
lised Seeds. 




Inches. 


Inches. 


I. 


m 


17 






17| 


16 






17f 


13 






20J 


15 




II. 


20 







i5 l 


16 








15 




III. 


19 


13 1 




18ft 


14 






151 


13 




IV. 


1*1 


16 | 




185 


144 




178 


16 




15f 


152 




14 1 


14? 


V. 


18ft 


16 








16 






161 


14 






15| 


14 






M| 


16 




VI. 


181 


16i 




18 j 


15 




"1 


151 


VII. 


18 


16 






M| 


14 






181 


13 




VIII. 


20 1 


158 




17J 


163 




13| 


20 1 




19 


16 j 


Total in inches. 


520-38 


449-88 



The average height of the thirty crossed plants is here 
17-34, and that of the twenty-nine self-fertilised plants (one 



CHAP. IV. PAPAVER VAGUM. 107 

having died) 15 '51, or as 100 to 89. I am surprised that the 
difference did not prove somewhat greater, considering that in 
the last experiment it was as 100 to 86; but this latter ratio, as 
before explained, was probably too great. It should, however, 
be observed that in the last experiment (Table XXXI.), the 
crossed plants competed with plants of the third self-fertilised 
generation ; whilst in the present case, plants derived from a 
cross with a fresh stock competed with self-fertilised plants of 
the first generation. 

The crossed plants in the present case, as in the last, were 
more fertile than the self-fertilised, both lots being left un- 
covered in the greenhouse. The thirty crossed plants produced 
103 seed-bearing flower-heads, as well as some heads which 
yielded no seeds ; whereas the twenty-nine self-fertilised plants 
produced only 81 seed-bearing heads; therefore thirty such 
plants would have produced 83*7 heads. We thus get the 
ratio of 100 to 81, for the number of seed-bearing flower-heads 
produced by the crossed and self-fertilised plants. Moreover, a 
number of seed-bearing heads from the crossed plants, com- 
pared with the same number from the self-fertilised, yielded 
seeds by weight, in the ratio of 100 to 92. Combining these 
two elements, viz., the number of seed-bearing heads and the 
weight of seeds in each head, the productiveness of the crossed 
to the self-fertilised plants was as 100 to 75. 

The crossed and self-fertilised seeds, which remained after 
the above pairs had been planted, (some in a state of germina- 
tion and some not so), were sown early in the year out of doors 
in two rows. Many of the self-fertilised seedlings suffered 
greatly, and a much larger number of them perished than of 
the crossed. In the autumn the surviving self-fertilised plants 
were plainly less well-grown than the crossed plants. 

VII. PAPAVEBACE.E. PAPAVEB VAGUM. 

A sub-species of P. dub I urn, from the south of Frame. 
The poppy does not secrete nectar, but the flowers are highly 
conspicuous and are visited by many pollen-collecting bees, 
flies and beetles. The anthers shed their pollen very early, and 
in the case of P. rhaas, it falls on the circumference of the 
radiating stigmas, so that this species must often be self-ferti- 
lised; but with P. dubium the same result does not follow 
(according to H. Muller, ' Die Befruchtung,' p. 128), owing to 



108 PAPAVEB VAGUM. CHAP. IV 

the shortness of the stamens, unless the flower happens to stand 
inclined. The present species, therefore, does not seem so well 
fitted for self-fertilisation as most of the others. Nevertheless 
P. vagum produced plenty of capsules in my garden when insects 
were excluded, but only late in the season. I may here add that 
P. somniferum produces an abundance of spontaneously self- 
fertilised capsules, as Professor H. Hoffmann likewise found to 
be the case.* Some species of Papaver cross freely when growing 
in the same garden, as I have known to be the case with P, 
bracteatum and orientale. 

Plants of Papaver vagum were raised from seeds sent me from 
Antibes through the kindness of Dr. Bornet. Some little time 
after the flowers had expanded, several were fertilised with 
their own pollen, and others (not castrated) with pollen from a 
distinct individual ; but I have reason to believe, from observa- 
tions subsequently made, that these flowers had been already 
fertilised by their own pollen, as this process seems to take place 
soon after their expansion.! I raised, however, a few seedlings 
of both lots, and the self-fertilised rather exceeded the crossed 
plants in height. 

Early in the following year I acted differently, and fertilised 
seven flowers, very soon after their expansion, with pollen from 
another plant, and obtained six capsules. From counting the 
seeds in a medium-sized one, I estimated that the average 
number in each was at least 120. Four out of twelve capsules, 
spontaneously self-fertilised at the same time, were found to 
contain no good seeds ; and the remaining eight contained on 
an average 6'6 seeds per capsule. But it should be observed 
that later in the season the same plants produced under a net 
plenty of very fine spontaneously self-fertilised capsules. 

The above two lots of seeds, after germinating on sand, were 
planted in pairs on opposite sides of five pots. The two lots of 
seedlings, when half an inch in height, and again when 6 inches 
high, were measured to the tips of their leaves, but presented 

* 'Zur Speciesfrage,' 1875, p. 53. -done " on the second day, or even 

* Mr. J. Scott found ('Keport a few hours after the expansion 
on the Experimental Culture of of the flower on the first day, a 
the Opium Poppy :' Calcutta, 1874, partial fertilisation had already 
p. 47), in the case of Papaver som- been effected, and a few good 
niferum, that if he cut away the seeds were almost invariably pro- 
stigmatic surface before the duced." This proves at how early 
flower had expanded, no seeds a period fertilisation takes place, 
were produced; but if this was 



CHAP. IV. 



ESCHSCHOLTZIA CALIFORNICA. 



109 



DO difference. When fully grown, the flower-stalks were 
measured to the summits of the seed capsules, with the follow- 
ing result : 

TABLE XXXIH. 

Papaver vagum. 



No. of Pot. 


Crowed Plants. 


Self-fertilised Plants. 


- I. 


Inches. 
24 1 
30 

m 


Inches. 
21 

26| 
16 


II. 


14 3 

22 
19| 
21| 


15 

20 
14 
16 

19| 
13| 
18 


III. 


20| 
20 
20 1 


IV. 


25 1 
24J 


23 
23 


V. 


20 
27 J 
19 


18? 
27 
21 


Total in inches. 


328-75 


293-13 



The fifteen crossed plants here average 21 '91 inches, and the 
fifteen self-fertilised plants 19 -54 inches in height, or as 100 to 
89. These plants did not differ in fertility, as far as could be 
judged by the number of capsules produced, for there were 
seventy-five on the crossed side and seventy-four on the self- 
fertilised side. 

EscnscnoLTziA CALIFORNIOA. 

This plant is remarkable from the crossed seedlings not ex- 
ceeding in height or vigour the self-fertilised. On the other 
hand, a cross greatly increases the productiveness of the flowers 
on the parent-plants, or, as it would be more correct to say, self- 
fertilisation lessens their productiveness. A cross is indeed 
sometimes necessary in order that the flowers should produce 
any seed. Moreover, plants derived from a cross are themselves 
much more fertile than those raised from self-fertilised flowers 



nn 



ESCHSCHOLTZIA CALIFOENICA. 



CHAP. IV. 



BO that the whole advantage of a cross is confined to the re- 
productive system. It will be necessary for me to give this 
singular case in considerable detail. 

Twelve flowers on some plants in my flower-garden were 
fertilised with pollen from distinct plants, and produced twelve 
capsules ; but one of these contained no good seed. The seeds 
of the eleven good capsules weighed 17 '4 grainy. Eighteen 
flowers on the same plants were fertilised with their own pollen 
and produced twelve good capsules, which contained 13 '61 
grains weight of seed. Therefore an equal number of crossed 
and self-fertilised capsules would have yielded seed by weight 
as 100 to 71.* If we take into account the fact that a much 
greater proportion of flowers produced capsules when crossed 
than when self-fertilised, the relative fertility of the crossed to 
the self-fertilised flowers was as 100 to 52. Nevertheless these 
plants, whilst still protected by the net, spontaneously produced 
a considerable number of self-fertilised capsules. 

The seeds of the two lots after germinating on sand were 
planted in pairs on the opposite sides of four large pots. At 
first there was no difference in their growth, but ultimately 
the crossed seedlings exceeded the self-fertilised considerably in 
height, as shown in the following table. But I believe from 

TABLE XXXIV. 

Eschscholtzia ccdifornica. 



No. of Pot. 


Crossed Plants. 


Self-fertilised Plants. 


I. 


Inches. 
33 1 


Inches. 
25 


II. 


34| 


35 


III. 


29 


271 


IV. 


22 


15 


Total in inches. 


118-75 


102-25 



* Prof. Hildebrand experi- 
mented on plants in Germany on 
a larger scale than I did, and 
found them much more self-sterile. 
Eighteen capsules, produced by 
cross-fertilisation, contained on an 



average eighty-five seeds, whilst 
fourteen capsules from self-ferti- 
lised flowers contained on an 
average only nine seeds ; that is. 
as 100 to 11 : Jahrb. fur Wisseni 
Botanik.' B. vii. p. 467. 



CHAP. IV. ESCHSCHOLTZIA CALIFORNIOA. Ill 

the cases which follow that this result was accidental, owing to 
only a few plants having been measured, and to one of the 
self-fertilised plants having grown only to a height of 15 inches. 
The plants had been kept in the greenhouse, and from being 
drawn up to the light had to be tied to sticks in this and the 
following trials. They were measured to the summits of their 
flower-stems. 

The four crossed plants here average 29 ' 68 inches, and the 
four self-fertilised 25 '56 in height; or as 100 to 86. The 
remaining seeds were sown in a large pot in which a Cineraria 
had long been growing ; and in this case again the two crossed 
plants on the one side greatly exceeded in height the two self- 
fertilised plants on the opposite side. The plants in the above 
four pots from having been kept in the greenhouse did not 
produce on this or any other similar occasion many capsules ; 
but the flowers on the crossed plants when again crossed were 
much more productive than the flowers on the self-fertilised 
plants when again self-fertilised. These plants after seeding 
were cut down and kept in the greenhouse; and in the 
following year, when grown again, their relative heights were 
reversed, as the self-fertilised plants in three out of the four 
pots were now taller than and flowered before the crossed 
plants. 

Crossed and self-fertilised Plants of the Second Generation. The 
fact just given with respect to the growth of the cut-down 
plants made me doubtful about my first trial, so I determined 
to make another on a larger scale with crossed and self-fertilised 
seedlings raised from the crossed and self-fertilised plants on 
the last generation. Eleven pairs were raised and grown in 
competition in the usual manner; and now the result was 
different, for the two lots were nearly equal during their whole 
growth. It would therefore be superfluous to give a table of 
their heights. When fully grown and measured, the crossed 
averaged 32 -47, and the self-fertilised 32 '81 inches in height; 
or as 100 to 101. There was no great difference in the number 
of flowers and capsules produced by the two lots when both 
were left freely exposed to the visits of insects. 

Plants raised from Brazilian Seed. Fritz Mullersent me from 
South Brazil seeds of plants which were there absolutely 
sterile when fertilised with pollen from the same plant, but 
were perfectly fertile when fertilised with pollen from any 
other plant. The plants raised by me in England from these 



112 ESOHSCHOLTZIA CALIFOKNICA. CHAP. IV 

eeeds were examined by Professor Asa Gray, and pronounced 
to belong to E. calif arnica, with which they were identical in 
general appearance. Two of these plants were covered by a 
net, and were found not to be so completely self-sterile as in 
Brazil. But I shall recur to this subject in another part of 
this work. Here it will suffice to state that eight flowers on 
these two plants, fertilised with pollen from another plant 
under the net, produced eight fine capsules, each containing on 
an average about eighty seeds. Eight flowers on these same 
plants, fertilised with their own pollen, produced seven capsules, 
which contained on an average only twelve seeds, with a maxi- 
mum in one of sixteen seeds. Therefore the cross-fertilised 
capsules, compared with the self-fertilised, yielded seeds in the 
ratio of about 100 to 15. These plants of Brazilian parentage 
differed also in a marked manner from the English plants in 
producing extremely few spontaneously self-fertilised capsules 
under a net. 

Crossed and self-fertilised seeds from the above plants, after 
germinating on bare sand, were planted in pairs on the opposite 
sides of five large pots. The seedlings thus raised were the 
grandchildren of the plants which grew in Brazil ; the parents 
having been grown in England. As the grand-parents in 
Brazil absolutely require cross-fertilisation in order to yield 
any seeds, I expected that self-fertilisation would have proved 
very injurious to these seedlings, and that the crossed ones 
would have been greatly superior in height and vigour to 
those raised from self-fertilised flowers. But the result showed 
that my anticipation was erroneous; for as in the last experi- 
ment with plants of the English stock, so in the present one, 
the self-fertilised plants exceeded the crossed by a little in 
height. It will be sufficient to state that the fourteen crossed 
plants averaged 44 '64, and the fourteen self-fertilised 45-12 
inches in height; or as 100 to 101. 

The Effects of a Cross with afresh Stock. I now tried a different 
experiment. Eight flowers on the self-fertilised plants of the 
last experiment (i.e., grandchildren of the plants which grew in 
Brazil) were again fertilised with pollen from the same plant, 
and produced five capsules, containing on an average 27 '4 
seeds, with a maximum in one of forty-two seeds. The seedlings 
raised from these seeds formed the second se 1 f -fertilised generation 
of the Brazilian stock. 

Eight flowers on )ne of the crossed plants of the last experi 



CHAP. IV. CROSS WITH A FRESH STOCK. 113 

ment were crossed -with pollen from another grandchild, and 
produced five capsules. These contained on an average 31*6 
seeds, with a maximum in one of forty-nine seeds. The seedlings 
raised from these seeds may be called the Intercrossed. 

Lastly, eight other flowers on the crossed plants of the last 
experiment were fertilised with pollen from a plant of the 
English stock, growing in my garden, and which must have 
been exposed during many previous generations to very different 
conditions from those to which the Brazilian progenitors of the 
mother-plant had been subjected. These eight flowers produced 
only four capsules, containing on an average 63 '2 seeds, with a 
maximum in one of ninety. The plants raised from these seeds 
may be called the English-crossed. As far as the above averages 
can be trusted from so few capsules, the English-crossed capsules 
contained twice as many seeds as the intercrossed, and rather 
more than twice as many as the self-fertilised capsules. The 
plants which yielded these capsules were grown in pots in the 
greenhouse, so that their absolute productiveness must not be 
compared with that of plants growing out of doors. 

The above three lots of seeds, viz., the self- fertilised, inter- 
crossed, and English-crossed, were planted in an equal state of 
germination (having been as usual sown on bare sand) in nine 
large pots, each divided into three parts by superficial partitions. 
Many of the self-fertilised seeds germinated before those of the 
two crossed lots, and these were of course rejected. The 
seedlings thus raised are the great-grandchildren of the plants 
which grew in Brazil. When they were from 2 to 4 inches 
in height, the three lots were equal. They were measured when 
four-fifths grown, and again when fully grown, and as their 
relative heights were almost exactly the same at these two 
ages, I will give only the last measurements. The average 
height of the nineteen English-crossed plants was 45 -92 inches; 
that of the eighteen intercrossed plants (for one died), 43 '38; 
and that of the nineteen self-fertilised plants, 50 '3 inches. So 
that we have the following ratios in height : 

The English-crossed to the self-fertilised plants, as 100 to 109 
The English-crossed to the intercrossed plants, as 100 to 94. 
The intercrossed to the self-fertilised plants, as 100 to 116 

After the seed-capsules had been gathered, all these plants 
were cut down close to the ground and weighed. The nineteen 
English-crossed plants weighed 18*25 ounces; the intercrossed 

I 



114 ESCHSCHOLTZIA CALIFORNICA. CHAP. IV 

plants (with their weight calculated as if there had been nine- 
teen) weighed 18' 2 ounces; and the nineteen self-fertilised 
plants, 21'5 ounces. We have therefore for the weights of the 
three lots of plants the following ratios : 

The English-crossed to the self-fertilised plants, as 100 to 118 
The English-crossed to the intercrossed plants, as 100 to 100 
The intercrossed to the self-fertilised plants, as 100 to 118 

We thus see that in weight, as in height, the self-fertilised 
plants had a decided advantage over the English-crossed and 
intercrossed plants. 

The remaining seeds of the three kinds, whether or not in a 
state of germination, were sown in three long parallel rows in 
the open ground; and here again the self-fertilised seedlings 
exceeded in height by between 2 and 3 inches the seedlings 
in the two other rows, which were of nearly equal heights. The 
three rows were left unprotected throughout the winter, and all 
the plants were killed, with the exception of two of the self- 
fertilised ; so that as far as this little bit of evidence goes, some 
of the self-fertilised plants were more hardy than any of the 
crossed plants of either lot. 

We thus see that the self-fertilised plants which were grown 
in the nine pots were superior in height (as 116 to 100), and in 
weight (as 118 to 100), and apparently in hardiness, to the inter- 
crossed plants derived from a cross between the grandchildren 
of the Brazilian stock. The superiority is here much more 
strongly marked than in the second trial with the plants of the 
English stock, in which the self-fertilised were to the crossed in 
height as 101 to 100. It is a far more remarkable fact if we 
bear in mind the effects of crossing plants with pollen from a 
fresh stock in the cases of Ipomoea, Mimulus, Brassica, and 
Iberis that the self-fertilised plants exceeded in height (as 109 
to 100), and in weight (as 118 to 100), the offspring of the 
Brazilian stock crossed by the English stock; the two stocks 
having been long subjected to widely different conditions. 

If we now turn to the fertility of the three lots of plants we 
find a very different result. I may premise that in five out of 
the nine pots the first plant which flowered was one of the English- 
crossed ; in four of the pots it was a self-fertilised plant ; and in 
not one did an intercrossed plant flower first; so that these 
latter plants were beaten in this respect, as in so many other 
ways. The three closely adjoining rows of plants growing in 



CHAP. IV. CROSS WITH A FRESH STOCK. 115 

the open ground flowered profusely, and the flowers were inces- 
santly visited by bees, and certainly thus intercrossed. The 
manner in which several plants in the previous experiments 
continued to be almost sterile as long as they were covered by a 
net, but set a multitude of capsules immediately that they were 
uncovered, proves how effectually the bees carry pollen from 
plant to plant. My gardener gathered, at three successive 
times, an equal number of ripe capsules from the plants of the 
three lots, until he had collected forty-five from each lot. It is 
not possible to judge from external appearance whether or not a 
capsule contains any good seeds ; so that I opened all the cap- 
sules. Of the forty-five from the English-crossed plants, four 
were empty ; of those from the intercrossed, five were empty ; 
and of those from the self-fertilised, nine were empty. The 
seeds were counted in twenty-one capsules taken by chance out 
of each lot, and the average number of seeds in the capsules 
from the English-crossed plants was 67 ; from the intercrossed, 
6; and from the self-fertilised, 48 '52. It therefore follows that 

Seeds. 

The forty-five capsules (the four empty ones in- 
cluded) from the English-crossed plants contained 2747 

The forty-five capsules (the five empty ones in- 
cluded) from the intercrossed plants contained . 2240 

The forty-five capsules (the nine empty ones in- 
cluded) from the self fertilised plants contained . 1746 7 

The reader should remember that these capsules are the pro- 
duct of cross-fertilisation, effected by the bees; and that the 
difference in the number of the contained seeds must depend on 
the constitution of the plants ; that is, on whether they were 
derived from a cross with a distinct stock, or from a cross 
between plants of the same stock, or from self-fertilisation. 
From the above facts we obtain the following ratios : 

Number of seeds contained in an equal nun^sr of naturally 
fertilised capsules produced 

By the English-crossed and self-fertilised plants, as 100 to 63 
By the English-crossed and intercrossed plants, &s 100 to 81 
By the intercrossed and self-fertilised plants, as 100 to 78 

But to have ascertained the productiveness of the three lots 
of plants, it would have been necessary to know how many 
capsules were produced by the same number of plants. The 

I 2 



116 ESCHSCHOLTZIA CALIFOKNICA. CHAP. IV. 

throe long rows, however, were not of quite equal lengths, and 
the plants were much crowded, so that it would have been ex- 
tremely difficult to have ascertained how many capsules were 
produced by them, even if I had been willing to undertake so 
laborious a task as to collect and count all the capsules. But 
this was feasible with the plants grown in pots in the green- 
house; and although these were much less fertile than those 
growing out of doors, their relative fertility appeared, after care- 
fully observing them, to be the same. The nineteen plants of 
the English-crossed stock in the pots produced altogether 240 
capsules; the intercrossed plants (calculated as nineteen) pro- 
duced 137 '22 capsules; and the nineteen self-fertilised plants, 
152 capsules. Now, knowing the number of seeds contained in 
forty-five capsules of each lot, it is easy to calculate the relative 
numbers of seeds produced by an equal number of the plants of 
the three lots. 

Number of seeds produced by an equal number of naturally- 
fertilised plants. 

Seeds. 
Plants of English-crossed and self-fertilised 

parentage as 100 to 40 

Plants of the English-crossed and intercrossed 

parentage as 100 to 45 

Plants of the intercrossed and self-fertilised 
parentage as 100 to 89 

The superiority in productiveness of the intercrossed plants 
(that is, the product of a cross between the grandchildren of the 
plants which grew in Brazil) over the self-fertilised, small as it is, 
is wholly due to the larger average number of seeds contained in 
the capsules ; for the intercrossed plants produced fewer cap- 
sules in the greenhouse than did the self-fertilised plants. The 
great superiority in productiveness of the English-crossed over 
the self-fertilised plants is shown by the larger number of 
capsules produced, the larger average number of contained seeds, 
and the smaller number of empty capsules. As the English- 
crossed and intercrossed plants were the offspring of crosses in 
every previous generation (as must have been the case from the 
flowers being sterile with their own pollen), we may conclude that 
the great superiority in productiveness of the English-crossed 
over the intercrossed plants is due to the two parents of the 
former having been long subjected to different conditions. 



CHAP. IV. RESEDA LUTEA. 117 

The English-crossed plants, though so superior in productive- 
ness, were, as we have seen, decidedly inferior in height and 
weight to the self-fertilised, and only equal to, or hardly superior 
to, the intercrossed plants. Therefore, the whole advantage of a 
cross with a distinct stock is here confined to productiveness, and 
I have met with no similar case. 



. KESEDACEJ3. RESEDA LUTEA. 

Seeds collected from wild plants growing in this neighbour- 
hood were sown in the kitchen- garden ; and several of the 
seedlings thus raised were covered with a net. Of these, some 
were found (as will hereafter be more fully described) to be 
absolutely sterile when left to fertilise themselves spontaneously, 
although plenty of pollen fell on their stigmas ; and they were 
equally sterile when artificially and repeatedly fertilised with 
their own pollen; whilst other plants produced a few spon- 
taneously self-fertilised capsules. The remaining plants were 
left uncovered, and as pollen was carried from plant to plant by 
the hive and humble-bees which incessantly visit the flowers, 
they produced an abundance of capsules. Of the necessity of 
pollen being carried from one plant to another, I had ample 
evidence in the case of this species and of It. odorata ; for those 
plants, which set no seeds or very few as long as they were 
protected from insects, became loaded with capsules immediately 
that they were uncovered. 

Seeds from the flowers spontaneously self -fertilised under the 
net, and from flowers naturally crossed by the bees, were sown on 
opposite sides of five large pots. The seedlings were thinned as 
soon as they appeared above ground, so that an equal number 
were left on the two sides. After a time the pots were plunged 
into the open ground. The same number of plants of crossed 
and self-fertilised parentage were measured up to the summits 
of their flower-stems, with the result given in the following 
table (XXXV.). Those which did not produce flower-stems were 
not measured. 

The average height of the twenty-four crossed plants is here 
17 17 inches, and that of the same number of self- fertilised plants 
14 61; or as 100 to 85. Of the crossed plants all but five 
flowered, whilst several of the self-fertilised did not do so. The 
above pairs, whilst still in flower, but with some capsules already 
formed, were afterwards cut down and weighed. The crossed 



118 



RESEDA LUTEA. 



CHAP. IV. 



weighed 90 '5 ounces; and an equal number of the self-fertfased 
only 19 ounces, or as 100 to 21; and this is an astonishing 
difference. 

TABLE XXXV. 

Reseda lutea, in pots. 



No. of Pot 


Crossed Plants. 


Self-fertilised Plants. 


L 


Inche 
21 
14 
19 

15 


s. 
\ 


Inche 
12 
16 
11 
15 
19 


8. 

beii 


II. 


20 
17 
23 
17 

20 


; 


12 
16 
16 
13 
13 




HI. 


16 
17 
16 
10 
10 




14 
19 
20 
7 
17 


i:J 


IV. 


22 
19 
18 

16 
19 


L*. 


9 

I! 1 

16 
161 


V. 


25, 
22 
8 
14 




14 
16 
14 
14 


!;v 


Total in inches. 


412-25 


350-88 



Seeds of the same two lots were also sown in two adjoining 
rows in the open ground. There were twenty crossed plants in 
the one row and thirty-two self-fertilised plants in the other 
row, so that the experiment was not quite fair ; but not so un- 
fair as it at first appears, for the plants in the same row were not 
crowded so much as seriously to interfere with each other's 
growth, and the ground was bare on the outside of both rows. 



CHAP. IV. 



RESEDA ODORATA. 



119 



These plants were better nourished than those in the pets and 
grew to a greater height. The eight tallest plants in each row 
were measured in the same manner as before, with the following 
result : 

TABLB XXXVI. 

Reseda lutea, growing in the open ground. 



Crossed Plant*. 


Self-fertilised Plants. 


Inches. 


Inches. 


28 


33 jj 


27 1 




23 


27 




III 


28! 




20| 


29 . 




21 i 


26 




22 


26' 




21 } 


30 j 




2lf 


224-75 


185-13 



Lhe average height of the crossed plants, whilst in full flower, 
here 28 '09, and that of the self-fertilised 23 "14 inches ; or as 
100 to 82. It is a singular fact that the tallest plant in the two 
rows, was one of the self-fertilised. The self-fertilised plants had 
smaller and paler green leaves than the crossed. All the plants 
in the two rows were afterwards cut down and weighed. The 
twenty crossed plants weighed 65 ounces, and twenty self-ferti- 
lised (by calculation from the actual weight of the thirty-two self- 
fertilised plants) weighed 26 25 ounces ; or as 100 to 40. There- 
fore the crossed plants did not exceed in weight the self-fertilised 
plants in nearly so great a degree as those growing in the 
pots, owing probably to the latter having been subjected to more 
severe mutual competition. On the other hand, they exceeded 
the self-fertilised in height in a slightly greater degree. 

RESEDA ODOBATA. 

Plants of the common mignonette were raised from purchased 
seed, and several of them were placed under separate nets. Of 
these some became loaded with spontaneously self-fertilised cap- 
sules ; others produced a few, and others not a single one. It 
must not be supposed that these latter plants produced no seed 



120 



RESEDA ODORATA. 



CHAP. IV. 



because their stigmas did not receive any pollen, for they were 
repeatedly fertilised with pollen from the same plant with no 
effect ; but they were perfectly fertile with pollen from any other 
plant Spontaneously self-fertilised seeds were saved from one 
of the highly self-fertile plants, and other seeds were collected 
from the plants growing outside the nets, which had been 
crossed by the bees. These seeds after germinating on sand 
were planted in pairs on the opposite sides of five pots. The 
plants were trained up sticks, and measured to the summits of 
their leafy stems the flower-stems not being included. We here 
have the result : 

TABLE XXXVII. 

Reseda odorata (seedlings from a highly Self -fertile Plant). 



No. of Pot. 


Crossed Plants. 


Self -fertilised Plants. 




Inches. 


Inche 


s. 


J. 


20 




22 


i 




34 




28 






26 




23 






32 


30| 


II. 


34 




28 






34 




30 






11 




23 






33 




30 J 


III. 


"I 


26 1 
25 1 




27 




30 






30 




IV. 


21 J 


22 






28 


25 






32 




15 






32 




24 




V. 


21 


"I 




25 




1*1 




26 






i 


Total in inches. 


522-25 


428-50 



The average height of the nineteen crossed plants is here 
27 '48, and that of the nineteen self-fertilised 22 55 inches ; or as 
100 to 82. All these plants were cut down in the early autumn 



CHAP. IV. 



RESEDA ODORATA. 



121 



and weighed : the crossed weighed 11 '5 ounces, and the self- 
fertilised 7'75 ounces, or as 100 to 67. These two lots having 
been left freely exposed to the visits of insects, did not present 
any difference to the eye in the number of seed-capsules which 
they produced. 

The remainder of the same two lots of seeds were sown in two 
adjoining rows in the open ground ; so that the plants were ex- 
posed to only moderate competition. The eight tallest on each 
side were measured, as shown in the following table : 

TABLE XXXVIH. 

Reseda odorata, growing in the open ground. 



Crossed Plants. 1 Self-fertilised Plants. 




Inches. Inches. 




244 
27 


26| 
25J 




24 


25 




268 


28 




25 


29 




26 


25 




27 j 


26 




25j 


28 


Total in 
inches. 


} 206 -13 


216-75 



The average height of the eight crossed plants is 25 -76, and 
1 at of the eight self-fertilised 27'09 ; or as 100 to 105. 

We here have the anomalous result of the self-fertilised plants 
being a little taller than the crossed ; of which fact I can offer 
no explanation. It is of course possible, but not probable, that 
the labels may have been interchanged by accident. 

Another experiment was now tried: all the self-fertilised 
capsules, though very few in number, were gathered from one of 
the semi-self-sterile plants under a net ; and as several flowers on 
this same plant had been fertilised with pollen from a distinct 
individual, crossed seeds were thus obtained. I expected that the 
seedlings from this semi-self-sterile plant would have profited 
in a higher degree from a cross, than did the seedlings from 
the fully self-fertile plants. But my anticipation was quite wrong, 
for they profited in a less degree. An analogous result followed in 
the case of Eschscholtzia, in which the offspring of the plants of 
Brazilian parentage (which were partially self-sterile) did not 



122 



EESEDA ODORATA. 



CHAP. IV 



profit more from a cross, than did the plants of the far more 
self-fertile English stock. The above two lots of crossed and 
self-fertilised seeds from the same plant of Reseda odorata, after 
germinating on sand, were planted on opposite sides of five pots, 
and measured as in the last case, with the following result : 

TABLE XXXIX. 

Reseda odorata (seedlings from a semi-self-sterile Plant). 



No. of Pot. 


Crossed Plants. 


Self-fertilised Plants. 




Inches. 


Inches. 


I. 


33 




31 




30 




28 




29 




131 




20 


32 


II. 


22 


21 




33 




26 f 




31 




25 1 




32 


30 1 


IIL 


30 




17 




32 




29 




31 




24 




32 




34 


IV. 


19 




20 1 




30 




32 1 




24 1 


31 1 




30 2 


36 1 


V. 


34 




24 1 




37 




34 




31 


22 1 




33 


37J 


Total in inches. 


599-75 


554-25 



The average height of the twenty crossed plants is here 29 98, 
and that of the twenty self-fertilised 27 '71 inches; or as 100 to 
92. These plants were then cut down and weighed ; and the 
crossed in this case exceeded the self-fertilised in weight by a mere 
trifle, viz., in the ratio of 100 to 99. The two lots, left freely 
exposed to insects, seemed to be equally fertile. 

The remainder of the seed was sown in two adjoining rows in 



CHAP. IV. 



VIOLA TRICOLOR. 



123 



the open ground ; and the eight tallest plants in each row were 
measured, with the following result : 

TABLE XL. 

Reseda odorata (seedlings from a semi-seJf-sterile Plant, planted 
in the open ground). 



Crossed Plants. 


Self-fertilised Plants. 


Inches. 


Inches. 


28 


22 




22 i 


24 




25 
25 i 
29 1 


23 
g 




27 i 


27 




22| 


27 




M| 


19 


'SJIJaW-M 


188-38 



The average height of the eight crossed plants is here 26 '92, 
and that of the eight self-fertilised plants 23 '54 inches; or as 
100 to 90. 

IX. VIOLACE^}. VIOLA TBICOLOB. 

Whilst the flowers of the common cultivated heartsease are 
young, the anthers shed their pollen into a little semi-cylin- 
drical passage, formed by the basal portion of the lower petal, 
and surrounded by papillae. The pollen thus collected lies 
close beneath the stigma, but can seldom gain access into its 
cavity, except by the aid of insects, which pass their proboscides 
down this passage into the nectary.* Consequently when I 
covered up a large plant of a cultivated variety, it set only 
eighteen capsules, and most of these contained very few good 
seeds several from only one to three; whereas an equally fine 



* The flowers of this plant 
have been fully described by 
Sprengel, Hildebrand, Delpino, 
and H. Muller. The latter author 
sums up all the previous obser- 
vations in hia l Befruchtung der 
Blumen,' and in ' Nature,' Nov. 
20, 1873, p. 44. See also Mr. A. W. 



Bennett, in 'Nature,' May 15, 
1873, p. 50; and some remarks 
by Mr. Kitchener, ibid. p. 143. 
The facts which follow on the 
effects of covering up a plant 
of V. tricolor have been quoted 
by Sir J. Lubbock in hig ' British 
Wild Flowers,' &c. p. 62. 



124 VIOLA TRICOLOK. CHAP. IV. 

uncovered plant of the same variety, growing close by, produced 
105 fine capsules. The few flowers which produce capsules when 
insects are excluded, are perhaps fertilised by the curling inwards 
of the petals as they wither, for by this means pollen- grains 
adhering to the papillae might be inserted into the cavity of tha 
stigma. But it is more probable that their fertilisation is effected, 
as Mr. Bennett suggests, by Thrips and certain minute beetles 
which haunt the flowers, and which cannot be excluded by any 
net. Humble-bees are the usual fertilisers ; but I have more than 
once seen flies (Bhingfa rostrata) at work, with the under sides of 
their bodies, heads and legs dusted with pollen; and having 
marked the flowers which they visited, I found them after a few 
days fertilised.* It is curious for how long a tune the flowers of 
the heartsease and of some other plants may be watched without 
an insect being seen to visit them. During the summer of 1841, 1 
observed many times daily for more than a fortnight some large 
clumps of heartsease growing in my garden, before I saw a single 
humble-bee at work. During another summer I did the same, but 
at last saw some dark-coloured humble-bees visiting on three suc- 
cessive days almost every flower in several clumps ; and almost 
all these flowers quickly withered and produced fine capsules. 
I presume that a certain state of the atmosphere is necessary 
for the secretion of nectar, and that as soon as this occurs the 
insects discover the fact by the odour emitted, and immediately 
frequent the flowers. 
As the flowers require the aid of insects for their complete 



* I should add that this fly of these bees doing so. H. Muller 

apparently did not suck the nee- has also seen the hive-bee at work, 

tar, but was attracted by the pa- but only on the wild small- 

pillse which surround the stigma. flowered form. He gives a list 

H. Muller also saw a small bee, au (' Nature,' 1873, p. 45) of all the 

Andrena, which could not reach insects which he has seen visiting 

the nectar, repeatedly inserting both the large and small-flowered 

its proboscis beneath the stigma, forms. From his account, I sus- 

where the papillae are situated ; pect that the flowers of plants in 

so that these papillae must be in a state of nature are visited more 

some way attractive to insects. A frequently by insects than those 

writer asserts ( ' Zoologist,' vol. of the cultivated varieties. He 

iii.-iv. p. 1225) that a moth has seen several butterflies suck- 

(Plusia) frequently visits the ing the flowers of wild plants, 

flowers of the pansy. Hive-bees and this I have never observed in 

do not ordinarily visit them, but gardens, though I have watched 

a case has been recorded (' Gar- the flowers during many years, 
deners' Clrouicle,' 1844, p. 374) 



CHAP IV VIOLA TRICOLOR. 125 

fertilisation, and as they are not visited by insects nearly so often 
as most other nectar-secreting flowers, we can understand the 
remarkable fact discovered by H. Miiller and described by him 
in ' Nature,' namely, that this species exists under two forms. 
One of these bears conspicuous flowers, which, as we have seen, 
require the aid of insects, and are adapted to be cross-fer- 
tilised by them ; whilst the other form has much smaller and 
less conspicuously coloured flowers, which are constructed on a 
slightly different plan, favouring self-fertilisation, and are thus 
adapted to ensure the propagation of the species. The self- 
fertile form, however, is occasionally visited, and may be crossed 
by insects, though this is rather doubtful. 

In my first experiments on Viola tricolor I was unsuccessful in 
raising seedlings, and obtained only one full-grown crossed and 
self-fertilised plant. The former was 12i inches and the latter 8 
inches in height. On the following year several flowers on a 
fresh plant were crossed with pollen from another plant, which 
was known to be a distinct seedling; and to this point it is im- 
portant to attend. Several other flowers on the same plant 
were fertilised with their own pollen. The average number 
of seeds in the ten crossed capsules was 18 '7, and in the twelve 
self-fertilised capsules 12 '83; or as 100 to 69. These seeds, 
after germinating on bare sand, were planted in pairs on the 
opposite sides of five pots. They were first measured when 
about a third of their full size, and the crossed plants then 
averaged 3 '87 inches, and the self-fertilised only 2 '00 inches in 
height ; or as 100 to 52. They were kept in the greenhouse, and 
did not grow vigorously. Whilst in flower they were again 
measured to the summits of their stems (see Table XLL), with 
the following result : 

The average height of the fourteen crossed plants is hero 5 '58 
inches, and that of the fourteen self-fertilised 2 '37; or as 100 to 
42. In four out of the five pots, a crossed plant flowered before 
any one of the self-fertilised ; as likewise occurred with the pair 
raised during the previous year. These plants without being 
disturbed were now turned out of their pots and planted in the 
open ground, so as to form five separate clumps. Early in the 
following summer (1869) they flowered profusely, and being 
visited by humble-bees set many capsules, which were carefully 
collected from all the plants on both sides. The crossed plants 
produced 167 capsules, and the self- fertilised only 17; or as 
100 to 10. So that the crossed plants were more thaix twice ^be 



126 



VIOLA TRICOLOR. 



CHAP. IV. 



height of the self-fertilised, generally flowered first, and produced 
ten times as many naturally fertilised capsules. 

TABLE XLL 

Viola tricolor. 



No. of Pot. 


Crossed Plants. 


Self-fertilised Plants. 


I. 


Inches. 
81 

I 1 


Inches. 
01 

[1 


II. 


5 
4 

H 


6 
4 
3| 


III. 


i 

3| 
83 


?! 

H 


IV. 


4] 
4] 

4 


?! 

2J 


V. 


6 
3J 


3 
1| 


Total in inches. 


78-13- 


33-25 



By the early part of the summer of 1870 the crossed plants in 
all the five clumps had grown and spread so much more than 
the self-fertilised, that any comparison between them was 
superfluous. The crossed plants were covered with a sheet of 
bloom, whilst only a single self-fertilised plant, which was much 
finer than any of its brethren, flowered. The crossed and self- 
fertilised plants had now grown all matted together on the 
respective sides of the superficial partitions still separating them ; 
and in the clump which included the finest self-fertilised plant, 
I estimated that the surface covered by the crossed plants was 
about nine times as large as that covered by the self-fertilised 
plants. The extraordinary superiority of the crossed over the 
self-fertilised plants in all five clumps, was no doubt due to 
the crossed plants at first having had a decided advantage over 
the self-fertilised, and then robbing them more and more of their 
faod during the succeeding seasons. But we should remember 



CHAP. IV. 



VIOLA TRICOLOR. 



127 



that the same result would follow in a state of nature even to a 
greater degree; for my plants grew in ground kept clear of 
weeds, so that the self-fertilised had to compete only with the 
crossed plants; whereas the whole surface of the ground is 
naturally covered with various kinds of plants, all of which 
have to struggle together for existence. 

The ensuing winter was very severe, and in the following 
spring (1871) the plants were again examined. All the self- 
fertilised were now dead, with the exception of a single branch on 
one plant, which bore on its summit a minute rosette of leaves 
about as large as a pea. On the other hand, all the crossed 
plants without exception were growing vigorously. So that the 
self-fertilised plants, besides their inferiority in other respects, 
were more tender. 

Another experiment was now tried for the sake of ascertaining 
how far the superiority of the crossed plants, or to speak more 
correctly, the inferiority of the self-fertilised plants, would be 
transmitted to their offspring. The one crossed and one self- 
fertilised plant, which were first raised, had been turned out of 
their pot and planted in the open ground. Both produced an 
abundance of very fine capsules, from which fact we may safely 
conclude that they had been cross-fertilised by insects. Seeds 
from both, after germinating on sand, were planted in pairs on 
the opposite sides of three pots. The naturally crossed seedlings 



TABLE 

Viola tricolor : seedlings from crossed and self-fertilised Plants, the 
parents of both sets having been left to be naturally fertilised. 



No. afPot. 


Naturally crossed 
Plants from artifi- 
cially crossed Plants. 


Naturally crossed 
Plants from self- 
fertilised Plants. 


L 


Inches. 
Wj 

Hi 


Inches. 
9f 
8| 


II. 


131 
10 


9 
Hj 


III. 


14 1 
13| 


UJ 

Hi 


Total in inches.. 


75-38 


61-88 



128 



ADONIS ^STIVALIS. 



CHAT. IV. 



derived from the crossed plants flowered in all three pots before 
the naturally crossed seedlings derived from the self- fertilised 
plants. When both lots were in full flower, the two tallest 
plants on each side of each pot were measured, and the result 
is shown in the preceding table. 

The average height of the six tallest plants derived from the 
crossed plants is 12 '56 inches; and that of the six tallest plants 
derived from the self-fertilised plants is 10 '31 inches; or as 
100 to 82. We here see a considerable difference in height 
between the two sets, though very far from equalling that in the 
previous trials between the offspring from crossed and self- 
fertilised flowers. This difference must be attributed to the 
latter set of plants having inherited a weak constitution from 
their parents, the offspring of self-fertilised flowers ; notwith- 
standing that the parents themselves had been freely inter- 
crossed with other plants by the aid of insects. 

X. EANUNCULACE^S. ADONIS JBSTIVALIS. 
The results of my experiments on this plant are hardly worth 
giving, as I remark in my notes made at the time, "seedlings, 
from some unknown cause, all miserably unhealthy." Nor did they 
ever become healthy ; yet I feel bound to give the present case, 
as it is opposed to the general results at which I have arrived. 
Fifteen flowers were crossed and all produced fruit, containing 
on an average 32 5 seeds ; nineteen flowers were fertilised with 
their own pollen, and they likewise all yielded fruit, containing 
a rather larger average of 34 5 seeds ; or as 100 to 106. Seedlings 
were raised from these seeds. In one of the pots all the self- 
fertilised plants died whilst quite young; in the two others, the 
measurements were as follows : 

TABLE XLHL 

Adonis xstivalis. 



No. of PW. 


Crossed Plants. 


Self-fertilised Plants. 


I. 


Inches. 
14 
13| 


Inches. 
13| 
13* 


II. 


16f 
13 - 


11* 


Tbhl in inches. 57 '00 57 '25 



CHAP. IV. DELPHINIUM CONSOLIDA. 129 

The average height of the four crossed plants is 14 '25, and 
that of the four self-fertilised plants 14 -31; or as 100 to 100 -4; 
go that they were in fact of equal height. According io Professor 
H. Hoffmann,* this plant is proterandrous ; nevertheless it yields 
plenty of seeds when protected from insects. 

DELPHINIUM CONSOLIDA. 

It has been said in the case of this plant, as of so many 
others, that the flowers are fertilised in the bud, and that 
distinct plants or varieties can never naturally intercross.! But 
this is an error, as we may infer, firstly from the flowers being 
proterandrous, the mature stamens bending up, one after the 
other, into the passage which leads to the nectary, and afterwards 
the mature pistils bending in the same direction; secondly, from 
the number of humble-bees which visit the flowers $ ; and thirdly, 
from the greater fertility of the flowers when crossed with pollen 
from a distinct plant than when spontaneously self -fertilised. In 
the year 1863 I enclosed a large branch in a net, and crossed five 
flowers with pollen from a distinct plant; these yielded capsules 
containing on an average 35 2 very fine seeds, with a maximum of 
forty-two in one capsule. Thirty-two other flowers on the same 
branch produced twenty-eight spontaneously self-fertilised cap- 
sules, containing on an average 17 ' 2 seeds, with a maximum in 
one of thirty-six seeds. But six of these capsules were very poor, 
yielding only from one to five seeds ; if these are excluded, the 
remaining twenty-two capsules give an average of 20 '9 seeds, 
though many of these seeds were small. The fairest ratio, 
therefore, for the number of seeds produced by a cross and by 
spontaneous self-fertilisation is as 100 to 59. These seeds were 
not sown, as I had too many other experiments in progress. 

In the summer of 1867, which was a very unfavourable one, 
I again crossed several flowers under a net with pollen from a 
distinct plant, and fertilised other flowers on the same plant with 
their own pollen. The former yielded a much larger proportion 
of capsules than the latter ; and many of the seeds in the self- 
fertilised capsules, though numerous, were so poor that an equal 
number of seeds from the crossed and self-fertilised capsules 



* ' Zur Speciesfrage,' 1875, $ Their structure is described 

p. 11. byH MuJJor, ' Befruohtung,' &c v 

f Decaisne, ' Comptee-Kcndus,' p. I/ 1. 
July, 1863, p. 5. 



130 



VISCARIA OCULATA. 



CHAP. IV. 



were in weight as 100 to 45. The two lots were allowed to 
germinate on sand, and pairs were planted on the opposite sides 
of four pots. When nearly two-thirds grown they were 
measured, as shown in the following table : 

TABLE XLIV. 

Delphinium consolida. 



No. of Pot. 1 Crossed Plants. 


Self-fertilised Plants. 


I. 


Inches. 
11 


Inches. 
11 


II. 


19 
161 


16 
HI 


III. 


26 


22 


IV. 


$ 


81 

6| 


Total in inches. 


89-75 


75-50 



The six crossed plants here average 14 95, and the six self- 
fertilised 12-50 inches in height: or as 100 to 84. When fully 
grown they were again measured, but from want of time only a 
single plant on each side was measured ; so that I have thought 
it best to give the earlier measurements. At the later period 
the three tallest crossed plants still exceeded considerably in 
height the three tallest self-fertilised, but not in quite so great 
a degree as before. The pots were left uncovered in the green- 
house, but whether the flowers were intercrossed by bees or self- 
fertilised I do not know. The six crossed plants produced 282 
mature and immature capsules, whilst the six self-fertilised 
plants produced only 159 ; or as 100 to 56. So that the crossed 
plants were very much more productive than the self-fertilised. 



XL CABYOPHYLLACTLE. VISCABIA OCULATA. 

Twelve flowers were crossed with pollen from another plant, 
and yielded ten capsules, containing by weight 5 77 grains of 
seeds. Eighteen flowers were fertilised with their own pollen 
and yielded twelve capsules, containing by weight 2 63 grains. 
Therefore the seeds from an equal number of crossed and self- 



CHAP. IV. VISCAR1A OCULATA. 131 

fertilised flowers would have been in weight as 100 to 38. I had 
previously selected a medium-sized capsule from each lot, and 
counted the seeds in both ; the crossed one contained 284, and 
the self-fertilised one 126 seeds; or as 100 to 44. These seeds 
were sown on opposite sides of three pots, and several seedlings 
raised; but only the tallest flower-stem of one plant on each 
side was measured. The three on the crossed side averaged 32 '5 
inches, and the three on the self-fertilised side 34 inches in 
height ; or as 100 to 104. But this trial was on much too small 
a scale to be trusted ; the plants also grew BO unequally that 
one of the three flower-stems on the crossed plants was very 
nearly twice as tall as that on one of the others; and one of 
the three flower-stems on the self-fertilised plants exceeded in 
an equal degree one of the others. 

In the following year the experiment was repeated on a larger 
scale: ten flowers were crossed on a new set of plants and 
yielded ten capsules containing by weight 6 54 grains of seed. 
Eighteen spontaneously self-fertilised capsules were gathered, 
of which two contained no seed ; the other sixteen contained by 
weight 6 '07 grains of seed. Therefore the weight of seed from 
an equal number of crossed and spontaneously self-fertilised 
flowers (instead of artificially fertilised as in the previous case) 
was as 100 to 58. 

The seeds after germinating on sand were planted in pairs on 
the opposite sides of four pots, with all the remaining seeds sown 
crowded in the opposite sides of a fifth pot ; in this latter pot 
only the tallest plant on each side was measured. Until the 
seedlings had grown about 5 inches in height no difference 
could be perceived in the two lots. Both lots flowered at nearly 
the same time. When they had almost done flowering, the 
tallest flower-stem on each plant was measured, as shown in the 
following table (XLV.). 

The fifteen crossed plants here average 34 '5, and the fifteen 
self-fertilised 33 '55 inches in height; or as 100 to 97. So that 
the excess of height of the crossed plants is quite insignificant. In 
productiveness, however, the difference was much more plainly 
marked. All the capsules were gathered from both lots of plants 
(except from the crowded and unproductive ones in Pot V.), and 
at the close of the season the few remaining flowers were added 
in. The fourteen crossed plants produced 381, whilst the four- 
teen self-fertilised plants produced only 293 capsules and flowers, 
or as 100 to 77. 

K 2 



132 



DIANTHUS CARYOPHYLLUS. 



CHAP. IV 



TABLE XLV. 
Viscaria oculata. 



No. of Pot. 


Crossed Plants. 


Self-fertilised Plants. 


I. 


Inches. 
19 
33 
41 
41 


Inches. 
32 3 
38 
38 
281 


II. 


37 1 
36 1 
38 


34 

32 1 
35| 


III. 


44| 

39 1 
39 


36 
20 1 
30 1 


IV. 


30] 

31 
33J 
24 


36 
39 
29 
38 1 


V. 

Crowded. 


30 1 


32 


Total in inches. 


517-63 


503-38 



DIANTHUS CABYOPHYLLUS. 

The common carnation is strongly proterandrous, and there- 
fore depends to a large extent upon insects for fertilisation. I 
have seen only humble-bees visiting the flowers, but I dare say 
other insects likewise do so. It is notorious that if pure seed is 
desired, the greatest care is necessary * to prevent the varieties 
which grow in the same garden from intercrossing. The pollen, 
is generally shed and lost before the two stigmas in the same 
flower diverge and are ready to be fertilised. I was therefore 
often forced to use for self-fertilisation pollen from the same 
plant instead of from the same flower. But on two occasions, 
when I attended to this point, I was not able to detect any 
marked difference in the number of seeds produced by these two 
forms of self-fertilisation. 



* 'Gardeners' Chronicle,' .'847, p. 268 



CHAP. IV. CROSSED AND SELF-FERTILISED PLANTS. 133 

Several single-flowered carnations were planted ;n good soil, 
and were all covered with a net. Eight flowers were crossed 
with pollen from a distinct plant and yielded six capsules, 
containing on an average 88 * 6 seeds, with a maximum in one of 
112 seeds. Eight other flowers were self-fertilised in the 
manner above described, and yielded seven capsules containing 
on an average 82 seeds, with a maximum in one of 112 seeds. 
So that there was very little difference in the number of seeds 
produced by cross-fertilisation and self-fertilisation, viz., as 
100 to 92. As these plants were covered by a net, they pro- 
duced spontaneously only a few capsules containing any seeds, 
and these few may perhaps be attributed to the action of 
Thrips and other minute insects which haunt the flowers. A 
large majority of the spontaneously self-fertilised capsules pro- 
duced by several plants contained no seeds, or only a single one. 
Excluding these latter capsules, I counted the seeds in eighteen 
of the finest ones, and these contained on an average 18 seeds. 
One of the plants was spontaneously self-fertile in a higher degree 
than any of the others. On another occasion a single covered-up 
plant produced spontaneously eighteen capsules, but only two of 
these contained any seed, namely 10 and 15. 

Crossed and self-fertilised Plants of the First Generation. The 
many seeds obtained from the above crossed and artificially 
self-fertilised flowers were sown out of doors, and two large beds 
of seedlings, closely adjoining one another, thus raised. This 
was the first plant on which I experimented, and I had not 
then formed any regular scheme of operation. When the two 
lots were in full flower, I measured roughly a large number of 
plants, but record only that the crossed were on an average 
fully 4 inches taller than the self-fertilised. Judging from 
subsequent measurements, we may assume that the crossed 
plants were about 28 inches, and the self-fertilised about 
24 inches in height; and this will give us a ratio of 100 to 
86. Out of a large number of plants, four of the crossed ones 
flowered before any one of the self-fertilised plants. 

Thirty flowers on these crossed plants of the first generation 
were again crossed with pollen from a distinct plant of the same 
lot, and yielded twenty-nine capsules, containing on an average 
55 '62 seeds, with a maximum in one of 110 seeds. 

Thirty flowers on the self-fertilised plants were again self- 
fertilised ; eight of them with pollen from the same flower, and 
the remainder with pollen from another flower on the same 



134 DIANTHUS CARYOPHYLLUS. CHAP. IV. 

plant ; and these produced twenty-two capsules, containing on an 
average 35 "95 seeds, with a maximum in one of 61 seeds. We 
thus see, judging by the number of seeds per capsule, that the 
crossed plants again crossed were more productive than the 
self-fertilised again self-fertilised, in the ratio of 100 to 65. 
Both the crossed and self-fertilised plants, from having grown 
much crowded in the two beds, produced less fine capsules and 
fewer seeds than did their parents. 

Crossed and self -fertilised Plants of the Second Generation. The 
crossed and self-fertilised seeds from the crossed and self-fertilised 
plants 01 the last generation were sown on opposite sides of two 
pots ; but the seedlings were not thinned enough, so that both lots 
grew very irregularly, and most of the self-fertilised plants after 
a time died from being smothered. My measurements were, 
therefore, very incomplete. From the first the crossed seedlings 
appeared the finest, and when they were on an average, by esti- 
mation, 5 inches high, the self-fertilised plants were only 4 
inches. In both pots the crossed plants flowered first. The two 
tallest flower-stems on the crossed plants in the two pots were 
17 and 16i inches in height ; and the two tallest flower-stems 
on the self-fertilised plants 10j and 9 inches; so that their 
heights were as 100 to 58. But this ratio, deduced from only 
two pairs, obviously is not in the least trustworthy, and would 
not have been given had it not been otherwise supported. I 
state in my notes that the crossed plants were very much more 
luxuriant than their opponents, and seemed to be twice as 
bulky. This latter estimate may be believed from the ascertained 
weights of the two lots in the next generation. Some flowers 
on these crossed plants were again crossed with pollen from 
another plant of the same lot, and some flowers on the self- 
fertilised plants again self-fertilised; and from the seeds thus 
obtained the plants of the next generation were raised. 

Crossed and stlf -fertilised Plants of the Third Generation. The 
seeds just alluded to were allowed to germinate on bare sand, 
and were planted in pairs on the opposite sides of four pots. 
When the seedlings were in full flower, the tallest stem on each 
plant was measured to the base of the calyx. The measurements 
are given in the following table (XL VI.). In Pot I. the crossed 
and self-fertilised plants flowered at the same time ; but in the 
other three pots the crossed flowered first. These latter plants 
also continued flowering much later in the autumn -han the 
self-fertilised. 



CHAP. IV. CROSSED AND SELF-FERTILISED PLANTS. 135 



TABLE XLYL 
Dianthus caryophyllus {Third Generation'). 



No. of Pot. 


Crossed Plants. 


Self-fertilised Plants. 


I. 


Inches. 
28 g 
27 \ 


Inches. 
30 
. 26 


II. 


29 
29 1 


30? 
27 1 


III. 


881 

233 


31 1 
24 1 


IV. 


27 
33| 


30 
25 


Total in inches. 


227-13 


225-75 



The average height of the eight crossed plants is here 28 '39 
inches, and of the eight self-fertilised 28 -21; or as 100 to 99. 
So that there was no difference in height worth speaking of' 
but in general vigour and luxuriance there was an astonishing 
difference, as shown by their weights. After the seed-capsules 
had been gathered, the eight crossed and the eight self-fertilised 
plants were cut down and weighed ; the former weighed 43 
ounces, and the latter only 21 ounces ; or as 100 to 49. 

These plants were all kept under a net, so that the capsules 
which they produced must have been all spontaneously self- 
fertilised. The eight crossed plants produced twenty-one such 
capsules, of which only twelve contained any seed, averaging 
8' 5 pei capsule. On the other hand, the eight self-fertilised 
plants produced no less than thirty-six capsules, of which I 
examined twenty-five, and, with the exception of three, all 
contained seeds, averaging 10*63 seeds per capsule. Thus the 
proportional number of seeds per capsule produced by the plants 
of crossed origin to those produced by the plants of self-fertilised 
origin (both lots being spontaneously self-fertilised) was as 100 
to 125. This anomalous result is probably due to some of the 
self-fertilised plants having varied so as to mature their pollen 
and stigmas more nearly at the same time than is proper to 
the species ; and we have already seen that some plants in the 



136 BIANTHUS CAKYOPHYLLUS. CHAP. IV. 

first experiment differed from the others in, being slightly more 
self-fertile. 

The Effects of a Cross with afresh Stock. Twenty flowers on the 
self-fertilised plants of the last or third generation, in Table XLVL, 
were fertilised with their own pollen, but taken from other 
flowers on the same plants. These produced fifteen capsules, 
which contained (omitting two with only three and six seeds) 
on an average 47 -Q3 seeds, with a maximum of seventy in one. 
The self-fertilised capsules from the self-fertilised plants of the 
first generation yielded the much lower average of 35 ' 95 seeds ; 
but as these latter plants grew extremely crowded, nothing can 
be inferred with respect to this difference in their self-fertility. 
The seedlings raised from the above seeds constitute the plants 
of the fourth self-fertilised generation in the following table 
(XLVIL). 

Twelve flowers on the same plants of the third self-fertilised 
generation, in Table XL VI., were crossed with pollen from the 
crossed plants in the same table. These crossed plants had been 
intercrossed for the three previous generations; and many of 
them, no doubt, were more or less closely inter-related, but not 
so closely as in some of the experiments with other species ; for 
several carnation plants had been raised and crossed in the 
earlier generations. They were not related, or only in a distant 
degree, to the self-fertilised plants. The parents of both the 
self-fertilised and crossed plants had been subjected to as nearly 
as possible the same conditions during the three previous genera- 
tions. The above twelve flowers produced ten capsules, contain- 
ing on an average 48*66 seeds, with a maximum in one of 
seventy-two seeds. The plants raised from these seeds may be 
called the intercrossed. 

Lastly, twelve flowers on the same self-fertilised plants of the 
third generation were crossed with pollen from plants which 
had been raised from seeds purchased in London. It is almost 
certain that the plants which produced these seeds had grown 
under very different conditions to those to which my self- 
fertilised and crossed plants had been subjected ; and they were 
in no degree related. The above twelve flowers thus crossed 
all produced capsules, but these contained the low average of 
37 '41 seeds per capsule, with a maximum in one of sixty-four 
seeds. It is surprising that this cross with a fresh stock did not 
give a much higher average number of seeds ; for, as we shall 
immediately see, the plants raised from these seeds, which may 



CHAP. IV. 



CJIOSS WITH A FRESH STOCK. 



137 



be called the London-crossed, benefited greatly by the cross, both 
in growth and fertility. 

The above three lots of seeds were allowed to germinate on 
bare sand. Many of the London-crossed germinated before the 
others, and were rejected ; and many of the intercrossed later 
than those of the other two lots. The seeds after thus germina- 
ting were planted in ten pots, made tripartite by superficial 

TABLE XLVII. 

Dianthus caryophyllus. 



No. of Pot. 


London-crossed 
Plants. 


Intercrossed Plants. 


Self-fertilised 
Plants. 


I. 


Inches. 
39 1 
30| 


Inches. 
25 1 

21] 


Inches. 
291 


II. 


361 






22 1 


III. 


?< 


301 
234 




IV. 


33 1 

281 


35 1 
32 


30 
24j 


V. 


28 



34 1 
241 


J 


VI. 


32| 
31 


241 
26 


303 
24j 


VII. 


55 

341 


29? 


271 
27 


VIII. 


SI 


29 



2+ 6 


IX. 


V 


28 1 





X. 


38 
32J 


M| 


V 


Total in inches. 


525-13 


420-00 


265-50 



138 DIANTHUS CARYOPHYLLUS. CHAP. IV 

divifiions ; but when only two kinds of seeds germinated at the 
same time, they were planted on the opposite sides of other pots ; 
and this is indicated by blank spaces in one of the three columns 
in Table XLVH. An in the table signifies that the seedling 
died before it was measured; and a + signifies that the plant 
did not produce a flower-stem, and therefore was not measured. 
It deserves notice that no less than eight out of the eighteen self- 
fertilised plants either died or did not flower; whereas only 
three out of the eighteen intercrossed, and four out of the twenty 
London-crossed plants, were in this predicament. The self- 
fertilised plants had a decidedly less vigorous appearance 
than the plants of the other two lots, their leaves being 
smaller and narrower. In only one pot did a self-fertilised plant 
flower before one of the two kinds of crossed plants, between 
which there was no marked difference in the period of flowering. 
The plants were measured to the base of the calyx, after they 
had completed their growth, late in the autumn. 

The average height of the sixteen London-crossed plants in 
the preceding table is 32 -82 inches; that of the fifteen inter- 
crossed plants, 28 inches; and that of the ten self-fertilised 
plants, 26-55. 

So that in height we have the following ratios : 

The London -crossed to the self-fertilised as 100 to 81 
The London-crossed to the intercrossed as 100 to 85 
The Intercrossed to the self-fertilised as 100 to 95 

These three lots of plants, which it should be remembered 
were all derived on the mother-side from plants of the third 
self-fertilised generation, fertilised in three different ways, were 
left exposed to the visits of insects, and their flowers were freely 
crossed by them. As the capsules of each lot became ripe they 
were gathered and kept separate, the empty or bad ones being 
thrown away. But towards the middle of October, when the 
capsules could no longer ripen, all were gathered and were 
counted, whether good or bad. The capsules were then crushed, 
and the seed cleaned by sieves and weighed. For the sake of 
uniformity the results are given from calculation, as if there had 
been twenty plants in each lot. 

The sixteen London-crossed plants actually produced 286 
capsules; therefore twenty such plants would have produced 
357 '5 capsules; and from the actual weight of the seeds, the 
twenty plants would have yielded 462 grains weight of seeds. 



C1.AP. IV. COLOUR OF THE FLOWERS. 139 

The fifteen intercrossed plants actually produced 157 capsules ; 
therefore twenty of them would have produced 209 '3 capsules, 
and the seeds would have weighed 208 '48 grains. 

The ten self-fertilised plants actually produced 70 capsules ; 
therefore twenty of them would have produced 140 capsules ; 
and the seeds would have weighed 153 '2 grains. 

From these data we get the following ratios : 

Number of capsules produced by an equal number of plants of 
the three lots. 

Number of Capsules. 

The London-crossed to the self-fertilised, as 100 to 39 
The London-crossed to the intercrossed, as 100 to 45 
The Intercrossed to the self-fertilised as 100 to 67 

Weight of seeds produced by an equal number of plants of th 
three lots. 

Weight of Seed. 

The London-crossed to the self- fertilised, as 100 to 33 
The London-crossed to the intercrossed, as 100 to 45 
The Intercrossed to the self-fertilised, as 100 to 73 

We thus see how greatly the offspring from the self-fertilised 
plants of the third generation crossed by a fresh stock, had 
their fertility increased, whether tested by the number of cap- 
sules produced or by the weight of the contained seeds; this 
latter being the more trustworthy method. Even the offspring 
from the self-fertilised plants crossed by one of the crossed 
plants of the same stock, notwithstanding that both lots had 
been long subjected to the same conditions, had their fertility 
considerably increased, as tested by the same two methods. 

In conclusion it may be well to repeat in reference to the 
fertility of these three lots of plants, that their flowers were 
left freely exposed to the visits of insects and were undoubtedly 
crossed by them, as may be inferred from the large number of good 
capsules produced. These plants were all the offspring of the 
same mother-plants, and the strongly marked difference in their 
fertility must be attributed to the nature of the pollen employed 
in fertilising their parents ; and the difference in the nature of the 
pollen must be attributed to the different treatment to which 
the pollen-bearing parents had been subjected during several 
previous generations. 

Colour of the Flowers. The flowers produced by the self-fertilised 



140 



HIFISCUS AFEICANUS. 



CHAP. IV. 



plants of the last or fourth generation were as uniform in tint 
as those of a wild species, being of a pale pink or rose colour. 
Analogous cases with Mimulus and Ipomcea, after several 
generations of self-fertilisation, have been already given. The 
flowers of the intercrossed plants of the fourth generation were 
likewise nearly uniform in colour. On the other hand, the flowers 
of the London-crossed plants, or those raised from a cross with 
the fresh stock which bore dark crimson flowers, varied extremely 
in colour, as might have been expected, and as is the general 
rule with seedling carnations. It deserves notice that only two 
or three of the London-crossed plants produced dark crimson 
flowers like those of their fathers, and only a very few of a pale 
pink like those of their mothers. The great majority had their 
petals longitudinally and variously striped with the two colours, 
the groundwork tint being, however, in some cases darker 
than that of the mother-plants. 

XII. MALVACE2E. HIBISCUS APRICANUS. 

Many flowers on this Hibiscus were crossed with pollen from 
a distinct plant, and many others were self-fertilised. A rather 
larger proportional number of the crossed than of the self- 
fertilised flowers yielded capsules, and the crossed capsules con- 
tained rather more seeds. The self-fertilised seeds were a little 
heavier than an equal number of the crossed seeds, but they 
germinated badly, and I raised only four plants of each lot. In 
three out of the four pots, the crossed plants flowered first. 

TABLE XLVTQ. 

Hibiscus africanus. 



No. of Pot. 


Crossed Plants. 


Self-fertilised Plants. 


I. 


Inches. 
1SJ 


Inches. 
16| 


II. 


14 


14 


III. 


8 


7 


IV. 


17* 


20 1 


Total in inches. 


S3 -00 


57-75 



OHAI-. IV. HIBISCUS AFK1CANUS. 141 

The four crossed plants average 13 ''25, and the focr self-fer- 
tilised 14-43 inches in height; or as 100 to 109. Here we have 
the nnusual case of self-fertilised plants exceeding the crossed 
in height ; but only four pairs were measured, and these did not 
grow well or equally. I did not compare the fertility ef the two 
Iota, 



142 PELABGONIUM ZONALE. CHAP. V. 



CHAPTEE V. 

GERANIACE.E, LEGUMINOS.K, ONAJBACUZE, ETC. 

Pelargonium zonale, a cross between plants propagated by cuttiuge 
does no good Tropseolum minus Limnanthes douglasii Lupinus 
luteus and pilosus Phaseolus rnultiflorus and vulgaris Lathyrus 
odoratus, varieties of, never naturally intercross in England Pisum 
sativum, varieties of, rarely intercross, but a cross between them 
highly beneficial Sarothamnus scoparius, wonderful effects of a 
cross Ononis minutissima, cleistogene flowers of Summary on 
the Leguminosse Clarkia elegans L'artonia aurea Passiflora 
gracilis Apium petroselinum Scabiosa atropurpurea Lactuca 
sativa Specularia speculum Lobelia ramosa, advantages of a 
cross during two generations Lobelia fulgens Nemophila insignia, 
great advantages of a cross Borago ofScinalis Nolana prostrata. 

XIII. G^JEANIACE^. PELAEGONITTM ZONAI/B. 

THIS plant, as a general rule, is strongly proterandrous,* and 
is therefore adapted for cross-fertilisation by the aid of insects. 
Some flowers on a common scarlet variety were self-fertilised, 
and other flowers were crossed with pollen from another plant ; 
but no sooner had I done so, than I remembered that these 
plants had been propagated by cuttings from the same stock, 
and were therefore parts in a strict sense of the same individual. 
Nevertheless, having made the cross I resolved to save the seeds, 
which, after germinating on sand, were planted on the opposite 



* Mr. J. Denny, a great raiser which also the pistil is frequently 

of new varieties of pelargoniums, short, so when it expands it is 

after stating that this species is smothered as it were by the 

proterandrous, adds (' The Florist bursting anthers ; these varieties 

and Pomologist,' Jan. 1872, p. 11) are great seeders, each pip being 

"there are some varieties, espe- fertilised by its own pollen. I 

cially those with petals of a pink would instance Christine as an 

colour, or which possess a weakly example of this fact." We have 

constitution, where the pistil ex- here an interesting case of va- 

pands as soon as or even before riability in an important funo- 

the pollen-bag bursts, and in tional point. 



CHAP. V. 



PELARGONIUM ZONALE. 



143 



sides of three pots. In one pot the quasi-crossed plant was very 
soon and ever afterwards taller and finer than the self-fertilised. 
In the two other pots the seedlings on both sides were for a time 
exactly equal ; but when the self-fertilised plants were about 
10 inches in height, they surpassed their antagonists by a little, 
and ever afterwards showed a more decided and increasing 
advantage ; so that the self-fertilised plants, taken altogether, 
were somewhat superior to the quasi-crossed plants. In this 
case, as in that of the Origanum, if individuals which have been 
asexually propagated from the same stock, and which have been 
long subjected to the same conditions, are crossed, no advantage 
whatever is gained. 

Several flowers on another plant of the same variety were 
fertilised with pollen from the younger flowers on the same plant, 
so as to avoid using the old and long-shed pollen from the same 
flower, as I thought that this latter might be less efficient than 
fresh pollen. Other flowers on the same plant were crossed with 
fresh pollen from a plant which, although closely similar, was 
known to have arisen as a distinct seedling. The self-fertilised 
seeds germinated rather before the others ; but as soon as I got 
equal pairs they were planted on the opposite sides of four pots. 

TABLE XLIX. 

Pelargonium zonale. 



No. of Pot. 


Crossed Plants. 


Self-fertilised Plants. 


I. 


Inches. 
22 jj 

19) 


Inches. 
25 1 
12| 


II. 


15 

121 


19| 

22i 


HI. 


30 1 
18J 


191 
73 


IV. 


38 


9J 


Total in inches. 


156-50 


116-38 



When the two lots of seedlings were between 4 and 5 inches in 
height they were equal, excepting in Pot IV., in which the crossed 
plant was much the tallest. When between 11 and 14 inches 
in height, they were measured to the tips of their uppermost 



14.4. TROP^EOLUM MINUS. CHAP V 

leaves; the crossed averaged 13 '46, and the self-fertilised 11 '07 
inches in height, or as 100 to 82. Five months later they were 
again measured in the same manner, and the results are given 
in the preceding table. 

The seven crossed plants now averaged 22 '35, and the seven 
self-fertilised 16 62 inches in height, or as 100 to 74. But from 
the great inequality of the several plants, the result is less trust- 
worthy than in most other cases. In Pot IE. the two self- 
fertilised plants always had an advantage, except whilst quite 
young, over the two crossed plants. 

As I wished to ascertain how these plants would behave 
during a second growth, they were cut down close to the ground 
whilst growing freely. The crossed plants now showed their 
superiority in another way, for only one out of the seven was 
killed by the operation, whilst three of the self-fertilised plants 
never recovered. There was, therefore, no use in keeping any of 
the plants excepting those in Pots I. and III. ; and in the 
following year the crossed plants in these two pots showed during 
their second growth nearly the same relative superiority over 
the self-fertilised plants as before. 

TBOP.ZEOLUM MINUS. 

The flowers are proterandrous, and are manifestly adapted 
for cross-fertilisation by insects, as shown by Sprengel and 
Delpino. Twelve flowers on some plants growing out of doors 
were crossed with pollen from a distinct plant and produced 
eleven capsules, containing altogether twenty-four good seeds. 
Eighteen flowers were fertilised with their own pollen and 
produced only eleven capsules, containing twenty-two good 
seeds ; so that a much larger proportion of the crossed than of 
the self-fertilised flowers produced capsules, and the crossed 
capsules contained rather more seed than the self-fertilised in 
the ratio of 100 to 92. The seeds from the self-fertilised capsules 
were however the heavier of the two, in the ratio of 100 to 87. 

Seeds in an equal state of germination were planted on the 
opposite sides of four pots, but only the two tallest plants on 
each side of each pot were measured to the tops of their stems. 
The pots were placed in the greenhouse, and the plants trained 
up sticks, so that they ascended to an unusual height. In three 
of the pots the crossed plants flowered first, but in the fourth 
at the same time with the self-fertilised. When the seedlings 
were between 6 and 7 inches in height, the crossel began to 






CHAP. V. 



LIMNANTHES DOUGLASII. 



145 



show a slight advantage over their opponents. When grown to 
a considerable height the eight tallest crossed plants averaged 
44-43, and the eight tallest self-fertilised plants 37 '34 inches, 
or as 100 to 84. When their growth was completed they were 
again measured, as shown in the following table : 

TABLE L. 

, Tropceolum minus. 



No. of Pot. 


Crossed Plants. 


Self-fertilised Plants. 


I. 


Inches. 
65 
50 


Inches. 
31 
45 


II. 


69 
35 


4-2 
45 


III. 


70 

59 1 


50 1 
55| 


IV. 


1 

W| 


37 1 
61| 


Total in inches. 


467-5 


368-0 



The eight tallest crossed plants now averaged 58*43, and the 
eight tallest self-fertilised plants 46 inches in height, or as 100 
to 79. 

There was also a great difference in the fertility of the two 
lots which were left uncovered in the greenhouse. On the 17th 
of September the capsules from all the plants were gathered, 
and the seeds counted. The crossed plants yielded 243, whilst 
the same number of self-fertilised plants yielded only 155 seeds, 
or as 100 to 64. 

LIMNANTHES DOUGLASH. 

Several flowers were crossed and self-fertilised in the usual 
manner, but there was no marked difference in the number of 
seeds which they yielded. A vast number of spontaneously self- 
fertilised capsules were also produced under the net. Seedlings 
were raised in five pots from the above seeds, and when the, 
crossed were about 3 inches in height they showed a slight 
advantage over the self-fertilised. When double this height, the 

L 



146 



LIMNANTHES DOUGLASII. 



CHAP. V. 



sixteen crossed and sixteen self-fertilised plants were measured 
to the tips of their leaves; the former averaged 7 '3 inches, and 
the self-fertilised 6 '07 inches in height, or as 100 to 83. In 
all the pots, excepting IV., a crossed plant flowered before any 
one of the self-fertilised plants. The plants, when fully grown, 
were again measured to the summits of their ripe capsules, with 
the following result : 

TABLE LI. 

Limnanthes douglasii. 



No. of Pot. 


Crossed Plants. 


Self-fertilised Plants. 




Inches. 


Inches. 


I. 


17 1 


15 1 




17 1 


16 






13 


11 




II. 


20 


14 






22 


15 






21 


16 


i . 




18J 


17 




III. 


15 f 







If] 




14 


IV. 


ft 


13 j 

13 




18 


121 


V. 


17 


14 






18| 


14 








12 




Total in inches. 


279-50 


207-75 



The sixteen crossed plants now averaged 17 -46, and the 
fifteen (for one had died) self-fertilised plants 13 -85 inches in 
height, or as 100 to 79. Mr. Galton considers that a higher ratio 
would be fairer, viz., 100 to 76. He made a graphical representa- 
tion of the above measurements, and adds the words "very 
good " to the curvature thus formed. Both lots of plants pro- 
duced an abundance of seed-capsules, and, as far as could be 
judged by the eye, there was no difference in their fertility. 



CHAP.V. LUPINUS LUTEUS. 147 

XIV. LEGUMINOS^E. 

In this family I experimented on the following six 
genera, Lupinus, Phaseolus, Lathyrus, Pisum, Saro- 
thamnus, and Ononis. 

LUPINUS LUTKUS.* 

A few flowers were crossed with pollen from a distinct plant 
but owing to the unfavourable season only two crossed seeds 
were produced. Nine seeds were saved from flowers spon- 
taneously self-fertilised under a net, on the same plant which 
yielded the two crossed seeds. One of these crossed seeds was 
sown in a pot with two self-fertilised seeds on the opposite side ; 
the latter came up between two and three days before the crossed 
seed. The second crossed seed was sown in like manner with 
two self-fertilised seeds on the opposite side ; these latter also came 
up about a day before the crossed one. In both pots, therefore, 
the crossed seedlings from germinating later, were at first com- 
pletely beaten by the self -fertilised ; nevertheless, this state of 
tilings was afterwards completely reversed. The seeds were 
sown late in the autumn, and the pots, which were much too 
small, were kept in the greenhouse. The plants in consequence 
grew badly, and the self-fertilised suflered most in both pots. 
The two crossed plants when in flower during the following spring 
were 9 inches in height ; one of the self-fertilised plants was 
8, and the three others only 3 inches in height, being thus 
mere dwarfs. The two crossed plants produced thirteen pods, 
whilst the four self-fertilised plants produced only a single 
one. Some other self-fertilised plants which had been raised 
separately in larger pots produced several spontaneously self- 
fertilised pods under a net, and seeds from these were used in the 
following experiment. 

Crossed and self -fertilised Plants of the Second Generation. The 



* The structure of the flowers (' Nature,' 1872, p. 499) that 

of this plant, and their manner of " there is a cavity at the back and 

fertilisation, have been described base of the vexillum, in which I 

by H. Muller, * Befruchtung,' &c. have not been able to find nectar, 

p. 243. The flowers do not But the bees, which constantly 

secrete free nectar, and bees gen- visit these flowers, certainly go to 

erally visit them for their pollen. this cavity for what they want, 

Mr. Fairer, however, remarks and not to the staminal tube." 

L 2 



148 



LUPINUS LUTEUS. 



CHAI V 



spontaneously self-fertilised seeds just mentioned, and crossed 
seeds obtained by intercrossing the two crossed plants of the last 
generation, after germinating on sand, were planted in pairs on 
the opposite sides of three large pots. When the seedlings were 
only 4 inches in height, the crossed had a slight advantage 
over their opponents. When grown to their full height, every 
one of the crossed plants exceeded its opponent in height. 
Nevertheless the self-fertilised plants in all three pots flowered 
before the crossed! The measurements are given in the 
following table : 

TABLE LH. 

Lupinus lutaus. 



No. of Pot. 


Crossed Plants. 


Self-fertilised Plants. 


I. 


Inches. 
33 1 
30 
30 


Inches. 
24 1 
18| 
28 


II. 


29J 

30 


26 
25 


III. 


30 1 
31 
31| 


28 
27 1 

2*3 


Total in inches. 


246-25 


201'75 



The eight crossed plants here average 30 '78, and the eight 
self-fertilised 25 '21 inches in height; or as 100 to 82. These 
plants were left uncovered in the greenhouse to set their pods, 
but they produced very few good ones, perhaps in part owing to 
few bees visiting them. The crossed plants produced nine pods, 
containing on an average 3*4 seeds, and the self-fertilised plants 
seven pods, containing on an average 3 seeds, so that the seeds 
from an equal number of plants were as 100 to 88. 

Two other crossed seedlings, each with two self-fertilised 
seedlings on the opposite sides of the same large pot, were 
turned out of their pots early in the season, without being 
disturbed, into open ground of good quality. They were thus 
subjected to but little competition with one another, in com- 
parison with the plants in the above three pots. In the autumn 



CHAP. V. . LUPINUS PILOSUS. 149 

the two crossed plants were about 3 inches taller than the four 
self-fertilised plants; they looked also more vigorous and pro- 
duced many more pods. 

Two other crossed and self-fertilised seeds of the same lot, 
after germinating on sand, were planted on the opposite sides of 
& large pot, in which a Calceolaria had long been growing, 
and were therefore exposed to unfavourable conditions: the 
two crossed plants ultimately attained a height of 20i and 
20 inches, whilst the two self-fertilised were only 18 and 9J 
inches high. 

LUPINTJS PIL08U8. 

From a series of accidents I was again unfortunate in obtaining 
a sufficient number of crossed seedlings ; and the following 
results would not be worth giving, did they not strictly accord 
with those just given with respect to L. luteus. I raised at first 
only a single crossed seedling, which was placed in competition 
with two self-fertilised ones on the opposite side of the same 
pot. These plants, without being disturbed, were soon after- 
wards turned into the open ground. By the autumn the crossed 
plant had grown to so large a size that it almost smothered 
the two self-fertilised plants, which were mere dwarfs; and 
the latter died without maturing a single pod. Several self- 
fertilised seeds had been planted at the same time separately 
in the open ground ; and the two tallest of these were 33 and 
32 inches, whereas the one crossed plant was 38 inches in height 
This latter plant also produced many more pods than did any 
one of the self-fertilised plants, although growing separately. A 
few flowers on the one crossed plant were crossed with pollen 
from one of the self-fertilised plants, for I had no other crossed 
plant from which to obtain pollen. One of the self-fertilised 
plants having been covered by a net produced plenty of spon- 
taneously self-fertilised pods. 

Crossed and self-fertilised Plants of the Second Generation. From 
crossed and self-fertilised seeds obtained in the manner just 
described, I succeeded in raising to maturity only a pair of 
plants, which were kept in a pot in the greenhouse. The crossed 
plant grew to a height of 33 inches, and the self-fertilised to 
that of 26J inches. The former produced, whilst still kept in 
the greenhouse, eight pods, containing on an average 2*77 seeds; 
and the latter only two pods, containing on an average 2 - 5 
seeds. The average height of the two crossed plants of the two 



150 PHASEOLUS MULTIFI OKUS. CHAP. V 

generations taken together was 35 * 5, and that of the three self- 
fertilised plants of the same two generations 30*5; or as 100 
to 86.* 

PHASEOLUS MULTIFLOKUS. 

This plant, the scarlet-runner of English gardeners and the P. 
coccineus of Lamarck, originally came from Mexico, as I am in- 
formed by Mr. Bentham. The flowers are so constructed that 
hive and humble-bees, which visit them incessantly, almost always 
alight on the left wing-petal, as they can best suck the nectar 
from this side. Their weight and movements depress the petal, 
and this causes the stigma to protrude from the spirally- wound 
keel, and a brush of hairs round the stigma pushes out the pollen 
before it. The pollen adheres to the head or proboscis of the 
bee which is at work, and is thus placed either on the stigma 
of the same flower, or is carried to another flower.t Several 
years ago I covered some plants under a large net, and these 
produced on one occasion about one-third, and on another occa- 
sion about one-eighth, of the number of pods which the same 
number of uncovered plants growing close alongside produced.^ 
This lessened fertility -was not caused by any injury from the 
net, as I moved the wing-petals of several protected flowers, in 
the same manner as bees do, and these produced remarkably 



* We here see that both Lupi- in the ' Annals and Mag. of Nat. 
nus luteus and pilosus seed freely Hist.' vol. ii. (4th series) Oct. 
when insects are excluded; but 1868, p. 256. My son Francis 
Mr. Swale, of Christchurch, in has explained ('Nature,' Jan. 8, 
New Zealand, informs me (see 1874;, p. 189) the use of one pecu- 
' Gardeners' Chronicle,' 1858, p. liarity in their structure, namely, 
828) that the garden varieties of a little vertical projection on the 
the lupine are not there visited by single free stamen near its base, 
any bees, and that they seed less which seems placed as if to guard 
freely than any other introduced the entrance into the two nectar- 
leguminous plant, with the excep- holes in the staminal sheath. 
tion of red clover. He adds, " I He shows that this projection pre- 
have, for amusement, during the vents the bees reaching the nectar, 
summer, released the stamens with unless they go to the left side of 
a pin, and a pod of seed has always the flower, and it is absolutely 
rewarded me for my trouble, the necessary for cross-fertilisation 
adjoining flowers not so served that they should alight on the 
having all proved blind." I do left wing-petal, 
not know to what species this J ' Gardeners' Chronicle,' 1857. 
statement refers. p. 725, and more especially ibid! 

t The flowers have been de- 1858, p. 828. Also 'Annals and 

scribed by Delpino, and in an Mag. of Nat. Hist.' (3rd series) 

admirable manner by Mr. Farrer vol. ii. 1858, p. 462. 



CHAP. V. PHASEOLUS MULTIFLORU8. 151 

fine pods. When the net was taken off, the flowers were imme- 
diately visited by bees, and it was interesting to observe how 
quickly the plants became covered with young pods. As the 
flowers are much frequented by Thrips, the self-fertilisation of 
most of the flowers under the net may have been due to the action 
of these minute insects. Dr. Ogle likewise covered up a large 
portion of a plant, and " out of a vast number of blossoms thus 
protected not a single one produced a pod, while the unprotected 
blossoms were for the most part fruitful." Mr. Belt gives a 
more curious case ; this plant grows well and flowers in Nicaraguaj 
but as none of the native bees visit the flowers, not a single pod 
is ever produced.* 

From the facts now given we may feel nearly sure that 
individuals of the same variety or of different varieties, if growing 
near each other and in flower at the same time, would inter- 
cross ; but I cannot myself advance any direct evidence of such 
an occurrence, as only a single variety is commonly cultivated in 
England. I have, however, received an account from the Kev. 
W. A. Leighton, that plants raised by him from ordinary seed 
produced seeds differing in an extraordinary manner in colour 
and shape, leading to the belief that their parents must have 
been crossed. In France M. Fermond more than once planted 
close together varieties which ordinarily come true and which 
bear differently coloured flowers and seeds; and the offspring 
thus raised varied so greatly that there could hardly be a doubt 
that they had intercrossed.! On the other hand, Professor H. 
Hoffmann J does not believe in the natural crossing of the 
varieties ; for although seedlings raised from two varieties growing 
close together produced plants which yielded seeds of a mixed 
character, he found that this likewise occurred with plants sepa- 
rated by a space of from 40 to 150 paces from any other variety ; 
he therefore attributes the mixed character of the seed to sponta- 



* Dr. Ogle, ' Pop. Science Re- proper manner, 

view,' 1870, p. 168. Mr. Belt, f ' Fe'condation chez les Ve'g- 

4 The Naturalist in Nicaragua,' taux,' 1859, pp. 34-40. He adds 

1874, p. 70. The latter author that M. Villiers has described a 

gives a case (.' Nature,' 1875, spontaneous hybrid, which he 

p. 26) of a late crop of P. multi- calls P. coccineue hybridus, in the 

florus near London, which " was ' Annales de la Soc. R. de Horti- 

rendered barren " by the humble- culture,' June 1844. 

bees cutting, as they frequently \ ' Bestimmung des Werthes 

do, holes at the bases of the flowers von Species und Varietit,' 1869, 

instead of entering them in the pp. 47-72. 



152 



PHASEOLUS MULTIFLORUS. 



CHAP. V. 



neous variability. But the above distance would be very far from 
sufficient to prevent intercrossing : cabbages have been known to 
cross at several times this distance ; and the careful Gartner* 
gives many instances of plants growing at from 600 to 800 yards 
apart fertilising one another. Professor Hoffmann even maintains 
that the flowers of the kidney-bean are specially adapted for 
self-fertilisation. He enclosed several flowers in bags ; and as 
the buds often dropped off, he attributes the partial sterility of 
these flowers to the injurious effects of the bags, and not to the 
exclusion of insects. But the only safe method of experimenting 
is to cover up a whole plant, which then never suffers. 

Self-fertilised seeds were obtained by moving up and down in 
the same manner as bees do the wing-petals of flowers protected 
by a net ; and crossed seeds were obtained by crossing two of the 
plants under the same net. The seeds after germinating on sand 
were planted on the opposite sides of two large pots, and equal- 
sized sticks were given them to twine up. When 8 inches 
in height, the plants on the two sides were equal. The crossed 
plants flowered before the self-fertilised in both pots. As soon 
as one of each pair had grown to the summit of its stick both 
were measured. 

TABLE LIII. 
Phaseolus multiflorus. 



No. of Pot. Crossed Plants. 


Self-fertilised Plants. 


I. 


Inches. 
87 
88 
82 1 


Inches. 

S s 

76 


II. 


90 
82 1 


| 


Total in inches. 


430-00 


411-75 



The average height of the five crossed plants is 86 inches, and 
chat of the five self-fertilised plants 82 35 ; or as 100 to 96. The 
pots were kept in the greenhouse, and there was little or no 
difference in the fertility of the two lots. Therefore as far as 
these few observations serve, the advantage gained by a cross is 
yery small. 

* 'Kenntniss der Befruchtuug,' 1844, pp. 573, 577. 



CHAP.V. LATHYRUS ODORATUS. 153 

PHASEOLUS VULGARIS. 

With respect to this species, I merely ascertained that the 
flowers were highly fertile when insects were excluded, as indeed 
must be the case, for the plants are often forced during the 
winter when no insects are present. Some plants of two varieties 
(viz., Canterbury and Fulmer's Forcing Bean) were covered with 
a net, and they seemed to produce as many pods, containing as 
many beans, as some uncovered plants growing alongside ; but 
neither the pods nor the beans were actually counted. This 
difference in self-fertility between P. vulgaris and midtiflorus is 
remarkable, as these two species are so closely related that 
Linnaeus thought that they formed one. When the varieties of P. 
vulgaris grow near one another in the open ground, they some- 
times cross largely, notwithstanding their capacity for self- 
fertilisation. Mr. Coe has given me a remarkable instance of 
this fact with respect to the negro and a white-seeded and 
a brown-seeded variety, which were all grown together. The 
diversity of character in the seedlings of the second generation 
raised by me from his plants was wonderful. I could add other 
analogous cases, and the fact is well known to gardeners.* 

LATHYRUS ODORATUS. 

Almost everyone who has studied the structure of papi- 
lionaceous flowers has been convinced that they are specially 
adapted for cross-fertilisation, although many of the species are 
likewise capable of self-fertilisation. The case therefore of 
Lathyrus odoratus or the sweet-pea is curious, for in this 
country it seems invariably to fertilise itself. I conclude that 
this is so, as five varieties, differing greatly in the colour of their 
flowers but in no other respect, are commonly sold and come 
true ; yet on inquiry from two great raisers of seed for sale, I 
find that they take no precautions to insure purity the five 
varieties being habitually grown close together.! I have myself 
purposely made similar trials with the same result. Although 
the varieties always come true, yet, as we shall presently see, one 



* I have given Mr. Coe's case ture,' 1872, p. 242, to the same 
in the ' Gardeners' Chronicle,' effect. He once, however, saw 
1858, p. 829. See also for another bees visiting the flowers, and sup- 
case, ibid. p. 845. posed that on this occasion they 

t See Mr. W. Farley in 'Na- would have been intercrosses. 



154 LATHYBUS ODORATUS. CHAP. V. 

of the five well-known varieties occasionally gives birth to another, 
which exhibits all its usual characters. Owing to this curious 
fact, and to the darker-coloured varieties being the most pro- 
ductive, these increase, to the exclusion of the others, as I was 
informed by the late Mr. Masters, if there be no selection. 

In order to ascertain what would be the effect of crossing two 
varieties, some flowers on the Purple sweet-pea, which has a 
dark reddish-purple standard-petal with violet-coloured wing- 
petals and keel, were castrated whilst very young, and were 
fertilised with pollen of the Painted Lady. This latter variety 
has a pale cherry-coloured standard, with almost white wings 
and keel. On two occasions I raised from a flower thus crossed 
plants perfectly resembling both parent-forms ; but the greater 
number resembled the paternal variety. So perfect was the 
resemblance, that I should have suspected some mistake in the 
label, had not the plants, which were at first identical in appear- 
ance with the father or Painted Lady, later in the season produced 
flowers blotched and streaked with dark purple. This is an in- 
teresting example of partial reversion in the same individual 
plant as it grows older. The purple-flowered plants were thrown 
away, as they might possibly have been the product of the 
accidental self-fertilisation of the mother-plant, owing to the 
castration not having been effectual. But the plants which 
resembled in the colour of their flowers the paternal variety or 
Painted Lady were preserved, and their seeds saved. Next 
summer many plants were raised from these seeds, and they 
generally resembled their grandfather the Painted Lady, but 
most of them had their wing-petals streaked and stained with 
dark pink ; and a few had pale purple wings with the standard 
of a darker crimson than is natural to the Painted Lady, so 
that they formed a new sub-variety. Amongst these plants 
a single one appeared having purple flowers like those of the 
grandmother, but with the petals slightly streaked with a paler 
tint : this was thrown away. Seeds were again saved from the 
foregoing plants, and the seedlings thus raised still resembled 
the Painted Lady, or great-grandfather; but they now varied 
much, the standard petal varying from pale to dark red, in a 
few instances with blotches of white ; and the wing-petals varied 
from nearly white to purple, the keel being in all nearly white. 

As no variability of this kind can be detected in plants raised 
from seeds, the parents of which have grown during many suc- 
cessive generations in close proximity, we may infer that they 



CHAP. V LATHYRUS ODOBATUS. 155 

cannot have intercrossed. What does occasionally occtir is that 
in a row of plants raised from seeds of one variety, another 
variety true of its kind appears ; for instance, in a long row of 
Scarlets (the seeds of which had been carefully gathered from 
Scarlets for the sake of this experiment) two Purples and one 
Painted Lady appeared. Seeds from these three aberrant plants 
were saved and sown in separate beds. The seedlings from both 
the Purples were chiefly Purples, but with some Painted Ladies 
and some Scarlets. The seedlings from the aberrant Painted 
Lady were chiefly Painted Ladies with some Scarlets. Each 
variety, whatever its parentage may have been, retained all its 
characters perfect, and there was no streaking or blotching of 
the colours, as in the foregoing plants of crossed origin. Another 
variety, however, is often sold, which is striped and blotched 
with dark purple ; and this is probably of crossed origin, for I 
found, as well as Mr. Masters, that it did not transmit its 
characters at all truly. 

From the evidence now given, we may conclude that the 
varieties of the sweet^pea rarely or never intercross in this 
country ; and this is a highly remarkable fact, considering, firstly, 
the general structure of the flowers ; secondly, the large quantity 
of pollen produced, far more than is requisite for self-fertilisation ; 
and thirdly, the occasional visits of insects. That insects should 
sometimes fail to cross-fertilise the flowers is intelligible, for I 
have thrice seen humble-bees of two kinds, as well as hive-bees, 
sucking the nectar, and they did not depress the keel-petals so 
as to expose the anthers and stigma ; they were therefore quite 
inefficient for fertilising the flowers. One of these bees, namely, 
Bomlus lapidarius, stood on one side at the base of the standard 
and inserted its proboscis beneath the single separate stamen, as 
I afterwards ascertained by opening the flower and finding this 
stamen prised up. Bees are forced to act in this manner from 
the slit in the staminal tube being closely covered by the broad 
membranous margin of the single stamen, and from the tube 
not being perforated by nectar-passages. On the other hand, 
in the three British species of Lathyrus which I have examined, 
and in the allied genus Vicia, two nectar-passages are present. 
Therefore British bees might well be puzzled how to act in 
the case of the sweet-pea. I may add that the staminal tube 
of another exotic species, Lathyrus grandijlorus, is not per- 
forated by nectar-passages, and this species has rarely set any 
pods in my garden, unless the wing-petals were moved up and 



156 LATHYRUS ODORATUS. CHAP. V. 

down, in the same manner as bees ought to do ; and then pods 
were generally formed, but from some cause often dropped off 
afterwards. One of my sons caught an elephant sphinx-moth 
whilst visiting the flowers of the sweet-pea, but this insect would 
not depress the wing-petals and keel. On the other hand, I have 
Been on one occasion hive-bees, and two or three occasions the 
Megachile willuylibiella, in the act of depressing the keel; and 
these bees had the under sides of their bodies thickly covered 
with pollen, and could not thus fail to carry pollen from one 
flower to the stigma of another. Why then do not the varieties 
occasionally intercross, though this would not often happen, as 
insects so rarely act in an efficient manner ? The fact cannot, as 
it appears, be explained by the flowers being self-fertilised at a 
very early age ; for although nectar is sometimes secreted and 
pollen adheres to the viscid stigma before the flowers are fully 
expanded, yet in five young flowers which were examined 
by me the pollen-tubes were not exserted. "Whatever the cause 
may be, we may conclude, that in England the varieties never or 
very rarely intercross. But it does not follow from this, that 
they would not be crossed by the aid of other and larger insects 
in their native country, which in botanical works is said to be 
the south of Europe and the East Indies. Accordingly I wrote 
to Professor Delpino, in Florence, and he informs me " that it is 
the fixed opinion of gardeners there that the varieties do inter- 
cross, and that they cannot be preserved pure unless they are 
sown separately." 

It follows also from the foregoing facts that the several varieties 
of the sweet-pea must have propagated themselves in England 
by self-fertilisation for very many generations, since the time 
when each new variety first appeared. From the analogy of the 
plants of Mimulus and Ipomoaa, which had been self-fertilised 
for several generations, and from trials previously made with 
the common pea, which is in nearly the same state as the sweet- 
pea, it appeared to me very improbable that a cross between the 
individuals of the same variety would benefit the offspring. A 
cross of this kind was therefore not tried, which I now regret. 
But some flowers of the Painted Lady, castrated at an early 
age, were fertilised with pollen from the Purple sweet-pea; and 
it should be remembered that these varieties differ in nothing 
except in the colour of their flowers. The cross was manifestly 
effectual (though only two seeds were obtained), as was shown 
by the two seedlings, when they flowered, closely resemWing 



CHAP. V. 



LATHYRUS ODORATUS. 



157 



their father, the Purple pea, excepting that they were a little 
lighter coloured, with their keels slightly streaked with pale 
purple. Seeds from flowers spontaneously self-fertilised under a 
net were at the same time saved from the same mother-plant, the 
Painted Lady. These seeds unfortunately did not germinate on 
sand at the same time with the crossed seeds, so that they could 
not be planted simultaneously. One of the two crossed seeds in 
a state of germination was planted in a pot (No. I.) in which a 
self-fertilised seed in the same state had been planted four days 
before, so that this latter seedling had a great advantage over 
the crossed one. In Pot II. the other crossed seed was planted 
two jdays before a self-fertilised one ; so that here the crossed 
seedling had a considerable advantage over the self-fertilised one. 
But this crossed seedling had its summit gnawed off by a slug, 
and was in consequence for a time quite beaten by the self- 
fertilised plant. Nevertheless I allowed it to remain, and so 
great was its constitutional vigour that it ultimately beat its un- 
injured self-fertilised rival. When all four plants were almost 
fully grown they were measured, as here shown : 

TABLE LIV. 

Lathyrus odoratus. 



No. of Pot. 


Crossed Plants. 


Self-fertilised Plants. 


I. 


Inches. 
80 


Inches. 
64| 


II. 


78 $ 


63 


Total in inches. 


158-5 


127-5 



The two crossed plants here average 79*25, and the two self- 
fertilised 63-75 inches in height, or as 100 to 80. Six flowers on 
these two crossed plants were reciprocally crossed with pollen 
from the other plant, and the six pods thus produced contained 
on an average six peas, with a maximum in one of seven. Eigh- 
teen spontaneously self-fertilised pods from the Painted Lady, 
which, as already stated, had no doubt been self-fertilised for 
many previous generations, contained on an average only 3 '93 
peas, with a maximum in one of five peas ; so that the number 
of peas in the crossed and self-fertilised pods was as 100 to 65. 



158 



LATHYKUS ODOKATUS 



CHAP. V. 



The self-fertilised peas were, however, quite as heavy as those 
from the crossed pods. From these two lots of seeds, the plants 
of the next generation were raised. 

Plants of the Second Generation. Many of the self-fertilised 
peas just referred to germinated on sand before any of the 
crossed ones, and were rejected. As soon as I got equal pairs, 
they were planted on the opposite sides of two large pots, which 
were kept in the greenhouse. The seedlings thus raised were the 
grandchildren of the Painted Lady, which was first crossed by 
the Purple variety. When the two lots were from 4 to 6 inches 
in height there was no difference between them. Nor was there 
any marked difference in the period of their flowering. When 
fully grown they were measured, as follows : 

TABLE LV. 

Lathyrus odoratus (Second Generation). 



No. of Pot 


Seedlings from Plants 
crossed during the 
two previous Genera- 
tions. 


Seedlings from Plants 
self-fertilised during 
many previous 
Generations. 


I. 


Inches. 
72J 
71 
52 1 


Inches. 
57 J 
67 
56 


II. 


81 1 

s 1 


66 1 
381 
46 


Total in inches. 


377-50 


331-86 



The average height of the six crossed plants is here 62-91, and 
that of the six self-fertilised 55 31 inches ; or as 100 to 88. There 
was not much difference in the fertility of the two lots ; the 
crossed plants having produced in the greenhouse thirty-five 
pods, and the self-fertilised thirty-two pods. 

Seeds were saved from the self-fertilised flowers on these two 
lots of plants, for the sake of ascertaining whether the seedlings 
thus raised would inherit any difference in growth or vigour. 
It must therefore be understood that both lots in the following 
trial are plants of self-fertilised parentage ; but that in the one 
lot the plants were the children of plants which had been crossed 
during two previous generations, having been before that self- 



CHAP.V. 



LATHYRUS ODORATUS. 



159 



fertilised for many generations; and that in the other lot they 
were the children of plants which had not been crossed for very 
many previous generations. The seeds germinated on sand and 
were planted in pairs on the opposite sides of four pots. They 
were measured, when fully grown, with the following result : 

TABLE LVI. 

Lathyrus odoratus. 



No. of Pot. 


Self-fertilised Plants 
from Crossed Plants. 


Self-fertilised Plants 
from Self-fertilised 
Plants. 


I. 


Inches. 
72 
72 


Inches. 
65 
61| 


II. 


58 
68 
72| 


64 

681 
56 j 


III. 


81 


60f 


IV. 


77, 


76J 


Total in inches. I 501 

i 


452 



The average height of the seven self-fertilised plants, the off- 
spring of crossed plants, is 71'57, and that of the seven self-fer- 
tilised plants, the offspring of self-fertilised plants, is 64' 57 ; or 
as 100 to 90. The self-fertilised plants from the self-fertilised 
produced rather more pods viz., thirty-six than the self-fer- 
tilised plants from the crossed, for these produced only thirty-one 
pods. 

A few seeds of the same two lots were sown in the opposite 
corners of a large box in which a Brugmansia had long been 
growing, and in which the soil was so exhausted that seeds of 
Ipomcea purpurea would hardly vegetate ; yet the two plants of 
tie sweet-pea which were raised flourished well. For a long 
time the self-fertilised plant from the self-fertilised beat the self- 
fertilised plant from the crossed plant ; the former flowered first, 
and was at one time 77 i inches, whilst the latter was only 68i in 
height; but ultimately the plant from the previous cross showed 
its superiority and attained a height of 108 i inches, whilst the 
other was only 95 inches. I also sowed some of the same two 



160 PISUM SATIVUM. CHAP. V 

lots of seeds in poor soil in a shady place in a shrubbery. Here 
again the self-fertilised' plants from the self-fertilised for a long 
time exceeded considerably in height those from the previously 
crossed plants; and this may probably be attributed, in the 
present as in the last case, to these seeds having germinated 
rather sooner than those from the crossed plants ; but at the 
close of the season the tallest of the self-fertilised plants from 
the crossed plants was 30 inches, whilst the tallest of the self- 
fertilised from the self-fertilised was 29f inches in height. 

From the various facts now given we see that plants derived 
from a cross between two varieties of the sweet-pea, which differ 
in no respect except in the colour of their flowers, exceed 
considerably in height the offspring from self-fertilised plants, 
both in the first and second generations. The crossed plants 
also transmit their superiority in height and vigour to their 
self-fertilised offspring. 

PISUM SATIVUM. 

The common pea is perfectly fertile when its flowers are pro- 
tected from the visits of insects; I ascertained this with two or 
three different varieties, as did Dr. Ogle with another. But the 
flowers are likewise adapted for cross-fertilisation; Mr. Farrer 
specifies * the following points, namely : " The open blossom dis- 
playing itself in the most attractive and convenient position for 
insects ; the conspicuous vexillum ; the wings forming an alight- 
ing place; the attachment of the wings to the keel, by which 
any body pressing on the former must press down the latter ; 
the staminal tube enclosing nectar, and affording by means of its 
partially free stamen with apertures on each side of its base an 
open passage to an insect seeking the nectar; the moist and 
sticky pollen placed just where it will be swept out of the apex 
of the keel against the entering insect ; the stiff elastic style so 
placed that on a pressure being applied to the keel it will be 
pushed upwards out of the keel ; the hairs on the style placed 
on that side of the style only on which there is space for the 
pollen, and in such a direction as to sweep it out; and the 
stigma so placed as to meet an entering insect, all these 
become correlated parts of one elaborate mechanism, if we 



* 'Nature,' Oct. 10, 1872, p. description of the flowers, 
479. H. Muller gives an elaborate fruchtung,' &c. p. 247. 



CHAP. V. PISTJM SATIVUM. 161 

suppose that the fertilisation of these flowers is effected by the 
carriage of pollen from one to the other." Notwithstanding these 
manifest provisions for cross-fertilisation, varieties which have 
been cultivated for very many successive generations in close 
proximity, although flowering at the same time, remain pure. I 
have elsewhere * given evidence on this head, and if required 
could give. more. There can hardly be a doubt that some of 
Knight's varieties, which we/re originally produced by an artificial 
cross and were very vigorous, lasted for at least sixty years, and 
during all these years were self-fertilised ; for had it been other- 
wise, they would not have kept true, as the several varieties 
are generally grown near together. Most of the varieties, how- 
over, endure for a shorter period ; and this may be in part due 
to their weakness of constitution from long-continued self- 
fertilisation. 

It is remarkable, considering that the flowers secrete much 
nectar and afford much pollen, how seldom they are visited by 
insects either in England or, as H. Muller remarks, in North 
Germany. I have observed the flowers for the last thirty years, 
and in aU this time have only thrice seen bees of the proper kind at 
work (one of them being Bombus muscorum), such as were suf- 
ficiently powerful to depress the keel, so as to get the undersides ot 
their bodies dusted with pollen. These bees visited several flowers, 
and could hardly have failed to cross-fertilise them. Hive-bees 
and other small kinds sometimes collect pollen from old and 
already fertilised flowers, but this is of no account. The rarity 
of the visits of efficient bees to this exotic plant is, I believe, the 
chief cause of the varieties so seldom intercrossing. That a 
cross does occasionally take place, as might be expected from what 
has just been stated, is certain, from the recorded cases of the direct 
action of the pollen of one variety on the seed- coats of another, f 
The late Mr. Masters, who particularly attended to the raising of 
new varieties of peas, was convinced that some of them had 
originated from accidental crosses. But as such crosses are 
rare, the old varieties would not often be thus deteriorated, more 
especially as plants departing from the proper type are generally 
rejected by those who collect seed for sale. There is another 
cause which probably tends to render cross-fertilisation rare; 



* 'Variation of Animals and f 'Var. under Domestication, 
Plants under Domestication,' chap. xi. 2nd edit. vol. i. p. 428. 
chap. ix. 2nd edit. vol. i. p. 3-48. 



162 



PISUM SATIVUM. 



CHAP. "V. 



namely, the early age at which the pollen-tubes are exserted; 
eight flowers not fully expanded were examined, and in seven ot 
these the pollen-tubes were in this state; but they had not as 
yet penetrated the stigma. Although so few insects visit the 
flowers of the pea in this country or in North Germany, and 
although the anthers seem here to open abnormally soon, it does 
not follow that the species in its native country would be thus 
circumstanced. 

Owing to the varieties having been self-fertilised for many 
generations, and to their having been subjected in each genera- 
tion to nearly the same conditions (as will be explained in a 
future chapter), I did not expect that a cross between two such 
plants would benefit the offspring ; and so it proved on trial. In 
1867 I covered up several plants of the Early Emperor pea, which 
was not then a very new variety, so that it must already have 
been propagated by self-fertilisation for at least a dozen genera- 
tions. Some flowers were crossed with pollen from a distinct 
plant growing in the same row, and others were allowed to 
fertilise themselves under a net. The two lots of seeds thus 
obtained were sown on opposite sides of two large pots, but only 
four pairs came up at the same time. The pots were kept in the 
greenhouse. The seedlings of both lots when between 6 and 7 
inches in height were equal. When nearly full-grown they 
were measured, as in the following table : 

TABLE LVII. 
Pisum sativum. 



Xo. of Pot. 


Crossed Plants. 


ielf-fertilised Plants. 


I. 


Inches. 
35 


Inches. 
29| 


II. 


31 1 
35 
37 


51 
45 
33 


Total in inches. 


138-50 


158-75 



The average height of the four crossed plants is here 34-62, 
and that of the four self-fertilised plants 39 -68, or as 100 to 115. 
So that the crossed plants, faiffrOTn beating the self-fertilised, 
were completely beaten by them. 



CHAP. V. SABOTHAMNUS SCOPARIUS. 163 

There can be no doubt that the result would have been 
widely differe.it, if any two varieties out of the numberless ones 
which exist had been crossed. Notwithstanding that both had 
been self-fertilised for many previous generations, each would 
almost certainly have possessed its own peculiar constitution; 
and this degree of differentiation would have been sufficient to 
make a cross highly beneficial. I have spoken thus confidently 
of the benefit which would have been derived from crossing any 
two varieties of the pea from the following facts: Andrew 
Knight in speaking of the results of crossing reciprocally very 
tall and short varieties, says,* "I had in this experiment a 
striking instance of the stimulative effects of crossing the breeds ; 
for the smallest variety, whose height rarely exceeded 2 feet, 
was increased to 6 feet; whilst the height of the large and 
luxuriant kind was very little diminished." Eecently Mr. Laxton 
has made numerous crosses, and everyone has been astonished at 
the vigour and luxuriance of the new varieties which he has thus 
raised and afterwards fixed by selection. He gave me seed-peas 
produced from crosses between four distinct kinds; and the 
plants thus raised were extraordinarily vigorous, being in each 
case from 1 to 2 or even 8 feet taller than the parent-forms, 
which were raised at the same time close alongside. But as 
I did not measure their actual height I cannot give the exact 
ratio, but it must have been at least as 100 to 75. A similar 
trial was subsequently made with two other peas from a different 
cross, and the result was nearly the same. For instance, a crossed 
seedling between the Maple acd Purple-podded pea was planted 
in poor soil and grew to the extraordinary height of 116 inches ; 
whereas the tallest plant of either parent variety, namely, a 
Purple-podded pea, was only 70 inches in height ; or as 100 to 60. 

SAEOTHAMNUS SCOPARIUB. 

P>ees incessantly visit the flowers of the common Broom, and 
these are adapted by a curious mechanism for cross-fertilisation. 
When a bee alights on the wing-petals of a young flower, the 
keel is slightly opened and the short stamens spring out, which 
rub their pollen against the abdomen of the bee. If a rather 
older flower is visited for the first time (or if the bee exerts great 
force on a younger flower), the keel opens along its whole 
length, and the longer as well as the shorter stamens, together 

* 'Philosophical Transactions,' 1799, p. 200. 

M 2 



164 SAKOTHAMNUS SCOPAEIUS. CHAP. V. 

with the much elongated curved pistil, spring forth with violence. 
The flattened, spoon-like extremity of the pistil rests for a time 
on the back of the bee, and leaves on it the load of pollen with 
which it is charged. As soon as the bee flies away, the pistil 
instantly curls round, so that the stigmatic surface is now up- 
turned and occupies a position, in which it would be rubbed 
against the abdomen of another bee visiting the same flower. 
Thus, when the pistil first escapes from the keel, the stigma 
is rubbed against the back of the bee, dusted with pollen 
from the longer stamens, either of the same or another flower ; 
and afterwards against the lower surface of the bee dusted 
with pollen from the shorter stamens, which is often shed a 
day or two before that from the longer stamens. * By this 
mechanism cross-fertilisation is rendered almost inevitable, and 
we shall immediately see that pollen from a distinct plant is 
more effective than that from the same flower. I need only add 
that, according to H. Muller, the flowers do not secrete nectar, 
and he thinks that bees insert their proboscides only in the hope 
of finding nectar ; but they act in this manner so frequently and 
for so long a time that I cannot avoid the belief that they 
obtain something palatable within the flowers. 

If the visits of bees are prevented, and if the flowers are 
not dashed by the wind against any object, the keel never 
opens, so that the stamens and pistil remain enclosed. Plants 
thus protected yield very few pods in comparison with those 
produced by neighbouring uncovered bushes, and sometimes 
none at all. I fertilised a few flowers on a plant growing 
almost in a state of nature with pollen from another plant 
close alongside, and the four crossed capsules contained on 
an average 9'2 seeds. This large number no doubt was due 
to the bush being covered up, and thus not exhausted by 
producing many pods ; for fifty pods gathered from an adjoining 
plant, the flowers of which had been fertilised by the bees, 
contained an average of only 7' 14 seeds. Ninety-three pods 
spontaneously self-fertilised on a large bush which had been 
covered up, but had been much agitated by the wind, contained 
an average of 2*93 seeds. Ten of -the finest of these ninety- 



* These observations have been ix. 1866, p. 358. H. Muller has 

quoted in an abbreviated form by since published a full and excel- 

the Eev. G. Henslow, in the lent account of the flower in his 

' Journal of Linn. Soc. Bot.' vol. ' Befruchtung,' &c. p. 240. 



CHAP. V. 8AROTHAMNUS SCOPARIUS. 165 

three capsules yielded an average of 4-30 seeds, that is less than 
half the average number in the four artificially crossed capsules. 
The ratio of 7 -14 to 2-93, or as 100 to 41, is probably the 
fairest for the number of seeds per pod, yielded by naturally- 
crossed and spontaneously self-fertilised flowers. The crossed 
seeds compared with an equal number of the spontaneously self- 
fertilised seeds were heavier, in the ratio of 100 to 88. We thus 
see that besides the mechanical adaptations for cross-fertilisation, 
the flowers are much more productive with pollen from a 
distinct plant than with their own pollen. 

Eight pairs of the above crossed and self-fertilised seeds, after 
they had germinated on sand, were planted (1867) on the 
opposite sides of two large pots. When several of the seedlings 
were an inch and a half in height, there was no marked difference 
between the two lots. But even at this early age the leaves of 
the selMertilised seedlings were smaller and of not so bright a 
green as those of the crossed seedlings. The pots were kept in 
the greenhouse, and as the plants in the following spring (1868) 
looked unhealthy and had grown but little, they were plunged, 
still in their pots, into the open ground. The plants all suffered 
much from the sudden change, especially the self-fertilised, and 
two of the latter died. The remainder were measured, and I 
give the measurements in the following table, because I have 
not seen in any other species so great a difference between the 
crossed and self-fertilised seedlings at so early an age. 

TABLE LVITL 
Sarothamnus scoparius (very young plants). 



No. of Pot 


Crossed Plants. 


Self-fertilised Plants. 


I. 


Inches. 

? 

2 


Inches. 

P 


II. 


ii 

o! 


i! 


Total 'n inches. 


17-5 


8-0 



The six crossed plants here average 2 -91, and the six self- 



166 



SAROTHAMNUS SCOPARIUS. 



CIIAP. \" 



fertilised 1 ' 33 inches in height ; so that the former "were more 
than twice as high as the latter, or as 100 to 46. 

In the spring of the succeeding year (1869) the three crossed 
plants in Pot I. had all grown to nearly a foot in height, and they 
had smothered the three little self-fertilised plants so completely 
that two were dead ; and the third, only an inch and a half 
in height, was dying. It should be remembered that these 
plants had been bedded out in their pots, so that they were 
subjected to very severe competition. This pot was now thrown 
away. 

The six plants in Pot II. were all alive. One of the self- 
fertilised was an inch and a quarter taller than any one of the 
crossed plants ; but the other two self-fertilised plants were in a 
very poor condition. I therefore resolved to leave these plants to 
struggle together for some years. By the autumn of the same 
year (1869) the self-fertilised plant which had been victorious 
was now beaten. The measurements are shown in the following 
table : 

TABLE LIX. 
Pot H. Sarotliamnus scoparius. 



Crossed Plants. 


Self-fertilised Plants. 


Inches. 


Inches. 


9 i 


I S B 


81 


M 



The same plants were again measured in tho autumn of the 
following year, 1870. 

TABLE LX. 
Pot II. Sarothamnus scoparius. 



Crossed Plants. 


Self-fertilised Plants. 


Inches. 
26 i 

Ml 

14 


Inches. 
14f 
111 
\ 


56-75 


35-50 



OHAP.V. ONONIS MINU11SSIMA. 167 

The three crossed plants now averaged 18 '91, and the three 
self-fertilised 11 83 inches in height ; or as 100 to 63. The three 
crossed plants in Pot I., as already shown, had beaten the three 
self-fertilised plants so completely, that any comparison between 
them was superfluous. 

The winter of 1870-1871 was severe. In the spring the three 
crossed plants in Pot II. had not even the tips of their shoots in 
the least injured, whereas all three self-fertilised plants were 
killed half-way down to the ground ; and this shows how much 
more tender they were. In consequence not one of these latter 
plants bore a single flower during the ensuing summer of 1871, 
whilst all three crossed plants flowered. 



ONONIS MINUTI88IMA. 

This plant, of which seeds were sent me from North Italy, pro- 
duces, besides the ordinary papilionaceous flowers, minute, imper- 
fect, closed or cleistogamic flowers, which can never be cross-ferti- 
lised, but are highly self-fertile. Some of the perfect flowers were 
crossed with pollen from a distinct plant, and six capsules thus 
produced yielded on an average 3 '66 seeds, with a maximum 
of five in one. Twelve perfect flowers were marked and allowed 
to fertilise themselves spontaneously under a net, and they 
yielded eight capsules, containing on an average 2 38 seeds, with 
a maximum of three seeds in one. So that the crossed and self- 
fertilised capsules from the perfect flowers yielded seeds in the 
proportion of 100 to 65. Fifty-three capsules produced by the 
cleistogamic flowers contained on an average 4'1 seeds, so that 
these were the most productive of all; and the seeds them- 
selves looked finer even than those from the crossed perfect 
flowers. 

The seeds from the crossed perfect flowers and from the self- 
fertilised cleistogamic flowers were allowed to germinate on sand ; 
but unfortunately only two pairs germinated at the same time. 
These were planted on the opposite sides of the same pot, which 
was kept in the greenhouse. In the summer of the same year, 
when the seedlings were about 4i inches in height, the two lots 
were equal. In the autumn of the following year (1868) the two 
crossed plants were of exactly the same height, viz., llf inches, 
and the two self-fertilised plants 12f and 7| inches ; so that one 
of the self-fertilised exceeded considerably in height all the others. 
By the autumn of 1869 the two crossed plants had acquired the 



168 



SUMMAKY ON THE LEGUMINOSJS. 



CHAP. 



supremacy ; their height being 16| and 15J, whilst that of the 
two self-fertilised plants was 14f and llf inches. 
By the autumn of 1870, the heights were as follows : 

TABLE LXI. 
Ononis minutissima. 



Crossed Plants. 


Self-fertilised Plants. 


Inches. 
20| 
19| 


Inches. 
17 1 
lf| 


39-63 


34 '75 



So that the mean height of the two crossed plants was 19 - 81, 
and that of the two self-fertilised 17 '37 inches ; or as 100 to 88. 
It should be remembered that the two lots were at first equal in 
height ; that one of the self-fertilised plants then had the advan- 
tage, the two crossed plants being at last victorious. 

Summary on the Leguminosas. Six genera in this 
family were experimented on, and the results are in 
some respects remarkable. The crossed plants of the 
two species of Lupinus were conspicuously superior to 
the self-fertilised plants in height and fertility ; and 
when grown under very unfavourable conditions, in 
vigour. The scarlet-runner (Phaseolus multiflorus) is 
partially sterile if the visits of bees are prevented, and 
there is reason to believe that varieties growing near 
one another intercross. The five crossed plants, how- 
ever, exceeded in height the five self-fertilised only 
by a little. Phaseolus vulgaris is perfectly self-fertile ; 
nevertheless, varieties growing in the same garden 
sometimes intercross largely. The varieties ofLathyrus 
odoratus, on the other hand, appear never to intercross 
in this country ; and though the flowers are not often 
visited by efficient insects, I cannot account for this 
fact, more especially as the varieties are believed to 



CHAP. V. CLARKIA ELEGANS. 169 

intercross in North Italy. Plants raised from a cross 
between two varieties, differing only in the colour of 
their flowers, grew much taller and were under un- 
favourable conditions more vigorous than the self-ferti- 
lised plants ; they also transmitted, when self-fertilised, 
their superiority to their offspring. The many varieties 
of the common Pea (Pisum sativum), though growing in 
close proximity, very seldom intercross ; and this seems 
due to the rarity in this country of the visits of bees 
sufficiently powerful to effect cross-fertilisation. A 
cross between the self-fertilised individuals of the same 
variety does no good whatever to the offspring ; whilst 
a cross between distinct varieties, though closely allied, 
does great good, of which we have excellent evidence. 
The flowers of the Broom (Sarothamnus) are almost 
sterile if they are not disturbed and if insects are ex- 
cluded. The pollen from a distinct plant is more 
effective than that from the same flower in producing 
seeds. The crossed seedlings have an enormous advan- 
tage over the self-fertilised when grown together in 
close competition. Lastly, only four plants of the 
Ononis minutissima, were raised; but as these were 
observed during their whole growth, the advantage of 
the crossed over the self-fertilised plants may, I think, 
be fully trusted. 

XV. ONAGKACEjE. CLABKIA ELEGANS. 

Owing to the season being very unfavourable (1867), few of 
the flowers which I fertilised formed capsules ; twelve crossed 
flowers produced only four, and eighteen self-fertilised flowers 
yielded only one capsule. The seeds after germinating on sand 
were planted in three pots, but all the self-fertilised plants died 
in one of them. When the two lots were between 4 and 5 
inches in height, the crossed began to show a slight superiority 
over the self-fertilised. When in full flower they were measured, 
with the following result:- 



170 



BAETONIA AUREA. 



CHAP.V 



TABLE LXH. 
Clarkia elegans. 



No. of Pot 


Crossed Plants. 


Self-fertilised Plants. 


I. 


Inches. 
40 1 
35 
25 


Inches. 
33 
24 
23 


II. 


33 1 


30| 


Total in inches. 


134-0 


110-5 



The average height of the four crossed plants is 33 5, and 
that of the four self-fertilised plants 27 '62 inches, or as 100 to 
82. The crossed plants altogether produced 105 and the self- 
fertilised plants 63 capsules; or as 100 to 60. In both pots a 
self-fertilised plant flowered before any one of the crossed plants. 

XVI. LOASACE^. BABTONIA AUEEA. 
Some flowers were crossed and self-fertilised in the usual 
manner during two seasons; but as I reared on the first occasion 

TABLE LXIII. 

Sartonia aurea. 






No. of Pot. 


Crossed Plants. 


Self-fertilised Plants. 


I. 


Inches. 
31 


Inches. 
37 


II. 


18| 


20 1 


IIL 


ll 


40 1 


IV. 


25 
36 


35 
153 


V. 


31 
16 


18 
"1 


VI. 


20 


32J 


Total in inches. 


197-0 


210-5 



CHAP. V. 



PASSIFLORA GRACILIS. 



171 



only two pairs, the results are given together. On both occasions 
the crossed capsules contained slightly more seeds than the self- 
fertilised. During the first year, when the plants were about 
7 inches in height, the self-fertilised were the tallest, and in the 
second year the crossed were the tallest. When the two lots were 
in full flower they were measured, as in the preceding table. 

The average height of the eight crossed plants was 24*62, and 
that of the eight self-fertilised '26 31 inches ; or as 100 to 107. So 
that the self-fertilised had a decided advantage over the crossed. 
But the plants from some cause never grew well, and finally be- 
came so unhealthy that only three crossed and three self-fertilised 
plants survived to set any capsules, and these were few in number. 
The two lots seemed to be about equally unproductive. 

XVn. PASSIFLOKACE.E. PASSIFLOBA OBAOILIB. 
This annual species produces spontaneously numerous fruits 
xvhen insects are excluded, and behaves in this respect very 
differently from most of the other species in the genus, which 
are extremely sterile unless fertilised with pollen from a distinct 
plant.* Fourteen fruits from crossed flowers contained on an 
average 24 '14 seeds. Fourteen fruits (two poor ones being 
rejected), spontaneously self-fertilised under a net, contained on 
un average 20 '58 seeds per fruit; or as 100 to 85. These seeds 
were sown on the opposite sides of three pots, but only two pairs 
came up at the same time ; and therefore a fair judgment cannot 
be formed. 

TABLE LXTV. 
Passiflora, gracilis. 



No. of Pot. 


Crossed Plants. 


Self-fertilised Plants. 


I. 


Inches. 
56 


Inches. 
38 


IL 


42 


64 


Total in inche*. 


98 


102 



The mean of the two crossed is 49 inches, and that of the two 
aolf-fertilised 51 inches ; or as 100 to 104. 



* Variation of Animals and chap. xvii. 2nd edit. vol. ii. p. 
Plants under Domestication ' 118. 



172 



SCABIOSA ATKO-PURPUREA. 



CHA.P. V 



XVIII. UMBELLIFEE^. APIUM PETROSELINUM. 
The Umbelliferse are proterandrous, and can hardly fail to lie 
cross-fertilised by the many flies and small Hymenoptera which 
visit the flowers.* A plant of the common parsley was covered 
by a net, and it apparently produced as many and as fine 
spontaneously self-fertilised fruits or seeds as the adjoining 
uncovered plants. The flowers on the latter were visited by so 
many insects that they must have received pollen from one 
another. Some of these two lots of seeds were left on sand, but 
nearly all the self-fertilised seeds germinated before the others, 
so that I was forced to throw all away. The remaining seeds 
were then sown on the opposite sides of four pots. At first the 
self-fertilised seedlings were a little taller in most of the pots 
than the naturally crossed seedlings, and this no doubt was due 
to the self-fertilised seeds having germinated first. But in 
the autumn all the plants were so equal that it did not seem 
worth while to measure them. In two of the pots they were 
absolutely equal ; in a third, if there was any difference, it was 
in favour of the crossed plants, and in a somewhat plainer 
manner in the fourth pot. But neither side had any substantial 
advantage over the other ; so that in height they may be said 
to be as 100 to 100. 

XIX. DIPSACE^:. SCABIOSA ATBO-PTJRPUREA. 
The flowers, which are proterandrous, were fertilised during 

TABLE LXV. 

Scabiosa atro-purpurea. 



No. of Pot. 


Crossed Plants. 


Self fertilised Plants. 


I. 


Inches. 
14 


Inches. 
20 


II. 


15 


m 


HI. 


21 
18j 


14 
13 


Total in inches. 


68-5 


61-5 



* H.MuIler, ( Befruchtun<j,'&c. 
p. 96. According to M. Muriel 
(as stated by Godron, ' De 1'Es- 



pece,' torn. ii.p. 58, 1859), varieties 
of the carrot growing near each 
other readily intercross. 



CHAP V. LACTUCA SATIVA. 173 

the unfavourable season of 1867, so that I got few seeds, 
especially from the self-fertilised heads, which were extremely 
sterile. The crossed and self-fertilised plants raised from these 
seeds were measured before they were in full flower, as in the 
preceding table. 

The four crossed plants averaged 17 '12, and the four self-fer- 
tilised 15-37 inches in height; or as 100 to 90. One of the self- 
fertilised plants in Pot III. was killed by an accident, and its 
fellow pulled up; so that when they were again measured to the 
summits of their flowers, there were only three on each side ; 
the crossed now averaged in height 32 -83, and the self-fertilised 
30-16 inches; or as 100 to 92. 

XX. COMPOSITE. LACTUOA SATIVA. 
Three plants of Lettuce* (Great London Cos var.) grew close 
together in my garden ; one was covered by a net, and produced 
self-fertilised seeds, the other two were allowed to be naturally 
crossed by insects; but the season (1867) was unfavourable, and 
I did not obtain many seeds. Only one crossed and one self- 
fertilised plant were raised in Pot I., and their measurements are 
given in the following table (LXVI.)- The flowers on this one 
self-fertilised plant were again self-fertilised under a net, not 
with pollen from the same floret, but from other florets on the 
same head. The flowers on the two crossed plants were left to 
be crossed by insects, but the process was aided by some pollen 
being occasionally transported by me from plant to plant. These 
two lots of seeds, after germinating on sand, were planted in 
pairs on the opposite sides of Pots II. and III., which were at 
first kept in the greenhouse and then turned out of doors. The 
plants were measured when in full flower. The following table, 
therefore, includes plants belonging to two generations. When 
the seedlings of the two lots were only 5 or 6 inches in height 
they were equal. In Pot in. one of the self-fertilised plants 
died before flowering, as has occurred in so many other cases. 



* The Composite are well- It is very improbable that all the 

adapted for cross-fertilisation, but varieties which were thus culti- 

a nurseryman on whom I can vated near together flowered at 

rely, told me tliat he had been in different times ; but two which I 

the habit of sowing several kinds selected by hazard and sowed 

of lettuce near together for the near each other did not flower at 

sake of seed, and had never ob- the same time ; and my trial 

t>( r-'ed that they became crossed. faUcd. 



174 



SPECULAEIA SPECULUM. 



CHAI-. V. 



TABLE LXVI. 
Lactuca sativa. 



No. of Pot. 


Crossed Plants. 


Self-fertilised Plants. 


I. 

First generation, 
planted in open 
ground. 


Inches. 
27 
25 


Inches. 
21 i 

20 


II. 

Second generation, 
planted in open 
ground. 


29| 
17f 


24 
10 
11 


III. 

Second generation, 
kept in the pot. 


14 
10J 


S! 


Total in inches. 


136 


96 



The average height of the seven crossed plants is 19 -43, and 
that of the six self-fertilised plants 16 inches ; or as 100 to 82. 



XXI. CAMPANULACE^. SPECULABIA SPECULUM. 

In the closely allied genus, Campanula, in which Specularia 
was formerly included, the anthers shed at an early period their 
pollen, and this adheres to the collecting hairs which surround 
the pistil beneath the stigma ; so that without some mechanical 
aid the flowers cannot be fertilised. For instance, I covered up 
a plant of Campanula carpathica, and it did not produce a single 
capsule, whilst the surrounding uncovered plants seeded pro- 
fusely. On the other hand, the present species of Specularia 
appears to set almost as many capsules when covered up, as 
when left to the visits of the Diptera, which, as far as I have 
seen, are the only insects that frequent the flowers.* I did not 
ascertain whether the naturally crossed and spontaneously self- 
fertilised capsules contained an equal number of seeds, but a 
comparison of artificially crossed and self-fertilised flowers, 



* It has long been known that 
another species of the genus, 
Specularia perfoliata, produces 



cleistogamic as well as perfect 
flowers, and the former are ot 
course self-fertile. 



CHAP. V. 



SPECULARIA SPECULUM. 



175 



showed that the former were probably the most productive. Jt 
appears that this plant is capable of producing a large number 
of self-fertilised capsules owing to the petals closing at night, as 
well as during cold weather. In the act of closing, the margins 
of the petals become reflexed, and their inwardly projecting 
midribs then pass between the clefts of the stigma, and in doing 
so push the pollen from the outside of the pistil on to the 
stigmatic surfaces.* 

Twenty flowers were fertilised by me with their own pollen, 
but owing to the bad season, only six capsules were produced ; 
they contained on an average 21 '7 seeds, with a maximum of 
forty-eight in one. Fourteen flowers were crossed with pollen 
from another plant, and these produced twelve capsules, contain- 
ing on an average 30 seeds, with a maximum in one of fifty- 
seven seeds ; so that the crossed seeds were to the self-fertilised 
from an equal number of capsules as 100 to 72. The former 
were also heavier than an equal number of self-fertilised seeds, 
in the ratio of 100 to 86. Thus, whether we judge by the number 
of capsules produced from an equal number of flowers, or by the 
average number of the contained seeds, or the maximum number 
in any one capsule, or by their weight, crossing does great good 
in comparison with self-fertilisation. The two lots of seeds were 



TABLE LXVII. 

Specularia speculum. 



No. of Pot. 


Tallest Crossed Plant 
in each Pot. 


Tallest Self-fertilised 
Plant in each Pot 


I. 


Inches. 
18 


Inches. 
15g 


II. 


17 


19 


IIL 


22} 


18 


IV. 


20 


23 


Total in inches. 


77-13 


75-75 





* Mr. Meehan has lately shown 
( Proc. Acad Nat. So. Philadel- 
phia,' May 16, 1876, p. 84) that 
the closing of the flowers of Clay- 



tonia virginica and Ranunculus but- 
bosus during the night causes their 
self-fertilisation. 



176 LOBELIA KAMOSA. CHAP. V. 

sown on the opposite sides of four pots ; but tha seedlings were 
not sufficiently thinned. Only the tallest plant on each side was 
measured, when fully grown. The measurements are given in 
the preceding table. In all four pots the crossed plants flowered 
first. When the seedlings were only about an inch and a half in 
height both lots were equal. 

The four tallest crossed plants averaged 19 '28, and the four 
tallest self-fertilised 18 '93 inches in height; or as 100 to 98. 
So that there was no difference worth speaking of between the 
two lots in height ; though other great advantages are derived, 
as we have seen, from cross-fertilisation. From being grown in 
pots and kept in the greenhouse, none of the plants produced 
any capsules. 

LOBELIA EAJIOSA.* 
far. Snow-flake. 

The well-adapted means by which cross-fertilisation is en- 
sured in this genus have been described by several authors, t 
The pistil as it slowly increases in length pushes the pollen 
out of the conjoined anthers, by the aid of a ring of bristles ; the 
two lobes of the stigma being at this time closed and incapable 
of fertilisation. The extrusion of the pollen is also aided by 
insects, which rub against the little bristles that project from 
the anthers. The pollen thus pushed out is carried by insects 
to the older flowers, in which the stigma of the now freely 
projecting pistil is open and ready to be fertilised. I proved 
the importance of the gaily-coloured corolla, by cutting off the 
large lower petal of several flowers of Lobelia erinus ; and these 
flowers were neglected by the hive-bees which were incessantly 
visiting the other flowers. 

A capsule was obtained by crossing a flower of L. ramose 



* I have adopted the name Mag. of .Nat. Hist.' vol. ii. (4th 

given to this plant in the 'Gar- series) 1868, p. 260. In the allied 

deners' Chronicle,' 1866. Prof. genus Isotoma, the curious spike 

T. Dyer, however, informs me which projects rectangularly from 

that it probably is a white variety the anthers, and which when 

of L. tenuior of R. Brown, from shaken causes the pollen to fall 

W . Australia. on the back of an entering insect, 

t See the works of Hildebrand seems to have been developed 

and Delpino. Mr. Farrer also from a bristle, like one of those 

has given a remarkably clear which spring from the anthers in 

description of the mechanism by some of or all the species of Lo- 

which cross-fertilisation is effected belia, as described by Mr. Farrer. 
in this genus, in the ' Annals and 



CHAP. V. 



LOBELIA EAMOSA. 



177 



with pollen from another plant, and two other capsules from 
artificially self-fertilised flowers. The contained seeds were 
sown on the opposite sides of four pots. Some of the crossed 
seedlings which came up before the others had to be pulled up 
and thrown away. Whilst the plants were very small there was 
not much difference in height between the two lots ; but in Pot 
in. the self-fertilised were for a time the tallest. When in full 
flower the tallest plant on each side of each pot was measured, 
and the result is shown in the following table. In all four 
pots a crossed plant flowered before any one of its opponents. 

TABLE LXVIII. 

Lobelia ramosa (First Oeneration). 



No. of Pot. 


Tallest Crossed Plant 
in each Pot. 


Tallest Self-fertilised 
Plant in each Pot. 


I. 


Inches. 
22 1 


Inches. 
17| 


II. 


27| 


24 


III. 


Wj 


15 


IV. 


22| 


17 


Total in inches. 


89-0 


73-5 



The four tallest crossed plants averaged 22 -25, and the four 
tallest self-fertilised 18 '37 inches in height ; or as 100 to 82. I 
was surprised to find that the anthers of a good many of these 
self-fertilised plants did not cohere and did not contain any 
pollen ; and the anthers even of a very few of the crossed plants 
were-*n the same condition. Some flowers on the crossed plants 
were again crossed, four capsules being thus obtained ; and some 
flowers on the self-fertilised plants were again self-fertilised, 
seven capsules being thus obtained. The seeds from both lots 
were weighed, and it was calculated that an equal number of 
capsules would have yielded seed in the proportion by weight of 
100 for the crossed to 60 for the self-fertilised capsules. So that 
the flowers on the crossed plants again crossed were much 
more fertile than those on the self-fertilised plants again self- 
fertilised. 



178 



LOBELIA EAMOSA. 



CHAP. V. 



Plants of the Second Generation. The above two lots of seeds 
were placed on damp sand, and many of the crossed seeds 
germinated, as on the last occasion, before the self-fertilised, and 
were rejected. Three or four pairs in the same state of germina- 
tion were planted on the opposite sides of two pots ; a single 
pair in a third pot ; and all the remaining seeds were sown crowded 
in a fourth pot. When the seedlings were about one and a half 
inches in height, they were equal on both sides of the three first 
pots ; but in Pot IV., in which they grew crowded and were 
thus exposed to severe competition, the crossed were about a 
third taller than the self-fertilised. In this latter pot, when 
the crossed averaged 5 inches in height, the self-fertilised were 
about 4 inches; nor did they look nearly such fine plants. 
In all four pots the crossed plants flowered some days before 
the self-fertilised. When in full flower the tallest plant on each 
side was measured ; but before this time the single crossed 
plant in Pot in., which was taller than its antagonist, had died 
and was not measured. So that only the tallest plant on each 
side of three pots was measured, as in the following table : 



TABLE LXIX. 

Lobelia ramosa (Second Generation). 



No. of Pot. 


Tallest Crossed Plant 
in each Pot. 


Tallest Self-fertilised 
Plant in each Pot. 


i. 


Inches. 
27 1 


Inches. 
18| 


n. 


21 


19| 


IV. 

Crowded. 


21| 


19 


Total in inches. 


70 


57 



The average height of the three tallest crossed plants is here 
23-33, and that of the three tallest self-fertilised 19 inches ; or as 
100 to 81. Besides this difference in height, the crossed plants 
were much more vigorous and more branched than the self- 
fertilised plants, and it is unfortunate that they were not 
weighed. 



CHAP. V LOBELIA FULGENS. 179 



LOBELIA FULGENS. 

This species offers a somewhat perplexing case In the first 
generation the self-fertilised plants, though few in number, 
greatly exceeded the crossed in height ; whilst in the second 
generation, when the trial was made on a much larger scale, 
the crossed beat the self-fertilised plants. As this species 
is generally propagated by off-sets, some seedlings were first 
raised, in order to have distinct plants. On one of these plants 
several flowers were fertilised with their own pollen ; and as the 
pollen is mature and shed long before the stigma of the same 
flower is ready for fertilisation, it was necessary to number each 
flower and keep its pollen in paper with a corresponding number. 
By this means well-matured pollen was used for self-fertilisation. 
Several flowers on the same plant were crossed with pollen from 
a distinct individual, and to obtain this the conjoined anthers of 
young flowers were roughly squeezed, and as it is naturally 
protruded very slowly by the growth of the pistil, it is probable 
that the pollen used by me was hardly mature, certainly less 
mature than that employed for self-fertilisation. I did not at 
the time think of this source of error, but I now suspect that 
the growth of the crossed plants was thus injured. Anyhow the 
trial was not perfectly fair. Opposed to the belief that the 
pollen used in crossing was not in so good a state as that used 
for self-fertilisation, is the fact that a greater proportional number 
of the crossed than of the self-fertilised flowers produced cap- 
sules; but there was no marked difference in the amount of seed 
contained in the capsules of the two lots.* 

As the seeds obtained by the above two methods would not 
germinate when left on bare sand, they were sown on the 
opposite sides of four pots ; but I succeeded in raising only a 
single pair of seedlings of the same age in each pot. The self- 
fertilised seedlings, when only a few inches in height, were in 
most of the pots taller than their opponents ; and they flowered 
so much earlier in all the pots, that the height of the flower- 
stems could be fairly compared only in Pots I. and II. 



* Gartner has shown that cer- but none of the plants on which 

tain plants of Lobelia fulgens are I experimented, which were kept 

quite sterile with pollen from the in the greenhouse, were in this 

same plant, though this pollen is peculiar condition, 
efficient on any other individual ; 

H 2 



180 



LOBELIA FULGENS. 



TABLE LXX. 
Lobelia fulyens (First Generation}. 



No. of Pot. 


Height of Flower- 
stems on the Crossed 
Plauts. 


Height of Flower- 
stems on the Self-fer- 
tilised Plants. 


I. 


Inches. 
33 


Inches. 
50 


II. 


36| 


38| 


III. 


21 

Not in full flower. 


43 


IV. 


12 
Not in full flower. 


35 1 



The mean height of the flower-stems of the two crossed plants 
in Pots I. and EL is here 34 '75 inches, and that of the two self- 
fertilised plants in the same pots 44 -25 inches; or as 100 to 127. 
The self-fertilised plants in Pots III. and IV. were in every 
respect very much finer than the crossed plants. 

I was so much surprised at this great superiority of the self- 
fertilised over the crossed plants, that I determined to try how 
they would behave in one of the pots during a second growth. 
The two plants, therefore, in Pot I. were cut down, and repotted 
without being disturbed in a much larger pot. In the following 
year the self-fertilised plant showed even a greater superiority 
than before; for the two tallest flower-stems produced by the 
one crossed plant were only 29 J and 30|- inches in height, 
whereas the two tallest stems on the one self-fertilised plant 
were 49f and 49f inches ; and this gives a ratio of 100 to 167. 
Considering all the evidence, there can be no doubt that these 
self-fertilised plants had a great superiority over the crossed 
plants. 

Crossed and self-fertilised Plants of the Second Generation. I 
determined on this occasion to avoid the error of using pollen of 
not quite equal maturity for crossing and self-fertilisation ; so 
that I squeezed pollen out of the conjoined anthers of youug 
flowers for both operations. Several flowers on the crossed plant 
in Pot I. in Table LXX. were again crossed with pollen from a 
distinct plant. Several other flowers on the self-fertilised plant 



CHAP. V. 



LOBELIA FULGENS. 



181 



TABLE LXXL 
Lobelia fulgens (Second Generation). 



No. of Pot 


Crossed Plants. 
Height of Flower- 
stems. 


Self-fertilised Plants. 
Height of Flower- 
stems. 


I. 


Inches. 


Inche 
32 
26 
25 
26 


k 


II. 


34 
26 
25 

26 




36 
28 
30 
32 




III. 


40 1 
37 1 
32J 


30 
28 
23 




IV. 


34 
32 
29 
27 




29 
28 
26 
25 


! 


V. 


28 
27 
25 

24 


i 


29 
24 
23 

24 




VI. 


33 1 
32 
26 1 
25 


44 
37 
37 
35 




VII. 


30 i 
30 i 
29 1 


27 
21 


VIII. 


39 1 
37 
36 
36 


23 j 
23 
25 
25 




IX. 


33 1 
25 
25 
21 


I 






19 
16 
19 
Ii| 


. 


Total in inches. 1014- 


00 


921-63 



182 NEMOPHILA INSIGNIS. CHAP. V, 

in the same pot were again self-fertilised with pollen from the 
anthers of other flowers on the same plant. Therefore the degree 
of self-fertilisation was not quite so close as in the last genera- 
tion, in which pollen from the same flower, kept in paper, was 
used. These two lots of seeds were thinly sown on opposite 
sides of nine pots ; and the young seedlings were thinned, an 
equal number of nearly as possible the same age being left on 
the two sides. In the spring of the following year (1870), when 
the seedlings had grown to a considerable size, they were 
measured to the tips of their leaves ; and the twenty-three 
crossed plants averaged 14 04 inches in height, whilst the twenty- 
three self-fertilised seedlings were 13 '54 inches; or as 100 to 96. 

In the summer of the same year several of these plants 
flowered, the crossed and self-fertilised plants flowering almost 
simultaneously, and all the flower-stems were measured. Those 
produced by eleven of the crossed plants averaged 30 71 inches, 
and those by nine of the self-fertilised plants 29 '43 inches in 
height; or as 100 to 96. 

The plants in these nine pots, after they had flowered, were 
repotted without being disturbed in much larger pots ; and in 
the following year, 1871, all flowered freely; but they had 
grown into such an entangled mass, that the separate plants 
on each side could no longer be distinguished. Accordingly 
three or four of the tallest flower-stems on each side of each 
pot were measured; and the measurements in the preceding 
table are, I think, more trustworthy than the previous ones, 
from being more numerous, and from the plants being well 
established and growing vigorously. 

The average height of the thirty-four tallest flower-stems on 
the twenty-three crossed plants is 29 '82 inches, and that of the 
same number of flower-stems on the same number of self- 
fertilised plants is 27-10 inches; or as 100 to 91. So that the 
crossed plants now showed a decided advantage over their self- 
fertilised opponents. 



XXII. POLEMONIACE^. NEMOPHILA INSIGNIS. 

Twelve flowers were crossed with pollen from a distinct plant, 
but produced only six capsules, containing on an average 18 3 
seeds. Eighteen flowers were fertilised with their own pollen 
and produced ten capsules, containing on an average 12- 7 



CHAT.V. 



NEMOPHILA INSIGNIS. 



183 



seeds ; so that the seeds per capsule were as 100 to 69.* The 
crossed sueds weighed a little less than an equal number of self- 
fertilised seeds, in the proportion of 100 to 105 ; but this was 
clearl v due to some of the self-fertilised capsules containing very 
few seeds, and these were much bulkier than the others, from 
having been better nourished. A subsequent comparison of the 
number of seeds in a few capsules did not show so great a 
superiority on the side of the crossed capsules as in the present 
case. 

The seeds were placed on sand, and after germinating were 
planted in pairs on the opposite sides of five pots, which were 
kept in the greenhouse. When the seedlings were from 2 to 
3 inches in height, most of the crossed had a slight advantage 
over the self-fertilised. The plants were trained up sticks, and 
thus grew to a considerable height. In four out of the five 
pots a crossed plant flowered before any one of the self-fertilised. 

TABLE LXXII. 

Nemophila insignis ; means that the plant died. 



No. of -Pot. 


Crossed Plants. 


Self-fertilised Plants. 


I. 


Inches. 
32| 


Inches. 
21 


II. 


8*1 


23| 


III. 


331 
22 
29 


19 

.?! 


IV. 


35 j 
33j 


W 


V. 


35 
38 
36 
37 1 
32J 


o 

18 

> 




Total in inches. 


399-38 


199-00 



* Several species of Polemo 
niaci-te are known to be proter- 
androus, but I did not attend to 
thw point in Nemophila. Verlot 



says Des Varies,' 1865, p. 66) 
that varieties growing near one 
another spontaneously intercross. 



184 



NEMOPHILA INSIGNIS. 



CHAP. V 



The plants were first measured to the tips of their leaves, before 
they had flowered and when the crossed were under a foot 
in height. The twelve crossed plants averaged 11 '1 inches in 
height, whilst the twelve self-fertilised were less than half of this 
height, viz., 5 45 ; or as 100 to 49. Before the plants had grown 
to their full height, two of the self-fertilised died, and as I feared 
that this might happen with others, they were again measured 
to the tops of their stems, as shown in the preceding table. 

The twelve crossed plants now averaged 33' 28, and the ten self- 
fertilised 19-9 inches in height, or as 100 to 60; so that they 
differed somewhat less than before. 

The plants in Pots III. and V. were placed under a net in the 
greenhouse, two of the crossed plants in the latter pot being 
pulled up on account of the death of two of the self-fertilised ; 
so that altogether six crossed and six self-fertilised plants were 
left to fertilise themselves spontaneously. The pots were rather 
small, and the plants did not produce many capsules. The 
small size of the self-fertilised plants will largely account foi 
the fewness of the capsules which they produced. The six crossed 
plants bore 105, and the six self-fertilised only 30 capsules ; or as 
100 to '29. 

The self-fertilised seeds thus obtained from the crossed and 
self-fertilised plants, after germinating on sand, were planted 

TABLE LXXHI. 

Nemophila insignis. 



No. of Pot. 


Self-fertilised Plants 
from Crossed Plants. 


Self-fertilised Plants 
from Self-fertilised 
Plants. 


I. 


Inches. 
27 
14 


Inches. 
27 1 
34| 


IL 


17| 

24| 


23 
32 


III. 


16 


7 


IV. 


l\ 


i! 1 


Total in inches. 


110-13 


147-00 



CHAP. V. BORAGO OFFICINALIS. 185 

on the opposite sides of four small pots, and treated as before. 
But many of the plants were unhealthy, and their heights were so 
unequal some on both sides being five times as tall as the others 
that the averages deduced from the measurements in the pre- 
ceding table are not in the least trustworthy. Nevertheless I 
have felt bound to give them, as they are opposed to my general 
conclusions. 

The seven self-fertilised plants from the crossed plants here 
average 15 '73, and the seven self-fertilised from the self-fertilised 
21 inches in height ; or as 100 to 133. Strictly analogous ex- 
periments with Viola tricolor and Lathyrus odoratus gave a very 
different result. 



XXIII. BOEAGINACE^:. BOEAGO OFFICINALIS. 

This plant is frequented by a greater number of bees than 
almost any other one which I have observed. It is strongly 
proterandrous (H. Muller, ' Befruchtung,' &c., p. 267), and the 
flowers can hardly fail to be cross-fertilised ; but should this 
not occur, they are capable of self-fertilisation to a limited 
extent, as some pollen long remains within the anthers, and is 
apt to fall on the mature stigma. In the year 1863 I covered 
up a plant, and examined thirty-five flowers, of which only 
twelve yielded any seeds ; whereas of thirty-five flowers on an 
exposed plant growing close by, all with the exception of two 
yielded seeds. The covered-up plant, however, produced alto- 
gether twenty-five spontaneously self-fertilised seeds ; the exposed 
plant producing fifty-five seeds, the product, no doubt, of cross- 
fertilisation. 

In the year 1868 eighteen flowers on a protected plant were 
crossed ^ith pollen from a distinct plant, but only seven of these 
produced fruit ; and I suspect that I applied pollen to many of 
the stigmas before they were mature. These fruits contained 
on an average 2 seeds, with a maximum in one of three seeds. 
Twenty-four spontaneously self-fertilised fruits were produced 
by the same plant, and these contained on an average 1*2 seeds, 
with a maximum of two in one fruit. So that the fruits from 
the artificially crossed flowers yielded seeds compared with those 
from the spontaneously self-fertilised flowers, in the ratio of 100 
to 60. But the self-fertilised seeds, as often occurs when few 
are produced, were heavier than the cr / >ssed seeds in ihe ratio oi 
100 to 90 



186 



NOLANA PKOSTEATA. 



CHAP. V. 



These two lots of seeds were sown on opposite sides of two 
large pots ; but I succeeded in raising only four, pairs of equal 
age. When the seedlings on both sides were about 8 inches 
in height they were equal. When in full flower they were 
measured, as follows : 

TABLE LXXIV. 

Us. 



No. of Pot. 


Crossed Plants. 


Self-fertilised Plants. 


I. 


Inches. 
19 
21 
l 


Inches. 

181 

18| 

20 1 


II. 


26 


321 


Total in inches. 


82-75 


84-75 



The average height of the four crossed plants is here 20 68, and 
that of the four self-fertilised 21 '18 inches; or as 100 to 102. 
The self-fertilised plants thus exceeded the crossed in height by 
a little ; but this was entirely due to the tallness of one of the 
self-fertilised. The crossed plants in both pots flowered before 
the self-fertilised. Therefore I believe if more plants had been 
raised, the result would have been different. I regret that I did 
not attend to the fertility of the two lots. 



XXIV. NOLANACE2E. NOLANA PKOSTBATA. 

In some of the flowers the stamens are considerably shorter 
than the pistil, in others equal to it in length. I suspected, 
therefore, but erroneously as it proved, that this plant was 
dimorphic, like Primula, Linum, &c., and in the year 1862 twelve 
plants, covered by a net in the greenhouse, were subjected to 
trial. The spontaneously self-fertilised flowers yielded 64 grains 
weight of seeds, but the product of fourteen artificially crossed 
flowers is here included, which falsely increases the weight of 
the self-fertilised seeds. Nine uncovered plants, the flowers of 
which were eagerly visited by bees for their pollen and were no 
doubt intercrossed by them, produced 79 grains weight of seeds: 
therefore twelve plants thus treated would have yielded 105 



CHAP. V. 



NOLANA PROSTRATA 



187 



grains. Thus the seeds produced by the flowers on an equal 
number of plants, when crossed by bees, and spontaneously self- 
fertilised (the product of fourteen artificially crossed flowers 
being, however, included in the latter) were in weight as 
100 to 61. 

In the summer of 1867 the trial was repeated ; thirty flowers 
were crossed with pollen from a distinct plant and produced 
twenty-seven capsules, each containing five seeds. Thirty-two 
flowers were fertilised with their own pollen, and produced only 
six capsules, each with five seeds. So that the crossed and self- 
fertilised capsules contained the same number of seeds, though 
many more capsules were produced by the cross-fertilised than 
by the self-fertilised flowers, in the ratio of 100 to 21. 

An equal number of seeds of both lots were weighed, and the 
crossed seeds were to the self-fertilised in weight as 100 to 82. 
Therefore a cross increases the number of capsules produced and 
the weight of the seeds, but not the number of seeds in each 
capsule. 

These two lots of seeds, after germinating on sand, were 
planted on the opposite sides of three pots. The seedlings 
when from 6 to 7 inches in height were equal. The plants 
were measured when fully grown, but their heights were so 
unequal in the several pots, that the result cannot be folly 
trusted. 

TABLE LXXV. 
Nolana prostrata. 



No. of Pot. 


Crossed Plants. 


Self-fertilised Plants. 


I. 


Inches. 

8 


Inches. 

5 


II. 


8* 


W 


III. 


20 


22| 


Total in inches. 


63-75 


67-00 



The five crossed plants average 12 '75, and the five self- 
fertilised 13-1 inches in height; or as 100 to 105. 



188 PETUNIA VIOLACEA. CHAP. VI. 



CHAPTEE VI. 

SOLANACE-iE, PRIMULACKS, PoLYGONE^, ETC. 

Petunia violacea, crossed and self-fertilised plants compared for four 
generations Effects of a cross with a fresh stock Uniform colour 
of the flowers on the self-fertilised plants of the fourth generation 
Nicotiana tabacum, crossed and self-fertilised plants of equal 
height Great effects of a cross with a distinct sub-variety on the 
height, but not on the fertility, of the offspring Cyclamen per- 
sicum, crossed seedlings greatly superior to the self-fertilised 
Anagallis collina Primula veris Equal-styled variety of Primula 
veris, fertility of, greatly increased by a cross with a fresh stock 
Fagopyrum esculentum Beta vulgaris Canna warscewiczi, crossed 
and self-fertilised plants of equal height Zea mays Phalaris 
canariensis. 

XXV. SOLANACE^E. PETUNIA VIOLACEA. 

Dingy purple variety. 

THE flowers of this plant are so seldom visited during the day 
by insects in this country, that I have never seen an instance ; 
but my gardener, on whom I can rely, once saw some humble- 
bees at work. Mr. Meehan says,* that in the United States 
bees bore through the corolla for the nectar, and adds that their 
" fertilisation is carried on by night-moths." 

In France M. Naudin, after castrating a large number of flowers 
whilst in bud, left them exposed to the visits of insects, and 
about a quarter produced capsules ;t but I am convinced that 
a much larger proportion of flowers in my garden are cross- 
fertilised by insects, for protected flowers which had their 
own pollen placed on the stigmas never yielded nearly a full 
complement of seed ; whilst those left uncovered produced fine 
capsules, showing that pollen from other plants must have been 
brought to them, probably by moths. Plants growing vigorously 
and flowering in pots in the green-house, never yielded a single 



* 'Proc. Acad.Nat. Sc. of Phil- in Germany. So it is, as I hear 

adelphia,' Aug. 2nd. 1870, p. 90. from Mr. Boulger, with moths in 

Prof. Hildebrand also informs me England. 

that moths, especially Sphinx con- t ' Annales des Sc. Nat.' 4th 

volvuli, largely haunt the flowers series, Bot. torn. ix. cha. 5. 



CHAP. VI. CROSSED AND SELF-FERTILISED PLANTS. 189 



capsvue ; and this may be attributed, at least in chief part, to 
the exclusion of moths. 

Six flowers on a plant covered by a net were crossed with 
pollen from a distinct plant and produced six capsules, containing 
by weight 4*44 grains of seed. Six other flowers were fertilised 
with their own pollen and produced only three capsules, con- 
taining only 1*49 grain weight of seed. From this it follows 
that an equal number of crossed and self-fertilised capsules would 
have contained seeds by weight as 100 to 67. I should not have 
thought the proportional contents of so few capsules worth 
giving, had not nearly the same result been confirmed by several 
subsequent trials. 

Seeds of the two lots were placed on sand, and many of the 
self-fertilised seeds germinated before the crossed, and were 
rejected. Several pairs in an equal state of germination were 
planted on the opposite sides of Pots I. and II. ; but only the 
tallest plant on each side was measured. Seeds were also sown 
thickly on the two sides of a large pot (III.), the seedlings being 
afterwards thinned, so that an equal number was left on each 
side; the three tallest on each side being measured. The pots 
were kept in the greenhouse, and the plants were trained up 
sticks. For some time the young crossed plants had no ad- 
vantage in height over the self-fertilised ; but their leaves 
were larger. When fully grown and in flower the plants were 
measured, as follows : 

TABLE LXXVI. 

Petunia violacea (First Generation). 



No. of Pot. 


Crossed Plants. 


Self-fertilised Plants. 


i. 


Inches. 
30 


Inches. 
20* 


II. 


*l 


27| 


in. 


34 281 

30j 271 
25 26 


Total in inches. 


154 ' 130 



The five tallest crossed plants here average 30 '8, and the five 
tallest self-fertilised 26 inches in height, or as 100 to 84. 



190 



PETUNIA VIOLACEA. 



CHAP. VI. 



Three capsules were obtained by crossing flowers on the 
above crossed plants, and three other capsules by again self- 
fertilising flowers on the self-fertilised plants. One of the latter 
capsules appeared as fine as any one of the crossed capsules ; 
but the other two contained many imperfect seeds. From these 
two lots of seeds the plants of the following generation were 
raised. 

Crossed and self -fertilised Plants of the Second Generation. As in 
the last generation, many of the self-fertilised seeds germinated 
before the crossed. 

Seeds in an equal state of germination were planted on the 
opposite sides of three pots. The crossed seedlings soon greatly 
exceeded in height the self-fertilised. In Pot I., when the tallest 
crossed plant was 10i inches high, the tallest self-fertilised was 
only 82 inches ; in Pot II. the excess in height of the crossed was 
not quite so great. The plants were treated as in the last gene- 
ration, and when fully grown measured as before. In Pot III. 
both the crossed plants were killed at an early age by some 
animal, so that the self-fertilised had no competitors. Neverthe- 
less these two self-fertilised plants were measured, and are in- 
cluded in the following table. The crossed plants flowered long 
before their self-fertilised opponents in Pots I. and II., and before 
those growing separately in Pot III. 

TABLE LXXVII. 
Petunia violacea (Second Generation). 



No. of Pot. 


Crossed Plants. 


Self-fertilised Plants. 


L 


Inches. 
57 
361 


Inches. 

I 1 


11. 


44| 
24 


II 1 


III. 






46 
28< 


Total in inches. 


162-0 


157-5 



The four crossed plants average 40 '5, and the six self-fer- 
tilised 26-25 inches in height ; or as 100 to 65. But this great 
inequality is in part accidental, owing to some of the self- 



CHAP. VI. CROSSED AND SELF-FERTILISED PLANTS. 191 



fertilised plants being very short, and to one of the crossed being 
very tall. 

Twelve flowers on these crossed plants were again crossed, and 
eleven capsules were produced ; of these, five were poor and six 
good; the latter contained by weight 3 '75 grains of seeds. 
Twelve flowers on the self-fertilised plants were again fertilised 
with their own pollen and produced no less than twelve capsules, 
and the six finest of these contained by weight 2 '57 grains of 
seeds. It should however be observed that these latter capsules 
were produced by the plants in Pot HE., which were not exposed 
to any competition. The seeds in the six fine crossed capsules 
to those in the six finest self-fertilised capsules were in weight 
as 100 to 68. From these seeds the plants of the next generation 
were raised. 

Crossed and self-fertilised Plants of the Tfiird Generation. The 
above seeds were placed on sand, and after germinating were 
planted in pairs on the opposite sides of four pots ; and all the 
remaining seeds were thickly sown on the two sides of a fifth large 
pot. The result was surprising, for the self-fertilised seedlings 
very early in life beat the crossed, and at one time were nearly 
double their height. At first the case appeared like that of 
Mimulus, in which after the third generation a tall and highly 
self-fertile variety appeared. But as in the two succeeding 
generations the crossed plants resumed their former superiority 
over the self-fertilised, the case must be looked at as an anomaly. 
The sole conjecture which I can form is that the self-fertilised 

TABLE LXXYIII. 
Petunia violacea (Third Generation; plants very young). 



No. of Pot. 


Crossed Plants. 


Self-fertilised Plants. 


I. 


Inches. 

M 


Inches. 

51 

4 1 


II. 


51 

s| 


*i 

6? 


III. 


4 


M 


IV. 


M 


58 


Total in inches. 


19-63 36-50 



192 



PETUNIA VIOLACEA. 



CHAJ VI. 



seeds had not been sufficiently ripened, and thus produced 
weakly plants, which grew at first at an abnormally quick rate, 
as occurred with seedlings from not well-ripened self-fertilised 
seeds of Iberis. When the crossed plants were between 3 and 4 
inches in height, the six finest in four of the pots were measured 
to the summits of their stems, and at the same time the six 
finest of the self-fertilised plants. The measurements are given 
in the preceding table (LXXVHI), and it may be here seen that 
all the self-fertilised plants exceed their opponents in height, 
whereas when subsequently measured the excess of the self- 
fertilised depended chiefly on the unusual tallness of two of the 
plants in Pot II. The crossed plants here average 3 '27, and 
the self-fertilised 6 '08 inches in height; or as 100 to 186. 
When fully grown they were again measured, as follows : 

TABLE LXXIX. 

Petunia violacea (Third Generation ; plants fully grown). 



No. of Pot. 


Crossed Plants. 


Self-fertilised Plants. 


It 


Inches. 

1 
48 
36 


Inches. 
40 
39 
48 


II. 


36 
21 
36 


47 
80? 
86 


in. 


52 


46 


IV. 


57 


43| 


Total in inches. 


327-75 


431-00 



The eight crossed plants now averaged 40 96, and the eight self- 
fertilised plants 53 87 inches in height, or as 100 to 131 ; and this 
excess chiefly depended, as already stated, on the unusual tallness 
of two of the self-fertilised plants in Pot H. The self-fertilised 
had therefore lost some of their former great superiority over the 
crossed plants. In three of the pots the self-fertilised plants 
flowered first ; but in Pot III. at the same time with the crossed. 

The case is rendered the more strange, because the crossed 
plants in the fifth pot (not included in the two last tables), ir 



CHAP. VL CROSSED AND SELF-FERTILISED PLANTS. 193 

which all the remaining seeds had been thickly sown, were from 
the first finer plants than the self-fertilised, and had larger 
leaves. At the period when the two tallest crossed plants in 
this pot were 6| and 4| inches high, the two tallest self-fertilised 
were only 4 inches. When the two crossed plants were 12 and 
10 inches high, the two self-fertilised were only 8 inches. These 
latter plants, as well as many others on the same side of this pot, 
never grew any higher, whereas several of the crossed plants 
grew to the height of two feet! On account of this great 
superiority of the crossed plants, the plants on neither side of 
this pot have been included in the two last tables. 

Thirty flowers on the crossed plants in Pots I. and IV. (Table 
LXXIX.) were again crossed, and produced seventeen capsules. 
Thirty flowers on the self-fertilised plants in the same two pots 
were again self-fertilised, but produced only seven capsules. 
The contents of each capsule of both lots were placed in separate 
watch-glasses, and the seeds from the crossed appeared to the 
eye to be at least double the number of those from the self- 



In order to ascertain whether the fertility of the self-fertilised 
plants had been lessened by the plants having been self-ferti- 
lised for the three previous generations, thirty flowers on the 
crossed plants were fertilised with their own pollen. These 
yielded only five capsules, and their seeds being placed in 
separate watch-glasses did not seem more numerous than those 
from the capsules on the self-fertilised plants self-fertilised for 
the fourth time. So that as far as can be judged from so few 
capsules, the self-fertility of the self-fertilised plants had not 
decreased in comparison with that of the plants which had 
been intercrossed during the three previous generations. It 
should, however, be remembered that both lots of plants 
had been subjected in each generation to almost exactly similar 
conditions. 

Seeds from the crossed plants again crossed, and from the self- 
fertilised again self-fertilised, produced by the plants in Pot I. 
(Table LXXIX.), in which the three self-fertilised plants were 
on an average only a little taller than the crossed, were used in 
the following experiment. They were kept separate from two 
similar lots of seeds produced by the two plants in Pot IV. in 
the same table, in which the crossed plant was much taller than 
its self-fertilised opponent. 

Crossed and self-fertilised Plants of the Fourth Generation 



194 



PETUNIA VIOLACEA. 



CHAP. VL 



(raised from the Plants in Pot I., Table LXXIX.). Crossed and 
self-fertilised seeds from plants of the last generation in Pot I., 
in Table LXXIX., were placed on sand, and after germinating, 
were planted in pairs on the opposite sides of four pots. The 
seedlings when in full flower were measured to the base of the 
calyx. The remaining seeds were sown crowded on the two 
sides of Pot V. ; and the four tallest plants on each side of this 
pot were measured in the same manner. 

TABLE LXXX. 

Petunia violacea (Fourth Generation; raised from Plants of the 
Third Generation in Pot /., Table LXXIX.). 



No. of Pot. 


Crossed Plants. 


Self-fertilised Plants. 




Inches. 


Inches. 


I. 


29 g 


30 i 




36 


34 f 




49 


31f 


II. 


33 1 


31 1 




37 i 


38 f 




M] 


38 1 


HI. 


46 
671 


$ 




54 


23 


IV. 


Ml 


34 




511 





V. 


49 1 


22 i 


Crowded nlants. 


46 1 


24 




40 


24 




53 


30 


Total in inches. 


701-88 


453-50 



The fifteen crossed plants average 46 '79, and the fourteen 
(one having died) self-fertilised plants 32 '39 inches in height; or 
as 100 to 69. So that the crossed plants in this generation had 
recovered their wonted superiority over the self-fertilised plants ; 
though the parents of the latter in Pot I., Tatle LXXIX., were a 
little taller than their crossed opponents. 

Grossed and self-fertilised Plants of the Fourth Generation 



CIIAV VI. CROSSED AND SELF-FERTILISED PLANTS. 195 



(raised from the Plants in Pot IV., in Table L XXIX.). Two 
similar lots of seeds, obtained from the plants in Pot IV. in 
Table LXXIX., in -which the single crossed plant was at 
first shorter, but ultimately much taller than its self-fertilised 
opponent, were treated in every way like their brethren of the 
same generation in the last experiment We have in the follow- 
ing Table LXXXI. the measurements of the present plants. 
Although the crossed plants greatly exceeded in height the self- 
fertilised ; yet in three out of the five pots a self-fertilised plant 
flowered before any one of the crossed ; in a fourth pot simul- 
taneously ; and in a fifth (viz., Pot II.) a crossed plant flowered 
first. 

TABLE LXXXI. 

Petunia violacea (Fourth Generation ; raised from Plants of the 
Third Generation in Pot IV., Table LXXIX.). 



No. of Pot 


Crossed Plants. 


Self-fertilised Plants. 


I. 


Inches. 
46 
46 


Inches. 
30 
28 


II. 


50 1 
40 
37J 


25 
811 

22j 


III. 


541 

% 


22 1 
26 
32 


IV. 


30 
29J 


28 j 
26 


V. 

Crowded plants. 


37 j 
63 
41 


40 1 
1ft] 

17 j 


Total in inches. 


581-63 


349-38 



The thirteen crossed plants here average 44 '74, and the 
thirteen self-fertilised plants 26 '87 inches in height; or as 100 
to 60. The crossed parents of these plants were much taller, 
relatively to the self-fertilised parents, than in the last case ; and 
apparently they transmitted some of this superiority to theii 

o 2 



196 PETUNIA VIOL ACE A. CHAP. VI. 

crossed offspring. It is unfortunate that I did not turn these 
plants out of doors, so as to observe their relative fertility, for I 
compared the pollen from some of the crossed and self-fertilised 
plants in Pot I, Table LXXXI., and there was a marked dif- 
ference in its state ; that of the crossed plants contained hardly 
any bad and empty grains, whilst such abounded in the pollen 
of the self-fertilised plants. 

The Effects of a Gross with a fresh Stock. I procured from a 
garden in Westerham, whence my plants originally came, a 
fresh plant differing in no respect from mine except in the 
colour of the flowers, which was a fine purple. But this plant 
must have been exposed during at least four generations to very 
different conditions from those to which my plants had been 
subjected, as these had been grown in pots in the green- 
house. Eight flowers on the self-fertilised plants in Table 
LXXXI., of the last or fourth self-fertilised generation, were 
fertilised with pollen from this fresh stock ; all eight produced 
capsules containing together by weight 5 '01 grains of seeds. 
The plants raised from these seeds may be called the Westerham- 
crossed. 

Eight flowers on the crossed plants of the last or fourth genera- 
tion in Table LXXXI. were again crossed with pollen from one 
of the other crossed plants, and produced five capsules, contain- 
ing by weight 2 '07 grains of seeds. The plants raised from 
these seeds may be called the intercrossed ; and these form the 
fifth intercrossed generation. 

Eight flowers on the self-fertilised plants of the same genera- 
tion in Table LXXXI. were again self-fertilised, and produced 
seven capsules, containing by weight 2'1 grains of seeds. The 
self-fertilised plants raised from these seeds form the fifth self- 
fertilised generation. These latter plants and the intercrossed 
are comparable in all respects with the crossed and self-fertilised 
plants of the four previous generations. 

From the foregoing data it is easy to calculate that, 

Or. Weight 

of Seed. 

Ten Westerham-crossed capsules would have contained 6 '26 
Ten intercrossed capsules would have contained . . 4 ' 14 
Ten self-fertilised capsules would have contained 3 '00 

We thus get the following ratios : 



CHAP. VI. CROSS WITH A FRESH STOCK. 197 

Seeds from the Westerham-crossecl capsules to 
those from the capsules of the fifth self-fer- 
tilised generation, in weight . . .as 100 to 48 

Seeds from the Westerham-erossed capsules to 
those from the capsules of the fifth intercrossed 
generation as 100 to 66 

Seeds from the intercrossed to those from the 
self-fertilised capsules . . . . as 100 to 72 

So that a cross with pollen from a fresh stock greatly increased 
the productiveness of the flowers on plants which had been self- 
fertilised for the four previous generations, in comparison not 
only with the flowers on the same plants self-fertilised for the fifth 
time, but with the flowers on the crossed plants crossed with 
pollen from another plant of the same old stock for the fifth 
time. 

These three lots of seeds were placed on sand, and were 
planted in an equal state of germination in seven pots, each made 
tripartite by three superficial partitions. Some of the remaining 
seeds, whether or not in a state of germination, were thickly 
sown in an eighth pot. The pots were kept in the greenhouse, 
and the plants trained up sticks. They were first measured to 
the tops of their stems when coming into flower ; and the twenty- 
two Westerham-erossed plants then averaged 25 51 inches ; the 
twenty-three intercrossed plants 30 '38; and the twenty-three 
self-fertilised plants 23 '40 inches in height. We thus get the 
following ratios : 

The Westerham-erossed plants in height to the 
self-fertilised as 100 to 91 

The Westerham-erossed plants in height to the 
intercrossed as 100 to 119 

The intercrossed plants in height to the self- 
fertilised . . . . . . . as 100 to 77 

These plants were again measured when their growth appeared 
on a casual inspection to be complete. But in this I was mis- 
taken, for after cutting them down, I found that the summits 
of the stems of the Westerham-erossed plants were still growing 
vigorously; whilst the intercrossed had almost, and the self- 
fertilised had quite completed their growth. Therefore I do 
not doubt, if the three lots had been left to grow for another 
month, that the ratios would have been somewhat different 



198 



PETUNIA VIOLACEA. 



CHAP. VI. 



from those deduced from the measurements in the following 
table : 

TABLE LXXXH. 

Petunia vioiacea. 



No. of Pot. 


Westerham-crossed 
Plants (from Self- 
fertilised Plants of 
Fourth Generation 
crossed by a fresh 
Stock). 


Intercrossed Plants 
(Plants of one and Self-fertilised Plants 
the same Stock (self-fertilised for 
intercrossed for Five Generations). 
Five Generations). 


I. 


Inches. 
64 1 
24 
51 1 


Inches. 

IV 

581 


Inches. 
43 f 
56 1 
31 1 


II. 


48 1 
54 
58| 


591 
58 
53 


41 1 
41 i 

181 


III. 


62 
53 1 
621 


521 
54 1 
61jj 


$ 

19| 


IV. 


44| 
491 


58 J 
651 
59 1 


37 1 
331 


V. 


43 J 
53 Z 
53| 


35 1 
34 f 
54 


41 1 

2 et 


VI. 


37 1 

61 



56 
63 1 
571 


46 1 
29 i 
*\ 


VII. 


59 1 
43 1 
50| 


51 
49 f 



43 
12| 



VIII. 
Crowded. 


37 J 
371 


38 1 
44| 


21| 
1*1 


Total in inches. 


1051-25 


1190-50 


697-88 



The twenty-one Westerham-crossed plants now averaged 50 '05 
inches; the twenty-two intercrossed plants, 54 -11 inches; and 
the twenty-one self-fertilised plants, 33-23 inches in height. We 
thus get the following ratios: 



CUAF. VI. CROSS WITH A FRESH STOCK. 199 

The Westerham-crossed plants in height to the 
self-fertilised as 100 to 66 

The Westerham-crossed plants in height to the 
intercrossed as 100 to 108 

The intercrossed plants in height to the self- 
fertilised as 100 to 61 

We here see that the Westerham-crossed (the offspring of 
plants self-fertilised for four generations and then crossed with a 
fresh stock) have gained greatly in height, since they were first 
measured, relatively to the plants self-fertilised for five genera- 
tions. They were then as 100 to 91, and now as 100 to 66 in 
height. The intercrossed plants (i.e., those which had been in- 
tercrossed for the last five generations) likewise exceed in 
height the self-fertilised plants, as occurred in all the previous 
generations with the exception of the abnormal plants of the 
third generation. On the other hand, the Westerham-crossed 
plants are exceeded in height by the intercrossed ; and this is a 
surprising fact, judging from most of the other strictly analogous 
cases. But as the Westerham-crossed plants were still growing 
vigorously, while the intercrossed had almost ceased to grow, 
there can hardly be a doubt that if left to grow for another 
month they would have beaten the intercrossed in height. That 
they were gaining on them is clear, as when measured before they 
were as 100 to 119, and now as only 100 to 108 in height. The 
Westerham-crossed plants had also leaves of a darker green, and 
looked altogether more vigorous than the intercrossed ; and what 
is much more important, they produced, as we shall presently 
see, much heavier seed-capsules. So that in fact the offspring 
from the self-fertilised plants of the fourth generation crossed by 
a fresh stock were superior to the intercrossed, as well as to the 
self-fertilised plants of the fifth generation of which latter fact 
there could not be the least doubt. 

These three lots of plants were cut down close to the ground 
and weighed. The twenty-one Westerham-crossed plants weighed 
32 ounces ; the twenty-two intercrossed plants, 34 ounces, and the 
twenty-one self-fertilised plants 7i ounces. The following ratios 
are calculated for an equal number of plants of each kind. But 
as the self-fertilised plants were just beginning to wither, their 
relative weight is here slightly too small ; and as the Westerham- 
crossed were still growing vigorously, their relative weight 
with time allowed would no doubt have greatly increased. 



200 PETUNIA VIOLACEA. CHAT. VI, 

The Westerham-crossed plants in weight to 
the self-fertilised as 100 to 22 

The Westerham-crossed plants in weight to 
the intercrossed as 100 to 101 

The intercrossed plants in weight to the self- 
fertilised as 100 to 22-3 

We here see, judging by weight instead of as before by height, 
that the Westerham-crossed and the intercrossed have an 
immense advantage over the self-fertilised. The Westerham- 
crossed are inferior to the intercrossed by a mere trifle ; but it is 
almost certain that if they had been allowed to go on growing for 
another month, the former would have completely beaten the 
latter. 

As I had an abundance of seeds of the same three lots, from 
which the foregoing plants had been raised, these were sown in 
three long parallel and adjoining rows in the open ground, so as to 
ascertain whether under these circumstances the results would be 
nearly the same as before. Late in the autumn (Nov. 13) the ten 
tallest plants were carefully selected out of each row, and theii 
heights measured, with the following result : 



TABLE LXXXHL 

Petunia violacea (plants growing in the open ground). 



Westerham-crossed 
Plants (from Self- 
fertilised Plants of the 
Fourth Generation 
crossed by a fresh 
Stock). 


Intercrossed Plants 
(Plants of one and the 
same Stock inter- 
crossed for Five 
Generations). 


Self-fertilised Plants 
(Self-fertilised for 
Five Generations). 


Inches. 


Inches. 


Inches. 


34| 




38 


27 


36 1 




36 


23 


35 1 




39 jj 


25 


32 j 


37 


24 


37 




36 


22 


36^ 




41 1 


23 


40 1 




37 


21 


37 j 




40 


23 


38 1 




41 


213 


38 1 




36 


21 


366- 


75 


382-75 


233-13 



CHAP. VI. CROSS WITH A FRESH STOCK. 201 

The ten Westerham-crossed plants here average 36 '67 inches 
in height ; the ten intercrossed plants, 38 '27 inches ; and the ten 
self-fertilised, 23 -31 inches. These three lots of plants were also 
weighed ; the Westerham-crossed plants weighed 28 ounces ; the 
intercrossed, 41 ounces; and the self-fertilised, 14 '75 ounces. 
We thus get the following ratios : 

The Westerham-crossed plants in height to the 
self-fertilised as 100 to 63 

The Westerham-crossed plants in weight to the 
self-fertilised as 100 to 53 

The Westerham-crossed plants in height to the 
intercrossed as 100 to 104 

The Westerham-crossed plants in weight to the 
intercrossed as 100 to 146 

The intercrossed plants in height to the self- 
fertilised as 100 to 61 

The intercrossed plants in weight to the self- 
fertilised . . . . . . . as 100 to 36 

Here the relative heights of the three lots are nearly the same 
(within three or four per cent.) as with the plants in the pots. 
In weight there is a much greater difference : the Westerham- 
crossed exceed the self-fertilised by much less than they did 
before; but the self-fertilised plants in the pots had become 
slightly withered, as before stated, and were in consequence 
unfairly light. The Westerham-crossed plants are here inferior 
in weight to the intercrossed plants in a much higher degree 
than in the pots ; and this appeared due to their being much 
less branched, owing to their having germinated in greater 
numbers and consequently being much crowded. Their leaves 
were of a brighter green than those of the intercrossed and 
self -fertilised plants. 

Relative Fertility of the Three Lots of Plants. None of the plants 
in pots in the greenhouse ever produced a capsule ; and this may 
be attributed in chief part to the exclusion of moths. There- 
fore the fertility of the three lots could be judged of only by that 
of the plants growing out of doors, which from being left 
uncovered were probably cross-fertilised. The plants in the 
three rows were exactly of the same age and had been subjected 
to closely similar conditions, so that any difference in their fer- 
tility must be attributed to their different origin ; namely, to the 



202 PETUNIA VIOLACEA. CHAP. VI. 

one lot being derived from plants self-fertilised for four genera- 
tions and then crossed with a fresh stock ; to the second lot being 
derived from plants of the same old stock intercrossed for five 
generations ; and to the third lot being derived from plants self- 
fertilised for five generations. All the capsules, some nearly 
mature and some only half-grown, were gathered, counted, and 
weighed from the ten finest plants in each of the three rows, of 
which the measurements and weights have already been given. 
The intercrossed plants, as we have seen, were taller and con- 
siderably heavier than the plants of the other two lots, and they 
produced a greater number of capsules than did even the 
Westerham-crossed plants ; and this may be attributed to the 
latter having grown more crowded and being in consequence less 
branched. Therefore the average weight of an equal number of 
capsules from each lot of plants seems to be the fairest standard 
of comparison, as their weights will have been determined chiefly 
by the number of the included seeds. As the intercrossed plants 
were taller and heavier than the plants of the other two lots, it 
might have been expected that they would have producedthe finest 
or heaviest capsules ; but this was very far from being the case. 

The ten tallest Westerham-crossed plants produced 111 ripe 
and unripe capsules, weighing 121 2 grains. Therefore 100 of 
such capsules would have weighed 109 '18 grains. 

The ten tallest intercrossed plants produced 129 capsules, 
weighing 76 45 grains. Therefore 100 of these capsules would 
have weighed 59 '26 grains. 

The ten tallest self-fertilised plants produced only 44 capsules, 
weighing 22 '35 grains. Therefore 100 of these capsules would 
have weighed 50 '79 grains. 

From these data we get the following ratios for the fertility of 
the three lots, as deduced from the relative weights of an equal 
number of capsules from the finest plants in each lot : 

Westerham-crossed plants to self-fertilised 

plants as 100 to 46 

Westerham-crossed plants to intercrossed plants as 100 to 54 

Intercrossed plants to self-fertilised plants . as 100 to 86 

We here see how potent the influence of a cross with pollen 
from a fresh stock has been on the fertility of plants self-fertilised 
for four generations, in comparison with plants of the old stock 
when either intercrossed or self-fertilised for five generations ; the 



CHAP. VI. COLOUR OF THE FLOWERS. 203 

flowers on all these plants having been left to be freely crossed 
by insects or to fertilise themselves. The Westerham-crossed 
plants were also much taller and heavier plants than the self- 
fertilised, both in the pots and open ground ; but they were less 
tall and heavy than the intercrossed plants. This latter result, 
however, would almost certainly have been reversed, if the 
plants had been allowed to grow for another month, as the 
Westerham-crossed were still growing vigorously, whilst the 
intercrossed had almost ceased to grow. This case reminds us of 
the somewhat analogous one of Eschscholtzia, in which plants 
raised from a cross with a fresh stock did not grow higher than 
the self-fertilised or intercrossed plants, but produced a greater 
number of seed-capsules, which contained a far larger average 
number of seeds. 

Colour of the Flowers on the above Three Lots of Plants. The 
original mother-plant, from which the five successive self-fertilised 
generations were raised, bore dingy purple flowers. At no time 
was any selection practised, and the plants were subjected in 
each generation to extremely uniform conditions. The result 
was, as in some previous cases, that the flowers on all the self- 
fertilised plants, both in the pots and open ground, were 
absolutely uniform in tint; this being a dull, rather peculiar 
flesh colour. This uniformity was very striking in the long row 
of plants growing in the open ground, and these first attracted 
my attention. I did not notice in which generation the original 
colour began to charge and to become uniform, but I have every 
reason to believe that the change was gradual. The flowers on 
the intercrossed plants were mostly of the same tint, but not 
nearly so uniform as those on the self-fertilised plants, and many of 
them were pale, approaching almost to white. The flowers on the 
plants from the cross with the purple-flowered Westerham stock 
were, as might have been expected, much more purple and not 
nearly so uniform in tint. The self-fertilised plants were also 
remarkably uniform in height, as judged by the eye; the inter- 
crossed less so, whilst the Westerham-crossed plants varied much 
in height. 

NlCOTIANA TABAOUM. 

This plant offers a curious case. Out of six trials with crossed 
and self-fertilised plants, belonging to three successive genera- 
tions, in one alone did the crossed show any marked superiority 
in height over the self-fertilised ; in four of the trials they were 



204 NICOTIANA TABACUM. CHAP. VL 

approximately equal ; and in one (i.e., in the first generation) 
the self-fertilised plants were greatly superior to the crossed. 
In no case did the capsules from flowers fertilised with pollen 
from a distinct plant yield many more, and sometimes they yielded 
much fewer seeds than the capsules from self-fertilised flowers. 
But when the flowers of one variety were crossed with pollen 
from a slightly different variety, which had grown under 
somewhat different conditions, that is, by a fresh stock, the 
seedlings derived from this cross exceeded in height and weight 
those from the self-fertilised flowers in an extraordinary degree. 
Twelve flowers on some plants of the common tobacco, raised 
from purchased seeds, were crossed with pollen from a distinct 
plant of the same lot, and these produced ten capsules. Twelve 
flowers on the same plants were fertilised with their own pollen, 
and produced eleven capsules. The seeds in the ten crossed 
capsules weighed 31 '7 grains, whilst those in ten of the self- 
fertilised capsules weighed 47 '67 grains; or as 100 to 150. The 
much greater productiveness of the self-fertilised than of the 
crossed capsules can hardly be attributed to chance, as all the 
capsules of both lots were very fine and healthy ones. 

The seeds were placed on sand, and several pairs in an equal 
state of germination were planted on the opposite sides of three 
pots. The remaining seeds were thickly sown on the two sides 
of Pot IV., so that the plants in this pot were much crowded. 
The tallest plant on each side of each pot was measured. Whilst 
the plants were quite young the four tallest crossed plants 
averaged 7 -87 inches, and the four tallest self-fertilised 14 '87 
inches in height ; or as 100 to 189. The heights at this age are 
given in the two left-hand columns of the following table. 

When in full flower the tallest plants on each side were again 
measured (see the two right-hand columns), with the following 
result. But I should state that the pots were not large enough, 
and the plants never grew to their proper height. The four 
tallest crossed plants now averaged 18 -5, and the four tallest 
self-fertilised plants 32 -75 inches in height; or as 100 to 178. 
In all four pots a self-fertilised plant flowered before any one of 
the crossed. 

In Pot IV., in which the plants were extremely crowded, the 
two lots were at first equal ; and ultimately the tallest crossed 
plant exceeded by a trifle the tallest self-fertilised plant. This 
recalled to my mind an analogous case in the one generation of 
Petunia, in which the self-fertilised plants were throughout 



CHAP. VI. CROSSED AND SELF-FERTILISED PLANTS. 205 



TABLE LXXXIV. 

Nicotiana, tabacum (First Generation). 



No. of Pot. 


May 2 

Crossed 
Plants. 


, 1868. 


December 6, 1868 


Self-fertilised 
Plants. 


Crossed 
Plants. 


Self-fertilised 
Plants. 


I. 


Inches. 

t5| 


Inches. 
26 


Inches. 
40 


Inches. 
44 


II. 


3 


15 


6J 


43 


III. 


8 


13] 


16 


33 


IV. 
Crowded. 


5 


5 


HI 


11 


Total in\ 
inches./ 


31-5 


59-5 


74-0 


131-0 



their growth taller than the crossed in all the pots except, 
in the crowded one. Accordingly another trial was made, and 
some of the same crossed and self-fertilised seeds of tobacco 
were sown thickly on opposite sides of two additional pots ; the 
plants being left to grow up much crowded. When they were 
between 13 and 14 inches in height there was no difference 
between the two sides, nor was there any marked difference 
when the plants had grown as tall as they could ; for in one pot 
the tallest crossed plant was 26 inches in height, and exceeded 
by 2 inches the tallest self-fertilised plant, whilst in the other 
pot, the tallest crossed plant was shorter by 85 inches than the 
tallest self-fertilised plant, which was 22 inches in height. 

As the plants did not grow to their proper height in the above 
small pots in Table LXXXIV., four crossed and four self-fertilised 
plants were raised from the same seed, and were planted in pairs 
on the opposite sides of four very large pots containing rich soil ; 
so that they were not exposed to at all severe mutual competition. 
When these plants were in flower I neglected to measure them, 
but record in my notes that all four selMertilised plants ex- 
ceeded in height the four crossed plants by 2 or 3 inches. We 
have seen that the flowers on the original or parent-plants which 
were crossed with pollen from a distinct plant yielded much fewer 
seeds than those fertilised with their own pollen ; and the trial 
just given, as well as that in Table LXXXIV., show us clearly 



206 



NICOTIANA TABACUM. 



CHAP. VI. 



that the plants raised from the crossed seeds were inferior in 
height to those from the self- fertilised seeds ; but only when not 
greatly crowded. When crowded and thus subjected to very severe 
competition, the crossed and self-fertilised plants were nearly 
equal in height. 

Crossed and self -fertilised Plants of the Second Generation. 
Twelve flowers on the crossed plants of the last generation 
growing in the four large pots just mentioned, were crossed with 
pollen from a crossed plant growing in one of the other pots ; 
and twelve flowers on the self-fertilised plants were fertilised 
with their own pollen. All these flowers of both lots pro- 
duced fine capsules. Ten of the crossed capsules contained by 
weight 38'92 grains of seeds, and ten of the self-fertilised 
capsules 37*74 grains ; or as 100 tp 97. Some of these seeds in 
an equal state of germination were planted in pairs on the 
opposite sides of five large pots. A good many of the crossed 
seeds germinated before the self-fertilised, and were of course 
rejected. The plants thus raised were measured when several 
of them were in full flower. 

TABLE LXXXV. 

Nicotiana tabacum (Second Generation'). 



No. of Pot. 


Crossed Plants. 


Self-fertilised Plants. 


I. 


Inches. 
14 3 

7 ^ 


Inches. 
27 f 

5e 88 


II. 


60 | 

44f 
10 


V 

50| 


III. 


5 ;t 


87 (A) 
S1|(B) 


IV. 


# 

69| 


19 

431 


V. 


99| 
29 


I 1 


Total in inches. 


511-63 


413-75 



CHAP. VT. CROSSED AND SELF-FERTILISED PLANTS. 207 



The thirteen crossed plants here average 39 '35, and the 
thirteen self- fertilised plants 31*82 inches in height; or as 100 
to 81. But it would be a very much fairer plan to exclude all 
the starved plants of only 10 inches and under in height ; and 
in this case the nine remaining crossed plants average 53 '84, 
and the seven remaining self-fertilised plants 51 '78 inches in 
height, or as 100 to 96 ; and this difference is so small that the 
crossed and self-fertilised plants may be considered as of equal 
heights. 

In addition to these plants, three crossed plants were planted 
separately in three large pots, and three self-fertilised plants in 
three other large pots, so that they were not exposed to any 
competition; and now the self-fertilised plants exceeded the 
crossed in height by a little, for the three crossed averaged 55 '91, 
and the three self-fertilised 59'16 inches; or as 100 to 106. 

Crossed and self-fertilised Plants of the Third Generation. As I 
wished to ascertain, firstly, whether those self-fertilised plants of 
the last generation, which greatly exceeded in height their crossed 
opponents, would transmit the same tendency. to their offspring, 
and secondly, whether they possessed the same sexual constitu- 
tion, I selected for experiment the two self-fertilised plants 
marked A and B in Pot III. in Table LXXXV., as these two 

TABLE LXXXVI. 

Nicotiana tabacum (Third Generation). 

Seedlings from the Self -fertilised Plant A in Pot III., 

Table LXXXV., of the last or Second Generation. 



No.ofPrt. 


From Self-fertilised 
Plant, crossed by a 
Crossed Plant. 


From Self-fertilised 
Plant again self-ferti- 
lised, forming the 
Third Self-fertilised 
Generation. 


I. 


Inches. 
100? 
91 


Inches. 
98 
79 


II. 


no 

lOOj 


59 1 

66$ 


III. 


104 


79| 


IV. 


84 1 
1*1 


110| 
6iJ 


Tola' in inche? 


666-75 


557-25 



208 



NICOTIANA TABACUM. 



CHAP. VI. 



were of nearly equal height, and were greatly superior to their 
crossed opponents. Four flowers on each plant were fertilised 
with their own pollen, and four others on the same plants were 
crossed with pollen from one of the crossed plants growing in 
another pot. This plan differs from that before followed, in 
which seedlings from crossed plants again crossed, have been 
compared with seedlings from self-fertilised plants again self- 
fertilised. The seeds from the crossed and self-fertilised capsules 
of the above two plants were placed in separate watch-glasses and 
compared, but were not weighed ; and in both cases those from 
the crossed capsules seemed to be rather less numerous than 
those from the self-fertilised capsules. These seeds were planted 
in the usual manner, and the heights of the crossed and self- 
fertilised seedlings, when fully grown, are given in the preceding 
and following table, LXXXVI. and LXXXVII. 

The seven crossed plants in the first of these two tables average 
95- 25, and the seven self-fertilised 79 '6 inches in height ; or as 
100 to 83. In half the pots a crossed plant, and in the other 
half a self-fertilised plant flowered first. 

We now come to the seedlings raised from the other parent- 
plant B. 

TABLE LXXXVII. 

Nicotiana tdbacum (Third Generation). 

Seedlings from the Self-fertilised Plant B in Pot III., 

Table LXXXV., of the last or Second Generation. 



No. of Pot. 


From Self-fertilised 
Plant, crossed by a 
Crossed Plant. 


From Self-fertilised 
Plant again self-ferti- 
lised, forming the 
Third Self-fertilised 
Generation. 


I. 


Inches. 

# 


Inches. 
72| 
1*1 


II. 


?' 


73 
llOg 


III. 


99 
151 


106 g 
73| 


IV. 


97 1 


48 1 


V. 


, 


81 
611 


Total in inches. 


495-50 


641-75 



CHAP. VI. CROSSED AND SELF-FERTILISED PLANTS. 209 

The seven crossed plants (for two of them died) here average 
70 '78 inches, and the nine self-fertilised plants 71 '3 inches in 
height ; or as 100 to barely 101. In four out of these five pots, 
a self-fertilised plant flowered before any one of the crossed 
plants. So that, differently from the last case, the self-fertilised 
plants are in some respects slightly superior to the crossed. 

If we now consider the crossed and self-fertilised plants of the 
three generations, we find an extraordinary diversity in their 
relative heights. In the first generation, the crossed plants were 
inferior to the self-fertilised as 100 to 178 ; and the flowers on 
the original parent-plants which were crossed with pollen from a 
distinct plant yielded much fewer seeds than the self-fertilised 
flowers, in the proportion of 100 to 150. But it is a strange fact 
that the self-fertilised plants, which were subjected to very severe 
competition with the crossed, had on two occasions no advan- 
tage over them. The inferiority of the crossed plants of this first 
generation cannot be attributed to the immaturity of the seeds, 
for I carefully examined them ; nor to the seeds being diseased 
or in any way injured in some one capsule, for the contents of 
the ten crossed capsules were mingled together and a few taken 
by chance for sowing. In the second generation the crossed and 
self-fertilised plants were nearly equal in height. In the third 
generation, crossed and self-fertilised seeds were obtained from 
two plants of the previous generation, and the seedlings raised 
from them differed remarkably in constitution ; the crossed in the 
one case exceeded the self- fertilised in height in the ratio of 100 
to 83, and in the other case were almost equal. This difference 
between the two lots, raised at the same tune from two plants 
growing in the same pot, and treated in every respect alike, as 
well as the extraordinary superiority of the self-fertilised over 
the crossed plants in the first generation, considered together, 
make me believe that some individuals of the present species 
differ to a certain extent from others in their sexual affinities (to 
use the term employed by Gartner), like closely allied species of 
the same genus. Consequently if two plants which thus differ 
are crossed, the seedlings suffer and are beaten by those from 
the self-fertilised flowers, in which the sexual elements are of 
the same nature. It is known* that with our domestic animals 



*I have given evidence on mastication,' chap, xviii. 2nd edit, 
this head in my Variation of vol. ii. p. 146. 
Animals and Plants under Do- 



210 NICOTIANA TABACUM. CnAF.VI. 

certain individuals are sexually incompatible, and will not 
produce offspring, although fertile with other individuals. But 
Kolreuter has recorded a case * which bears more closely on our 
present one, as it shows that in the genus Nicotiana the varieties 
differ in their sexual affinities. He experimented on five 
varieties of the common tobacco, and proved that they were 
varieties by showing that they were perfectly fertile when re- 
ciprocally crossed ; but one of these varieties, if used either as 
the father or the mother, was more fertile than any of the others 
when crossed with a widely distinct species, N. glutinosd. As the 
different varieties thus differ in their sexual affinities, there is 
nothing surprising in the individuals of the same variety differ- 
ing in a like manner to a slight degree. 

Taking the plants of the three generations altogether, the 
crossed show no superiority over the self-fertilised, and I can 
account for this fact only by supposing that with this species, 
which is perfectly self-fertile without insect aid, most of the indi- 
viduals are in the same condition, as those of the same variety 
of the common pea and of a few other exotic plants, which 
have been self-fertilised for many generations. In such cases a 
cross between two individuals does no good ; nor does it in any 
case, unless the individuals differ in general constitution, either 
from so-called spontaneous variation, or from their progenitors 
having been subjected to different conditions. I believe that 
this is the true explanation in the present instance, because, as 
we shall immediately see, the offspring of plants, which did not 
profit at all by being crossed with a plant of the same stock, 
profited to an extraordinary degree by a cross with a slightly 
different sub-variety. 

The Effects of a Cross with afresh Stock. I procured some seed 
of N. tabacum from Kew and raised some plants, which formed 
a slightly different sub- variety from my former plants ; as the 
flowers were a shade pinker, the leaves a little more pointed, and 
the plants not quite so tall. Therefore the advantage in height 
which the seedlings gained by this cross cannot be attributed to 
direct inheritance. Two of the plants of the third self-fertilised 
generation, growing in Pots II. and V. in Table LXXXVIL, 
which exceeded in height their crossed opponents (as did their 
parents in a still higher degree) were fertilised with pollen 
from the Kew plants, that is, by a fresh stock. The seedlings 



* ' Das Geschlecht der Pflanzen, Zweite Fortsetzung,' 1764, p. 55-0. 



CHAP. VL CROSS WITH A FRESH STOCK. 211 

thus raised may be called the Kew-crossed. Some other flowers 
on the same two plants were fertilised with their own pollen, 
and the seedlings thus raised form the fourth self-fertilised 
generation. The crossed capsules produced by the plant in 
Pot II., Table LXXXVH., were plainly less fine than the self- 
fertilised capsules on the same plant. In Pot V. the one finest 
capsule was also a self-fertilised one; but the seeds produced 
by the two crossed capsules together exceeded in number those 
produced by the two self-fertilised capsules on the same plant. 
Therefore as far as the flowers on the parent-plants are con- 
cerned, a cross with pollen from a fresh stock did little or no 
good ; and I did not expect that the offspring would have re- 
ceived any benefit, but in this I was completely mistaken. 

The crossed and self-fertilised seeds from the two plants were 
placed on bare sand, and very many of the crossed seeds of both 
sets germinated before the self-fertilised seeds, and protruded 
their radicles at a quicker rate. Hence many of the crossed 
seeds had to be rejected, before pairs in an equal state of germina- 
tion were obtained for planting on the opposite sides of sixteen 
large pots. The two series of seedlings raised from the parent- 
plants in the two Pots II. and V. were kept separate, and when 
fully grown were measured to the tips of their highest leaves, as 
shown in the following double table. But as there was no uniform 
difference in height between the crossed and self-fertilised seed- 
lings raised from the two plants, their heights have been added 
together in calculating the averages. I should state that by the 
accidental fall of a large bush in the greenhouse, several plants 
in both the series were much injured. These were at once 
measured together with their opponents and afterwards thrown 
away. The others were left to grow to their full height, and 
were measured when in flower. This accident accounts for the 
small height of some of the pairs ; but as all the pairs, whether 
only partly or fully grown, were measured at the same time, the 
measurements are fair. 

The average height of the twenty-six crossed plants in the six- 
teen pots of the two series is 63 '29, and that of the twenty- 
six self-fertilised plants is 41 '67 inches; or as 100 to 66. The 
superiority of the crossed plants was shown in another way, 
for in every one of the sixteen pots a crossed plant flowered 
before a self-fertilised one, with the exception of Pot VI. of the 
second series, in which the plants on the two sides flowered 
simultaneously. 

p 2 



212 



NICOTIANA TABACUM. 



CHAP. VI. 



TABLE LXXXVHL 

Nicotiana tabacum. 

Plants raised from two Plants of the Third Self-fertilised 
Generation in Pots II. and V., in Table LKXXVIL 



From Pot II., Table LXXXVH. 


From Pot V., Table LXXXVII. 


No. of Pot. 


Kew-crossed 
Plants. 


Plants of the 
Fourth Self- 
fertilised Gen- 
eration. 


No. of Pot. 


Kew-crossed 
PUmts. 


Plants of the 
Fourth Self- 
rrtilised Gen- 
eration. 


I. 


Inches. 
84 f 
31 


Inches. 

J 


I. 


Inches. 

M 


Inches. 
56 

y 


II. 


78$ 
48 


S 1 


II. 


55 1 

18 


27 


III. 


77 

77 1 


121 
I 


III. 


76| 


60 1 


IV. 


49 
15 f 


29 1 
32 


IV. 


904 
22f 


"! 


v. 


89 
17 


85 
N 


V. 


941 


28 1 


VI. 


90 80 


VI. 


78 


78f 


VII. 


84 1 
76 j 


48 1 
56| 


VII. 


85 1 


61| 


VIII. 


88* 


8*1 


VIII. 


65 1 
72 


78i 
27 1 


Total in\ 
inches./ 


902-63 


636-13 


T tL} 


447-38 



Some of the remaining seeds of both series, whether or not in 
a state of germination, were thickly sown on the opposite sides 
of two very large pots ; and the six highest plants on each side 
of each pot were measured after they had grown to nearly their 
full height. But their heights were much less than in the 
former trials, owing to their extremely crowded condition. Even 
whilst quite young, the crossed seedlings manifestly had m uch 
broader and finer leaves than the self-fertilised seedlings. 



CHAP. VI. 



CROSS WITH A FRESH STOCK. 



213 



TABLE LXXXIX. 

Nicotiana tabacum, 

Plants of the same parentage as those in Table LXXXVIIL, 
but grown extremely crowded in two large pots. 



From Pot II., Table LXXXVII. 


From Pot V., Table LXXXVII. 


Kew-crossed 
Plants. 


Plants of the 
Fourth Self-ferti- 
lised Generation. 


Kew-crossed 
Plants. 


Plants of the 
Fourth Self-ferti- 
lised Generation. 


Inches. 


Inches. 


Inches. 


Inches. 


42 1 


22| 


44| 


22j 


34 


19| 


42 1 


21 


304 


14 1 


27 1 


18 


23 j 


16 


31 


151 


26 


13 i 


32 


13 I 


18 


16 


24| 


u| 


175-63 


101-50 


202-75 


105-13 



The twelve tallest crossed plants in the two pots belonging to 
the two series average here 31 53, and the twelve tallest self-ferti- 
lised plants 17-21 inches in height; or as 100 to 54. The plants 
on both sides, when fully grown, some time after they had been 
measured, were cut down close to the ground and weighed. 
The twelve crossed plants weighed 21*25 ounces; and the 
twelve self-fertilised plants only 7 '83 ounces; or in weight as 
100 to 37. 

The rest of the crossed and self-fertilised seeds from the two 
parent-plants (the same as in the last experiment) was sown on 
the 1st of July in four long parallel and separate rows in good soil 
in the open ground ; so that the seedlings were not subjected to 
any mutual competition. The summer was wet and unfavourable 
for their growth. Whilst the seedlings were v$ry small the two 
crossed rows had a clear advantage over the two self-fertilised 
rows. When fully grown the twenty tallest crossed plants and 
the twenty tallest self-fertilised plants were selected and mea- 
sured on the llth of November to the extremities of their leaves, 
as shown in the following table (XC.). Of the twenty crossed 
plants, twelve had flowered ; whilst of the twenty self-fertilised 
plants, one alone had flowered. 



214 



NICOTIAN A TABACUM. 



CHAP. VI. 



TABLE XC. 
Nicotiana tabacum. 

Plants raised from the same seeds as in the last two experiments, 

but sown separately in the open ground, so as not to compete 

together. 



From Pot II., Table LXXXVII. 


From Pot V., Table LXXXVII. 


Kew-crossed 
Plants. 


Plants of the 
Fourth Self-ferti- 
lised Generation. 


Kew-crossed 
Plants. 


Plants of the 
Fourth Self-ferti- 
lised Generation. 


Inches. 


Inches. 


Inches. 


Inches. 


42 




22 f 


54 1 


34 J 


54 




37 1 


51 1 


38 1 


39 




S4 


45 


40 1 


53 




30 


43 


43 


49 




28f 


43 


40 


50 




31 


48 f 


38 1 


47 




25 1 


44 


35 1 


57 




26 j 


48 


39 1 


37 


22 i 


55 


47 1 


48 


28 


63 


58 1 


478-75 


286-86 


496-13 


417-25 



The twenty tallest crossed plants here average 48 '74, and the 
twenty tallest self-fertilised 35 '2 inches in height; or as 100 to 
72. These plants after being measured were cut down close to 
the ground, and the twenty crossed plants weighed 195-75 
ounces, and the twenty self-fertilised plants 123 25 ounces ; or 
as 100 to 63. 

In the three preceding tables, LXXXVIIL, LXXXIX., and 
XC., we have the measurements of fifty-six plants derived from 
two plants of the third self-fertilised generation crossed with 
pollen from a fresh stock, and of fifty-six plants of the fourth self- 
fertilised generation derived from the same two plants. These 
crossed and self-fertilised plants were treated in three different 
ways, having been put, firstly, into moderately close competition 
with one another in pots ; secondly, having been subjected to 
unfavourable conditions and to very severe competition from 
being greatly crowded in two large pots ; and thirdly, having 
being sown separately in open and good ground, so as not to 
snffer from any mutual competition. In all these cases the 
crossed plants in each lot were greatly superior to the self- 



CHAP. VI. CYCLAMEN PERSICUM. 215 

fertilised. This was shown in several ways, by the earlier 
germination of the crossed seeds, by the more rapid growth of 
the seedlings whilst quite young, by the earlier flowering of the 
mature plants, as well as by the greater height which they 
ultimately attained. The superiority of the crossed plants was 
shown still more plainly when the two lots were weighed ; the 
weight of the crossed plants to that of the self-fertilised in the 
two crowded pots being as 100 to 37. Better evidence could 
hardly be desired of the immense advantage derived from a 
cross with afresh stock. 

XXVI. PBIMULAOELEL CYCLAMEN PERBICUM.* 

Ten flowers crossed with pollen from plants known to be 
distinct seedlings, yielded nine capsules, containing on an 
average 34 '2 seeds, with a maximum of seventy-seven in one. 
Ten flowers self-fertilised yielded eight capsules, containing on 
an average only 13 1 seeds, with a maximum of twenty-five in one. 
This gives a ratio of 100 to 38 for the average number of seeds 
per capsule for the crossed and self-fertilised .flowers. The 
flowers hang downwards, and as the stigmas stand close beneath 
the anthers, it might have been expected that pollen would, 
have fallen on them, and that they would have been spontaneously 
self- fertilised ; but these covered-up plants did not produce a 
single capsule. On some other occasions uncovered plants in 
the same greenhouse produced plenty of capsules, and I suppose 
that the flowers had been visited by bees, which could hardly 
fail to carry pollen from plant to plant. 

The seeds obtained in the manner just described were placed 
on sand, and after germinating were planted in pairs, three 
crossed and three self-fertilised plants on the opposite sides of 
four pots. When the leaves were 2 or 3 inches in length, 
including the foot-stalks, the seedlings on both sides were 
equal. In the course of a month or two the crossed plants began 
to show a slight superiority over the self-fertilised, which 
steadily increased ; and the crossed flowered in all four pots some 
weeks before, and much more profusely than the self-fertilised. 
The two tallest flower-stems on the crossed plants in each pot 
were now measured, and the average height of the eight stems 



* Cyclamen repandum, accord- p. 150), is proterandrous, and this 
ingtoLecoq ('Geographic Botan- I believe to be the case with C. 
ipue de 1'Europe,' torn. viii. 1858, persieum. 



216 



CYCLAMEN PEKSICUM. 



CHAP. VI 



was 9'49 inches. After a considerable interval of time the 
self-fertilised plants flowered, and several of their flower-stems 
(but I forgot to record how many) were roughly measured, and 
their average height was a little under 7'5 inches; so that the 
flower-stems on the crossed plants to those on the self-fertilised 
were at least as 100 to 79. The reason why I did not make 
more careful measurements of the self-fertilised plants was, that 
they looked such poor specimens that I determined to have them 
re-potted in larger pots and in the following year to measure 
them carefully ; but we shall see that this was partly frustrated 
by so few flower-stems being then produced. 

These plants were left uncovered in the greenhouse ; and the 
twelve crossed plants produced forty capsules, whilst the 
twelve self-fertilised plants produced only five ; or as 100 to 12. 
But this difference does not give a just idea of the relative 
fertility of the two lots. I counted the seeds in one of the finest 
capsules on the crossed plants, and it contained seventy-three ; 
whilst the finest of the five capsules produced by the self- 
fertilised plants contained only thirty-five good seeds. In the 
other four capsules most of the seeds were barely half as large 
as those in the crossed capsules. 

TABLE XCI. 

Cyclamen persicum : implies that no /lower-stem ivas produced. 



No. of Pot. 


Crossed Plants. 


Self-fertilised Plants. 


I. 


Inches. 
10 
91 

101 


Inches. 






II. 


91 

10 

101 







III. 


9J 
9| 
9 i 


8 
61 
i 


IV. 


HJ 

lot 
10] 




'o ! 


Total in inches. 


119-88 


29-50 



CHAP. VI. ANAGALLIS COLLINA. 217 

In the following year the crossed plants again bore many 
flowers before the self-fertilised bore a single one. The three 
tallest flower-stems on the crossed plants in each of the pots 
were measured, as shown in Table XCI. In Pots I. and II. the 
self-fertilised plants did not produce a single flower-stem; in 
Pot IV. only one ; and in Pot III. six, of which the three tallest 
were measured. 

The average height of the twelve flower-stems on the crossed 
plants is 9 '99, and that of the four flower-stems on the self- 
fertilised plants 7 37 inches ; or as 100 to 74. The self-fertilised 
plants were miserable specimens, whilst the crossed ones looked 
very vigorous. 

ANAGALLIS. 

Anagattis eottina, var. grandiftora (pale red and blue-flowered 
sub-varieties). 

Firstly, twenty-five flowers on some plants of the red variety 
were crossed with pollen from a distinct plant of the same 
variety, and produced ten capsules; thirty-one flowers were 
fertilised with their own pollen, and produced eighteen capsules. 
These plants, which were grown in pots in the greenhouse, were 
evidently in a very sterile condition, and the seeds in both 
sets of capsules, especially in the self-fertilised, although 
numerous, were of so poor a quality that it was very difficult 
to determine which were good and which bad. But as far as I 
could judge, the crossed capsules contained on an average 6 - 3 
good seeds, with a maximum in one of thirteen; whilst the 
self- fertilised contained 6 '05 such seeds, with a maximum in 
one of fourteen. 

Secondly, eleven flowers on the red variety were castrated 
whilst young and fertilised with pollen from the blue variety, 
and this cross evidently much increased their fertility; for the 
eleven flowers yielded seven capsules, which contained on an 
average twice as many good seeds as before, viz., 12'7; with a 
maximum in two of the capsules of seventeen seeds. Therefore 
these crossed capsules yielded seeds compared with those in the 
foregoing self-fertilised capsules, as 100 to 48. These seeds were 
also conspicuously larger than those from the cross between two 
individuals of the same red variety, and germinated much more 
freely. The flowers on most of the plants produced by the cross 
between the two-coloured varieties (of which several were raised). 



218 



ANAGALLIS COLLINA. 



CHAP. VI. 



took after their mother, and were red-coloured. But on two of 
the plants the flowers were plainly stained with blue, and to 
such a degree in one case as to be almost intermediate in tint. 

The crossed seeds of the two foregoing kinds and the self- 
fertilised were sown on the opposite sides of two large pots, and 
the seedlings were measured when fully grown, as shown in the 
two following tables : 

TABLE XCII. 

Anagallis collina. 



Red Variety crossed by a distinct Plant of the Red Variety, 
and Red Variety Self-fertilised. 


No. of Pot. 


Crossed Plants. 


Self-fertilised Plants. 


I. 


Inches. 
23 1 
21 
171 


Inches. 

1 


Total in inches. 


61-75 


45-00 


Red Variety crossed by Blue Variety, and Red Variety 
Self-fertilised. 


No. of Pot. I Crossed Plants. 


Self-fertilised Plants. 


Inches. 
II. 304 
27 1 

1 25 


Inches. 
24| 
18 j 

Hi 


Total in inches. 


82-88 


54 '75 


Total of both lots. 


144-63 


99-75 



As the plants of the two lots are few in number, they may be 
run together for the general average ; but I may first state that 
the height of the seedlings from the cross between two individuals 
of the red variety is to that of the self-fertilised plants of the red 
variety as 100 to 73 ; whereas the height of the crossed offspring 
from the two varieties to the self-fertilised plants of the red 
variety is as 100 to 66. So that the cross between the two 
varieties is here seen to be the most advantageous. The average 
weight of all six crossed plants in the two lots taken together is 



CHAP. VI. PRIMULA VERIS. 219 

48-20, and that of the six self-fertilised plants 33 -23 ; or as 100 
to 69. 

These six crossed plants produced spontaneously twenty-six 
capsules, whilst the six self-fertilised plants produced only two, 
or as 100 to 8. There is therefore the same extraordinary 
difference in fertility between the crossed and self-fertilised 
plants as in the last genus, Cyclamen, which belongs to the same 
family of the Primulacefe. 

PBIMULA VERIS. Brit. Flora. 
(Far. officinalis, Linn.). The Cowslip. 

Most of the species in this genus are heterostyled or 
dimorphic ; that is, they present two forms, one long-styled 
with short stamens, and the other short-styled with long 
stamens.* For complete fertilisation it is necessary that 
pollen from the one form should be applied to the stigma 
of the other form ; and this is effected under nature by insects. 
Such unions, and the seedlings raised from them, I have 
called legitimate. If one form is fertilised with pollen 
from the same form, the full complement of seed is not pro- 
duced ; and in the case of some heterostyled genera no seed at 
all is produced. Such unions, and the seedlings raised from 
them, I have called illegitimate. These seedlings are often 
dwarfed and more or less sterile, like hybrids. I possessed 
some long-styled plants of P. veris, which during four successive 
generations had been produced from illegitimate unions be- 
tween long-styled plants ; they were, moreover, in some degree 
inter-related, and had been subjected all the time to similar 
conditions in pots in the greenhouse. As long as they were 
cultivated in this manner, they grew well and were healthy and 
fertile. Their fertility even increased in the later generations, 
as if they were becoming habituated to illegitimate fertilisation. 
Plants of the first illegitimate generation when taken from the 
greenhouse and planted in moderately good soil out of doors 
grew well and were healthy ; but when those of the two last 
illegitimate generations were thus treated they became exces- 
sively sterile and dwarfed, and remained so during the following 



* See my work, ' The Different papers in ' Journal of Proc. Linn 
Forms of Flowers on Plants of Soc.' vol. vi. 1862, p. 77, and vol 
the same Species/ 1877, or my x. 1867, p. 393. 



220 PRIMULA VERIS. CHAP. VI. 

year, by which time they ought to have become accustomed to 
growing out of doors, so that they must have possessed a weak 
constitution. 

Under these circumstances, it seemed advisable to ascertain 
what would be the effect of legitimately crossing long-styled 
plants of the fourth illegitimate generation with pollen taken from 
non-related short-styled plants, growing under different con- 
ditions. Accordingly several flowers on plants of the fourth 
illegitimate generation (i.e., great-great-grandchildren of plants 
which had been legitimately fertilised), growing vigorously in pots 
in the greenhouse, were legitimately fertilised with pollen from 
an almost wild short-styled cowslip, and these flowers yielded 
some fine capsules. Thirty other flowers on the same illegi- 
timate plants were fertilised with their own pollen, and these 
yielded seventeen capsules, containing on an average thirty-two 
seeds. This is a high degree of fertility ; higher, I believe, than 
that which generally obtains with illegitimately fertilised long- 
styled plants growing out of doors, and higher than that of the 
previous illegitimate generations, although their flowers were 
fertilised with pollen taken from a distinct plant of the same 
form. 

These two lots of seeds were sown (for they will not germinate 
well when placed on bare sand) on the opposite sides of four 
pots, and the seedlings were thinned, so that an equal number 
were left on the two sides. For some time there was no marked 
difference in height between the two lots ; and in Pot III., Table 
XCIIL, the self-fertilised plants were rather the tallest. But by 
the time that they had thrown up young flower-stems, the 
legitimately crossed plants appeared much the finest, and had 
greener and larger leaves. The breadth of the largest leaf on 
each plant was measured, and those on the crossed plants were 
on an average a quarter of an inch (exactly '28 of an inch) 
broader than those on the self-fertilised plants. The plants, 
from being too much crowded, produced poor and short flower- 
stems. The two finest on each side were measured ; the eight 
on the legitimately crossed plants averaged 4 08, and the eight on 
the illegitimately self-fertilised plants averaged 2 '93 inches in 
height; or as 100 to 72. 

These plants after they had flowered were turned out of their 
pots, and planted in fairly good soil in the open ground. In 
the following year (1870), when in full flower, the two tallest 
flower -stems on each side were again measured, as shown in the 



CHAP. VI. 



PRIMULA VERIS. 



221 



following table, which likewise gives the number of flower-stems 
produced on both sides of all the pots. 

TABLE XCUL 

PrimuJ.a veris. 



No. of Pot. 


Legitimately crossed Plants' 


Illegitimately self-fertilised 


Height in 
inches. 


No. of Flower- 
stems pro- 
duced. 


Height in 
inches. 


No. of Flower- 
stems pro- 
duced. 


I. 


9 
8 


16 


II 


3 


II. 


7 
6| 


16 


6 
*| 


3 


III. 


6 

n 


16 


3 
l 


4 


IV. 7 jj 

6J 


14 


2| 
2| 


5 


Total. 


56-26 


62 


25-75 


15 



The average height of the eight tallest flower-stems on the 
crossed plants is here 7 '03 inches, and that of the eight tallest 
flower-stems on the self-fertilised plants 3 '21 inches; or as 
100 to 46. We see, also, that the crossed plants bore sixty-two 
flower-stems; that is, above four times as many as those (viz., 
fifteen) borne by the self-fertilised plants. The flowers were 
left exposed to the visits of insects, and as many plants of 
both forms grew close by, they must have been legitimately 
and naturally fertilised. Under these circumstances the 
crossed plants produced 324 capsules, whilst the self-fertilised 
produced only 16; and these were all produced by a single 
plant in Pot II., which was much finer than any other self- 
fertilised plant. Judging by the number of capsules produced, 
the fertility of an equal number of crossed and self-fertilised 
plants was as 100 to 5. 

In the succeeding year (1871) I did not count all the flower- 
stems on these plants, but only those which produced cap- 
sules containing good seeds. The season was unfavourable, and 
the crossed plants produced only forty snch flower-stems, bearing 



222 PRIMULA VEPJS. CHAP. VI. 

168 good capsules, whilst the self-fertilised plants produced 
only two such flower-stems, bearing only 6 capsules, half of 
which were very poor ones. So that the fertility of the two lots, 
judging by the number of capsules, was as 100 to 3 '5. 

In considering the great difference in height and the wonderful 
difference in fertility between the two sets of plants, we should 
bear in mind that this is the result of two distinct agencies. 
The self-fertilised plants were the product of illegitimate fertili- 
sation during five successive generations, in all of which, ex- 
cepting the last, the plants had been fertilised with pollen taken 
from a distinct individual belonging to the same form, but which 
was more or less closely related. The plants had also been 
subjected in each generation to closely similar conditions. This 
treatment alone, as I know from other observations, would have 
greatly reduced the size and fertility of the offspring. On the 
other hand, the crossed plants were the offspring of long-styled 
plants of the fourth illegitimate generation legitimately crossed 
with pollen from a short-styled plant, which, as well as its pro- 
genitors, had been exposed to very different conditions ; and this 
latter circumstance alone would have given great vigour to the 
offspring, as we may infer from the several analogous cases 
already given. How much proportional weight ought to be at- 
tributed to these two agencies, the one tending to injure the 
self-fertilised offspring, and the other to benefit the crossed 
offspring, cannot be determined. But we shall immediately 
see that the greater part of the benefit, as far as increased 
fertility is concerned, must be attributed to the cross having 
been made with a fresh stock. 

PBIMULA VEEIS. 
Equal-styled and red-flowered var. 

I have described in my paper ' On the Illegitimate Unions of 
Dimorphic and Trimorphic Plants' this remarkable variety, which 
was sent to me from Edinburgh by Mr. J. Scott. It possessed a 
pistil proper to the long-styled form, and stamens proper to the 
short-styled form ; so that it had lost the heterostyled or dimor- 
phic character common to most of the species of the genus, 
and may be compared with an hermaphrodite form of a bi- 
sexual animal. Consequently the pollen and stigma of the 
same flower are adapted for complete mutual fertilisation, instead 
of its being necessary that pollen should be brought from oae 



CHAP. VI. EQUAL-STYLED VARIETY. 223 

form to another, as in the common cowslip. From the stigma 
and anthers standing nearly on the same level, the flowers are 
perfectly self-fertile when insects are excluded. Owing to the 
fortunate existence of this variety, it is possible to fertilise its 
flowers in a legitimate manner with their own pollen, and to 
cross other flowers in a legitimate manner with pollen from 
another variety or fresh stock. Thus the offspring from both 
unions can be compared quite fairly, free from any doubt from 
the injurious effects of an illegitimate union. 

The plants on which I experimented had been raised during 
two successive generations from spontaneously self-fertilised 
seeds produced by plants under a net ; and as the variety is 
highly self-fertile, its progenitors in Edinburgh may have been 
self-fertilised during some previous generations. Several flowers 
on two of my plants were legitimately crossed with pollen from 
a short-styled common cowslip growing almost wild in my 
orchard ; so that the cross was between plants which had been 
subjected to considerably different conditions. Several other 
flowers on the same two plants were allowed to fertilise them- 
selves under a net ; and this union, as already explained, is a 
legitimate one. 

The crossed and self-fertilised seeds thus obtained were sown 
thickly on the opposite sides of three pots, and the seedlings 
thinned, so 'that an equal number were left on the two sides. 
The seedlings during the first year were nearly equal in 
height, excepting in Pot III., Table XCIV., in which the self- 
fertilised plants had a decided advantage. In the autumn the 
plants were bedded out, in their pots; owing to this circum- 
stance, and to many plants growing in each pot, they did not 
flourish, and none were very productive in seeds. But the 
conditions were perfectly equal and fair for both sides. In the 
following spring I record in my notes that in two of the pots 
the crossed plants are " incomparably the finest in general 
appearance," and in all three pots they flowered before the self- 
fertilised. When in full flower the tallest flower-stem on each 
side of each pot was measured, and the number of the flower- 
stems on both sides counted, as shown in the following table. 
The plants were left uncovered, and as other plants were growing 
close by, the flowers no doubt were crossed by insects. When 
the capsules were ripe they were gathered and counted, and 
the result is likewise shown in the following table : 



224 



PKIMULA VERIS. 



CHAP. VI 



TABLE XCIV. 

Primula veris (equal-styled, red-flowered variety). 



No. of Pot. 


Crossed Plants. 


Self-fertilised Plants. 


Height of 
tallest 
Flower-stem 
in inches. 


No. of 
Flower- 
stems. 


No. of good 
Capsules. 


Height of 
tallest 
Flower-stem 
in inches. 


No. of 

Flower- 
stems. 


No. of good 
Capsules. 


I. 


10 


14 


163 


6 I 


6 


6 


II. 


8| 


* 


Several, 
not 
counted. 


5 


2 





III. 


7| 


1 


43 


leg 


5 


26 


Totals. 


26-0 


33 


206 


22-0 


13 


32 



The average height of the three tallest flower-stems on the 
crossed plants is 8 '66 inches, and that of the three on the 
self-fertilised plants 7 '33 inches; or as 100 to 85. 

All the crossed plants together produced thirty-three flower- 
stems, whilst the self-fertilised bore only thirteen. The number 
of the capsules was counted only on the plants in Pots I. and III., 
for the self-fertilised plants in Pot II. produced none ; therefore 
those on the crossed plants on the opposite side were not 
counted. Capsules not containing any good seeds were rejected. 
The crossed plants in the above two pots produced 206, and the 
self-fertilised in the same pots only 32 capsules; or as 100 
to 15. Judging from the previous generations, the extreme 
unproductiveness of the self-fertilised plants in this experiment 
was wholly due to their having been subjected to unfavourable 
conditions, and to severe competition with the crossed plants ; 
for had they grown separately in good soil, it is almost certain 
that they would have produced a large number of capsules. 
The seeds were counted in twenty capsules from the crossed 
plants, and they averaged 24 '75; whilst in twenty capsules 
from the self-fertilised plants the average was 17 '65; or as 
100 to 71. Moreover, the seeds from the self-fertilised plants 
were not nearly so fine as those from the crossed plants. If 
we consider together the number of capsules produced and 
the average number of contained seeds, the fertility of the 
crossed plants to the self-fertilised plants was as 100 to 11. 



CUAI-. VI. PRIMULA SINENSIS. 225 

We thus see what a great effect, as far as fertility is concerned, 
was produced by a cross between the two varieties, which had 
been long exposed to different conditions, in comparison with 
self-fertilisation ; the fertilisation having been in both cases of 
the legitimate order. 

PBIMULA SINENSIS. 

As the Chinese primrose is a heterostyled or dimorphic plant, 
like the common cowslip, it might have been expected that the 
flowers of both forms when illegitimately fertilised with their 
own pollen or with that from flowers on another plant of the 
same form, would have yielded less seed than the legitimately 
crossed flowers; and that the seedlings raised from illegiti- 
mately self-fertilised seeds would have been somewhat dwarfed 
and less fertile, in comparison with the seedlings from legiti- 
mately crossed seeds. This holds good in relation to the fer- 
tility of the flowers ; but to my surprise there was no difference 
in growth between the offspring from a legitimate union bet ween 
two distinct plants, and from an illegitimate union whether 
between the flowers on the same plant, or between distinct plants 
of the same form. But I have shown, in the work lately referred 
to, that in England this plant is in an abnormal condition, 
such as, judging from analogous cases, would tend to render a 
cross between two individuals of no benefit to the offspring. 
Our plants have been commonly raised from self-fertilised 
seeds ; and the seedlings have generally been subjected to nearly 
uniform conditions in pots in greenhouses. Moreover, many of 
the plants are now varying and changing their character, so as 
to become in a greater or less degree equal-styled, and in con- 
sequence highly self-fertile. From the analogy of P. veris there 
can hardly be a doubt that if a plant of P. sinensis could have 
been procured direct from China, and if it had been crossed 
with one of our English varieties, the offspring would have 
shown wonderful superiority in height and fertility (though 
probably not in the beauty of their flowers) over our ordinary 
plants. 

My first experiment consisted in fertilising many flowers on 
long-styled and short-styled plants with their own pollen, and 
other flowers on the same plants with pollen taken from distinct 
plants belonging to the same form ; so that all the unions were 
illegitimate. There was no uniform and marked difference in 

Q 



226 PRIMULA SINENSIS. CHAP. VI. 

the number of seeds obtained from these two modes of self-fer- 
tilisation, both of which were illegitimate. The two lots of seeds 
from both forms were sown thickly on opposite sides of four pots, 
and numerous plants thus raised. But there was no difference 
in their growth, excepting in one pot, in which the offspring 
from the illegitimate union of two long-styled plants exceeded 
in a decided manner in height the offspring of flowers on the 
same plants fertilised with their own pollen. But in all four 
pots the plants raised from the union of distinct plants belonging 
to the same form, flowered before the offspring from the self- 
fertilised flowers. 

Some long-styled and short-styled plants were now raised from 
purchased seeds, and flowers on both forms were legitimately 
crossed with pollen from a distinct plant; and other flowers on 
both forms were illegitimately fertilised with pollen from the 
flowers on the same plant. The seeds were sown on opposite sides 
of Pots I. to IV. in the following table (XCV.) ; a single plant 
being left on each side. Several flowers on the illegitimate long- 
styled and short-styled plants described in the last paragraph, 
were also legitimately and illegitimately fertilised in the manner 
just described, and their seeds were sown in Pots V. to VIII. in 
the same table. As the two sets of seedlings did not differ in 
any essential manner, their measurements are given in a single 
table. I should add that the legitimate unions in both cases 
yielded, as might have been expected, many more seeds than the 
illegitimate unions. The seedlings whilst half-grown presented 
no difference in height on the two sides of the several pots. 
When fully grown they were measured to the tips of their 
longest leaves, and the result is given in Table XCV. 

In six out of the eight pots the legitimately crossed plants 
exceeded in height by a trifle the illegitimately self-fertilised 
plants ; but the latter exceeded the former in two of the pots in a 
more strongly marked manner. The average height of the eight 
legitimately crossed plants is 9*01, and that of the eight illegi- 
timately self-fertilised 9'03 inches; or as 100 to 100 '2. The 
plants on the opposite sides produced, as far as could be judged 
by the eye, an equal number of flowers. I did not count the cap- 
sules or the seeds produced by them ; but undoubtedly, judging 
from many previous observations, the plants derived from the 
legitimately crossed seeds would have been considerably more 
fertile than those from the illegitimately self-fertilised seeds. 
The crossed plants, as in the previous case, flowered before the 



CHAP. VI. 



PRIMULA SINENSIS. 



227 



TABLE XCV. 

Primula sinensis. 



No. of Pot 


Plants from legiti- 
mately crossed Seeds. 


Plants from illegiti- 
mately self-fertilised 
Seeds. 


I. 

From short-styled 
mother. 


Inches. 
1 


Inches. 
8 


II. 
From short -styled 
mother. 


7j 


83 


III. 
From long-styled 
mother. 


ftj 


93 


IV. 

From long-styled 
mother. 


8| 


81 


V. 
From illegitimate 
short-styled 
mother. 


91 


9 


VI. 

From illegitimate 
short-styled 
mother. 


9? 


9 I 


VII. 

From illegitimate 
long-styled mother. 


8* 


n 


VIII. 
From {legitimate 
long-styled mother. 


10J 


10 


Total in inches. I 72'13 


72-25 



self-fertilised plants in all the pots except in Pot EL, in which the 
two sides flowered simultaneously; and this early flowering 
may, perhaps, be considered as an advantage. 

Q 2 



228 FAGOPYRUM ESCULENTUM. CHAP. VI. 

XXVII. POLYGOKE^E. FAGOPYBTJM KSCTJLENTTJM. 

This plant was discovered by Hildebrand to be heterostyled, 
that is, to present, like the species of Primula, a long-styled and a 
short-styled form, which are adapted for reciprocal fertilisation. 
Therefore the following comparison of the growth of the crossed 
and self-fertilised seedlings is not fair, for we do not know 
whether the difference in their heights may not be wholly due to 
the illegitimate fertilisation of the self-fertilised flowers. 

I obtained seeds by legitimately crossing flowers on long-styled 
and short-styled plants, and by fertilising other flowers on both 
forms with pollen from the same plant. Bather more seeds were 
obtained by the former than by the latter process ; and the 
legitimately crossed seeds were heavier than an equal number 
of the illegitimately self-fertilised seeds, in the ratio of 100 to 82. 
Crossed and self-fertilised seeds from the short-styled parents, 
after germinating on sand, were planted in pairs on the opposite 
sides of a large pot ; and two similar lots of seeds from long- 
styled parents were planted in a like manner on the opposite 
sides of two other pots. In all three pots the legitimately crossed 
seedlings, when a few inches in height, were taller than the self- 
fertilised; and in all three pots they flowered before them by one 
or two days. When fully grown they were all cut down close 
to the ground, and as I was pressed for time, they were placed 
in a long row, the cut end of one plant touching the tip of 
another, and the total length of the legitimately crossed plants 
was 47 ft. 7 in., and of the illegitimately self-fertilised plants 
32 ft. 8 in. Therefore the average height of the fifteen crossed 
plants in all three pots was 38 '06 inches, and that of the fifteen 
self-fertilised plants 26 "13 inches; or as 100 to 69. 

XXVHL CHENOPODIACE2E. BETA VULGABIB. 
A single plant, no others growing in the same garden, was 
left to fertilise itself, and the self-fertilised seeds were collected. 
Seeds were also collected from a plant growing in the midst of a 
large bed in another garden ; and as the incoherent pollen is 
abundant, the seeds of this plant will almost certainly have been 
the product of a cross between distinct plants by means of the 
wind. Some of the two lots of seeds were sown on the opposite 
sides of two very large pots; and the young seedlings were 
thinned, so that an equal but considerable number was left on 
the two sides. These plants were thus subjected to very severe 



CHAP. VI. 



BETA VULGAKIS. 



229 



competition, as well as to poor conditions. The remaining seeds 
were sown out of doors in good soil in two long and not closely 
adjoining rows, so that these seedlings were placed under favour- 
able conditions, and were not subjected to any mutual com- 
petition. The self-fertilised seeds in the open ground came up 
very badly ; and on removing the soil in two or three places, it 
was found that many had sprouted under ground and had 
then died. No such case had been observed before. Owing to 
the large number of seedlings which thus perished, the sur- 
viving self-fertilised plants grew thinly in the row, and thus had 
an advantage over the crossed plants, which grew very thickly 
in the other row. The young plants in the two rows were pro- 
tected by a little straw during the winter, and those in the two 
large pots were placed in the greenhouse. 

There was no difference between the two lots in the pots until 
the ensuing spring, when they had grown a little, and then some 
of the crossed plants were finer and taller than any of the self- 
fertilised. When in full flower their stems were measured, and 
the measurements are given in the following table : 

TABLE XCVI. 

Beta vulgaris. 



No. of Pot. 


[ Crossed Plants. ( Self-fertilised Plants. 


I. 


Inches. 
34f 
30 
338 
34| 


Inches. 
36 
801 

321 
32 


IL 


42 f 
331 
31 1 
33 


42 J 
26 1 
29$ 
MJ 


Total in inches. 


272-75 


238-50 



The average height of the eight crossed plants is here 
34-09, and that of the eight self-fertilised plants 29 '81 ; or as 
100 to 87. 

With respect to the plants in the open ground, each long row 
was divided into half, so as to diminish the chance of any 
accidental advantage in one part of either row; and the four 
tallest plants in the two halves of the two rows were carefully 



230 CANNA WABSCEWICZI. CHAP. VI 

selected and measured. The eight tallest crossed plants averaged 
30-92, and the eight tallest self-fertilised 30 '7 inches in height, 
or as 100 to 99 ; so that they were practically equal. But we 
should bear in mind that the trial was not quite fair, as the 
self-fertilised plants had a great advantage over the crossed 
in being much less crowded in their own row, owing to the 
large number of seeds which had perished under ground after 
sprouting. Nor were the lots in the two rows subjected to any 
mutual competition. 

XXIX. CANNACE.ZE. CANNA WARSCEWICZI. 
In most or all the species belonging to this genus, the pollen 
is shed before the flower expands, and adheres in a mass to the 
foliaceous pistil close beneath the stigmatic surface. As the 
edge of this mass generally touches the edge of the stigma, and 
as it was ascertained by trials purposely made that a very few 
pollen -grains suffice for fertilisation, the present species and 
probably all the others of the genus are highly self-fertile. 
Exceptions occasionally occur in which, from the stamen being 
slightly shorter than usual, the pollen is deposited a little beneath 
the stigmatic surface, and such flowers drop off unimpreg- 
nated unless they are artificially fertilised. Sometimes, though 
rarely, the stamen is a little longer than usual, and then the 
whole stigmatic surface gets thickly covered with pollen. As 
some pollen is generally deposited in contact with the edge of 
the stigma, certain authors have concluded that the flowers are 
invariably self-fertilised. This is an extraordinary conclusion, 
for it implies that a great amount of pollen is produced for no 
purpose. On this view, also, the large size of the stigmatic 
surface is an unintelligible feature in the structure of the flower, 
as well as the relative position of all the parts, which is such 
that when insects visit the flowers to suck the copious nectar, 
they cannot fail to carry pollen from one flower to another. * 



* Delpino has described (' Bot. are fertilised in the bud, and that 

Zeitung,' 1867, p. 277, and ' Scien- self-fertilisation is inevitable. I 

tific Opinion,' 1870, p. 135) the presume that they were misled by 

structure of the flowers in this the pollen being deposited at a 

genus, but he was mistaken in very early period on the pistil : see 

thinking that self-fertilisation is ' Journal of Linn. Soc. Bot.' vol. 

impossible, at least in the case of x. p. 55, and ' Variability dcs 

the present species. Dr. Dickie and Especes,' 1868, p. 158. 
Prof. Faivre state that the flowers 



CHAP. VI. CANNA WARSCEWICZI. 231 

According to Dclpino, bees eagerly visit the flowers in North 
Italy, but I have never seen any insect visiting the flowers of the 
present species in my hothouse, although many plants grew 
there during several years. Nevertheless these plants produced 
plenty of seed, as they likewise did when covered by a net; they 
are therefore fully capable of self-fertilisation, and have probably 
been self-fertilised in this country for many generations. As 
they are cultivated in pots, and are not exposed to competition 
with surrounding plants, they have also been subjected for a 
considerable time to somewhat uniform conditions. This, there- 
fore, is a case exactly parallel with that of the common pea, in 
which we have no right to expect much or any good from 
intercrossing plants thus descended and thus treated; and 
no good did follow, excepting that the cross-fertilised flowers 
yielded rather more seeds than the self-fertilised. This species 
was one of the earlier ones on which I experimented, and as I 
had not then raised any self-fertilised plants for several successive 
generations under uniform conditions, I did not know or even 
suspect that such treatment would interfere with the advantages 
to be gained from a cross. I was therefore much surprised at 
the crossed plants not growing more vigorously than the self- 
fertilised, and a large number of plants were raised, notwith- 
standing that the present species is an extremely troublesome 
one to experiment on. The seeds, even those which have been 
long soaked in water, will not germinate well on bare sand ; and 
those that were sown in pots (which plan I was forced to follow) 
germinated at very unequal intervals of time; so that it was 
difficult to get pairs of the same exact age, and many seedlings 
had to be pulled up and thrown away. My experiments were 
continued during three successive generations; and in each 
generation the self-fertilised plants were again self-fertilised, 
their early progenitors in this country having probably been self- 
fertilised for many previous generations. In each generation, 
also, the crossed plants were fertilised with pollen from another 
crossed plant. 

Of the flowers which were crossed in the three generations, 
taken together, a rather larger proportion yielded capsules thar 
did those which were self-fertilised. The seeds were counted in 
forty-seven capsules from the crossed flowers, and they con- 
tained on an average 9 '95 seeds; whereas forty-eight capsules 
from the self-fertilised flowers contained on an average 8 '45 
K3eds ; or as 100 to 85. The seeds from the crossed flowers were 



232 CANNA WABSCEWICZI. CHAP. VL 

not heavier, on the contrary a little lighter, than those from the 
self-fsrtilised flowers, as was thrice ascertained. On one occasion 
I weighed 200 of the crossed and 106 of the self-fertilised seeds, 
and the relative weight of an equal number was as 100 for the 
crossed to 101 5 for the self-fertilised. With other plants, when 
the seeds from the self-fertilised flowers were heavier than those 
from the crossed flowers, this appeared to be due generally 
to fewer having been produced by the self-fertilised flowers, and 
to their having been in consequence better nourished. But in 
the present instance the seeds from the crossed capsules were 
separated into two lots, namely, those from the capsules con- 
taining over fourteen seeds, and those from capsules containing 
under fourteen seeds, and the seeds from the more productive 
capsules were the heavier of the two ; so that the above explana- 
tion here fails. 

As pollen is deposited at a very early age on the pistil, gene- 
rally in contact with the stigma, some flowers whilst still in 
bud were castrated for my first experiment, and were afterwards 
fertilised with pollen from a distinct plant. Other flowers were 
fertilised with their own pollen. From the seeds thus ob- 
tained, I succeeded in rearing only three pairs of plants of equal 
age. The three crossed plants averaged 32 -79 inches, and 
the three self-fertilised 2 '08 inches in height; so that they 
were nearly equal, the crossed having a slight advantage. As 
the same result followed in all three generations, it would be 
superfluous to give the heights of all the plants, and I will give 
only the averages. 

In order to raise crossed and self-fertilised plants of the second 
generation, some flowers on the above crossed plants were crossed 
within twenty-four hours after they had expanded with pollen 
from a distinct plant ; and this interval would probably not be too 
great to allow of cross-fertilisation being effectual. Some flowers 
on the self-fertilised plants of the last generation were also self- 
fertilised. From these two lots of seeds, ten crossed and twelve 
self-fertilised plants of equal ages were raised ; and these were 
measured when fully grown. The crossed averaged 36 -98, and 
the self-fertilised averaged 37 '42 inches in height; so that here 
again the two lots were nearly equal ; but the selMertilised had 
a slight advantage. 

In order to raise plants of the third generation, a better plan 
was followed, and flowers on the crossed plants of the second 
generation were selected in which the stamens were too short tc 



CHAP. VI. ZEA MAYS. 233 

reacli the stigmas, so that they could not possibly have been 
self-fertilised. These flowers were crossed with pollen from a 
distinct plant. Flowers on the self-fertilised plants of the second 
generation were again self-fertilised. From the two lots of seeds 
thus obtained, twenty-one crossed and nineteen self- fertilised 
plants of equal age, and forming the third generation, were raised 
in fourteen large pots. They were measured when fully grown, 
and by an odd chance the average height of the two lots was 
exactly the same, namely, 35 96 inches ; so that neither side had 
the least advantage over the other. To test this result, all the 
plants on both sides in ten out of the above fourteen pots were 
cut down after they had flowered, and in the ensuing year the 
stems were again measured; and now the crossed plants ex- 
ceeded by a little (viz., 1-7 inches) the self-fertilised. They were 
again cut down, and on their flowering for the third time, the 
self-fertilised plants had a slight advantage (viz., 1 54 inches) 
over the crossed. Hence the result arrived at with these plants 
during the previous trials was confirmed, namely, that neither 
lot had any decided advantage over the other. It may, however, 
be worth mentioning that the self-fertilised plants showed some 
tendency to flower before the crossed plants : this occurred with 
all three pairs of the first generation ; and with the cut down 
plants of the third generation, a self-fertilised plant flowered 
first in nine out of the twelve pots, whilst in the remaining three 
pots a crossed plant flowered first. 

If we consider all the plants of the three generations taken 
together, the thirty-four crossed plants average 35 '98, and the 
thirty-four self-fertilised plants 36 '39 inches in height; or as 
100 to 101. We may therefore conclude that the two lots 
possessed equal powers of growth ; and this I believe to be the 
result of long-continued self-fertilisation, together with exposure 
to similar conditions in each generation, so that all the indivi- 
duals had acquired a closely similar constitution. 

XXX. GKAMINACE^}. ZBA MAYS. 

This plant is monoecious, and was selected for trial on this ac- 
count, no other such plant having been experimented on.* It is 



* Hildebrand remarks that male flowers standing above the 

this species eeems at first sight female flowers ; but practically it 

adapted to be fertilised by pollen must generally be fertilised by 

from the same plant, owing to the pollen from another plant, as the 



234 



ZEA MAYS. 



CHAP. VI. 



also anemophilous, or is fertilised by the wind ; and of such plants 
only the common beet had been tried. Some plants were raised 
in the greenhouse, and were crossed with pollen taken from a 
distinct plant ; and a single plant, growing quite separately in a 
different part of the house, was allowed to fertilise itself spon- 
taneously. The seeds thus obtained were placed on damp sand, 
and as they germinated in pairs of equal age were planted on 
the opposite sides of four very large pots; nevertheless they 
were considerably crowded. The pots were kept in the hothouse. 
The plants were first measured to the tips of their leaves when 
only between 1 and 2 feet in height, as shown in the following 
table: 

TABLE XCVIL 
Zea mays. 



No. of Pot. 


Crossed Plants. 


Self-fertilised Plants. 


I. 


Inches. 
23 j 
12 
21 


Inches. 
17| 
20 1 
20 


II. 


22 
191 

21| 


20 

191 

18! 


III. 


22 J 
20i 
18 
21 

23 


18| 

I 5 i 

16f 
18 
16| 


IV. 


21 
22 J 
23 
12 


18 
12| 

IN 

18 


Total in inches. 


302-88 


263-63 



The fifteen crossed plants here average 20 '19, and the fifteen 
self-fertilised plants 17 '57 inches in height; or as 100 to 87. 
Mr. Galton made a graphical representation, in accordance with 
the method described in the introductory chapter, of the above 



male flowers usually shed their K. Akad.' 
pollen before the female flowers p. 743. 
we mature: ' Mouatsbericht der 



Berlin, Oct. 1872, 



CHAP. VI. PHALAEIS CANARIENSIS. 285 

measurements, and adds the words " very good " to the curves 
thus formed. 

Shortly afterwards one of the crossed plants in Pot I. died ; 
another became much diseased and stunted ; and the third never 
grew to its full height. They seemed to have been all injured, 
probably by some larva gnawing their roots. Therefore all 
the plants on both sides of this pot were rejected in the subse- 
quent measurements. When the plants were fully grown they 
were again measured to the tips of the highest leaves, and the 
eleven crossed plants now averaged 68*1, and the eleven self- 
fertilised plants 62 34 inches in height ; or as 100 to 91. In all 
four pots a crossed plant flowered before any one of the self-fer- 
tilised ; but three of the plants did not flower at all. Those that 
flowered were also measured to the summits of the male flowers : 
the ten crossed plants averaged 66 '51, and the nine self-fertilised 
plants 61 59 inches in height ; or as 100 to 93. 

A large number of the same crossed and self-fertilised seeds 
were sown in the middle of the summer in the open ground in 
two long rows. Very much fewer of the self-fertilised than of 
the crossed plants produced flowers ; but those that did flower, 
flowered almost simultaneously. "When fully grown the ten 
tallest plants in each row were selected and measured to the 
tips of their highest leaves, as well as to the summits of their 
male flowers. The crossed averaged to the tips of their leaves 
54 inches in height, and the self-fertilised 44 "65, or as 100 
to 83; and to the summits of their male flowers, 53 '96 and 
43-45 inches; or as 100 to 80. 

PHALABIS CAKABIENSIB. 

Hildebrand has shown in the paper referred to under the 
last species, that this hermaphrodite grass is better adapted 
for cross-fertilisation than for self-fertDisation. Several plants 
were raised in the greenhouse close together, and their flowers 
were mutually intercrossed. Pollen from a single plant growing 
quite separately was collected and placed on the stigmas of the 
same plant. The seeds thus produced were self-fertilised, for 
they were fertilised with pollen from the same plant, but it will 
have been a mere chance whether with pollen from the same 
flowers. Both lots of seeds, after germinating on sand, were 
planted in pairs on the opposite sides of four pots, which were 
kept in the greenhouse. "When the plants were a little over a 



236 



PHALARIS CANARIENSIS. 



CHAP. VL 



foot in height they were measured, and the crossed plants 
averaged 13 '38, and the self-fertilised 12 '29 inches in height; 
or as 100 to 92. 

When in full flower they were again measured to the ex- 
tremities of their culms, as shown in the following table : 

TABLE XCVIH. 

Phalaris canariensis. 



Xo. ufPot. 


Crossed Plants. 


Self-fertilised Plants. 


L 


Inches. 

42 
39 


Inches. 
41 
45| 


H. 


37 
49 1 
29 
37 


31 
37 
42 
34 




IIL 


37 

II 1 


28 
28 
34 


IV. 


8' 


35 1 
l 


Total in inches. 


428-00 


392-63 



The eleven crossed plants now averaged 38 9, and the eleven 
self-fertilised plants 35 -69 inches in height; or as 100 to 92, 
which is the same ratio as before. Differently to what occurred 
with the maize, the crossed plants did not flower before the self- 
fertilised; and though both lots flowered very poorly from 
having been kept in pots in the greenhouse, yet the self-fertilised 
plants produced twenty-eight flower-heads, whilst the crossed 
produced only twenty ! 

Two long rows of the same seeds were sown out of doors, and 
care was taken that they were sown in nearly equal number : 
but a far greater number of the crossed than of the self-fertilised 
seeds yielded plants. The self-fertilised plants were in con- 
sequence not so much crowded as the crossed, and thus had an 
advantage over them. When in full flower, the twelve tallest 
plants were carefully selected from both rows and measured, 
as shown in the following table : 



CHAP. VI. 



PHALARIS OANARIENSIS. 



237 



TABLE XCIX. 
Phdlaris canariensis (growing in the open ground). 



Crossed Plants, twelve 
tallest. 


Self-fertilised Plants, 
twelve tallest. 


Inches. 


Inches. 


34 i 


35 g 


35 


31J 


36 


33 


35, 




32 


35 




31 1 


36 




36 


36 




33 


38 




32 


36 




35 J 


35 




33 1 


34 




34 


34, 




35 


T tadb(} 429-5 


402-0 



The twelve crossed plants here average 85 '78, and the tweivo 
self-fertilised 33*5 inches in height ; or as 100 to 93. In this 
case the crossed plants flowered rather before the self-fertilised, 
and thus differed from those growing in the pots. 



238 SUMMARY OF MEASUREMENTS. CHAP. VII. 



CHAPTER VII. 

SUMMARY OF THE HEIGHTS AND WEIGHTS or THE CROSSED AND 
SELF-FEBTILISED PLANTS. 

Number of species and plants measured Tables given Preliminary 
remarks on the offspring of plants crossed by a fresh stock Thirteen 
cases specially considered The effects of crossing a self-fertilised 
plant either by another self-fertilised plant or by an intercrossed plant 
of the old stock Summary of the results Preliminary remarks on 
the crossed and self-fertilised plants of the same stock The twenty- 
six exceptional cases considered, in which the crossed plants did not 
exceed greatly in height the self-fertilised Most of these cases 
shown not to be real exceptions to the rule that cross-fertilisation 
is beneficial Summary of results Kelative weights of the crossed 
and self-fertilised plants. 

THE details which have been given under the head 
of each species are so numerous and so intricate, that 
it is necessary to tabulate the results. In Table A, the 
number of plants of each kind which were raised from 
a cross between two individuals of the same stock and 
from self-fertilised seeds, together with their mean 
or average heights at or near maturity, are given. In 
the right-hand column, the mean height of the crossed 
to that of the self-fertilised plants, the former being 
taken as 100, is shown. To make this clear, it may 
be advisable to give an example. In the first genera- 
tion of Ipomcea, six plants derived from a cross 
between two plants were measured, and their mean 
height is 86 '00 inches; six plants derived from 
flowers on the same parent-plant fertilised with their 
own pollen were measured, and their mean height is 
65 66 inches. From this it follows, as shown in the 
right-hand colnmn, that if the mean height of the 
crossed plants be taken as 100, that of the self-fer- 



CHAP. VII. SUMMARY OF MEASUREMENTS. 239 

tilised plants is 76. The same plan is followed with 
all the other species. 

The crossed and self-fertilised plants were generally 
grown in pots in competition with one another, and 
always under as closely similar conditions as could 
be attained. They were, however, sometimes grown in 
separate rows in the open ground. With several of 
the species, the crossed plants were again crossed, and 
the self-fertilised plants again self-fertilised, and thus 
successive generations were raised and measured, as 
may be seen in Table A. Owing to this manner of 
proceeding, the crossed plants became in the later 
generations more or less closely inter-related. The 
later generations of Mimulus are not included, as a 
new tall variety then prevailed on one side alone, so 
that a fair comparison between the two sides was no 
longer possible. With Ipomoea the variety Hero has 
been excluded for nearly the same reason. 

In Table B the relative weights of the crossed and 
self-fertilised plants, after they had flowered and had 
been cut down, are given in the few cases in which 
they were ascertained. The results are, I think, more 
striking and of greater value as evidence of constitu- 
tional vigour than those deduced from the relative 
heights of the plants. 

The most important table is that of C, as it includes 
the relative heights, weights, and fertility of plants 
raised from parents crossed by a fresh stock (that is, by 
non-related plants grown under different conditions), 
or by a distinct sub-variety, in comparison with self- 
fertilised plants, or in a few cases with plants of the 
same old stock intercrossed during several generations. 
The relative fertility of the plants in this and the 
other tables will be more fully considered in a future 
chapter. 



240 



SUMMARY OF MEASUREMENTS. 



CHAP. VII 



TABLE A. Relative Heights of Plants from Parents crossed with 
Pollen from other Plants of the same Stock, and self -fertilised . 










j, 


S3 


T7T 




I . 


I 


a"S 


if J 


fl 




B| 


S| 


ij 


-1 


1J 


NAMES OF PLANTS. 


II 

s! 


15 

la 


i| 


11 


E.e - 
"5 *" S'o" 




p 


f 


1 Number 
1 lised PI 


Average 
fertilised 


III! 


Ipomoea purpurea 1st generation 


6 


86-00 


6 


65-66 


as 100 to 76 


Ipomoea purpurea 2nd generation 


6 


84-16 


6 


66-33 


n 79 


Ipomoea purpurea 3rd generation 


6 


77-41 


6 


52-83. 


?! 68 


Ipomcea purpurea 4th generation 
Ipomcea purpurea 5th generation 
Ipomcea purpurea 6th generation 


7 
6 
6 


69-78 
82-54 
87-50 


7 
6 
6 


60-14 
62-33 
63-16 


n 86 

,, 75 
,. 72 


Ipomcea purpurea 7th generation 
Ipomcea purpurea 8th generation 
Ipomcea purpurea 9th generation 


9 
8 
14 


83-94 
113-25 
81-39 


9 
8 
14 


68-25 
96-65 
64-07 


81 
85 
79 


Ipomcea purpurea-lOth generation 
Number and average height of all 


5 


93-70 


5 


50-40 




the plants of the ten genera- 


73 


85-84 


73 


66-02 


> 77 


tions . 












Mimulus luteus three first gene- 












rations, before the new and taller 


10 


8-19 


10 


5-29 


it 65 


self-fertilised variety appeared 












Digitalis purpurea . 


16 


51-33 


8 


35 -.87 


70 


Calceolaria (common greenhouse} 
varietv^ 1 


1 


19-50 


1 


15-00 


77 


Linaria vulgaris . ... 


3 


7-08 


3 


5-75 


n 81 


Verbascum thapsus . . . . 


6 


65-34 


6 


56-50 


86 


Vandellia nummularifolia crossed ) 












and self-fertilised plants, raised | 


20 


4-30 


20 


4-27 


99 


from perfect flowers . . . . J 












Vandellia nummularifolia crossed 












and self-fertilised plants, raised 
from perfect flowers : second 


24 


3-60 


24 


3-38 


94 


trial, plants crowded . . . 












Vandellia nummularifolia crossed \ 












plants raised from perfect flowers, 1 
and self-fertilised plants fromj 


20 


4-30 


20 


4-06 


34 


cleistogene flowers . . . . J 
Gesneria pendulina 


8 


32 06 


8 


29-14 


90 


Salvia coccinea 


6 


27*85 


6 


21-16 




Origanum vulgaro 


4 


20-00 


4 


17-12 


86 


Thnnbergia alata 


6 


60-00 


6 


65-00 


it 108 




9 


41-08 


9 


39-00 


95 


Iberis umbellata the self-fertilised \ 












plants of the 3rd generation . / 


7 


19-12] 


7 


16-39 


n > * 



CHAP. VII. SUMMARY OF MEASUREMENTS. 

TABLE A continued. 



241 





1 


I 


!,: 


1| 


I'S| 


N MBS OF PLANTS. 


r the Cro< 
measured. 


ight of Crc 
in inches. 


the Se!f-f 
its measure 


fl 


il 




1 


3 


a 


MR 

ftl 


,2 o d 2 




S. 


f 


fj 


fl 


til! 
Jell 


Papaver vagum 


15 


21-91 


15 


19*54 


as 100 to 89 


Eschscholtzia californica English} 
stock, 1st generation . . . / 


4 


29-68 


4 


25-56 


ii 86 


Eschscholtzia californica English "1 
stock, 2nd generation . . ./ 


11 


32-47 


11 


32-81 


101 


Eschscholtzia californica Bra-} 
zilian stock, 1st generation . . / 


14 


44-64 


14 


45-12 


,, 101 


Eschscholtzia californica Bra- 
zilian stock, 2nd generation. . 


18 


43-38 


19 


50-30 


,, ,, H6 


Eschschjltzia californica average 












height and number of all the 


47 


40-03 


48 


42-72 


ii ii 107 


plants of Eschscholtzia . . . 












Re.->eda lutea grown in pots . 


24 


17-17 


24 


14-61 


,, 85 


Reseda lutea grown in open ground 


8 


28-09 


8 


23-14 


" ,, 82 


Reseda odorata self - fertilised 












seeds from a highly self-fertile 


19 


27-48 


19 


22-55 


82 


plant, grown in pots. . . 
Reseda odorata self -fertilised 












seeds from a highly self-fertile 


8 


25-76 


8 


27-09 


105 


plant, grown in open ground . 
Reseda odorata self- fertilised 












seeds from a semi-self-sterile 


20 


29-98 


20 


27-71 


ii ii 92 


plant, grown in pots. . . . 












Reseda odorata self -fertilised 












seeds from a semi-self-steril 


8 


25-92 


8 


23-54 


,, 90 


plant, grown in open ground . 
Viola tricolor . 


14 


5-58 


14 


2-37 


42 


\donis sostivalis . . 


4 


14-25 


4 


14-31 


ii ii *^ 

100 


Delphinium consolida .... 


6 


14-95 


6 


12-50 


;; ;; 84 


Viscaria oculata . . . 


15 


34-50 


15 


33-55 


97 


Dianthus caryophyllus opeu^ 
ground, about . . . . \ 


3? 


28? 


6? 


24? 


,, ,, 86 


Dianthus caryophyllus 2nd gen-1 
eration, in pots, crowded . . J 


2 


16-75 


2 


9-75 


,, 58 


Dianthus caryophyllus 3rd gen-1 
eration, in pots j 


8 


28-39 


8 


28-21 


99 


Dianthus caryophyllus offspring^ 












from plants of the 3rd self- ferti- 












lised generation crossed by inter- 1 
crossed plants of 3rd generation, 


15 


28-00 


10 


26-55 


>i 95 


compared with plants of 4th self- 
fertilised generation .... 













242 



SUMMABY OF MEASUREMENTS. 
TABLE A continued. 



CHAP. VII. 







1 


i 


4 


jd| 




i 





Si 


$ 


~<I 




*P 


o 


~ a 


<*--S 


*g j <2 




1- 


gl 


& g 


.s 


5?*. 


NAMES OF PLANTS. 


Jl 


"iS 


fl 


11 


ifii 




{2 

L. 


W 

1 


1 Number < 
lised Pli 


ij 

li 


ii 


Dianthus caryophyllus number! 












and average height of all the 
plants of Dianthus . . . . j 


31 


27-37 


26 


25-18 


as 100 to 92 


Hibiscus africanus 


4 


13-25 


4 


14-43 


109 


Pelargonium zonale .... 


7 


22-35 


7 


16-62 


" " 74 


Tropsjolum minus ..... 


8 


58-43 


8 


46-00 


79 


Limnanthes douglasii .... 


16 


17-46 


16 


13-85 


11 79 


Lupinus luteus 2nd generation . 
Lupinus pilosus plants of two) 


8 
2 


30-78 
35-50 


8 
3 


25-21 
30-50 


,, 82 


Phaseolus multiflorus .... 


5 


86-00 


5 


82-35 


96 


Pisum sativum ..... 


4 


34-62 


4 


39-68 


115 


Sarothamnus scoparius small} 
seedlings . . . , J 


6 


2-91 


6 


1-33 




Sarothamnus scoparius the three! 












survivors on each side after three > 




18-91 




11-83 


63 


years' growth ) 












Ononis minutissima .... 


2 


19-81 


2 


17-37 


88 


Clarkia elegans ...... 


4 


33-50 


4 


27-62 


82 


Bartonia aurea 


8 


24-62 


8 


26-31 


107 


Passiflora gracilis ..... 


2 


49-00 


2 


51-00 


" '^ 104 


Apium petroselinum .... 




not 




not 
measured. 


[ 100 


Scabiosa atro-purpurea .... 


4^ 


17-12 


4 


15-37 


M 90 


Lactuca sativa plants of two gen-} 
erations j 


7 


19-43 


6 


16-00 


82 


Specularia speculum .... 


4 


19-28 


4 


18-93 


it 98 


Lobelia ramosa 1st generation . 


4 


22-25 


4 


18-37 


>i 82 


Lobelia ramosa 2nd generation . 


3 


23-33 


3 


19-00 


it 81 


Lobelia fulgens 1st generation . 


2 


34-75 


2 


44-25 


>, ' 127 


Lobelia fulgens 2nd generation . 


23 


29-82 


23 


27-10 


91 


Nemophila insignis half-grown . 
Nemophila insignis the same fully j 
grown ... . . . . / 


12 


11-10 
33-28 


12 


5-45 
19-90 


i> 60 


Borago officinalis 


4 


20-68 


4 


21-18 


102 


\olana prostrata ..... 


5 


12-75 


5 


13-40 




Petunia violacea 1st generation . 


5 


30-80 


5 


26-00 


" 84 


Petunia violacea 2nd generation . 
Petunia violacea 3rd generation . 
Petunia violacea 4th generation . 


4 
8 
15 


40-50 
40-96 
46-79 


6 
8 
14 


26-25 
53-87 
32-39 


!! I 69 



CHAP. VII. SUMMARY OF MEASUREMENTS. 

TABLE A. continued. 



243 









!_ 


!! 


||| 


NAMES OF PLANTS. 


r of the Cr 

ntg measured 


3 height of Ci 
ints In inches 


1 


1 


1| 




f 


r 


P 


5* 


{111 


Petunia Yiolacea 4th generation,) 
from a distinct parent . . ,J 


13 


44-74 


13 


26-87 


as 100 to 60 


Petunia violacea 5th generation . 


22 


54-11 


21 


33-23 


61 


Petunia violacea 5th generation,) 
in open ground . . . . . 1 


10 


38-27 


10 


23-31 


61 


Petunia violacea Number and j 












average height of all the plants 


67 


46-53 


67 


33-12 


71 


in pots of Petunia . . . . j 
Nicotiana tabacum 1st generation 
Nicotiana tabacum 2nd generation 
Nicotiana tabacum 3rd generation 


4 
9 
7 


18-50 
53-84 
95-25 


4 

7 
7 


32-75 
51-78 
79-60 


" " 96 
83 


Nicotiana tabacum 3rd generation} 
but raised from a distinct plant J 


7 


70-78 


9 


71-30 


,, 101 


Nicotiana tabacum number and 












average height of all the plants 


27 


63-73 


27 


61-31 


96 

i ii 


of Nicotiana . 












Cyclamen persicum 


8 


9-49 


8? 


7-50 


> 79 


\na cp allis collina ..... 


6 


42-20 


6 


33-35 


69 


Primula sinensis a dimorphic 
species 


8 


9-01 


8 


9-03 


100 


Fagopyrnm esculentum a dimor- 
phic species 


15 


'38-06 


15 


26-13 


69 


Beta vulgaris in pots. 


8 


34-09 


8 


29-81 


i, 87 


Beta vulgaris in open ground 


8 


30-92 


8 


30-70 


99 


Canna warscewiczi plants of three' 
venerations . 


34 


35-98 


34 


36-39 


101 


Zea mays in pots, whilst young,' 
measured to tips of leaves . 


15 


20-19 


15 


17-57 


87 


Zea mays when full grown, after 












the death of some, measured to 




68-10 




62-34 


91 


tips of leaves 












Zea mays when full grown, after 












the death of some, measured to 




66-51 




61-59 


93 


tips of flowers ..... 












Zea mays grown in open ground, 
measured to tips of leaves . 


10 


54-00 


10 


44-55 


.1 83 


Zea mays grown in open ground,' 
measured to tips of flowers . 




53-96 




43-45 


80 


Phalaris canariensis in pots . . 


11 


38-90 


11 


35-69 


ii 92 


Phalaris canariensis in open ground 


12 


35-78 


12 


33-50 


i 93 



R 2 



244 



SUMMARY OF MEASUREMENTS. 



CHAP. VII. 



TABLE B. Relative Weights of Plants from Parents crossed with 
Pollen from distinct Plants of the same Stock, and Self-fertilised. 



NAMES OF PLANTS. 


Number 
of Crossed 
Plants. 


Number 
of Self- 
fertilised 
Plants. 


Weight of the 
Crossed Plants 
taken as 100. 


Ipomoea purpurea plants of the 10th"l 


6 


6 


as 100 to 44 


Vandellia nummularifolia 1st genera- \ 
tion J 


41 


41 


97 


Brassica oleracea 1st generation . . 
Eschscholtzia californica plants of the"! 
2nd generation ....../ 
Reseda lutea 1st generation, grown in| 
pots / 
Reseda lutea 1st generation, grown inj 


9 
19 

24 
8 


9 
19 

24 
8 


37 
118 

21 
,, 40 


Reseda odorata 1st generation, de- 
scended from a highly self-fertile 
plant, grown in pots 
Reseda odorata 1st generation, de- 
scended from a semi-self-sterile plant, 


19 
20 


19 
20 


67 
9- 


Dianthus caryophyllus plants of the"l 
3rd generation / 
Petunia violacea plants of the 5thj 
generation, in pots / 
Petunia violacea plants of the 5th) 
generation, in open ground . . . J 


8 

22 
10 


8 
21 
10 


,, ,. 49 
,, 22 
36 



CHAP. VII. 



SUMMARY OF MEASUREMENTS. 



245 



TABLE C. Relative Heights, Weights, and Fertility of Plants fron 
Parents crossed by a fresh Stock, and from Parents either self- 
fertilised or intercrossed with Plants of the same Stock. 





<9 


1 


il 


1 


11 




Q 


| 


If* 


1 


|l| 


NAMES OF PLANTS AND NATURE 


1* 


i| 


J B . 


"t fcn 




OF THE EXPERIMENTS. 


J| 


P 


ill 


fi 


*a'V-'CQ 




P 


! 


ill 


f 


II 


Ipomoea purpurea offspring of\ 
plants intercrossed for nine gen- 












erations and then crossed by a| 
fresh stock, compared withj 


19 


84-03 


19 


65-78 


as 100 to 76 


plants of the 10th intercrossed 












generation J 












Ipomcea purpurea offspring of 
plants intercrossed for nine gen- 
erations and then crossed by a 












fresh stock, compared with 












51 


plants of the 10th intercrossed 












generation, in fertility . 












Mimulus luteus offspring of plants i 
self-fertilised for eight genera- 1 












tions and then crossed by a fresh > 


28 


21-62 


19 


10-44 


, 52 


stock, compared with plants ofl 












the 9th self-fertilised generation^ 












Mimulus luteus offspring of plan ts^ 












self-fertilised for eight genera- 












tions and then crossed by a fresh 1 










> 


stock, compared with plants off 













the 9th self-fertilised generation, 












in fertility J 












Mimulus luteus offspring of plants 












self-fertilised for eight genera- 












tions and then crossed by a fresh 












stock, compared with the off- 












spring of a plant self-fertilised 


28 


21-62 


27 


12-20 


58 


for eight generations, and then 












intercrossed with another self- 












fertilised plant of the same gen- 













246 



SUMMAKY OF MEASUREMENTS. 
TABLE C continued. 



CHAP. VIL 





H 


| 


,m Self- 
Parents J 


1 


flj 


HAMES OF PLANTS AND NATURE 


1 


1* 


ii 


k 


III 


OF THE EXPERIMENTS. 


If 


1* 


!! 


1* 


III 




II 


1 


ill 


1 


+f V 3 




Z 


< 


i* 


H 


K 


Mimulusluteus offspring of plants 












self-fertilised for eight genera- 












tions and then crossed by a fresh 












stock, compared with the off- 












spring of a plant self-fertilised 
for eight generations, and then 












as 100 to 4 


intercrossed with another self- 












fertilised plant of the same gen- 












eration, in fertility .... 












Brassica oleracea offspring of) 












plants self-fertilised for two gen- 












erations and then crossed by a! 












fresh stock, compared withj 










n )> -'- 


plants of the 3rd self-fertilised 












generation, by weight . . J 












Iberis umbellata offspring froml 












English variety crossed by 












slightly different Algerine va-j 
riety, compared with the self- j 


30 


17-34 


29 


15-51 


89 


fertilised offspring of the English 












variety . 












Iberis umbel lata offspring from 












English variety, crossed by 












slightly different Algerine 












variety, compared with the self- 














75 


fertilised offspring of the English 












variety, in fertility .... 












Eschscholtziacalifornica offspring 1 ) 












of a Brazilian stock crossed byl 












an English stock, compared with> 


19 


45-92 


19 


50-30 


109 

" " 


plants of the Brazilian stock of 












the 2nd self-fertilised generation] 












Eschscholtziacalifornica offspring 












of a Brazilian stock crossed by 












an English stock, compared with 
plants of the Brazilian stock of 


.. 


.. 


. . 


. . 


,. 118 


the 2nd self-fertilised generation, 












in weight 













VII. SUMMARY OF MEASUREMENTS. 

TABLE C continued. 



247 





9,' 


1 


if 


1 


f|3 




"a"? 


1 


I; 


I 


!j 


NAMES OF PLANTS AND NATURE 
OF THE EXPERIMENTS. 


of the Plan 
with a Fresh 


S! 

i* 


i 


9 


Ml 

III 




|1 


Average 


ji! 


I 


flfi 


Eschscholtzia californica offspring"! 












of a Brazilian stock crossed by 












an English stock, compared with! 
plants of the Brazilian stock off 


.. 




.. 


.. 


as 100 to 40 


the 2nd self-fertilised generation, 












in fertility .... J 












Eschscholtzia californica offspring 












of a Brazilian stock crossed by 












an English stock, compared with 
plants of the Brazilian stock of 


19 


45-92 


18 


43-38 


94 


the 2nd intercrossed generation, 












in height 












Eschscholtzia californica offspring' 












of a Brazilian stock crossed by 












an English stock, compared with 












plants of the Brazilian stock of 













100 


the 2nd intercrossed generation, 












in weight 












Eschscholtzia californica offspring^ 












of a Brazilian stock crossed by 












an English stock, compared with! 
plants of the Brazilian stock off 


.. 


,. 


.. 


.. 


i **** 


the 2nd intercrossed generation, 












in fertility J 












Dianthus caryophyllus offspring^ 
of plants self-fertilised for three 












generations and then crossed by! 
a fresh stock, compared withf 


16 


32-82 


10 


26-55 


> 81 


plants of the 4th self-fertilised 












generation, . ) 












Dianthus caryophyllus offspring 1 ) 
of plants self-fertilised for three 












generations and then crossed by! 










" 


a fresh stock, compared withf 








' ' 


" 


n w * 


plants of the 4th self-fertilised 












generation, in fertility . . .J 













248 



SUMMAEY OF MEASUREMENTS. 



CHAP.YIL 



TABLE continued. 





09 

a* 


1 


if 


1 


m 




IS 

s So 


1 


I 




ill 


NAMES OF PLANTS AND NATURE 
OF THE EXPERIMENTS. 


II 


S 


1 


P 


III 




Number 
Cross 


! 


ft 


I 


fi 1 


Dianthus caryophyllus offspring 












of plants self-fertilised for three 
generations and then crossed by 
a fresh stock, compared with the 
offspring of plants self-fertilised 
for three generations and then 


16 


32-82 


15 


28-00 


as 100 to 85 


crossed by plants of the 3rd 












intercrossed generation . . .. 












Dianthus caryophyllus offspring 












of plants self-fertilised for three 












generations and then crossed by 
a fresh stock, compared with the 












offspring of plants self-fertilised 






.. 




45 


for three generations and then 












crossed by plants of the 3rd 












intercrossed generation, in fer- 












tility 












Pisum sativum offspring from a' 












cross between two closely allied 












varieties, compared with the self- 


p 




p 




If 


fertilised offspring of one of the 










" " JTC 


varieties, or with intercrossed 










(75 


plants of the same stock 












Lathyrus odoratus offspring from 












two varieties, differing only in 












colour of their flowers, compared 
with the self-fertilised offspring 


2 


79-25 


2 


63-75 


80 


of one of the varieties : in 1st 
























Lathyrus odoratus offspring froml 
two varieties, differing only in 












colour of their flowers, compared 1 
with the self-fertilised offspring f 


6 


62-91 


6 


55-31 


,. 88 


of one of the varieties : in 2nd! 





































CHIP. VU. SUMMARY OF MEASUEEMENT8. 

TABLE C continued. 



249 



NAMES OF PLANTS AND NATURE 
OF THE EXPERIMENTS. 


1 Number of the Plants from a 
Cross with a Fresh Stock. 


Average Height in inches and 
Weight 


9 

i 


Average Height in Inches and 
Weight 


Height, Weight, and Fertility 
of the Plants from the Cross 
with a Fresh Stock taken as 

* 


Petunia violacea offspring of 
plants self-fertilised for four 
generations and then crossed by 
a fresh stock, compared with 
plants of the 5th self-fertilised 
generation, in height 
Petunia violacea offspring of 
plants self-fertilised for four 
generations and then crossed by 


21 


50-05 


21 


33-23 


as 100 to 66 
> 2H 


a fresh stock, compared with 
plants of the 5th self-fertilised 
generation, in weight . . 
Petunia violacea offspring of 
plants self-fertilised for four 
generations and then crossed by 
a fresh stock, compared with 
plants of the 5th self-fertilised 
generation, grown in open ground, 


10 


36-67 


10 


23-31 


63 


Petunia violacea offspring of 
plants self-fertilised for four 
generations and then crossed by 
a fresh stock, compared with 
plants of the 5th self-fertilised 
generation, grown in open ground, 








" 


' 


* ., 53 


Petunia violacea offspring of 
plants self-fertilised for four 
generations and then crossed by 
a fresh stock, compared with 
plants of the 5th self-fertilised 
generation, grown in open ground, 
in fertility 














46 


Petunia violacea offspring of 
plants self-fertilised for four 
generations and then crossed by 
a fresh stock, compared with 
plants of the 5th intercrossed 
generation, in height . . 


21 


50-05 


22 


54-11 


108 



250 SUMMARY OF MEASUREMENTS. 

TABLE C continued. 



CHAP. VII. 





c* 


1 
1 


fromSelf- 
a Parent* 


1 
1 


U 1 




II 


L 


II 


a 
c ** 


|i| 


NAMES OF PLANTS AND NATURE 


P 


11 


1L 






OF THE EXPERIMENTS. 


~ja 


jS 


jll 


II 


|f| 




1 Number of 
Cross wit 


* 


I 


3r 

1 
3 


|fl 


Petunia violacea offspring of 












plants self-fertilised for four 












generations and then crossed by 
a fresh stock, compared with 


.. 


.. 


.. 


.. 


as 100 to 101 


plants of the 5th intercrossed 












generation, in weight . . 












Petunia violacea offspring ofj 












plants self fertilised for four 












generations and then crossed by 
a fresh stock, compared with I- 


10 


33-67 


10 


38-27 


,, .j lU't 


plants of the 5th intercrossed 












generation, grown in open ground, 
























Petunia violacea offspring of) 












plants self-fertilised for four 












generations and then crossed by 
a fresh stock, compared with^ 










146 


plants of the 5th intercrossed 












generation, grown in open ground, 












in weight. 












Petunia violacea offspring of 












plants self-fertilised for four 












generations and then crossed by 












a fresh stock, compared with 


, . 




m . 




54 


plants of the 5th intercrossed 












generation, grown in open ground, 












. infertility , 












Nicotiana tabacum offspring of) 
plants self-fertilised for three 












generations and then crossed Ly 
a slightly different variety, com- 1 
pared with plants of the 4th f 


,6 


63-29 


26 


41-67 


66 


self-fertilised generation, grown 












not much crowded in pots, in 












height ... . J 




























CHAP. VII. 



SUMMARY OF MEASUREMENTS. 



251 



TABLE C continued. 





** 


1 


it 


1 


ti; 




jjS 


I 


!i 


1 


1*! 


AMES OF PLANTS AND NATURE 


'II 


'as 


IL 


1-a 


3J| 


OF T11E EXPERIMENTS. 


I* 


fl 


SI? 


iS 


III 




sf 


w 




w 


s 




|J 



jjj 


1 


! 


|?fl 


Nicotiana tabacum offspring oft 












plants self-fertilised for three 












generations and then crossed by! 












a slightly different variety, com-> 


12 


31-53 


12 


17-21 


as 103 to 54 


pared with plants of the 4th 












self-fertilised generation, grown! 












much crowded in pots, in height] 












Nicotiana tabacum offspring oft 












plants self-fertilised for three 












generations and then crossed by I 












a slightly different variety, com- > 


, . 


. . 


.. 


.. 


37 


pared with plants of the 4th 












self- fertilised generation, grown! 












much crowded in pots, in weight] 












Nicotiana tabacum offspring of 












plants self-fertilised for three 












generations and then crossed by 
a slightly different variety, com- 


20 


48-74 


20 


35-20 


72 


pared with plants of the 4th 












self-fertilised generation, grown 












in open ground, in height . 












Sicotiana tabacum offspring of 












plants self-fertilised for three 












generations and then crossed by 










63 


pared with plants of the 4th 












self-fertilised generation, grown 












in open ground, in weight . 












Anagallis collina offspring from a 
Jed variety crossed by a blue 












\ariety, compared with the selt- 


3 


27-62 


3 


18 21 


i n & 


fertilised offspring of the red 

























252 SUMMARY OF MEASUREMENTS. 

TABLE C continued. 



CHAI-. VIL 





cs 


I 


1 


1 


i 


NAMES OF PLANTS AND NATURE 


li 


is 


II 


|i 


511 


OF THE EXPERIMENTS. 


*! 


Sfe 


**i 


3? 


111 




li 


w 

ft 




ft 


lie 




|l 


0> 


i 


& 
t 


m 


Anagallis collina offspring from a 












red variety crossed by a blue 












variety, compared with the self- 




> - t 






as 100 to 6 


fertilised offspring of the red 












variety, in fertility .... 












Primula veris offspring from long- 












styled plants of the 3rd illegiti- 












mate generation, crossed by a 
fresh stock, compared with 


8 


7-03 


8 


3-21 


46 


plants of the 4th illegitimate 












and self-fertilised generation 












Primula veris offspring from long- 
styled plants of the 3rd illegiti- 












mate generation, crossed by a 












fresh stock, compared with 


>< 








i> 5 


plants of the 4th illegitimate 












and self-fertilised generation, in 












'fertility . . . 












Primula veris offspring from long- 
styled plants of the 3rd illegiti- 












mate generation, crossed by a 












fresh stock, compared with 


9i 








f> 3 5 


plants of the 4th illegitimate 












and self-fertilised generation, in 












fertility in following year . 












Primula veris (equal-styled, red- 












flowered variety) offspring from 












plants self-fertilised for two 












generations and then crossed by a 


1 3 


8-66 


3 


7-33 


85 


different variety, compared with 












plants of the 3rd self-fertilised 
generation . 












Primula veris (equal-styled, red- 












flowered variety) offspring from 












plants self-fertilised for two 












generations and then crossed by a 










It 


different variety, compared with 












plants of the 3rd self-fertilised 












generation, in fertility . . . 













CHAP. VtL TABLE C. 253 

In tnese tkree tables the measurements of fifty-seven 
species, belonging to fifty-two genera and to thirty 
great natural families, are given. The species are 
natives of various parts of the world. The number 
of crossed plants, including those derived from a cross 
between plants of the same stock and of two different 
stocks, amounts to 1,101 ; and the number of self-fer- 
tilised plants (including a few in Table C derived 
from a cross between plants of the same old stock) 
is 1,076. Their growth was observed from the germi- 
nation of the seeds to maturity; and most of them 
were measured twice and some thrice. The various 
precautions taken to prevent either lot being unduly 
favoured, have been described in the introductory 
chapter. Bearing all these circumstances in mind, it 
may be admitted that we have a fair basis for judging 
of the comparative effects of cross-fertilisation and of 
self-fertilisation on the growth of the offspring. 

It will be the most convenient plan first to consider 
the results given in Table C, as an opportunity will thus 
be afforded of incidentally discussing some important 
points. If the reader will look down the right-hand 
column of this table, he will see at a glance what an 
extraordinary advantage in height, weight, and fer- 
tility the plants derived from a cross with a fresh stock 
or with another sub-variety have over the self-fertilised 
plants, as well as over the intercrossed plants of the 
same old stock. There are only two exceptions to this 
rule, and these are hardly real ones. In the case of 
Eschscholtzia, the advantage is confined to fertility. 
In that of Petunia, though the plants derived from a 
cross with a fresh stock had an immense superiority in 
height, weight, and fertility over the self-fertilised 
plants, they were conquered by the intercrossed plants 
of the same old stock in height and weight, but not 



254 SUMMARY OF MEASUREMENTS. CHAP. VII. 

in fertility. It has, however, been shown that the 
superiority of these intercrossed plants in height and 
weight was in all probability not real ; for if the two 
sets had been allowed to grow for another month, it is 
almost certain that those from a cross with the fresh 
stock would have been victorious in every way over 
the intercrossed plants. 

Before we consider in detail the several cases given 
in Table C, some preliminary remarks must be made. 
There is the clearest evidence, as we shall presently 
see, that the advantage of a cross depends wholly on 
the plants differing somewhat in constitution ; and that 
the disadvantages of self-fertilisation depend on the two 
parents, which are combined in the same hermaphrodite 
flower, having a closely similar constitution. A certain 
amount of differentiation in the sexual elements seems 
indispensable for the full fertility of the parents, and 
for the full vigour of the offspring. All the individuals 
of the same species, even those produced in a state of 
nature, differ somewhat, though often very slightly, 
from one another in external characters and probably in 
constitution. This obviously holds good between the 
varieties of the same species, as far as external characters 
are concerned ; and much evidence could be advanced 
with respect to their generally differing somewhat in 
constitution. There can hardly be a doubt that the 
differences of all kinds between the individuals and 
varieties of the same species depend largely, and as I 
believe exclusively, on their progenitors having been 
subjected to different conditions ; though the conditions 
to which the individuals of the same species are ex- 
posed in a state of nature often falsely appear to us the 
same. For instance, the individuals growing together 
are necessarily exposed to the same climate, and they 
seem to us at first sight to be subjected to identically 






CHAP. VII. TARLE C. 255 

the same conditions ; but this can hardly be the case, 
except under the unusual contingency of each individual 
being surrounded by other kinds of plants in exactly 
the 'same proportional numbers. For the surround- 
ing plants absorb different amounts of various sub- 
stances from the soil, and thus greatly affect the 
nourishment and even the life of the individuals of 
any particular species. These will also be shaded and 
otherwise affected by the nature of the surrounding 
plants. Moreover, seeds often lie dormant in the 
ground, and those which germinate during any one 
year will often have been matured during very different 
seasons. Seeds are widely dispersed by various means, 
and some will occasionally be brought from distant 
stations, where their parents have grown under some- 
what different conditions, and the plants produced 
from such seeds will intercross with the old residents, 
thus mingling their constitutional peculiarities in all 
sorts of proportions. 

Plants when first subjected to culture, even in their 
native country, cannot fail to be exposed to greatly 
changed conditions of life, more especially from 
growing in cleared ground, and from not having to 
compete with many or any surrounding plants. They 
are thus enabled to absorb whatever they require 
which the soil may contain. Fresh seeds are often 
brought from distant gardens, where the parent- 
plants have been subjected to different conditions. 
Cultivated plants like those in a state of nature 
frequently intercross, and will thus mingle their 
constitutional peculiarities. On the other hand, as 
long as the individuals of any species are culti- 
vated in the same garden, they will apparently be 
subjected to more uniform conditions than plants in a 
state of nature, as the individuals have not to compete 



256 SUMMAKY OF MEASUREMENTS. CHAP. VII. 

with various surrounding species. The seeds sown at 
the same time in a garden have generally been matured 
during the same season and in the same place ; and in 
this respect they differ much from the seeds sown by 
the hand of nature. Some exotic plants are not 
frequented by insects in their new home, and there- 
fore are not intercrossed ; and this appears to be a 
highly important factor in the individuals acquiring 
uniformity of constitution. 

In my experiments the greatest care was taken that 
in each generation all the crossed and self-fertilised 
plants should be subjected to the same conditions. 
Not that the conditions were absolutely the same, for 
the more vigorous individuals will have robbed the 
weaker ones of nutriment, and likewise of water when 
the soil in the pots was becoming dry ; and both lots 
at one end of the pot will have received a little more 
light than those at the other end. In the successive 
generations, the plants were subjected to somewhat 
different conditions, for the seasons necessarily varied, 
and they were sometimes raised at different periods of 
the year. But as they were all kept under glass, they 
were exposed to far less abrupt and great changes of 
temperature and moisture than are plants growing out 
of doors. With respect to the intercrossed plants, theii 
first parents, which were not related, would almosl 
certainly have differed somewhat in constitution ; and 
such constitutional peculiarities would be variously 
mingled in each succeeding intercrossed generation, 
being sometimes augmented, but more commonly 
neutralised in a greater or less degree, and sometimes 
revived through reversion ; just as we know to be the 
case with the external characters of crossed species and 
varieties. With the plants which were self-fertilised 
during the successive generations, this latter important 



CHAP. VII. TABLE C. 257 

source of some diversity of constitution will have been 
wholly eliminated ; and the sexual elements produced 
by the same flower must have been developed under as 
nearly the same conditions as it is possible to conceive. 

In Table C the crossed plants are the offspring of a 
cross with a fresh stock, or with a distinct variety ; and 
they were put into competition either with self-fertilised 
plants, or with intercrossed plants of the same old stock. 
By the term fresh stock I mean a non-related plant, 
the progenitors of which have been raised during some 
generations in another garden, and have consequently 
been exposed to somewhat different conditions. In the 
case of Nicotiana, Iberis, the red variety of Primula, the 
common Pea, and perhaps Anagallis, the plants which 
were crossed may be ranked as distinct varieties or 
sub-varieties of the same species ; but with Ipomoea, 
Mimulus, Dianthus, and Petunia, the plants which 
were crossed differed exclusively in the tint of their 
flowers ; and as a large proportion of the plants raised 
from the same lot of purchased seeds thus varied, the 
differences may be estimated as merely individual. 
Having made these preliminary remarks, we will now 
consider in detail the several cases given in Table C, 
and they are well worthy of full consideration. 

(1.) Ipomoea purpurea. Plants growing in the same 
pots, and subjected in each generation to the same 
conditions, were intercrossed for nine consecutive 
generations. These intercrossed plants thus became in 
the later generations more or less closely inter-related. 
Flowers on the plants of the ninth intercrossed genera- 
tion were fertilised with pollen taken from a fresh 
stock, and seedlings thus raised. Other flowers on the 
same intercrossed plants were fertilised with pollen 
from another intercrossed plant, producing seedlings of 
the tenth intercrossed generation. These two sets of 



258 SUMMARY OF MEASUREMENTS. CHAP. VII. 

seedlings were grown in competition with one another, 
and differed greatly in height and fertility. For the 
offspring from the cross with a fresh stock exceeded in 
height the intercrossed plants in the ratio of 100 to 78 ; 
and this is nearly the same excess which the inter- 
crossed had over- the self-fertilised plants in all ten 
generations taken together, namely, as 100 to 77. The 
plants raised from the cross with a fresh stock were 
also greatly superior in fertility to the intercrossed, 
namely, in the ratio .of 100 to 51, as judged by the 
relative weight of the seed-capsules produced by an 
equal number of plants of the two sets, both having 
been left to be naturally fertilised. It should be 
especially observed that none of the plants of either lot 
were the product of self-fertilisation. On the contrary, 
the intercrossed plants had certainly been crossed for the 
last ten generations and probably during all previous 
generations, as we may infer from the structure of the 
flowers and from the frequency of the visits of humble- 
bees. And so it will have been with the parent-plants 
of the fresh stock. The whole great difference in height 
and fertility between the two lots must be attributed to 
the one being the product of a cross with pollen from a 
fresh stock, and the other of a cross between plants of 
the same old stock. 

This species offers another interesting case. In the 
five first generations in which intercrossed and self- 
fertilised plants were put into competition with one 
another, every single intercrossed plant beat its self- 
fertilised antagonist, except in one instance, in w 
they were equal in height. But in the sixth gen 
ration a plant appeared, named by me the Hero, 
markable for its tallness and increased self-fertility, 
and which transmitted its characters to the next th 
generations. The children of Hero were again self- 




CHAP. VII. TABLE 0. 259 

fertilised, forming the eighth self-fertilised generation, 
and were likewise intercrossed one with another ; but 
this cross between plants which had been subjected 
to the same conditions and had been self-fertilised 
during the seven previous generations, did not effect 
the least good ; for the intercrossed grandchildren were 
actually shorter than the self-fertilised grandchildren, 
in the ratio of 100 to 107. We here see that the 
mere act of crossing two distinct plants does not by 
itself benefit the offspring. This case is almost the 
converse of that in the last paragraph, in which the 
offspring profited so greatly by a cross with a fresh 
stock. A similar trial was made with the descendants 
of Hero in the following generation, and with the same 
result. But the trial cannot be fully trusted, owing 
to the extremely unhealthy condition of the plants. 
Subject to this same serious cause of doubt, even a 
cross with a fresh stock did not benefit the great- 
grandchildren of Hero ; and if this were really the case, 
it is the greatest anomaly observed by me in all my 
experiments. 

(2.) Mimulus luteus. During the three first genera- 
tions the intercrossed plants taken together exceeded 
in height the self-fertilised taken together, in the ratio 
of 100 to 65, and in fertility in a still higher degree. 
In the fourth generation a new variety, which grew 
taller and had whiter and larger flowers than the old 
varieties, began to prevail, especially amongst the self- 
fertilised plants. This variety transmitted its characters 
with remarkable fidelity, so that all the plants in the 
later self-fertilised generations belonged to it. These 
consequently exceeded the intercrossed plants consider- 
ably -in height. Thus in the seventh generation the 
intercrossed plants were to the self-fertilised in height 
as 100 to 137. It is a more remarkable fact that the 

s2 



260 SUMMARY OF MEASUREMENTS. CHAP. VIL 

self-fertilised plants of the sixth generation had become 
much more fertile than the intercrossed plants, judging 
by the number of capsules spontaneously produced, in 
the ratio of 147 to 100. This variety, which as we 
have seen appeared amongst the plants of the fourth 
self-fertilised generation, resembles in almost all its 
constitutional peculiarities the variety called Hero, 
which appeared in the sixth self- fertilised generation 
of Ipomoea. No other such case, with the partial ex- 
ception of that of Nicotiana, occurred in my experi- 
ments, carried on during eleven years. 

Two plants of this variety of Mimulus, belonging to 
the sixth self-fertilised generation, and growing in 
separate pots, were intercrossed ; and some flowers on 
the same plants were again self-fertilised. From the 
seeds thus obtained, plants derived from a cross 
between the self-fertilised plants, and others of the 
seventh self-fertilised generation, were raised. But 
this cross did not do the least good, the intercrossed 
plants being inferior in height to the self-fertilised, in 
the ratio of 100 to 110. This case is exactly parallel 
with that given under Ipomoea, of the grandchildren 
of Hero, and apparently of its great-grandchildren ; 
for the seedlings raised by intercrossing these plants 
were not in any way superior to those of the cor- 
responding generation raised from the self-fertilised 
flowers. Therefore in these several cases the crossing 
of plants, which had been self-fertilised for several 
generations and which had been cultivated all the 
time under as nearly as possible the same conditions, 
was not in the least beneficial. 

Another experiment was now tried. Firstly, plants 
of the eighth self-fertilised generation were again 
self-fertilised, producing plants of the ninth self- 
lertilised generation. Secondly, two of the plants of the 



CHAP. VII. TABLE C. 261 

eighth self-fertilised generation were intercrossed one 
with another, as in the experiment above referred to ; 
but this was now effected on plants which had been 
subjected to two additional generations of self-fer- 
tilisation. Thirdly, the same plants of the eighth self- 
fertilised generation were crossed with pollen from 
plants of a fresh stock brought from a distant garden. 
Numerous plants were raised from these three sets of 
seeds, and grown in competition with one another 
The plants derived from a cross between the self-fer- 
tilised plants exceeded in height by a little the self- 
fertilised, viz., as 100 to 92; and in fertility in a greater 
degree, viz., as 100 to 73. I do not know whether 
this difference in the result, compared with that in the 
previous case, can be accounted for by the increased 
deterioration of the self-fertilised plants from two 
additional generations of self-fertilisation, and the 
consequent advantage of any cross whatever, although 
merely between the self-fertilised plants. But however 
this may be, the effects of crossing the self-fertilised 
plants of the eighth generation with a fresh stock were 
extremely striking ; for the seedlings thus raised were 
to the self-fertilised of the ninth generation as 100 to 
52 in height, and as 100 to 3 in fertility ! They were 
also to the intercrossed plants (derived from crossing 
two of the self-fertilised plants of the eighth generation) 
in height as 100 to 56, and in fertility as 100 to 4. 
Better evidence could hardly be desired of the potent 
influence of a cross with a fresh stock on plants which 
had been self-fertilised for eight generations, and had 
been cultivated all the time under nearly uniform 
conditions, in comparison with plants self-fertilised 
for nine generations continuously, or then once inter- 
crossed, namely in the last generation. 

(3.) Brassica oleraeea. Some flowers on cabbage 



262 SUMMARY OF MEASUREMENTS. CHAP. VII. 

plants of the second self-fertilised generation were 
crossed with pollen from a plant of the same variety 
brought from a distant garden, and other flowers were 
again self-fertilised. Plants derived from a cross with 
a fresh stock and plants of the third self-fertilised 
generation were thus raised. The former were to 
the self-fertilised in weight as 100 to 22 ; and this 
enormous difference must be attributed in part to 
the beneficial effects of a cross with a fresh stock, 
and in part to the deteriorating effects of self-fertilisa- 
tion continued during three generations. 

(4.) Iberis umbellata. Seedlings from a crimson 
English variety crossed by a pale-coloured variety 
which had been grown for some generations in Algiers, 
were to the self-fertilised seedlings from the crimson 
variety in height as 100 to 89, and as 100 to 75 in 
fertility. I am surprised that this cross with another 
variety did not produce a still more strongly marked 
beneficial effect ; for some intercrossed plants of the 
crimson English variety, put into competition with 
plants of the same variety self-fertilised during three 
generations, were in height as 100 to 86, and in 
fertility as 100 to 75. The slightly greater difference 
in height in this latter case, may possibly be attributed 
to the deteriorating effects of self-fertilisation carried 
on for two additional generations. 

(5.) Eschsclioltzia calif ornica. This plant offers an 
almost unique case, inasmuch as the good effects of a 
cross or the evil effects of self-fertilisation are confined 
to the reproductive system. Intercrossed and self- 
fertilised plants of the English stock did not differ 
in height (nor in weight, as far as was ascertained,) in 
any constant manner ; the self-fertilised plants usually 
having the advantage. So it was with the offspring 
of plants of the Brazilian stock, tried in the same 



CHAP. VII. TABLE C. 263 

manner. The parent-plants, however, of the English 
stock produced many more seeds when fertilised with 
pollen from another plant than when self-fertilised ; 
and in Brazil the parent-plants were absolutely sterile 
unless they were fertilised with pollen from another 
plant. Intercrossed seedlings, raised in England from 
the Brazilian stock, compared with self-fertilised seed- 
lings of the corresponding second generation, yielded 
seeds in number as 100 to 89 ; both lots of plants being 
left freely exposed to the visits of insects. If we now 
turn to the effects of crossing plants of the Brazilian 
stock with pollen from the English stock, so that 
plants which had been long exposed to very different 
conditions were intercrossed, we find that the off- 
spring were, as before, inferior in height and weight to 
the plants of the Brazilian stock after two genera- 
tions of self-fertilisation, but were superior to them 
in the most marked manner in the number of seeds 
produced, namely, as 100 to 40 ; both lots of plants 
being left freely exposed to the visits of insects. 

In the case of Ipomoea, we have seen that the 
plants derived from a cross with a fresh stock were 
superior in height as 100 to 78, and in fertility as 100 
to 51, to the plants of the old stock, although these 
had been intercrossed during the last ten generations. 
With Eschscholtzia we have a nearly parallel case, 
but only as far as fertility is concerned, for the plants 
derived from a cross with a fresh stock were superior 
in fertility in the ratio of 100 to 45 to the Brazilian 
plants, which had been artificially intercrossed in 
England for the two last generations, and which must 
have been naturally intercrossed by insects during all 
previous generations in Brazil, where otherwise they 
are quite sterile. 

(6.) Dianthus caryophyllus. Plants self-fertilised 



264 SUMMARY OF MEASUREMENTS. CHAP. VIL 

for three generations were crossed with pollen from a 
fresh stock, and their offspring were grown in compe- 
tition with plants of the fourth self-fertilised genera- 
tion. The crossed plants thus obtained were to the 
self-fertilised in height as 100 to 81, and in fertility 
(both lots being left to be naturally fertilised by 
insects) as 100 to 33. 

These same crossed plants were also to the off- 
spring from the plants of the third self-fertilised gene- 
ration crossed by the intercrossed plants of the cor- 
responding generation, in height as 100 to 85, and in 
fertility as 100 to 45. 

We thus see what a great advantage the offspring 
from a cross with a fresh stock had, not only over the 
self-fertilised plants of the fourth generation, but 
over the offspring from the self-fertilised plants of the 
third generation, when crossed by the intercrossed 
plants of the old stock. 

(7.) Pisum sativum. It has been shown under the 
head of this species, that the several varieties in this 
country almost invariably fertilise themselves, owing 
to insects rarely visiting the flowers; and as the 
plants have been long cultivated under nearly similar 
conditions, we can understand why a cross between 
two individuals of the same variety does not do the 
least good to the offspring either in height or fertility. 
This case is almost exactly parallel with that of 
Mimulus, or that of the Ipomosa named Hero; for 
in these two instances, crossing plants which had been 
self-fertilised for seven generations did not at all 
benefit the offspring. On the other hand, a cross 
between two varieties of the pea causes a marked 
superiority in the growth and vigour of the offspring, 
over the self-fertilised plants of the same varieties, 
as shown by two excellent observers. From my own 



CHAP. VII. TABLE O. 265 

observations (not made with great care) the offspring 
from crossed varieties were to self-fertilised plants in 
height, in one case as 100 to about 75, and in a second 
case as 100 to 60. 

(8.) Lathy rus odoratus. The sweet-pea is in the 
same state in regard to self-fertilisation as the common 
pea ; and we have seen that seedlings from a cross 
between two varieties, which differed in no respect 
except in the colour of their flowers, were to the self- 
fertilised seedlings from the same mother-plant in 
height as 100 to 80 ; and in the second generation as 
100 to 88. Unfortunately I did not ascertain whether 
crossing two plants of the same variety failed to pro- 
duce any beneficial effect, but I venture to predict such 
would be the result. 

(9.) Petunia violacea. The intercrossed plants of 
the same stock in four out of the five successive gene- 
rations plainly exceeded in height the self-fertilised 
plants. The latter in the fourth generation were 
crossed by a fresh stock, and the seedlings thus obtained 
were put into competition with the self-fertilised plants 
of the fifth generation. The crossed plants exceeded 
the self-fertilised in height in the ratio of 100 to 66, 
and in weight as 100 to 23; but this difference, 
though so great, is not much greater than that between 
the intercrossed plants of the same stock in comparison 
with the self-fertilised plants of the corresponding 
generation. This case, therefore, seems at first sight 
opposed to the rule that a cross with a fresh stock is 
much more beneficial than a cross between individuals 
of the same stock. But as with Eschscholtzia, the 
reproductive system was here chiefly benefited ; for 
the plants raised from the cross with the fresh stock 
were to the self-fertilised plants in fertility, both lots 
being naturally fertilised, as 100 to 46, whereas the 



266 SUMMARY OF MEASUREMENTS. CHAP. VIL 

intercrossed plants of the same stock were to the self- 
fertilised plants of the corresponding fifth generation 
in fertility only as 100 to 86. 

Although at the time of measurement the plants 
raised from the cross with the fresh stock did not 
exceed in height or weight the intercrossed plants of 
the old stock (owing to the growth of the former not 
having been completed, as explained under the head 
of this species), yet they exceeded the intercrossed 
plants in fertility in the ratio of 100 to 54. This fact 
is interesting, as it shows that plants self-fertilised 
for four generations and then crossed by a fresh stock, 
yielded seedlings which were nearly twice as fertile as 
those from plants of the same stock which had been 
intercrossed for the five previous generations. We 
here see, as with Eschscholtzia and Dianthus, that the 
mere act of crossing, independently of the state of the 
crossed plants, has little efficacy in giving increased 
fertility to the offspring. The same conclusion holds 
good, as we have already seen, in the analogous cases of 
Ipomoea, Mimulus, and Dianthus, with respect to height. 

(10.) Nicotiana tabacum. My plants were remark- 
ably self-fertile, and the capsules from the self-fertilised 
flowers apparently yielded more seeds than those which 
were cross-fertilised. No insects were seen to visit the 
flowers in the hothouse, and I suspect that the stock 
on which I experimented had been raised under glass, 
and had been self-fertilised during several previous 
generations ; if so, we can understand why, in the course 
of three generations, the crossed seedlings of the same 
stock did not uniformly exceed in height the self-ferti- 
lised seedlings. But the case is complicated by indi- 
vidual plants having different constitutions, so that some 
of the crossed and self-fertilised seedlings raised at the 
same time from the same parents behaved differently. 



CHAP. VII. TABLE O. 267 

However this may be, plants raised from self-fertilised 
plants of the third generation crossed by a slightly 
different sub-variety, exceeded greatly in height and 
weight the self-fertilised plants of the fourth genera- 
tion ; and the trial was made on a large scale. They 
exceeded them in height when grown in pots, and not 
much crowded, in the ratio of 100 to 66 ; and when 
much crowded, as 100 to 54. These crossed plants, when 
thus subjected to severe competition, also exceeded 
the self-fertilised in weight in the ratio of 100 to 37. 
So it was, but in a less degree (as may be seen in 
Table C), when the two lots were grown out of doors 
and not subjected to any mutual competition. Never- 
theless, strange as is the fact, the flowers on the 
mother-plants of the third self-fertilised generation 
did not yield more seed when they were crossed with 
pollen from plants of the fresh stock than when they 
were self-fertilised. 

(11.) Anagallis collina. Plants raised from a red 
variety crossed by another plant of the same variety 
were in height to the self-fertilised plants from the 
red variety as 100 to 73. When the flowers on the 
red variety were fertilised with pollen from a closely 
similar blue-flowered variety, they yielded double the 
number of seeds to what they did when crossed by 
pollen from another individual of the same red variety, 
and the seeds were much finer. The plants raised 
from this cross between the two varieties were to the 
self-fertilised seedlings from the red variety, in height 
as 100 to 66, and in fertility as 100 to 6. 

(12.) Primula veris. Some flowers on long-styled 
plants of the third illegitimate generation were legiti- 
mately crossed with pollen from a fresh stock, and 
others were fertilised with their own pollen. From 
the seeds thus produced crossed plants, and self- 



268 SUMMARY OF MEASUREMENTS. CHAP. VII. 

fertilised plants of the fourth illegitimate generation, 
were raised. The former were to the latter in 
height as 100 to 46, and in fertility during one 
year as 100 to 5, and as 100 to 3 5 during the next 
year. In this case, however, we have no means of 
distinguishing between the evil effects of illegitimate 
fertilisation continued during four generations (that is, 
by pollen of the same form, but taken from a distinct 
plant) and strict self-fertilisation. But these two 
processes perhaps do not differ so essentially as at 
first appears to be the case. In the following experi- 
ment any doubt arising from illegitimate fertilisation 
was completely eliminated. 

(13.) Primula veris. (Equal-styled, red-flowered 
variety). Flowers on plants of the second self-fertilised 
generation were crossed with pollen from a distinct 
variety or fresh stock, and others were again self- 
fertilised. Crossed plants and plants of the third self- 
fertilised generation, all of legitimate origin, were 
thus raised ; and the former was to the latter in height 
as 100 to 85, and in fertility (as judged by the number 
of capsules produced, together with the average number 
of seeds) as 100 to 11. 

Summary of the Measurements in Table C. This 
table includes the heights and often the weights of 
292 plants derived from a cross with a fresh stock, 
and of 305 plants, either of self-fertilised origin, or 
derived from an intercross between plants of the same 
stock. These 597 plants belong to thirteen species 
and twelve genera. The various precautions which 
were taken to ensure a fair comparison have already 
been stated. If we now look down the right-hand 
column, in which the mean height, weight, and 
fertility of the plants derived from a cross with 
a fresh stock are represented by 100, we shall sec 



CHAP. VII. TABLE O. 269 

by the other figures how wonderfully superior they 
are both to the self-fertilised and to the intercrossed 
plants of the same stock. With respect to height and 
weight, there are only two exceptions to the rule, 
namely, with Eschscholtzia and Petunia, and the 
latter is probably no real exception. Nor do these 
two species offer an exception in regard to fertility, 
for the plants derived from the cross with a fresh stock 
.vere much more fertile than the self-fertilised plants. 
The difference between the two sets of plants in the 
table is generally much greater in fertility than in 
height or weight. On the other hand, with some of 
the species, as with Nicotiana, there was no difference 
in fertility between the two sets, although a great dif- 
ference in height and weight. Considering all the 
cases in this table, there can be no doubt that plants 
profit immensely, though in different ways, by a cross 
with a fresh stock or with a distinct sub-variety. It 
cannot be maintained that the benefit thus derived is 
due merely to the plants of the fresh stock being per- 
fectly healthy, whilst those which had been long inter- 
crossed or self-fertilised had become unhealthy ; for in 
most cases there was no appearance of such unhealthi- 
ness, and we shall see under Table A that the inter- 
crossed plants of the same stock are generally superior 
to a certain extent to the self-fertilised, both lots 
having been subjected to exactly the same conditions 
and being equally healthy or unhealthy. 

We further learn from Table C, that a cross between 
plants that have been self-fertilised during several 
successive generations and kept all the time under 
nearly uniform conditions, does not benefit the offspring 
in the least or only in a very slight degree. Mimulus 
and the descendants of Ipomrea named Hero offer 
instances of this rule. Again, plants self-fertilised 



270 SUMMARY OF MEASUKEMENTS. CHAP. VII. 

during several generations profit only to a small extent 
by a cross with intercrossed plants of the same stock 
(as in the case of Dianthus), in comparison with the 
effects of a cross by a fresh stock. Plants of the same 
stock intercrossed during several generations (as with 
Petunia) were inferior in a marked manner in fertility 
to those derived from the corresponding self- fertilised 
plants crossed by a fresh stock. Lastly, certain plants 
which are regularly intercrossed by insects in a state 
of nature, and which were artificially crossed in each 
succeeding generation in the course of my experi- 
ments, so that they can never or most rarely have 
suffered any evil from self-fertilisation (as with Esch- 
scholtzia and Ipomoea), nevertheless profited greatly 
by a cross with a fresh stock. These several cases 
taken together show us in the clearest manner that it 
is not the mere crossing of any two individuals which 
is beneficial to the offspring. The benefit thus derived 
depends on the plants which are united differing in some 
manner, and there can hardly be a doubt that it is 
in the constitution or nature of the sexual elements. 
Anyhow, it is certain that the differences are not of an 
external nature, for two plants which resemble each 
other as closely as the individuals of the same species 
ever do, profit in the plainest manner when inter- 
crossed, if their progenitors have been exposed during 
several generations to different conditions. But to this 
latter subject I shall have to recur in a future chapter. 

TABLE A. 

We will now turn to our first table, which re- 
lates to crossed and self-fertilised plants of the same 
stock. These consist of fifty-four species belonging to 
thirty natural orders. The total number of crossed 
plants of which measurements are given is 796, and 



CHAP. VII. TABLE A. 271 

of self-fertilised plants 809 ; that is altogether 1,605 
plants. Some of the species were experimented on 
during several successive generations ; and it should 
be borne in mind that in such cases the crossed plants 
in each generation were crossed with pollen from 
another crossed plant, and the flowers on the self- 
fertilised plants were almost always fertilised with 
their own pollen, though sometimes with pollen from 
other flowers on the same plant. The crossed plants thus 
became more or less closely inter-related in the later 
generations ; and both lots were subjected in each ge- 
neration to almost absolutely the same conditions, and 
to nearly the same conditions in the successive gene- 
rations. It would have been a better plan in some re 
spects if I had always crossed some flowers either on the 
self-fertilised or intercrossed plants of each generation 
with pollen from a non-related plant, grown under dif- 
ferent conditions, as was done with the plants in Table 
C ; for by this procedure I should have learnt how much 
the offspring became deteriorated through continued 
self-fertilisation in the successive generations. As the 
case stands, the self-fertilised plants of the successive 
generations in Table A were put into competition with 
and compared with intercrossed plants, which were 
probably deteriorated in some degree by being more 
or less inter-related and grown under similar conditions. 
Nevertheless, had I always followed the plan in Table 
C, I should not have discovered the important fact 
that, although a cross between plants which are rather 
closely related and which had been subjected to 
closely similar conditions, gives during several genera- 
tions some advantage to the offspring, yet that after a 
time they may be intercrossed with no advantage what- 
ever to the offspring. Nor should I have learnt that 
the self-fertilised plants of the later generations might 



272 SUMMARY OF MEASUREMENTS. CHAP. VII. 

be crossed with intercrossed plants of the same stock 
with little or no advantage, although they profited to 
an extraordinary degree by a cross with a fresh stock. 

With respect to the greater number of the plants 
in Table A, nothing special need here be said ; full 
particulars may be found under the head of each 
species by the aid of the Index. The figures in the 
right-hand column show the mean height of the self- 
fertilised plants, that of the crossed plants with which 
they competed being represented by 100. No notice 
is here taken of the few cases in which crossed and 
self-fertilised plants were grown in the open ground, 
so as not to compete together. The table includes, 
as we have seen, plants belonging to fifty-four species, 
but as some of these were measured during several 
successive generations, there are eighty-three cases in 
which crossed and self-fertilised plants were compared. 
As in each generation the number of plants which 
were measured (given in the table) was never very large 
and sometimes small, whenever in the right-hand 
column the mean height of the crossed and self-fertilised 
plants is the same within five per cent., their heights 
may be considered as practically equal. Of such cases, 
that is, of self-fertilised plants of which the mean 
height is expressed by figures between 95 and 105, 
there are eighteen, either in some one or all the gene- 
rations. There are eight cases in which the self- 
fertilised plants exceed the crossed by above five per 
cent., as shown by the figures in the right-hand column 
being above 105. Lastly, there are fifty-seven cases 
in which the crossed plants exceed the self-fertilised in 
a ratio of at least 100 to 95, and generally in a much 
higher degree. 

If the relative heights of the crossed and self-fertilised 
plants had been due to mere chance, there would have 



CHAP. VII. TABLE A. 273 

been about as many cases of self-fertilised plants 
exceeding the crossed in height by above five per cent, 
as of the crossed thus exceeding the self-fertilised ; but 
we see that of the latter there are fifty-seven cases, and 
of the former only eight cases ; so that the cases in 
which the crossed plants exceed in height the self- 
fertilised in the above proportion are more than seven 
times as numerous as those in which the self-fertilised 
exceed the crossed in the same proportion. For our 
special purpose of comparing the powers of growth 
of crossed and self-fertilised plants, it may be said 
that in fifty-seven cases the crossed plants exceeded 
the self-fertilised by more than five per cent., and that 
in twenty-six cases (18 + 8) they did not thus exceed 
them. But we shall now show that in several of these 
twenty-six cases the crossed plants had a decided ad- 
vantage over the self-fertilised in other respects, though 
not in height ; that in other cases the mean heights 
are not trustworthy, owing to too few plants having 
been measured, or to their having grown unequally 
from being unhealthy, or to both causes combined. 
Nevertheless, as these cases are opposed to my general 
conclusion I have felt bound to give them. Lastly, the 
cause of the crossed plants having no advantage over 
the self-fertilised can be explained in some other cases. 
Thus a very small residue is left in which the self- 
fertilised plants appear, as far as my experiments 
serve, to be really equal or superior to the crossed 
plants. 

We will now consider in some little detail the eigh- 
teen cases in which the self-fertilised plants equalled 
in average height the crossed plants within five per 
cent. ; and the eight cases in which the self-fertilised 
plants exceeded in average height the crossed plants 
by above five per cent. ; making altogether twenty-six 



274; SUMMARY OF MEASUREMENTS. CHAP. VII. 

cases in which the crossed plants were not taller than 
the self-fertilised plants in any marked degree. 

(1.) Dianthus caryopliyllus (third generation). This plant was 
experimented on during four generations, in three of which the 
crossed plants exceeded in height the self-fertilised generally by 
much more than five per cent. ; and we have seen under Table 
C that the offspring from the plants of the third self-fertilised 
generation crossed by a fresh stock profited in height and fer- 
tility to an extraordinary degree. But in this third generation 
the crossed plants of the same stock were in height to the self- 
fertilised only as 100 to 99, that is, they were practically equal. 
Nevertheless, when the eight crossed and eight self-fertilised 
plants were cut down and weighed, the former were to the latter 
in weight as 100 to 49 ! There can therefore be not the least 
doubt that the crossed plants of this species are greatly superior 
in vigour and luxuriance to the self-fertilised ; and what was the 
cause of the self-fertilised plants of the third generation, though 
so light and thin, growing up so as almost to equal the crossed 
in height, I cannot explain. 

(2.) Lobelia fulgens {first generation'). The crossed plants of 
this generation were much inferior in height to the selfcfertilised, 
in the proportion of 100 to 127. Although only two pairs were 
measured, which is obviously much too few to be trusted, 
yet from other evidence given under the head of this species, 
it is certain that the self-fertilised plants were very much 
more vigorous than the crossed. As I used pollen of unequal 
maturity for crossing and self-fertilising the parent-plants, it is 
possible that the great difference in the growth of their offspring 
may have been due to this cause. In the next generation this 
source of error was avoided, and many more plants were raised, 
and now the average height of the twenty-three crossed plants 
was to that of the twenty-three self-fertilised plants as 100 to 91. 
We can therefore hardly doubt that a cross is beneficial to this 
species. 

(3.) Petunia violacea (third generation"). Eight crossed plants 
were to eight self-fertilised of the third generation in average 
height as 100 to 131; and at an early age the crossed were 
inferior even in a still higher degree. But it is a remarkable 
fact that in one pot in which plants of both lois grew extremely 
crowded, the crossed were thrice as tall as the self-fertilised. As 
in the two preceding and two succeeding generations, as well as 



CHAP. Vn. TABLE A. 275 

with plants raised by a cross with a fresh stock, the crossed 
greatly exceeded the self-fertilised in height, weight, and fertility 
(when these two latter points were attended to), the present case 
must be looked at as an anomaly not affecting the general rule. 
The most probable explanation is that the plants grew pre- 
maturely, owing to the seeds of the last generation not having 
been well ripened; for I have observed an analogous case with 
Iberis. Self-fertilised seedlings of this latter plant, which were 
known to have been produced from seeds not well matured, 
grew from the first much more quickly than the crossed plants, 
which were raised from better matured seeds ; so that having 
thus once got a great start they were enabled ever afterwards to 
retain their advantage. Some of these same seeds of the Iberis 
were sown on the opposite sides of pots filled with burnt earth 
and pure sand, not containing any organic matter ; and now the 
young crossed seedlings grew during their short life to double 
the height of the self-fertilised, in the same manner as occurred 
with the above two sets of seedlings of Petunia which were much 
crowded and thus exposed to very unfavourable conditions. We 
have seen also in the eighth generation of Ipomoea that self- 
fertilised seedlings raised from unhealthy parents grew at first very 
much more quickly than the crossed seedlings, so that they were 
for a long time much taller, though ultimately beaten by them. 

(4, 5, 6.) Eschscholtzia californica. Four sets of measure- 
ments are given in Table A. In one of these the crossed plants 
exceed the self- fertilised in average height, so that this is not 
one of the exceptions here to be considered. In two other 
cases the crossed equalled the self-fertilised in height within five 
per cent. ; and in the fourth case the self-fertilised exceeded the 
crossed by above this limit. We have seen in Table C that the 
whole advantage of a cross by a fresh stock is confined to the 
number of seeds produced, and so it was with the disadvantage 
from self-fertilisation with the intercrossed plants of the same 
stock compared with the self-fertilised, for the former were in 
fertility to the latter as 100 to 89. The intercrossed plants thus 
have at least one important advantage over the self-fertilised. 
Moreover, the flowers on the parent-plants when fertilised with 
pollen from another individual of the same stock yield far more 
seeds than when self-fertilised ; the flowers in this latter case 
being often quite sterile. We may therefore conclude that a 
cross does some good, though it does not give to the crossed 
seedlings increased powers of growth. 

T 2 



276 SUMMARY OF MEASUEEMENTS. CHAP. Vll 

(7.) Viscaria oculata.The average height of the fifteen inter- 
crossed plants to that of the fifteen self-fertilised plants was only 
as 100 to 97 ; but the former produced many more capsules than 
the latter, in the ratio of 100 to 77. Moreover, the flowers on the 
parent-plants which were crossed and self-fertilised, yielded seeds 
on one occasion in the proportion of 100 to 38, and on a second 
occasion in the proportion of 100 to 58. So that there can be 
no doubt about the beneficial effects of a cross, although the 
mean height of the crossed plants was only three per cent, above 
that of the self-fertilised plants. 

(8.) Specularia speculum. Only the four tallest of the crossed 
and the four tallest of the self-fertilised plants, growing in four 
pots, were measured ; and the former were to the latter in height 
as 100 to 98. In all four pots a crossed plant flowered before 
any one of the self-'fertilised plants, and this is usually a safe 
indication of some real superiority in the crossed plants. The 
flowers on the parent- plants which were crossed with pollen from 
another plant yielded seeds compared with the self-fertilised 
flowers in the ratio of 100 to 72. We may therefore draw the 
same conclusion as in the last case with respect to a cross being 
decidedly beneficial. 

(9.) Borago officinalis. Only four crossed and four self- 
fertilised plants were raised and measured, and the former were 
to the latter in height as 100 to 102. So small a number of 
measurements ought never to be trusted ; and in the present in- 
stance the advantage of the self-fertilised over the crossed plants 
depended almost entirely on one of the self- fertilised plants 
having grown to an unusual height. All four crossed plants 
flowered before their self-fertilised opponents. The cross- 
fertilised flowers on the parent-plants in comparison with the 
self-fertilised flowers yielded seeds in the proportion of 100 to 60. 
So that here again we may draw the same conclusion as in the 
two last cases. 

(10.) Passiflora gracilis.Oaly two crossed and two self- 
fertilised plants were raised ; and the former were to the latter in 
height as 100 to 104. On the other hand, fruits from the cross- 
fertilised flowers on the parent-plants contained seeds in number, 
compared with those from the self-fertilised flowers, in the pro- 
portion of 100 to 85. 

(11.) I'haseolus multiflorus. The five crossed plants \vere to 
the five self-fertilised in height as 100 to 96. Although the 
crossed plants were thus only four per cent, taller than the 



CHAP. VII. TABLE A. 277 

self-fertilised, they flowered in both pots before them. It i 
therefore probable that they had some real advantage over the 
self-fertilised plants. 

(12.) Adonis cestivalis. The four crossed plants were almost 
exactly equal in height to the four self-fertilised plants, but as 
so few plants were measured, and as these were all " miserably 
unhealthy," nothing can be inferred with safety with respect to 
their relative heights. 

(13.) Bartonia aurea. The eight crossed plants were to the 
eight self-fertilised in height as 100 to 107. This number of 
plants, considering the care with which they were raised and 
compared, ought to have given a trustworthy result. But from 
some unknown cause they grew very unequally, and they be- 
came so unhealthy that only three of the crossed and three 
of the self-fertilised plants set any seeds, and these few in 
number. Under these circumstances the mean height of neither 
lot can be trusted, and the experiment is valueless. The cross- 
fertilised flowers on the parent-plants yielded rather more seeds 
than the self-fertilised flowers. 

(14.) T/iunbergia alata. The six crossed plants were to the 
six self-fertilised in height as 100 to 108. Here the self-fertilised 
plants seem to have a decided advantage ; but both lots grew 
unequally, some of the plants in both being more than twice as 
tall as others. The parent-plants also were in an odd semi- 
sterile condition. Under these circumstances the superiority of 
the self-fertilised plants cannot be fully trusted. 

(15.) N'Kana prostrata. The five crossed plants were to the five 
self- fertilised in height as 100 to 105; so that the latter seem 
here to have a small but decided advantage. On the other hand, 
the flowers on the parent-plants which were cross-fertilised 
produced very many more capsules than the self-fertilised flowers, 
in the ratio of 100 to 21 ; and the seeds which the former con- 
tained were heavier than an equal number from the self-fertilised 
capsules in the ratio of 100 to 82. 

(16.) Hibiscus a/Hcanus Only four pairs were raised, and tie 
crossed were to the self-fertilised in height as 100 to 109. 
Excepting that too few plants were measured, I know of nothing 
else to cause distrust in the result. The cross-fertilised 
flowers on the parent-plants were, on the other hand, rather 
more productive than the self-fertilised flowers. 

(17.) Apium petroselinum. A few plants (number not re- 
corded) derived from flowers believed to have been crossed by 



278 SUMMAEY OF MEASUKEMENTS. CHAP. VII. 

insects and a few self-fertilised plants were grown on the opposite 
Bides of four pots. They attained to a nearly equal height, the 
crossed having a very slight advantage. 

(18.) Vandellia nummular! folia. Twenty crossed plants raised 
from the seeds of perfect flowers were to twenty self-fertilised 
plants, likewise raised from the seeds of perfect flowers, in height 
as 100 to 99. The experiment was repeated, with the sole 
difference that the plants were allowed to grow more crowded ; 
and now the twenty-four tallest of the crossed plants were to 
the twenty-four tallest self-fertilised plants in height as 100 to 
94, and in weight as 100 to 97. Moreover, a larger number of the 
crossed than of the self-fertilised plants grew to a moderate 
height. The above-mentioned twenty crossed plants were also 
grown in competition with twenty self-fertilised plants raised 
from the closed or cleistogamic flowers, and their heights were as 
100 to 94. Therefore had it not been for the first trial, in which 
the crossed plants were to the self-fertilised in height only as 
100 to 99, this species might have been classed with those in 
which the crossed plants exceed the self-fertilised by above five 
per cent. On the other hand, the crossed plants in the second 
trial bore fewer capsules, and these contained fewer seeds, than 
did the self- fertilised plants, all the capsules having been 
produced by cleistogamic flowers. The whole case therefore must 
be left doubtful. 

(19.) Pisum sativum (common pea). Four plants derived from 
a cross between individuals of the same variety wore in height 
to four self- fertilised plants belonging to the same variety as 100 
to 115. Although this cross did no good, we have seen under 
Table C that a cross between distinct varieties adds greatly to 
the height and vigour of the offspring ; and it was there explained 
that the fact of a cross between the individuals of the same variety 
not being beneficial, is almost certainly due to their having been 
self- fertilised for many generations, and in each generation 
grown under nearly similar conditions. 

(20, 21, 22.) Canna warscewiczi. Plants belonging to three 
generations were observed, and in all of three the crossed were 
approximately equal to the self-fertilised ; the average height of 
the thirty- four crossed plants being to that of the same number 
of self-fertilised plants as 100 to 101. Therefore the crossed 
plants had no advantage over the self-fertilised ; and it is pro- 
bable that the same explanation here holds good as in the case 
of Pisum sativum ; for the flowers of this Canna are perfectly 



CHAP. VII. TABLE A. 279 

self-fertile, and were never seen to be visited by insects in the 
hothouse, so as to be crossed by them. This plant, moreover, 
has been cultivated under glass for several generations in pots, 
and therefore under nearly uniform conditions. The capsules 
produced by the cross-fertilised flowers on the above thirty-four 
crossed plants contained more seeds than did the capsules 
produced by the self-fertilised flowers on the self-fertilised plants, 
in the proportion of 100 to 85 ; so that in this respect crossing 
was beneficial. 

(23.) Primula, sinensis. The offspring of plants, some of 
which were legitimately and others illegitimately fertilised with 
pollen from a distinct plant, were almost exactly of the same 
height as the offspring of self-fertilised plants ; but the former 
with rare exceptions flowered before the latter. I have shown 
in my work on heterostyled plants that this species is commonly 
raised in England from self-fertilised seed, and the plants from 
having been cultivated in pots have been subjected to nearly 
uniform conditions. Moreover, many of them are now varying 
and changing their character, so as to become in a greater or 
less degree equal-styled, and in consequence highly self-fertile. 
Therefore I believe that the cause of the crossed plants not 
exceeding in height the self-fertilised is the same as in the two 
previous cases of Pisum sativum and Canna. 

(24, 25, 26.) Nicotiana tabacum.Fonr sets of measurements 
were made ; in one, the self-fertilised plants greatly exceeded in 
height the crossed, in two others they were approximately equal 
to the crossed, and in the fourth were beaten by them ; but this 
latter case does not here concern us. The individual plants 
differ in constitution, so that the descendants of some profit by 
their parents having been intercrossed, whilst others do not 
Taking all three generations together, the twenty-seven crossed 
plants were in height to the twenty-seven self-fertib'sed plants 
as 100 to 96. This excess of height in the crossed plants is so 
small compared with that displayed by the offspring from the 
same mother-plants when crossed by a slightly different variety, 
that we may suspect (as explained under Table C) that most of 
the individuals belonging to the variety which served as the 
mother-plants in my experiments, had acquired a nearly similar 
constitution, so as not to profit by being mutually intercrossed. 

Reviewing these twenty-six cases, in which the 
crossed plants either do not exceed the self-fertilised 



280 SUMMARY OF MEASUREMENTS. CHAP. VIL 

by above five per cent, in height, or are inferior to 
them, we may conclude that much the greater number 
of the cases do not form real exceptions to the rule, 
that a cross between two plants, unless these have 
been self-fertilised and exposed to nearly the same 
conditions for many generations, gives a great 
advantage of some kind to the offspring. Of the 
twenty-six cases, at least two, namely, those of Adonis 
and Bartonia, may be wholly excluded, as the trials 
were worthless from the extreme unhealthiness of the 
plants. In twelve other cases (three trials with Esch- 
scholtzia here included) the crossed plants either were 
superior in height to the self-fertilised in all the other 
generations excepting the one in question, or they 
showed their superiority in some different manner, as 
in weight, fertility, or in flowering first ; or again, the 
cross-fertilised flowers on the mother-plant were much 
more productive of seed than the self-fertilised. 

Deducting these fourteen cases, there remain twelve 
in which the crossed plants show no well-marked 
advantage over the self-fertilised. On the other hand, 
we have seen that there are fifty-seven cases in which 
the crossed plants exceed the self-fertilised in height 
by at least five per cent., and generally in a much 
higher degree. But even in the twelve cases just 
referred to, the want of any advantage on the crossed 
side is far from certain : with Thuubergia the parent- 
plants were in an odd semi-sterile condition, and the 
offspring grew very unequally; with Hibiscus and 
Apium much too few plants were raised for the measure- 
ments to be trusted, and the cross-fertilised flowers of 
Hibiscus produced rather more seed than did the self- 
fertilised ; with Vandellia the crossed plants were a 
little taller and heavier than the self-fertilised, but as 
they were less fertile the case must be left doubtful 



CHAP. VII TABLE A. 281 

Lastly, with Pisum, Primula, the three generations of 
Canna, and the three of Nicotiana (which together 
complete the twelve cases), a cross between two plants 
certainly did no good or very little good to the off- 
spring ; but we have reason to suspect that this is the 
result of these plants having been self-fertilised and 
cultivated under nearly uniform conditions for several 
generations. The same result followed with the experi- 
mental plants of Ipomcea and Mimulus, and to a certain 
extent with some other species, which had been inten- 
tionally treated by me in this manner; yet we know that 
these species in their normal condition profit greatly by 
being intercrossed. There is, therefore, not a single 
case in Table A which affords decisive evidence against 
the rule that a cross between plants, the progenitors of 
which have been subjected to somewhat diversified 
conditions, is beneficial to the offspring. This is a 
surprising conclusion, for from the analogy of domesti- 
cated animals it could not have been anticipated, that 
the good effects of crossing or the evil effects of self- 
fertilisation would have been perceptible until the 
plants had been thus treated for several generations. 

The results given in Table A may be looked at 
under another point of view. Hitherto each genera- 
tion has been considered as a separate case, of which 
there are eighty-three ; and this no doubt is the more 
correct method of comparing the crossed and self- 
fertilised plants. 

But in those cases in which plants of the same 
species were observed during several generations, a 
general average of their heights in all the generations 
together may be made ; and such averages are 
given in Table A ; for instance, under Ipomoea the 
general average for the plants of all ten generations 
is as 100 for the crossed, to 77 for the self-fertilised 



282 SUMMARY OF MEASUREMENTS. CHAP. VII. 

plants. This having been done in each case in which 
more than one generation was raised, it is easy to 
calculate the average of the average heights of the 
crossed and self-fertilised plants of all the species 
included in Table A. It should however be observed 
that as only a few plants of some species, whilst a 
considerable number of others, were measured, the 
value of the mean or average heights of the several 
species is very different. Subject to this source of 
error, it may be worth while to give the mean of the 
mean heights of the fifty-four species in Table A ; and 
the result is, calling the mean of the mean heights 
of the crossed plants 100, that of the self-fertilised 
plants is 87. But it is a better plan to divide the 
fifty-four species into three groups, as was done with 
the previously given eighty-three cases. The first 
group consists of species of which the mean heights 
of the self-fertilised plants are within five per cent, 
of 100 ; so that the crossed and self-fertilised plants 
are approximately equal ; and of such species there 
are twelve about which nothing need be said, the 
mean of the mean heights of the self-fertilised being 
of course very nearly 100, or exactly 99 '58. The 
second group consists of the species, thirty-seven in 
number, of which the mean heights of the crossed 
plants exceed that of the self-fertilised plants by 
more than five per cent.; and the mean of their 
mean heights is to that of the self-fertilised plants 
as 100 to 78. The third group consists of the species, 
only five in number, of which the mean heights of 
the self-fertilised plants exceed that of the crossed by 
more than five per cent. ; and here the mean of the 
mean heights of the crossed plants is to that of the 
self-fertilised as 100 to 109. Therefore if we exclude 
the species which are approximately equal, there are 



CHAP. VII. TABLE B. 283 

thirty-seven species in which the mean of the mean 
heights of the crossed plants exceeds that of the self- 
fertilised by twenty-two per cent. ; whereas there are 
only five species in which the mean of the mean heights 
of the self-fertilised plants exceeds that of the crossed, 
and this only by nine per cent. 

The truth of the conclusion that the good effects of 
a cross depend on the plants having been subjected 
to different conditions or to their belonging to differ- 
ent varieties, in both of which cases they would almost 
certainly differ somewhat in constitution is supported 
by a comparison of the Tables A and C. The latter 
table gives the results of crossing plants with a fresh 
stock or with a distinct variety ; and the superiority of 
the crossed offspring over the self-fertilised is here 
much more general and much more strongly marked 
than in Table A, in which plants of the same stock 
were crossed. We have just seen that the mean of the 
mean heights of the crossed plants of the whole fifty- 
four species in Table A is to that of the self-fertilised 
plants as 100 to 87 ; whereas the mean of the mean 
heights of the plants crossed by a fresh stock is to that 
of the self-fertilised in Table C as 100 to 74. So that 
the crossed plants beat the self-fertilised plants by 
thirteen per cent, in Table A, and by twenty-six per 
cent., or double as much, in Table C, which includes 
the results of a cross by a fresh stock. 

TABLE B. 

A few words must be added on the weights of 
the crossed plants of the same stock, in comparison 
with the self-fertilised. Eleven cases are given in 
Table B, relating to eight species. The number of 
plants which were weighed is shown in the two left 
columns, and their relative weights in the right 



284 SUMMARY OF MEASUREMENTS. CHAP. VIL 

column, that of the crossed plants being taken as 
100. A few other cases have already been recorded 
in Table C in reference to plants crossed by a fresh 
stock. I regret that more trials of this kind were not 
made, as the evidence of the superiority of the crossed 
over the self-fertilised plants is thus shown in a more 
conclusive manner than by their relative heights. But 
this plan was not thought of until a rather late period, 
and there were difficulties in the way, as the seeds 
had to be collected when ripe, by which time the plants 
had often begun to wither. In only one out of the 
eleven cases in Table B, that of Eschscholtzia, do the 
self-fertilised plants exceed the crossed in weight ; and 
we have already seen they are likewise superior to them 
in height, though inferior in fertility, the whole ad- 
vantage of a cross being here confined to the repro- 
ductive system. With Vandellia the crossed plants 
were a little heavier, as they were also a little taller 
than the self-fertilised ; but as a greater number of 
more productive capsules, were produced by the cleis- 
togamic flowers on the self-fertilised plants than by 
those on the crossed plants, the case must be left, as 
remarked under Table A, altogether doubtful. The 
crossed and self-fertilised offspring from a partially 
self-sterile plant of Reseda odorata were almost equal 
in weight, though not in height. In the remaining 
eight cases, the crossed plants show a wonderful 
superiority over the self-fertilised, being more than 
double their weight, except in one case, and here 
the ratio is as high as 100 to 67. The results thus 
deduced from the weights of the plants confirm in a 
striking manner the former evidence of the beneficial 
effects of a cross between two plants of the same stock ; 
and in the few cases in which plants derived from a 
cross with a fresh stock were weighed, the results are 
similar or eveu more striking. 



CHAP. Vlll. CONSTITUTIONAL VIGOUR. 285 



CHAPTER VIII. 

DIFFERENCE BETWEEN CROSSED AND SELF-FERTILISED PLANTS ns 
CONSTITUTIONAL VIGOUR AND IN OTHER RESPECTS. 

Greater constitutional vigour of crossed plants The effects of great 
crowding Competition with other kinds of plants Self-fertilised 
plants more liable to premature death Crossed plants generally 
flower before the self-fertilised Negative effects of intercrossing 
flowers on the same plant Cases described Transmission of the 
good effects of a cross to later generations Effects of crossing 
plants of closely related parentage Uniform colour of the flowers 
on plants self-fertilised during several generations and cultivated 
under similar conditions. 

Crreater constitutional Vigour of crossed Plants. As in 
almost all my experiments an equal number of crossed 
and self-fertilised seeds, or more commonly seedlings 
just beginning to sprout, were planted on the oppo- 
site sides of the same pots, they had to compete 
with one another ; and the greater height, weight, and 
fertility of the crossed plants may be attributed to 
their possessing greater innate constitutional vigour. 
Generally the plants of the two lots whilst very young 
were of equal height; but afterwards the crossed 
gained insensibly on their opponents, and this shows 
that they possessed some inherent superiority, though 
not displayed at a very early period of life. There 
were, however, some conspicuous exceptions to the 
rule of the two lots being at first equal in height ; thus 
the crossed seedlings of the broom (Saroihamnus 
scoparius) when under three inches in height were more 
than twice as tall as the self-fertilised plants. 



286 CONSTITUTIONAL VIGOUR CHAP. VIII. 

After the crossed or the self-fertilised plants had 
once grown decidedly taller than their opponents, a 
still increasing advantage would tend to follow 
from the stronger plants robbing the weaker ones 
of nourishment and overshadowing them. This was 
evidently the case with the crossed plants of Viola tri- 
color, which ultimately quite overwhelmed the self- 
fertilised. But that the crossed plants have an inherent 
superiority, independently of competition, was some- 
times well shown when both lots were planted 
separately, not far distant from one another, in good 
soil in the open ground. This was likewise shown in 
several cases, even with plants growing in close compe- 
tition with one another, by one of the self-fertilised 
plants exceeding for a time its crossed opponent, which 
had been injured by some accident or was at first 
sickly, but being ultimately conquered by it. The 
plants of the eighth generation of Ipomoea were raised 
from small seeds produced by unhealthy parents, and 
the self-fertilised plants grew at first very rapidly, 
so that when the plants of both lots were about three 
feet in height, the mean height of the crossed to that 
of the self-fertilised was as 100 to 122 ; when they 
were about six feet high the two lots were very nearly 
equal, but ultimately when between eight and nine feet 
in height, the crossed plants asserted their usual 
superiority, and were to the self-fertilised in height as 
100 to 85. 

The constitutional superiority of the crossed over the 
self-fertilised plants was proved in another way in the 
third generation of Mimulus, by self-fertilised seeds 
being sown on one side of a pot, and after a certain 
interval of time crossed seeds on the opposite side. The 
self-fertilised seedlings thus had (for I ascertained that 
the seeds germinated simultaneously) a clear advantage 



CHAP. VIII. OF THE CROSSED PLANTS. 287 

over the crossed in the start for the race. N evertheless 
they were easily beaten (as may be seen under the 
head of Mimulus) when the crossed seeds were sown 
two whole days after the self-fertilised. But when the 
interval was four days, the two lots were nearly equal 
throughout life. Even in this latter case the crossed 
plants still possessed an inherent advantage, for after 
both lots had grown to their full height they were 
cut down, and without being disturbed were transferred 
to a larger pot, and when in the ensuing year they 
had again grown to their full height they were 
measured ; and now the tallest crossed plants were to 
the tallest self-fertilised plants in height as 100 to 75, 
and in fertility (i.e., by weight of seeds produced by an 
equal number of capsules from both lots) as 100 to 34. 
My usual method of proceeding, namely, to plant 
several pairs of crossed and self-fertilised seeds in an 
equal state of germination on the opposite sides of the 
same pots, so that the plants were subjected to 
moderately severe mutual competition, was I think 
the best that could have been followed, and was a fair 
test of what occurs in a state of nature. For plants 
sown by nature generally come up crowded, and are 
almost always exposed to very severe competition 
with one another and with other kinds of plants. This 
latter consideration led me to make some trials, chiefly 
but not exclusively with Ipomcea and Mimulus, by 
sowing crossed and self-fertilised seeds on the opposite 
sides of large pots in which other plants had long been 
growing, or in the midst of other plants out of doors. 
The seedlings were thus subjected to very severe 
competition with plants of other kinds; and in all 
such cases, the crossed seedlings exhibited a great 
superiority in their power of growth over the self- 
fertilised. 



288 CONSTITUTIONAL VIGOUR CHAP. VIII 

After the germinating seedlings had been planted 
in pairs on the opposite sides of several pots, the 
remaining seeds, whether or not in a state of germina- 
tion, were in most cases sown very thickly on the two 
sides of an additional large pot ; so that the seedlings 
came up extremely crowded, and were subjected to 
extremely severe competition and unfavourable condi- 
tions. In such cases the crossed plants almost invari- 
ably showed a greater superiority over the self-fertilised, 
than did the plants which grew in pairs in the pots. 

Sometimes crossed and self-fertilised seeds were 
sown in separate rows in the open ground, which was 
kept clear of weeds ; so that the seedlings were not 
subjected to any competition with other kinds of 
plants. Those however in each row had to struggle 
with the adjoining ones in the same row. When fully 
grown, several of the tallest plants in each row were 
selected, measured, and compared. The result was 
in several cases (but not so invariably as might have 
been expected) that the crossed plants did not exceed 
in height the self-fertilised in nearly so great a degree 
as when grown in pairs in the pots. Thus with the 
plants of Digitalis, which competed together in pots, the 
crossed were to the self-fertilised in height as 100 to 
70 ; whilst those which were grown separately were only 
as 100 to 85. Nearly the same result was observed 
with Brassica. With Nicotiana the crossed were to 
the self-fertilised plants in height, when grown 
extremely crowded together in pots, as 100 to 54; 
when grown much less crowded in pots as 100 to 66, 
and when grown in the open ground, so as to be sub- 
jected to but little competition, as 100 to 72. On the 
other hand with Zea, there was a greater difference in 
height between the crossed and self-fertilised plants 
growing out of doors, than between the pairs which 



CHA*. VIII. OF THE CROSSED PLANTS. 289 

grew in pots in the hothouse; but this may be 
attributed to the self-fertilised plants being more 
tender, so that they suffered more than the crossed, 
when both lots were exposed to a cold and wet summer 
Lastly, with one out of two series of Eeseda odorata, 
grown out of doors in rows, as well as with Beta 
vidgaris, the crossed plants did not at all exceed the self- 
fertilised in height, or exceeded them by a mere trifle. 

The innate power of the crossed plants to resist 
unfavourable conditions far better than did the self- 
fertilised plants, was shown on two occasions in a 
curious manner, namely, with Iberis and in the third 
generation of Petunia, by the great superiority in 
height of the crossed over the self-fertilised seedlings, 
when both sets were grown under extremely unfavourable 
conditions; whereas owing to special circumstances 
exactly the reverse occurred with the plants raised from 
the same seeds and grown in pairs in pots. A nearly 
analogous case was observed on two other occasions 
with plants of the first generation of Nicotiana. 

The crossed plants always withstood the injurious 
effects of being suddenly removed into the open air 
after having been kept in the greenhouse better than 
did the self-fertilised. On several occasions they also 
resisted much better cold and intemperate weather. 
This was manifestly the case with some crossed and 
self-fertilised plants of Ipomcea, which were suddenly 
moved from the hothouse to the coldest part of a cool 
greenhouse. The offspring of plants of the eighth 
self-fertilised generation of Mimulus crossed by a fresh 
stock, survived a frost which killed every single self- 
rertilised and intercrossed plant of the same old stock. 
Nearly the same result followed with some crossed and 
self-fertilised plants of Viola tricolor. Even the tips 
of the shoots of the crossed plants (f Sarothamnus 

u 



290 CONSTITUTIONAL VIGOUR CHAP. VIII 

seoparius were not touched by a very severe winter ; 
whereas all the self-fertilised plants were killed half- 
way down to the ground, so that they were not able to 
flower during the next summer. Young crossed 
seedlings of Nicotiana withstood a cold and wet 
summer much better than the self-fertilised seedlings. 
I have met with only one exception to the rule of 
crossed plants being hardier than the self-fertilised : 
three long rows of Eschscholtzia plants, consisting of 
crossed seedlings from a fresh stock, of intercrossed 
seedlings of the same stock, and of self-fertilised ones, 
were left unprotected during a severe winter, and all 
perished except two of the self-fertilised. But this 
case is not so anomalous as it at first appears, for it 
should be remembered that the self-fertilised plants 
of Eschscholtzia always grow taller and are heavier 
than the crossed ; the whole benefit of a cross with this 
species being confined to increased fertility. 

Independently of any external cause which could 
be detected, the self-fertilised plants were more liable 
to premature death than were the crossed ; and this 
seems to me a curious fact. Whilst the seedlings 
were very young, if one died its antagonist was pulled 
up and thrown away, and I believe that many more of 
the self-fertilised died at this early age than of the 
crossed ; but I neglected to keep any record. With 
Beta vulgaris, however, it is certain that a large number 
of the self-fertilised seeds perished after germinating 
beneath the ground, whereas the crossed seeds sown at 
the same time did not thus suffer. When a plant 
died at a somewhat more advanced age the fact was 
recorded ; and I find in my notes that out of several 
hundred plants, only seven of the crossed died, whilst 
of the self-fertilised at least twenty-nine were thus 
lost, that is more than four times as many. Mr. Galton, 



CHAP. VIII. OP THE CROSSED PLANTS. 291 

after examining some of my tables, remarks : " It is very 
evident that the columns with the self-fertilised plants 
include the larger number of exceptionally small 
plants ; " and the frequent presence of such puny plants 
no doubt stands in close relation with their liability to 
premature death. The self-fertilised plants of Petunia 
completed their growth and began to wither sooner 
than did the intercrossed plants; and these latter 
considerably before the offspring from a cross with a 
fresh stock. 

Period of Flowering. In some cases, as with Digitalis, 
Dianthus, and Keseda, a larger number of the crossed 
than of the self-fertilised plants threw up flower-stems ; 
but this probably was merely the result of their greater 
power of growth ; for in the first generation of Lobelia 
fulgens, in which the self-fertilised plants greatly ex- 
ceeded in height the crossed plants, some of the latter 
failed to throw up flower-stems. With a large number 
of species, the crossed plants exhibited a well-marked 
tendency to flower before the self-fertilised ones 
growing in the same pots. It should however be 
remarked that no record was kept of the flowering of 
many of the species; and when a record was kept, 
the flowering of the first plant in each pot was alone 
observed, although two or more pairs grew in the same 
pot. I will now give three lists, one of the species 
in which the first plant that flowered was a crossed 
one, a second in which the first that flowered was a 
self-fertilised plant, and a third of those which 
flowered at the same time. 

Species, of which the first Plants that flowered were 

of Crossed Parentage. 

Ipomcea purpurea. I record in my notes that in all ten genera- 
tions many of the crossed plants flowered before the self- 
fertilised ; but no details were kept. 

TJ 2 



292 PERIOD OF FLOWERING OF CHAP. VIII. 

Mimulus luteus (First Generation). Ten flowers on the crossed 
plants were fully expanded before one on the self-fertilised. 

Mimulus luteus (Second and Third Generation). In both these 
generations a crossed plant flowered before one of the self- 
fertilised in all three pots. 

Mimulus luteus (Fifth Generation). In all three pots a crossed 
plant flowered first; yet the self-fertilised plants, which 
belonged to the new tall variety, were in height to the 
crossed as 126 to 100. 

Mimulus luteus. Plants derived from a cross with a fresh stock, 
as well as the intercrossed plants of the old stock, flowered 
before the self-fertilised plants in nine out of the ten pots. 

Salvia coccinea. A crossed plant flowered before any one of the 
self-fertilised in all three pots. 

Origanum vulgare. During two successive seasons several 
crossed plants flowered before the self-fertilised. 

Brassica oleracea (First Generation). All the crossed plants 
growing in pots and in the open ground flowered first. 

Brassica oleracea (Second Generation). A crossed plant in 
three out of the four pots flowered before any one of the 
self-fertilised. 

Iberis umbellata. In both pots a crossed plant flowered first. 

Eschscholtzia californica. Plants derived from the Brazilian 
stock crossed by the English stock flowered in five out of 
the nine pots first; in four of them a self-fertilised plant 
flowered first ; and not in one pot did an intercrossed plant 
of the old stock flower first. 

Viola tricolor. A crossed plant in five out of the six pots 
flowered before any one of the self-fertilised. 

Dianthus caryophyllus (First Generation). In two large beds 
of plants, four of the crossed plants flowered before any one 
of the self-fertilised. 

Dianthus caryophyllus (Second Generation). In both pots a 
crossed plant flowered first. 

Dianthus caryophyllus (Third Generation). In three out of 
the four pots a crossed plant flowered first ; yet the crossed 
were to the self-fertilised in height only as 100 to 99, but in 
weight as 100 to 49. 

Dianthus caryophyllus. Plants derived from a cross with a fresh 
stock, and the intercrossed plants of the old stock, both 
flowered before the self-fertilised in nine out of the ten pots, 

Hibiscus africanus. In three out of the four pots a crossed 



CHAP. VIII. CROSSED AND 8ELF-FEKTILISED PLANTS. 293 

plant flowered before any one of the self-fertilised ; yet the 

latter were to the crossed in height as 109 to 100. 
Tropxolum minus. A crossed plant flowered before any one of 

the self-fertilised in three out of the four pots, and simul- 
taneously in the fourth pot. 
Limnanthes douglasii. A crossed plant flowered before any one 

of the self-fertilised in four out of the five pots. 
Phaseolus multiflorus. In both pots a crossed plant flowered 

first. 
Spectilaria speculum. In all four pots a crossed plant flowered 

first. 
Lobelia ramosa (First Generation). In all four pots a crossed 

plant flowered before any one of the self-fertilised. 
Lobelia ramosa (Second Generation). In all four pots a crossed 

plant flowered some days before any one of the self- 
fertilised. 
Nemophila insignis. In four out of the five pots a crossed plant 

flowered first. 

Borago officinalis. In both pots a crossed plant flowered first. 
Petunia violacea (Second Generation). In all three pots a 

crossed plant flowered first. 
Nicotiana tabacum. A plant derived from a cross with a fresh 

stock flowered before any one of the self-fertilised plants of 

the fourth generation, in fifteen out of the sixteen pots. 
Cyclamen persicum. During two successive seasons a crossed 

plant flowered some weeks before any one of the self-fertilised 

in all four pots. 
Primula veris (equal-styled var.). In all three pots a crossed 

plant flowered first. 
Primula sinensis. In all four pots plants derived from an 

illegitimate cross between distinct plants flowered before 

any one of the self-fertilised plants. 
Primula sinensis. A legitimately crossed plant flowered before 

any one of the self-fertilised plants in seven out of the eight 

pots. 
Fagopyrvm esculentum. A legitimately crossed plant flowered 

from one to two days before any one of the self-tertilised 

plants in all three pots. 

Zea mays. In all four pots a crossed plant flowered first. 
Phalaris canarieitsis. The crossed plants flowered' before the 

self-fertilised in the open ground, but simultaneously in the 

pots. 



'294. PERIOD OF FLOWERING OF CHAP. VIII. 

Species, of which the first Plants that flowered were of 
Self-fertilised Parentage. 

Eschscholtzia californica (First Generation). The crossed plants 
were at first taller than the self-fertilised, but on their second 
growth during the following year the self-fertilised exceeded 
the crossed in height, and now they flowered first in three 
out of the four pots. 

Lupinus luteus. Although the crossed plants were to the self- 
fertilised in height as 100 to 82 ; yet in all three pots the 
self-fertilised plants flowered first. 

Clarkia elegans. Although the crossed plants were, as in the 
last case, to the self-fertilised in height as 100 to 82, yet in 
the two pots the self-fertilised flowered first. 

Lobelia fulgens (First Generation). The crossed plants were to 
the self-fertilised in height only as 100 to 127, and the latter 
flowered much before the crossed. 

Petunia violacea (Third Generation). The crossed plants were 
to the self-fertilised in height as 100 to 131, and in three 
out of the four pots a self-fertilised plant flowered first ; in 
the fourth pot simultaneously. 

Petunia violacea (Fourth Generation). Although the crossed 
plants were to the self-fertilised in height as 100 to 69, yet 
in three out of the five pots a self-fertilised plant flowered 
first ; in the fourth pot simultaneously, and only in the fifth 
did a crossed plant flower first. 

Nicotiana tabacum (First Generation). The crossed plants 
were to the self-fertilised in height only as 100 to 178, and 
a self-fertilised plant flowered first in all four pots. 

Nicotiana tabacum (Third Generation). The crossed plants 
were to the self-fertilised in height as 100 to 101, and in 
four out of the five pots a self-fertilised plant flowered first. 

Canna warscewiczi. In the three generations taken together the 
crossed were to the self-fertilised in height as 100 to 101 ; in 
the first generation the self-fertilised plants showed some 
tendency to flower first, and in the third generation they 
flowered first in nine out of the twelve pots. 

Species in which the Crossed and Self-fertilised Plants 



Mimulus luteus (Sixth Generation). The crossed plants were 
inferior in height and vigour to the self-fertilised plants 



CHAP. VIII. CBOSSED AND SELF-FERTILISED PLANTS. 295 

which all belonged to the new white-flowered tall variety, 
yet in only half the pots did the self-fertilised plants flower 
first, and in the other half the crossed plants. 

Viscaria oculato. The crossed plants were only a little taller 
than the self-fertilised (viz., as 100 to 97), but con- 
siderably more fertile, yet both lots flowered almost 
simultaneously. 

Lathyrus odoratus (Second Generation). Although the crossed 
plants were to the self-fertilised in height as 100 to 88, yefc 
there was no marked difference in their period of flowering. 

Lobelia fulyens (Second Generation). Although the crossed 
plants were to the self-fertilised in height as 100 to 91, yet 
they flowered simultaneously. 

Nicotiana tabacum (Third Generation). Although the crossed 
plants were to the self-fertilised in height as 100 to 83, yet 
in half the pots a self-fertilised plant flowered first, and in 
the other half a crossed plant. 

These three lists include fifty-eight cases, in which 
the period of flowering of the crossed and self-fertilised 
plants was recorded. In forty-four of them a crossed 
plant flowered first either in a majority of the pots or 
in all ; in nine instances a self-fertilised plant flowered 
first, and in five the two lots flowered simultaneously. 
One of the most striking cases is that of Cyclamen, in 
which the crossed plants flowered some weeks before 
the self-fertilised in all four pots during two seasons. 
In the second generation of Lobelia ramosa, a crossed 
plant flowered in all four pots some days before any 
one of the self-fertilised. Plants derived from a 
cross with a fresh stock generally showed a very 
strongly marked tendency to flower before the self- 
fertilised and the intercrossed plants of the old stock ; 
all three lots growing in the same pots. Thus with 
Mimulus and Dianthus, in only one pot out of ten, and 
in Nicotiana in only one pot out of sixteen, did a self* 
fertilised plant flower before the plants of the two crossed 
kinds, these latter flowering almost simultaneously. 



296 PERIOD OP FLOWLKING OF CHAP. VIII. 

A consideration of the two first lists, especially of 
the second one, shows that a tendency to flower first is 
generally connected with greater power of growth, that 
is, with greater height. But there are some remarkable 
exceptions to this rule, proving that some other cause 
comes into play. Thus the crossed plants both of 
Lupinus luteus and Clarkia elegans were to the self- 
fertilised plants in height -as 100 to 82, and yet the 
latter flowered first. In the third generation of Nico- 
tiana, and in all three generations of Canna, the 
crossed and self-fertilised plants were of nearly equal 
height, yet the self-fertilised tended to flower first. 
On the other hand, with Primula sinensis, plants 
raised from a cross between two distinct individuals 
whether these were legitimately or illegitimately 
crossed, flowered before the illegitimately self-fertilised 
plants, although all the plants were of nearly equal 
height in both cases. So it was with respect to height 
and flowering with Phaseolus, Specularia, and Borago. 
The crossed plants of Hibiscus were inferior in height 
to the self-fertilised, in the ratio of 100 to 109, and yet 
they flowered before the self-fertilised in three out of 
the four pots. On the whole, there can be no doubt 
that the crossed plants exhibit a tendency to flower 
before the self-fertilised, almost though not quite so 
strongly marked as to grow to a greater height, to 
weigh more, and to be more fertile. 

A few other cases not included in the above three 
lists deserve notice. In all three pots of Viola tricolor, 
naturally crossed plants the offspring of crossed plants 
flowered before naturally crossed plants the offspring 
of self-fertilised plants. Flowers on two plants, both of 
self-fertilised parentage, of the sixth generation of 
Mimulus luteus were intercrossed, and other flowers on 
the same plants were fertilised with their own pollen ; 



CHAP. VIII. CROSSED AND SELF-FERTILISED PLANTS. 297 

intercrossed seedlings and seedlings of the seventh 
self-fertilised generation were thus raised, and the 
latter flowered before the intercrossed in three out of 
the five pots. Flowers on a plant both of Mimulus 
luteus and of Ipomoea purpurea were crossed with pollen 
from other flowers on the same plant, and other flowers 
were fertilised with their own pollen; intercrossed 
seedlings of this peculiar kind, and others strictly self- 
fertilised being thus raised. In the case of the 
Mimulus the self-fertilised plants flowered first in seven 
out of the eight pots, and in the case of the Ipomoea 
in eight out of the ten pots ; so that an intercross 
between the Sowars on the same plant was very far 
from giving to the offspring thus raised, any advantage 
over the strictly self-fertilised plants in their period 
of flowering. 

The Effects of crossing Flowers on the same Plant. 

In the discussion on the results of a cross with a fresh 
stock, given under Table C in the last chapter, it was 
shown that the mere act of crossing by itself does no 
good ; but that the advantages thus derived depend on 
the plants which are crossed, either consisting of 
distinct varieties which will almost certainly differ 
somewhat in constitution, or on the progenitors of the 
plants which are crossed, though identical in every 
external character, having been subjected to somewhat 
different conditions and having thus acquired some 
slight difference in constitution. All the flowers 
produced by the same plant have been developed 
from the same seed ; those which expand at the same 
time have been exposed to exactly the same climatic 
influences ; and tke stems have all been nourished by 
the same roots. Therefore in accordance with the con- 
clusion just referred to, no good ought to result from 



298 THE EFFECTS OF CKOSSING CHAP. VIIL 

crossing flowers on the same plant.* In opposition to 
this conclusion is the fact that a bud is in one sense 
a distinct individual, and is capable of occasionally or 
even not rarely assuming new external characters, as 
well as new constitutional peculiarities. Plants raised 
from buds which have thus varied may be propagated 
for a great length of time by grafts, cuttings, &c., and 
sometimes even by seminal generation.! There exist 
also numerous species in which the flowers on the 
same plant differ from one another, as in the sexual 
organs of monoecious and polygamous plants, in the 
structure of the circumferential flowers in many Com- 
positae, Umbelliferee, &c., in the structure of the 
central flower in some plants, in the two kinds of 
flowers produced by cleistogamic species, and in 
several other such cases. These instances clearly 
prove that the flowers on the same plant have often 
varied independently of one another in many im- 
portant respects, such variations having been fixed, 



* It is, however, possible that ments have been made with re- 
the stamens which differ in length spect to the stamens of Pelargo- 
or construction in the same flower nium. With some of the Mela- 
may produce pollen differing in stomacese, seedlings raised by me 
nature, and in this manner a cross from flowers fertilised by pollen 
might be made effective between from the shorter stamens, cer- 
the several flowers on the same tainly differed in appearance from 
plant. Mr. Macnab states (in a those raised from the longer sta- 
communication to M. Verlot, ' La mens, with differently coloured 
Production des Varietes,' 1865, anthers ; but here, again, there is 
p. 42) that seedlings raised from some reason for believing that the 
the shorter and longer stamens of shorter stamens are tending to- 
rhododendron differ in character ; wards abortion. In the very dif- 
but the shorter stamens appa- ferent case of trimorphic hetero- 
rently are becoming rudimentary, styled plants, the two sets of sta- 
and the seedlings are dwarfs, so mens in the same flower have 
that the result may be simply due widely different fertilising powers, 
to a want of fertilising power in f I have given numerous cases 
the pollen, as in the case of the of such bud-variations in my ' Ya- 
dwarfed plants of Mirabilis raised riation of Animals and Plants un- 
by Naudin by the use of too few der Domestication,' chap. xi. 2ud 
pollen-grains. Analogous state- edit. vol. i. p. 448. 



CHAP. VIII. FLOWERS ON THE SAME PLANT. 299 

like those on distinct plants during the develop- 
ment of species. 

It was therefore necessary to ascertain by experiment 
what would be the effect of intercrossing flowers on 
the same plant, in comparison with fertilising them 
with their own pollen or crossing them with pollen 
from a distinct plant. Trials were carefully made on 
five genera belonging to four families ; and in only 
one case, namely, Digitalis, did the offspring from a 
cross between the flowers on the same plant receive 
any benefit, and the benefit here was small compared 
with that derived from a cross between distinct plants. 
In the chapter on Fertility, when we consider the 
effects of cross-fertilisation and self-fertilisation on the 
productiveness of the parent-plants we shall arrive at 
nearly the same result, namely, that a cross between 
the flowers on the same plant does not at all increase 
the number of the seeds, or only occasionally and to a 
slight degree. I will now give an abstract of the 
results of the five trials which were made. 

(1.) Digitalis purpurea. Seedlings raised from inter- 
crossed flowers on the same plant, and others from 
flowers fertilised with their own pollen, were grown in 
the usual manner in competition with one another on 
the opposite sides of ten pots. In this and the four 
following cases, the details may be found under the 
head of each species. In eight pots, in which the 
plants did not grow much crowded, the flower-stems 
on sixteen intercrossed plants were in height to those 
on sixteen self-fertilised plants, as 100 to 94. In the 
two other pots in which the plants grew much crowded, 
the flower-stems on nine intercrossed plants were in 
height to those on nine self-fertilised plants, as 100 
to 90. That the intercrossed plants in these two latter 
pots had a real advantage over their self-fertilised 



300 THE EFFECTS OF CROSSING CHAP. VIII. 

opponents, was well shown by their relative weights 
when cut down, which was as 100 to 78. The mean 
height of the flower-stems on the twenty-five inter- 
crossed plants in the ten pots taken together, was to 
that of the flower-stems on the twenty-five self-ferti- 
lised plants, as 100 to 92. Thus the intercrossed 
plants were certainly superior to the self-fertilised in 
some degree ; but their superiority was small compared 
with that of the offspring from a cross between distinct 
plants over the self-fertilised, this being in the ratio 
of 100 to 70 in height. Nor does this latter ratio 
show at all fairly the great superiority of the plants 
derived from a cross between distinct individuals over 
the self-fertilised, as the former produced more than 
twice as many flower-stems as the latter, and were 
much less liable to premature death. 

(2.) Ipomceapurpurea. Thirty-one intercrossed plants 
raised from a cross between flowers on the same plants 
were grown in ten pots in competition with the same 
number of self-fertilised plants, and the former were 
to the latter in height as 100 to 105. So that the 
self-fertilised plants were a little taller than the inter- 
crossed ; and in eight out of the ten pots a self-fertilised 
plant flowered before any one of the crossed plants in 
the same pots. The plants which were not greatly 
crowded in nine of the pots (and these offer the fairest 
standard of comparison) were cut down and weighed ; 
and the weight of the twenty-seven intercrossed plants 
was to that of the twenty -seven self-fertilised as 100 
to 124; so that by this test the superiority of the 
self-fertilised was strongly marked. To this subject of 
the superiority of the self-fertilised plants in certain 
cases, I shall have to recur in a future chapter. If we 
now turn to the offspring from a cross between 
distinct plants when put into competition with self- 



CHAP. VIII. FLOWERS ON THE SAME PLANT. 301 

fertilised plants, we find that the mean height of 
seventy-three such crossed plants, in the course of ten 
generations, was to that of the same number of 
self-fertilised plants as 100 to 77 ; and in the case of 
the plants of the tenth generation in weight as 100 to 
44. Thus the contrast between the effects of crossing 
flowers on the same plant, and of crossing flowers on 
distinct plants, is wonderfully great. 

(3.) Mimulus luteus. Twenty-two plants raised by 
crossing flowers on the same plant were grown in 
competition with the same number of self-fertilised 
plants ; and the former were to the latter in height as 
100 to 95, or if four dwarfed plants are excluded as 
100 to 101 ; and in weight as 100 to 103. In seven out 
of the eight pots a self-fertilised plant flowered before 
any of the intercrossed. So that here again the self- 
fertilised exhibit a trifling superiority over the inter- 
crossed plants. For the sake of comparison, I may 
add that seedlings raised during three generations 
from a cross between distinct plants were to the self- 
fertilised plants in height as 100 to 65. 

(4.) Pelargonium zonale. Two plants growing in 
separate pots, which had been propagated by cuttings 
from the same plant, and therefore formed in fact 
parts of the same individual, were intercrossed, and 
other flowers on one of these plants were self-fertilised ; 
but the seedlings obtained by the two processes did 
not differ in height. When, on the other hand, flowers 
on one of the above plants were crossed with pollen 
taken from a distinct seedling, and other flowers were 
self-fertilised, the crossed offspring thus obtained were 
to the self-fertilised in height as 100 to 74. . 

(5.) Origanum vulgrare. A plant which had been 
long cultivated in my kitchen garden, had spread by 
stolons so as to form a large bed or clump. Seedlings 



302 THE EFFECTS OF CROSSING CHAP. VIII. 

raised by intercrossing flowers on these plants, which 
strictly consisted of the same plant, and other seedlings 
raised from self-fertilised flowers, were carefully com- 
pared from thei < earliest youth to maturity ; and they 
did not differ at all in height or in constitutional 
vigour. Some flowers on these seedlings were then 
crossed with pollen taken from a distinct seedling, and 
other flowers were self-fertilised ; two fresh lots of 
seedlings being thus raised, which were the grand- 
children of the plant that had spread by stolons and 
formed a large clump in my garden. These differed 
much in height, the crossed plants being to the 
self-fertilised as 100 to 86. They differed, also, to a 
wonderful degree in constitutional vigour. The crossed 
plants flowered first, and produced exactly twice as 
many flower-stems ; and they afterwards increased by 
stolons to such an extent as almost to overwhelm the 
self-fertilised plants. 

Reviewing these five cases, we see that in four of 
them, the effect of a cross between flowers on the same 
plant (even on offsets of the same plant growing on 
separate roots, as with the Pelargonium and Origa- 
num) does not differ from that of the strictest self- 
fertilisation. Indeed, in two of the cases the self-fer- 
tilised plants were slightly superior to such intercrossed 
plants. With Digitalis a cross between the flowers on 
the same plant certainly did do some good, yet very 
slight compared with that from a cross between distinct 
plants. On the whole the results here arrived at, if 
we bear in mind that the flower-buds are to a certain 
extent distinct individuals and occasionally vary inde- 
pendently of one another, agree well with our general 
conclusion, that the advantages of a cross depend on 
the progenitors of the crossed plants possessing some- 
what different constitutions, either from having been 



CHAP. VIII. FLOWERS ON THE SAME PLANT. 303 

exposed to different conditions, or to their having 
varied from unknown causes in a manner which we in 
our ignorance are forced to speak of as spontaneous. 
Hereafter I shall have to recur to this subject of the 
inefficiency of a cross between the flowers on the same 
plant, when we consider the part which insects play in 
the cross-fertilisation of flowers. 

On the Transmission of the good Effects from a Cross 
and of the evil Effects from Self-fertilisation. We have 
seen that seedlings from a cross between distinct plants 
almost always exceed their self-fertilised opponents in 
height, weight, and constitutional vigour, and, as will 
hereafter be shown, often in fertility. To ascertain 
whether this superiority would be transmitted beyond 
the first generation, seedlings were raised on three 
occasions from crossed and self-fertilised plants, both 
sets being fertilised in the same manner, and therefore 
not as in the many cases given in Tables A, B, and C, 
in which the crossed plants were again crossed and the 
self-fertilised again self-fertilised. 

Firstly, seedlings were raised from self-fertilised 
seeds produced under a net by crossed and self-fer- 
tilised plants of Nemophila insignis; and the latter 
were to the former in height as 133 to 100. But these 
seedlings became very unhealthy early in life, and grew 
so unequally that in both lots some were five times 
as tall as the others. Therefore this experiment was 
quite worthless ; but I have felt bound to give it, as 
opposed to my general conclusion. I should state that 
in this and the two following trials, both sets of plants 
were grown on the opposite sides of the same pots, and 
treated in all respects alike. The details of the experi- 
ments may be found under the head of each species. 

Secondly, a crossed and a self-fertilised plant of 
Heartsease (Viola tricolor) grew near together in the 



304 TRANSMITTED EFFECTS OF A CROSS. CHAP. VIII 

open ground and near to other plants of heartsease, 
and as both produced an abundance of very fine cap- 
sules, the flowers on both were certainly cross-fertilised 
by insects. Seeds were collected from both plants, and 
seedlings raised from them. Those from the crossed 
plants flowered in all three pots before those from the 
self-fertilised plants ; and when fully grown the former 
were to the latter in height as 100 to 82. As both sets 
of plants were the product of cross-fertilisation, the 
difference in their growth and period of flowering was 
clearly due to their parents having been of crossed and 
self-fertilised parentage ; and it is equally clear that 
they transmitted different constitutional powers to their 
offspring, the grandchildren of the plants which were 
originally crossed and self-fertilised. 

Thirdly, the Sweet Pea (Laihyrus odoratus) habi- 
tually fertilises itself in this country. As I possessed 
plants, the parents and grandparents of which had 
been artificially crossed and other plants descended 
from the same parents which had been self-fertilised 
for many previous generations, these two lots of plants 
were allowed to fertilise themselves under a net, and 
their self-fertilised seeds saved. The seedlings thus 
raised were grown in competition with each other in the 
usual manner, and differed in their powers of growth. 
Those from the self-fertilised plants which had been 
crossed during the two previous generations were to 
those from the plants self -fertilised during many pre- 
vious generations in height as 100 to 90. These two 
lots of seeds were likewise tried by being sown under 
very unfavourable conditions in poor exhausted soil, and 
the plants whose grandparents and great-grandparents 
had been crossed showed in an unmistakable manner 
their superior constitutional vigour. In this case, as 
in that of the heartsease, there could be no doubt that 



CHAP. VIII. TRANSMITTED EFFECTS OF A CBOSS. 305 

the advantage derived from a cross between two plants 
was not confined to the offspring of the first generation. 
That constitutional vigour due to cross-parentage is 
transmitted for many generations may also be inferred 
as highly probable, from some of Andrew Knight's 
varieties of the common pea, which were raised by 
crossing distinct varieties, after which time they no 
doubt fertilised themselves in each succeeding gene- 
ration. These varieties lasted for upwards of sixty 
years, " but their glory is now departed." * On the 
other hand, most of the varieties of the common pea, 
which there is no reason to suppose owe their origin 
to a cross, have had a much shorter existence. Some 
also of Mr. Laxton's varieties produced by artificial 
crosses have retained their astonishing vigour and 
luxuriance for a considerable number of generations ; 
but as Mr. Laxton informs me, his experience does 
not extend beyond twelve generations, within which 
period he has never perceived any diminution of vigour 
in his plants. 

An allied point may be here noticed. A& the force 
of inheritance is strong with plants (of which abundant 
evidence could be given), it is almost certain that seed- 
lings from the same capsule or from the same plant 
would tend to inherit nearly the same constitution ; and 
as the advantage from a cross depends on the plants 
which are crossed differing somewhat in constitution, 
it may be inferred as probable that under similar con- 
ditions a cross between the nearest relations would 
not benefit the offspring so much as one between non- 
related plants. In support of this conclusion we have 
some evidence, as Fritz Miiller has shown by his 



* See the evidence on this mestication,' chip. ix. vol. i. 2nd 
head in my Variation -under Do- edit. p. R97 

X 



306 UNIFORM COLOUR OF THE FLOWERS CHAP. VIII. 

valuable experiments on hybrid Abutilons, that the 
union of brothers and sisters, parents and children, 
and of other near relations is highly injurious to the 
fertility of the offspring. In one case, moreover, seed- 
lings from such near relations possessed very weak 
constitutions.* This same observer also found f three 
plants of a Bignonia growing near together. He fer- 
tilised twenty-nine flowers on one of them with their 
own pollen, and they did not set a single capsule. 
Thirty flowers were then fertilised with pollen from 
a distinct plant, one of the three growing together, 
and they yielded only two capsules. Lastly, five 
flowers were fertilised with pollen from a fourth plant 
growing at a distance, and all five produced capsules. 
It seems therefore probable, as Fritz Miiller suggests, 
that the three plants growing near together were 
seedlings from the same parent, and that from being 
closely related they had little power of fertilising one 
another.^ 

Lastly, the fact of the intercrossed plants in 
Table A not exceeding in height the self-fertilised 
plants in a greater and greater degree in the later 
generations, is probably due to their having become 
more and more closely inter-related. 

Uniform Colour of the Flowers on Plants, self -fertilised 
and grown under similar conditions for several Genera- 
tions. At the commencement of my experiments, the 
parent-plants of Mimulus luteus, Ipomoea purpurea, 
Dianthus caryophyllus, and Petunia violacea, raised 
from purchased seeds, varied greatly in the colour 

* 'Jenaische Zeitschrift fur Domestication' ("chap, xvii. 2nd 

Naturw.; B. vii., pp. 22 and 45, edit. vol. 2, p. 121) of hybrids of 

1872 ; and 1873, pp. 441-450. Gladiolus and Cistus, any one of 

t ' Bot. Zeitunt?,' 1868, p. 626. which could be fertilised by pollen 

j Some remarkable caaea are from any other, but nc t by its 

given in my ' Variation under own pollen. 




OHAP. VIII. ON SELF-FERTILISED PLANTS. 307 

of their flowers. This occurs with many plants which 
have been long cultivated as an ornament for the 
flower-garden, and which have been propagated by 
seeds. The colour of the flowers was a point to which 
I did not at first in the least attend, and no selection 
whatever was practised. Nevertheless, the flowers 
produced by the self-fertilised plants of the above 
four species became absolutely uniform in tint, or very 
nearly so, after they had been grown for some gene- 
rations under closely similar conditions. The inter- 
crossed plants, which were more or less closely 
inter-related in the later generations, and which had 
been likewise cultivated all the time under similar 
conditions, became more uniform in the colour of 
their flowers than were the original parent-plants, but 
much less so than the self-fertilised plants. When 
self-fertilised plants of one of the later generations 
were crossed with a fresh stock, and seedlings thus 
raised, these presented a wonderful contrast in the 
diversified tints of their flowers compared with those of 
the self-fertilised seedlings. As such cases of flowers 
becoming uniformly coloured without any aid from 
selection seem to me curious, I will give a full 
abstract of my observations. 

Mimulus luteus. A tall variety, bearing large, almost 
white flowers blotched with crimson, appeared amongst 
intercrossed and self-fertilised plants of the third 

.d fourth generations. This variety increased so 
rapidly, that in the sixth generation of self-fertilised 
plants every single one consisted of it. So it was 
with all the many plants which were raised, up to thf> 
last or ninth self-fertilised generation. Although this 
variety first appeared amongst the intercrossed plants, 
yet from their offspring being intercrossed in each 
succeeding generation, it never prevailed amongst 

x 2 



308 UNIFOKM COLOUK OF THE FLOWERS CHAP. VIII. 

them ; and the flowers on the several intercrossed 
plants of the ninth generation differed considerably in 
colour. On the other hand, the uniformity in colour 
of the flowers on the plants of all the later self-fer- 
tilised generations was quite surprising ; on a casual 
inspection, they might have been said to be quite alike, 
but the crimson blotches were not of exactly the same 
shape, or in exactly the same position. Both my 
gardener and myself believe that this variety did 
not appear amongst the parent-plants, raised from pur- 
chased seeds, but from its appearance amongst both the 
crossed and self-fertilised plants of the third and fourth 
generations ; and from what I have seen of the variation 
of this species on other occasions, it is probable that it 
would occasionally appear under any circumstances. 
We learn, however, from the present case that under 
the peculiar conditions to which my plants were 
subjected, this particular variety, remarkable for its 
colouring, largeness of the corolla, and increased 
height of the whole plant, prevailed in the sixth and 
all the succeeding self-fertilised generations to the 
complete exclusion of every other variety. 

Ipomcea purpurea. My attention was first drawn to 
the present subject by observing that the flowers on all 
the plants of the seventh self-fertilised generation were 
of a uniform, remarkably rich, dark purple tint. The 
many plants which were raised during the three suc- 
ceeding generations, up to the last or tenth, all produced 
flowers coloured in the same manner. They were 
absolutely uniform in tint, like those of a constant 
species living in a state of nature ; and the self-fertilised 
plants might have been distinguished with certainty, 
as my gardener remarked, without the aid of labels, 
from the intercrossed plants of the later generations. 
These, however, had more uniformly coloured flowers 



CHAP. VIII. ON SELF-FERTILISED PLANTS. 309 

than those which were first raised from the purchased 
seeds. This dark purple variety did not appear, as 
far as my gardener and myself could recollect, before 
the fifth or sixth self-fertilised generation. However 
this may have been, it became, through continued 
self-fertilisation and the cultivation of the plants 
under uniform conditions, perfectly constant, to the 
exclusion of every other variety. 

Dianthus caryophyllus. The self-fertilised plants of 
the third generation all bore flowers of exactly the 
same pale rose-colour ; and in this respect they differed 
quite remarkably from the plants growing in a large 
bed close by and raised from seeds purchased from the 
same nursery garden. In this case it is not improbable 
that some of the parent-plants which were first self- 
fertilised may have borne flowers thus coloured ; but 
as several plants were self-fertilised in the first genera- 
tion, it is extremely improbable that all bore flowers 
of exactly the same tint as those of the self-fertilised 
plants of the third generation. The intercrossed plants 
of the third generation likewise produced flowers 
almost, though not quite so uniform in tint as those 
of the self-fertilised plants. 

Petunia violacea. In this case I happened to record 
in my notes that the flowers on the parent-plant which 
was first self- fertilised were of a " dingy purple colour." 
In the fifth self-fertilised generation, every one of the 
twenty-one self-fertilised plants growing in pots, and 
all the many plants in a long row out of doors, 
produced flowers of absolutely the same tint, namely, 
of a dull, rather peculiar and ugly flesh colour ; there- 
fore, considerably unlike those on the parent-plant. I 
believe that this change of colour supervened quite 
gradually ; but I kept no record, as the point did not 
interest me until I was struck with the uniform tint 



310 UNIFOKM COLOUR OF THE FLOWERS CHAP. VIIL 

of the flowers on the self-fertilised plants of the fifth 
generation. The flowers on the intercrossed plants of 
the corresponding generation were mostly of the same 
dull flesh colour, but not nearly so uniform as those on 
the self-fertilised plants, some few being very pale, 
almost white. The self-fertilised plants which grew in 
a long row in the open ground were also remarkable for 
their uniformity in height, as were the intercrossed 
plants in a less degree, both lots being compared with 
a large number of plants raised at the same time under 
similar conditions from the self-fertilised plants of the 
fourth generation crossed by a fresh stock. I regret 
that I did not attend to the uniformity in height of 
the self-fertilised seedlings in the later generations of 
the other species. 

These few cases seem to me to possess much interest. 
We learn from them that new and slight shades of 
colour may be quickly and firmly fixed, independently 
of any selection, if the conditions are kept as nearly 
uniform as is possible, and no intercrossing be per- 
mitted. With Mimulus, not only a grotesque style of 
colouring, but a larger corolla and increased height of 
the whole plant were thus fixed ; whereas with most 
plants which have been long cultivated for the flower- 
garden, no character is more variable than that of 
colour, excepting perhaps that of height. From the 
consideration of these cases we may infer that the 
variability of cultivated plants in the above respects 
is due, firstly, to their being subjected to somewhat 
diversified conditions, and, secondly, to their being 
often inter-crossed, as would follow from the free access 
of insects. I do not see how this inference can be 
avoided, as when the above plants were cultivated 
for several generations under closely similar conditions, 
and were intercrossed in each generation, the colour 



CHAP. VIII. ON SELF-FERTILISED PLANTS. 311 

of their flowers tended in some degree to change and to 
become uniform. When no intercrossing with other 
plants of the same stock was allowed, that is, when 
the flowers were fertilised with their own pollen in 
each generation their colour in the later generations 
became as uniform as that of plants growing in a 
state of nature, accompanied at least in one instance 
by much uniformity in the height of the plants. But 
in saying that the diversified tints of the flowers on 
cultivated plants treated in the ordinary manner are 
due to differences in the soil, climate, &c., to which 
they are exposed, I do not wish to imply that such 
variations are caused by these agencies in any more 
direct manner than that in which the most diversified 
illnesses, as colds, inflammation of the lungs or pleura, 
rheumatism, &c., may be said to be caused by expo- 
sure to cold. In both cases the constitution of the 
being which is acted on is of pieponderant importance. 






312 FERTILITY OF CROSSED CHAP. IX. 



CHAPTER IX. 

THE EFFECTS OF CROSS-FEBTILISATION AND SELF-FERTILISATION OK 
THE PRODUCTION OF SEEDS. 

Fertility of plants of crossed and self-fertilised parentage, both lota 
being fertilised in the same manner Fertility of the parent-plants 
when first crossed and self-fertilised, and of their crossed and self- 
fertilised offspring when again crossed and self-fertilised Com- 
parison of the fertility of flowers fertilised with their own pollen 
and with that from other flowers on the same plant Self-sterile 
plants Causes of self-sterility The appearance of highly self- 
fertile varieties Self-fertilisation apparently in some respects bene- 
ficial, independently of the assured production of seeds. Kelative 
weights and rates of germination of seeds from crossed and telf- 
fertilised flowers. 

THE present chapter is devoted to the Fertility of 
plants, as influenced by cross-fertilisation and self- 
fertilisation. The subject consists of two distinct 
branches ; firstly, the relative productiveness or fertility 
of flowers crossed with pollen from a distinct plant and 
with their own pollen, as shown by the proportional 
number of capsules which they produce, together 
with the number of the contained seeds. Secondly, 
the degree of innate fertility or sterility of the seed- 
lings raised from crossed and self-fertilised seeds ; such 
seedlings being of the same age, grown under the same 
conditions, and fertilised in the same manner. These 
two branches of the subject correspond with the two 
which have to be considered by any one treating of 
hybrid plants; namely, in the first place the comparative 
productiveness of a species when fertilised with pollen 
from a distinct species and with its own pollen ; and 



CHAP. IX. AND SELF-FERTILISED PLANTS. 313 

in the second place, the fertility of its hybrid off- 
spring. Thes-j two classes of cases do not always run 
parallel ; thus some plants, as Gartner has shown, can 
be crossed with great ease, but yield excessively sterile 
hybrids ; while others are crossed with extreme diffi- 
culty, but yield fairly fertile hybrids. 

The natural order to follow in this chapter would 
have been first to consider the effects on the fertility 
of the parent-plants of crossing them, and of fertilising 
them with their own pollen ; but as we have discussed 
in the two last chapters the relative height, weight, 
and constitutional vigour of crossed and self-fertilised 
plants that is, of plants raised from crossed and 
self-fertilised seeds it will be convenient here first 
to consider their relative fertility. The cases observed 
by me are given in the following table, D, in which 
plants of crossed and self-fertilised parentage were left 
to fertilise themselves, being either crossed by insects 
or spontaneously self-fertilised. It should be observed 
that the results cannot be considered as fully trust- 
worthy, for the fertility of a plant is a most variable 
element, depending on its age, health, nature of the 
soil, amount of water given, and temperature to which 
it is exposed. The number of the capsules produced 
and the number of the contained seeds, ought to have 
been ascertained on a large number of crossed and self- 
fertilised plants of the same age and treated in every 
respect alike. In these two latter respects my observa- 
tions may be trusted, but a sufficient number of capsules 
were counted only in a few instances. The fertility, 
or- as it may perhaps better be called the productive- 
ness, of a plant depends on the number of capsules 
produced, and on the number of seeds which these 
contain. But from various causes, chiefly from the 
want of time, I was often compelled to rely on the 



314 



FEETILITY OF CROSSED 



CHAP IX. 



number of the capsules alone. Nevertheless, in the 
more interesting cases, the seeds were also counted 
or weighed. The average number of seeds per capsule 
is a more valuable criterion of fertility than the 
number of capsules produced. This latter circum- 
stance depends partly on the size of the plant ; and we 
know that crossed plants are generally taller and 
heavier than the self- fertilised ; but the difference in 
this respect is rarely sufficient to account for the 
difference in the number of the capsules produced. It 
need hardly be added that in the following table the 
same number of crossed and self-fertilised plants are 
always compared. Subject to the foregoing sources of 
doubt I will now give the table, in which the parentage 
of the plants experimented on, and the manner of 
determining their fertility are explained. Fuller 
details may be found in the previous part of this work, 
Tinder the head of each species. 



TABLE D. Relative Fertility of Plants of crossed and self -fertilise I 
Parentage, loth sets being fertilised in the same manner. Fer- 
tility judged of by various Standards. That of the crossed Plants 
taken as 100. 



IPOM<EA PURPUREA first generation: seeds per capsule 
on crossed and self-fertilised plants, not growing much 
crowded, spontaneously self-fertilised under a net, in 
number 

IPOMCEA PURPUREA seeds per capsule on crossed and 
self-fertilised plants from the same parents as in the last 
case, but growing much crowded, spontaneously self- 
fertilised under a net, in number 

IPOMCEA PURPUREA productiveness of the same plants, as 
judged by the number of capsules produced, and average 
number of seeds per capsule 

IPOMCEA PURPUREA third generation: seeds per capsule 
on crossed and self-fertilised plants, spontaneously self- 
fertilised under a net, in number 

IPOMCEA PURPUREA productiveness of the same plants, 
as judged by number of capsules produced, and ayjrage 
number of seeds per capsule 



as 100 to 9S 

93 

45 

94 

35 



CHAP. IX. AND SELF-FERTILISED PLANTS. 
TABLE D continued. 



315 






IPOMCEA PURPUREA fifth generation : seeds per capsule 

on crossed and self-fertilised plants, left uncovered in the as 100 to 89 
hothouse, and spontaneously fertilised 

IPOMCEA PURPUREA ninth gcr&ration : number of capsules 

on crossed plants to those on self-fertilised plants, spon- 26 
taneously self-fertilised under a net 

MIMULUS LUTEUS an equal number of capsules on plants' 
descended from self-fertilised plants of the 8th genera- 
tion crossed by a fresh stock, and on plants of the 9th 
self-fertilised generation, both sets having been left 
uncovered and spontaneously fertilised, contained seeds, 
by weight 

MIMULUS LDTEUS productiveness of the same plants, as 
judged by number of capsules produced, and average 
weight of seeds per capsule 

VANOELLIA NUMMULARIFOLIA seeds per capsule from 
cleistogamic flowers on the crossed and self-fertilised 
plants, in number 

SALVIA COCCINEA crossed plants, compared with self-fer-j 
tiiised plants, produced flowers, in number . . . .) 

IBERIS UMBELLATA plants left uncovered in greenhouse; 

intercrossed plants of the 3rd generation, compared with _. 

self-fertilised plants of the 3rd generation, yielded seeds, " " 
in number 

IBERIS UMBELLATA plants from a cross between two] 

varieties, compared with self- fertilised plants of the 3rd> 75 
generation, yielded seeds, by weight J 

PAPAVER VAGUM crossed and self-fertilised plants, leffl 

uncovered, produced capsules, in number / " " 

ESCHSCHOLTZIA CALIFORNICA Brazilian stock ; plants left 
uncovered and cross-fertilised by bees ; capsules on 
intercrossed plants of 2nd generation, compared with 78 
capsules on self-fertilised plants of 2nd generation, con- 
tained seeds, in number 

ESCHSCHOLTZIA CALIFORNICA productiveness of the same] 

plants, as judged by number of capsules produced, and> ,, 89 
average number of seeds per capsule j 

ESCHSCHOLTZIA CALIFORNICA plants left uncovered and' 
cross-fertilised by bees : capsules on plants derived from 
intercrossed plants of 2nd generation of the Brazilian 
stock crossed by English stock, compared with capsules 
on self-fertilised plants of 2nd generation, contained 
seeds, in number t 

ESCHSCHOLTZIA CALIFORNICA productiveness of the same 

plants, as judged by number of capsules produced, and 40 
average number of seeds per capsule 



316 



FERTILITY OP CROSSED 
TABLE D continued. 



CHAP. IX, 



RESEDA ODORATA crossed and self-fertilised plants, left 
uncovered and cross-fertilised by bees, produced capsules 
in number (about) 

VIOLA TBICOLOR crossed and self-fertilised plants, left 
uncovered and cross-fertilised by bees, produced capsules 
in number 

DELPHINIUM CONSOLIDA crossed and self-fertilised plants, 
left uncovered in the greenhouse, produced capsules in 
number 

VISCARIA OCULATA crossed and self-fertilised plants, left 
uncovered in the greenhouse, produced capsules in number 

DIANTHUS CARYOPHYLLUS plants spontaneously self-ferti- 
lised under a net ; capsules oa intercrossed and self- 
fertilised plants of the 3rd generation contained seeds in 
number 

DIANTHUS CARYOPHYLLUS plants left uncovered and cross- 
fertilised by insects : offspring from plants self-fertilised 
for three generations and then crossed by an inter- 
crossed plant of the same stock, compared with plants 
of the 4th self-fertilised generation, produced seeds by 
weight t 

DIANTHUS CARYOPHYLLUS plants left uncovered and cross-1 
fertilised by insects : offspring from plants self-fertilised 
*br three generations and then crossed by a fresh 
stock, compared with plants of the 4th self-fertilised 
generation, produced seeds by weight , 

TROP^EOLUM MINUS crossed aud self-fertilised plants, left 
uncovered in the greenhouse, produced seeds in number . 

LIMNANTHES DOUGLASii crossed and self-fertilised plants, 
left uncovered in greenhouse, produced capsules in 
number (about) 

LUPINUS LUTEUS crossed and self-fertilised plants of the 
2nd generation, left uncovered in the greenhouse, pro- 
duced seeds in number (judged from only a few pods) 

PHASEOLUS MULTIFLORUS crossed and self-fertilised plants, 
left uncovered in the greenhouse, produced seeds in 
number (about) 

LATHYRUS ODORATUS crossed and self-fertilised plants of 
the 2nd generation, left uncovered in the greenhouse, but 
certainly self-fertilised, produced pods in number 

CLARKIA ELEGANS crossed and self-fertilised plants, left' 
uncovered in the greenhouse, produced capsules in number 

NEMOP&ILA INSIGNIS crossed and self-fertilised plants, 
covered by a net and spontaneously self-fertilised in the 
greenhouse, produced capsules in number 

PETUNIA VIOLACEA left uncovered and cross-fertilised by 
insects : plants of the 5th intercrossed and self-fertilised 
generations produced seeds, as judged by the weight of an i 
equal number of capsules J 



CHAP. IX. AND SELF-FERTILISED PLANTS. 
TABLE D continued. 



317 



PETUNIA VIOLACEA left uncovered as above: offspring oft 
plants self-fertilised for four generations and then crossed] 
by a fresh stock, compared with plants of the 5th self- 



5th self4 
by the 



as 100 to 46 



fertilised generation, produced seeds, as judged 
weight of an equal number of capsule 

CYCLAMEN PERSICUM crossed and self-fertilised plants, left"* 
uncovered in the greenhouse, produced capsules in number/ 

ANAGALLIS COLLINA crossed and self-fertilised plants, lefU 
uncovered in the greenhouse, produced capsules in number/ 

PRIMULA VERIS left uncovered in open ground and cross- 
fertilised by insects : offspring from plants of the 3rd 
illegitimate generation crossed by a fresh stock, compared 
with plants of the 4th illegitimate and self-fertilised 

generation, produced capsules in number 

Same plants in the following year 

PRIMULA VERIS (equal-styled variety): left uncovered in^ 
open ground and cross-fertilised by insects: offspring 
from plants self-fertilised for two generations and thenx 
crossed by another variety, compared with plants of the 3rd 
self-fertilised generation, produced capsules in number J 

PRIMULA VERIS (equal-styled var.) same plants ; ayerage \ 
number of seeds per capsule 

PRIMULA VERIS (equal-styled var.) productiveness of the 
same plants, as judged by number of capsules produced 
and average number of seeds per capsule 



12 



71 



11 



This table includes thirty-three cases relating to 
twenty-three species, and shows the degree of innate 
fertility of plants of crossed parentage in comparison 
with those of self-fertilised parentage ; both lots being 
fertilised in the same manner. With several of the 
species, as with Eschscholtzia, Eeseda, Viola, Dian- 
thus, Petunia, and Primula, both lots were certainly 
cross-fertilised by insects, and so it probably was with 
several of the others ; but in some of the species, as 
with Nemophila, and in some of the trials with Ipomcea 
and Dianthus, the plants were covered up, and both 
lots were spontaneously self-fertilised. This also was 
necessarily the case with the capsules produced by the 
cleistogamic flowers of Vandellia. 



318 FERTILITY OF CROSSED CIIAP. IX. 

The fertility of the crossed plants is represented in 
the table by 100, and that of the self-fertilised by the 
other figures. There are five cases in which the fertility 
of the self-fertilised plants is approximately equal to 
that of the crossed ; nevertheless, in four of these cases 
the crossed plants were plainly taller, and in the fifth 
somewhat taller than the self-fertilised. But I should 
state that in some of these five cases the fertility of 
the two lots was not strictly ascertained, as the capsules 
were not actually counted, from appearing equal in 
number and from all apparently containing a full com- 
plement of seeds. In only two instances in the table, 
viz., with Vandellia and in the third generation of 
Dianthus, the capsules on the self-fertilised plants 
contained more seed than those on the crossed plants. 
With Dianthus the ratio between the number of seeds 
contained in the self-fertilised and crossed capsules 
was as 125 to 100 ; both sets of plants were left to 
fertilise themselves under a net; and it is almost 
certain that the greater fertility of the self-fertilised 
plants was here due merely to their having varied 
and become less strictly dichogamous, so as to mature 
their anthers and stigmas more nearly at the same 
time than is proper to the species. Excluding the 
seven cases now referred to, there remain twenty-six 
in which the crossed plants were manifestly much 
more fertile, sometimes to an extraordinary degree, 
than the self-fertilised with which they grew in com- 
petition. Tile most striking instances are those in 
which plants derived from a cross with a fresh stock 
are compared with plants of one of the later self-fer- 
tilised generations ; yet there are some striking cases, 
as that of Viola, between the intercrossed plants of the 
same stock and the self-fertilised, even in the first 
generation. The results most to be trusted are those 



CHAP. IX. 



AND SELF-FERTILISED PLANTS. 



319 



in which the productiveness of the plants was ascer- 
tained by the number of capsules produced by an 
equal number of plants, together with the actual or 
average number of seeds in each capsule. Of such 
cases there are twelve in the table, and the mean of 
their mean fertility is as 100 for the crossed plants, 
to 59 for the self-fertilised plants. The Primulacese 
seem eminently liable to suffer in fertility from self- 
fertilisation. 

The following short table, E, includes four cases 
which have already been partly given in the last table. 

TABLE E. Innate Fertility of Plants from a Cross with a fresh 
Stock, compared with that of Intercrossed Plants of the same 
Stock, and with that of Self-fertilised Plants, all of the corre- 
sponding Generation ; all these sets being fertilised in the same 
manner. Fertility judged of by the number or weight of seeds 
produced by an equal number of Plants. 





ante from a 
'ross with a 
'resh Stock. 


ntercrossed 
lants of the 
line Stock. 


1 
1| 




S 


Hip, 55 


** 


MIMULUS LUTEUS the intercrossed plants are de- 








rived from a cross between two plants of the 
8th self-fertilised generation. The self-fertilised 


100 


4 


3 


plants belong to the 9th generation .... 








ESCHSCHOLTZIA CALIFORNIA the intercrossed and \ 
self-fertilised plants belong to the 2nd generation/ 


100 


45 


40 


DIANTHUS CARYOPHYLLUS the intercrossed plants 








are derived from self-fertilised of the 3rd ge- 








neration, crossed by intercrossed plants of the 


100 


45 


33 


3rd generation. The self-fertilised plants belong 








to the 4th generation 








PETUNIA VIOLACEA the intercrossed and self-fer-1 
tilled plants belong to the 5th generation . . / 


100 


54 


46 



N B. In the above cases, excepting in that of Eschscholtzia, the plants 
derived from a cross with a fresh stock belong on the mother-side to the 
same stock with the intercrossed and self-fertilised plants, and to the cor- 
responding generation. 



320 FERTILITY OF CROSSED CHAP. IX 

These casos show us how greatly superior in innate 
fertility the seedlings from plants self-fertilised or 
intercrossed for several generations and then crossed 
by a fresh stock are, in comparison with the seedlings 
from plants of the old stock, either intercrossed or 
self-fertilised for the same number of generations. The 
three lots of plants in each case were left freely ex- 
posed to the visits of insects, and their flowers without 
doubt were cross-fertilised by them. 

This table further shows us that in all four cases the 
intercrossed plants of the same stock still have a 
decided though small advantage in fertility over the 
self-fertilised plants. 

With respect to the state of the reproductive organs 
in the self-fertilised plants of the two last tables, 
only a few observations were made. In the seventh 
and eighth generation of Ipomoea, the anthers in the 
flowers of the self-fertilised plants were plainly smaller 
than those in the flowers of the intercrossed plants. 
The tendency to sterility in these same plants was 
also shown by the first-formed flowers, after they had 
been carefully fertilised, often dropping off, in the 
same manner as frequently occurs with hybrids. The 
flowers likewise tended to be monstrous. In the 
fourth generation of Petunia, the pollen produced 
by the self-fertilised and intercrossed plants was 
compared, and there were' far more empty and shrivelled 
grains in the former. 

Relative Fertility of Flowers crossed with Pollen from a 
distinct Plant and with their own Pollen. This heading 
includes flowers on the Parent-plants, and on the crossed 
and self -fertilised Seedlings of the first or a succeeding Ge- 
neration. I will first treat of the parent-plants, which 






CHAP. IX. AND SELF-FERTILISED FLOWERS. 321 

were raised from seeds purchased from nursery -gardens, 
or taken from plants growing in my garden, or 
growing wild, and surrounded in every case by many 
individuals of the same species. Plants thus circum- 
stanced will commonly have been intercrossed by 
insects ; so that the seedlings which were first ex- 
perimented on will generally have been the product 
of a cross. -Consequently any difference in the 
fertility of their flowers, when crossed and self-fer- 
tilised, will have been caused by the nature of the 
pollen employed ; that is, whether it was taken from 
a distinct plant or from the same flower. The de- 
grees of fertility shown in the following table, F, 
were determined in each case by the average number 
of seeds per capsule, ascertained either by counting 
or weighing. 

Another element ought properly to have been taken 
into account, namely, the proportion of flowers which 
yielded capsules when they were crossed and self-fer- 
tilised; and as crossed flowers generally produce a 
larger proportion of capsules, their superiority in fer- 
tility, if this element had been taken into account, 
would have been much more strongly marked than 
appears in Table F. But had I thus acted, there 
would have been greater liability to error, as pollen 
applied to the stigma at the wrong time fails to pro- 
duce any effect, independently of its greater or less 
potency. A good illustration of the great difference 
in the results which sometimes follows, if the number 
of capsules produced relatively to the number of flowers 
fertilised be included in the calculation, was afforded 
by Nolana prostrata. Thirty flowers on some plants 
of this species were crossed and produced twenty-seven 
capsules, each containing five seeds ; thirty-two flowers 
n the same plants were self-fertilised and produced 

T 



322 



FERTILITY OF CROSSED 



CHAP. IX. 



only six capsules, each containing five seeds. As the 
number of seeds per capsule is here the same, the fer- 
tility of the crossed and self-fertilised flowers is given 
in Table F as equal, or as 100 to 100. But if the 
flowers which failed to produce capsules be included, 
the crossed flowers yielded on an average 4*50 seeds, 
whilst the self-fertilised flowers yielded only 94 seeds, 
so that their relative fertility would have been as 100 
to 21. I should here state that it has been found con- 
venient to reserve for separate discussion the cases of 
flowers which are usually quite sterile with their own 
pollen. 



TABLE F. Relative Fertility of the Flowers on the Parent-plants 
used in my Experiments, when fertilised with Pollen from a 
distinct Plant and with their own Pollen. Fertility judged of 
by the average Number of Seeds per Capsule. Fertility of 
Crossed Flowers taken as 100. 



IPOMCEA PURPUBEA crossed and self-fertilised flowers'! 

yielded seeds as (about) / 

MIMULUS LUTEUS crossed and self-fertilised flowers yielded"! 

seeds as (by weight) J 

LINARIA VULGARIS crossed and self-fertilised flowers') 

yielded seeds as / 

VANDELLIA NUMMULARIFOLIA crossed and self-fertilised") 

flowers yielded seeds as 

GESNERIA PENDULINA crossed and self-fertilised flowers) 

yielded seeds as (by weight) j 

SALVIA COCCINEA crossed and self-fertilised flowers yielded"! 

seeds as (about) / 

BRASSICA OLERACEA crossed and self-fertilised flowers'! 

yielded seeds as J 

ESCHSCHOLTZIA CALIFORNICA (English stock) crossed and"! 

self-fertilised flowers yielded seeds as (by weight) . ./ 
ESCHSCHOLTZIA CALIFORNICA (Brazilian stock grown in) 

England) crossed and self-fertilised flowers yielded seeds} 

(by weight) as (about) j 

DELPHINIUM CONSOLIDA crossed and self-fertilised flowers) 

(self-fertilised capsules spontaneously produced, b^t result} 



supported by other evidence) yielded seeds as . 



100 to 100 
> 79 
14 
67? 

n ii 100 

100 

25 

n ,, 71 

n n " 

, 58 



CHAP. IX. AND SELF-FERTILISED FLOWERS. 323 

TABLE F continued. 



VISCARIA OCCLATA crossed and self-fertilised flowers 1Aft . 

yielded seeds as (by weight) 

VISCARIA OCULATA crossed and self-fertilised flowers 

(crossed capsules compared on following year with spon- 58 

taneously self-fertilised capsules) yielded seeds as . . . 
DIANTHUS CARYOPHYLLUS crossed and self-fertilised flowers 

yielded seeds as 

TROP^OLUM MINUS crossed and self-fertilised flowers! 

yielded seeds as /"* 

TROP^EOLDM TRICOLORUM* crossed and self-fertilked! 

Jowers yielded seeds as 

LIMNANTHES DOUGLASii crossed and self-fertilised flowers! 1 nn 

yielded seeds as (about) / 

SAROTHAMNUS SCOPARIUS crossed and self-fertilised flowers "I . 1 

yielded seeds as " " 

OXONIS MIXUTISSIMA crossed and self-fertilised flowers 

yielded seeds as 

CUPHEA PURPUREA crossed and self-fertilised flowers ... 

yielded seeds as " " il 

PASSIFLORA GRACILIS crossed and self-fertilised flowers ,. 

yielded seeds as " " 

SPECDLARIA SPECULUM crossed and self-fertilised flowers! 

yielded seeds as / 

LOBELIA FULGENS crossed and self-fertilised flowers y ielded \ 

seeds as (about) / 

NEMOPHILA IXSIGXIS crossed and self-fertilised flowers 

yielded seeds as (by weight) 

BORAGO OFFICINALIS crossed and self-fertilised flowers 

yielded seeds as 

NOLANA PROSTRATA crossed and self-fertilised flowers 

yielded seeds as 

PETUNIA VIOLACEA crossed and self-fertilised flowers\ fi? 

yielded seeds as (by weight) / 

NICOTIANA TABACUM crossed and self-fertilised flowers! 

yielded seeds as (by weight) / 

CYCLAMEN PERSICUM crossed and self-fertilised flowers! 

yielded seeds as ./ 

ANAGALLJS COLLINA crossed and self-fertilised flowers! 

yielded seeds as / 

CANNA WARSCEWICZI crossed and self-fertilised flowers (on J 

three generations of crossed and self-fertilised plants taken > 85 

all together) yielded seeds as . j 



* Tropxolum tricolorum and 
Cuphea purpurea have been intro- 
duced into this table, although 
seedlings were not raised from 
them ; but of the Cuphea only 
six crossed and six self-ferti- 
lised capsulen, and of the Tropse- 



olum only six crossed and eleven 
self-fertilised capsules, were com- 
pared. A larger proportion of 
the self-fertilised tlian of the 
crossed flowers of the Tropseolnm 
produced fruit. 

T 2 



324 



FEETILITY OF CROSSED 



CHAP. IX. 



A second table, G-, gives the relative fertility of 
flowers on crossed plants again cross-fertilised, and of 
flowers on self- fertilised plants again self-fertilised, 
either in the first or in a later generation. Here two 
causes combine to diminish the fertility of the self- 
fertilised flowers ; namely, the lesser efficacy of pollen 
from the same flower, and the innate lessened fertility 
of plants derived from self-fertilised seeds, which as we 
have seen in the previous Table D is strongly marked. 
The fertility was determined in the same manner as 
in Table F, that is, by the average number of seeds per 
capsule ; and the same remarks as before, with respect 
to the different proportion of flowers which set capsules 
when they are cross-fertilised and self-fertilised, are 
here likewise applicable. 

TABLE G Relative Fertility of Flowers on Crossed and Self- 
fertilised Plants of the First or some succeeding Generation ; the 
former being again fertilised with Pollen from a distinct Plant, 
and the latter again with their own Pollen. Fertility judged 
of by the average Number of Seeds per Capsule. Fertility of 
Crossed Flowers taken as 100. 



IPOMCEA PURPUEEA crossed and self-fertilised flowers on 
the crossed and self-fertilised plants of the 1st generation 
yielded seeds as 

IPOMCEA PURPUKEA crossed and self-fertilised flowers on 
the crossed and self-fertilised plants of the 3rd generation 
yielded seeds as 

IPOMCEA PURPUREA crossed and self-fertilised flowers on 
the crossed and self-fertilised pi ints of the 4th generation 
yielded seeds as 

IPOMCEA PURPUREA crossed and self-fertilised flowers on 
the crossed and self-fertilised plants of the 5th generation 
yielded seeds as ) 

MIMULUS LUTEUS crossed and self-fertilised flowers on the 
crossed and self-fertilised plants of the 3rd generation 
yielded seeds as (by weight) 

MIMULUS LUTEUS same plants treated in the same manner 
on following year yielded seeds as (by weight) . . 

MIKULUS LUTEUS crossed and self-fertilised flowers on the 
crossed and self-fertilised plants of the 4th generation 
yielded seeds as (by \v tight) 



100 to 93 



107 



40 






CHAP. IX. AND SELF-FERTILISED FLOWERS. 325 

TABLB G continued. 



VIOLA TRICOLOR crossed and self-fertilised flowers on the 
crossed and self-fertilised plants of the 1st generation 
yieldod seeds as 

OIANTHUS CARYOPHYLLUS crossed and self-fertilised flowers 
on the crossed and self-fertilised plants of the 1st genera- 
tion yielded seeds as 

DIANTHUS CARYOPHYLLUS flowers on self-fertilised plants 
of the 3rd generation crossed by intercrossed plants, and 
other flowers again self-fertilised yielded seeds as 
)IANTHUS CARYOPHYLLUS flowers on self-fertilised plants 
of the 3rd generation crossed by a fresh stock, and other 
flowers again self-fertilised yielded seeds as .... 

^.ATHYRUS ODORATUS crossed and self-fertilised flowers on 
the crossed and self-fertilised plants of the 1st generation 
yielded seeds as 

LOBELIA RAMOSA crossed and self-fertilised flowers on the 
crossed and self-fertilised plants of the 1st generation 
yielded seeds as (by weight) 

PETUNIA VIOLACEA crossed and self-fertilised flowers on 
the crossed and self-fertilised plants of the 1st generation 
yielded seeds as (by weight) 

PETUNIA VIOLACEA crossed and self-fertilised flowers on 
the crossed and self-fertilised plants of the 4th generation 
yielded seeds as (by weight) I 

PETUNIA VIOLACEA flowers on self-fertilised plants of the 
4th generation crossed by a fresh stock, and other flowers 
again self-fertilised yielded seeds as (by weight) . 

NICOTIANA TABACUM crossed and self-fertilised flowers on 
the crossed and self-fertilised plants of the 1st generation 
yielded seeds as (by weight) 

NICOTIANA TABACUM flowers on self-fertilised plants of 
the 2nd generation crossed by intercrossed plants, and 
other flowers again self-fertilised yielded seeds as (by es- 
timation) 

NICOTIANA TABACUM flowers on self-fertilised plants of 
the 3rd generation crossed by a fresh stock, and other 
flowers again self-fertilised yielded seeds as (by estimation) 

ANAQALLIS COLLINA flowers on a red variety crossed by a 
blue variety, and other flowers on the red variety self- 
fertilised yielded seeds as 

CANNA WARSCEWICZI crossed and self-fertilised flowers on 
the crossed and self-fertilised plants of three generations 
taken together yielded seeds as 



100 to 



127 



6,3 



'0 



72 



48 



97 



110 



110 



48 



As both these tables relate to the fertility of 
flowers fertilised by pollen from another plant and by 
their own pollen, they may be considered together. 
The difference between them consists in the self- 



326 FERTILITY OP CROSSED CHAP. IX. 

fertilised flowers in the second table, G-, being 
produced by self-fertilised parents, and the crossed 
flowers by crossed parents, which in the later generations 
had become somewhat closely inter-related, and had 
been subjected all the time to nearly the same condi- 
tions. These two tables include fifty cases relating to 
thirty-two species. The flowers on many other species 
were crossed and self-fertilised, but as only a few were 
thus treated, the results cannot be trusted, as far as fer- 
tility is concerned, and are not here given. Some other 
cases have been rejected, as the plants were in an 
unhealthy condition. If we look to the figures in the 
two tables expressing the ratios between the mean 
relative fertility of the crossed and self-fertilised 
flowers, we see that in a majority of the cases (i.e., 
in thirty-five out of fifty) flowers fertilised by pollen 
from a distinct plant yield more, sometimes many more, 
seeds than flowers fertilised with their own pollen ; and 
they commonly set a larger proportion of capsules. The 
degree of infertility of the self-fertilised flowers differs 
extremely in the different species, and even, as we 
shall see in the section on self-sterile plants, in the 
individuals of the same species, as well as under 
slightly changed conditions of life. Their fertility 
ranges from zero to fertility equalling that of the 
crossed flowers ; and of this fact no explanation can 
be offered. There are fifteen cases in the two tables 
in which the number of seeds per capsule produced by 
the self-fertilised flowers equals or even exceeds that 
yielded by the crossed flowers. Some few of these 
cases are, I believe, accidental; that is, would not 
recur on a second trial. This was apparently the 
case with the plants of the fifth generation of Ipomoea, 
and in one of the experiments with Dianthus. 
Nicotiana offers the most anomalous case of any, 



CHAP. IX. AND SELF-FERTILISED FLOWERS. 327 

as the self-fertilised flowers on the parent-plants, and 
on their descendants of the second and third genera- 
tions, produced more seeds than did the crossed 
flowers ; but we shall recur to this case when we treat 
of highly self-fertile varieties. 

It might have been expected that the difference in 
fertility between the crossed and self-fertilised flowers 
would have been more strongly marked in Table G-, in 
which the plants of one set were derived from self- 
fertilised parents, than in Table F, in which flowers on 
the parent-plants were self-fertilised for the first time. 
But this is not the case, as far as my scanty materials 
allow of any judgment. There is therefore no evi- 
dence at present, that the fertility of plants goes on 
diminishing in successive self-fertilised generations, 
although there is some rather weak evidence that 
this does occur with respect to their height or growth. 
But we should bear in mind that in the later genera- 
tions the crossed plants had become more or less closely 
inter-related, and had been subjected all the time to 
nearly uniform conditions. 

It is remarkable that there is no close correspondence, 
either in the parent-plants or in the successive genera- 
tions, between the relative number of seeds produced 
by the crossed and self-fertilised flowers, and the 
relative powers of growth of the seedlings raised from 
such seeds. Thus, the crossed and self-fertilised 
flowers on the parent-plants of Ipomoea, Gesneria, 
Salvia, Limnanthes, Lobelia fulgens, and Nolana pro- 
duced a nearly equal number of seeds, yet the plants 
raised from the crossed seeds exceeded considerably in 
height those raised from the self-fertilised seeds. 
The crossed flowers of Linaria and Viscaria yielded 
far more seeds than the self-fertilised flowers; and 
although the plants raised from the former were tallei 



328 FERTILITY OF CROSSED CHAP. IX 

than those from the latter, they were not so in any 
corresponding degree. With Mcotiana the flowers 
fertilised with their own pollen were more productive 
than those crossed with pollen from a slightly different 
variety ; yet the plants raised from the latter seeds 
were much taller, heavier, and more hardy than those 
raised from the self-fertilised seeds. On the othuv 
hand, the crossed seedlings of Eschscholtzia were 
neither taller nor heavier than the self- fertilised, 
although the crossed flowers were far more productive 
than the self-fertilised. But the best evidence of a 
want of correspondence between the number of seeds 
produced by crossed and self-fertilised flowers, and 
the vigour of the offspring raised from them, is afforded 
by the plants of the Brazilian and European stocks 
of Eschscholtzia, and likewise by certain individual 
plants of Reseda odorata ; for it might have been ex- 
pected that the seedlings from plants, the flowers of 
which were excessively self-sterile, would have profited 
in a greater degree by a cross, than the seedlings from 
plants which were moderately or fully self-fertile, and 
therefore apparently had no need to be crossed. But 
no such result followed in either case: for instance, 
the crossed and self-fertilised offspring from a highly 
self-fertile plant of Eeseda odorata were in average 
height to each other as 100 to 82 ; whereas the similar 
offspring from an excessively self-sterile plant were as 
100 to 92 in average height. 

With respect to the innate fertility of the plants 
of crossed and self-fertilised parentage, given in the 
previous Table D that is, the number of seeds pro- 
duced by both lots when their flowers were fertilised 
in the same manner, nearly the same remarks are 
applicable, in reference to the absence of any close 
correspondence between their fertility and powers of 



CHAP. IX. AND SELF-FERTILISED FLOWERS. 329 

growth, as in the case of the plants in the Tables F 
and G, just considered. Thus the crossed and self-fer- 
tilised plants of Ipomoea, Papaver, Reseda odorata, and 
Limnanthes were almost equally fertile, yet the former 
exceeded considerably in height the self-fertilised 
plants. On the other hand, the crossed and self-fer- 
tilised plants of Mimulus and Primula differed to an 
extreme degree in innate fertility, but by no means to 
a corresponding degree in height or vigour. 

In all the cases of self-fertilised flowers included in 
Tables E, F, and G, these were fertilised with their 
own pollen ; but there is another form of self-fertilisa- 
tion, viz., by pollen from other flowers on the same 
plant; but this latter method made no difference in 
comparison with the former in the number of seeds 
produced, or only a slight difference. Neither with 
Digitalis nor Dianthus were more seeds produced by 
the one method than by the other, to any trustworthy 
degree. With Ipomoea rather more seeds, in the pro- 
portion of 100 to 91, were produced from a cross 
between flowers on the same plant than from strictly 
self-fertilised flowers ; but I have reason to suspect that 
the result was accidental. With Origanum vulgare, 
however, a cross between flowers on plants propagated 
by stolons from the same stock certainly increased 
slightly their fertility. This likewise occurred, as we 
shall see in the next section, with Eschscholtzia, 
perhaps with Corydalis cava and Oncidium ; but not 
so with Bignonia, Abutilon, Tabernsemontana, Senecio, 
and apparently Eeseda odorata. 

Self-sterile Plants. 

The cases here to be described might have been 
introduced in Table F, which gives the relative fer- 
tility of flowsrs fertilised with their own pollen, and 



330 SELF-STERILE PLANTS. CHAP. IX, 

with that from a distinct plant ; but it has been found 
more convenient to keep them for separate discussion. 
The present cases must not be confounded with those 
to be given in the next chapter relatively to flowers 
which are sterile when insects are excluded ; for such 
sterility depends not merely on the flowers being 
incapable of fertilisation with their own pollen, but on 
mechanical causes, by which their pollen is prevented 
from reaching the stigma, or on the pollen and stigma 
of the same flower being matured at different periods. 

In the seventeenth chapter of my 'Variation of 
Animals and Plants under Domestication 'I had occasion 
to enter fully on the present subject ; and I will there- 
fore here give only a brief abstract of the cases there 
described, but others must be added, as they have an 
important bearing on the present work. Kolreuter 
long ago described plants of Verbascum pliceniceum 
which during two years were sterile with their own 
pollen, but were easily fertilised by that of four other 
species ; these plants however afterwards became more 
or less self-fertile in a strangely fluctuating manner. 
Mr. Scott also found that this species, as well as two of 
its varieties, were self-sterile, as did Gartner in the 
case of Verbascum nigrum. So it was, according to 
this latter author, with two plants of Lobelia fulgens, 
though the pollen and ovules of both were in an 
efficient state in relation to other species. Five species 
of Passiflora and certain individuals of a sixth species 
have been found sterile with their own pollen; but slight 
changes in their conditions, such as being grafted on 
another stock or a change of temperature, rendered 
them self-fertile. Flowers on a completely self-im- 
potent plant of Passiflora alata fertilised with pollen 
from its own self-impotent seedlings were quite fertile. 
Mr. Scott, and afterwards Mr. Munro, found that some 






CHAP. IX. SELF-STERILE PLANTS. 331 

species of Oncidium and of Maxillaria cultivated in a 
hothouse in Edinburgh were quite sterile with their 
own pollen; and Fritz Muller found this to be the 
case with a large number of Orchidaceous genera 
growing in their native home of South Brazil.* He 
also discovered that the pollen-masses of some orchids 
acted on their own stigmas like a poison; and it 
appears that Gartner formerly observed indications of 
this extraordinary fact in the case of some other 
plants. 

Fritz Muller also states that a species of Bignonia 
and Tabermemontana echinata are both sterile with 
their own pollen in their native country of Brazil, f 
Several Amaryllidaceous and Liliaceous plants are in 
the same predicament. Hildebrand observed with care 
Corydalis eava, and found it completely self-sterile ; t 
but according to Caspary a few self-fertilised seeds 
are occasionally produced : Corydalis halleri is only 
slightly self-sterile, and G. intermedia not at all so. 
In another Fumariaceous genus, Hypecoum, Hildebrand 
observed Q that H, grandiflorum was highly self-sterile, 
whilst H.procumbens was fairly self -fertile. Thuribergia 
alata kept by me in a warm greenhouse was self-sterile 
early in the season, but at a later period produced 
many spontaneously self-fertilised fruits. So it was 
with Papaver vagum : another species, P. alpinum, was 
found by Professor H. Hoffmann to be quite self- 
sterile excepting on one occasion ;!" whilst P. somni- 
ferum has been with me always completely self-fertile. 

Eschscholtzia calif ornica. This species deserves a 
fuller consideration. A plant cultivated by Fritz 

* ' Bot. Zeitung,' 1868, p. 114. 'Bot. Zeitung,' June 27, 1873. 

t Ibid. 1868, p. 626, and 1870, || Jahrb. fur wiss. Botanik,' 

p. 274. B. viL p. 464. 

\ ' Report of the International t ' Zur Speciesfrago,' 1875, 

Hort. Congress,' 1866. p. 47. 



332 SELF-STEEILE PLANTS. CHAP. IX. 

Miiller in South Brazil happened to flower a month before 
any of the others, and it did not produce a single 
capsule. This led him to make further observations 
during the next six generations, and he found that all 
his plants were completely sterile, unless they were 
crossed by insects or were artificially fertilised with 
pollen from a distinct plant, in which case they were 
completely fertile.* I was much surprised at this fact, 
as I had found that English plants, when covered by 
a net, set a considerable number of capsules ; and that 
these contained seeds by weight, compared with those 
on plants intercrossed by the bees, as 71 to 100. 
Professor Hildebrand, however, found this species 
much more self-sterile in Germany than it was with 
me in England, for the capsules produced by self- 
fertilised flowers, compared with those from intercrossed 
flowers, contained seeds in the ratio of only 11 to 100. 
At my request Fritz Miiller sent me from Brazil seeds 
of his self-sterile plants, from which I raised seedlings. 
Two of these were covered with a net, and one produced 
spontaneously only a single capsule containing no good 
seeds, but yet, when artificially fertilised with its own 
pollen, produced a few capsules. The other plant pro- 
duced spontaneously under the net eight capsules, one 
of which contained no less than thirty seeds, and on 
an average about ten seeds per capsule. Eight flowers 
on these two plants were artificially self-fertilised, and 
produced seven capsules, containing on an average 
twelve seeds ; eight other flowers were fertilised with 
pollen from a distinct plant of the Brazilian stock, and 
produced eight capsules, containing on an average 
about eighty seeds : this gives a ratio of 15 seeds for 
the self-fertilised capsules to 100 for the crossed 



'Bot. Zeitung,' 1868, p. 115, and 1869, p. 223. 



OHAP. IX. SELF-STERILE PLANTS. 333 

capsules. Later in the season twelve other flowers on 
these two plants were artificially self-fertilised ; but 
they yielded only two capsules, containing three and 
six seeds. It appears therefore that a lower tem- 
perature than that of Brazil favours the self-fertility 
of this plant, whilst a still lower temperature lessens it. 
As soon as the two plants which had been covered by 
the net were uncovered, they were visited by many 
bees, and it was interesting to observe how quickly 
they became, even the more sterile plant of the two, 
covered with young capsules. On the following year 
eight flowers on plants of the Brazilian stock of self- 
fertilised parentage (i.e., grandchildren of the plants 
which grew in Brazil) were again self-fertilised, and 
produced five capsules, containing on an average 27*4 
seeds, with a maximum in one of forty-two seeds ; so 
that their self-fertility had evidently increased greatly 
by being reared for two generations in England. On 
the whole we may conclude that plants of the Brazilian 
stock are much more self-fertile in this country than 
in Brazil, and less so than plants of the English stock 
in England ; so that the plants of Brazilian parentage 
retained by inheritance some of their former sexual 
constitution. Conversely, seeds from English plants 
sent by me to Fritz Muller and grown in Brazil, were 
much more self-fertile than his plants which had been 
cultivated there for several generations ; but he informs 
me that one of the plants of English parentage which 
did not flower the first year, and was thus exposed for 
two seasons to the climate of Brazil, proved quite self- 
sterile, like a Brazilian plant, showing how quickly 
the climate had acted on its sexual constitution. 

Abutilon darwinii. Seeds of this plant were sent 
me by Fritz Muller, who found it, as well as some 
other species of the same genus, quite sterile in its 



334 SELF-STERILE PLANTS. CHAP. IX. 

native home of South Brazil, unless fertilised with 
pollen from a distinct plant, either artificially or 
naturally by humming-birds.* Several plants were 
raised from these seeds and kept in the hothouse. 
They produced flowers very early in the spring, and 
twenty of them were fertilised, some with pollen from 
the same flower, and some with pollen from other 
flowers on the same plants ; but not a single capsule 
was thus produced, yet the stigmas twenty-seven hours 
after the application of the pollen were penetrated by 
the pollen-tubes. At the same time nineteen flowers 
were crossed with pollen from a distinct plant, and 
these produced thirteen capsules, all abounding with 
fine seeds. A greater number of capsules would have 
been produced by the cross, had not some of the nine- 
teen flowers been on a plant which was afterwards 
proved to be from some unknown cause completely 
sterile with pollen of any kind. Thus far these plants 
behaved exactly like those in Brazil ; but later in the 
season, in the latter part of May and in June, they 
began to produce under a net a few spontaneously 
self-fertilised capsules. As soon as this occurred, 
sixteen flowers were fertilised with their own pollen, 
and these produced five capsules, containing on an 
average 3*4 seeds. At the same time I selected by 
chance four capsules from the uncovered plants grow- 
ing close by, the flowers of which I had seen visited 
by humble-bees, and these contained on an average 
21 * 5 seeds ; so that the seeds in the naturally inter- 
crossed capsules to those in the self-fertilised capsules 
were as 100 to 16. The interesting point in this case 
is that these plants, which were unnaturally treated 
by being grown in pots in a hothouse, under another 

* Jenaische Zeitschr. fur Natiirwiss.' B. vii. 1872, p. 22, and 1873, 
p. 441. 



CHAP IX. SELF-STERILE PLANTS. 335 

hemisphere, with a complete reversal of the seasons, 
were thus rendered slightly self-fertile, whereas they 
seem always to be completely self-sterile in their 
native home. 

Senecio cruentus (greenhouse varieties, commonly 
called Cinerarias, probably derived from several fruticose 
or herbaceous species much intercrossed*). Two purple- 
flowered varieties were placed under a net in the 
greenhouse, and four corymbs on each were re- 
peatedly brushed with flowers from the other plant, 
so that their stigmas were well covered with each 
other's pollen. Two of the eight corymbs thus treated 
produced very few seeds, but the other six produced 
on an average 41 3 seeds per corymb, and these ger- 
minated well. The stigmas on four other corymbs on 
both plants were well smeared with pollen from the 
flowers on their own corymbs; these eight corymbs 
produced altogether ten extremely poor seeds, which 
proved incapable of germinating. I examined many 
flowers on both plants, and found the stigmas sponta- 
neously covered with pollen ; but they produced not a 
single seed. These plants were afterwards left un- 
covered in the same house where many other Cinerarias 
were in flower ; and the flowers were frequently visited 
by bees. They then produced plenty of seed, but one 
of the two plants less than the other, as this species 
shows some tendency to be dioecious. 

The trial was repeated on another variety with 
white petals tipped with red. Many stigmas on two 
corymbs were covered with pollen from the foregoing 
purple variety, and these produced eleven and twenty- 

* I am much obliged to Mr. lieves that Senecio cruentus, tw- 

Moore and to Mr. Thiselton Dyer silaginis, and perhaps heritieri, 

for giving me information with maderensis and populifoUus have 

respect to the varieties on which all been more or less blended to- 

I experimented. Mr. Moore be- gether in our Cinerarias. 






336 SELF-STERILE PLANTS. CHAP. IX 

two seeds, which germinated well. A large number of 
the stigmas on several of the other corymbs were re- 
peatedly smeared with pollen from their own corymb ; 
but they yielded only five very poor seeds, which were 
incapable of germination. Therefore the above three 
plants belonging to two varieties, though growing 
vigorously and fertile with pollen from either of the 
other two plants, were utterly sterile with pollen from 
other flowers on the same plant. 

Reseda odorata. Having observed that certain in- 
dividuals were self-sterile, I covered during the 
summer of 1868 seven plants under separate nets, and 
will call these plants A, B, C, D, E, F, G. They all 
appeared to be quite sterile with their own pollen, 
but fertile with that of any other plant. 

Fourteen flowers on A were crossed with pollen 
from B or C, and produced thirteen fine capsules. 
Sixteen flowers were fertilised with pollen from other 
flowers on the same plant, but yielded not a single 
capsule. 

Fourteen flowers on B were crossed with pollen 
from A, C, or D, and all produced capsules ; some of 
these were not very fine, yet they contained plenty of 
seeds. Eighteen flowers were fertilised with pollen 
from other flowers on the same plant, and produced 
not one capsule. 

Ten flowers on C were crossed with pollen from A, 
B, D, or E, and produced nine fine capsules. Nineteen 
flowers were fertilised with pollen from other flowers 
on the same plant, and produced no capsules. 

Ten flowers on D were crossed with pollen from 
A, B, C, or E, and produced nine fine capsules. 
Eighteen flowers were fertilised with pollen from other 
flf wers on the same plant, and produced no capsules. 

Seven flowers on E were crossed with pollen from 



CHAP. IX. SELF-STEEILE PLANTS. 337 

A, C, or D, and all produced fine capsules. Eight 
flowers were fertilised with pollen from other flowers 
on the same plant, and produced no capsules. 

On the plants F and G no flowers were crossed, but 
very many (number not recorded) were fertilised with 
pollen from other flowers on the same plants, and these 
did not produce a single capsule. 

We thus see that fifty-five flowers on five of the 
above plants were reciprocally crossed in various ways ; 
several flowers on each of these plants being ferti- 
lised with pollen from several of the other plants. 
These fifty-five flowers produced fifty-two capsules, 
almost all of which were of full size and contained 
an abundance of seeds. On the other hand, seventy- 
nine flowers (besides many others not recorded) were 
fertilised with pollen from other flowers on the same 
plants, and these did not produce a single capsule. 
In one case in which I examined the stigmas of the 
flowers fertilised with their own pollen, these were 
penetrated by the pollen-tubes, although such pene- 
tration produced no effect. Pollen falls generally, 
and I believe always, from the anthers on the stigmas 
of the same flower; yet only three out of the 
above seven protected plants produced spontaneously 
any capsules, and these it might have been thought 
must have been self-fertilised. There were altogether 
seven such capsules ; but as they were all seated close 
to the artificially crossed flowers, I can hardly doubt 
that a few grains of foreign pollen had accidentally 
fallen on their stigmas. Besides the above seven 
plants, four others were kept covered under the same 
large net; and some of these produced here and 
there in the most capricious manner little groups 
of capsules ; and this makes me believe that a bee, 
many of which settled on tho outside of the net, being 

z 



338 SELF-STERILE PLANTS. CHAP. IX. 

attracted by the odour, had on some one occasion 
found an entrance, and had intercrossed a few of the 
flowers. 

In the spring of 1869 four plants raised from fresh 
seeds were carefully protected under separate nets; 
and .now the result was widely different to what it was 
before. Three of these protected plants became actually 
loaded with capsules, especially during the early part 
of the summer ; and this fact indicates that tempera- 
ture produces some effect, but the experiment given 
in the following paragraph shows that the innate con- 
stitution of the plant is a far more important element. 
The fourth plant produced only a few capsules, many 
of them of small size ; yet it was far more self-fertile 
than any of the seven plants tried during the previous 
year. The flowers on four small branches of this 
semi-self-sterile plant were smeared with pollen from 
one of the other plants, and they all produced fine 
capsules. 

As I was much surprised at the difference in the 
results of the trials made during the two previous 
years, six fresh plants were protected by separate nets 
in the year 1870. Two of these proved almost com- 
pletely self-sterile, for on carefully searching them I 
found only three small capsules, each containing either 
one or two seeds of small size, which, however, ger- 
minated. A few flowers on both these plants were 
reciprocally fertilised with each other's pollen, and 
a few with pollen from one of the following self- 
fertile plants, and all these flowers produced fine 
capsules. The four other plants whilst still remaining 
protected beneath the nets presented a wonderful 
contrast (though one of them in a somewhat less 
degree than the others), for they became actually 
covered with spontaneously self-fertilised capsules, as 



CHAP. IX. SELF-STEBILE PLANTS. 339 

numerous as, or very nearly so, and as fine as those 
on the unprotected plants growing near. 

The above three spontaneously self-fertilised cap 
sules produced by the two almost completely self- 
sterile plants, contained altogether five seeds ; and 
from these I raised in the following year (1871) five 
plants, which were kept under separate nets. They 
grew to an extraordinarily large size, and on August 
29th were examined. At first sight they appeared 
entirely destitute of capsules ; but on carefully search- 
ing their many branches, two or three capsules were 
found on three of the plants, half-a-dozen on the 
fourth, and about eighteen on the fifth plant. But all 
these capsules were small, some being empty; the 
greater number contained only a single seed, and very 
rarely more than one. After this examination the 
nets were taken off, and the bees immediately carried 
pollen from one of these almost self-sterile plants 
to the other, for no other plants grew near. After a 
few weeks the ends of the branches on all five plants 
became covered with capsules, presenting a curious 
contrast with the lower and naked parts of the same 
long branches. These five plants therefore inherited 
almost exactly the same sexual constitution as their 
parents ; and without doubt a self-sterile race of 
Mignonette could have been easily established. 

Reseda lutea. Plants of this species were raised 
from seeds gathered from a group of wild plants grow- 
ing at no great distance from my garden. After 
casually observing that some of these plants were self- 
sterile, two plants taken by hazard were protected 
under separate nets. One of these soon became 
covered with spontaneously self-fertilised capsules, as 
numerous as those on the surrounding unprotected 
plants; so that it was evidently quite self-fertile. 

z 2 



340 SELF-STERILE PLANTS. CHAP. IX. 

The other plant was partially self-sterile, producing 
very few capsules, many of which were of small 
size. When, however, this plant had grown tall, 
the uppermost branches became pressed against the 
net and grew crooked, and in this position the bees 
were able to suck the flowers through the meshes, and 
brought pollen to them from the neighbouring plants. 
These branches then became loaded with capsules; 
the other and lower branches remaining almost bare. 
The sexual constitution of this species is therefore 
similar to that of Reseda odorata. 



Concluding Remarks on self-sterile Plants. 

In order to favour as far as possible the self-fer- 
tilisation of some of the foregoing plants, all the 
flowers on Reseda odorata and some of those on the 
Abutilon were fertilised with pollen from other 
flowers on the same plant, instead of with their own 
pollen, and in the case of the Senecio with pollen from 
other flowers on the same corymb ; but this made no 
difference in the result. Fritz Miiller tried both kinds 
of self-fertilisation in the case of Bignonia, Tabernse- 
montana and Abutilon, likewise with no difference in 
ihe result. With Eschscholtzia, however, he found 
that pollen from other flowers on the same plant 
was a little more effective than pollen from the 
same flower. So did Hildebrand* in Germany ; as 
thirteen out of fourteen flowers of Eschscholtzia thus 
fertilised set capsules, these containing on an average 
9 5 seeds ; whereas only fourteen flowers out of twenty- 
one fertilised with their own pollen set capsules, 
these containing on an average 9 seeds. Hildebrand 



; Pringsheim's Jahrbuch. fur wiss. Botanik,' vii. p. 467 



CHAP. IX. SELF-STERILE PLANTS. 341 

found a trace of a similar difference with Corydalis 
cava, as did Fritz Miiller with an Oncidium.* 

In considering the several cases above given of 
complete or almost complete self-sterility, we are first 
struck with their wide distribution throughout the 
vegetable kingdom. Their number is not at present 
large, for they can be discovered only by protecting 
plants from insects and then fertilising them with 
pollen from another plant of the same species and with 
their own pollen ; and the latter must be proved to 
be in an efficient state by other trials. Unless all 
this be done, it is impossible to know whether their 
self-sterility may not be due to the male or female 
reproductive organs, or to both, having been affected 
by changed conditions of life. As in the course of my 
experiments I have found three new cases, and as Fritz 
Muller has observed indications of several others, it is 
probable that they will hereafter be proved to be far 
from rare.f 

As with plants of the same species and parentage, 
some individuals are self-sterile and others self-fertile, 
o which fact Reseda odorata offers the most striking 
instances, it is not at all surprising that species of 
the same genus differ in this same manner. Thus 
Verbascum phceniceum and nigrum are self- sterile, whilst 
V. thapsus and lychnitis are quite self-fertile, as I 
know by trial. There is the same difference between 
some of the species of Papaver, Corydalis, and of other 
genera. Nevertheless, the tendency to self-sterility 
certainly runs to a certain extent in groups, as we see 



* ' Var. under Dom.' chap. auratum, Impatient pallida and 

xvii. 2nd edit. vol. ii. pp. 113-115. fulva, cannot be fertilised with 

t Mr. Wilder, the editor of a their own pollen. Bimpan shows 

horticultural journal in the U. that rye is probably sterile with 

btates (quoted in ' Gard. Chron.' its own pollen. 
1868, p. 1286) states that Lilium 



342 SELF-STEEILE PLANTS. CHAP. IX. 

in the genus Passiflora, and with the Vandese amongst 
Orchids. 

Self-sterility differs much in degree in different 
plants. In those extraordinary cases in which pollen 
from the same flower acts on the stigma like a poison, 
it is almost certain that the plants would never yield a 
single self-fertilised seed. Other plants, like Corydalis 
cava, occasionally, though very rarely, produce a few 
self-fertilised seeds. A large number of species, as 
may be seen in Table F, are less fertile with their own 
pollen than with that from another plant ; and lastly, 
some species are perfectly self-fertile. Even with the 
individuals of the same species, as just remarked, 
some are utterly self-sterile, others moderately so, and 
some perfectly self-fertile. The cause, whatever it may 
be, which renders many plants more or less sterile 
with their own pollen, that is, when they are self- 
fertilised, must be different, at least to a certain extent, 
from that which determines the difference in height, 
vigour, and fertility of the seedlings raised from self- 
fertilised and crossed seeds; for we have already 
seen that the two classes of cases do not by any means 
run parallel. This want of parallelism would be 
intelligible, if it could be shown that self-sterility 
depended solely on the incapacity of the pollen-tubes 
to penetrate the stigma of the same flower deeply 
enough to reach the ovules ; whilst the greater or less 
vigorous growth of the seedlings no doubt depends on 
the nature of the contents of the pollen-grains and 
ovules. Now it is certain that with some plants the 
stigmatic secretion does not properly excite the pollen- 
grains, so that the tubes are not properly developed, 
if the pollen is taken from the same flower. This is 
the case according to Fritz Muller with Eschscholtzia, 
for he found that the pollen-tubes did not penetrate 



CHAP. IX. SELF-STERILE PLANTS. 343 

the stigma deeply ;* and with the Orchidaceous genus 
Notylia they failed altogether to penetrate it. 

With dimorphic and trimorphic species, an illegiti- 
mate union between plants of the same form presents 
a close analogy with self-fertilisation, whilst a legi- 
timate union closely resembles cross-fertilisation ; and 
here again the lessened fertility or complete sterility of 
an illegitimate union depends, at least in part, on the 
incapacity for interaction between the pollen-grains 
and stigma. Thus with Linum grandiflorum, as I 
have elsewhere shown,f not more than two or three 
out of hundreds of pollen-grains, either of the long- 
styled or short-styled form, when placed on the 
stigma of their own form, emit their tubes, and 
these do not penetrate deeply; nor does the stigma 
itself change colour, as occurs when it is legitimately 
fertilised. 

On the other hand the difference in innate fertility, 
as well as in growth between plants raised from crossed 
and self-fertilised seeds, and the difference in fertility 
and growth between the legitimate and illegitimate 
offspring of dimorphic and trimorphic plants, must 
depend on some incompatibility between the sexual 
elements contained within the pollen-grains and ovules, 
as it is through their union that new organisms are 
developed. 

If we now turn to the more immediate cause of 
self-sterility, we clearly see that in most cases it is de- 
termined by the conditions to which the plants have 
been subjected. Thus Eschscholtzia is completely self- 
sterile in the hot climate of Brazil, but is perfectly 
fertile there with the pollen of any other individual. 
The offspring of Brazilian plants became in England 

* <Bot. Zeitung,'1868,pp.ll4, t 'The Different Forma of 
115. Flowers,' &c., p. 87 



344 SELF-STEEILE PLANTS. CHAP. IX. 

in a single generation partially self-fertile, and still 
more so in the second generation. Conversely, the 
offspring of English plants, after growing for two 
seasons in Brazil, became in the first generation quite 
self-sterile. Again, Abutilon darwinii, which is self- 
sterile in its native home of Brazil, became mode- 
rately self-fertile in a single generation in an English 
hothouse. Some other plants are self-sterile during the 
early part of the year, and later in the season become 
self-fertile. Passiflora alata lost its self-sterility when 
grafted on another species. With Reseda, however, 
in which some individuals of the same parentage are 
self-sterile and others are self-fertile, we are forced in 
our ignorance to speak of the cause as due to spon- 
taneous variability ; but we should remember that the 
progenitors of these plants, either on the male or 
female side, may have been exposed to somewhat 
different conditions. The power of the environment 
thus to affect so readily and in so peculiar a manner 
the reproductive organs, is a fact which has many 
important bearings; and I have therefore thought 
the foregoing details worth giving. For instance, the 
sterility of many animals and plants under changed 
conditions of life, such as confinement, evidently comes 
within the same general principle of the sexual 
system being easily affected by the environment. It 
has already been proved, that a cross between plants 
which have been self-fertilised or intercrossed during 
several generations, having been kept all the time 
under closely similar conditions, does not benefit 
the offspring; and on the other hand, that a cross 
between plants that have been subjected to different 
conditions benefits the offspring to an extraordinary 
degree. We may therefore conclude that some degree 
of differentiation in the sexual system is necessary fot 



CHAP. IX. SELF-STERILE PLANTS. 345 

the full fertility of the parent-plants and for the full 
vigour of their offspring. It seems also probable that 
with those plants which are capable of complete self- 
fertilisation, the male and female elements and organs 
already differ to an extent sufficient to excite their 
mutual interaction ; but that when such plants are 
taken to another country, and become in consequence 
self-sterile, their sexual elements and organs are so 
acted on as to be rendered too uniform for such inter- 
action, like those of a self-fertilised plant long 
cultivated under the same conditions. Conversely, we 
may further infer that plants which are self-sterile in 
their native country, but become self-fertile under 
changed conditions, have their sexual elements so acted 
on, that they become sufficiently differentiated for 
mutual interaction. 

We know that self-fertilised seedlings are inferior in 
many respects to those from a cross ; and as with 
plants in a state of nature pollen from the same 
flower can hardly fail to be often left by insects or by 
the wind on the stigma, it seems at first sight highly 
probable that self-sterility has been gradually acquired 
through natural selection in order to prevent self- 
fertilisation. It is no valid objection to this belief 
that the structure of some flowers, and the dichogamoua 
condition of many others, suffice to prevent the pollen 
reaching the stigma of the same flower ; for we should 
remember that with most species many flowers 
expand at the same time, and that pollen from the 
same plant is equally injurious or nearly so as 
that from the same flower. Nevertheless, the belief 
that self-sterility is a quality which has been gradually 
acquired for the special purpose of preventing self- 
fertilisation must, I believe, be rejected. In the 
first place, there is no close correspondence in degree 



346 SELF-STERILE PLANTS. CHAP. IX. 

between the sterility of the parent-plants when self- 
fertilised, and the extent to which their offspring suffer 
in vigour by this process; and some such correspon- 
dence might have been expected if self-sterility had 
been acquired on account of the injury caused by self- 
fertilisation. The fact of individuals of the same 
parentage differing greatly in their degree of self- 
sterility is likewise opposed to such a belief; unless, 
indeed, we suppose that certain individuals have 
been rendered self-sterile to favour intercrossing, 
whilst other individuals have been rendered self- 
fertile to ensure the propagation of the species. The 
fact of self-sterile individuals appearing only occa- 
sionally, as in the case of Lobelia, does not counte- 
nance this latter view. But the strongest argument 
against the belief that self-sterility has been . acquired 
to prevent self-fertilisation, is the immediate and 
powerful effect of changed conditions in either causing 
or in removing self-sterility. We are not therefore 
justified in admitting that this peculiar state of the 
reproductive system has been gradually acquired 
through natural selection ; but we must look at it as 
an incidental result, dependent on the conditions to 
which the plants have been subjected, like the ordinary 
sterility caused in the case of animals by confinement, 
and in the case of plants by too much manure, heat, &c. 
I do not, however, wish to maintain that self-sterility 
may not sometimes be of service to a plant in preventing 
self-fertilisation ; but there are so many other means 
by which this result might be prevented or rendered 
difficult, including as we shall see in the next chapter 
the prepotency of pollen from a distinct individual 
over a plant's own pollen, that self-sterility seems aD 
almost superfluous acquirement for this purpose. 
Finally, the most interesting point in regard to self- 



CHAP. IX SELF-FERTILE VARIETIES. 347 

sterile plants is the evidence which they afford of the 
advantage, or rather of the necessity, of some degree or 
kind of differentiation in the sexual elements, in order 
that they should unite and give birth to a new being. 
It was ascertained that the five plants of Reseda odorata 
which were selected by chance, could be perfectly 
fertilised by pollen taken from any one of them, but 
not by their own pollen ; and a few additional trials 
were made with some other individuals, which I have 
not thought worth recording. So again, Hildebrand 
and Fritz Muller frequently speak of self-sterile plants 
being fertile with the pollen of any other individual ; 
and if there had been any exceptions to the rule, these 
could hardly have escaped their observation and my 
own. We may therefore confidently assert that a 
self-sterile plant can be fertilised by the pollen of any 
one out of a thousand or ten thousand individuals of 
the same species, but not by its own. Now it is 
obviously impossible that the sexual organs and 
elements of every individual can have been specialised 
with respect to every other individual. But there 
is no difficulty in believing that the sexual elements 
of each differ slightly in the same diversified manner 
as do their external characters ; and it has often been 
remarked that no two individuals are absolutely 
alike. Therefore we can hardly avoid the conclusion, 
that differences of an analogous and indefinite nature 
in the reproductive system are sufficient to excite the 
mutual action of the sexual elements, and that unless 
there be such differentiation fertility fails. 

The appearance of highly self-fertile Varieties. We 
have just seen that the degree to which flowers are 
capable of being fertilised with their own pollen differs 
much, both with the species of the same genus, and 



348 SELF-FEKTILE VAEIETIES. CHAP. IX 

sometimes with the individuals of the same species. 
Some allied cases of the appearance of varieties which, 
when self-fertilised, yield more seed and produce off- 
spring growing taller than their self-fertilised parents, 
or than the intercrossed plants of the corresponding 
generation, will now be considered. 

Firstly, in the third and fourth generations of 
Mimulus luteus, a tall variety, often alluded to, 
having large white flowers blotched with crimson, 
appeared amongst both the intercrossed and self- 
fertilised plants. It prevailed in all the later self- 
fertilised generations to the exclusion of every other 
variety, and transmitted its characters faithfully, but 
disappeared from the intercrossed plants, owing no 
doubt to their characters being repeatedly blended by 
crossing. The self-fertilised plants belonging to this 
variety were not only taller, but more fertile than the 
intercrossed plants ; though these latter in the earlier 
generations were much taller and more fertile than the 
self-fertilised plants. Thus in the fifth generation the 
self-fertilised plants were to the intercrossed in height 
as 126 to 100. In the sixth generation they were 
likewise much taller and finer plants, but were not 
actually measured ; they produced capsules compared 
with those on the intercrossed plants, in number, as 147 
to 100 ; and the self-fertilised capsules contained a 
greater number of seeds. In the seventh generation 
the self-fertilised plants were to the crossed in height 
as 137 to 100 ; and twenty flowers on these self-fer- 
tilised plants fertilised with their own pollen yielded 
nineteen very fine capsules, a degree of self-fertility 
which I have not seen equalled in any other case. This 
variety seems to have become specially adapted to profit 
in every way by self-fertilisation, although this process 
was so injurious to the parent-plants during the first 






CHAP. IX. SELF-FERTILE VARIETIES. 349 

four generations. It should however be remembered 
that seedlings raised from this variety, when crossed by 
a fresh stock, were wonderfully superior in height and 
fertility to the self-fertilised plants of the corresponding 
generation. 

Secondly, in the sixth self-fertilised generation of 
Ipomoea a single plant named the Hero appeared, which 
exceeded by a little in height its intercrossed opponent, 
a case which had not occurred in any previous 
generation. Hero transmitted the peculiar colour of 
its flowers, as well as its increased tallness and a high 
degree of self-fertility, to its children, grandchildren, 
and great-grandchildren. The self-fertilised children 
of Hero were in height to other self-fertilised plants 
of the same stock as 100 to 85. Ten self-fertilised 
capsules produced by the grandchildren contained on 
an average 5 '2 seeds; and this is a higher average 
than was yielded in any other generation by the 
capsules of self-fertilised flowers. The great-grand- 
children of Hero derived from a cross with a fresh 
stock were so unhealthy, from having been grown at 
an unfavourable season, that their average height in 
comparison with that of the self-fertilised plants 
cannot be judged of with any safety ; but it did not 
appear that they had profited even by a cross of this 
kind. 

Thirdly, the plants of Nicotiana on which I experi- 
mented appear to come under the present class of 
cases ; for they varied in their sexual constitution 
and were more or less highly self-fertile. They 
were probably the offspring of plants which had been 
spontaneously self-fertilised under glass for several 
generations in this country. The flowers on the 
parent-plants which were first fertilised by me with their 
own pollen yielded half again as many seeds as did 



350 SELF-FEBTILE VABIETIES. CHAP. IX. 

those which were crossed ; and the seedlings raised 
from these self-fertilised seeds exceeded in height 
those raised from the crossed seeds to an extraordinary 
degree. In the second and third generations, although 
the self-fertilised plants did not exceed the crossed in 
height, yet their self-fertilised flowers yielded on two 
occasions considerably more seeds than the crossed 
flowers, even than those which were crossed with pollen 
from a distinct stock or variety. 

Lastly, as certain individual plants of Reseda odorata 
and lutea are incomparably more self-fertile than other 
individuals, the former might be included under the 
present heading of the appearance of new and highly 
self-fertile varieties. But in this case we should have 
to look at these two species as normally self-sterile ; 
and this, judging by my experience, appears to be the 
correct view. 

We may therefore conclude from the facts now given, 
that varieties sometimes arise which when self-fer- 
tilised possess an increased power of producing seeds 
and of growing to a greater height, than the inter- 
crossed or self-fertilised plants of the corresponding 
generation all the plants being of course subjected 
to the same conditions. The appearance of such 
varieties is interesting, as it bears on the existence 
under nature of plants which regularly fertilise them- 
selves, such as Ophrys apifera and some other orchids, 
or as Leersia oryzvides, which produces an abundance 
of cleistogamic flowers, but most rarely flowers capable 
of cross-fertilisation.* 

Some observations made on other plants lead me 
to suspect that self-fertilisation is in some respects 
beneficial ; although the benefit thus derived is as a 



* On Leersia, see ' Different Forms of Flowers,' &c., p. 335. 



CHAP. IX. SELF-FERTILE VARIETIES. 351 

rule very small compared with that from a cross with 
a distinct plant. Thus we have seen in the last chapter 
that seedlings of Ipomcea and Mimulus raised from 
flowers fertilised with their own pollen, which is the 
strictest possible form of self-fertilisation, were superior 
in height, weight, and in early flowering to the seedlings 
raised from flowers crossed with pollen from other flowers 
on the same plant ; and this superiority apparently was 
too strongly marked to be accidental. Again, the cul- 
tivated varieties of the common pea are highly self- 
fertile, although they have been self-fertilised for many 
generations; and they exceeded in height seedlings 
from a cross between two plants belonging to the same 
variety in the ratio of 115 to 100 ; but then only four 
pairs of plants were measured and compared. The 
self-fertility of Primula veris increased after several 
generations of illegitimate fertilisation, which is a 
process analogous to self-fertilisation, but only as long 
as the plants were cultivated under the same favour- 
able conditions. I have also elsewhere- shown* that 
with several species of Primula equal-styled varieties 
occasionally appear which possess the sexual organs 
of the two forms combined in the same flower. Con- 
sequently they fertilise themselves in a legitimate 
manner and are highly self-fertile ; but the remarkable 
fact is that they are rather more fertile than ordinary 
plants of the same species legitimately fertilised by 
pollen from a distinct individual. Formerly it appeared 
to me probable, that the increased fertility of these 
heterostyled plants might be accounted for by the 
stigma lying so close to the anthers that it was im 
pregnated at the most favourable age and time of 
the day ; but this explanation is not applicable to the 

* 'Different Forms of Flower*' &o., p. 272. 



352 



WEIGHT AND GERMINATION OF CHAP. IX. 



above given cases, in which the flowers were artificially 
fertilised with their own pollen. 

Considering the facts now adduced, including the 
appearance of those varieties which are more fertile 
and taller than their parents and than the intercrossed 
plants of the corresponding generation, it is difficult 
to avoid the suspicion that self-fertilisation is in some 
respects advantageous; though if this be really the 
case,* any such advantage is as a rule quite insignifi- 
cant compared with that from a cross with a distinct 
plant, and especially with one of a fresh stock. Should 
this suspicion be hereafter verified, it would throw 
light, as we shall see in the next chapter, on the exist- 
ence of plants bearing small and inconspicuous flowers 
which are rarely visited by insects, and therefore are 
rarely intercrossed. 

Relative Weight and Period of Germination of Seeds 
from crossed and self-fertilised Flowers. An equal 
number of seeds from flowers fertilised with pollen from 
another plant, and from flowers fertilised with their own 
pollen, were weighed, but only in sixteen cases. Their 
relative weights are given in the following list ; that 
of the seeds from the crossed flowers being taken as 100. 



Ipomoea purpurea (parent plants) 
n (third generation) 


. as 100 to 127 
. .. 87 


Salvia coccinea 




, 100 


Brassica oleracea 
Iberis umbellata (second generation) .... 
Delphinium consolida 
Hibiscus africanus 




, 103 

, ,. 136 
, ,, 45 
, 105 


Tropseolum minus 
Lathyrus odoratus (about) 
Sarothamnus scoparius 


, 115 
, 100 
, 88 



* M. Errara, who intends pub- 
lishing on the present subject, 
has been so kind as to send me 
his MS. to rend. He is convinced 
that self-fertilisation is never 
more beneficial than a cross with 



another flower. I hope that his 
view may hereafter be proved 
correct, as the subject of cross 
and self-fertilisation would be 
thus much simplified. 



CHAK IX. CROSSED AND SELF-FERTILISED SEEDS. 353 

Specnlaria speculum as 100 to 86 

Nemophila insignis 105 

Borago officinalis 111 

Cyclamen persicum (about) 50 

Fagopyrum esculentum 82 

Canna warscewiczi (three generations) 102 

It is remarkable that in ten out of these sixteen 
cases the self-fertilised seeds were either superior or 
equal to the crossed in weight ; nevertheless, in six out 
of the ten cases (viz., with Ipomcea, Salvia, Brassica, 
Tropaeolum, Lathyrus, and Nemophila; the plants 
raised from these self-fertilised seeds were very inferior 
in height and in other respects to those raised from the 
crossed seeds. The superiority in weight of the self- 
fertilised seeds in at least six out of the ten cases, 
namely, with Brassica, Hibiscus, Tropaeolum, Nemophila, 
Borago, and Canna, may be accounted for in part by 
the selMertilised capsules containing fewer seeds ; for 
when a capsule contains only a few seeds, these will be 
apt to be better nourished, so as to be heavier, than 
when many are contained in the same capsule. It 
should, however, be observed that in some of the above 
cases, in which the crossed seeds were the heaviest, as 
with Sarothanmus and Cyclamen, the crossed capsules 
contained a larger number of seeds. Whatever may be 
the explanation of the self-fertilised seeds being often 
the heaviest, it is remarkable in the case of Brassica 
Tropaeolum, N emophila, and of the first generation of 
Ipomoea, that the seedlings raised from them were 
inferior in height and in other respects to the seed- 
lings raised from the crossed seeds. This fact shows 
how superior in constitutional vigour the crossed seed- 
lings must have been, for it cannot be doubted that 
heavy and fine seeds tend to yield the finest plants. 
Mr. Galton has shown that this holds good with Lathyrus 
)doratus ; an has Mr. A. J. Wilson with the Swedish 

2 A 



854 WEIGHT AND GERMINATION OF CHAP. IX 

turnip, Brassica campestris ruta laga. Mr. Wilson 
separated the largest and smallest seeds of this latter 
plant, the ratio between the weights of the two lots 
being as 100 to 59, and he found that the seedlings 
" from the larger seeds took the lead and maintained 
their superiority to the last, both in height and thick- 
ness of stem."* Nor can this difference in the growth 
of the seedling turnips be attributed to the heavier 
seeds having been of crossed, and the lighter of self- 
fertilised origin, for it is known that plants belonging 
to this genus are habitually intercrossed by insects. 

With respect to the relative period of germination of 
crossed and self-fertilised seeds, a record was kept in 
only twenty-one cases ; and the results are very per- 
plexing. Neglecting one case in which the two lots 
germinated simultaneously, in ten cases or exactly one- 
half many of the self-fertilised seeds germinated before 
the crossed, and in the other half many of the crossed 
before the self-fertilised. In four out of these twenty 
cases, seeds derived from a cross with a fresh stock 
were compared with self-fertilised seeds from one of the 
later self-fertilised generations ; and here again in half 
the cases the crossed seeds, and in, the other half the 
self-fertilised seeds, germinated first. Yet the plants 
of Mimulus raised from such self-fertilised seeds were 
inferior in all respects to the crossed plants, and in 

* ' Gardeners' Chronicle/ 1867, by long-continued selection, may 
p. 107. Loiseleur-Deslongchamp have given to the grains of the 
(' Les Ce'reales,' 1842, pp. 208-219) cereals a greater amount of starch 
was led by his observations to or other matter, than the seed- 
the extraordinary conclusion that lings can utilise for their growth, 
the smaller grains of cereals pro- There can be little doubt, as 
duce as fine plants as the large. Humboldt long ago remarked, 
This conclusion is, however, con- that the grains of cereals have 
tradicted by Major Hallet's great been rendered attractive to birds 
success in improving wheat by in a degree which is highly ra- 
the selection of the finest grains. jurious to the species. 
It is possible, however, that man, 



CHAP. IX. CROSSED AND SELF-FERTILISED SEEDS. 355 



the case of Eschscholtzia they were inferior in fertility. 
Unfortunately the relative weight of the two lots of 
seeds was ascertained in only a few instances in which 
their germination was observed ; but with Ipomoaa and 
I believe with some of the other species, the relative 
lightness of the self-fertilised seeds apparently deter- 
mined their early germination, probably owing to the 
smaller mass being favourable to the more rapid com- 
pletion of the chemical and morphological changes 
necessary for germination.* On the other hand, Mr. 
Galton gave me seeds (no doubt all self-fertilised) of 
Lathyrus odoratw, which were divided into two lots of 
heavier and lighter seeds ; and several of the former 
germinated first. It is evident that many more obser- 
vations are necessary before anything can be decided 
with respect to the relative period of germination of 
crossed and self-fertilised seeds. 



* Mr. J. Scott remarks (' Man- 
ual of Opium Husbandry,' 1877, 
p. 131) that the smaller seeds of 
Papaver somniferum germinate 
first. He also states that the 
larger seeds yield the finer crop 
of plants. With respect to this 



latter subject see an abstract in 
Burbidge's 'Cultivated Plants,' 
1877, p. 33, on the important 
experiments show'ng the same 
results, by Dr. M >rck and Prof. 
Lehmann. 



9. L 2 



356 MEANS OF FEETILISATION. CHAF. X, 



CHAPTER X. 

MEANS OF FEBTILISATION. 

Sterility and fertility of plants when insects are excluded The means 
by which flowers are cross-fertilised Structures favourable to self- 
fertilisation Relation between the structure and conspicuousness 
of flowers, the visits of insects, and the advantages of cross-fertilisa- 
tion The means by which flowers are fertilised with pollen 
from a distinct plant Greater fertilising power of such pollen 
Anemophilous species Conversion of anemophilous species into 
entomophilous Origin of nectar Anemophilous plants generally 
have their sexes separated Conversion of diclinous into herma- 
phrodite flowers Trees often have their sexes separated. 

IN the introductory chapter I briefly specified the 
various means by which cross-fertilisation is favoured 
or ensured, namely, the separation of the sexes, the 
maturity of the male and female sexual elements at 
different periods, the heterostyled or dimorphic 
and trimorphic condition of certain plants, many 
mechanical contrivances, the more or less complete 
inefficiency of a flower's own pollen on the stigma, and 
the prepotency of pollen from any other individual 
over that from the same plant. Some of these points 
require further consideration ; but for full details I 
must refer the reader to the several excellent works 
mentioned in the introduction. I will in the first place 
give two lists : the first, of plants which are either quite 
sterile or produce less than about half the full com- 
plement of seeds, when insects are excluded ; and a 
second list of plants which, when thus treated, are fully 
fertile or produce at least half the full complement 



CHAP. X. MEANS OF FERTILISATION. 357 

of seeds. These lists have been compiled from the 
several previous tables, with some additional oases from 
my own observations and those of others. The species 
are arranged nearly in the order followed by Lindley 
in his 'Vegetable Kingdom.' The reader should 
observe that the sterility or fertility of the plants in 
these two lists depends on two wholly distinct causes ; 
namely, the absence or presence of the proper means 
by which pollen is applied to the stigma, and its less 
or greater efficiency when thus applied. As it is 
obvious that with plants in which the sexes are separate, 
pollen must be carried by some means from flower to 
flower, such species are excluded from the lists ; as 
are likewise heterostyled plants, in which the same 
necessity occurs to a limited extent. Experience has 
proved to me that, independently of the exclusion of 
insects, the seed-bearing power of a plant is not 
lessened by covering it while in flower under a thin 
net supported on a frame; and this might indeed 
have been inferred from the consideration of the two 
following lists, as they include a considerable number 
of species belonging to the same genera, some of which 
are quite sterile and others quite fertile when protected 
by a net from the access of insects. 

List of Plants which, when Insects are excluded, are either 
quite sterile, or produce, as far as I could judge, less 
than half the number of Seeds produced by unpro- 
tected Plants. 

Passiflora alata, racemosa, cosrulea, edulis, laurifolia, and some 
individuals of P. quadrangularis (Passifloracese), are quite 
sterile under these conditions: see 'Variation of Animals 
and Plants under Domestication,' chap. xvii. 2nd edit. vol. ii. 
p. 118. 

Viola canina (Violacese). Perfect flowers quite sterile unleai 
fertilised by bees, or artificially fertilised. 



358 PLANTS STERILE WITHOUT INSECT-AID. CHAP. X. 



V. tricolor. Sets very few and poor capsules. 
Reseda odorata (Resedaceae). Some individuals quite sterile. 
B. lutea. Some individuals produce very few and poor cap- 



Abutilon darwinii (Malvaceae). Quite sterile in Brazil: see 
previous discussion on self-sterile plants. 

Nymphcea (Nymphaeaceae). Professor Caspary informs me that 
some of the species are quite sterile if insects are excluded. 

Euryale amazonica (Nymphaeaceae). Mr. J. Smith, of Kew, in- 
forms me that capsules from flowers left to themselves, and 
probably not visited by insects, contained from eight to fif- 
teen seeds ; those from flowers artificially fertilised with 
pollen from other flowers on the same plant contained from 
fifteen to thirty seeds ; and that two flowers fertilised with 
pollen brought from another plant at Chatsworth contained 
respectively sixty and seventy-five seeds. I have given 
these statements because Professor Caspary advances this 
plant as a case opposed to the doctrine of the necessity or 
advantage of cross-fertilisation: see Sitzungsberichte der 
Phys.-okon. Gesell. zu Konigsberg, B. vi. p. 20. 

Delphinium consolida (Banunculaceae). Produces many capsules, 
but these contain only about half the number of seeds com- 
pared with capsules from flowers naturally fertilised by 
bees. 

EschscJioltzia californica (Papaveraceae). Brazilian plants quite 
sterile : English plants produce a few capsules. 

Papaver vagum (Papaveracese). In the early part of the summer 
produced very few capsules, and these contained very few 



P. alpinum. H. Hoffmann (' Speciesfrage/ 1875, p. 47) states 
that this species produced seeds capable of germination only 
on one occasion. 

Corydalis cava (Fumariaceae). Sterile : see the previous discus- 
sion on self-sterile plants. 

0. srtida. I had a single plant in my garden (1863), and saw 
many hive-bees sucking the flowers, but not a single seed 
was produced. I was much surprised at this fact, as Pro- 
fessor Hildebrand's discovery that C. cava is sterile with its 
own pollen had not then been made. He likewise concludes 
from the few experiments which he made on the present 
species that it is self-sterile. The two foregoing cases are 
interesting, because botanists formerly thought (see, for 



CHAP. X. PLANTS STERILE WITHOUT INSECT- AID. 359 

instance, Lecoq, ' De la Fecondation et de 1'Hybridation, 
1845, p. 61, and Liudley, 'Vegetable Kingdom/ 1853, p. 436) 
that all the species of the Fumariacese were specially adapted 
for self-fertilisation. 

C. lutea. A covered-up plant produced (1861) exactly half as 
many capsules as an exposed plant of the same size grow- 
ing close alongside. When humble-bees visit the flowers 
(and I repeatedly saw them thus acting) the lower petals 
suddenly spring downwards and the pistil upwards; this 
is due to the elasticity of the parts, which takes effect, as 
soon as the coherent edges of the hood are separated by the 
entrance of an insect. Unless insects visit the flowers the 
parts do not move. Nevertheless, many of the flowers on 
the plants which I had protected produced capsules, not- 
withstanding that their petals and pistils still retained their 
original position ; and I found to my surprise that these 
capsules contained more seeds than those from flowers, the 
petals of which had been artificially separated and allowed 
to spring apart. Thus, nine capsules produced by undis- 
turbed flowers contained fifty-three seeds ; whilst nine cap- 
sules from flowers, the petals of which had been artificially 
separated, contained only thirty- two seeds. But we should 
remember that if bees had been permitted to visit these 
flowers, they would have visited them at the best time for 
fertilisation. The flowers, the petals of which had been 
artificially separated, set their capsules before those which 
were left undisturbed under the net. To show with what 
certainty the flowers are visited by bees, I may add that 
on one occasion all the flowers on some unprotected plants 
were examined, and every single one had its petals sepa- 
rated; and, on a second occasion, forty-one out of forty- 
three flowers were in this state. Hildebrand states (Pring. 
Jahr. f. wiss. Botanik, B. vii., p. 450) that the mechanism 
of the parts in this species is nearly the same as in C. ochro- 
leuca, which he has fully described. 

FFypecoum grandiflorum (Fumariaceae). Highly self-sterile (Hil- 
debrand, ibid.). 

l\almia latifolUi (Ericaceae). Mr. W. J. Beal says (' American 
Naturalist," 1867) that flowers protected from insects wither 
and drop off, with " most of the anthers still remaining in 
the pockets." 

Pelargonium zonalt (Geraniaceae). Almost sterile; one plant 



360 PLANTS STEEILE WITHOUT INSECT-AID. CHAP. X. 

produced two fruits. It is probable that different varieties 
would differ in this respect, as some are only feebly dicho- 
gamous. 

Dianthus caryophyllus (Caryophyllacese). Produces very few 
capsules, which contain any good seeds. 

Phaseolus multiflorus (Leguminosse). Plants protected from 
insects produced on two occasions about one-third and one- 
eighth of the full number of seeds: see my article in 
'Gardeners' Chronicle,' 1857, p. 225, and 1858, p. 828; also 
' Annals and Mag. of Natural History/ 3rd series, vol. ii. 
1858, p. 462. Dr. Ogle (' Pop. Science Eeview,' 1870, p. 168) 
found that a plant was quite sterile when covered up. The 
flowers are not visited by insects in Nicaragua, and, accord- 
ing to Mr. Belt, the species is there quite sterile: 'The 
Naturalist in Nicaragua,' p. 70. 

Vidafaba (Leguminosae). Seventeen covered-up plants yielded 
40 beans, whilst seventeen plants left unprotected and 
growing close alongside produced 135 beans; these latter 
plants were, therefore, between three and four times more 
fertile than the protected plants : see ' Gardeners' Chronicle ' 
for fuller details, 1858, p. 828. 

Erythrina (sp. ?) (Leguminosae). Sir W. MacArthur informed 
me that in New South Wales the flowers do not set, unless 
the petals are moved in the same manner as is done by 
insects. 

Lathyrus grandiflorus (Leguminosse). Is in this country more or 
less sterile. It never sets pods unless the flowers are visited 
by humble-bees (and this happens only rarely), or unless. 
they are artificially fertilised : see my article in ' Gardeners' 
Chronicle/ 1858, p. 828. 

Sarothamnus scoparius (Leguminosae). Extremely sterile when 
the flowers are neither visited by bees, nor disturbed by 
being beaten by the wind against the surrounding net. 

Melilotus officinalis (Leguminosse). An unprotected plant visited 
by bees produced at least thirty times more seeds than a 
protected one. On this latter plant many scores of racemes 
did not produce a single pod; several racemes produced 
each one or two pods ; five produced three ; six produced 
four; and one produced six pods. On the unprotected plant 
each of several racemes produced fifteen pods ; nine pro- 
duced between sixteen and twenty-two pods, and one 
produced thirty pods. 



CHAP. X. PLANTS STERILE WITHOUT INSEOT-AID. 301 

Lotus corniculatus (Leguminosse). Several covered-up plants 
produced only two empty pods, and not a single good seed. 

Tri folium, repens (Leguminosse). Several plants were protected 
from insects, and the seeds from ten flower-heads on these 
plants, and from ten heads on other plants growing outside 
the net (which I saw visited by bees), were counted ; and 
the seeds from the latter plants were very nearly ten times 
as numerous as those from the protected plants. The ex- 
periment was repeated on the following year ; and twenty 
protected heads now yielded only a single aborted seed, 
whilst twenty heads on the plants outside the net (which I 
saw visited by bees) yielded 2290 seeds, as calculated by 
weighing all the seed, and counting the number in a weight 
of two grains. 

T. pratense. One hundred flower-heads on plants protected by 
a net did not produce a single seed, whilst 100 heads on 
plants growing outside, which were visited by bees, yielded 
68 grains weight of seeds ; and as eighty seeds weighed two 
grains, the 100 heads must have yielded 2,720 seeds. I have 
often watched this plant, and have never seen hive-bees 
sucking the flowers, except from the outside through holes 
bitten by humble-bees, or deep down between the flowers, as 
if in search of some secretion from the calyx, almost in the 
same manner as described by Mr. Farrer, in the case of 
Coronilla ('Nature/ 1874, July 2, p. 169). I must, how- 
ever, except one occasion, when an adjoining field of sainfoin 
(Hedysarum onobrychis) had just been cut down, and when 
the bees seemed driven to desperation. On this occasion 
most of the flowers of the clover were somewhat withered, 
and contained an extraordinary quantity of nectar, which 
the bees were able to suck. An experienced apiarian, 
Mr. Miner, says that in the United States hive-bees never 
suck the red clover ; and Mr. E. Colgate informs me that 
he has observed the same fact in New Zealand after the 
introduction of the hive-bee into that island. On the other 
hand, H. Miiller (' Befruchtung,' p. 224) has often seen hive- 
bees visiting this plant in Germany, for the sake both of 
pollen and nectar, which latter they obtained by breaking 
apart the petals. It is at least certain that humble-bees are 
the chief fertilisers of the common red clover. 

T. incarnatum. The flower-heads containing ripe seeds, on some 
covered and uncovered plants, appeared equally fine, but 



362 PLANTS STERILE WITHOUT INSECT-AID. CHAP. X. 

this was a false appearance ; 60 heads on the latter yielded 
349 grains weight of seeds, whereas GO on the covered-up 
plants yielded only 63 grains, and many of the seeds in the 
latter lot were poor and aborted. Therefore the flowers 
which were visited by bees produced between five and six 
times as many seeds as those which were protected. The 
covered-up plants not having been much exhausted by seed- 
bearing, bore a second considerable crop of flower-stems, 
whilst the exposed plants did not do so. 

Cytisus laburnum (Leguminosae). Seven flower-racemes ready to 
expand were enclosed in a large bag made of net, and they 
did not seem in the least injured by this treatment. Only 
three of them produced any pods, each a single one ; and 
these three pods contained one, four, and five seeds. So 
that only a single pod from the seven racemes included a 
fair complement of seeds. 

CupJiea purpurea (Lythracese). Produced no seeds. Other flowers 
on the same plant artificially fertilised under the net yielded 



Vinca major (Apocynaceae). Is generally quite sterile, but some- 
times sets seeds when artificially cross-fertilised : see my 
notice, ' Gardeners' Chronicle,' 1861, p. 552. 

V. rosea. Behaves in the same manner as the last species: 
'Gardeners' Chronicle,' 1861, pp. 699, 736, 831. 

Taberncemontana echinata (Apocynacese). Quite sterile. 

Petunia violacea (Solanacese). Quite sterile, as far as I have 
observed. 

Solatium tuberosum (Solanaceae). Tinzmann says ('Gardeners' 
Chronicle/ 1846, p. 183) that some varieties are quite sterile 
unless fertilised by pollen from another variety. 

Primula scotica (Primulaceae). A non-dimorphic species, which 
is fertile with its own pollen, but is extremely sterile if 
insects are excluded. J. Scott, in ' Journal Linn. Soc. Bot.' 
vol. viii. 1864, p. 119. 

Cortusa matthioli (Primulaceae). Protected plants completely 
sterile; artificially self-fertilised flowers perfectly fertile. 
J. Scott, ibid. p. 84. 

Cyclamen persicum (Primulaceae). During one season several 
covered-up plants did not produce a single seed. 

Borago officinalis (Boraginacese). Protected plants produced 
about half as many seeds as the unprotected. 

Salvia tenon (Labiatse). Quite sterile ; but two or three flowers 



CHAP. X. PLANTS STERILE WITHOUT INSECT-AID. 363 

on the summits of three of the spikes, which touched the 
net when the wind blew, produced a few seeds. This 
sterility \vas not due to the injurious effects of the net, for I 
fertilised five flowers with pollen from an adjoining plant, 
and these all yielded fine seeds. I removed the net, whilst 
one little branch still bore a few not completely faded 
flowers, and these were visited by bees and yielded seeds. 
8. coca'necr. Some covered-up plants produced a good many 
fruits, but not, I think, half as many as did the uncovered 
plants ; twenty-eight of the fruits spontaneously produced 
by the protected plant contained on an average only 1 * 45 
seeds, whilst some artificially self-fertilised fruits on the 
same plant contained more than twice as many, viz., 3 3 



Bignonia (unnamed species) (Bignoniacese). Quite sterile : see 
my account of self-sterile plants. 

Digitalis purpurea (Scrophulariacese). Extremely sterile, only a 
few poor capsules being produced. 

Linaria vulgaris (Scrophulariaceae). Extremely sterile. 

Antirrhinum majus, red var. (Scrophulariacese). Fifty pods 
gathered from a large plant under a net contained 9 8 grains 
weight of seeds ; but many (unfortunately not counted) of 
the fifty pods contained no seeds. Fifty pods on a plant 
fully exposed to the visits of humble-bees contained 23 1 
grains weight of seed, that is, more than twice the weight ; 
but in this case again, several of the fifty pods contained no 



A. majus (white var., with a pink mouth to the corolla). 
Fifty pods, of which only a very few were empty, on a 
covered-up plant contained 20 grains weight of seed; so 
that this variety seems to be much more self-fertile than 
the previous one. With Dr. W. Ogle ('Pop. Science 
Review,' Jan. 1870, p. 52) a plant of this species was much 
more sterile when protected from insects than with me, for 
it produced only two small capsules. As showing the 
efficiency of bees, I may add that Mr. Crocker castrated some 
young flowers and left them uncovered ; and these produced 
as many seeds as the unmutilated flowers. 

A majus (peloric var.). This variety is quite fertile when arti- 
ficially fertilised with its own pollen, but is utterly sterile 
when left to itself and uncovered, as humble-bees cannot 
crawl intc the narrow tubular flowers. 



364 PLANTS STERILE WITHOUT INSECT-AID. CHAP. X. 

Verlascumphoeniceum(ScrophMlaxiacesB). Quite sterile) S 66 m y ac- 
F. nigrum. Quite sterile jSE&JLX 

Campanula carpathica (Lobeliaceae). Quite sterile. 

Lobelia ramosa (Lobeliaceae). Quite sterile. 

L.fulgens. This plant is never visited in my garden by bees, 
and is quite sterile ; but in a nursery-garden at a few miles' 
distance I saw humble-bees visiting the flowers, and they 
produced some capsules. 

Isotoma (a white-flowered var.) (Lobeliacese). Five plants left 
unprotected in my greenhouse produced twenty-four fine 
capsules, containing altogether 12' 2 grains weight of seed, 
and thirteen other very poor capsules, which were rejected. 
Five plants protected from insects, but otherwise exposed 
to the same conditions as the above plants, produced sixteen 
fine capsules, and twenty other very poor and rejected ones. 
The sixteen fine capsules contained seeds by weight in such 
proportion that twenty-four would have yielded 4 '66 
grains. So that the unprotected plants produced nearly 
thrice as many seeds by weight as the protected plants. 

Lescltenaultia formosa (Goodeniaceae). Quite sterile. My experi- 
ments on this plant, showing the necessity of insect aid, 
are given in the ' Gardeners' Chronicle,' 1871, p. 1166. 

Senecio cruentus (Composite). Quite sterile : see my account of 
self-sterile plants. 

Heterocentron mexicanum (Melastomaceae). Quite sterile ; but 
this species and the following members of the group pro- 
duce plenty of seed when artificially self-fertilised. 

Rhexia glandulosa (Melastomaceae). Set spontaneously only twc 
or three capsules. 

Ceniradenia floribunda (Melastomaceae). During some years pro- 
duced spontaneously two or three capsules, sometimes 
none. 

PUroma (unnamed species from Kew) (Melastomaceae). During 
some years produced spontaneously two or three capsules, 
sometimes none. 

Monochcetum ensiferum (Melastomaceae). During some years pro- 
duced spontaneously two or three capsules, sometimes 
none. 

Hedychium (unnamed species) (Marantacese). Almost self-sterile 
without aid. 

Orchideoe.An immense proportion of the species sterile, if 
insects are excluded. 



OHAI-. X. PLANTS FERTILE WITHOUT INSECT-AID. 36o 

List of Plants, which when protected from Insects are 
either quite Fertile, or yield more than half the Number 
of Seeds produced by unprotected Plants. 

Passiflora gracilis (Passifloraceee). Produces many fruits, but 
these contain fewer seeds than fruits from intercrossed flowers. 

Brassica oleracea (Cruciferse). Produces many capsules, but 
these generally not so rich in seed as those on uncovered 
plants. 

Raphanus sativus (Cruciferse). Half of a large branching plant 
was covered by a net, and was as thickly covered with 
capsules as the other and unprotected half; but twenty of 
the capsules on the latter contained on an average 3 '5 
seeds, whilst twenty of the protected capsules contained only 
1*85 seeds, that is, only a little more than half the number. 
This plant might perhaps have been more properly included 
in the former list. 

Iberis umbellata (Cruciferse). Highly fertile. 

/. amara. Highly fertile. 

Reseda odorata and lutea (Eesedacese). Certain individuals com- 
pletely self-fertile. 

Euryaleferox (Nymphseaceee). Professor Caspary informs me that 
this plant is highly self-fertile when insects are excluded . He 
remarks in the paper before referred to, that his plants (as 
well as those of the Victoria regia) produce only one flower 
at a time ; and that as this species is an annual, and was 
introduced in 1809, it must have been self-fertilised for the 

Flast fifty-six generations; but Dr. Hooker assures me that to 
his knowledge it has been repeatedly introduced, and that at 
Kew the same plant both of the Euryale and of the Victoria 
produce several flowers at the same time. 
Nymphcea (Nymphseacese). Some species, as I am informed by 
Professor Caspary, are quite self-fertile when insects are 
excluded. 

Adonis cestivalis (Ranunculacese). Produces, according to Pro- 
fessor H. Hoffmann (' Speciesfrage,' p. 11), plenty of seeds 
when protected from insects. 
Ranunculus acris (Ranunculacese). Produces plenty of seeds 

under a net. 

Pipaver somniferum (Papaveracese). Thirty capsules from un- 
covered plants yielded 15 '6 grains weight of seed, and thirty 
capsules from covered-up plants, growing in the same bed, 



366 PLANTS FEETILE WITHOUT INSECT-AID. CHAP. X. 

yielded 16'5 grains weight; so that the latter plants were 
more productive than the uncovered. Professor H. Hoffmann 
(' Speciesfrage,' 1875, p. 53) also found this species self-fertile 
when protected from insects. 

P. vagum. Produced late in the summer plenty of seeds, which 
germinated well. 

P. argemonoides . . . . "j According to Hildebrand (' Jahr- 

Glaucium luteum (Papaverace*) . tL^-f 

Argemone ochroleuca (Papaveraceae) . J are by no means sterile. 

Adlumia cirrhosa (Fumariacese). Sets an abundance of capsules. 

Hypecoum procumbens (Fumariaceae). Hildebrand says (idem), 
with respect to protected flowers, that ' ' eine gute Frucht- 
bildung eintrete." 

Fumaria officinalis (Fumariacese). Covered-up and unprotected 
plants apparently produced an equal number of capsules, 
and the seeds of the former seemed to the eye equally good. 
I have often watched this plant, and so has Hildebrand, and 
we have never seen an insect visit the flowers. H. Miiller 
has likewise been struck with the rarity of the visits of insects 
to it, though he has sometimes seen hive-bees at work. 
The flowers may perhaps be visited by small moths, as is 
probably the case with the following species. 

F. capreolata. Several large 'beds of this plant growing wild 
were watched by me during many days, but the flowers 
were never visited by any insects, though a humble-bee 
was once seen closely to inspect them. Nevertheless, as 
the nectary contains much nectar, especially in the evening, 
I felt convinced that they were visited, probably by moths. 
The petals do not naturally separate or open in the least ; 
but they had been opened by some means in a certain pro- 
portion of the flowers, in the same manner as follows when 
a thick bristle is pushed into the nectary ; so that in this 
respect they resemble the flowers of Corydalis lutea. Thirty- 
four heads, each including many flowers, were examined, 
and twenty of them had from one to four flowers, whilst 
fourteen had not a single flower thus opened. It is there- 
fore clear that some of the flowers had been visited by 
insects, while the majority had not ; yet almost all produced 
capsules. 

Linum usitatissimum (Linacese). Appears to be quite fertile. 
H. Hoffmann, ' Bot. Zeitung,' 1876, p. 566. 

Impatient larbigera (Balsaminaceae). The fl pwers, though ex- 



CIUP. X. PLANTS FERTILE WITHOUT INSECT-AID. 367 

cellently adapted for cross-fertilisation by the bees which 
freely visit them, set abundantly under a net. 

7. noli-me-tangere (Balsaminacese). This species produces cleis- 
togamic and perfect flowers. A plant was covered with a net, 
and some perfect flowers, marked with threads, produced 
eleven spontaneously self-fertilised capsules, which contained 
on an average 3 '45 seeds. I neglected to ascertain the 
number of seeds produced by perfect flowers exposed to the 
visits of insects, but I believe it is not greatly in excess of 
the above average. Mr. A. W. Bennett has carefully described 
the structure of the flowers of /. fulva in ' Journal Linn. Soc.' 
vol. xiii. Bot. 1872, p. 147. This latter species is said to 
be sterile with its own pollen (' Gard. Chronicle,' 1868, p. 
1286), and if so, it presents a remarkable contrast with /. 
burbigerum and noli-me-tangerf. 

Limnanthes douglasii (Geraniacese). Highly fertile. 

Viscaria oculata (Caryophyllaceae). Produces plenty of capsules 
with good seeds. 

Stellaria media (Caryophyllaceae). Covered-up and uncovered 
plants produced an equal number of capsules, and the seeds 
in both appeared equally numerous and good. 

Beta vulgaris (Chenopodiacese). Highly self-fertile. 

Vicfo sativa (Leguminosse). Protected and unprotected plants 
produced an equal number of pods and equally fine seeds, 
If there was any difference between the two lots, the covered- 
up plants were the most productive. 

V. hirsute. This species bears the smallest flowers of any 
British leguminous plant. The result of covering up plants 
was exactly the same as in the last species. 

Pisum sativum (Leguminosffi). Fully fertile. 

Lathyrus odoratus (Leguminosse). Fully fertile. 

L. nissolia. Fully fertile. 

Lupinus luteus (Leguminosse). Fairly productive. 

L. pUosus. Produced plenty of pods. 

Ononis minutissima (Leguminosse). Twelve perfect flowers on a 
plant under a net were marked by threads, and produced 
eight pods, containing on an average 2 - 38 seeds. Pods 
produced by flowers visited by insects would probably have 
contained on an average 3 '66 seeds, judging from the effects 
of artificial cross-fertilisation. 

Phaseolus vulgaris (Leguminosse). Quite fertile. 

Trifotium arvense (Leguminosffi). The excessively small flowers 



368 PLANTS FERTILE WITHOUT INSECT-AID. CHAP. X 

are incessantly visited by hive and humble-bees. When 
insects were excluded the flower-heads seemed to produce as 
many and as fine seeds as the exposed heads. 

T. procumbens. On one occasion covered-up plants seemed to 
yield as many seeds as the uncovered. On a second occasion 
sixty uncovered flower-heads yielded 9 ' 1 grains weight of 
seeds, whilst sixty heads on protected plants yielded no less 
than 17*7 grains; so that these latter plants were much 
more productive ; but this result I suppose was accidental. 
I have often watched this plant, and have never seen the 
flowers visited by insects ; but I suspect that the flowers of 
this species, and more especially of Trifolium minus, are 
frequented by small nocturnal moths which, as I hear from 
Mr. Bond, haunt the smaller clovers. 

Medicago lupulina (Leguminosffi). On account of the danger of 
losing the seeds, I was forced to gather the pods before they 
were quite ripe ; 150 flower-heads on plants visited by bees 
yielded pods weighing 101 grains; whilst 150 heads on 
protected plants yielded pods weighing 77 grains. The 
inequality would probably have been greater if the mature 
seeds could have been all safely collected and compared. 
Ig. Urban (Keimung, Bluthen, &c., bei Medicago, 1873) has 
described the means of fertilisation in this genus, as has the 
Eev. G. Henslow in the ' Journal of Linn. Soc. Bot.' vol. ix. 
1866, pp. 327 and 355. 

Nicotiana talacum (Solanacese). Fully self-fertile. 

Jpom&a purpurea (Convolvulacese). Highly self-fertile. 

Leptosiphon androsaceus (Polemoniacese). Plants under a net 
produced a good many capsules. 

Primula mollis (Primulacese). A homomorphic species, self-fer- 
tile: J. Scott, in' Journal Linn. Soc. Bot.' vol. viii. 1864, p. 120. 

Nolana prostrata (Nolanacese). Plants covered up in the green- 
house, yielded seeds by weight compared with uncovered 
plants, the flowers of which were visited by many bees. 
in the ratio of 100 to 61. 

Ajuga reptans (Labiatse). Set a good many seeds ; but none of 
the stems under a net produced so many as several un- 
covered stems growing closely by. 

Euphrasia officinalis (Scrophulariaceae). Covered-up plants pro- 
duced plenty of seed ; whether less than the exposed plants 1 
cannot say. I saw two small Dipterous insects (Dolichopo* 
nigripennis and Empis chioptera) repeatedly sucking the 



CHAP. X. PLANTS FERTILE WITHOUT INSECT-AID. 369 

flowers ; as they crawled into them, they rubbed against the 
bristles which project from the anthers, and became dusted 
with pollen. 

Veronica agrestis (Scrophulariacese). Co vered-up plants produced 
an abundance of seeds. I do not know whether any insects 
visit the flowers ; but I have observed Syrphid repeatedly 
covered with pollen visiting the flowers of V. hedercefolia and 
chamoedrys. 

Mimulus luteus (Scrophulariaceso). Highly self-fertile. 

Calceolaria (greenhouse variety) (Scrophulariacese). Highly self- 
fertile. 

Verbascum thapsus (Scrophulariacese). Highly self-fertile. 

V. lychnitis. Highly self-fertile. 

Vandellia nummularifolia (Scrophulariacese). Perfect flowers 
produce a good many capsules. 

Bartsia odontites (Scrophulariacese). Covered- up plants produced 
a good many seeds ; but several of these were shrivelled, nor 
were they so numerous as those produced by unprotected 
plants, which were incessantly visited by hive and humble- 
bees. 

Specularia speculum (Lobeliaceae). Covered plants produced 
almost as many capsules as thf uncovered. 

Lactuca sativa (Composite). Covered plants produced some 
seeds, but the summer was wet and unfavourable. 

Galium aparine (Kubiacese). Covered plants produced quite as 
many seeds as the uncovered. 

Apium petrosdinum (Umbelliferse). Covered plants apparently 
were as productive as the uncovered. 

Zea mays (Graminese). A single plant in the greenhouse 
produced a good many grains. 

Canna warscewiczi (Marantace). Highly self-fertile. 

OrcMdacece. In Europe Ophrys apt/era is as regularly self- 
fertilised as is any cleistogamic flower. In the United States, 
South Africa, and Australia there are a few species which 
are perfectly self-fertile. These several cases are given in 
the 2nd edit, of my work on the Fertilisation of Orchids. 

Allium cepa (blood red var.) (Liliacese). Four flower-heads were 
covered with a net, and they produced somewhat fewer and 
smaller capsules thar those on the uncovered heads. The 
capsules were counted on one uncovered head, and were 289 
in number ; whilst those on a fine head from under the net 
were only 199. 

2 B 



370 MEANS OF CROSS-FEBTILISATION. CHAP. X. 

Each of these lists contains by a mere accident the 
same number of genera, viz., forty -nine.* The genera 
in the first list include sixty-five species, and those in 
the second sixty species ; the Orchideas in both being 
excluded. If the genera in this latter order, as well as 
in the Asclepiadse and Apocynacese, had been included, 
the number of species which are sterile if insects are 
excluded would have been greatly increased ; but the 
lists are confined to species which were actually expe- 
rimented on. The results can be considered as only 
approximately accurate, for fertility is so variable a 
character, that each species ought to have been tried 
many times. The above number of species, namely, 
125, is as nothing to the host of living plants ; but 
the mere fact of more than half of them being sterile 
within the specified degree, when insects are excluded, 
is a striking one ; for whenever pollen has to be carried 
from the anthers to the stigma in order to ensure full 
fertility, there is at least a good chance of cross-fertili- 
sation. I do not, however, believe that if all known 
plants were tried in the same manner, half would be 
found to be sterile within the specified limits; for 



* The plants in these two lists anthers from the florets of one 

are entomophilous, or adapted for variety of wheat, which neverthe- 

fertilisation by insects, with the less produced a considerable num- 

exception of Zeaand Beta, which ber of grains, being fertilised by 

are anemophilous or fertilised by the surrounding plants. I state 

the wind. I may therefore here this fact, because Mr. A. S. Wil- 

repeat that, according to Rim- son concludes from his excellent 

pan (' Landwirth. Jarbuch,' B. vi. experiments (' Gardeners' Chroni- 

1877, pp. 192-233, and p. 1073), cle ' 1874, March 21, p. 375) that 

Eye is sterile if the access of wheat is invariably self-fertilised, 

pollen from other plants is pre- and no doubt it is so generally, 

vented ; whereas wheat and barley Mr. Wilson believes that all the 

are quite fertile under these condi- pollen shed by the exserted anthers 

tions. Rimpan states (p. 199) that is absolutely useless. This is a 

the different varieties of wheat be- conclusion which it would require 

have differently with respect to very rigid proof to make me to 

self and cross-fertilisation. He admit, 
removed at an early ag3 all the 



CHAP. X 



MEANS OF CROSS-FERTILISATION. 



371 



many flowers were selected for experiment which pre- 
sented some remarkable structure; and such flowers 
often require insect-aid. Thus out of the forty-nine 
genera in the first list, about thirty-two have flowers 
which are asymmetrical or present some remarkable 
peculiarity ; whilst in the second list, including species 
which are fully or moderately fertile when insects were 
excluded, only about twenty-one out of the forty-nine 
are asymmetrical or present any remarkable peculiarity. 
Means of cross-fertilisation. The most important of 
all the means by which pollen is carried from the 
anthers to the stigma of the same flower, or from flower 
to flower, are insects, belonging to the orders of 
Hymenoptera, Lepidoptera, and Diptera ; and in some 
parts of the world, birds.* Next in importance, but 



* I will here give all the cases 
known to me of birds fertilising 
flowers. In South Brazil, hum- 
ming - birds certainly fertilise 
various plants which are sterile 
without their aid: (Fritz Miiller, 
4 Bot. Zeit.' 1870, pp. 274-5, and 
4 Jen. Zeit. f. Naturwiss.' B. vii. 
1872, 24.) Long-beaked hum- 
ming-birds visit the flowers of 
Brugmansia, whilst some of the 
short-beaked species often pene- 
trate its large corolla in order to 
obtain the nectar in an illegitimate 
manner, in the same manner as 
do bees in all parts of the world. 
It appears, indeed, that the beaks 
of humming-birds are specially 
adapted to the various kinds 
of flowers which they visit: on 
the Cordillera they suck the 
Salviae, and lacerate the flowers 
of the Tacsonise; in Nicaragua, 
Mr. Belt saw them sucking the 
flowers of Marcgravia and Ery- 
thrina, and thus they carried 
pollen from flower to flower. In 
North America they are said to 
frequent the flowers of Impatiens : 



(Gould, ' Introduction to the Tro- 
chilida, 1 1861, pp. 15, 120 ; ' Gard. 
Chronicle, 1 1869, p. 389; 'The 
Naturalist in Nicaragua,' p. 129 ; 
' Journal of Linn. Soc. Bot.' vol. 
xiii. 1872, p. 151.) I may add 
that I often saw in Chile a Mimus 
with its head yellow with pollen 
from, as I believe, a Cassia. I 
have been assured that at the 
Cape of Good Hope, Strelitzia is 
fertilised by the Nectarinidse. 
There can hardly be a doubt that 
many Australian flowers are fer- 
tilised by the many honey-sucking 
birds of that country. Mr. Wal- 
lace remarks (Address to the Bio- 
logical Section, Brit. Assoc. 1876) 
that he has "often observed the 
beaks and faces of the brush- 
tongued lories of the Moluccas 
covered with pollen." In New 
Zealand many specimens of the 
Anthorms melanura had their 
heads coloured with pollen from 
the flowers of an endemic species 
of Fuchsia: (Potts, 'Transact 
New Zealand Institute,' vol. iii. 
1870, p. 72.) 

2 B 2 



372 MEANS OF CROSS-FEKTILISATION. CHAP. X. 

in a quite subordinate degree, is the wind ; and with 
some aquatic plants, according to Delpino,* currents of 
water. The simple fact of the necessity in many cases 
of extraneous aid for the transport of the pollen, and the 
many contrivances for this purpose, render it highly 
probable that some great benefit is thus gained ; and 
this conclusion has now been firmly established by the 
proved superiority in growth, vigour, and fertility of 
plants of crossed parentage over those of self-fertilised 
parentage. But we should always keep in mind that 
two somewhat opposed ends have to be gained; the 
first and more important one being the production 
of seeds by any means, and the second, cross-ferti- 
lisation. 

The advantages derived from cross-fertilisation throw 
a flood of light on most of the chief characters of flowers. 
We can thus understand their large size and bright 
colours, and in some cases the bright tints of the 
adjoining parts, such as the peduncles, bracteae, even 
true leaves, as with Poinsettia, &c. By this means 
they are rendered conspicuous to insects, on the same 
principle that almost every fruit which is devoured by 
birds presents a strong contrast in colour with the 
green foliage, in order that it may be seen and its 
seeds freely disseminated. With some flowers con- 
spicuousness is gained at the expense even of the 
reproductive organs, as with the ray-florets of many 
Composite, the exterior flowers of Hydrangea, and the 
terminal flowers of the Feather-hyacinth or Muscari. 
There is also reason to believe, and this was the opinion 
of Sprengel, that flowers differ in colour in accordance 
with the kinds of insects which frequent them. 



* See also Dr. Ascherson's interesting essay in ' B( t. Zeitung,' 
1871, p. 444. 



CHAP. X. MEANS OF CKOSS-FERTILISATION. 373 

Not only do the bright colours of flowers serve to 
attract insects, but dark-coloured streaks and marks 
are often present, which Sprengel long ago maintained 
served as guides to the nectary. These marks follow 
the veins in the petals, or lie between them. They 
may occur on only one, or on all excepting one or 
more of the upper or lower petals ; or they may form 
a dark ring round the tubular part of the corolla, or 
be confined to the lips of an irregular flower. In the 
white varieties of many flowers, such as of Digitalis 
purpurea, Antirrhinum majus, several species of Dian- 
thus, Phlox, Myosotis, Rhododendron, Pelargonium, 
Primula, and Petunia, the marks generally persist, 
whilst the rest of the corolla has become of a pure 
white ; but this may be due merely to their colour 
being more intense and thus less readily obliterated. 
Sprengel's notion of the use of these marks as guides 
appeared to me for a long time fanciful ; for insects, 
without such aid, readily discover the nectary and 
bite holes through it from the outside. They also 
discover the minute nectar-secreting glands on the 
stipules and leaves of certain plants. Moreover, some 
few plants, such as certain poppies, which are not 
nectariferous, have guiding marks ; but we might 
perhaps expect that some few plants would retain 
traces of a former nectariferous condition. On the other 
hand, these marks are much more common on asymme- 
trical flowers, the entrance into which would be apt to 
puzzle insects, than on regular flowers. Sir J. Lubbock 
has also proved that bees readily distinguish colours, 
and that they lose much time if the position of honey 
M hich they have once visited be in the least changed.* 
The following case affords, I think, the best evidence 



Briti.-ili WM F'r wors 'n relation to Insects,' 1875, p. 14. 



374 MEANS OF CBOSS-FERTILISATION. CHAP. X. 

that these marks have really been developed in corre- 
lation with the nectary. The two upper petals of the 
common Pelargonium are thus marked near their bases; 
and I have repeatedly observed that when the flowers 
vary so as to become peloric or regular, they lose their 
nectaries and at the same time the dark marks. 
Wnen the nectary is only partially aborted, only one 
of the upper petals loses its mark. Therefore the nec- 
tary and these marks clearly stand in some sort of close 
relation to one another ; and the simplest view is that 
they were developed together for a special purpose; 
the only conceivable one being that the marks serve as 
a guide to the nectary. It is, however, evident from 
what has been already said, that insects could discover 
the nectar without the aid of guiding marks. They 
are of service to the plant, only by aiding insects to 
visit and suck a greater number of flowers within a 
given time than would otherwise be possible ; and thus 
there will be a better chance of fertilisation by pollen 
brought from a distinct plant, and this we know is of 
paramount importance. 

The odours emitted by flowers attract insects, as I 
have observed in the case of plants covered by a muslin 
net. Nageli affixed artificial flowers to branches, 
scenting some with essential oils and leaving others 
unscented ; and insects were attracted to the former in 
an unmistakable manner.* It would appear that they 
must be guided by the simultaneous action of sight 
and smell, for M. Plateau f found that excellently 
made, but not scented, artificial flowers never deceived 
them. It will be shown in the next chapter that the 
flowers of certain plants remain fully expanded for 

* ' Enstehung, &c., der Natur- Assoc. for the Advancement of 
hist. Art.' 1865, p. 23. Science,' 1876. 

f ' Proceedings of the French 



CHAP. X. MEANS OF CROSS-FERTILISATION. 375 

days or weeks and do not attract any insects ; and it is 
probable that they are neglected from not having as 
yet secreted any nectar or become odoriferous. Nature 
may be said occasionally to try on a large scale the 
same experiment as that by M. Plateau. Not a few 
flowers are both conspicuous and odoriferous. Of all 
colours, white is the prevailing one; and of white 
flowers a considerably larger proportion smell sweetly 
than of any other colour, namely, 14 6 per cent. ; of 
red, only 8 2 per cent, are odoriferous.* The fact of 
a larger proportion of white flowers smelling sweetly 
may depend in part on those which are fertilised by 
moths requiring the double aid of conspicuousness in 
the dusk and of odour. Most flowers which are fer- 
tilised by crepuscular or nocturnal insects emit their 
odour chiefly or exclusively in the evening, and they 
are thus less likely to be visited and have their nectar 
stolen by ill-adapted diurnal insects. Some flowers, 
however, which are highly odoriferous depend solely 
on this quality for their fertilisation, such as the night- 
flowering stock (Hesperis) and some species of Daphne ; 
and these present the rare case of flowers which are 
fertilised by insects being obscurely coloured. 

The storage of a supply of nectar in a protected place 
is manifestly connected with the visits of insects. So 
is the position which the stamens and pistils occupy, 
either permanently or at the proper period through 
their own movements ; for when mature they invariably 
stand in the pathway leading to the nectary. The 
shape of the nectary and of the adjoining parts are 
likewise related to the particular kinds of insects which 



* The colours and odours of I have not seen their original 

the flowers of 4200 species have works, but a very full abstract 

been tabulated by Landgrabe, is given in London's ' Gardeners' 

and by Schubler and KShler. Mag.' vol. xiii. 1837, p. 367. 



376 MEANS OF CROSS-FERTILISATION. CHAP. X. 

habitually visit the flowers ; this has been well shown 
by H. Miiller by his comparison of lowland species 
which are chiefly visited by bees, with alpine species 
belonging to the same genera which are visited by 
butterflies.* Flowers may also be adapted to certain 
kinds of insects, by secreting nectar particularly attrac- 
tive to them, and unattractive to other kinds ; of which 
fact Epipactis latifolia offers the most striking instance 
known to me, as it is visited exclusively by wasps. 
Structures also exist, such as the hairs within the 
corolla of the foxglove (Digitalis), which apparently 
serve to exclude insects that are not well fitted to bring 
pollen from one flower to another.f I need say nothing 
here of the endless contrivances, such as the viscid 
glands attached to the pollen-masses of the Orchideae 
and Asclepiadse, or the viscid or roughened state of 
the pollen-grains of many plants, or the irritability of 
their stamens which move when touched by insects, &c., 
as all these contrivances evidently favour or ensure 
cross-fertilisation. 

All ordinary flowers are so far open that insects can 
force an entrance into them, notwithstanding that 
some, like the Snapdragon (Antirrhinum), various 
Papilionaceous and Fumariaceous flowers, are in 
appearance closed. It cannot be maintained that their 
openness is necessary for fertility, as cleistogamic flowers 
which are permanently closed yield a full complement 
of seeds. Pollen contains much nitrogen and phos- 



* 'Nature,' 1874, p. 110; 1875, &c. protect the flowers from the 

p. 190 ; 1876, pp. 210, 289. access of crawling or wingless 

t Belt, ' The Naturalist in Ni- insects, which would steal the 

caragua,' 1874, p. 132. Kerner nectar, and yet, as they do not 

has shown in his admirable essay, commonly carry pollen from one 

' Die Sclnitzmittel der Bliithen plant to another, but only from 

gegen unberufene Gaste, 1826,' flower to flower on the sanif 

that many structures hairs, viscid plant, would confer DO benrfit to 

glands, the position of the parts, the species. 



CHAP X. MEANS OP CROSS-FERTILISATION. 377 

phons the two most precious of all the elements for 
the growth of plants but in the case of most open 
flowers, a large quantity of pollen is consumed by 
pollen-devouring insects, and a large quantity is 
destroyed during long-continued rain. With many 
plants this latter evil is guarded against, as far as 
is possible, by the anthers opening only during dry 
weather,* by the position and form of some or all of 
the petals, by the presence of hairs, &c., and as Kerner 
has shown in his interesting essay, f by the movements 
of the petals or of the whole flower during cold and wet 
weather. In order to compensate the loss of pollen in 
so many ways, the anthers produce a far larger amount 
than is necessary for the fertilisation of the same flower. 
I know this from my own experiments on Ipomcea, 
given in the Introduction ; and it is still more plainly 
shown by the astonishingly small quantity produced 
by cleistogamic flowers, which lose none of their pollen, 
in comparison with that produced by the open flowers 
borne by the same plants ; and yet this small quantity 
suffices for the fertilisation of all their numerous seeds. 
Mr. Hassall took pains in estimating the number of 
pollen-grains produced by a flower of the Dandelion 
(Leontodon), and found the number to be 243,600, 
and in a Paeony 3,654,000.f A single plant of Typha 
produced 144 grains by weight of pollen, and as this 
plant is anemophilous with very small pollen-grains, 



* Mr. Blackley observed that up in the atmosphere, during the 
the ripe anthers of rye did not first fine and dry days after wet 
dehisce whilst kept under a bell- weather, than at other times : 
glass in a damp atmosphere, ' Experimental Researches on 
whilst other anthers exposed to Hay Fever,' 1873, p. 127. 
the same temperature in the open t ' Die Schutzmittel des Pol- 
air dehisced freely. He also found lens,' 1873. 
much more pollen adhering to J 'Annals and Mag. of Nat 
the sticky slides, which were Hist.' vol. yiii. 1842, p. 108. 
attache! to kites and sent high 



378 MEANS OF CROSS-FERTILISATION. CHAP. X 

their number in the above weight must have been 
prodigious. We may judge of this from the following 
facts : Dr. Blackley ascertained * by an ingenious 
method, that in the three following anemophilous plants, 
a single grain-weight of the pollen of Lolium perenne 
contained 6,032,000 grains; the same weight of the 
pollen of Plantago lanceolata contained 10,124,000 
grains ; and that of Scirpus lacustris, 27,302,050 grains. 
Again Mr. A. S. Wilson estimated by micro-measure- 
mentf that a single floret of rye yielded 60,000 pollen- 
grains, whilst one of spring wheat yielded only 6864 
grains. The editor of the ' Botanical Kegister ' counted 
the ovules in the flowers of Wistaria sinensis, and care- 
fully estimated the number of pollen-grains, and he 
found that for each ovule there were 7000 grains.:}: With 
Mirabilis, three or four of the very large pollen-grains 
are sufficient to fertilise an ovule ; but I do not know 
how many grains a flower produces. With Hibiscus, 
Kolreuter found that sixty grains were necessary to fer- 
tilise all the ovules of a flower, and he calculated that 
4863 grains were produced by a single flower, or eighty- 
one times too many. With Geum urbanum, however, 
according to Gartner, the pollen is only ten times too 
much. As we thus see that the open state of all 
ordinary flowers, and the consequent loss of much 
pollen, necessitate the development of so prodigious an 
excess of this precious substance, why, it may be asked, 
are flowers always left open ? As many plants exist 
throughout the vegetable kingdom which bear cleisto- 
gamic flowers, there can hardly be a doubt that all 



* 'New Observations on Hay 1846, p. 771. 

Fever,' 1877, p. 14. Kolreuter, ' Vorliiufige Nach- 

t ' Gardeners' Chronicle,' March richt,' 1761, p. 9. Gartner, ' Bei- 

1874, p. 376. trage zur Kenntniss,' &c. p. 346. 

$ Quoted in ' Gard. Chron.' 



CHAP. X. MEANS OF CROSS-FERTILISATION. 379 

open flowers might easily have been converted into 
closed ones. The graduated steps by which this pro- 
cess could have been effected may be seen at the 
present time in Lathyrus nissolia, Biophytum sen- 
sitivum, and several other plants. The answer to the 
above question obviously is, that with permanently 
closed flowers there could be no cross fertilisation. 

The frequency, almost regularity, with which pollen 
is transported by insects from flower to flower, often 
from a considerable distance, well deserves attention.* 
This is best shown by the impossibility in many cases 
of raising two varieties of the same species pure, if they 
grow at all near together ; but to this subject I shall 
presently return ; also by the many cases of hybrids 
which have appeared spontaneously both in gardens and 
a state of nature. With respect to the distance from 
which pollen is often brought, no one who has had any 
experience would expect to obtain pure cabbage-seed, 
for instance, if a plant of another variety grew within 
two or three hundred yards. An accurate observer, 
the late Mr. Masters of Canterbury, assured me that 
he once had his whole stock of seeds " seriously affected 
with purple bastards," by some plants of purple kale 
which flowered in a cottager's garden at the distance of 
half a mile ; no other plant of this variety growing any 



* An experiment made by K61- wards he counted the seeds of 

reuter (' Fortsetsuug,' &c. 1763, both lots: the flowers which he 

p. 69) affords good evidence on had fertilised with such astonish- 

this head. Hibiscus vesicarius is ing care produced 11,237 seeds, 

strongly diohogamous, its pollen whilst those left to the insects 

being shed before the stigmas are produced 10,886 ; that is, a less 

mature. Kolreuter marked 310 number by only 351; and this 

flowers, and put pollen from small inferiority is fully accounted 

other flowers on their stigmas for by the insects not having 

every day, so that they were worked during some diys, when 

thoroughly fertilised ; and he left the weather was cold with son- 

the same number of other flowers tinued rain, 
to the agency of insects. After- 



380 MEANS OF CROSS-FERTILISATION. CHAP. X 

nearer.* But the most striking case which has been re- 
corded is that by M. Godron,f who shows by the nature 
of the hybrids produced that Primula grandiflora must 
have been crossed with pollen brought by bees from 
P. offieinalis, growing at the distance of above two 
kilometres, or of about one English mile and a quarter. 
All those who have long attended to hybridisation, 
insist in the strongest terms on the liability of castrated 
flowers to be fertilised by pollen brought from distant 
plants of the same species.^ The following case shows 
this in the clearest manner : Gartner, before he had 
gained much experience, castrated and fertilised 520 
flowers on various species with pollen of other genera 
or other species, but left them unprotected ; for, as he 
says, he thought it a laughable idea that pollen should 
be brought from flowers of the same species, none of 
which grew nearer than between 500 and 600 yards. 
The result was that 289 of these 520 flowers yielded no 
seed, or none that germinated ; the seed of 29 flowers 
produced hybrids, such as might have been expected 
from the nature of the pollen employed ; and lastly, 
the seed of the remaining 202 flowers produced per- 



* Mr. W. C. Marshall caught in his ' Bastarderzeugung,' 1849, 

no less than seven specimens of a p. 670 ; and ' Kenntniss der Be- 

moth (Oucullia umbratica) with fruchtung,' 1844, pp. 510, 573. 

the pollinia of the butter fly-orcL is Also Lecoq, ' De la Fecondation,' 

(Habenaria chlorantha') sticking &c., 1845, p. 27. Some statements 

to their eyes, and, therefore, in have been published during late 

the proper position for fertilising years of the extraordinary ten- 

the flowers of this species, on an etency of hybrid plants to revert 

island in Derwentwater, at the to their parent forms ; but as it is 

distance of half a mile from any not said how the flowers were 

place where this plant grew : protected from insects, it may be 

' Nature,' 1872, p. 393. suspected that they were often 

t 'Kevue des Sc. Nat.' 1875, fertilised with pollen brought 

p. 331. from a distance from the parent- 

J See, for instance, the remarks species. 

by Herbert, ' Amaryllidaoese,' ' Kenntniss der Befruchtung, 

1837, p. 349. Also Gartner's pp. 539, 550, 575, 576. 
strong expressions on this subject 



CHAP. X. CROSS-FERTILISATION. 381 

fectly pure plants, so that these flowers must haye 
been fertilised by pollen brought by insects from a 
distance of between 500 and 600 yards.* It is of 
course possible that some of these 202 flowers might 
have been fertilised by pollen left accidentally in 
them when they were castrated; but to show how 
improbable this is, I may add that Gartner, during the 
next eighteen years, castrated no less than 8042 flowers 
and hybridised them in a closed room ; and the seeds 
from only seventy of these, that is considerably less 
than 1 per cent., produced pure or unhybridised 
offspring.! 

From the various facts now given, it is evident that 
most flowers are adapted in an admirable manner for 
cross-fertilisation. Nevertheless, the greater number 
likewise present structures which are manifestly 
adapted, though not in so striking a manner, for self- 
fertilisation. The chief of these is their hermaphrodite 
condition ; that is, their including within the same 
corolla both the male and female reproductive organs. 
These often stand close together and are mature at 
the same time ; so that pollen from the same flower 
cannot fail to be deposited at the proper period on the 
stigma. There are also various details of structure 
adapted for self-fertilisation.J Such structures are 
best shown in those curious cases discovered by fi. 
Miiller, in which a species exists under two forms, 
one bearing conspicuous flowers fitted for cross-fertilisa- 
tion, and the other smaller flowers fitted for self-fer- 



* Henschel's experiments two genera, and put on their 

(quoted by Gartner, ' Kenntniss,' stigmas either no pollen, or pollen 

&c., p. 574), which are worthless from distinct genera, yet they all 

in all other respects, likewise seeded, and all the seedlings raised 

show how largely flowers are in- from them were of course pure, 
tercrossed by insects. He cas- f ' Kenntniss,' &c. pp. 555, 57& 
trated many flowers on thirty- j H. Muller, ' Die Befruchtung, 

seven epecies, belonging to twenty- &c. p. 448. 



382 CROSS-FERTILISATION. CHAP. X. 

tilisation, with many parts in the latter slightly 
modified for this special purpose.* 

As two objects in most respects opposed, namely, 
cross-fertilisation and self-fertilisation, have in many 
cases to be gained, we can understand the co-existence 
in so many flowers of structures which appear at first 
sight unnecessarily complex and of an opposed nature. 
We can thus understand the great contrast in structure 
between cleistogamic flowers, which are adapted exclu- 
sively for self-fertilisation, and ordinary flowers on the 
same plant, which are adapted so as to allow of at least 
occasional cross-fertilisation.t The former are always 
minute, completely closed, with their petals more or 
less rudimentary and never brightly coloured ; they 
never secrete nectar, never are odoriferous, have very 
small anthers which produce only a few grains of pollen, 
and their stigmas are but little developed. Bearing 
in mind that some flowers are cross-fertilised by the 
wind (called anemophilous by Delpino), and others 
by insects (called entomophilous), we can further 
understand, as was pointed out by me several years 
ago,J the great contrast in appearance between these 
two classes of flowers. Anemophilous flowers resemble 
in many respects cleistogamic flowers, but differ widely 
in not being closed, in producing an extraordinary 



* Nature,' 1873, pp. 44, 433. the old nest. The fully-deve- 

f Fritz Miiller has discovered loped males and females are 

in the animal kingdom ( ' Je- winged, and individuals from dis- 

naische Zeitschr.' B. iv. p. 451) tinct nests can hardly fail often 

a case curiously analogous to that to intercross. In the act of 

of the plants which bear oleis- swarming they are destroyed in 

togamic and perfect flowers. He almost infinite numbers by a host 

finds in the nests of Termites, in of enemies, so that a queen may 

Brazil, males and females with often fail to enter an old nest; 

imperfect wings, which do not and then the imperfectly deve- 

leave the nests and propagate the loped males and females propagate 

species in a cleistogamic manner, and keep up the stock, 
but only if a fully-developed queen J 'Journal of Linn. Soc.' vol 

after swarming does not enter vii. Bot. 1863, p. 77. 



CHAP. X. CROSS-FERTILISATION. 383 

amount of pollen which is always incoherent, and 
in the stigma often being largely developed or 
plumose. We certainly owe the beauty and odour of 
our flowers and the storage of a large supply of honey 
to the existence of insects. 

On the Relation between the Structure and Conspicuous- 
ness of Flowers, the Visits of Insects, and the Advan- 
tages of Cross-fertilisation. 

It has already been shown that there is no close 
relation between the number of seeds produced by 
flowers when crossed and self-fertilised, and the degree 
to which their offspring are affected by the two pro- 
cesses. I have also given reasons for believing that 
the inefficiency of a plant's own pollen is in most cases 
an incidental result, or has not been specially acquired 
for the sake of preventing self-fertilisation. On the 
other hand, there can hardly be a doubt that dichogamy, 
which prevails according to Hildebrand* in the greater 
number of species, that the heterostyled condition of 
certain plants, and that many mechanical structures 
have all been acquired so as both to check self- 
fertilisation and to favour cross-fertilisation. The 
means for favouring cross-fertilisation must have been 
acquired before those which prevent self-fertilisation ; 
as it would manifestly be injurious to a plant that 
its stigma should fail to receive its own pollen, 
unless it had already become well adapted for receiv- 
ing pollen from another individual. It should be 
observed that many plants still possess a high power 
of self-fertilisation, although their flowers are excel- 
lently constructed for cross-fertilisation for instance, 
those of many papilionaceous species. 



* ' Die Geschlechter Vertheilung,' &c. p. 32. 



.. 

lorrm 



384 CKOSS-FERTILISATION. CHAP, 

It may be admitted as almost certain that some 
structures, such as a narrow elongated nectary, or a 
long tubular corolla, have been developed in order 
that certain kinds of insects alone should obtain the 
nectar. These insects would thus find a store of nectar 
preserved from the attacks of other insects ; and 
they would thus be led to visit frequently such 
flowers and to carry pollen from one to the other.* 
It might perhaps have been expected that plants 
having their flowers thus peculiarly constructed would 
profit in a greater degree by being crossed, than 
ordinary or simple flowers ; but this does not seem 
to hold good. Thus Tropeeolum minus has a long 
nectary and an irregular corolla, whilst Limnanihes 
douglasii has a regular flower and no proper nectary, 
yet the crossed seedlings of both species are to the 
self-fertilised in height as 100 to 79. Salvia coccinea 
has an irregular corolla, with a curious apparatus by 
which insects depress the stamens, while the flowers 
of Ipomoaa are regular; and the crossed seedlings of 
the former are in height to the self-fertilised as 
100 to 76, whilst those of the Ipomcea are as 100 to 
77. Fagopyrum is heterostyled and Anagallis edllina 
is homostyled, and the crossed seedlings of both are 
in height to the self-fertilised as 100 to 69. 

With all European plants, excepting the compara- 
tively rare anemophilous kinds, the possibility of 
distinct individuals intercrossing depends on the 
visits of insects; and H. Muller has proved by his 
valuable observations, that large conspicuous flowers 
are visited much more frequently and by many more 
kinds of insects, than are small inconspicuous flowers. 
He further remarks that the flowers which are rarely 



* See the interesting discussion on this subject by H Muller, 
Die Befruchtung,' &c. p. 431. 



CHAP.X. INCONSPICUOUS FLOWERS. 385 

visited must be capable of self-fertilisation, otherwise 
they would quickly become extinct. * There is, how- 
ever, some liability to error in forming a judgment 
on this head, from the extreme difficulty of ascertain- 
ing whether flowers which are rarely or never visited 
during the day (as in the above given case of Fumaria 
capreolata) are not visited by small nocturnal Lepi- 
doptera, which are so numerous and are known to be 
strongly attracted by sugar, f The two lists given in 
the early part of this chapter support Muller's con- 
clusion that small and inconspicuous flowers are com- 
pletely self-fertile ; for only eight or nine out of the 
125 species in the two lists come under this head, and 
all of these were proved to be highly fertile when in- 
sects were excluded. The singularly inconspicuous 
flowers of the JFly Ophrys (0. muscifera), as I have 
elsewhere shown, are rarely visited by insects ; and it 
is a strange instance of imperfection, in contradiction 
to the above rule, that these flowers are not self-fertile, 
so that a large proportion of them do not produce seeds. 
The converse of the rule that plants bearing small 
and inconspicuous flowers are self- fertile, namely, that 
plants with large and conspicuous flowers are self- 
sterile, is far from true, as may be seen in our second 
list of spontaneously self-fertile species ; for this list 
includes such species as Ipomcea purpurea, Adonis 
ffistivalis, Verbascum thapsus, Pisum sativwni, Lathyrus 
odoratus, some species of Papaver and of Nymphaea, 
and others. 

The rarity of the visits of insects to small flowers, 

* ' Befruchtung,' &c., p. 426. collector of Noctuw, come very 

4 Nature,' 1873, p. 433. freely to sugar, and no doubt 

t In answer to a question by naturally visit flowers :" the 'En- 

tne, the editor of an entomological tomologists' Weekly Intelligencer,' 

iournal writes " The Depres- 1860, p. 103. 
tr i se, as is notorious to every 

2 o 



386 CKOSS-FERTILISATION. CHAP. X 

does not depend altogether on their inconspicuousness, 
but likewise on the absence of some sufficient attraction ; 
for the flowers of Trifolium arvense are extremely 
small, yet are incessantly visited by hive and humble- 
bees, as are the small and dingy flowers of the 
asparagus. The flowers of Linaria cymbalaria are 
small and not very conspicuous, yet at the proper time 
they are freely visited by hive-bees. I may add that, 
according to Mr. Bennett,* there is another and quite 
distinct class of plants which cannot be much frequented 
by insects, as they flower either exclusively or often 
during the winter, and these seem adapted for self- 
fertilisation, as they shed their pollen before the flowers 
expand. 

That many flowers have been rendered conspicuous 
for the sake of guiding insects to them is highly 
probable or almost certain ; but it may be asked, have 
other flowers been rendered inconspicuous so that they 
may not be frequently visited, or have they merely 
retained a former and primitive condition ? If a plant 
were much reduced in size, so probably would be the 
flowers through correlated growth, and this may possibly 
account for some cases ; but the corolla, as I have else- 
where shown (' Different Forms of Flowers,' 1877, p. 
143), is also liable to be greatly reduced, through the 
direct action of unfavourable climate. Size and colour 
are both exiremely variable characters, and it can 
hardly be doubted that if large and brightly-coloured 
flowers were advantageous to any species, these could be 
acquired through natural selection within a moderate 
lapse of time. Papilionaceous flowers are manifestly 
constructed in relation to the visits of insects, and it 
seems improbable, from the usual character of the 



* ' Nature,' 1869, p. 11. 



CHAP. X. INCONSPICUOUS FLOWERS. 387 

group, that the progenitors of the genera Vicia and 
Trifolium produced such minute and unattractive 
flowers as those of V. hirsuta and T. procumbens. We 
are thus led to infer that some plants either have not 
had their flowers increased in size, or have actually 
had them reduced and purposely rendered incon- 
spicuous, so that they are now but little visited by 
insects. In either case they must also have acquired 
or retained a high degree of self-fertility. 

If it became from any cause advantageous to a spe- 
cies to have its capacity for self-fertilisation increased, 
there is little difficulty in believing that this could 
readily be effected; for three cases of plants varying 
in such a manner as to be more fertile with their own 
pollen than they originally were, occurred in the 
course of my few experiments, namely, with Mimulus, 
Ipomoaa, and Nicotiana. Nor is there any reason to 
doubt that many kinds of plants are capable under 
favourable circumstances of propagating themselves 
for very many generations by self-fertilisation. This 
is the case with the varieties of Pisum sativum and of 
Lathyrus odoratus which are cultivated in England, and 
with Ophrys apifera and some other plants in a state 
of nature. Nevertheless, most or all of these plants 
retain structures in an efficient state which cannot be 
of the least use except for cross-fertilisation. We have 
also seen reason to suspect that self-fertilisation is in 
some peculiar manner beneficial to certain plants : 
but if this be really the case, the benefit thus derived 
is far more than counterbalanced by a cross with a 
fresh stock or with a slightly different variety. 

Notwithstanding the several considerations just 
advanced, it seems to me highly improbable that 
plants bearing small and inconspicuous flowers have 
been or should continue to be subjected to self- 

2 c 2 



388 MEANS OF CROSS-FERTILISATION. CHAP. X. 

fertilisation for a long series of generations. I think 
so, not from the evil which manifestly follows from 
self-fertilisation, in many cases even in the first gene- 
ration, as with Viola tricolor, Sarothamnus, Nemo- 
phila, Cyclamen, &c. ; nor from the probability of the 
evil increasing after several generations, for on this 
latter head I have not sufficient evidence, owing to the 
manner in which my experiments were conducted. But 
if plants bearing small and inconspicuous flowers were 
not occasionally intercrossed, and did not profit by the 
process, all their flowers would probably have been 
rendered cleistogamic, as they would thus have largely 
benefited by having to produce only a small quantity 
of safely-protected pollen. In coming to this con- 
clusion, I have been guided by the frequency with 
which plants belonging to distinct orders have been 
rendered cleistogamic. But I can hear of no instance 
of a species with all its flowers rendered permanently 
cleistogamic. Leersia makes the nearest approach to 
this state ; but as already stated, it has been known 
to produce perfect flowers in one part of Germany. 
Some other plants of the cleistogamic class, for instance 
Aspicarpa, have failed to produce perfect flowers during 
several years in a hothouse ; but it does not follow that 
they would fail to do so in their native country, any 
more than with a Vandellia and Viola, which with me pro- 
duced only cleistogamic flowers during certain years.* 
Plants belonging to this class commonly bear both 
kinds of flowers every season, and the perfect flowers 
of Viola eanina vield fine capsules, but only when 
visited by bees. We have also seen that the seedlings 
of Ononis minutissima, raised from the perfect flowers 
fertilised with pollen from another plant, were finer 



* These cases are given in ch. viii. of my * Different Forma of Flowers.' 



CiiAF. X. INCONSPICUOUS FLOWERS. 389 

than those from self-fertilised flowers; and this was 
likewise the case to a certain extent with Vandellia. 
As therefore no species which at one time bore perfect 
though small and inconspicuous flowers has had all its 
flowers rendered cleistogamic, I must believe that 
plants now bearing small and inconspicuous flowers 
profit by their still remaining open, so as to be occa- 
sionally intercrossed by insects. It has been one of 
the greatest oversights in my work that I did not 
experimentise on such flowers, owing to the difficulty 
of fertilising them, and to my not having seen the 
importance of the subject.* 

It should be remembered that in two of the cases in 
which highly self-fertile varieties appeared amongst 
my experimental plants, namely, with Mimulus and 
Nicotiana, such varieties were greatly benefited by a 
cross with a fresh stock or with a slightly different 
variety; and this likewise was the case with the 
cultivated varieties of Pisum sativum and Lathyrus 
odoratus, which have been long propagated by self- 
fertilisation. Therefore until the contrary is distinctly 
proved, I must believe that as a general rule small and 
inconspicuous flowers are occasionally intercrossed by 
insects ; and that after long-continued self-fertilisation, 

* Some of the species of Sola- On the other hand, the flowers of 

num would be good ones for such the common potato ( tuberosum'j, 

experiments, for they are said by though they do not secrete nectar 

H. Muller (' Befruchtung,' p. 434) (Kurr, Bedeutung der Nekta- 

to be unattractive to insects from rien," 1833, p. 40), yet cannot be 

not secreting nectar, not producing considered as inconspicuous, and 

much pollen, and not being very they are sometimes visited by 

conspicuous. Hence probably it Diptera (Muller) and, as I have 

is that, according to Verlot(' Pro- seen, by humble-bees. Tinz- 

d action dcsVarie'tes,' 1865, p. 72), mann (as quoted in 'Gardeners' 

the varieties of "les aubergines Chronicle, 1 1846, p. 183) found 

et les tomates " (species of Solu- that some of the varieties did not 

num) do not intercross when they bear seed when fertilised with 

are cultivated near together ; but pollen from the same variety, but 

it should be remembered that were fertile with that from an- 

these are not endemic epecies. otlmr variety. 



390 MEANS OF CROSS-FERTILISATION. CHAP. X 

if they are crossed with pollen brought from a plaiit 
growing under somewhat different conditions, or 
descended from one thus growing, their offspring 
would profit greatly. It cannot be admitted, under 
our present state of knowledge, that self-fertilisation 
continued during many successive generations is evei 
the most beneficial method of reproduction. 

The Means which favour or ensure Flowers "being fer- 
tilised with Pollen from a distinct Plant. We have seen 
in four cases that seedlings raised from a cross between 
flowers on the same plant, even on plants appearing 
distinct from having been propagated by stolons or cut- 
tings, were not superior to seedlings from self-fertilised 
flowers ; and in a fifth case (Digitalis) superior only 
in a slight degree. Therefore we might expect that 
with plants growing in a state of nature a cross between 
the flowers on distinct individuals, and not merely 
between the flowers on the same plant, would generally 
or often be effected by some means. The fact of bees 
and of some Diptera visiting the flowers of the same 
species as long as they can, instead of promiscuously 
visiting various species, favours the intercrossing of 
distinct plants. On the other hand, insects usually 
search a large number of flowers on the same plant 
before they fly to another, and this is opposed to cross- 
fertilisation. The extraordinary number of flowers 
which bees are able to search within a very short space 
of time, as will be shown in a future chapter, increases 
the chance of cross-fertilisation ; as does the fact 
that they are not able to perceive without entering a 
flower whether other bees have exhausted the nectar. 
For instance, H. Miiller found* that four-fifths of the 



* ' Die Befruchtung.' &c. p. 311. 



CHAP. X. MEANS OF CROSS-FERTILISATION. 391 

flowers of Lamium album which a humble-bee visited 
had been already exhausted of their nectar. In order 
that distinct plants should be intercrossed, it is of course 
indispensable that two or more individuals should grow 
uear one another ; and this is generally the case. Thus 
A. de Candolle remarks that in ascending a mountain 
the individuals of the same species do not commonly 
disappear near its upper limit quite gradually, but 
rather abruptly. This fact can hardly be explained 
by the nature of the conditions, as these graduate away 
in an insensible manner, and it probably depends in 
large part on vigorous seedlings being produced only 
as high up the mountain as many individuals can 
subsist together. 

With respect to dioecious plants, distinct individuals 
must always fertilise each other. With monoecious 
plants, as pollen has to be carried from flower to flower, 
there will always be a good chance of its being carried 
from plant to plant. Delpino has also observed * the 
curious fact that certain individuals of the monoecious 
walnut (Juglans regia) are proterandrous, and others 
proterogynous, and these will reciprocally fertilise each 
other. So it is with the common nut (Corylus avellana),] 
and, what is more surprising, with some few her- 
maphrodite plants, as observed by H. Muller.t These 
latter plants cannot fail to act on each other like 
dimorphic or trimorphic heterostyled species, in which 
the union of two individuals is necessary for full 
and normal fertility. With ordinary hermaphrodite 
species, the expansion of only a few flowers at the same 
time is one of the simplest means for favouring the 
intercrossing of distinct individuals; but this would 



* 'Ult. Osservazioni,' &c., part J 'Die Befntchtung ' &c. pt\ 
li. fuse. ii. p. 337. 285, 339. 

t ' Nature,' 1875, p. 26. 



392 MEANS OF CROSS-FERTILISATION. CHAP. X. 

render the plants less conspicuous to insects, unless 
the flowers were of large size, as in the case of several 
bulbous plants. Kerner thinks * that it is for this 
object that the Australian Villarsia parnassifolia pro- 
duces daily only a single flower. Mr. Cheeseman also 
remarks,! that as certain Orchids in New Zealand 
which require insect-aid for their fertilisation bear only 
a single flower, distinct plants cannot fail to intercross. 
So it is with the American species of Drosera,t and, as 
I hear from Professor Caspary, with water-lilies. 

Dichogamy, which prevails so extensively throughout 
the vegetable kingdom, much increases the chance of 
distinct individuals intercrossing. With proterandrous 
species, which are far more common than pro- 
terogynous, the young flowers are exclusively male 
in function, and the older ones exclusively female; 
and as bees habitually alight low down on the spikes 
of flowers in order to crawl upwards, they get dusted 
with pollen from the upper flowers, which they carry 
to the stigmas of the lower and older flowers on 
the next spike which they visit. The degree to which 
distinct plants will thus be intercrossed depends on 
the number of spikes in full flower at the same time 
on the same plant. With proterogynous flowers and 
with depending racemes, the manner in which insects 
visit the flowers ought to be reversed in order that- 
distinct plants should be intercrossed. But this whole 
subject requires further investigation, as the great 
importance of crosses between distinct individuals, 
instead of merely between distinct flowers, has hitherto 
been hardly recognised. 

* ' Die Schutzmittel,' &c. p. 23. work, in ' American Journal of 

t ' Transact. New Zealand In- Science,' vol. xiii., Feb. 1877, p. 

ptitute,' vol. v. 1873, p. 356. 135. 
J Asa Gray, in a review of this 



CHAP. X. PREPOTENT POLLEN. 393 

In some few cases the special movements of certain 
organs almost ensure pollen being carried from plant 
to plant. Thus with many orchids, the pollen-masses 
after becoming attached to the head or proboscis of an 
insect do not move into the proper position for striking 
the stigma, until ample time has elapsed for the insect 
to fly to another plant. With Spiranthes autumnalis, 
the pollen-masses cannot be applied to the stigma until 
the labellum and rostellum have moved apart, and 
this movement is very slow.* With Posoqueria fra- 
grans (one of the Kubiaceae) the same end is gained by 
the movement of a specially constructed stamen, as 
described by Fritz Miiller. 

We now come to a far more general and therefore 
more important means by which the mutual fertilisation 
of distinct plants is effected, namely, the fertilising 
power of pollen from another variety or individual 
being greater than that of a plant's own pollen. The 
simplest and best known case of prepotent action 
in pollen, though it does not bear directly on our 
present subject, is that of a plant's own pollen over that 
from a distinct species. If pollen from a distinct species 
be placed on the stigma of a castrated flower, and then 
after the interval of several hours, pollen from the same 
species be placed on the stigma, the effects of the 
former are wholly obliterated, excepting in some rare 
cases. If two varieties are treated in the same manner, 
the result is analogous, though of a directly opposite 
nature ; for pollen from any other variety is often or 
generally prepotent over that from the same flower. I 
will give some instances : the pollen of Mimulus luteus 
regularly falls on the stigma of its own flower, for the 



'The Various Contrivances Orchids are fertilised,' 1st edit, 
which British and Foreign p. 128. Second edit. 1877, p. 110 



394 MEANS OF CROSS-FERTILISATION. CHAP. X. 

plant is highly fertile when insects are excluded. Now 
several flowers on a remarkably constant whitish variety 
were fertilised without being castrated with pollen from 
a yellowish variety ; and of the twenty-eight seedlings 
thus raised, every one bore yellowish flowers, so that 
the pollen of the yellow variety completely overwhelmed 
that of the mother-plant. Again, Iberis umbellata is 
spontaneously self-fertile, and I saw an abundance of 
pollen from their own flowers on the stigmas ; neverthe- 
less, of thirty seedlings raised from non-castrated flowers 
of a crimson variety crossed with pollen from a pink 
variety, twenty-four bore pink flowers, like those of the 
male or pollen-bearing parent. 

In these two cases flowers were fertilised with pollen 
from a distinct variety, and this was shown to be 
prepotent by the character of the offspring. Nearly 
similar results often follow when two or more self-fertile 
varieties are allowed to grow near one another and are 
visited by insects. The common cabbage produces a 
large number of flowers on the same stalk, and when 
insects are excluded these set many capsules, moderately 
rich in seeds. I planted a white Kohl-rabi, a purple 
Kohl-rabi, a Portsr.outh broccoli, a Brussels sprout, 
and a Sugar-loaf cabbage near together and left them 
uncovered. Seeds collected from each kind were sown 
in separate beds ; and the majority of the seedlings in 
all five beds were mongrelised in the most complicated 
manner, some taking more after one variety, and some 
after another. The effects of the Kohl-rabi were 
particularly plain in the enlarged stems of many of the 
seedlings. Altogether 233 plants were raised, of which 
155 were mongrelised in the plainest manner, and of 
the remaining 78 not half were absolutely pure. I 
repeated the experiment by planting near together 
two varieties of cabbage with purple-green and white- 



CHAP. X. PREPOTENT POLLEN. 395 

green laciniated leaves; and of the 325 seedlings 
raised from the purple-green variety, 165 had white- 
green and 160 purple-green leaves. Of the 466 seed- 
lings raised from the white-green variety, 220 had 
purple-green and 246 white-green leaves. These cases 
show how largely pollen from a neighbouring variety 
of the cabbage effaces the action of the plant's own 
pollen. We should bear in mind that pollen must be 
carried by the bees from flower to flower on the same 
large branching stem much more abundantly than 
from plant to plant; and in the case of plants the 
flowers of which are in some degree dichogamous, 
those on the same stem would be of different ages, and 
would thus be as ready for mutual fertilisation as the 
flowers on distinct plants, were it not for the prepotency 
of pollen from another variety.* 

Several varieties of the radish (Baphanus sativus), 
which is moderately self-fertile when insects are ex- 
cluded, were in flower at the same time in my garden. 
Seed was collected from one of them, and out of twenty- 
two seedlings thus raised only twelve were true to their 
kind.t 

The onion produces a large number of flowers, all 
crowded together into a large globular head, each 
flower having six stamens ; so that the stigmas receive 
plenty of pollen from their own and the adjoining 
anthers. Consequently the plant is fairly self-fertile 
when protected from insects. A blood-red, silver, 
globe and Spanish onion were planted near together ; 



* A writer in the ' Gardeners' ling was true to its kind, aud 

Chronicle' (1855, p. 730) says several closely resembled rape, 

that he planted a bed of turnips f Duhamel, as quoted by God- 

(Brassica rapa) and of rape (B. ron, De 1'Espeoe,' torn. i. p. 50, 

napiis) close together, and sowed makes an analogous statement 

the seeds of the former. Tho with respect to this plant. 
icsult was that scarcely one seed- 



396 MEANS OF CROSS-FERTILISATION. CHAP. X 

and seedlings were raised from each kind in four 
separate beds. In all the beds mongrels of various 
kinds were numerous, except amongst the ten seedlings 
from the blood-red onion, which included only two. 
Altogether forty-six seedlings were raised, of which 
thirty-one had been plainly crossed. 

A similar result is known to follow with the varieties 
of many other plants, if allowed to flower near together : 
I refer here only to species which are capable of 
fertilising themselves, for if this be not the case, they 
would of course be liable to be crossed by any other 
variety growing near. Horticulturists do not commonly 
distinguish between the effects of variability and inter- 
crossing ; but I have collected evidence on the natural 
crossing of varieties of the tulip, hyacinth, anemone, 
ranunculus, strawberry, Leptosiphon androsaceus, orange, 
rhododendron and rhubarb, all of which plants I believe 
to be self-fertile.* Much other indirect evidence could 
be given with respect to the extent to which varieties 
of the same species spontaneously intercross. 

Gardeners who raise seed for sale are compelled by 
dearly bought experience to take extraordinary pre- 
cautions against intercrossing. Thus Messrs. Sharp 



* With respect to tulips and rhinum, the varieties of which are 
some other flowers, see Godron, known to cross freely, because 
1 De 1'Espece,' torn. i. p. 252. For these plants are not always self- 
anemones, ' Gard. Chron.' 1859, fertile. I know nothing about 
p. 98. For strawberries, see Her- the self-fertility of Trollius (Le- 
bert in ' Transact, of Hort. Soc. coq, ' De la Fe'condation,' 1862, 
vol. iv. p. 17. The same observer p. 93), Mahonia, and Crinum, in 
elsewhere speaks of the sponta- which genera the species intercross 
neous crossing of rhododendrons. largely. "With respect to Mahonia, 
Gallesio makes the same state- it is now scarcely possible to pro- 
ment with respect to oranges. I cure in this country pure speci- 
have myself known extensive mens of M, aquifolium or repens; 
crossing to occur with the common and the various species of Crinum 
rhubarb. For Leptosiphon, Verlot sent by Herbert (' Amaryllidacse,' 
'DesVarie'tes,'1865,p.20. I have p. 32) to Calcutta, crossed there 
not included in my list the Car- so freely ttat pure seed could not 
nation, Nemophila, or Antir- be saved. 



CHAP.X. PREPOTENT POLLEN. 397 

" have land engaged in the growth of seed in no less 
than eight parishes." The mere fact of a vast number 
of plants belonging to the same variety growing 
together is a considerable protection, as the chances 
are strong in favour of plants of the same variety inter- 
crossing ; and it is in chief part owing to this circum- 
stance, that certain villages have become famous for 
pure seed of particular varieties.* Only two trials 
were made by me to ascertain after how long an interval 
of time, pollen from a distinct variety would obliterate 
more or less completely the action of a plant's own 
pollen. The stigmas in two lately expanded flowers on 
a variety of cabbage, called Eagged Jack, were well 
covered with pollen from the same plant. After an 
interval of twenty-three hours, pollen from the Early 
Barnes Cabbage growing at a distance was placed on 
both stigmas; and as the plant was left uncovered, 
pollen from other flowers on the Eagged Jack would 
certainly have been left by the bees during the next 
two or three days on the same two stigmas. Under 
these circumstances it seemed very unlikely that the 
pollen of the Barnes cabbage would produce any effect ; 
but three out of the fifteen plants raised from the two 
capsules thus produced were plainly mongrelised : and 
I have no doubt that the twelve other plants were 
affected, for they grew much more vigorously than the 
self-fertilised seedlings from the Eagged Jack planted 
at the same time and under the same conditions. 
Secondly, I placed on several stigmas of a long-styled 
cowslip (Primula veris) 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 



With respect to Messrs. Sharp, p. 823. Lindley's ' Theory of f lor* 
'Gardeners' Chronicle,' 1856, tjculture,' p. 319. 



398 MEANS OF CROSS-FERTILISATION. CHAP. X. 

the cowslip. From the flowers thus treated thirty 
seedlings were raised, and all these without exception 
bore reddish flowers ; so that the effect of the plant's 
own pollen, though placed on the stigmas twenty- 
four hours previously, was quite destroyed by that of 
the red variety. It should, however, be observed that 
these plants are heterostyled, and that the second union 
was a legitimate one, whilst the first was illegitimate ; 
but flowers illegitimately fertilised with their own pollen 
yield a moderately fair supply of seeds. 

We have hitherto considered only the prepotent 
fertilising power of pollen from a distinct variety over 
a plant's own pollen, both kinds of pollen being 
placed on the same stigma. It is a much more re- 
markable fact that pollen from another individual of 
the same variety is prepotent over a plant's own pollen, 
as shown by the superiority of the seedlings raiser! 
from a cross of this kind over seedlings from self- 
fertilised flowers. Thus in Tables A, B, and C, there 
are at least fifteen species which are self-fertile when 
insects are excluded ; and this implies that their stigmas 
must receive their own pollen ; nevertheless, most of 
the seedlings which were raised by fertilising the non- 
castrated flowers of these fifteen species with pollen 
from another plant were greatly superior, in height, 
weight, and fertility, to the self-fertilised offspring.* 
For instance, with Ipomcea purpurea every single inter- 
crossed plant exceeded in height its self-fertilised 
opponent until the sixth generation ; and so it was 
with Mimulus luieus until the fourth generation. Out 
of six pairs of crossed and self-fertilised cabbages, every 

* These fifteen species consist of Iponuea purpurea, Mimidus luteut, 

Bra&sica oleracea, Reseda odorala Calceolaria, Verbascum thapsus, 

and lutea, Limnanthes douglasi'', Vandellia nummularifolia, Lue- 

J'apaver vagum, Viscaria oculata, tuca sativa, and Zea mays. 
Beta vulgaris, Lupinus luteus, 



CHAP. X. PREPOTENT POLLEN. 399 

one of the former was much heavier than the latter. 
With Papaver vagurn, out of fifteen pairs, all but 
two of the crossed plants were taller than their self- 
fertilised opponents. Of eight pairs of Lupinus luteus, 
all but two of the crossed were taller ; of eight pairs 
of Beta vulgaris all but one ; and of fifteen pairs of Zea 
mays all but two were taller. Of fifteen pairs of Lim- 
nanthes douglasii, and of seven pairs of Lactuca sativa, 
every single crossed plant was taller than its self-fer- 
tilised opponent. It should also be observed that in 
these experiments no particular care was taken to cross- 
fertilise the flowers immediately after their expansion ; 
it is therefore almost certain that in many of these 
cases some pollen from the same flower will have 
already fallen on and acted on the stigma. 

There can hardly be a doubt that several other 
species of which the crossed seedlings are more 
vigorous than the self-fertilised, as shown in Tables A, 
B, and C, besides the above fifteen, must have received 
their own pollen and that from another plant at nearly 
the same time ; and if so, the same remarks as those 
just given are applicable to them. Scarcely any result 
from my experiments has surprised me so much as this 
of the prepotency of pollen from a distinct individual 
over each plant's own pollen, as proved by the greater 
constitutional vigour of the crossed seedlings. The 
evidence of prepotency is here deduced from the com- 
parative growth of the two lots of seedlings ; but we 
have similar evidence in many cases from the mucn 
greater fertility of the non-castrated flowers on the 
mother-plant, when these received at the same time their 
own pollen and that from a distinct plant, in comparison 
with the flowers which received only their own pollen. 

From the various facts now given on the spontaneous 
intercrossing of varieties growing near together, and on 



400 MEANS OF CROSS-FERTILISATION. CHAP. X. 

the effects of cross-fertilising flowers which are self- 
fertile and have not been castrated, we may conclude 
that pollen brought by insects or by the wind from 
a distinct plant will generally prevent the action of 
pollen from the same flower, even though it may have 
been applied some time before; and thus the inter- 
crossing of plants in a state of nature will be greatly 
favoured or ensured. 

The case of a great tree covered with innumerable 
hermaphrodite flowers seems at first sight strongly 
opposed to the belief in the frequency of intercrosses 
between distinct individuals. The flowers which grow 
on the opposite sides of such a tree will have been 
exposed to somewhat different conditions, and a cross 
between them may perhaps be in some degree beneficial; 
but it is not probable that it would be nearly so bene- 
ficial as a cross between flowers on distinct trees, as we 
may infer from the inefficiency of pollen taken from 
plants which have been propagated from the same 
stock, though growing on separate roots. The number 
of bees which frequent certain kinds of trees when in 
full flower is very great, and they may be seen flying 
from tree to tree more frequently than might have 
been expected. Nevertheless, if we consider how 
numerous are the flowers on a great tree, an incom- 
parably larger number must be fertilised by pollen 
brought from other flowers on the same tree, than from 
flowers on a distinct tree. But we should bear in mind 
that with many species only a few flowers on the same 
peduncle produce a seed ; and that these seeds are 
often the product of only one out of several ovules 
within the same ovarium. Now we know from the 
experiments of Herbert and others* that if one flowei 



* ' Variation under Domestication,' ch. xvii. 2nd edit. vol. ii. p. 120. 



C*AF. X. ANEMOPHILOU8 PLANTS. 401 

is fertilised with pollen which is more efficient than 
that applied to the other flowers on the same peduncle, 
the latter often drop off ; and it is probable that this 
would occur with many of the self-fertilised flowers 
on a large tree, if other and adjoining flowers were 
cross-fertilised. Of the flowers annually produced 
by a great tree, it is almost certain that a large 
number would be self-fertilised ; and if we assume 
that the tree produced only 500 flowers, and that this 
number of seeds were requisite to keep up the stock, 
so that at least one seedling should hereafter struggle 
to maturity, then a large proportion of the seedlings 
would necessarily be derived from self-fertilised seeds. 
But if the tree annually produced 50,000 flowers, of 
which the self-fertilised dropped off without yielding 
seeds, then the cross-fertilised flowers might yield 
seeds in sufficient number to keep up the stock, and 
most of the seedlings would be vigorous from being 
the product of a cross between distinct individuals. 
In this manner the production of a vast number of 
flowers, besides serving to entice numerous insects and 
to compensate for the accidental destruction of many 
flowers by spring-frosts or otherwise, would be a very 
great advantage to the species ; and when we behold 
our orchard-trees covered with a white sheet of bloom 
in the spring, we should not falsely accuse nature of 
wasteful expenditure, though comparatively little fruit 
is produced in the autumn. 

Anemophilous Plants. The nature and relations of 
plants which are fertilised by the wind have been 
admirably discussed by Delpino* and H. Miiller ; and 

* Delpino, 'Ult. Osservazioni naggio anemofilo,' &c. 1871. H. 
sulla Dicogamia,' part ii. fasc. i. Miiller, 'Die Befruchtung,' &c. 
1870; and 'Stodi sopra \in Lig- pp. 412, 442. Both these authors 

2 D 



402 ANEMOPHILOUS PLANTS. CHAP. X. 

I have already made some remarks on the structure of 
their flowers in contrast with those of entomophilous 
species. There is good reason to believe that the first 
plants which appeared on this earth were cryptogamic ; 
and judging from what now occurs, the male fertilising 
element must either have possessed the power of spon- 
taneous movement through the water or over damp 
surfaces, or have been carried by currents of water to 
the female organs. That some of the most ancient 
plants, such as ferns, possessed true sexual organs there 
can hardly be a doubt ; and this shows, as Hildebrand 
remarks,* at how early a period the sexes were separated. 
As soon as plants became phanerogamic and grew on 
the dry ground, if they were ever to intercross, it would 
be indispensable that the male fertilising element 
should be transported by some means through the 
air ; and the wind is the simplest means of transport. 
There must also have been a period when winged 
insects did not exist, and plants would not then have been 
rendered entomophilous. Even at a somewhat later 
period the more specialised orders of the Hymenoptera, 
Lepidoptera, and Diptera, which are now chiefly con- 
cerned with the transport of pollen, did not exist. 
Therefore the earliest terrestrial plants known to us, 
namely, the Coniferae and Cycadeae, no doubt were ane- 
mophilous, like the existing species of these same 
groups. A vestige of this early state of things is 
likewise shown by some other groups of plants which 
are anemophilous, as these on the whole stand lower 
in the scale than entomophilous species. 

remark that plants must have came nectariferous and gradually 

been anemophilous before they acquired their present structure 

were entomophilous. H. Miiller through successive beneficial 

further discusses in a very in- changes. 

teresting manner the steps by * ' Die Geschlechter-Vertheil- 

which entomophilous flowers be- ung,' 1867, pp. 84-90. 



CHAP. X. SECRETION OP NECTAR. 

There is no great difficulty in understanding how an 
anemophilous plant might have been rendered entoino- 
philous. Pollen is a nutritious substance, and would 
soon have been discovered and devoured by insects 
and if any adhered to their bodies it would have been 
carried from the anthers to the stigma of the same 
flower, or from one flower to another. One of the chief 
characteristics of the pollen of anemophilous plants 
is its incoherence ; but pollen in this state can adhere 
to the hairy bodies of insects, as we see with some 
Leguininosae, Ericaceae, and Melastomaceae. We have, 
however, better evidence of the possibility of a tran- 
sition of the above kind in certain plants being now 
fertilised partly by the wind and partly by insects. 
The common rhubarb (Rheum rhaponticum) is so far 
in an intermediate condition, that I have seen many 
Diptera sucking the flowers, with much pollen adhering 
to their bodies; and yet the pollen is so incoherent, 
that clouds of it are emitted if the plant be gently 
shaken on a sunny day, some of which could hardly 
fail to fall on the large stigmas of the neighbouring 
flowers. According to Delpino and H. Miiller,* some 
species of Plantago are in a similar intermediate 
condition. 

Although it is probable that pollen was aboriginally 
the sole attraction to insects, and although many 
plants now exist whose flowers are frequented exclu- 
sively by pollen-devouring insects, yet the great 
majority secrete nectar as the chief attraction. Many 
years ago I suggested that primarily the saccharine 
matter in nectar was excreted f as a waste product of 
chemical changes in the sap ; and that when the ex- 

* DieBefruchtuiig,' &c. p. 342. excretion, as stated by Martinet 
t Nectar was regarded by in Annal. des Sc. Nat.' 1872, torn, 
De Candolle and Dunal as an xiv. p. 211. 

2 D 2 



404 ANEMOPHILOTTS PLANTS. CHAP. X 

cretion happened to occur within the envelopes of a 
flower, it was utilised for the important object of 
cross-fertilisation, being subsequently much increased 
in quantity and stored in various ways. This view 
is rendered probable by the leaves of some trees ex- 
creting, under certain climatic conditions, without the 
aid of special glands, a saccharine fluid, often called 
honey-dew. This is the case with the leaves of the 
lime; for although some authors have disputed the 
fact, a most capable judge, Dr. Maxwell Masters, 
informs me that, after having heard the discussions on 
this subject before the Horticultural Society, he feels 
no doubt on this head. Prof. H. Hoffmann has lately 
(1876) described the case of the leaves of a young 
camellia secreting profusely, without the possibility of 
the intervention of aphides. The leaves, as well as 
the cut stems, of the manna ash (Fraxinus ornus) 
secrete in a like manner saccharine matter.* According 
to Treviranus, so do the upper surfaces of the leaves 
of Carduus arctioides during hot weather. Many ana- 
logous facts could be given.f There are, however, 
a considerable number of plants which bear small 
glands J on their leaves, petioles, phyllodia, stipules, 



* ' Gard. Chron.' 1876, p. 242. excretion by many epiphytal or- 
t Kurr, ' Untersuchungen iiber chids and passion-flowers. Mr. 
die Bedeutung der Nektarien,' Rodgers has seen much nectar 
1833, p. 115. secreted from the bases of the 
J A large number of cases are flower-peduncles of Vanilla. Link 
given by Delpino in the ' Bui- says that the only example of a 
letino Entomologico,' Anno vi. hypopetalous nectary known to 
1874. To these may be added him is externally at the base of 
those given in my text, as well the flowers of Chironia decussata : 
as the excretion of saccharine see ' Reports on Botany, Ray So- 
matter from the calyx of two ciety,' 1846, p. 355. An impor- 
species of Iris, and from the brae- tant memoir bearing on this sub- 
teas of certain Orchideae : see Kurr, ject has lately appeared by Reinke 
1 Bedeutung der Nektarien,' 1833, ('Gottingen Nachrichten,' 1873, 
pp. 25, 28. Belt also refers (' Ni- p. 825), who shows that in many 
earagua,' p. 224) to a similar plants the tips of the serrations 



CHAP. .. SECRETION OF NECTAR. 405 

bracteae, or flower peduncles, or on the outside of their 
calyx, and these glands secrete minute drops of a sweet 
fluid, which is eagerly sought by sugar-loving insects, 
such as ants, hive-bees, and wasps. In the case of 
the glands on the stipules of Vicia sativa, the excre- 
tion manifestly depends on changes in the sap, con- 
sequent on the sun shining brightly ; for I repeatedly 
observed that as soon as the sun was hidden behind 
clouds the secretion ceased, and the hive-bees left the 
field ; but as soon- as the sun broke out again, they 
returned to their feast.* I have observed an analogous 
fact with the secretion of true nectar in the flowers of 
Lobelia erinus. 

Delpino, however, maintains that the power of 
secreting a sweet fluid by any extra-floral organ has 
been in every case specially gained, for the sake of 
attracting ants and wasps as defenders of the plant 
against their enemies ; but I have never seen any 
reason to believe that this is so with the three species 
observed by me, namely, Prunus laurocerasus, Vicia 
sativa, and V. faba. No plant is so little attacked by 
enemies of any kind in this country as the common 
bracken-fern (Pteris aquilina) ; and yet, as my son 



on the leaves in the bud bear (harz). 

glands which secrete only at a * I published a brief notice of 

very early age, and which have this case in the ' Gard. Chronicle.' 

the same morphological structure 1855, July 21, p. 487, and after- 

as true nectar-secreting glands. wards made further observations. 

He further shows that the nectar- Besides the hive-bee, another 

secreting glands on the petioles species of bee, a moth, ants, and 

of Prunus avium are not deve- two kinds of flies sucked the 

loped at a very early age, yet drops of fluid on the stipules, 

wither away on the old leaves. The larger drops tasted sweet. 

They are homologous with those The hive-bees never even looked 

on the serrations of the blades of at the flowers which were open 

the same leaves, as shown by at the same time; whilst two 

their structure and by transition- species of humble-bees neglected 

forms ; for the lowest serrations the stipules and visited only the 

on the blades of most of the leaves flowers, 
secrete nectar instead of resin 



106 ANEMOPHILOUS PLANTS. CHAP. X 

Francis has discovered, the large glands at the bases 
of the fronds, but only whilst young, excrete much 
sweetish fluid, which is eagerly sought by innumerable 
ants, chiefly belonging to Myrmica; and these ants 
certainly do not here serve as a protection against any 
enemy. In S. Brazil, however, ants attracted by the 
secretion to this plant, defend it, according to Fritz 
Miiller,* against other leaf-devouring and highly de- 
structive ants; so that, if this fern originated in tropical 
S. America, the capacity of secretion may have been 
acquired for this special purpose. Delpino argues 
that sugar-secreting glands ought never to be con- 
sidered as merely excretory, because if they were so, 
they would be present in every species ; but I cannot 
see much force in this argument, as the leaves of some 
plants excrete sugar only during certain states of the 
weather. That in some cases the secretion serves to 
attract insects as defenders of the plant, and may have 
been developed to a high degree for this special 
purpose, I have not the least doubt, from the observa- 
tions of Delpino, and more especially from those of 
Mr. Belt on Acacia sphxrocephala, and on passion- 
flowers. This acacia likewise produces, as an additional 
attraction to ants, small bodies containing much oil 
and protoplasm, and analogous bodies are developed 
by a Cecropia for the same purpose, as described by 
Fritz Mfiller.t 

The excretion of a sweet fluid by glands seated 

* See a letter in ' Nature,' June Acacia. With respect to the Ce- 

1877, p. 100, by my son Francis, cropia, see 'Nature,' 1876, p. 304. 

with interesting extracts from a My son Francis has described the 

letter by Fritz Miiller. microscopical structure and deve- 

f Mr. Belt has given a most lopment of these wonderful food- , 

interesting account (' The Natu- bodies in a paper read before the 

ralist in Nicaragua,' 1874, p. 218) Linnean Society. Bot. vol. XT. 

of the paramount importance of p. 398. 
ants as defenders of the above 






CHAP. X. QUANTITY OF POLLEN. 407 

outside of a flower is rarely utilised as a means for 
cross-fertilisation by the aid of insects ; but this is the 
case with several species of Euphorbia and with the 
bractese of the Marcgraviaceae, as the late Dr. Criiger 
informed me from actual observation in the West 
Indies, and as Delpino inferred with much acuteness 
from the relative position of the several parts of their 
flowers.* Mr. Farrer has also shown f that the flowers 
of Coronilla are curiously modified, so that bees may 
fertilise them whilst sucking the fluid secreted from 
the outside of the calyx. With one of Malpighiacese, 
bees gnaw the glands on the calyx, and in doing so 
get their abdomens dusted with pollen, which they 
carry to other flowers.} It further appears probable 
from the observations of Kev. W. A. Leighton, that the 
fluid so abundantly secreted by glands on the phyllodia 
of the Australian Acacia magnified, which stand near 
the flowers, is connected with their fertilisation.! 

The amount of pollen produced by anemophilous 
plants, and the distance to which it is often trans- 
ported by the wind, are both surprisingly great. Mr. 
Hassall found, as before stated, that the weight of 
pollen produced by a single plant of the bulrush 



* 'Ult. Oeservaz. Dicogamia,' contained in the intercellular 

1868-69, p. 188. spaces. I further suggested, in 

f 'Nature,' 1874, p. 169. the case of some other orchids 

j As described by Fritz Muller which do not secrete nectar, that 

in 'Nature,' Nov. 1877, p. 28. insects gnawed the labellum ; and 

'Annals and Mag. of Nat. this suggestion has since been 

Hist.' vol. xvi. 1865, p. 14. In proved true. H. Muller and Del- 

my work on the ' Fertilisation of pino have now shown that some 

Orchids,' and in a paper subse- other plants have thickened pe- 

quently published in the ' Annals tals which are sucked or gnawed 

and Mag. of Nut. History,' it has by insects, their fertilisation being 

been shown that although certain thus aided. All the known facts 

kinds of orchids possess a nectary, on this head have been collected 

no nectar is actually secreted by by Delpino in his ' Ult. Osserv." 

it; but that insects penetrate the part ii. fasc. ii. 1875, pp. 59-63. 
inner walla and suck the fluid 



408 ANEMOPHILOUS PLANTS. CHAP. X. 

(Typha) was 144 grains. Bucketfuls of pollen, chiefly 
of Coniferae and Gramineae, have been swept off the 
decks of vessels near the North American shore ; 
and Mr. Eiley has seen the ground near St. Louis, 
in Missouri, covered with pollen, as if sprinkled with 
sulphur; and there was good reason to believe that 
this had been transported from the pine-forests at 
least 400 miles to the south. Kerner has seen the 
snow-fields on the higher Alps similarly dusted ; and 
Mr. Blackley found numerous pollen-grains, in one 
instance 1200, adhering to sticky slides, which were 
sent up to a height of from 500 to 1 000 feet by means 
of a kite, and then uncovered by a special mechanism. 
It is remarkable that in these experiments there 
were on an average nineteen times as many pollen- 
grains in the atmosphere at the higher than at the 
lower levels.* Considering these facts, it is not so 
surprising as it at first appears that all, or nearly all 
the stigmas of anemophilous plants should receive 
pollen brought to them by mere chance by the wind. 
During the early part of summer every object is thus 
dusted with pollen; for instance, I examined for 
another purpose the labella of a large number of 
flowers of the Fly Ophrys (which is rarely visited by 
insects), and found on all very many pollen-grains of 
other plants, which had been caught by their velvety 
surfaces. 
The extraordinary quantity and lightness of the 

* For Mr. HassaU's observa- Kerner, 'Die Schutzmittel des 

tions see ' Annals and Mag. of Pollens,' 1873, p. 6. This author 

Nat. Hist.' vol. viii. 1842, p. 108. has also seen a lake in the Tyrol 

In the ' North American Journal so covered with pollen, that the 

of Science,' Jan. 1842, there is an water no longer appeared blue, 

account of the pollen swept off Mr. Blackley, ' Experimental Re- 

the decks of a vessel. Riley, searches on Hay-fever,' 1873, 

' Fifth Report on the Noxious pp. 132, 141-152. 
Insects of Missouri,' 1873, p. 86. 



CHAP. X. SEXUAL RELATIONS OF PLANTS. 409 

pollen of anemophilous plants are no doubt both 
necessary, as their pollen has generally to be carried 
to the stigmas of other and often distant flowers ; for, 
as we shall soon see, most anemophilous plants have 
their sexes separated. The fertilisation of these plants 
is generally aided by the stigmas being of large 
size or plumose ; and in the case of the Coniferse, 
by the naked ovules secreting a drop of fluid, as 
shown by Delpino. Although the number of ane- 
mophilous species is small, as the author just quoted 
remarks, the number of individuals is large in com- 
parison with that of entomophilous species. This 
holds good especially in cold and temperate regions, 
where insects are not so numerous as under a warmer 
climate, and where consequently entomophilous plants 
are less favourably situated. We see this in our 
forests of Coniferse and other trees, such as oaks, 
beeches, birches, ashes, &c. ; and in the Gramineae, 
Cyperaceae, and Juncaceaa, which clothe our meadows 
and swamps ; all these trees and plants being fertilised 
by the wind. As a large quantity of pollen is wasted 
by anemophilous plants, it is surprising that so many 
vigorous species of this kind abounding with individuals 
should still exist in any part of the world ; for if they 
had been rendered entomophilous, their pollen would 
have been transported by the aid of the senses and 
appetites of insects with incomparably greater safety 
than by the wind. That such a conversion is possible 
can hardly be doubted, from the remarks lately made 
on the existence of intermediate forms; and apparently 
it has been effected in the group of willows, as we may 
infer from the nature of their nearest allies.* 

It seems at first sight a still more surprising fact 



* H. Muller, 'Die Befruchtung,' &c. p. 149. 



110 SEXUAL RELATIONS OF PLANTS. CHAP. X 

that plants, after having been once rendered entomo- 
philous, should ever again have become anemophilous ; 
but this has occasionally though rarely occurred, for 
instance, with the common Poterium sanguisorba, as may 
be inferred from its belonging to the Rosacese. Such 
cases are, however, intelligible, as almost all plants 
require to be occasionally intercrossed ; and if any 
entomophilous species ceased altogether to be visited 
by insects, it would probably perish unless it were 
rendered anemophilous, or acquired a full capacity for 
self-fertilisation ; but in this latter case we may 
suspect that it would be apt to suffer from the long- 
continued want of cross-fertilisation. A plant would 
be neglected by insects if nectar failed to be secreted, 
unless indeed a large supply of attractive pollen was pre- 
sent ; and from what we have seen of the excretion of 
saccharine fluid from leaves and glands being largely 
governed in several cases by climatic influences, and 
from some few flowers which do not now secrete nec- 
tar still retaining coloured guiding-marks, the failure 
of the secretion cannot be considered as a very im- 
probable event. The same result would follow to a 
certainty, if winged insects ceased to exist in any 
district, or became very rare. Now there is only 
a single plant in the great order of the Cruciferae, 
namely, Pringlea, which is anemophilous, and this 
plant is an inhabitant of Kerguelen Land,* where 
there are hardly any winged insects, owing probably, 
as was suggested by me in the case of Madeira, 
to the risk which they run of being blown out to sea 
?nd destroyed. 

A remarkable fact with respect to anemophilous 
plants is that they are often diclinous, that is, they are 



The Rev. A. E. Eaton in ' Proc. Royal Soc.' vol. xxiii. 1875, p. 351 



CHAP. X. SEXUAL RELATIONS OF PLANTS. 411 

either monoecious with their sexes separated on the 
same plant, or dioecious with their sexes on distinct 
plants. In the class Monoecia of Linnaeus, Delpino 
shows* that the species of twenty-eight genera are 
anemophilous, and of seventeen genera entomophilous. 
In the class Dioecia, the species of ten genera are 
anemophilous and of nineteen entomophilous. The 
larger proportion of entomophilous genera in this 
latter class is probably the indirect result of insects 
having the power of carrying pollen to another and 
sometimes distant plant much more securely than the 
wind. In the above two classes taken together there 
are thirty-eight anemophilous and thirty-six ento- 
mophilous genera ; whereas in the great mass of 
hermaphrodite plants the proportion of anemophilous 
to entomophilous genera is extremely small. The 
cause of this remarkable difference may be attributed 
to anemophilous plants having retained in a greater 
degree than the entomophilous a primordial condi- 
tion, in which the sexes were separated and their 
mutual fertilisation effected by means of the wind. 
That the earliest and lowest members of the vegetable 
kingdom had their sexes separated, as is still the case 
to a large extent, is the opinion of a high authority, 
Nageli.f It is indeed difficult to avoid this con- 
clusion, if we admit the view, which seems highly 
probable, that the conjugation of the Algae and of 
some of the simplest animals is the first step towards 
sexual reproduction ; and if we further bear in mind 
that a greater and greater degree of differentiation 
between the cells which conjugate can be traced, 
thus leading apparently to the development of the 



* Studi sopra un Lignaggio t ' Entetehung nnd Begriff del 
anemofilo delle Composite,' 1871. naturhist. Art,' 1865, p. 22. 



112 SEXUAL DELATIONS OF PLANTS. CHAP. X. 

two sexual forms.* We have also seen that as 
plants became affixed to the ground and were more 
highly developed so as to be rendered phanerogamic, 
they would be compelled to be anemophilous in 
order to intercross. Therefore all plants which have 
not since been greatly modified, would tend still to 
be both diclinous and anemophilous; and we can 
thus understand the connexion between these two 
states, although they appear at first sight quite dis- 
connected. If this view is correct, plants must have 
been rendered hermaphrodites at a later though still 
very early period, and entomophilous at a yet later 
period, namely, after the development of winged insects. 
So that the relationship between hermaphroditism and 
fertilisation by means of insects is likewise to a certain 
extent intelligible. 

Why the descendants of plants which were originally 
dioecious, and which therefore profited by always inter- 
crossing with another individual, should have been 
converted into hermaphrodites, may perhaps be ex- 
plained by the risk which they ran, especially as long as 
they were anemophilous, of not being always fertilised, 
and consequently of not leaving offspring. This latter 



* See the interesting discus- Infusoria, whether permanent or 
tion on this whole subject by 0. temporary (in this latter case 
Butschli in his ' Studien fiber die called by him copulation) does not 
erstenEntwickelungsvorgangeder lead to the development of true 
Eizelle,' &c. 1876, pp. 207-219. ova, b'jt to the reorganisation or 
Also, Dr. A. Dodel, " Die Kraus- rejuvenescence of the individual. 
haar-Alge," ' Pringsheims Jahrb. There seems to be a close analogy 
f. wiss. Bot.' B. x. Also, En- in such a result with that which 
gelmann, "Ueber Entwickelung follows from the union of the 
von Infusorien," ' Morphol. Jahr- male and female elements of dis- 
buch,' B. i. p. 573. An abstract tinct plants, for the seedlings thus 
of this important memoir has raised may be said to show re- 
appeared in ' Archives de Zoolog. generation or rejuvenescence in 
expe'riinentale,' Tom. v. 1876, p. their greatly increased oonstitu- 
xxxiii. Engelmann concludes tional vigour, 
that the conjugation of various 



L-HAP. X. SEXUAL RELATIONS OF PLANTS. 41J5 

evil, the greatest of all to any organism, would have 
been much lessened by their becoming hermaphrodites, 
though with the contingent disadvantage of frequent 
self-fertilisation. By what graduated steps an herma- 
phrodite condition was acquired we do not know. But 
we can see that if a lowly organised form, in which 
the two sexes were represented by somewhat different 
individuals, were to increase by budding either before 
or after conjugation, the two incipient sexes would 
be capable of appearing by buds on the same stock, 
as occasionally occurs with various characters at the 
present day. The organism would then be in a 
monoecious condition, and this is probably the first 
step towards hermaphroditism ; for if very simple 
male and female flowers on the same stock, each con- 
sisting of a single stamen or pistil, were brought close 
together and surrounded by a common envelope, in 
nearly the same manner as with the florets of the 
Composite, we should have an hermaphrodite flower.* 
There seems to be no limit to the changes which 
organisms undergo under changing conditions of life ; 
and some hermaphrodite plants, descended as I am led 
to believe from aboriginally diclinous plants, have had 
their sexes again separated. That this has occurred, 
we may infer from the presence of rudimentary stamens 
in the flowers of some individuals, and of rudimentary 
pistils in the flowers of other individuals, for example 
in Lychnis dioica. But a conversion of this kind will 

* Mr. W. Tln'selton Dyer, in a isms much lower in the scale thai: 

very able review of this work Ferns or Selaginella. Mr. Dyer 

('Nature,' Feb. 1877, p. 329), adds that my notion of very 

takes an exactly opposite view, simple male and female flower* 

and advances weighty arguments being brought together and sur- 

in favour of the belief that all rounded by a common envelope, 

plants were aboriginally her- offers very considerable morpho- 

maphrodites. I will only remark logical difficulties, 
that I had in my mind organ- 



414 SEXUAL RELATIONS OF PLANTS. CHAP. X. 

not have occurred unless cross-fertilisation was already 
assured, generally by the agency of insects ; but why 
the production of male and female flowers on distinct 
plants should have been advantageous to the species, 
cross-fertilisation having been previously assured, is 
far from obvious. A plant might indeed produce twice 
as many seeds as were necessary to keep up its numbers 
under new or changed conditions of life ; and if it did 
not vary by bearing fewer flowers, and did vary in the 
state of its reproductive organs (as often occurs under 
cultivation), a wasteful expenditure of seeds and pollen 
would be saved by the flowers becoming diclinous. 

A related point is worth notice. I remarked in my 
Origin of Species that in Britain a much larger pro- 
portion of trees and bushes than of herbaceous plants 
have their sexes separated ; and so it is, according to 
Asa Gray and Hooker, in North America and New 
Zealand.* It is, however, doubtful how far this rule 
holds good generally, and it certainly does not do so 
in Australia. But I have been assured that the flowers 
of the prevailing Australian trees, namely, the 
Myrtaceae, swarm with insects, and if they are dicho- 



* I find in the ' London Cata- ing to thirty-five families. Of 

logue of British Plants,' that there these 108 trees, fifty-two, or 

are thirtj-two indigenous trees very nearly half, have their sexes 

and bushes in Great Britain, more or less separated. Of bushes 

classed under nine families; but there are 149, of which sixty- 

to err on the safe side, I have one have their sexes in the same 

counted only six species of wil- state; whilst of the remaining 

lows. Of the thirty-two trees and 500 herbaceous plants only 121, 

bushes, nineteen, or more than or less than a fourth, have their 

half, have their sexes separated ; sexes separated. Lastly, Prof, 

and this is an enormous proper- Asa Gray informs me that in the 

tion compared with other British United States there are 132 native 

plants. New Zealand abounds trees (belonging to twenty-five 

with diclinous plants and trees ; families) of which ninety-five (be- 

and Dr. Hooker calculates that longing to seventeen families) 

out of about 756 phanerogamic "have their sexes more or less 

plants inhabiting the islands, no separated, for the greater part 

leas than 108 are trees, belong- decidedly teparated." 



CHAP. X. SEXUAL RELATIONS OF PLANTS. 415 

gamous they would be practically diclinous.* As far 
as anemophilous plants are concerned, we know that 
they are apt to have their sexes separated, and we can 
see that it would be an unfavourable circumstance for 
them to bear their flowers very close to the ground, as 
their pollen is liable to be blown high up in the air ; | 
but as the culms of grasses give sufficient elevation, 
we cannot thus account for so many trees and bushes 
being diclinous. We may infer from our previous 
discussion that a tree bearing numerous hermaphrodite 
flowers would rarely intercross with another tree, 
except by means of the pollen of a distinct individual 
being prepotent over the plant's own pollen. Now the 
separation of the sexes, whether the plant were anemo- 
philous or entomophilous, would most effectually bar 
self-fertilisation, and this may be the cause of so many 
trees and bushes being diclinous. Or to put the case 
in another way, a plant would be better fitted for 
development into a tree, if the sexes were separated, 
than if it were hermaphrodite ; for in the former case 
its numerous flowers would be less liable to continued 
self-fertilisation. But it should also be observed that 
the long life of a tree or bush permits of the separation 
of the sexes, with much less risk of evil from impreg- 
nation occasionally failing and seeds not being pro- 
duced, than in the case of short-lived plants. Hence 
it probably is, as Lecoq has remarked, that annual 
plants are rarely dio3cious. 



* With respect to the Proteacese is held by the eunuch (i.e., one 

of Australia, Mr. Bentham re- of the stamens which is barren) 

marks (' Journal Linn. Soc. Bot.' safe from all pollution from her 

vol. xiii. 1871, pp. 58, 64) on the brother anthers, and is preserved 

various contrivances by which the intact for any pollen that may be 

stigma in the several genera is inserted by insects and other 

screened from the action of the agencies." 

pollen from the same flower. For t Kerner, ' Schutzmittel dea 

instance, in Synaphea " the stigma Pollens,' 1873, p. 4. 



416 SEXUAL RELATIONS OF PLANTS. CHAP. X 

Finally, we have seeii reason to believe that the 
higher plants are descended from extremely low forms 
which conjugated, and that the conjugating indi- 
viduals differed somewhat from one another, the one 
representing the male and the other the female so 
that plants were aboriginally dioacious. At a very 
early period such lowly organised dioecious plants 
probably gave rise by budding to monoecious plants 
with the two sexes borne by the same individual ; and 
by a still closer union of the sexes to hermaphrodite 
plants, which are now much the commonest form. * 
As soon as plants became affixed to the ground, their 
pollen must have been carried by some means from 
flower to flower, at first almost certainly by the wind, 
then by pollen-devouring, and afterwards by nectar- 
seeking insects. During subsequent ages some few 
entomophilous plants have been again rendered anemo- 
philous, and some hermaphrodite plants have had their 
sexes again separated; and we can vaguely see the 
advantages of such recurrent changes under certain 
conditions. 

Dioecious plants, however fertilised, have a great 
advantage over other plants in their cross-fertilisation 
being assured. But this advantage is gained in the 
case of anemophilous species at the expense of the 
production of an enormous superfluity of pollen, with 
some risk to them and to entomophilous species of 
their fertilisation occasionally failing. Half the in- 
dividuals, moreover, namely, the males, produce no 

* There is a considerable duals, which represented the two 

amount of evidence that all the incipient sexes. On this view, the 

higher animals are the descend- higher animals may now owe 

ants of hermaphrodites ; and it is their bilateral structure, with all 

a curious problem -whether such their organs double at an early 

hermiphroditism may not have embryonic period, to the fusion 

been the result of the conjugation or conjugation of two primordial 

of two slightly different indivi- individuals. 






CHAP. X. SEXUAL RELATIONS OF PLANTS. 417 

seed, and this might possibly be a disadvantage. 
Delpino remarks that dioecious plants cannot spread so 
easily as monoecious and hermaphrodite species, for & 
single individual which happened to reach some new 
site could not propagate its kind; but it may be 
doubted whether this is a serious evil. Monoecious 
anemophilous plants can hardly fail to be to a large 
extent dioecious in function, owing to the lightness of 
their pollen and to the wind blowing laterally, with 
the great additional advantage of occasionally or often 
producing some self-fertilised seeds. When they are 
also dichogamous, they are necessarily dioecious in 
function. Lastly, hermaphrodite plants can generally 
produce at least some self-fertilised seeds, and they are 
at the same time capable, through the various means 
specified in this chapter, of cross-fertilisation. Wl^fin 
their structure absolutely prevents self-fertilisation, 
they are in the same relative position to one another 
as monoecious or dioecious plants, with what may be 
an advantage, namely, that every flower is capable 
of yielding seeds. 



2 E 



418 HABITS OF INSECTS CHAK XL 



CHAPTER XI. 

THE HABITS OF IXSECTS IN RELATION TO THE FERTILISATION OP 
FLOWERS. 

Insects visit the flowers of the same species as long as they can Cause 
of this habit Means by which bees recognise the flowers of the 
same species Sudden secretion of nectar Nectar of certain flowers 
unattractive to certain insects Industry of bees, and the number 
of flowers visited within a short time Perforation of the corolla 
by bees Skill shown in the operation Hive-bees profit by the 
holes made by humble-bees Effects of habit The motive for per- 
forating flowers to save time Flowers growing in crowded masses 
chiefly perforated. 

BEES and various other insects must be directed by 
instinct to search flowers for nectar and pollen, as 
they act in this manner without instruction as soon 
as they emerge from the pupa state. Their instincts, 
however, are not of a specialised nature, for they visit 
many exotic flowers as readily as the endemic kinds, 
and they often search for nectar in flowers which do 
not secrete any ; and they may be seen attempting to 
suck it out of nectaries of such length that it cannot 
be reached by them.* All kinds of bees and certain 
other insects usually visit the flowers of the same species 
as long as they can, before going to another species. 
This fact was observed by Aristotle with respect to the 

* See, on this subject, H. Miil- Hymenoptera have inherited from 

ler, ' Befruchtung,' &c. p. 427; some early nectar-sucking pro- 

and Sir J. Lubbock's 'British genitor greater skill in robbing 

Wild Flowers,' &c. p. 20. Muller flowers than that which is dis- 

dssigns ('Bienen Zeitung,' June played by insects belonging to 

1876, p. 119) good reasons for his the other Orders, 
belief that bees and many other 



CHAP. XI. IN BELATION TO CROSS-FERTILISATION. 419 

hive-bee more than 2000 years ago, and was noticed 
by Dobbs in a paper published in 1736 in the Philo- 
sophical Transactions. It may be observed by any 
one, both with hive and humble-bees, in every flower- 
garden; not that the habit is invariably followed. Air. 
Bennett watched for several hours* many plants of 
Lamium album, L. purpureum, and another Labiate 
plant, Nepeta glechoma, all growing mingled togethei 
on a bank near some hives ; and he found that each 
bee confined its visits to the same species. The pollen 
of these three plants differs in colour, so that he was 
able to test his observations by examining that which 
adhered to the bodies of the captured bees, and he 
found one kind on each bee. 

Humble and hive-bees are good botanists, for they 
know that varieties may differ widely in the colour of 
their flowers and yet belong to the same species. I 
have repeatedly seen humble-bees flying straight from 
a plant of the ordinary red Dictamnus fraxinella to a 
white variety ; from one to another very differently 
coloured variety of Delphinium consolida and of 
Primula veris ; from a dark purple to a bright yellow 
variety of Viola tricolor; and with two species of 
Papaver, from one variety to another which differed 
much in colour; but in this latter case some of the 
bees flew indifferently to either species, although pass- 
ing by other genera, and thus acted as if the two spe- 
cies were merely varieties. H. Miiller also has seen 
hive-bees flying from flower to flower of Ranunculus 
lullosus and arvensis, and of Trifolium fragiferum 
and repens ; and . even from blue hyacinths to blue 
violets.f 

Some species of Diptera or flies keep to the flowers 

*' Nature,' 1874, June 4th, t ' Bienen Zeitung,' July 1 876 
p. <J2. p. 183. 

2 E 2 



420 HABITS OF INSECTS CHAP. XL 

of the same species with almost as much regularity as 
do bees ; and when captured they are found covered 
with pollen. I have seen Wiingia rostrata acting in 
this manner with the flowers of Lychnis dioica, Ajuga 
reptans, and Vicia sepium. Vdlucella plumosa and Empis 
cheiroptera flew straight from flower to flower of Myosotis 
sylvatica. Dolichopus nigripennis behaved in the same 
manner with PotentiUa tormentilla ; and other Diptera 
with Stellaria holostea, Helianthemum vulgare, Bellis 
perennis, Veronica hederssfolia and cliamoedrys ; but some 
flies visited indifferently the flowers of these two latter 
species. I have seen more than once a minute Thrips, 
with pollen adhering to its body, fly from one flower to 
another of the same kind ; and one was observed by 
me crawling about within a convolvulus with four 
grains of pollen adhering to its head, which were 
deposited on the stigma. 

Fabricius and Sprengel state that when flies have 
once entered the flowers of Aristolochia they never 
escape, a statement which I could not believe, as in 
this case the insects would not aid in the cross-fertili- 
sation of the plant ; and this statement has now been 
shown by Hildebrand to be erroneous. As the spathes 
of Arum maculatum are furnished with filaments appa- 
rently adapted to prevent the exit of insects, they 
resemble in this respect the flowers of Aristolochia; and 
on examining several spathes, from thirty to sixty 
minute Diptera belonging to three species were found 
in some of them ; and many of these insects were lying 
dead at the bottom, as if they had been permanently 
entrapped. In order to discover whether the living 
ones could escape and carry pollen to another plant, I 
tied in the spring of 1842 a fine muslin bag tightly 
round a spathe; and on returning in an hour's time 
several little flies were crawling about on the inner 



CHAP. XI. IN RELATION TO CROSS-FERTILISATION. 421 

surface of the bag. I then gathered a spathe and 
breathed hard into it ; several flies soon crawled out, 
and all without exception were dusted with arum pollen. 
These flies quickly flew away, and I distinctly saw 
three of them fly to another plant about a yard off; 
they alighted on the inner or concave surface of the 
spathe, and suddenly flew down into the flower. I then 
opened this flower, and although not a single anther 
had burst, several grains of pollen were lying at the 
bottom, which must have been brought from another 
plant by one of these flies or by some other insect. In 
another flower little flies were crawling about, and I 
saw them leave pollen on the stigmas. 

I do not know whether Lepidoptera generally keep 
to the flowers of the same species ; but I once observed 
many minute moths (I believe Lampronia (Tinea) 
caWiella) apparently eating the pollen of Mereurialis 
annua, and they had the whole front of their bodies 
covered with pollen. I then went to a female plant 
some yards off, and saw in the course of fifteen minutes 
three of these moths alight on the stigmas. Lepidoptera 
are probably often induced to frequent the flowers of the 
same species, whenever these are provided with a long 
and narrow nectary, as in this case other insects cannot 
suck the nectar, which will thus be preserved for those 
having an elongated proboscis. No doubt the Yucca 
moth* visits only the flowers whence its name is de- 
rived, for a most wonderful instinct guides this moth 
to place pollen on the stigma, so that the ovules may be 
developed on which the larvae feed. With respect to 
Coleoptera, I have seen Meligethes covered with pollen 
flying from flower to flower of the same species ; and 



* Described by Mr. Biley in the 'American Naturalist,' vol. vii. 
Oct. 1873. 



422 HABITS OF INSECTS CHAP. XL 

this must often occur, as, according to M. Brisout, 
" many of the species affect only one kind of plant." * 

It must not be supposed from these several statements 
that insects strictly confine their visits to the same 
species. They often visit other species when only a 
few plants of the same kind grow near together. In a 
flower-garden containing some plants of (Enothera, the 
pollen of which can easily be recognised, I found not 
only single grains but masses of it within many flowers 
of Mimulus, Digitalis, Antirrhinum, and Linaria. 
Other kinds of pollen were likewise detected in these 
same flowers. A large number of the stigmas of a plant 
of Thyme, in which the anthers were completely aborted, 
were examined ; and these stigmas, though scarcely 
larger than a split needle, were covered not only with 
pollen of Thyme brought from other plants by the bees, 
but with several other kinds of pollen. 

That insects should visit the flowers of the same 
species as long as they can, is of great importance 
to the plant, as it favours the cross-fertilisation of 
distinct individuals of the same species ; but no one 
will suppose that insects act in this manner for the good 
of the plant. The cause probably lies in insects being 
thus enabled to work quicker ; they have just learnt 
how to stand in the best position on the flower, and how 
far and in what direction to insert their proboscides.f 
They act on the same principle as does an artificer 
who has to make half-a-dozen engines, and who saves 
time by making consecutively each wheel and part for 
all of them. Insects, or at least bees, seem much in- 
fluenced by habit in all their manifold operations ; and 



* As quoted in ' American Nat.' conclusion -with respect to the 

May 1873, p. 270. cause of insects frequenting as 

t Since these remarks were long as they can the flowers of the 

written, I find that H. Miiller has same species : ' Bieiien Zeitung,' 

come to almost exactly the same July 1876, p. 182. 



UHAP. XI. IN GELATION TO CROSS-FERTILISATION. 423 

we shall presently see that this holds good in their 
felonious practice of biting holes through the corolla. 

It is a curious question how bees recognise the flowers 
of the same species. That the coloured corolla is the 
chief guide cannot be doubted. On a fine day, when 
hive-bees were incessantly visiting the little blue flowers 
of Lobelia erinus, I cut off all the petals of some, and 
only the lower striped petals of others, and these flowers 
were not once again sucked by the bees, although some 
actually crawled over them. The removal of the two 
little upper petals alone made no difference in their 
visits. Mr. J. Anderson likewise states that when he re- 
moved the corollas of the Calceolaria, bees never visited 
the flowers.* On the other hand, in some large masses of 
Geranium pliseum which had escaped out of a garden, I 
observed the unusual fact of the flowers continuing to 
secrete an abundance of nectar after all the petals had 
fallen off ; and the flowers in this state were still visited 
by humble-bees. But the bees might have learnt that 
these flowers with all their petals lost were still worth 
visiting, by finding nectar in those with only one or 
two lost. The colour alone of the corolla serves as 
an approximate guide : thus I watched for some time 
humble-bees which were visiting exclusively plants of 



* ' Gardeners' Chronicle,' 1853, would naturally produce seeds 
p. 534. Kurr cut off the nectaries under these circumstances ; but I 
from a large number of flowers of am greatly surprised that Delphi- 
several species, and found that nium consulida, as well as an- 
the greater number yielded seeds ; other species of Delphinium, and 
but insects probably would not Viola tricolor, should have pro- 
perceive the loss of the nectary duced a fair supply of seeds when 
until they had inserted their pro- thus treated ; but it does not ap- 
boscides into the holes thus pear that he compared the number 
formed, and in doing so would of the seeds thus produced with 
fertilise the flowers. He also re- those yielded by unmutilated 
moved the whole corolla from a flowers left to the free access ot 
considerable number of flowers, insects: 'Beduutung der Ntk- 
and these likewise yielded seeds. tarien,' 1833, pp. 123-135. 
Flowers which are self -fertile 



424 HABITS OF INSECTS CHAP. XL 

the white-flowered Spiranthes autumnalis, growing on 
short turf at a considerable distance apart ; and these 
bees often flew within a few inches of several other 
plants with white flowers, and then without further ex- 
amination passed onwards in search of the Spiranthes. 
Again, many hive-bees which confined their visits to the 
common ling (CaUuna vulgaris}, repeatedly flew towards 
Erica tetralix, evidently attracted by the nearly similar 
tint of their flowers, and then instantly passed on in 
search of the Calluna. 

That the colour of the flower is not the sole guide, is 
clearly shown by the six cases above given of bees 
which repeatedly passed in a direct line from one 
variety to another of the same species, although they 
bore very differently coloured flowers. I observed also 
bees flying in a straight line from one clump of a yellow- 
flowered CEnothera to every other clump of the same 
plant in the garden, without turning an inch from 
their course to plants of Eschscholtzia and others with 
yellow flowers which lay only a foot or two on either 
side. In these cases the bees knew the position of each 
plant in the garden perfectly well, as we may infer by 
the directness of their flight ; so that they were guided 
by experience and memory. But how did they discover 
at first that the above varieties with differently coloured 
flowers belonged to the same species ? Improbable as 
it may appear, they seem, at least sometimes, to recog- 
nise plants even from a distance by their general 
aspect, in the same manner as we should do. On three 
occasions I observed humble-bees flying in a perfectly 
straight line from a tall larkspur (Delphinium) which 
was in full flowei to another plant of the same species 
dt the distance of fifteen yards which had not as yet a 
single flower open, and on which the buds showed only 
a faint tinge of blue. Here neither odour nor the 






CHAP. XI. IK RELATION TO CROSS-FERTILISATION. 425 

memory of former visits iould have come into play, 
and the tinge of blue was so faint that it could hardly 
have served as a guide.* 

The conspicuousness of the corolla does not suffice 
to induce repeated visits from insects, unless nectar is 
at the same time secreted, together perhaps with 
some odour emitted. I watched for a fortnight many 
times daily a wall covered with Linaria cymbalaria 
in full flower, and never saw a bee even looking at 
one. There was then a very hot day, and suddenly 
many bees were industriously at work on the flowers. 
It appears that a certain degree of heat is necessary for 
the secretion of nectar; for I observed with Lobelia 
erinus that if the sun ceased to shine for only half an 
hour, the visits of the bees slackened and soon ceased. 
An analogous fact with respect to the sweet excretion 
from the stipules of Vicia sativa has been already 
given. As in the case of the Linaria, so with Pedicu- 
laris sylvatiea, Polygala vulgaris, Viola tricolor, and some 
species of Trifolium, I have watched the flowers day 
after day without seeing a bee at work, and then sud- 
denly all the flowers were visited by many bees. Now 
how did so many bees discover at once that the flowers 
were secreting nectar ? I presume that it must have been 
by their odour ; and that as soon as a few bees began 
to suck the flowers, others of the same and of different 
kinds observed the fact and profited by it. We shall 
presently see, when we treat of the perforation of the 
corolla, that bees are fully capable of profiting by the 



* A fact mentioned by H. flowers of the long-styled form, in 

Miiller ( Die Befruchtung,' &c., which the anthers are seated low 

p. 347) shows that bees possess down in the tubular corolla. Yet 

acute powers of vision and dis- the difference in aspect between 

crimination ; for those engaged in the long-styled and short-styled 

collecting pollen from Primula forms is extremely slight. 
elatior icvarial'.y passed by the 



426 HABITS OF INSECTS CHAP. XL 

labour of other species. Memory also comes into play, 
for, as already remarked, bees know the position of 
each clump of flowers in a garden. I have repeatedly 
seen them passing round a corner, but otherwise in as 
straight a line as possible, from one plant of Fraxinella 
and of Linaria to another and distant one of the same 
species ; although, owing to the intervention of other 
plants, the two were not in sight of each other. 

It would appear that either the taste or the odour of 
the nectar of certain flowers is unattractive to hive or to 
humble-bees, or to both ; for there seems no other reason 
why certain open flowers which secrete nectar are not 
visited by them. The small quantity of nectar secreted 
by some of these flowers can hardly be the cause of 
their neglect, as hive-bees search eagerly for the minute 
drops on the glands on the leaves of the Prunus lauro- 
cerasus. Even the bees from different hives sometimes 
visit different kinds of flowers, as is said to be the case 
by Mr. Grant with respect to the Polyanthus and Viola, 
tricolor.* I have known humble-bees to visit the flowers 
of Lobelia fulgens in one garden and not in another at 
the distance of only a few miles. The cupful of nectar 
in the labellum of Epipactis latifolia is never touched 
by hive- or humJble-bees, although I have seen them 
flying close by ; and yet the nectar has a pleasant 
taste to us, and is habitually consumed by the common 
wasp. As far as I have seen, wasps seek for nectar in 
this country only from the flowers of this Epipactis, 
Scropliularia aquatica, Heclera helix, Symphoricarpus 
racemosaj and Tritoma ; the three former plants being 
endemic, and the two latter exotic. As wasps are so 



* ' Gard. Chron.' 1844, p. 374. three plants are alone visited by 

t The same fact apparently wasps : ' Nettarit Eatrauuziali, 

holds good in Italy, for Delpino Bullettino Entomologico,' anno vi 

says that the flowers of these 






CHAP. XL IN RELATION TO CROSS-FERTILISATION. 427 

fond of sugar and of any sweet fluid, and as they do 
not disdain the minute drops on the glands of Prunus 
lauroeerasus, it is a strange fact that they do not suck 
the nectar of many open flowers, which they could do 
without the aid of a proboscis. Hive-bees visit the 
flowers of the Symphoricarpus and Tritoma, and this 
makes it all the stranger that they do not visit the 
flowers of the Epipactis, or, as far as I have seen, those 
of the Scroplwdaria aquatica; although they do visit 
the flowers of Scrophularia nodosa, at least in North 
America.* 

The extraordinary industry of bees and the number 
of flowers which they visit within a short time, so that 
each flower is visited repeatedly, must greatly increase 
the chance of each receiving pollen from a distinct 
plant. When the nectar is in any way hidden, bees 
cannot tell without inserting their proboscides whether 
it has lately been exhausted by other bees, and 
this, as remarked in a former chapter, forces them to 
visit many more flowers than they otherwise would. 
But they endeavour to lose as little time as they can; 
thus in flowers having several nectaries, if they find 
one dry they do not try the others, but as I have often 
observed, pass on to another flower. They work so in- 
dustriously and effectually, that even in the case of 
social plants, of which hundreds of thousands grow 
together, as with the several kinds of heath, every 
single flower is visited, of which evidence will presently 
be given. They lose no time and fly very quickly 
from plant to plant, but I do not know the rate at 
which hive-bees fly. Humble-bees fly at the rate of 
ten miles an hour, as I was able to ascertain in the case 
of the males from their curious habit of calling at 



' Silliinan's American Journal of Science,' Aug. 1871. 



42S HABITS OF INSECTS. CHAP. XI. 

certain fixed points, which made it easy to measure the 
time taken in passing from one place to another. 

Witn respect to the number of flowers which bees 
visit in a given time, I observed that in exactly one 
minute a humble-bee visited twenty-four of the closed 
flowers of the Linaria cymbalaria ; another bee visited 
in the same time twenty-two flowers of the Symphori- 
earpus racemosa ; and another seventeen flowers on two 
plants of a Delphinium. In the course of fifteen 
minutes a single flower on the summit of a plant of 
(Enothera was visited eight times by several humble- 
bees, and I followed the last of these bees, whilst 
it visited in the course of a few additional minutes 
every plant of the same species in a large flower- 
garden. In nineteen minutes every flower on a small 
plant of Nemophila insignis was visited twice. In one 
minute six flowers of a Campanula were entered by 
a pollen-collecting hive-bee ; and bees when thus 
employed work slower than when sucking nectar. 
Lastly, seven flower-stalks on a plant of Dictamnus 
fraxinella were observed on the 15th of June 1841 during 
ten minutes ; they were visited by thirteen humble-bees, 
each of which entered many flowers. On the 22nd the 
same flower-stalks were visited within the same time by 
eleven humble-bees. This plant bore altogether 280 
flowers, and from the above data, taking into con- 
sideration how late in the evening humble-bees work, 
each flower must have been visited at least thirty times 
daily, and the same flower keeps open during several 
days. The frequency of the visits of bees is also some- 
times shown by the manner in which the petals are 
scratched by their hooked tarsi ; I have seen large beds 
of Mimulus, Stachys, and Lathyrus with the beauty 
of their flowers thus sadly defaced. 

Perforation of the Corolla ly Bees. I have already 



CHAP. XI. PERFORATION OF THE COROLLA. 429 

alluded to bees biting holes in flowers for the sake of 
obtaining the nectar. They often act in this manner, 
both with endemic and exotic species, in many parts of 
Europe, in the United States, and in the Himalaya ; 
and therefore probably in all parts of the world. The 
plants, the fertilisation of which actually depends on 
insects entering the flowers, will fail to produce seed 
when their nectar is thus stolen from the outside ; and 
oven with those species which are capable of fertilising 
themselves without any aid, there can be no cross- 
fertilisation, and this, as we know, is a serious evil 
in most cases. The extent to which humble-bees 
carry on the practice of biting holes is surprising : a 
remarkable case was observed by me near Bourne- 
mouth, where there were formerly extensive heaths. 
I took a long walk, and every now and then gathered 
a twig of Erica tetraliae, and when I had got a hand- 
ful examined all the flowers through a lens. This 
process was repeated many times ; but though many 
hundreds were examined, I did not succeed in finding 
a single flower which had not been perforated. 
Humble-bees were at the time sucking the flowers 
through these perforations. On the following day a 
large number of flowers were examined on another 
heath with the same result, but here hive-bees were 
sucking through the holes. This case is all the 
more remarkable, as the innumerable holes had been 
made within a fortnight, for before that time I saw the 
bees everywhere sucking in the proper manner at the 
mouths of the corolla. In an extensive flower-garden 
some large beds of Salvia grahami, Stachys coccinea, 
and Pentstemon argutus (?) had every flower per- 
forated, and many scores were examined. I have seen 
whole fields of red clover (Trifolium pratense) in the 
same state. Dr. Ogle found that 90 per cent, of the 



430 HABITS OF INSECTS. CHAP. XI. 

flowers of Salvia glutinosa had been bitten. In the 
United States Mr. Bailey says it is difficult to find a 
blossom of the native Gerardia pedicularia without a 
hole in it ; and Mr. Gentry, in speaking of the intro- 
duced Wistaria sinensis, says " that nearly every flower 
had been perforated." * 

As far as I have seen, it is always humble-bees which 
first bite the holes, and they are well fitted for the work 
by possessing powerful mandibles ; but hive-bees after- 
wards profit by the holes thus made. Dr. H. Miiller, 
however, writes to me that hive-bees sometimes bite 
holes through the flowers of Erica tetralix. No insects 
except bees, with the single exception of wasps in the 
case of Tritoma, have sense enough, as far as I have 
observed, to profit by the holes already made. Even 
humble-bees do not always discover that it would be 
advantageous to them to perforate certain flowers. 
There is an abundant supply of nectar in the nectary 
of Tropseolum tricolor, yet I have found this plant 
untouched in more than one garden, while the flowers 
of other plants had been extensively perforated ; but 
a few years ago Sir J. Lubbock's gardener assured 
me- that he had seen humble-bees boring through 
the nectary of this Tropseolum. In the United States 
the common garden Tropseolum, as I hear from Mr. 
Bailey, is often pierced. Miiller has observed humble- 
bees trying to suck at the mouths of the flowers 
of Primula elatior and of an Aquilegia, and, failing 
in their attempts, they made holes through the 
corolla ; but they often bite holes, although they could 
with very little more trouble obtain the nectar in a 
legitimate manner by the mouth of the corolla. 

Dr. W. Ogle has communicated to me a curious case. 



* Dr. Ogle, 'Pop. Science Re- ' American Nat., ' Nov 1873. p. 690. 
view,' July 1869, p. 267. Bailey, Gentry, ibid. May 1875, p. 264. 



CHAP. XI. PERFORATION OF THE COROLLA. 431 

He gathered in Switzerland 100 flower-stems of the 
common blue variety of the monkshood (Aconitum 
napellus), and not a single flower was perforated ; he 
then gathered 100 stems of a white variety growing 
close by, and every one of the open flowers had been 
perforated. This surprising difference in the state of 
the flowers may be attributed with much probability 
to the blue variety being distasteful to bees, from the 
presence of the acrid matter which is so general in the 
Kanunculacese, and to its absence in the white variety 
in correlation with the loss of the blue tint. Accord- 
ing to Sprengel,* this plant is strongly proterandrous ; 
it would therefore be more or less sterile unless bees 
carried pollen from the younger to the older flowers. 
Consequently the white variety, the flowers of which 
were always bitten instead of being properly entered 
by the bees, would fail to yield the full number 
of seeds and would be a comparatively rare plant, 
as Dr. Ogle informs me was the case. 

Bees show much skill in their manner of working, 
for they always make their holes from the outside 
close to the spot where the nectar lies hidden within 
the corolla. All the flowers in a large bed of Stachys 
coccinea had either one or two slits made on the upper 
side of the corolla near the base. The flowers of a 
Mirabilis and of Salvia coceinea were perforated in the 
same manner ; whilst those of Salvia grahami, in which 
the calyx is much elongated, had both the calyx and the 
corolla invariably perforated. The flowers of Pentstemon 
argutm are broader than those of the plants just named, 
and two holes alongside each other had here always 
been made just above the calyx. In these several cases 
the perforations were on the upper side, but in Antir- 



* Dae Entdecke,' &c. p. 278. 



432 HABITS OF INSECTS. CHAP. XL 

rhinum majus one or two holes had been made on the 
lower side, close to the little protuberance which re- 
presents the nectary, and therefore directly in front of 
and close to the spot where the nectar is secreted. 

But the most remarkable case of skill and judgment 
known to me, is that of the perforation of the flowers of 
Lathyrus sylvestris, as described by my son Francis.* 
The nectar in this plant is enclosed within a tube, 
formed by the united stamens, which surround the 
pistil so closely that a bee is forced to insert its 
proboscis outside the tube ; but two natural rounded 
passages or orifices are left in the tube near the base, 
in order that the nectar may be reached by the bees. 
Now my son found in sixteen out of twenty-four flowers 
on this plant, and in eleven out of sixteen of those on 
the cultivated everlasting pea, which is either a variety 
of the same species or a closely allied one, that the 
left passage was larger than the right one. And here 
comes the remarkable point, the humble-bees bite holes 
through the standard-petal, and they always operated 
on the left side over the passage, which is generally 
the larger of the two. My son remarks : " It is difficult 
to say how the bees could have acquired this habit. 
Whether they discovered the inequality in the size of 
the nectar-holes in sucking the flowers in the proper 
way, and then utilised this knowledge in determining 
where to gnaw the hole ; or whether they found out 
the best situation by biting through the standard at 
various points, and afterwards remembered its situation 
in visiting other flowers. But in either case they show a 
remarkable power of making use of what they have 
learnt by experience." It seems probable that bees 
owe their skill in biting holes through flowers of all 



* Nature,' Jan. 8, 1874, p. J80. 



CHAP. XI. PERFORATION OF THE COROLLA. 433 

kinds to their having long practised the instinct of 
moulding cells and pots of wax, or of enlarging their 
old cocoons with tubes of wax; for they are thus 
compelled to work on the inside and outside of the 
same object. 

In the early part of the summer of 1857 I was 
led to observe during some weeks several rows of the 
scarlet kidney-bean (Phaseolus multiflorus), whilst 
attending to the fertilisation of this plant, and daily 
saw humble- and hive-bees sucking at the mouths 
of the flowers. But one day I found several humble- 
bees employed in cutting holes in flower after flower ; 
and on the next day every single hive-bee, without 
exception, instead of alighting on the left wing-petal 
and sucking the flower in the proper manner, flew 
straight without the least hesitation to the calyx, and 
sucked through the holes which had been made only 
the day before by the humble-bees; and they con- 
tinued this habit for many following days.* Mr. Belt 
has communicated to me (July 28th, 1874) a similar 
case, with the sole difference that less than half of the 
flowers had been perforated by the humble-bees; 
nevertheless, all the hive-bees gave up sucking at the 
mouths of the flowers and visited exclusively the bitten 
ones. Now how did the hive-bees find out so quickly 
that holes had been made ? Instinct seems to be out 
of the question, as the plant is an exotic. The holes 
cannot be seen by bees whilst standing on the wing- 
petals, where they had always previously alighted. 
From the ease with which bees were deceived when the 
petals of Lobelia erinus were cut off, it was clear that 
in this case they were not guided to the nectar by its 
iinell; and it may be doubted whether they were 



1 Gard. Chron.' 1857, p. 725. 

2 F 



434: HABITS OF INSECTS. CIIAF. XI. 

attracted to the holes in the flowers of the Phaseolus 
by the odour emitted from them. Did they perceive 
the holes by the sense of touch in their proboscides, 
whilst sucking the flowers in the proper manner, and 
then reason that it would save them time to alight on 
the outside of the flowers and use the holes? This 
seems almost too abstruse an act of reason for bees ; 
and it is more probable that they saw the humble-bees 
at work, and understanding what they were about, 
imitated them and took advantage of the shorter path 
to the nectar. Even with animals high in the scale, 
such as monkeys, we should be surprised at hearing 
that all the individuals of one species within the 
space of twenty-four hours understood an act per- 
formed by a distinct species, and profited by it. 

I have repeatedly observed with various kinds 
of flowers that all the hive and humble-bees which 
were sucking through the perforations, flew to them, 
whether on the upper or under side of the corolla, 
without the least hesitation ; and this shows how 
quickly all the individuals within the district had 
acquired the same knowledge. Yet habit comes into 
play to a certain extent, as in so many of the other 
operations of bees. Dr. Ogle, Messrs. Farrer and 
Belt have observed in the case of Phaseolus multiforus* 
that certain individuals went exclusively to the per- 
forations, while others of the same species visited 
only the mouths of the flowers. I noticed in 1861 
exactly the same fact with Trifolium pratense. So per- 
sistent is the force of habit, that when a bee which is 
visiting perforated flowers comes to one which has not 
been bitten, it does not go to the mouth, but instantly 

* Dr. Ogle, ' Pop. Science Ee- Hist.' 4th series, vol. ii. 1868, p. 
view,' April 1870, p. 167. Mr. 258. Mr. Belt in a letter to me. 
Farrer, ' Annals and Mag. of Nat. 



CHAP. XL PERFORATION OF THE COROLLA. 435 

Hies away in search of another bitten flower. Never- 
theless, I once saw a humble-bee visiting the hybrid 
Rhododendron azaloides, and it entered the mouths 
of some flowers and cut holes into the others. Dr. 
H. Miiller informs me that in the same district he has 
seen some individuals of Bombus mastrucatus boring 
through the calyx and corolla of Rhinanthus alectero- 
lophus, and others through the corolla alone. Different 
species of bees may, however, sometimes be observed 
acting differently at the same time on the same plant. 
I have seen hive-bees sucking at the mouths of the 
flowers of the common bean ; humble-bees of one kind 
sucking through holes bitten in the calyx, and humble- 
bees of another kind sucking the little drops of fluid 
excreted by the stipules. Mr. Beal of Michigan 
informs me that the flowers of the Missouri currant 
(Ribes aureum) abound with nectar, so that children 
often suck them; and he saw hive-bees sucking 
through holes made by a bird, the oriole, and at the 
same time humble-bees sucking in the proper manner 
at the mouths of the flowers.* This statement about 
the oriole calls to mind what I have before said of 
certain species of humming-birds boring holes through 
the flowers of the Brugrnansia, whilst other species 
entered by the mouth. 

The motive which impels bees to gnaw holes through 
the corolla seems to be the saving of time, for they 
lose much time in climbing into and out of large 
flowers, and in forcing their heads into closed ones. 
They were able to visit nearly twice as many flowers, 
as far as I could judge, of a Stachys and Pentstemon 



* The flowers of the Ribes are through and rob seven flowers 

however sometimes perforated by of their honey iu a minute : 

humble-bees, and Mr. Bundy says ' American Naturalist,' 1876, p. 

that they were able to bite 238. 

2 F 2 



436 HABITS OF INSECTS. CHAP. XI. 

by alighting on the upper surface of the corolla 
and sucking through the cut holes, as by entering 
in the proper way. Nevertheless each bee before 
it has had much practice, must lose some time in 
making each new perforation, especially when the per- 
foration has to be made through both calyx and 
corolla. This action therefore implies foresight, of 
which faculty we have abundant evidence in their 
building operations ; and may we not further believe 
that some trace of their social instinct, that is, of 
working for the good of other members of the com- 
munity, may here likewise play a part ? 

Many years ago I was struck with the fact that 
humble-bees as a general rule perforate flowers only 
when these grow in large numbers near together. In 
a garden where there were some very large beds of 
Stachys coccinea and of Pentstemon argutus, every single 
flower was perforated, but I found two plants of the 
former species growing quite separate with their petals 
much scratched, showing that they had been frequently 
visited by bees, and yet not a single flower was 
perforated. I found also a separate plant of the 
Pentstemon, and saw bees entering the mouth of the 
corolla, and not a single flower had been perforated. In 
the following year (1842) I visited the same garden 
several times : on the 19th of July humble-bees were 
sucking the flowers of Stachys coccinea and Salvia 
grdhami in the proper manner, and none of the corollas 
were perforated. On the 7th of August all the flowers 
were perforated, even those on some few plants of the 
Salvia which grew at a little distance from the great 
bed. On the 21st of August only a few flowers on the 
summits of the spikes of both species remained fresh, 
and not one of these was now bored. Again, in my own 
garden every plant in several rows of the common bean 



CHAP. XL PERFORATION OF THE COROLLA. 437 

had many flowers perforated ; but I found three plants 
in separate parts of the garden which had sprung up 
accidentally, and these had not a single flower per- 
forated. General Strachey formerly saw many per- 
forated flowers in a garden in the Himalaya, and he 
wrote to the owner to inquire whether this relation 
between the plants growing crowded and their per- 
foration by the bees there held good, and was answered 
in the affirmative. Mr. Bailey informs me that the 
Gerardia pedicularia which is so largely perforated, 
and Impatiens fulva, are both profuse flowerers. Hence 
it follows that the red clover (Trifolium pratense) and 
the common bean when cultivated in great masses in 
fields, that Erica tetrcdix growing in large numbers 
on heaths, rows of the scarlet kidney-bean in the 
kitchen-garden, and masses of any species in the 
flower-garden, are all eminently liable to be per- 
forated. 

The explanation of this fact is not difficult. Flowers 
growing in large numbers afford a rich booty to the 
bees, and are conspicuous from a distance. They are 
consequently visited by crowds of these insects, and I 
once counted between twenty and thirty bees flying 
about a bed of Pentstemon. They are thus stimulated 
to work quickly by rivalry, and, what is much more 
important, they find a large proportion of the flowers, 
as suggested by my son,* with their nectaries sucked 
dry. They thus waste much time in searching many 
empty flowers, and are led to bite the holes, so as 
to find out as quickly as possible whether there is any 
nectar present, and if so, to obtain it. 

Flowers which are partially or wholly sterile unless 
visited by insects in the proper manner, sucb as 



* ' Nature,' Jan. 8, 1874, p. 189. 



438 HABITS OF INSECTS. CHAP. XI 

those of most species of Salvia, of Trifolium pratense, 
Phaseolus multijiorus, &c., will more or less completely 
fail to produce seeds if the bees confine their visits 
to the perforations. The perforated flowers of those 
species, which are capable of fertilising themselves, 
will yield only self-fertilised seeds, and the seedlings 
will in consequence be less vigorous. Therefore all 
plants must suffer in some degree when bees obtain 
their nectar in a felonious manner by biting holes 
through the corolla ; and many species, it might be 
thought, would be thus exterminated. But here, as 
is so general throughout nature, there is a tendency 
towards a restored equilibrium. If a plant suffers 
from being perforated, fewer individuals will be 
reared, and if its nectar is highly important to the 
bees, these in their turn will suffer and decrease in 
number ; but, what is much more effective, as soon as 
the plant becomes somewhat rare so as not to grow 
in crowded masses, the bees will no longer _be stimu- 
lated to gnaw holes in the flowers, but will enter 
them in a legitimate manner. More seed will then be 
produced, and the seedlings being the product of 
cross-fertilisation will be vigorous, so that the species 
will tend to increase in number, to be again checked, 
as soon as the plant again grows in crowded masses. 



CHAP. XII. GENERAL RESULTS. 439 



CHAPTEK XII. 

GENERAL RESULTS. 

Cross-fertilisation proved to be beneficial, and self-fertilisation in- 
jurious Allied species differ greatly in the means by which cross- 
fertilisation is favoured and self-fertilisation avoided The benefits 
and evils of the two processes depend on the degree of differentiation 
in the sexual elements The evil effects not due to the combination of 
morbid tendencies in the parents Nature of the conditions to which 
plants are subjected when growing near together in a state of nature 
or under culture, and the effects of such conditions Theoretical 
considerations with respect to the interaction of differentiated sexual 
elements Practical lessons Genesis of the two sexes Close corre- 
spondence between the effects of cross-fertilisation and self-fertilisa- 
tion, and of the legitimate and illegitimate unions of heterostyled 
plants, in comparison with hybrid unions. 

THE first and most important of the conclusions which 
may be drawn from the observations given in this 
volume, is that generally cross-fertilisation is beneficial, 
and self-fertilisation often injurious, at least with the 
plants on which I experimented. Whether long- 
continued self -fertilisation is injurious to all plants 
is another and difficult question. The truth of these 
conclusions is shown by the difference in height, 
weight, constitutional vigour, and fertility of the 
offspring from crossed and self-fertilised flowers, and 
in the number of seeds produced by the parent-plants. 
With respect to the second of the two propositions, 
namely, that self-fertilisation is often injurious, we have 
abundant evidence. The structure of the flowers in 
such plants as Lobelia ramosa, Digitalis purpurea, &c., 
renders the aid of insects almost indispensable for 



440 GENERAL RESULTS. CHAP. XII 

their fertilisation; and bearing in mind the prepo- 
tency of pollen from a distinct individual over that 
from the same individual, such plants will almost cer- 
tainly have been crossed during many or all previous 
generations. So it must be, owing merely to the 
prepotency of foreign pollen, with cabbages and various 
other plants, the varieties of which almost invariably 
intercross when grown together. The same inference 
may be drawn still more surely with respect to those 
plants, such as of Keseda and Eschscholtzia, which 
are sterile with their own pollen, but fertile with 
that from any other individual. These several plants 
must therefore have been crossed during a long series 
of previous generations, and the artificial crosses in my 
experiments cannot have increased the vigour of the 
offspring beyond that of their progenitors. Therefore 
the difference between the self-fertilised and crossed 
plants raised by me cannot be attributed to the supe- 
riority of the crossed, but to the inferiority of the 
self-fertilised seedlings, due to the injurious effects of 
self-fertilisation. 

Notwithstanding the evil which many plants suffer 
from self-fertilisation, they can be thus propagated 
under favourable conditions for many generations, as 
shown by some of my experiments, and more especially 
by the survival during at least half a century of the 
same varieties of the common pea and sweet-pea. The 
same conclusion probably holds good with several other 
exotic plants, which are never or most rarely cross- 
fertilised in this country. But all these plants, as far 
as they have been tried, profit greatly by a cross with 
a fresh stock. Many species which bear small and 
inconspicuous flowers are never, or most rarely, visited 
by insects during the day; and Hermann Miiller 
infers that they must be always, or almost always, 



CHAP. XIL GENERAL RESULTS. 44l 

self-fertilised. But the evidence appears to me in- 
sufficient, until it can be shown that such flowers are 
not visited during the night by any of the innumerable 
kinds of small moths. From the simple fact of these 
small flowers expanding, and from some of them 
secreting nectar, it seems probable that they are at 
least occasionally visited and intercrossed by nocturnal 
insects. It is much to be desired that some one should 
cross and self-fertilise such plants and compare the 
growth, weight, and fertility of the offspring. The 
Rev. G. Henslow* remarks that the plants which have 
spread the most widely through the agency of man into 
new countries, and have there grown most vigorously, 
commonly bear small and inconspicuous flowers; and, 
as he assumes that these are always self-fertilised, 
he infers that this process cannot be at all injurious 
to plants. He believes that " as long as a plant is 
" self-fertilising, it remains in the same condition, and 
" retains its average standard, but does not degenerate 
"in any way. It cannot be benefited, as it cannot 
" introduce anything new into its system, so long as it 
" lives in the same place ; hence its results are negative. 
"If, however, self-fertilising plants can migrate, and 
"so obtain new peculiarities from fresh surrounding 
" media, then they may acquire astonishing vigour, 
" and even oust the native vegetation of the country 
"they have invaded." According to this view the 
male and female sexual elements must become in such 
cases differentiated through the action of the new 

* Mr. Henslow has published passages in this book, and en- 

an elaborate review of the present deavoured to make others clearer, 

work in the ' Gardeners' Chroni- owing to Mr. Henslow's criticisms, 

cle ' from Jan. 13th to May 5th, but I can by no means agree with 

1877, also in ' Science and Art,' many of his inferences. I have 

Muy 1st, 1877, p. 77 ; from which also profited by an able review by 

latter jourial the quotation is Hermann Mtiller in 'Kosmoe,' 

taken. I have modified some April 1877, p. 57. 



442 GENERAL EESULTS. CHAP. XII. 

conditions; and this seems not improbable, judging 
from the remarkable effects of changed conditions on 
the reproductive system of Abutilon and Eschscholtzia. 

Some few plants, owing to their structure, for in- 
stance, Ophrys apif&ra, have almost certainly been 
propagated in a state of nature for thousands of 
generations without having been once intercrossed ; 
and whether they would profit by a cross with a fresh 
stock is not known. But such cases ought not to make 
us doubt that as a general rule crossing is beneficial 
and self-fertilisation injurious, any more than the 
existence of plants which, in a state of nature are 
propagated asexually, that is, exclusively by rhizomes, 
stolons, &c.* (their flowers never producing seeds), 
should make us doubt that seminal generation must 
have some great advantage, as it is the common plan 
followed by nature. Whether any species has been 
reproduced asexually from a very remote period cannot, 
of course, be ascertained. Our sole means for forming 
any judgment on this head is the duration of the 
varieties of our fruit trees which have been long pro- 
pagated by grafts or buds. Andrew Knight formerly 
maintained that under these circumstances they always 
become weakly, but this conclusion has been warmly 
disputed by others. A recent and competent judge, 
Prof. Asa Gray,f leans to the side of Andrew Knight, 
which seems to me, from such evidence as I have 
been able to collect, the more probable view, notwith- 
standing many opposed facts. 

With respect to the first of the two propositions 
at the head of this chapter, namely, that cross-fertilisa- 
tion is generally beneficial, we have excellent evidence. 

* I have given several cases in f ' Darwiniana : Essays and 

my 'Variation under Domestica- Reviews pertaining to Darwinism,' 

tion,' ch. xviii. 2nd edit. vol. ii. 1876, p. 338 
p. 152. 



CHAP. XII. GENERAL RESULTS. 443 

Plants of Ipomoea were intercrossed for nine successive 
generations; they were then again intercrossed, and 
at the same time crossed with a plant of a fresh stock, 
that is, one brought from another garden ; and the 
offspring of this latter cross were to the intercrossed 
plants of the tenth generation in height as 100 to 78, 
and in fertility as 100 to 51. An analogous experi- 
ment with Eschscholtzia gave a similar result, as far 
as fertility was concerned. In neither of these cases 
were any of the plants the product of self-fertilisation. 
Plants of Dianthus were self- fertilised for three genera- 
tions, and this no doubt was injurious ; but when 
these plants were fertilised by a fresh stock and by 
intercrossed plants of the same stock, there was a great 
difference in fertility between the two sets of seedlings 
and some difference in their height. Petunia offers 
a nearly parallel case. With various other plants, the 
wonderful effects of a cross with a fresh stock may 
be seen in Table C. Several accounts have also been 
published* of the extraordinary growth of seedlings 
from a cross between two varieties of the same species, 
some of which are known never to fertilise themselves ; 
so that here neither self -fertilisation nor relationship 
even in a remote degree can have come into play. We 
may therefore conclude that the above two propositions 
are true, that cross-fertilisation is generally beneficial 
and self-fertilisation often injurious to the offspring. 

That certain plants, for instance, Viola tricolor, 
Digitalis purpurea, Sarothamnus scoparius, Cyclamen 
persicum, &c., which have been naturally cross-fertilised 
for many or all previous generations, should suffer to 
an extreme degree from a single act of self-fertilisation 
is an astonishing fact. The evil does not depend in 

* See 'Variation under Domestication,' ch. xix. 2nd edit. vol. ii. ix 
159. 



444 GENERAL RESULTS. CHAP. XII. 

any corresponding degree on the pollen of the self- 
fertilised parents acting inefficiently on the stigmas of 
the same flowers; for in the case of the Ipomosa, 
Mimulus, Digitalis, Brassica, &c., the self-fertilised 
parents yielded an abundant supply of seeds ; never- 
theless the plants raised from these seeds were 
markedly inferior in many ways to their cross-ferti- 
lised brethren. Again with Eeseda and Eschscholtzia 
the more self-sterile individuals profited in a less 
degree by cross-fertilisation than did the more self- 
fertile individuals. With animals no manifest evil 
has been observed to follow in the first few generations 
from close interbreeding ; but then we must remember 
that the closest possible interbreeding with animals, 
that is, between brothers and sisters, cannot be con- 
sidered as nearly so close a union as that between the 
pollen and ovules of the same flower. Whether with 
plants the evil from self-fertilisation goes on increas- 
ing during successive generations is not as yet known ; 
but we may infer from my experiments that the increase, 
if any, is far from rapid. After plants have been pro- 
pagated by self-fertilisation for several generations, a 
single cross with a fresh stock restores their pristine 
vigour ; and we have a strictly analogous result with 
our domestic animals.* The good effects of cross-fer- 
tilisation are transmitted by plants to the next gene- 
ration ; and judging from the varieties of the comma : 
pea, to many succeeding generations. But this may 
merely be that crossed plants of the first generation 
are extremely vigorous, and transmit their vigour, like 
any other character, to their successors. 

The means for favouring cross-fertilisation and pre- 
venting self-fertilisation, or conversely for favouring 



* * Variation under Domestication,' ch. xix. 2nd edit. vol. ii. p. 159. 



CHAP. XII. GENERAL RESULTS. 445 

self-fertilisation and preventing to a certain extent 
cross-fertilisation, are wonderfully diversified; and it 
is remarkable that these differ widely in closely allied 
plants,* in the species of the same genus, and some- 
times in the individuals of the same species. It is 
not rare to find hermaphrodite plants and others 
with separated sexes within the same genus ; and it is 
common to find some of the species dichogamous and 
others maturing their sexual elements simultaneously. 
The dichogamous genus Saxifraga contains proter- 
androus and proterogynous species, t Several genera 
include both heterostyled (dimorphic or trimorphic 
forms) and homostyled species. Ophrys offers a 
remarkable instance of one species having its structure 
manifestly adapted for self-fertilisation, and other 
species as manifestly adapted for cross-fertilisation. 
Some con-generic species are quite sterile and others 
quite fertile with their own pollen. From these several 
causes we often find within the same genus species 
which do not produce seeds, while others produce an 
abundance, when insects are excluded. Some species 
bear cleistogamic flowers which cannot be crossed, as 
well as perfect flowers, whilst others in the same genus 
never produce cleistogamic flowers. Some species exist 
under two forms, the one bearing conspicuous flowers 
adapted for cross-fertilisation, the other bearing in- 
conspicuous flowers adapted for self-fertilisation, whilst 
other species in the same genus present only a single 
form. Even with the individuals of the same species, 
the degree of self-sterility varies greatly, as in Keseda. 
With polygamous plants, the distribution of the sexes 

* Hildebrand has insisted natsbcricht K. Akad. Berlin,' Oct 

strongly to this effect in his 1872, p. 763. 

valuable observations on the fer- t Dr. Engler, < Bot. Zeitung, 

tilisatioc of the Graminese : ' Mo- 1868, p. 833. 



146 GENEEAL RESULTS. CHAP. XII. 

differs in the individuals of the same species. The rela- 
tive period at which the sexual elements in the same 
flower are mature, differs in the varieties of Pelar- 
gonium ; and Carriere gives several cases,* showing 
that the period varies according to the temperature to 
which the plants are exposed. 

This extraordinary diversity in the means for 
favouring or preventing cross- and self-fertilisation in 
closely allied forms, probably depends on the results 
of both processes being highly beneficial to the species, 
but in a directly opposed manner and dependent on 
variable conditions. Self-fertilisation assures the pro- 
duction of a large supply of seeds ; and the necessity 
or advantage of this will be determined by the average 
length of life of the plant, which largely depends on 
the amount of destruction suffered by the seeds and 
seedlings. This destruction follows from the most 
various and variable causes, such as the presence of 
animals of several kinds, and the growth of surround- 
ing plants. The possibility of cross-fertilisation de- 
pends mainly on the presence and number of certain 
insects, often of insects belonging to special groups, 
and on the degree to which they are attracted to the 
flowers of any particular species in preference to 
other flowers, all circumstances likely to change. 
Moreover, the advantages which follow from cross- 
fertilisation differ much in different plants, so that it 
is probable that allied plants would often profit in 
different degrees by cross-fertilisation. Under these 
extremely complex and fluctuating conditions, with 
two somewhat opposed ends to be gained, namely, the 
safe propagation of the species and the production of 
cross-fertilised, vigorous offspring, it is not surprising 



Des Yarietes,' 1865, p. 30. 



CHAP. XII. GENERAL RESULTS. 447 

that allied forms should exhibit an extreme diversity 
in the means which favour either end. If, as there is 
reason at least to suspect, self-fertilisation is in some 
respects beneficial, although more than counterbalanced 
by the advantages derived from a cross with a fresh 
stock, the problem becomes still more complicated. 

As I only twice experimented on more than a single 
species in a genus, I cannot say whether the crossed 
offspring of the several species within the same genus 
differ in their degree of superiority over their self- 
fertilised brethren ; but I should expect that this 
would often prove to be the case from what was 
observed with the two species of Lobelia and with the 
individuals of the same species of Nicotiana. The 
species belonging to distinct genera in the same family 
certainly differ in this respect. The effects of cross- 
and self-fertilisation may be confined either to the 
growth or to the fertility of the offspring, but generally 
extends to both qualities. There does not seem to 
exist any close correspondence between the degree to 
which the flowers of species are adapted for cross- 
fertilisation, and the degree to which their offspring 
profit by this process ; but we may -easily err on this 
head, as there are two means for favouring cross-ferti- 
lisation which are not externally perceptible, namely, , 
self-sterility and the prepotent fertilising influence of 
pollen from another individual. Lastly, it has been 
shown in a former chapter that the effect produced by 
cross and self-fertilisation on the fertility of the parent- 
plants does not always correspond with that produced 
on the height, vigour, and fertility of their offspring. 
The same remark applies to crossed and self-fertilised 
seedlings when these are used as the parent-plants. This 
want of correspondence probably depends, at least in 
part, on the number of seeds produced being chiefly 



448 GENERAL RESULTS. CHAP. XII 

determined by the number of the pollen-tubes which 
reach the ovules, and this will be governed by the re- 
action between the pollen and the stigmatic secretion 
or tissues; whereas the growth and constitutional vigour 
of the offspring will be chiefly determined, not only by 
the number of pollen-tubes reaching the ovules, but by 
the nature of the reaction between the contents of the 
pollen-grains and ovules. 

There are two other important conclusions which 
may be deduced from my observations : firstly, that the 
advantages of cross-fertilisation do not follow from 
some mysterious virtue in the mere union of two 
distinct individuals, but from such individuals having 
been subjected during previous generations to dif- 
ferent conditions, or to their having varied in a manner 
commonly called spontaneous, so that in either case 
their sexual elements have been in some degree differ- 
entiated. And secondly, that the injury from self- 
fertilisation follows from the want of such differentia- 
tion in the sexual elements. These two propositions 
are fully established by my experiments. Thus, when 
plants of the Ipomcea and of the Mimulus, which had 
been self-fertilised for the seven previous generations 
and had been kept all the time under the same condi- 
tions, were intercrossed one with another, the offspring 
did not profit in the least by the cross. Mimulus 
offers another instructive case, showing that the 
benefit of a cross depends on the previous treatment 
of the progenitors : plants which had been self-fer- 
tilised for the eight previous generations were crossed 
with plants which had been intercrossed for the same 
number of generations, all having been kept under 
the same conditions as far as possible ; seedlings from 
this cross were grown in competition with others 



CHAP. XII. GENERAL RESULTS. 449 

derived from the same self-fertilised mother-plant 
crossed by a fresh stock ; and the latter seedlings were 
to the former in height as 100 to 52, and in fertility 
as 100 to 4. An exactly parallel experiment was 
tried on Dianthus, with this difference, that the plants 
had been self-fertilised only for the three previous gene- 
rations, and the result was similar though not so strongly 
marked. The foregoing two cases of the offspring of 
Ipomoea and Eschscholtzia, derived from a cross with a 
fresh stock, being as much superior to the intercrossed 
plants of the old stock, as these latter were to the self- 
fertilised offspring, strongly support the same conclu- 
sion. A cross with a fresh stock or with another variety 
seems to be always highly beneficial, whether or 
not the mother-plants have been intercrossed or self- 
fertilised for several previous generations. The fact 
that a cross between two flowers on the same plant 
does no good or very little good, is likewise a strong 
corroboration of our conclusion ; for the sexual 
elements in the flowers on the same plant can rarely 
have been differentiated, though this is possible, as 
flower-buds are in one sense distinct individuals, 
sometimes varying and differing from one another in 
structure or constitution. Thus the proposition that 
the benefit from cross-fertilisation depends on the 
plants which are crossed having been subjected during 
previous generations to somewhat different conditions, 
or to their having varied from some unknown cause as 
if they had been thus subjected, is securely fortified on 
all sides. 

Before proceeding any further, the view which has 
been maintained by several physiologists must be 
noticed, namely, that all the evils from breeding 
animals too closely, and no doubt, as they would say, 

2 a 



450 GENERAL RESULTS. CHAP. XII. 

from the self- fertilisation of plants, is the result of the 
increase of some morbid tendency or weakness of consti- 
tution common to the closely related parents, or to 
the two sexes of hermaphrodite plants. Undoubtedly 
injury has often thus resulted ; but it is a vain 
attempt to extend this view to the numerous cases 
given in my Tables. It should be remembered that the 
same mother-plant was both self-fertilised and crossed, 
so that if she had been unhealthy she would have 
transmitted half her morbid tendencies to her crossed 
offspring. But plants appearing perfectly healthy, 
some of them growing wild, or the immediate offspring 
of wild plants, or vigorous common garden-plants, were 
selected for experiment. Considering the number of 
species which were tried, it is nothing less than absurd 
to suppose that in all these cases the mother-plants, 
though not appearing in any way diseased, were weak 
or unhealthy in so peculiar a manner that their self- 
fertilised seedlings, many hundreds in number, were 
rendered inferior in height, weight, constitutional 
vigour, and fertility to their crossed offspring. More- 
over, this belief cannot be extended to the strongly 
narked advantages which invariably follow, as far as 
my experience serves, from intercrossing the indivi- 
duals of the same variety or of distinct varieties, if 
these have been subjected during some generations to 
different conditions. 

It is obvious that the exposure of two sets of plants 
during several generations to different conditions can 
lead to no beneficial results, as far as crossing is con- 
cerned, unless their sexual elements are thus affected. 
That every organism is acted on to a certain extent by 
a change in its environment, will not, I presume, be 
disputed. It is hardly necessary to advance evidence 
OD this head ; we can perceive the difference between 



CHAP. XII. GENEBAI RESULTS. 451 

individual plants of the same species which have 
grown in somewhat more shady or sunny, dry or damp 
places. Plants which have been propagated for some 
generations under different climates or at different 
seasons of the year transmit different constitutions to 
their seedlings. Under such circumstances, the che- 
mical constitution of their fluids and the nature of 
their tissues are often modified.* Many other such 
facts could be adduced. In short, every alteration in 
the function of a part is probably connected with some 
corresponding, though often quite imperceptible change 
in structure or composition. 

Whatever affects an organism in any way, likewise 
tends to act on its sexual elements. We see this in the 
inheritance of newly acquired modifications, such as 
those from the increased use or disuse of a part, and 
even from mutilations if followed by disease.f We 
have abundant evidence how susceptible the repro- 
ductive system is to changed conditions, in the many 
instances of animals rendered sterile by confinement ; 
so that they will not unite, or if they unite do not 
produce offspring, though the confinement may be far 
from close ; and of plants rendered sterile by culti- 
vation. But hardly any cases afford more striking 
evidence how powerfully a change in the conditions of 
life acts on the sexual elements, than those already 
given, of plants which are completely self-sterile in 
one country, and when brought to another, yield, even 



* Numerous cases together with the different organs of animals 

references are given in my ' Vari- are excited into different degrees 

ation under Domestication,' ch. of activity by differences of tempi- 

xxiii. 2nd edit. voL ii. p. 264. lature and food, and become to a 

With respect to animals, Mr. certain extent adapted to them. 

Biackenridge has well shown f 'Variation under Domestica- 

(' A Contribution to the Theory of tion,' ch. xii. 2nd edit. vol. i. 

Diathesis,' Edinburgh, 1869) that p. 466. 

2 o 2 



452 GENERAL RESULTS. CHAP. XII. 

in the first generation, a fair supply of self-fertilised 
seeds. 

But it may be said, granting that changed conditions 
act on. the sexual elements, how can two or more 
plants growing close together, either in their native 
country or in a garden, be differently acted on, inasmuch 
as they appear to be exposed to exactly the same 
conditions ? Although this question has been already 
considered, it deserves further consideration from 
several points of view. In my experiments with 
Digitalis purpurea, some flowers on a wild plant were 
self-fertilised, and others were crossed with pollen 
from another plant growing within two or three feet's 
distance. The crossed and self-fertilised plants raised 
from the seeds thus obtained, produced flower-stems 
in number as 100 to 47, and in average height as 100 
to 70. Therefore the cross between these two plants 
was highly beneficial ; but how could their sexual 
elements have been differentiated by exposure to 
different conditions ? If the progenitors of the two 
plants had lived on the same spot during the last 
score of generations, and had never been crossed with 
any plant beyond the distance of a few feet, in all 
probability their offspring would have been reduced to 
the same state as some of the plants in my experiments, 
such as the intercrossed plants of the ninth genera- 
tion of Ipomoea, or the self-fertilised plants of the 
eighth generation of Mimulus, or the offspring from 
flowers on the same plant, and in this case a cross 
between the two plants of Digitalis would have done 
no good. But seeds are often widely dispersed by 
natural means, and one of the above two plants or 
one of their ancestors may have come from a distance, 
from a more shady or sunny, dry or moist place, or from 
a different kind of soil containing other organic or 



CHAP. Xn. GENERAL RESULTS. 453 

inorganic matter. We know from the admirable 
researches of Messrs. Lawes and Gilbert* that different 
plants require and consume very different amounts of 
inorganic matter. But the amount in the soil would 
probably not make so great a difference to the several 
individuals of any particular species as might at first 
be expected ; for the surrounding species with 
different requirements would tend, from existing in 
greater or lesser numbers, to keep each species in a 
sort of equilibrium, with respect to what it could obtain 
from the soil. So it would be even with respect to 
moisture during dry seasons ; and how powerful is the 
influence of a little more or less moisture in the soil 
on the presence and distribution of plants, is often 
well shown in old pasture fields which still retain 
traces of former ridges and furrows. Nevertheless, as 
the proportional numbers of the surrounding plants in 
two neighbouring places is rarely exactly the same, the 
individuals of the same species will be subjected to 
somewhat different conditions with respect to what they 
can absorb from the soil. It is surprising how the free 
growth of one set of plants affects others growing 
mingled with them ; I allowed the plants on rather 
more than a square yard of turf which had been closely 
mown for several years, to grow up ; and nine species 
out of twenty were thus exterminated; but whether 
this was altogether due to the kinds which grew up 
robbing the others of nutriment, I do not know. 

Seeds often lie dormant for several years in the 
ground, and germinate when brought near the surface 
by any means, as by burrowing animals. They would 
probably be affected by the mere circumstance of having 



* ' Journal of the Royal Agricultural Soc. of England,' voL xxir, 
part i. 



454 GENERAL RESULTS. CHAP. XII 

long lain dormant; for gardeners believe that the 
production of double flowers and of fruit is thus in- 
fluenced. Seeds, moreover, which were matured during 
different seasons, will have been subjected during the 
whole course of their development to different degrees 
of heat and moisture. 

It was shown in the last chapter that pollen is often 
carried by insects to a considerable distance from 
plant to plant. Therefore one of the parents or 
ancestors of our two plants of Digitalis may have been 
crossed by a distant plant growing under somewhat 
different conditions. Plants thus crossed often pro- 
duce an unusually large number of seeds ; a striking 
instance of this fact is afforded by the Bignonia, pre- 
viously mentioned, which was fertilised by Fritz Miiller 
with pollen from some adjoining plants and set hardly 
any seed, but when fertilised with pollen from a dis- 
tant plant, was highly fertile. Seedlings from a cross 
of this kind grow with great vigour, and transmit their 
vigour to their descendants. These, therefore, in the 
struggle for life, will generally beat and exterminate 
the seedlings from plants which have long grown near 
together under the same conditions, and will thus tend 
to spread. 

When two varieties which present well-marked 
differences are crossed, their descendants in the later 
generations differ greatly from one another in ex- 
ternal characters ; and this is due to the augmentation 
or obliteration of some of these characters, and to 
the reappearance of former ones through reversion; 
and so it will be, as we may feel almost sure, with any 
slight differences in the constitution of their sexual 
elements. Anyhow, my experiments indicate that 
crossing plants which have been long subjected to 
almost though not quite the same conditions, is the 



CHAP. XH. GENERAL RESULTS. 455 

most powerful of all the means for retaining some 
degree of differentiation in the sexual elements, as 
shown by the superiority in the later generations of the 
intercrossed over the self-fertilised seedlings. Never- 
theless, the continued intercrossing of plants thus 
treated does tend to obliterate such differentiation, as 
may be inferred from the lessened benefit derived from 
intercrossing such plants, in comparison with that from 
a cross with a fresh stock. It seems probable, as I may 
add, that seeds have acquired their endless curious 
adaptations for wide dissemination,* not only that the 
seedlings should thus be enabled to find new and fitting 
homes, but that the individuals which have been long 
subjected to the same conditions should occasionally 
intercross with a fresh stock. 

From the foregoing several considerations we may, 
I think, conclude that in the above case of the Digitalis, 
and even in that of plants which have grown for 
thousands of generations in the same district, as must 
often have occurred with species having a much 
restricted range, we are apt to over-estimate the 
degree to which the individuals have been subjected 
to absolutely the same conditions. There is at least 
no difficulty in believing that such plants have been 
subjected to sufficiently distinct conditions to differ- 
entiate their sexual elements ; for we know that a plant 
propagated for some generations in another garden in 
the same district serves as a fresh stock and has high 
fertilising powers. The curious cases of plants which 
can fertilise and be fertilised by any other individual 
of the same species, but are altogether sterile with their 
own pollen, become intelligible, if the view here pro- 
pounded is correct, namely, that the individuals of the 

* See Prof Hildebrand's excellent treatise, 'Verb eitungsmittel der 
Pflauzen,' 1873. 



456 GENERAL RESULTS. CHAP. XII. 

same species growing in a state of nature near together; 
have not really been subjected during several previous 
generations to quite the same conditions. 

Some naturalists assume that there is an innate 
tendency in all beings to vary and to advance in 
organisation, independently of external agencies ; and 
they would, I presume, thus explain the slight 
differences which distinguish all the individuals of the 
same species both in external characters and in con- 
stitution, as well as the greater differences in both 
respects between nearly allied varieties. No two 
individuals can be found quite alike ; thus if we sow a 
number of seeds from the same capsule under as nearly 
as possible the same conditions, they germinate at 
different rates and grow more or less vigorously. They 
resist cold and other unfavourable conditions differently. 
They would in all probability, as we know to be the 
case with animals of the same species, be somewhat 
differently acted on by the same poison, or by the same 
disease. They have different powers* of transmitting 
their characters to their offspring ; and many analogous 
facts could be given. Now, if it were true that 
plants growing near together in a state of nature had 
been subjected during many previous generations to 
absolutely the same conditions, such differences as those 
just specified would be quite inexplicable ; but they 
are to a certain extent intelligible in accordance with 
the views just advanced. 

As most of the plants on which I experimented 
were grown in my garden or in pots under glass, a few 
words must be added on the conditions to which they 
were exposed, as well as on the effects of cultivation. 
When a species is first brought under culture, it may 



Vilmorin, as juoted by Verlot, <Des VarieW pp. 32, 38, 39. 



CHAP. Xn. GENERAL RESULTS. 457 

or may not be mbjected to a change of climate-, but it 
is always grown in ground broken up, and more or less 
manured ; it is also saved from competition with other 
plants. The paramount importance of this latter 
circumstance is proved by the multitude of species 
which nourish and multiply in a garden, but cannot 
exist unless they are protected from other plants. 
When thus saved from competition they are able to 
get whatever they require from the soil, probably 
often in excess ; and they are thus subjected to a great 
change of conditions. It is probably in chief part 
owing to this cause that all plants with rare excep- 
tions vary after being cultivated for some generations. 
The individuals which have already begun to vary 
will intercross one with another by the aid of insects ; 
and this accounts for the extreme diversity of character 
which many of our long cultivated plants exhibit. 
But it should be observed that the result will be 
largely determined by the degree of their variability 
and by the frequency of the intercrosses ; for if a plant 
varies very little, like most species in a state of nature, 
frequent intercrosses tend to give uniformity of 
character to it. 

I have attempted to show that with plants growing 
naturally in the same district, except in the unusual 
case of each individual being surrounded by exactly 
the same proportional numbers of other species having 
certain powers of absorption, each will be subjected to 
slightly different conditions. This does not apply to 
the individuals of the same species when cultivated in 
cleared ground in the same garden. But if their 
flowers are visited by insects, they will intercross ; and 
this will give to their sexual elements during a 
considerable number of generations a sufficient amount 
of differentiation for a cross to be beneficial. More- 



458 GENEBAL RESULTS. CHAP. XTI. 

over, seeds are frequently exchanged or procured from 
other gardens having a different kind of soil ; and the 
individuals of the same cultivated species will thus be 
subjected to a change of conditions. If the flowers are 
not visited by our native insects, or very rarely so, 
as in the case of the common and sweet pea, and 
apparently in that of the tobacco when kept in a 
hothouse, any differentiation in the sexual elements 
caused by intercrosses will tend to disappear. This 
appears to have occurred with the plants just 
mentioned, for they were not benefited by being 
crossed one with another, though they were greatly 
benefited by a cross with a fresh stock. 

I have been led to the views just advanced with 
respect to the causes of the differentiation of the sexual 
elements and of the variability of our garden plants, 
by the results of my various experiments, and more 
especially by the four cases in which extremely incon- 
stant species, after having been self-fertilised and 
grown under closely similar conditions for several 
generations, produced flowers of a uniform and constant 
tint. These conditions were nearly the same as those 
to which plants, growing in a garden clear of weeds, 
are subjected, if they are propagated by self-fertilised 
seeds on the same spot. The plants in pots were, 
however, exposed to less severe fluctuations of climate 
than those out of doors ; but their conditions, though 
closely uniform for all the individuals of the same 
generation, differed somewhat in the successive gene- 
rations. Now, under these circumstances, the sexual 
elements of the plants which were intercrossed in each 
generation retained sufficient differentiation during 
several years for their offspring to be superior to 
the self-fertilised, but this superiority gradually and 
manifestly decreased, as was shown by the difference 



CHAP. XIL GENERAL RESULTS. 459 

in the result between a cross with one of the inter- 
crossed plants and with a fresh stock. These inter- 
crossed plants tended also in a few cases to become 
somewhat more uniform in some of their external cha- 
racters than they were at first. With respect to the 
plants which were self-fertilised in each generation, 
their sexual elements apparently lost, after some years, 
all differentiation, for a cross between them did no 
more good than a cross between the flowers on the 
same plant. But it is a still more remarkable fact, that 
although the seedlings of Mimulus, Ipomcea, Dianthus, 
and Petunia which were first raised, varied excessively in 
the colour of their flowers, their offspring, after being 
self-fertilised and grown under uniform conditions foi 
some generations, bore flowers almost as uniform in 
tint as those on a natural species. In one case also 
the plants themselves became remarkably uniform in 
height. 

The conclusion that the advantages of a cross 
depend altogether on the differentiation of the sexual 
elements, harmonises perfectly with the fact that an 
occasional and slight change in the conditions of life 
is beneficial to all plants and animals.* But the 
offspring from a cross between organisms which have 
been exposed to different conditions, profit in n in- 
comparably higher degree than do young or old beings 
from a mere change in their conditions. In this 
latter case we never see anything like the effect 
which generally follows from a cross with another 
individual, especially from a cross with a fresh stock. 
This might, perhaps, have been expected, for the 
blending together of the sexual elements of two dif- 
ferentiated beings will affect the whole constitution at 

* I have given sufficient evi- aticn under Domestication,' oh 
ilence on this head in my ' Vari- xviii. vol. ii. 2nd edit p. 127. 



460 GENERAL RESULTS. CHAP XIL 

a very early period of life, whilst the organisation is 
highly flexible. We have, moreover, reason to believe 
that changed conditions generally act differently on 
the several parts or organs of the same individual ;* 
and if we may further believe that these now slightly 
differentiated parts react on one another, the harmony 
between the beneficial effects on the individual due to 
changed conditions, and those due to the interaction of 
differentiated sexual elements, becomes still closer. 

That wonderfully accurate observer, Sprengel, who 
first showed how important a part insects play in the 
fertilisation of flowers, called his book ' The Secret 
of Nature Displayed ; ' yet he only occasionally saw 
that the object for which so many curious and beautiful 
adaptations have been acquired, was the cross-fertilisa- 
tion of distinct plants ; and he knew nothing of the 
benefits which the offspring thus receive in growth, 
vigour, and fertility. But the veil of secrecy is as 
yet far from lifted ; nor will it be, until we can say 
why it is beneficial that the sexual elements should 
be differentiated to a certain extent, and why, if the 
differentiation be carried still further, injury follows. 
It is an extraordinary fact that with many species, 
even when growing under their natural conditions, 
flowers fertilised with their own pollen are either 
absolutely or in some degree sterile ; if fertilised with 
pollen from another flower on the same plant, they are 
sometimes, though rarely, a little more fertile ; if 
fertilised with pollen from another individual or variety 
of tha same species, they are fully fertile ; but if 
with pollen from a distinct species, they are sterile 
in all possible degrees, until utter sterility is reached. 

* See, for instance, Brackenridge, Theory of Diathesis, Edinburgh, 



CHAP. XII. GENERAL RESULTS. 461 

We thus have a long series with absolute sterility at 
the two ends ; at one end due to the sexual elements 
not having been sufficiently differentiated, and at the 
other end to their having been differentiated in too 
great a degree, or in some peculiar manner. 

The fertilisation of one of the higher plants depends, 
in the first place, on the mutual action of the pollen- 
grains and the stigmatic secretion or tissues, and after- 
wards on the mutual action of the contents of the 
pollen- grains and ovules. Both actions, judging from 
the increased fertility of the parent-plants and from the 
increased powers of growth in the offspring, are favoured 
by some degree of differentiation in the elements 
which interact and unite so as to form a new being. 
Here we have some analogy with chemical affinity or 
attraction, which comes into play only between atoms 
or molecules of a different nature. As Prof. Miller 
remarks: "Generally speaking, the greater the dif- 
ference in the properties of two bodies, the more intense 
is their tendency to mutual chemical action. . . . But 
between bodies of a similar character the tendency to 
unite is feeble."* This latter proposition accords well 
with the feeble effects of a plant's own pollen on the 
fertility of the mother-plant and on the growth of the 
offspring ; and the former proposition accords well with 
the powerful influence in both ways of pollen from an 
individual which has been differentiated by exposure 
to changed conditions, or by so-called spontaneous 
variation. But the analogy fails when we turn to the 
negative or weak effects of pollen from one species on 
a distinct species ; for although some substances which 
are extremely dissimilar, for instance, carbon and 

* ' Elements of Chemistry,' 4th views with respect to chemical 
edit. 1867, part i. p. 11. Dr. affinity are general tjr accepted by 
Frankland informs me that similar chemists. 



462 GENERAL RESULTS. CHAP. XII 

chlorine, have a very feeble affinity for each other, 
yet it cannot be said that the weakness of the affinity 
depends in such cases on the extent to which the 
substances differ. It is not known why a certain 
amount of differentiation is necessary or favourable 
for the chemical affinity or union of two substances, 
any more than for the fertilisation or union of two 
organisms. 

Mr. Herbert Spencer has discussed this whole subject 
at great length, and after stating that all the forces 
throughout nature tend towards an equilibrium, 
remarks, " that the need of this union of sperm - 
cell and germ-cell is the need for overthrowing this 
equilibrium and re-establishing active molecular 
change in the detached germ a result which is 
probably effected by mixing the slightly-different 
physiological units of slightly different individuals."* 
But we must not allow this highly generalised view, 
or the analogy of chemical affinity, to conceal from us 
our ignorance. We do not know what is the nature or 
degree of the differentiation in the sexual elements 
which is favourable for union, and what is injurious for 
union, as in the case of distinct species. We cannot 
say why the individuals of certain species profit greatly, 
and others very little by being crossed. There are some 
few species which have been self-fertilised for a vast 
number of generations, and yet are vigorous enough 
to compete successfully with a host of surrounding 
plants. Highly self-fertile varieties sometimes arise 



* 'Principles of Biology,' vol. i. changes in the conditions and 

p. 274, 1864. In my ' Origin of from crossing widely distinct forms 

Species,' published in 1859, I (i.e., species), as a series of facts 

rke of the good effects from " connected together by some 

jht changes in the conditions of common but unknown bond, 

life and from cross-fertilisation, which is essentially related to 

and of the evil effects from great the principle of life." 



CHA.-. XIL GENERAL RESULTS. 463 

amoii plants which have been self-fertilised and 
grown under uniform conditions during several gene- 
rations. We can form no conception why the 
advantage from a cross is sometimes directed exclu- 
sively to the vegetative system, and sometimes to the 
reproductive system, but commonly to both. It is 
equally inconceivable why some individuals of the same 
species should be sterile, whilst others are fully fertile 
with their own pollen ; why a change of climate should 
either lessen or increase the sterility of self-sterile 
species; and why the individuals of some species should 
be even more fertile with pollen from a distinct species 
than with their own pollen. And so it is with many 
other facts, which are so obscure that we aland in 
awe before the mystery of life. 

Under a practical point of view, agriculturists and 
horticulturists may learn something from the conclu- 
sions at which we have arrived. Firstly, we see that 
the injury from the close breeding of animals and 
from the self-fertilisation of plants, does not necessarily 
depend on any tendency to disease or weakness of con- 
stitution common to the related parents, and only 
indirectly on their relationship, in so far as they are 
apt to resemble each other in all respects, including 
their sexual nature. And, secondly, that the advantages 
of cross-fertilisation depend on the sexual elements of 
the parents having become in some degree differentiated 
by the exposure of their progenitors to different 
conditions, or from their having intercrossed with 
individuals thus exposed, or, lastly, from what we call 
in our ignorance spontaneous variation. He therefore 
who wishes to pair closely related animals ought to 
keep them under conditions as different as possible. 
Some few breeders, guided by their keen powers of 



464 GENERAL RESULTS. CHAP. XII 

observation, have acted on this principle, and have kept 
stocks of the same animals at two or more distant and 
differently situated farms. They have then coupled 
the individuals from these farms with excellent results.* 
This same plan is also unconsciously followed whenever 
the males, reared in one place, are let out for propaga- 
tion to breeders in other places. As some kinds of 
plants suffer much more from self-fertilisation than do 
others, so it probably is with animals from too close 
interbreeding. The effects of close interbreeding on 
animals, judging again from plants, would be dete- 
rioration in general vigour, including fertility, with no 
necessary loss of excellence of form ; and this seems 
to be the usual result. 

It is a common practice with horticulturists to 
obtain seeds from another place having a very dif- 
ferent soil, so as to avoid raising plants for a long 
succession of generations under the same conditions ; 
but with all the species which freely intercross by the 
aid of insects or the wind, it would be an incomparably 
better plan to obtain seeds of the required variety, 
which had been raised for some generations under as 
different conditions as possible, and sow them in 
alternate rows with seeds matured in the old garden. 
The two stocks would then intercross, with a thorough 
blending of their whole organisations, and with no loss 
of purity to the variety ; and this would yield far more 
favourable results than a mere exchange of seeds. We 
have seen in my experiments how wonderfully the 
offspring profited in height, weight, hardiness, and fer- 
tility, by crosses of this kind. For instance, plants of 
Ipomoea thus crossed were to the intercrossed plants 
of the same stock, with which they grew in competition, 



* Variation of Animals and Plants under Domesticat'on,' ch. xvii 
2nd edit. vol. ii. pp. 98, 105. 



CHAP. XII. GENERAL RESULTS. 465 

as 100 to 78 in height, and as 100 to 51 in fertility ; 
and plants of Eschscholtzia similarly compared were 
as 100 to 45 in fertility. In comparison with self- 
fertilised plants the results are still more striking; 
thus cabbages derived from a cross with a fresh stock 
were to the self-fertilised as 100 to 22 in weight. 

Florists may learn from the four cases which have 
been fully described, that they have the power of fixing 
each fleeting variety of colour, if they will fertilise the 
flowers of the desired kind with their own pollen for 
half-a-dozen generations, and grow the seedlings under 
the same conditions. But a cross with any other in- 
dividual of the same variety must be carefully pre- 
vented, as each has its own peculiar constitution. After 
a dozen generations of self-fertilisation, it is probable 
that the new variety would remain constant even if 
grown under somewhat different conditions ; and there 
would no longer be any necessity to guard against inter- 
crosses between the individuals of the same variety. 

With respect to mankind, my son George has en- 
deavoured to discover by a statistical investigation * 
whether the marriages of first cousins are at all in- 
jurious, although this is a degree of relationship 
which would not be objected to in our domestic 
animals ; and he has come to the conclusion from his 
own researches and those of Dr. Mitchell that the 
evidence as to any evil thus caused is conflicting, but 
on the whole points to its being very small. From the 
facts given in this volume we may infer that with 
mankind the marriages of nearly related persons, some 
of whose parents and ancestors had lived under very 
different conditions, would be much less injurious than 
that of persons who had always lived in the same 

* 'Journal of Statistical Soc.' June 1875, p. 153; and Fortnightly 
Review,' Juno 1875. 

2 H 



GENERAL RESULTS. CHAP. XII. 

place and followed the same habits of life. Nor can I 
see reason to doubt that the widely different habits of 
life of men and women in civilised nations, especially 
amongst the upper classes, would tend to counter- 
balance any evil from marriages between healthy and 
somewhat closely related persons. 

Under a theoretical point of view it is some gain to 
science to know that numberless structures in her- 
maphrodite plants, and probably in hermaphrodite 
animals, are special adaptations for securing an occa- 
sional cross between two individuals; and that the 
advantages from such a cross depend altogether on the 
beings which are united, or their progenitors, having 
had their sexual elements somewhat differentiated, so 
that the embryo is benefited in the same manner as is 
a mature plant or animal by a slight change in its 
conditions of life, although in a much higher degree. 

Another and more important result may be deduced 
from my observations. Eggs and seeds are highly 
serviceable as a means of dissemination, but we now 
know that fertile eggs can .be produced without the 
aid of the male. There are also many other methods 
by which organisms can be propagated asexually. 
Why then have the two sexes been developed, and 
why do males exist which cannot themselves produce 
offspring ? The answer lies, as I can hardly doubt, in 
the great good which is derived from the fusion of two 
somewhat differentiated individuals ; and with the 
exception of the lowest organisms this is possible only 
by means of the sexual elements, these consisting of 
cells separated from the body, containing the germs of 
every part, and capable of being fused completely 
together. 
It has been shown in the present volume that the 



CHAP. xn. GENERAL RESULTS. 467 

offspring from the union of two distinct individuals, 
especially if their progenitors have been subjected to 
very different conditions, have an immense advantage 
in height, weight, constitutional vigour and fertility 
over the self-fertilised offspring from one of the same 
parents. And this fact is amply sufficient to account 
for the development of the sexual elements, that is, for 
the genesis of the two sexes. 

It is a different question why the two sexes are 
sometimes combined in the same individual and are 
sometimes separated. As with many of the lowest 
plants and animals the conjugation of two individuals 
which are either quite similar or in some degree dif- 
ferent, is a common phenomenon, it seems probable, 
as remarked in the last chapter, that the sexes were 
primordially separate. The individual which receives 
the contents of the other, may be called the female ; 
and the other, which is often smaller and more loco- 
motive, may be called the male ; though these sexual 
names ought hardly to be applied as long as the 
whole contents of the two forms are blended into one. 
The object gained by the tvo sexes becoming united 
in the same hermaphrodite form probably is to allow 
of occasional or frequent self-fertilisation, so as to 
ensure the propagation of the species, more especially 
in the case of organisms affixed for life to the same 
spot. There does not seem to be any great difficulty 
in understanding how an organism, formed by the 
conjugation of two individuals which represented the 
two incipient sexes, might give rise by budding first 
to a monoecious and then to an hermaphrodite form ; 
and in the case of animals even without budding to 
an hermaphrodite form, for the bilateral structure of 
animals perhaps indicates that they were aboriginally 
formed by the fusion of two individuals. 

2 H 2 



468 GENERAL RESULTS. CUAP. XII. 

It is a more difficult problem why some plants and 
apparently all the higher animals, after becoming her- 
maphrodites, have since had their sexes re-separated. 
This separation has been attributed by some natural- 
ists to the advantages which follow from a division of 
physiological labour. The principle is intelligible 
when the same organ has to perform at the same time 
diverse functions ; but it is not obvious why the male 
and female glands when placed in different parts of 
the same compound or simple individual, should not 
perform their functions equally well as when placed in 
two distinct individuals. In some instances the sexes 
may have been re-separated for the sake of preventing 
too frequent self-fertilisation; but this explanation 
does not seem probable, as the same end might have 
been gained by other and simpler means, for instance 
dichogamy. It may be that the production of the 
male and female reproductive elements and the 
maturation of the ovules was too great a strain and 
expenditure of vital force for a single individual to 
withstand, if endowed with a highly complex organi- 
sation ; and that at the same time there was no need 
for all the individuals to produce young, and conse- 
quently that no injury, on the contrary, good resulted 
from half of them, or the males, failing to produce 
offspring. 

There is another subject on which some light is 
thrown by the facts given in this volume, namely, 
hybridisation. It is notorious that when distinct 
species of plants are crossed, they produce with the 
rarest exceptions fewer seeds than the normal number. 
This unproductiveness varies in different species up to 
sterility so complete that not even an empty capsule 
is formed ; and all experimentalists have found that 
it is much influenced by the conditions to which the 



CHAP. XIL GENERAL RESULTS. 469 

crossed species are subjected. A plant's own pollen 
is strongly prepotent over that of any other species, 
so that if it is placed on the stigma some time after 
foreign pollen has been applied to it, any effect from 
the latter is quite obliterated. It is also notorious 
that not only the parent species, but the hybrids 
raised from them are more or less sterile ; and that 
their pollen is often in a more or less aborted con- 
dition. The degree of sterility of various hybrids 
does not always strictly correspond with the degree of 
difficulty in uniting the parent forms. When hybrids 
are capable of breeding inter se, their descendants are 
more or less sterile, and they often become still more 
sterile in the later generations ; but then close inter- 
breeding has hitherto been practised in all such cases. 
The more sterile hybrids are sometimes much dwarfed 
in stature, and have a feeble constitution. Other 
facts could be given, but these will suffice for us. 
Naturalists formerly attributed all these results to 
the difference between species being fundamentally 
distinct from that between the varieties of the same 
species ; and this is still the verdict of some naturalists. 
The results of my experiments in self-fertilising and 
cross-fertilising the individuals or the varieties of the 
same species, are strikingly analogous with those just 
given, though in a reversed manner. With the majority 
of species flowers fertilised with their own pollen yield 
fewer sometimes much fewer seeds, than those ferti- 
lised with pollen from another individual or variety. 
Some self-fertilised flowers are absolutely sterile ; but 
the degree of their sterility is largely determined by 
the conditions to which the parent plants have been 
exposed, as was well exemplified in the case of Esch- 
scholtzia and Abutilon. The effects of pollen from the 
same plant are obliterated by the prepotent influence 



J70 GENERAL RESULTS. CHAP. XII 

of pollen from another individual or variety, although 
the latter may have been placed on the stigma some 
hours afterwards. The offspring from self-fertilised 
flowers are themselves more or less sterile, sometimes 
highly sterile, and their pollen is sometimes in an 
imperfect condition ; but I have not met with any case 
of complete sterility in self-fertilised seedlings, as is 
so common with hybrids. The degree of their sterility 
does not correspond with that of the parent-plants when 
first self-fertilised. The offspring of self-fertilised 
plants suffer in stature, weight, and constitutional 
vigour more frequently and in a greater degree than 
do the hybrid offspring of the greater number of 
crossed species. Decreased height is transmitted to 
the next generation, but I did not ascertain whether 
this applies to decreased fertility. 

I have elsewhere shown * that by uniting in various 
ways dimorphic or trimorphic heterostyled plants, 
which belong to the same undoubted species, we get 
another series of results exactly parallel with those 
from crossing distinct species. Plants illegitimately 
fertilised with pollen from a distinct plant belonging 
to the same form, yield fewer, often much fewer seeds, 
than they do when legitimately fertilised with pollen 
from a plant belonging to a distinct form. They some- 
times yield no seed, not even an empty capsule, like 
a species fertilised with pollen from a distinct genus. 
The degree of sterility is much affected by the condi- 
tions to which the plants have been subjected. The 
pollen from a distinct form is strongly prepotent over 
that from the same form, although the former may 
have been placed on the stigma many hours afterwards. 



* ' The Different Forms of Flowers on Plants of the same specie*, 
1877, p. 240. 



CHAP. XII. GENERAL RESULTS. 471 

The offspring from a union between plants of the same 
form are more or less sterile, like hybrids, and have 
their pollen in a more or less aborted condition ; and 
some of the seedlings are as barren and as dwarfed as 
the most barren hybrid. They also resemble hybrids in 
several other respects, which need not here be specified 
in detail, such as their sterility not corresponding 
in degree with that of the parent plants, the unequal 
sterility of the latter, when reciprocally united, 
and the varying sterility of the seedlings raised from 
the same seed-capsule. 

We thus have two grand classes of cases giving results 
which correspond in the most striking manner with 
those which follow from the crossing of so-called true 
and distinct species. With respect to the difference 
between seedlings raised from cross and self fertilised 
flowers, there is good evidence that this depends alto- 
gether on whether the sexual elements of the parents 
have been sufficiently differentiated, by exposure to 
different conditions or by spontaneous variation. The 
manner in which plants have been rendered hetero- 
styled is an obscure subject, but it is probable that the 
two or three forms first became adapted for mutual 
fertilisation, that is for cross-fertilisation, through the 
variation of their stamens and pistils in length, and 
that afterwards their pollen and ovules became co- 
adapted ; the greater or less sterility of any one form 
with pollen from the same form being an incidental 
result.* Anyhow, the two or three forms of hetero- 
styled species belong to the same species as certainly 
as do the two sexes of any one species. We have 
therefore no right to maintain that the sterility of 
species when first crossed and of their hybrid offspring, 

* This subject has been discussed in my 'Different Formt of 
Flowers &o.,' pp. 260-268. 



472 GENERAL EESULTS. CHAP. XII. 

is determined by some cause fundamentally different 
from that which determines the sterility of the indi- 
viduals both of ordinary and of heterostyled plants 
when united in various ways. Nevertheless, I am 
aware that it will take many years to remove this 
prejudice. 

There is hardly anything more wonderful in nature 
than the sensitiveness of the sexual elements to external 
influences, and the delicacy of their affinities. We see 
this in slight changes in the conditions of life being 
favourable to the fertility and vigour of the parents, 
while certain other and not great changes cause them 
to be quite sterile without any apparent injury to their 
health. We see how sensitive the sexual elements of 
those plants must be, which are completely sterile with 
their own pollen, but are fertile with that of any other 
individual of the same species. Such plants become 
either more or less self-sterile if subjected to changed 
conditions, although the change may be far from great. 
The ovules of a heterostyled trimorphic plant are 
affected very differently by pollen from the three sets 
of stamens belonging to the same species. With ordi- 
nary plants the pollen of another variety or merely of 
another individual of the same variety is often strongly 
prepotent over its own pollen, when both are placed 
at the same time on the same stigma. In those great 
families of plants containing many thousand allied 
species, the stigma of each distinguishes with unerr 
ing certainty its own pollen from that of every 
other species. 

There can bo no doubt that the sterility of dis- 
tinct species when first crossed, and of their hybrid 
offspring, depends exclusively on the nature or affi- 
nities of their sexual elements. We see this in the 
want of any close correspondence between the degree 



CHAP XII. GENERAL RESULTS. 473 

of sterility and the amount of external difference in the 
species which are crossed ; and still more clearly in the 
wide difference in the results of crossing reciprocally 
the same two species ; that is, when species A is 
crossed with pollen from B, and then B is crossed with 
pollen from A. Bearing in mind what has just been 
said on the extreme sensitiveness and delicate affinities 
of the reproductive system, why should we feel any 
surprise at the sexual elements of those forms, which 
we call species, having been differentiated in such a 
manner that they are incapable or only feebly capable 
of acting on one another ? We know that species have 
generally lived under the same conditions, and have 
retained their own proper characters, for a much longer 
period than varieties. Long-continued domestication 
eliminates, as I have shown in my 'Variation under 
Domestication,' the mutual sterility which distinct 
species lately taken from a state of nature almost always 
exhibit when intercrossed; and we can thus understand 
the fact that the most different domestic races of animals 
are not mutually sterile. But whether this holds good 
with cultivated varieties of plants is not known, though 
some facts indicate that it does. The elimination of 
sterility through long-continued domestication may 
probably be attributed to the varying conditions to 
which our domestic animals have been subjected ; and 
no doubt it is owing to this same cause that they with- 
stand great and sudden changes in their conditions of 
life with far less loss of fertility than do natural species. 
From these several considerations it appears probable 
that the difference in the affinities of the sexual 
elements of distinct species, on which their mutual 
incapacity for breeding together depends, is caused by 
their having been habituated for a very long period 
each to its own conditions, and to the sexual elements 



474 GENERAL RESULTS. CHAP. XII 

having thus acquired firmly fixed affinities. However 
this may be, with the two great classes of cases before 
us, namely, those relating to the self-fertilisation and 
cross-fertilisation of the individuals of the same species, 
and those relating to the illegitimate and legitimate 
unions of heterostyled plants, it is quite unjustifiable to 
assume that the sterility of species when first crossed 
and of their hybrid offspring, indicates that they 
differ in some fundamental manner from the varieties 
or individuals of the same species. 



( 475 ) 



INDEX. 



Abutilon dartcinii, self- sterile in 
Brazil, 333, 358 ; moderately self- 
fertile in England, 344 ; fertilised 
by birda, 371 

Acacia sphxrocephala, 406 

Acanthacex, 96 

Aconitum napellus, 431 

Adlumia cirrhosa, 366 

Adonis xstivali*, * 128 ; measure- 
ments, 128; relative heights of 
crossed and self-fertilised plants, 
277 ; self-fertile, 365 

Ajuga reptans, 368 

Attium cepa (blood-red var.), 369 

AnagaUis collina (var. grandiftora), 
217, 267; measurements, 218; 
seeds, 316, 323, 325 

Anderson, J., on the Calceolaria, 87 ; 
removing the corollas, 423 

Anemone, 396 

Anemophilous plants, 401; often 
diclinous, 411 

Antirrhinum majus (red var.), 363 ; 
perforated corolla, 432 

(white var.), 363 

(peloric var.), 363 

Apium petroselinum, 172 ; result of 
experiments, 277 

Argemone ochroleuca, 366 

Aristotle on bees frequenting flowers 
of the same species, 418 

Aristolochia, 420 

Arum maculatum, 420 



Bailey, Mr.. 
430 



perforation of corolla, 



BENNETT. 

Bartonia aurea, 170 ; measurements, 
170, 171 ; result of experiments, 
277 

Bartsia odontites, 369 

Beal, W. J., sterility of Kalmia 
latifolia, 359 ; on nectar in Ribes 
aureum, 435 

Bean, the common, 435 

Bees distinguish colours, 373; fre- 
quent the flowers of the same 
species, 418, 423; guided by 
coloured corolla, 423; powers of 
vision and discrimination, 425; 
memory, 426; unattracted by 
odour of certain flowers, 426; 
industry, 427; profit by the co- 
rolla perforated by humble-bees, 
430 ; skill in working, 431 ; habit, 
434 ; foresight, 436 

, humble, recognise varieties 

as of one species, 419; colour 
not the sole guide, 424; rate of 
flying, 427; number of flowers 
visited, 428; corolla perforated 
by, 429, 436; skill and judgment, 
432 

Belt, Mr., the hairs of Digitalis 
purpurea, 82 ; Phaseolus multi- 
florus, 151 ; not visited by bees 
in Nicaragua, 360 ; humming- 
birds carrying pollen, 371 ; se- 
cretion of nectar, 404 ; in Acacia 
sphterocephalus and passion- 
flower, 406 ; perforation of corolla, 
433 

Bennett, A. W., on Viola tricolor, 
123; structure of Impatient f viva, 
367; plants flowering in winter, 
386 ; bees frequenting flowers of 
game species, 419 



476 



INDEX. 



Bentham, on protection of the 
stigma in Synaphea, 415 

Beta vulgaris, 228 ; measurements, 
229, 230; crossed not exceeded 
by self-fertilised, 289, 367; pre- 
potency of other pollen, 399 

Bignonia, 363 

Birds means of fertilisation, 371 

Blackley, Mr., weights of pollen of 
anemophilous plants, 377, 378 ; 
on anthers of rye, 378 ; pollen 
carried by wind, experiments with 
a kite, 408 

Boraginacex, 185 

Borago ojicinaUs, 185, 276; mea- 
surements, 186 ; early flowering 
of crossed, 293 ; seeds, 323 ; par- 
tially self-sterile, 362 

Boulger, Mr., on moths frequenting 
Petunias, 188 

Brackenridge, Mr., organism of ani- 
mals aifected by temperature and 
food, 446; difterent effect of 
changed conditions, 455 

Brassica oleracea, 98 ; measure- 
ments, 100; weight, 101, 102; 
remarks on experiments, 262; 
superiority of crossed, 288 ; period 
of flowering, 292; seeds, 322; 
self-fertile, 365 

- - napus, 395 

rapa, 395 

Brisout, M., insects frequenting 
flowers of same species, 422 

Broom, 163 

Brugmansia, 371 ; humming-birds 
boring the flower, 435 

Bulrush, weight of pollen produced 
by one plant, 407, 408 

Bundy, Mr., Bibes perforated by 
bees, 435 

Burbidge, references on the germi- 
nation of small seeds, 355 

Biitschli, O., sexual relations, 412 



C. 



Cabbage, 98 ; affected by pollen of 
purple bastard, 379; prepotency 
of other pollen, 395, 399 



CONVOLVULUS. 

Cabbage, Bagged Jack, 397 

Calceolaria, 87, 369 

Calluna vulgaris, 424 

Campanula carpathica, 174, 364 

Gampanulacege, 174 

Candolle, A. de, on ascending 
a mountain the flowers of the 
same species disappear abruptly, 
391 

Canna warscewiczi, 230 ; result of 
crossed and self-fertilised, 278; 
period of flowering, 294 ; seeds, 
323, 325 ; highly self-fertile, 369 

Cannaceae, 230 

Carduus arctioides, 404 

Carnation, 132 

Carriere, relative period of the ma- 
turity of the sexual elements on 
same flower, 446 

Caryophyllacese, 130 

Caspary, Professor, on Corydalis 
cava, 331; tfymphxacex, 358; 
Euryale ferox, 365 ; on flowers of 
water-lilies, 392 

Cecropia, food-bodies of, 404 

Centradenia floribunda, 364 

Cereals, grains of, 354 

Clieeseman, Mr., on Orchids in New 
Zealand, 392 

ChenopodiacetE, 228 

Cineraria, 335 

Clarkia elegans, 1 69 ; measurements, 
170 ; early flowering of self-fer- 
tilised, 294, 296 ; seeds, 316 

Cleistogamic flowers, 90 

Coe, Mr., crossing Phaseolus vul- 
garis, 153 

Colgate, R., red clover never sucked 
by hive-bees in New Zealand, 
361 

Colour, uniform, of flowers on plants 
self -fertilised and grown under 
similar conditions for several gene- 
rations, 306, 307 

Colours of flowers attractive to in- 
sects, 372 ; not the sole guide to 
bees, 424 

Composite, 173 

Coniferx, 402 

Convolvulus major, 28 

tricolor, 55 



INDEX. 



477 



OOBOLLA. 

Corolla, removal of, 423 ; perforation 
by bees, 4'>8 

Coronilla, 407 

Corydalis cava, 331, 358 

lialleri, 331 

intermedia, 331 

lutea, 359 

ochroleuca, 359 

Corydalis solida, 358 

Corylus avellana, 390 

Cowslip, 219 

Crinum, 396 

Crossed plants, greater constitu- 
tional vigour of, 285 

Cross-fertilisation, 371 : see Fertilisa- 
tion. 

Crossing flowers on same plant, 
effects of, 297 

Cruciferie, 98 

Criiger, Dr., secretion of sweet 
fluid in Marcgraviacese, 407 

Cuphm purpurea, 323, 362 

Cycadesi, 402 

Cyclamen persicum, 215 ; measure- 
ments, 216; early flowering of 
crossed, 293 ; seeds, 317, 323 ; 
self-sterile, 362, self-fertilization 
injurious, 448 

repandum, 215 

Cytisus laburnum, 362 



D. 

D.mdelion, number of pollen-grains, 
377 

Darwin, C., self-fertilisation in 
Pisum sativum, 161 ; sexual affini- 
ties, 209 ; on Primula, 219 ; bud 
variation, 298 ; constitutional 
vigour from cross parentage in 
common pea, 305; hybrids of 
Gladiolus and Cistus, 306 ; Pha- 
seolus multiflorus, 360; nectar 
in orchids, 407 ; on cross-ferti- 
lisation, 440, 442, 443; inheri- 
tance of acquired modifications, 
451 ; change in the conditions of 
life beneficial to plants and 
animals, 459 



DIPSACE^E. 

Darwin, P., structure of Phaseolut 
multiflorus, 150 ; Pteris aquilina, 
405 ; on nectar glands, 406 ; per- 
foration of Lathyrus sylvestris, 
432 

, G., on marriages with first 

cousins, 465 

Decaisne on Delphinium consolida, 
129 

De Candolle, nectar as an excretion, 
403 

Delphinium consolida, 129; mea- 
surements, 130 ; seeds, 322 ; par 
tially sterile, 358; corolli re- 
moved, 423 

Delpino, Professor, Viola tricolor, 
123 ; Phaseolus multiflorus, 150 ; 
intercrossing of sweet-pea, 156; 
Lobelia ramosa , 176 ; structure 
of the Cannacex, 230 ; wind and 
water carrying pollen, 372; 
Juglans regia, 391 ; anemophi- 
lous plants, 401; fertilisation of 
Plantago, 403 ; excretion of 
nectar, 404, 407; secretion of 
nectar to defend the plant, 406, 
407; anemophilous and entomo- 
philous plants, 411; dioecious 
plants, 417 

Denny, Pelargonium zonale, 142 

Diagram showing mean height of 
Ipomcea purpurea, 53 

Dianthus caryophyllus, 132 ; crossed 
and self-fertilised, 133-136 ; mea- 
surements, 135-138; cross with 
fresh stock, 136 ; weight of seed, 
139 ; colour of flowers, 139 ; re- 
marks on experiments, 263, 274 ; 
early flowering of crossed, 292 ; 
uniform colour of self-fertilised, 
309; seeds, 316, 319, 323, 325; 
few capsules, 360 

Dickie, Dr., self-fertilisation in 
Cannacex, 230 

Dictamnus fraxinella, 419 

Digitalis purpurea, 81 ; measure- 
ments, 84-87; effects of inter- 
crossing, 85, 299 ; superiority of 
crossed, 288, 452; self-sterile, 
363 

Dipsacese, 172 



478 



INDEX. 



Dobbs, bees frequenting flowers of 

same species, 419 
Dodel, Dr. A., sexual reproduction, 

412 
Duhamel on Raphanus sativus, 

395 
Dunal, nectar as an excretion, 

403 
Dyer, Mr. Thiselton, on Lobelia 

ramosa, 176 ; on Cineraria, 335 ; 

origin of Hermaphroditism, 413 



Barley, W., self-fertilisation of 
Lathyrus odoratus, 153 

Eaton, Kev. A. E., on Pringlea, 410 

Engelmann, development of sexual 
forms, 412 

Engler, Dr., on dichogamous Saxi- 
fraga, 440 

Entomophilous plants, 411 

Epipactis latifolia, attractive only 
to wasps, 376, 426 

Erica tetralix, 424 ; perforated 
corolla, 429, 437 

Errara, M., on self-fertilisation, 
352 

Erythrina, 360 

Eschscholtzia californica, 109 ; 
measurements, 110 ; plants raised 
from Brazilian seed, 111 ; weigbt, 
113; seeds, 115, 116, 315, 319, 
322 ; experiments on, 263, 275 ; 
superiority of self-fertilised over 
crossed, 290; early flowering, 
292, 294; artificially self-ferti- 
lised, 332; pollen from other 
flowers more effective, 340 ; self- 
sterile in Brazil, 343, 358; effects 
of changed conditions on repro- 
ductive system, 444, 449 

Euphrasia officinalis, 368 

Euryale amazonica, 358 

ferox, 365 

P. 

Fabriciua on Aristolochia, 420 
Faqopyrum esculentum, 228 ; early 
of crossed plant, 293 



Faivre, Professor, self-fertilisation 
of Cannacex, 230 

Farrer, T. H., papilionaceous 
flowers, 5 ; Lupinus luteus, 147 ; 
Phaseolus multiflorus, 150, 434 ; 
Pisum sativum, 160; cross-fer- 
tilisation of Lobelia ramosa, 176 ; 
on Coronilla, 407 

Fennond, M., Phaseolus multi- 
fonts, 151 ; P. coccineus hybridus, 
151 

Fertilisation, means of, 356 ; plants 
sterile, or partially so without 
insect-aid, 357-364; plants fer- 
tile without insect-aid, 365-369 ; 
means of cross-fertilisation, 371 ; 
humming-birds, 371; Australian 
flowers fertilised by honey- 
sucking birds, 371 ; in" New Zea- 
land by the Anthornis melanura, 
371 ; attraction of bright colours, 
372; of odours, 374; flowers 
adapted to certain kinds of insects, 
375 ; large amount of pollen- 
grains, 377, 378 ; transport of 
pollen by insects, 379-380 ; struc- 
ture and conspicuousness of 
flowers, 383 ; pollen from a dis- 
tinct plant, 390; prepotent 
pollen, 394-401 

Fertility, heights and weights, re- 
lative, of plants crossed by a 
fresh stock, self-fertilised, or 
intercrossed (Table C), 245- 
252 

Fertility of plants as influenced by 
cross and sell-fertilisation (Table 
D), 312 ; relative, of crossed and 
self-fertilised parents (Table E), 
314319; innate, from a cross 
with fresh stock (Table F), 319 ; 
relative, of flowers crossed with 
pollen from a distinct plant and 
their own pollen (Table G), 320 ; 
of crossed and self-fertilised 
flowers, 324, 325 

Flowering, period of, superiority ot 
crossed over self-fertilised, 291- 
297 

Flowers, artificial, 374 

Flowers, cleistogamic, 90; wuite, 



INDEX. 



479 



larger proportion smelling swot'- 7, 
375; structure and conspicuouo- 
ness of, 382 ; conspicuous and in- 
conspicuous, 386 ; papilionaceous, 
386 ; fertilised with pollen from 
a distinct plant, 390 

Fvrsythia viridissima, 341 

Foxglove, 81 

Frankland, Dr., chemical affinity, 
461 

Fraximts ornus, 404 

Fumaria capreolata, 366 

oficinalis, 366 



0. 

Galium aparine, 369 

Gallesio, spontaneous crossing of 
oranges, 396 

Galton, Mr., Limnantlies douglasii, 
146; report on the tables of 
measurements, 16-19, 146, 234 ; 
self-fertilised plants, 290, 291 ; 
superior vigour of crossed seed- 
lings in Lathyrus odoratus. 353, 
355 

Gartner, excess of pollen injurious, 
24 ; plants fertilising one another 
at a considerable distance, 152; 
Lobelia fulgens, 179, 330 ; sterility 
of Verbascumnigrum, 330 ; number 
of pollen-grains to fertilise Geum 
urbanum, 378 ; experiments with 
pollen, 380 

Gentry, Mr., perforation of corolla, 
430 

Geraniacex, 142 

Geranium phseum, 423 

Gerardia pedicularia, 430, 437 

Germination, period of, and relative 
weight of seeds from crossed and 
self-fertilised flowers, 352-355 

Gesneria pendulina, 92 ; measure- 
ments, 92 ; seeds, 322 

Gesneriaceae, 92 

Geum urbanum, number of pollen- 
grains for fertilisation, 378 

Glaucium luteum, 366 

Godron, intercrossing of carrot, 172 ; 
Primula grandiflora affected by 



HILDEBBAND. 

pollen of P. officinalis, 380 ; tulips, 

I Gould, humming-birds frequenting 

Impatient, 371 
I Graminaceae, 233, 445 
j Grant, Mr., bees of different hives 

visiting different kinds of flowers, 

426 
Gray, Asa, flowers of Drosera, 

392; sexual relations of trees 

in United States, 414 ; on sexual 

reproduction, 442 



Hallet, Major, on selection of grains 

of cereals, 354 

j Hassall, Mr., number of pollen- 
graius in Pseony and Dandelion, 
377 ; weight of pollen produced 
by one plant of Bulrush, 407-408 

Heartsease, 123 

Hedychium, 364 

Hedysarum onobrychis, 361 

Heights, relative, of crossed and 
self-fertilised plants (Table A,, 
240-243 

Heights, weights, and fertility, 
summary, 238-284 

Henschel's experiments with i >ollen, 
381 

Henslow, Rev. G., cross-fertilisa- 
tion in Sarothamnus scoparius, 
164; on self-fertilisation not in- 
jurious, 441 

Herbert on cross-fertilisation, 7; 
pollen brought from distant 
plants, 380 ; spontaneous crossing 
of rhododendrons, 396 

Hero, descendants of the plant, 47- 
51. 258 ; its self-fertilisation, 349 

Heterocentron maxicanum, 361 

Hibiscus africanus, 140; measure- 
ments, 140 ; result of experiments, 
277; early flowering of crossed 
plant, 292, 296 ; number of pollen- 
grains for fertilisation, 378 

Hildebrand on pollen of Digitalis 
purpurea, 82 ; Thunbergia a/a/a, 
96 ; experiments on Eschscholteia 



480 



INDEX 



HOFFMANN. 

californica, 110 ; Viola tricolor, 
123; Lobelia ramosa, 176 ; on moths 
frequenting Petunias, 188 ; Fago- 
pyrum esculentum, 228 ; self-fertili- 
sation of Zeamays, 233 ; Corydalis 
cava, 831; Bypecoum grandi- 
florum, 331, 359; and H. pro- 
cumbens, 331 , 366 ; sterility of Esch- 
scholtzia, 332 ; experiments on self- 
fertilisation, 340 ; Corydalis lutea, 
359 ; spontaneously self-fertilised 
flowers, 366 ; various mechanical 
structures to check self-fertilisa- 
tion, 383 ; early separation of the 
sexes, 400 ; on Aristolochia, 420 ; 
fertilisation of the Gramineas, 445 ; 
wide dissemination of seeds, 455 

Hoffmann, Prof. H., self-fertilised 
capsules of Papaver somniferum, 
108, 366; Adonis testivalis, 129, 
365 ; spontaneous variability of 
Phaseolus multiflorus, 151 ; self- 
fertilisation of kidney-bean, 152 ; 
Papaver alpinum, 331; sterility 
of Corydalis solida, 358; Linum 
usitatissimum, 366 ; on honey-dew 
from a camellia, 404 

Honey-dew, 404 

Hooker, Dr., Euryale ferox and 
Victoria regia, each producing 
several flowers at once, 365 ; on 
sexual relation of trees in New 
Zealand, 414 

Horse-chestnut, 401 

Humble-bees, 419 : see Bees 

Humboldt, on the grains of cereals, 
354 

Humming-birds a means of cross- 
fertilisation, 371 

Hyacinth, 396 

Hybrid plants, tendency to revert to 
their parent forms, 380 

Hypecoum grandifiorum, 331, 359 

procumbens, 331, 366 



Itieris umbellata (var. Ttermesiana~), 
103 ; measurement, 104-106 ; 



KEBNEB. 

cross by fresh stocks, 105 ; 
remarks on experiments, 262 ; 
superiority of crossed over self- 
fertilised seedlings, 289; early 
flowering, 292 ; number of seeds, 
315; highly self-fertile, 365; 
prepotency of other pollen, 394 

amara, 365 

Impatiens frequented by humming- 
birds, 371 

barbigera, 366 

fulva, 341, 367 

noli-me-tangere, 367 

pallida, 341 

Inheritance, force 01, in plants, 30.") 

Insects, means of cross-ftrtilisation, 
371 ; attracted by bright colours, 
372 ; by odours, 374 ; by con- 
spicuous flowers, 384; dark 
streaks and marks as guides for, 
373; flowers adapted to certain 
kinds, 376 

Ipomcea purpurea, 28; measure- 
ments, 29-49; flowers on same 
plant crossed, 41-44 ; cross with 
fresh stock, 45-47; descendants 
of Hero, 47-51 ; summary of 
measurements, 52 ; diagram show- 
ing mean heights, 53 ; summary 
of observations, 53-62 ; of experi- 
ments, 257-259; superiority of 
crossed, 289; early flowering, 
291, 297 effects of intercrossing, 
300; uniform colour of self-fer- 
tilised, 308 ; seeds, 314, 322, 324 : 
highly self-fertile, 368; prepo- 
tency of other pollen, 399 

Iris, secretion of saccharine matter 
from calyx, 404 

Isotoma, 176, 364 



J. 

Juglans regia, 391 



Kalmia latifolia, 359 

Kerner. on protection of flower* 



INDEX. 



481 



from crawling insects, 376; on 
protection ut the pollen, 377; 
on the single daily flower of 
ViUarsia parnassifolia, 392 ; pol- 
len carried by wind, 408, 415 

Kidney-bean, 152 

Kitchener, Mr., on the- action of the 
stigma, 61 ; on Viola tricolor, 123 

Knight, A., on thesexual intercourse 
of plants, 7 ; crossing varieties of 
peas, 163 ; sexual reproduction, 
442 

Kohl-rabi, prepotency of pollen, 
394 

Kolreuter on cross-fertilisation, 7; 
number of pollen-grains nectssary 
for fertilisation, 24 ; sexual affini- 
ties of Nicotiana, 210 ; Verbascum 
phneniceum, 330 ; experiments 
with pollen of Hibiscus vesi- 
carius, 378 

Kuhn adopts the term cleistogamic, 
90 

Kurr, on excretion of nectar, 404 ; 
removal of corolla, 423 



Labiate, 93 

Lactuca sativa, 173, 369 ; measure- 
ment, 174 ; prepotency of other 
pollen, 399 

Lamium album, 391, 419 

purpureum, 419 

Lathyrus odoratus, 153-160; mea- 
surements, 157-160 ; remarks 
on experiments, 265; period of 
flowering, 295 ; cross-fertilisation, 
304; beeds, 316, 325; b elf-fertile, 
367 

grandijtorus, 155, 360 

nissolia, 367 

sylvestris, perforation of corolla, 

432 

Lawes and Gilbert, Messrs., con- 
sumption of inorganic mutter by 
plants, 453 

Lax ton, Mr., crossing varieties of 
peas, 1 ;:{, :;o:> 

Leooq, Cyclamen repandum, 215 , on 



Fumariacex, 359 ; annual plants 
rarely dioecious, 415 

Leersia oryzoides, 350 

Leguminosa? , 147 ; summary on the, 
168 

Lehmanu. Prof., on seedlings from 
large and small seeds, 355 

Leighton, Rev. W. A., on Phaseolus 
multiflorus, 151 ; Acacia magnijica, 
407 

Leptosiphon androsaceus, 368 

Leschenaultia formosa, 364 

Lettuce, 173 

Lilium auratum, 341 

Limnanthesdouglasii, 145 ; measure- 
ments, 146 ; early flowering of 
crossed, 293; seeds, 316, 323; 
highly self-fertile, 367; prepo- 
tency of other pollen, 399 

Linaria vulgaris, 9, 88 ; seeds, 322 ; 
self-sterile, 363 

cymbalaria, 385, 426 

Lindley on Fumariacex, 359 

Link, hypopetalous nectary in 
Chironia decussata, 404 

Linum grandiflorum, 343 

usitatissimum, 366 

Loasacex, 170 

Lobelia erinus, 176; secretion of 
nectar in sunshine, 405 ; experi- 
ments with bees, 423 

Lobelia fulgens, 179 ; measurements, 
180-182; summary of experi- 
ments, 274; early flowering of 
self-fertilised, 291, 294, 295; 
seeds, 323 ; sterile unless visited 
by humble-bees, 364 

ramosa, 176; measurements. 

177, 178; early flowering of 
crossed, 293, 295 ; seeds, 325 ; 
self-sterile, 364 

tenuior, 176 

Loiseleur-Deslongchnmp, on the 
grains of cereals, 354 

Lotus corniculatus, 361 

Lubbock, Sir J., cross-fertilisation 
of flowers, 6; on Viola tricolor, 
123; bees distinguishing colours, 
373; inatinet of bees and iu^-ects 
sucking nectar, 418 

Lupinus luteus, 147 ; measurements, 



482 



INDEX. 



148 ; early flowering of self-ferti- 
lised, 294,' 296; self-fertile, 367; 
prepotency of other pollen, 399 

Lupinus pilosus. 149- self-fertile 
'667 

Lychnis dioica, 413 



Macnab, Mr., on the shorter or 
longer stamens of rhododendrons, 
298 

Mahonia aquifolium, 396 

repens, 396 

Malvacex, 140 

Marcgramacex, 407 

Marck, Dr., on seedlings from large 
and small seeds, 355 

Masters, Mr., cross-fertilisation in 
Pisum sativum, 161; cabbages 
affected by pollen at a distance, 
379 

, Dr. Maxwell, on honey-dew, 

404 

Measurements, summary of, 241 ; 
Table A, 240-243 : Table B, 
244 ; Table C, 245-252 

Medicago lupulina, 368 

Mechan, Mr., fertilising Petunia 
violacea l>y night moth, 188 

Melastomacex, 298 

Melilotus officinalis, 360 

Mercurialis annua, 421 

Miller, Professor, on chemical affi- 
nity, 461 

Miiiiulus luteus, effects of crossing, 
10; crossed and self-fertilised 
plants, 64-70 ; measurements, 70- 
78 ; cross with a distinct stock, 72- 
75 ; intercrossed on same plant, 
75-78 ; summary of observations, 
78-81 ; of experiments, 259-261 ; 
superiority of crossed plants, 286 ; 
simultaneous flowering, 294, 296 ; 
effects of intercrossing, 301 ; 
uniform colour of self-fertilised, 
307; seeds, 315, 319, 322, 324 ; 
highly self-fertile, 348, 369 ; pre- 
potency of other pollen, 393, 399 

rweus, 63 



Miner, Mr., red clover never sucked 
by hive-bees in the United States, 
361 

Mirnbilis, dwarfed plants raised by 
using too few pollen-grains, 298 : 
number of grains necessary for 
fertilisation, 378 

Mitchell, Dr., on first cousins inter- 
marrying, 465 

Monochxtum ensiferum, 361 

Moore, Mr., on Cinerarias, 335 

Miiller, Fritz, on Posoqueria 
fragrans, 5, 393 ; experiments on 
hybrid Abutilons and Bignnnias, 
305, 306; large number of 
orchidaceous genera sterile in 
their native home, also Bignonia 
and Tdbernxmontana echinata. 
331 ; sterility of Etchscholtzia 
californica, 332, 342; Abutilon 
darwinii, 334; experiments in 
self-fertilisation, 340 ; self-sUrile 
plants, 341 ; incapacity of pollen- 
tubes to penetrate the stigma, 
342 : cross-fertilisation by means 
of birds, 371 ; imperfectly deve 
loped male and female Termites, 
381 ; on ferns and ants, 406 ; food- 
bodies in Cecropia, 406; on the 
glands on calyx of Malpighiacese, 
407 

Muller, Hermann, fertilisation of 
flowers by insects, 6, 7; on 
Digitalis uurpurea, 82 ; Calceo- 
laria, 87 ; Linaria vulgaris, 88 ; 
Vei-bascum nigrum, 89 ; the 
common cabb.ige, 98; Papaver 
dubiurn, 107 ; Viola tricolor, 123, 
124; structure of Delphinium 
consolida, 129 ; of Lupinus luteus, 
147 ; flowers of Pisum sativum, 
ICO, 161 ; on Sarothamnus scopa- 
rius not secreting nectar, lb'4 ; 
Apium petroselinum, 172 ; Boragn 
officinalis, 185 ; red clover visited 
by hive-bees in Germany, 361 ; 
insects rarely visiting Fumaria 
officinalis, 366; comparison of 
lo\vlau<l and alpine species, 376; 
structure of plants adapted to 
cross and self- fertilisation, 381; 



INDEX. 



483 



large conspicuous flowers more 
frequently visited by insects than 
email inconspicuous ones, 384; 
SoJanum generally unattractive 
to insects, 389 ; Lamium album, 
390,391 ; on aneinophilous plants, 
401 ; fertil'sation of Plant<i<i<>. 
403 ; si cretion of nectar, 407 : 
instinct of bees sucking nectar, 
418; bees frequenting flowers of 
the sime species, 4l!; cause of 
it, -J21 ; powers of vision and 
discrimination of bees, 425 

Miiller, Dr. H., hive-beea occa- 
sionally perforate the flower of ; 
Erica tetralix, 430; calyx and , 
corolla of Rliinanthus alectero- 
lophus bored by Bombus mastru- ; 
cfituK, 435 

Munro, Mr., some species of Onci- j 
dium and Maxillaria sterile 
with own pollen, 334 

Myrtace<e,4l4: 



Nageli on odours attracting insects, 
374 ; si-xual relations, 411 

Natural selection, effect upon self- 
.-tei ility and self- fertilisation, 345, 
lilt; 

Xaudin on number of pollen-grains 
necessary for fertilisation, 24 ; 
Petunia'violacea, 188 

NVrtar regarded as an excretion, 403 

Nemophila insignia, 182; measure- 
ments, 183-185; early flowering 
of crossed plant, 293 ; effects of 
cross and self-fertilisation. 303; 
seeds, 316, 323 

Xepeta glechoma, 419 

\rcotiana glutinosa, 210 

tabacum, 203 ; measurements, 

205-208 ; cross with fresh stock, 
210; measuremtnts, 212-215; 
summary of experiments, 266, 
2'JT, '-79; superioiity of crossed 
plants, '288-290; early flowering, 
2H3-295; seeds. 323, 325; ex- 
periments on, 349; self-fertile, 
3;8 



Nolana prostrata, 186; measure- 
ments, 187; crossed and self- 
fertilised p'ants, 277; number of 
capsules and seeds, 321, 323; 
self-fertile, 368 

Nolanacex, 186 

Nymphxa, 358, 3t5 



0. 



Odours emitted by flowers attractive 
to insects, 374 

Ojje, Dr., on Digitalis purpurea, 
82 ; Gesneria, 92 ; Phaseolus mul- 
tiftorus, 151, 360, 434; perfora- 
tion of corolla, 429 ; case of the 
Monkshood, 431 

Onagracex, 169 

Onion, prepotency of other polk-n, 
395 

Ononis minutissima, i67 ; meaaure- 
ments, 168; seeds, 323; self- 
fertile, 367 

Ophrys apifera, 350, 369, 408, 442 

musct/era, 385, 408 

Oranges, spontaneous crossing, 395 

Orchidex, 364, 369; excretion of 
saccharine matter, 404 

Orchis, fly, 408 

Origanum vulgare, 94; measure- 
mentx. 95; early flowering of 
crossed plant, 292; effects of 
intercrossing, 301 



P. 

Pseony, number of pollen-grains, 

377 

Papaveracex, 107 
Papaver alpinum, 331, 358 

argemonoides, 366 

bracteatum, 108 

dubium, 107 

orientate, 108 

rhaas, Iu7 

somniferum, 108, 331, 365 

vagum, 107; measurementa, 



484 



INDEX. 



109; number of capsules, 315; 
seeds, 358 ; prepotency of other 
pollen, 398 

Papillaj of the Viola tricolor at- 
tractive to insects, 124 

Parsley, 172 

Passiflora alata, 330, 334 

gracilis, 171 ; measurements, 

171 ; crossed and self-fertilised 
276 ; seeds, 323 ; self - fertile, 
365 

Passifloracete, 171, 357 

Pea, common, 160, 351 

Pelargonium zonale, 142 ; measure- 
ments, 143 ; effects of inter- 
crossing, 301 ; almost self-sterile, 
359 

Pentstemon argutus, perforated co- 
rolla, 429, 431, 436 

Petunia violacea, 188; measure- 
ments, 189-203 ; weight of seed, 
196 ; cross with fresh stock, 196- 
201 ; relative fertility, 201-203 ; 
colour, 203 ; summary of experi- 
ments, 265, 274: superiority of 
crossed over self-fertilised, 289; 
early flowering, 293, 294; uniform 
colour of self-fertilised, 309 ; 
seeds, 316, 319, 323, 325 ; self- 
sterile, 362 

Phalaris canariensis, 235 ; measure- 
ments, 236, 237 ; early flowering 
of crossed, 293 

Phaseolus coccinem, 150 

multiflorus, 150 ; measurement, 

152; partially sterile, 168, 360; 
crossed and self-fertilised, 276 ; 
enrJy flowering of crossed, 293 ; 
seeds, 316 ; perforated by humble- 
bees, 433, 438 

Phaseolus vulgaris, 153; self-fertile, 
168, 367 ' 

Pisum sativum, 160 ; measurements, 
162 ; seldom intercross, 169 ; 
summary of experiments, 264. 
278; self-fertile, 367 

Plants, crossed, greater consti- 
tutional vigour, 285 

Plateau, M., on insects and arti- 
ficial flowers, 374, 375 

Pleroma, 364 



Polemoniacex, 182 

Pollen, relative fertility of flowers 
crossed from a distinct plant, or 
with their own, 320 ; difference 
of results in Xolana prostrata, 321 , 
323; crossed and self-fertilised 
plants, again crossed from a 
distinct plant and their own pol- 
len, 324 ; sterile with their own, 
330-338; semi self-sterile, 338- 
340; loss of, 377; number of 
grai'is in Dandelion and Pseony, 
377 ; in Lolium perenne, Plantago 
lanceolata, Scirpus lacustris, and 
Wistaria sinensis, 378 ; number 
necessary for fertilisation, 378 ; 
transported from flower to flower, 
379 ; prepotency, 393-401 ; abori- 
ginally the sole attraction to in- 
sects, 403 ; quantity produced by 
anemopliilous plants, 407 

Polyanthus, prepotency over cows- 
lip, 397-8 

Polygoneas, 228 

Posoqueriafragrans, 5, 393 

Potato, 389 

Poterium sanguisorba, 410 

Potts, heads of Anthornis melanura 
covered with pollen, 371 

Primrose, Chinese, 225 

Primula elatior, 425, 430 

grandiftora, 380 

mollis, 368 

officinalis, 380 

scotica, 3G2 

sinensis, 225, 279 ; measure- 
ments, 227; early flowering of 
crossed, 293, 296 

veris (var. officinalis'), 219 ; 

measurements, 221 ; result of 
experiments, 267, 268; early 
flowering of crossed, 293 ; seeds, 
317; self-fertility, 351; prepo- 
tency of dark red polyanthus, 
397-398 

Primulacex, 215 

Pringlea, 410 

Proteacete of Australia, 415 

Prunus amum, 40 f 

laurycerasus, 405 

Pteris aquilina, 4(6 



INDEX. 



485 



Radish, 395 

Ranunculaeex , 128 

Ranunculus acris, 365 

Raphanus sativus, 365, 395 

Re i nke, nectar-secreting glands of 
Prunus avium, 405 

Reseda lutea, 117; measurements, 
118, 119; result of experiments, 
339 ; self- fertile, 365 

odorata, 119; measurements, 

120-123 ; self-fertilised scarcely ex- 
ceeded by crossed, 289 ; seeds, 316 ; 
want of correspondence between 
seeds and vigour of offspring, 
328; result of experiments, 336; 
sterile and self-fertile, 358, 365 

Resedacese, 117 

Rheum rhaponticum, 403 

Rhexia glandulosa, 364 

Rhododendron, spontaneous cross- 
ing, 396 

Rhododendron aaaloides, 435 

Rhubarb, 396, 403 

Ribes aureum, 435 

Riley, Mr., pollen carried by wind, 
408; Yucca moth, 421 

Rimpan, on the cross-fertilisation 
of Kye, 341 ; on the self-fertility 
of wheat, 370 

Rodgers, Mr., secretion of nectar in 
Vanilla, 404 

Rye, experiment on pollen of, 377 



BCJ 
8ah, 



Salcia cocclnea, 93 ; measurements, 
93 ; early flowering of- crossed, 
292 ; seeds, 315, 322 ; partially 
self-sterile, 363 

glutinosa, 430 

Salvia graJiami, 429, 431, 436 

tenori, 362 

Barothamnus scoparius, 163; mea- 
surements, 165-167 ; superiority 
of crossed seedlings, 285, 289; 
seed-, 323; self-sterile, 360 



Scdbiosa atro-purpurea, 172; mea- 
surements, 172, 173 

ScarU t-runner, 150 

Scott, J., Papaver semniferum, 108; 
sterility of Verbascum, 330; On- 
cidium and Maxillaria, 331 ; on 
email seeds of Papaver, 355 ; on 
Primula scotica and Cortusa mat- 
thioli, 362 

Scrophulariac&e, 63 

Seeds, size and germination of, 352. 

SelagineUa, 413 

Self-fertile varieties, appearance of, 
347-351 

Self-fertilisation, mechanical struc- 
ture to check, 383 

Self-sterile plants, ?-29-347; wide 
distribution throughout the 
vegetable kingdom, 341 ; differ- 
ence in plants, 342; cause of 
self-sterility, 343; affected by 
changed conditions, 344-346 ; 
necessity of differentiation in the 
sexual elements, 317 

Senecio cruentus, 335, 364 

heritieri, 3 55 

maderensis, 335 

populifolius, 335 

tussilaginis, 335 

Sharp, Messrs., precautions against 
intercrossing, 396 

Snow-flake, 176 

Solanaceie, 188 

Solanum tuberosum, 362, 389 

Specularia perfoliata, 174 

speculum, 174 ; measurements, 

175, 176; crossed and self-ferti- 
lised, 276; early flowering of 
crossed, 293; seeds, 323; self- 
fertile, 369 

Spencer, Herbert, chemical affinity, 
462 

Spiranthes autumnalis, 391, 424 

Bprengel, C. K., fei tilisation of 
flowers by insects, 5, 6; Viola 
tricolor, 123 ; colours in flowers at- 
tract and suide insects, 372-374 ; 
on Arigtolochia, 41 9 ; Aconitum 
napellus, 431 ; importance of in- 
sects iii fertilising flowers, 460 

Staokys coccinea, 430, 431, 436 



486 



INDEX. 



Stellaria media, 367 

Strachey, General, perforated flowers 

in the Himalaya, 436 
Strawberry, 396 
Strelitzia fertilised by the Nectarini- 

dea?, 371 
Structure of plants adapted to cross 

and self fertilisation, 381 
Swale, Mr., garden lupine not visited 

by bees in New Zealand, 150 
Sweet-pi a, 153 



T. 



Tabernxmontana echinata, 331, 362 
Tables of mi asurements of heights, 

weights, and fertility of plants 

240-270 
Termites, imperfectly developed 

males and females, 382 
Thunbergia alata, 96, 277, 331 
Thyme, 421 
Tinzmaun, on Solanum tvherosum, 

362, 389 
Tobacco, 203 
Transmission of the good effects 

of a cross to later generations, 

303 

Trees, separated sexes, 414 
Trifolium arvense, 367, 386 

incarnatum, 361 
minus, 368 

pratense, 361, 429, 438 

procumbens, 368 

repens, 361 

Tropxolum minus, 144; measure- 
meuts, 145 ; early flowering of 
crossed, 293 ; seeds, 316, 323 

tricolor. 430 ; seeds, 323 

Tulips, 396 

Typha, 377, 408 



U. 

Umbelliferx, 172 

Urban. Ig., fertilisation of Medicago 
lupulina, 368 



V. 



Vandellia nummularifolia, 90, 278 
seeds, 315, 322 ; self-fertile, 369 

Vanilla, secretion of nectar, 404 

Verbascum lychnitis, 89, 341, 369 

niyrum, 89, 330, 341 

phceniceum, 330, 341, 364 

thapsus, 89 ; measurements, 

90; self-ferlile, 341,3ti9 

Verlot on Convolvulus tricolor, 55; 
intercrossing of Nemophila, 183 ; 
of Leptosiphon, 394 

Veronica agrestis, 369 

chamoedrys, 369 

hederxfolia, 36'J 

Viciafaba, 360, 405 

hirsute, 367 

sativa, 367, 405 

Victoria regia, 365 

Villarsia parnassifolia, 392 

Vilrnorin on transmitting character 
to offspring, 456 

Vinca major, 362 

rosea, 362 

Viola canina, 357 

tricolor, 123 ; measurements, 

126, 127; superiority of crossed 
plants, 286, 289; period of 
flowering, 292, 296; effects of 
cross-fertilisation, 304 ; seeds, 
316, 325 ; partially sterile, 358 ; 
corolla removed, 423 

Violacex, 123 

Viscaria oculata, 130; measure- 
ment, 132 ; average height of 
crossed and self-fertilised, 276; 
simultaneous flowering, 295 ; 
seeds, 316, 323 ; self-fertile, 367 



W. 

Wallace, Mr., the beaks and faces 
of brush-tongued lories covered 
with pollen, 371 

Wasps attracted by Epipactis lati- 
folia, 376 



INDEX. 



487 



WEIGHTS. 

Weights, relative, of crossed and 
self-fertilised plants, 244, 283; 
and period of germination of 
seeds, 352-355 

Wil.lcr, Mr., fertilisation of flowers 
with their own pollen, 841 

Wilson, A. J., superior vigour of 
crossed seedlings in Brassica 
campestris ruta baga, 353; self- 
fertility of wheat, 370, on size 
of pollen-grains, 378 

Wistaria sinensis, 378, 430 



Y. 



Yucca moth, 421 



Zea mat/8, 16, 233 ; measurements, 
16-18, 234 ; difference of height 
between crossed and self-fertilised, 
288 ; early flowering of crossed, 
293; self-fertile, 369; prepotency 
of other pollen, 3<J9 









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Darwin. 

The effects of cross and self 
fertilisation in the vegetable 
kingdom 



CALIFORNIA COLLEGE OF MEDICINE LIBRARY 

UNIVERSITY OF CALIFORNIA, IRVINE 

IRVINE, CALIFORNIA 92664