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Presented by
Dr. Pearl Oliphant

COLLEGE OF OSTEOPATHIC PHYSICIANS
AND SURGEONS • LOS ANGELES, CALIFORNIA

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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.

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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.

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.

VI.

VII.

VIII.

Crossed.

Self-fert.

Crossed.

Self-fert.

Crossed.

Self-fert.

Difference

Inches.

Pot I.

23|
12

17i

202

23 1
21

20 i

23 1
23 1

20 i
20

-*j

-31

l?i

-3

22 \

18|

-3J

22 i

181

Pot II.

19$

181

18|

18jj

21 1

1*1

18i

21 1

213

~3|

22 1

18|

-3

203

151

17 i

-8|

Pot III.

16|

20 1

l«j

-31

21I

16§

19|

16|

-2?

Pot IV.

23 §

21
22J

16§

18
12|

22J

151

18
18

18
12
12

15
15|
18

(M CO O
1 + +

15i

15|

til

CHAP. I.

INTRODUCTORY REMARKS.

" 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.

18?

19§

+o§

II.

20?

-13

III.

21 1

161

-*1

IV.

19|

~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.

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.

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.

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.

Inches.
87

Inche*.
67 1

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

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.

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.

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.

Inches.
84
47

Inches.
80
44J

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.

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 • 0 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.

Inches.
93
91

Inches.
50 i
65

II.

79
86 J
88

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.

Inches.
84 1
84f
761

Inches.

Si1

55 1

II.

8*1

90
82§

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.

Inches,
llli
127
130 J

Inches.
96
54
93 J

II.

97?
89 j

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 ;

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.

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 |

82 1
76 £

Crowded plants.

89 1
92 1

92J

67
741

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.')

No. of Pot.

Crossed Plants.

Self-fertilised Plants.

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.

TABLE XTL

No. of Pot.

Crossed Plants.

Self-fertilised Plants.

Inches.

77j

871

II.

78 3

86 3

65$

90 i

in.

61?

69 |

87|

IV.

803

73 1

88 i
8*3

663

76 i

77*

811

703

823

79|

553

VII.

84 1
79

?33

VIII.

763

80,

IX.

73 1

783
673

823

Crowded plants.

82
84|

36 f
693

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

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.

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$

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.

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.

Inches.
86 1
90|

Inches.
95 1
95|

II.

V7§

IIL

73
66
84j

86 §
82 1

70|

rv.

S1
51

66?

15i

78i

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

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.

86-00

65-66

as 100 to 76

Second generation .
Table II.

84-16

66-33

as 100 to 79

Third generation. . .
Table III.

77-41

52-83

is 100 to 68

Fourth generation
Table V.

69-78

60-14

as 100 to 86

Fifth generation .
Table VI.

82-54

62-33

as 100 to 75

Sixth generation .
Table VII.

87-50

63-16

as 100 to 72

Seventh generation .
Table VIII.

83-94

68-25

as 100 to 81

Eighth generation
Table IX.

113-25

96-65

as 100 to 85

Ninth generation . - - » J
Table X.

81-39 !

64-07

as 100 to 79

Tenth generation
Table XI.

93-70

50-40

as 100 to 54

All the ten generations'!
taken together . ./

85-84

66-02

is 100 to 77

CHAP. II.

SUMMARY OF OBSERVATIONS.

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.

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.

— 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 82 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.

Inches.
"1

Inches.
19J
18

II.

12 1

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|

10I
10

Inches
15|

!J!

II.

'?!
'?!

H3
*l

14|

in.

!?l

IV.

8 1
7|

Crowded.

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.

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.

Inches.
30 1
28i

Inches.
14
« 13g
131

Inches.
93

10J

II.

20 §
22|

llf

12§

•

23 1
24 1
25 1

12§

111
6|

IV.

22 1
22
17

9§
88

jj,

22§
19f
23|

9
11

£
13j

VI.

28|

178S
128

12
16|

VII.

12|
24 1
20 1
26 1

12|

VIII.

171

22 1
27

1*1

••

IX.

22|
6
20 i

'••'

Crowded Plants.

18i
168
17j

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,

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.

Inches.
17
9

Inches.
17
3J

II.

28 1
16|
13f

III.

4
2§

IS'

IV.

23 1
15|

133

VI.

VII.
Crowded.

21
H|
12*

Total inches.

210-88

140-75

CIIAP. III. FLOWERS ON SAME PLANT CROSSED.

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.

Inches.
12

104

Inches.
19 1
20 1
li|

II.

16 §

H§

191

17|

IIL

15
181

IV.

161

25f

22|

VI.

20 ii

27 1

191

VIL

ll8
13j

78«

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

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

DIGITALIS PUKPUREA.

CHAP. Ill

TABLE XXIIL

The tallest Flower-stem on each Plant measured : 0 means that
the Plant died before a Flower-stem was produced.

No. of Pot.

Crossed Plants.

Self-fertilised Plants.

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,

0
0

IV.

64j

37 |

23J
0

53
47 1
34f

0
0
0

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 : —

FLOWERS ON SAME PLANT CROSSED. CHAP. IIL

TABLE XXIV.
N.B. 0 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.

Inches.

46 1
43 §

Inches.
45 1
52
0

II.

881

47 1

III.

54J

46 1

IV.

32 J
0
43 1

41 1
29 1
37 1

46|
43

42 £

VI.

48 §
461

VII.

48 J
42

25
40|

VIII.

46|

39J

IX.
Crowded Plants.

46 1
0

361
ft

Crowded Plants.

46 j
35 j
24 j
41 i
17 1

4o'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

VANDELLIA NUMMULAKIFOLIA.
TABLE XXV.

CHAP. IIL

No. of Pot.

Crossed Plants.

Self-fertilised Plants
of the Second Gene-
ration.

Inches.
76

Inches.
53|

II.

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.

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*

Inches.
32 1
20

Inches.
25
18g

II.

32?
M|

20 1
19*

III.

29 1

25
18

Total inches.

167-13

127-00

* The admirable mechanical
adaptations in this genus for
favouring or ensuring cross-ferti-
li»ation, 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).

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 ; 0 signifies that a Flower-stem
was not formed.

No. of Pot.

Crossed Plants.

Self-fertilised Plants.

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.

Ounces.
130

Ounce*.
18]

II.

34?

III.

121

17J

IV.

127 1

11J

106 1

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.

Incnes.
18
21

Inches.
19
21

II.

19
17f

.1!

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 : 0 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.

17|

17f

20J

II.

20§

i5l

III.

19§

13 1

18ft

151

IV.

1*1

16|

185

144

178

15f

152

14 1

14?

18ft

161

15|

VI.

181

16i

18 j

151

VII.

181

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

Inches.
21

26|
16

II.

143

22
19|
21|

20
14
16

19|
13|
18

III.

20|
20 §
20 1

IV.

25 1
24J

23§
23

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

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.

Inches.
33 1

Inches.
25

II.

34|

III.

271

IV.

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 se1 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

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.

Inche
21
14
19

s.
\

Inche
12
16
11
15
19

beii

II.

20
17
23
17

;

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*.

I!1

16
161

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.

33 jj

27 1

III

28!

20|

29 .

21 i

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

30|

II.

30 J

III.

26 1
25 1

IV.

21 J

1*1

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

268

26§

27 j

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.

131

II.

21 §

26 f

25 1

30 1

IIL

IV.

20 1

32 1

24 1

31 1

30 2

36 1

24 1

31§

22 1

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.

28 §

22 i

25
25 i
29 1

23
g

27 i

22|

'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.

Inches.
81

Inches.
01

II.

5
4

6
4
3|

III.

•i

3|
83

IV.

4]
4]

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.

Inches.
Wj

Inches.
9f
8|

II.

131
10

9§
Hj

III.

14 1
13|

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.

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,' &cv

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.

Inches.
11

II.

19
161

16§
HI

III.

IV.

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.

Inches.
19
33
41
41

Inches.
32 3
38
38
281

II.

37 1
36 1
38

32 1
35|

III.

44|

39 1
39

36
20 1
30 1

IV.

30]

31
33J
24

36
39
29
38 1

Crowded.

30 1

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.

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.

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

28
0

34 1
241

VI.

32|
31

241
26

303
24j

VII.

341

29?

271
27

VIII.

29
0

2+6«

IX.

28 1

38
32J

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 0 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.

Inches.
1SJ

Inches.
16|

II.

III.

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.

Inches.
22 jj

19)

Inches.
25 1
12|

II.

121

19|

22i

HI.

30 1
18J

191
73

IV.

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.

Inches.
65
50

Inches.
31
45

II.

69
35

4-2
45

III.

59 1

50 1
55|

IV.

«1

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

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.

17 1

15 1

17 1

II.

i .

18J

III.

15 f

If]

IV.

13 j

121

18|

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.

Inches.
33 1
30
30

Inches.
24 1
18|
28

II.

29J

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.

Inches.
87
88
82 1

Inches.

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.

Inches.
80

Inches.
64|

II.

78 $

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.

Inches.
72J
71
52 1

Inches.
57 J
67
56§

II.

81 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.

Inches.
72
72

Inches.
65
61|

II.

58
68
72|

681
56 j

III.

60f

IV.

77,

76J

Total in inches. I 501

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.

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.

Inches.

II.

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.

ISB

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

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.

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.

Inches.
31

Inches.
37

II.

18|

20 1

IIL

l»l

40 1

IV.

25
36

35
153

31
16

18
"1

VI.

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.

Inches.
56

Inches.
38

Total in inche*.

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.

Inches.
14

Inches.
20

II.

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.

First generation,
planted in open
ground.

Inches.
27
25

Inches.
21 i

II.

Second generation,
planted in open
ground.

29|
17f

24
10
11

III.

Second generation,
kept in the pot.

14
10J

Total in inches.

136

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

Inches.
18

Inches.
15g

II.

IIL

22}

IV.

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.

Inches.
22 1

Inches.
17|

II.

27|

III.

IV.

22|

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.

Inches.
27 1

Inches.
18|

19|

IV.

Crowded.

21|

Total in inches.

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.

Inches.
33

Inches.
50

II.

36|

38|

III.

Not in full flower.

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.

Inches.

Inche
32
26
25
26

II.

34
26
25

36
28
30
32

III.

40 1
37 1
32J

30
28
23

IV.

34
32
29
27

29
28
26
25

28
27
25

29
24
23

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

•

„

19
16
19
Ii|

Total in inches. 1014-

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 ; 0 means that the plant died.

No. of -Pot.

Crossed Plants.

Self-fertilised Plants.

Inches.
32|

Inches.
21§

II.

8*1

23|

III.

331
22§
29

.?!

IV.

35 j
33j

35
38
36
37 1
32J

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 0 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.

Inches.
27
14

Inches.
27 1
34|

17|

24|

23
32

III.

IV.

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.

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.

Inches.

II.

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.

Inches.
30

Inches.
20*

II.

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.

Inches.
57 §
361

Inches.

11.

44|
24

II1

III.

0
0

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.

Inches.

4 1

II.

III.

IV.

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.

Inches.

« 1
48
36

Inches.
40 §
39
48

II.

36
21
36§

47
80?
86§

in.

IV.

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.

29 g

30 i

36§

34 f

31f

II.

33 1

31 1

37 i

38 f

38 1

HI.

46
671

54 §

23§

IV.

511

49 1

22 i

Crowded nlants.

46 1

24 §

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.

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

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).

Inches.
64 1
24
51 1

Inches.

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

43 J
53 Z
53|

35 1
34 f
54 §

41 1

2et

VI.

37 1

61
0

56
63 1
571

46 1
29 i
*\

VII.

59 1
43 1
50|

51
49 f
0

43
12|
0

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.

34|

27 §

36 1

36 §

35 1

39 jj

32 j

36^

41 1

40 1

37§

37 j

38 1

41 §

213

38 1

21§

366-

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.

Inches.

t5|

Inches.
26

Inches.
40

Inches.
44

II.

III.

13]

IV.
Crowded.

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.

Inches.
143

Inches.
27 f

5e88

II.

60 |

44f
10

50|

III.

5;t

87 (A)
S1|(B)

IV.

69|

431

99|
29 §

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.

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.

Inches.

Inches.
72|
1*1

II.

•?'

73
llOg

III.

99
151

106 g
73|

IV.

97 1

48 1

«,

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.

Inches.
84 f
31

Inches.

«J

Inches.

Inches.
56

II.

78$
48

II.

55 1

27 §

III.

77 §

77 1

121
«I

III.

76|

60 1

IV.

49 §
15 f

29 1
32

IV.

904
22f

89
17

85
N

941

28 1

VI.

90 80

VI.

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

TtL£} «••»

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.

42 1

22|

44|

22j

19|

42 1

304

14 1

27 1

23 j

151

26 £

13 i

13I

18§

24|

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.

22 f

54 1

34 J

37 1

51 1

38 1

40 1

43 §

28f

48 f

38 1

25 1

35 1

26 j

48§

39 1

22i

47 1

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 : 0 implies that no /lower-stem ivas produced.

No. of Pot.

Crossed Plants.

Self-fertilised Plants.

Inches.
10
91

101

Inches.
0
0

II.

101

0
0
0

III.

9J
9|
9i

8
61
«i

IV.

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.

Inches.
23 1
21
171

Inches.

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

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.

9
8

II.

7
6|

6
*|

III.

3
»l

IV. 7 jj

2|
2|

Total.

56-26

25-75

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.

163

II.

Several,
not
counted.

III.

leg

Totals.

26-0

206

22-0

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

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.

From short-styled
mother.

Inches.
»1

Inches.
8

II.
From short -styled
mother.

III.
From long-styled
mother.

ftj

IV.

From long-styled
mother.

V.
From illegitimate
short-styled
mother.

VI.

From illegitimate
short-styled
mother.

VII.

From illegitimate
long-styled mother.

VIII.
From {legitimate
long-styled mother.

10J

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.

Inches.
34f
30
338
34|

Inches.
36
801

321
32

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.

Inches.
23 j
12
21

Inches.
17|
20 1
20

II.

22
191

21|

191

18!

III.

22 J
20i
18§
21

23§

18|

I5i

16f
18
16|

IV.

21
22 J
23
12

18
12|

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.

Inches.

42§
39§

Inches.
41 §
45|

37
49 1
29
37

31
37
42
34

IIL

37 §

II1

28
28
34

IV.

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.

34 i

35 g

31J

35,

31 1

35 J

33 1

34§

34,

Ttadb(£} 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 .

S3«

T7T

I .

a"S

if J

«B|

-1

°1J

NAMES OF PLANTS.

•s!

•15

•E.e-
"5 *" S'o"

1 Number
1 lised PI

Average
fertilised

III!

Ipomoea purpurea — 1st generation

86-00

65-66

as 100 to 76

Ipomoea purpurea — 2nd generation

84-16

66-33

„ n 79

Ipomoea purpurea — 3rd generation

77-41

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

93-70

50-40

the plants of the ten genera-

85-84

66-02

» >» 77

tions .

Mimulus luteus — three first gene-

rations, before the new and taller

8-19

5-29

» it 65

self-fertilised variety appeared

Digitalis purpurea .

51-33

35 -.87

Calceolaria — (common greenhouse}
varietv^ 1

19-50

15-00

„ „ 77

Linaria vulgaris . ...

7-08

5-75

n » 81

Verbascum thapsus . . . .

65-34

56-50

» » 86

Vandellia nummularifolia — crossed )

and self-fertilised plants, raised |

4-30

4-27

from perfect flowers . . . . J

Vandellia nummularifolia — crossed

and self-fertilised plants, raised
from perfect flowers : second

3-60

3-38

» » 94

trial, plants crowded . . .

Vandellia nummularifolia — crossed \

plants raised from perfect flowers, 1
and self-fertilised plants fromj

4-30

4-06

„ „ 34

cleistogene flowers . . . . J
Gesneria pendulina

32 • 06

29-14

Salvia coccinea

27*85

21-16

Origanum vulgaro

20-00

17-12

Thnnbergia alata

60-00

65-00

it 108

41-08

39-00

» » 95

Iberis umbellata— the self-fertilised \

plants of the 3rd generation . /

19-12]

16-39

n > °*

CHAP. VII. SUMMARY OF MEASUREMENTS.

TABLE A — continued.

241

!,:

I'S|

N » MBS OF PLANTS.

r the Cro<
measured.

ight of Crc
in inches.

the Se!f-f
its measure

°1

«3

ftl

,2 o d 2

til!
Jell

Papaver vagum

21-91

19*54

as 100 to 89

Eschscholtzia californica — English}
stock, 1st generation . . . /

29-68

25-56

» ii 86

Eschscholtzia californica — English "1
stock, 2nd generation . . ./

32-47

32-81

„ „ 101

Eschscholtzia californica — Bra-}
zilian stock, 1st generation . . /

44-64

45-12

,, „ 101

Eschscholtzia californica — Bra-
zilian stock, 2nd generation. .

43-38

50-30

,, ,, H6

Eschschjltzia californica — average

height and number of all the

40-03

42-72

ii ii 107

plants of Eschscholtzia . . .

Re.->eda lutea — grown in pots .

17-17

14-61

„ ,, 85

Reseda lutea — grown in open ground

28-09

23-14

" ,, 82

Reseda odorata — self - fertilised

seeds from a highly self-fertile

27-48

22-55

„ „ 82

plant, grown in pots. . .
Reseda odorata — self -fertilised

seeds from a highly self-fertile

25-76

27-09

„ „ 105

plant, grown in open ground .
Reseda odorata — self- fertilised

seeds from a semi-self-sterile

29-98

27-71

ii ii 92

plant, grown in pots. . . .

Reseda odorata — self -fertilised

seeds from a semi-self-steril«

25-92

23-54

,, „ 90

plant, grown in open ground .
Viola tricolor .

5-58

2-37

\donis sostivalis • . . •

14-25

14-31

ii ii *^

100

Delphinium consolida ....

14-95

12-50

;; ;; 84

Viscaria oculata . . .

34-50

33-55

„ » 97

Dianthus caryophyllus — opeu^
ground, about . . . . • \

28?

24?

,, ,, 86

Dianthus caryophyllus — 2nd gen-1
eration, in pots, crowded . . J

16-75

9-75

,, „ 58

Dianthus caryophyllus — 3rd gen-1
eration, in pots j

28-39

28-21

„ „ 99

Dianthus caryophyllus— offspring^

from plants of the 3rd self- ferti-

lised generation crossed by inter- 1
crossed plants of 3rd generation,

28-00

26-55

>i » 95

compared with plants of 4th self-
fertilised generation ....

242

SUMMABY OF MEASUREMENTS.
TABLE A — continued.

CHAP. VII.

£4

j§d|

•

$•§

~<I §

o °°

~ a

<*--S

*g j£ <2

° 1-

•gl

& g

°.s

5?*.§

NAMES OF PLANTS.

"iS

ifii

1 Number <
lised Pli

Dianthus caryophyllus — number!

and average height of all the
plants of Dianthus . . . . j

27-37

25-18

as 100 to 92

Hibiscus africanus

13-25

14-43

109

Pelargonium zonale ....

22-35

16-62

" " 74

Tropsjolum minus .....

58-43

46-00

Limnanthes douglasii ....

17-46

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 ....

86-00

82-35

„ „ 96

Pisum sativum .....

34-62

39-68

115

Sarothamnus scoparius — small}
seedlings . . . , J

2-91

1-33

Sarothamnus scoparius — the three!

survivors on each side after three >

18-91

11-83

» „ 63

years' growth )

Ononis minutissima ....

19-81

17-37

» „ 88

Clarkia elegans ......

33-50

27-62

Bartonia aurea

24-62

26-31

107

Passiflora gracilis .....

49-00

51-00

" '^ 104

Apium petroselinum ....

not

not
measured.

[ „ „ 100

Scabiosa atro-purpurea ....

17-12

15-37

» M 90

Lactuca sativa — plants of two gen-}
erations j

19-43

16-00

„ „ 82

Specularia speculum ....

19-28

18-93

» it 98

Lobelia ramosa — 1st generation .

22-25

18-37

» >i 82

Lobelia ramosa — 2nd generation .

23-33

19-00

» it 81

Lobelia fulgens — 1st generation .

34-75

44-25

>, '» 127

Lobelia fulgens — 2nd generation .

29-82

27-10

„ „ 91

Nemophila insignis — half-grown .
Nemophila insignis — the same fully j
grown ... . . . . /

11-10
33-28

5-45
19-90

i> „ 60

Borago officinalis •

20-68

21-18

102

\olana prostrata .....

12-75

13-40

Petunia violacea — 1st generation .

30-80

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

•5*

{111

Petunia Yiolacea — 4th generation,)
from a distinct parent . . ,J

44-74

26-87

as 100 to 60

Petunia violacea — 5th generation .

54-11

33-23

„ „ 61

Petunia violacea — 5th generation,)
in open ground . . . . . 1

38-27

23-31

» » 61

Petunia violacea — Number and j

average height of all the plants

46-53

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

7
7

32-75
51-78
79-60

" " 96
83

Nicotiana tabacum — 3rd generation}
but raised from a distinct plant J

70-78

71-30

„ ,, 101

Nicotiana tabacum — number and

average height of all the plants

63-73

61-31

i ii

of Nicotiana • .

Cyclamen persicum

9-49

7-50

»> „ 79

\nacpallis collina .....

42-20

33-35

Primula sinensis — a dimorphic
species •

9-01

9-03

„ „ 100

Fagopyrnm esculentum — a dimor-
phic species

'38-06

26-13

„ » 69

Beta vulgaris — in pots.

34-09

29-81

i, » 87

Beta vulgaris — in open ground

30-92

30-70

„ » 99

Canna warscewiczi — plants of three'
venerations .

35-98

36-39

„ 101

Zea mays — in pots, whilst young,'
measured to tips of leaves .

20-19

17-57

„ „ 87

Zea mays — when full grown, after

the death of some, measured to

68-10

62-34

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 .

54-00

44-55

» .1 83

Zea mays — grown in open ground,'
measured to tips of flowers .

53-96

43-45

» » 80

Phalaris canariensis — in pots . .

38-90

35-69

» ii 92

Phalaris canariensis — in open ground

35-78

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

as 100 to 44

Vandellia nummularifolia — 1st genera- \
tion J

„ „ 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

» » 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

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.

£11

If*

|l|

NAMES OF PLANTS AND NATURE

J B .

"t fcn

OF THE EXPERIMENTS.

ill

*a'V-'CQ

ill

Ipomoea purpurea — offspring of\
plants intercrossed for nine gen-

erations and then crossed by a|
fresh stock, compared withj

84-03

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 >

21-62

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

21-62

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

,m Self-
Parents J

flj

HAMES OF PLANTS AND NATURE

III

OF THE EXPERIMENTS.

!«!

III

ill

+f V 3

•<

i*»

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

17-34

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-

• •

fertilised offspring of the English

variety, in fertility ....

Eschscholtziacalifornica — offspring1)

of a Brazilian stock crossed byl

an English stock, compared with>

45-92

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,'

f|3

"a"?

!«j

NAMES OF PLANTS AND NATURE
OF THE EXPERIMENTS.

of the Plan
with a Fresh

III

Average

ji!

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

45-92

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

32-82

26-55

>» »• 81

plants of the 4th self-fertilised

generation, • • . •)

Dianthus caryophyllus — offspring1)
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 0— continued.

sSo

•I

ill

NAMES OF PLANTS AND NATURE
OF THE EXPERIMENTS.

•S

III

Number
Cross

f«i 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

32-82

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-

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

79-25

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

62-91

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

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

50-05

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,

36-67

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 . .

50-05

54-11

„ „ 108

250 SUMMARY OF MEASUREMENTS.

TABLE C — continued.

CHAP. VII.

1
1

fromSelf-
a Parent*

1
1

a
c •**

|i|

NAMES OF PLANTS AND NATURE

P£

OF THE EXPERIMENTS.

~ja

•§jS

jll

|f|

1 Number of
Cross wit

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-

33-67

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 .

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

63-29

41-67

„ 66

self-fertilised generation, grown

not much crowded in pots, in

height ... . J

CHAP. VII.

SUMMARY OF MEASUREMENTS.

251

TABLE C — continued.

ti;

jjS

1*!

AMES OF PLANTS AND NATURE

'II

'as

1-a

3J|

OF T11E EXPERIMENTS.

SI?

III

•sf

£s£

«
jjj

|?fl

Nicotiana tabacum — offspring oft

plants self-fertilised for three

generations and then crossed by!

a slightly different variety, com->

31-53

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-

48-74

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-

27-62

18 21

»i n ®&

fertilised offspring of the red

252 SUMMARY OF MEASUREMENTS.

TABLE C— continued.

CHAI-. VIL

NAMES OF PLANTS AND NATURE

511

OF THE EXPERIMENTS.

•Sfe

**i

111

lie

&
t

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

7-03

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

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

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

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

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

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

» » 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|

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

plants belong to the 9th generation ....

ESCHSCHOLTZIA CALIFORNIA — the intercrossed and \
self-fertilised plants belong to the 2nd generation/

100

DIANTHUS CARYOPHYLLUS — the intercrossed plants

are derived from self-fertilised of the 3rd ge-

neration, crossed by intercrossed plants of the

100

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

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

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 0 • 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

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

110

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

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 • 0 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) S66 my 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*) . ££t£L^-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.
t»r 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

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.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

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),
314—319; 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

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

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; belf-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

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

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

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

Umbelliferx, 172

Urban. Ig., fertilisation of Medicago
lupulina, 368

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

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

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

3 1970008483700

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1900
Darwin.

The effects of cross and self
fertilisation in the vegetable
kingdom

CALIFORNIA COLLEGE OF MEDICINE LIBRARY

UNIVERSITY OF CALIFORNIA, IRVINE

IRVINE, CALIFORNIA 92664

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