CHAPTER 2.XVIII.

ON THE ADVANTAGES AND DISADVANTAGES OF CHANGED CONDITIONS OF LIFE: STERILITY

FROM VARIOUS CAUSES.

ON THE GOOD DERIVED FROM SLIGHT CHANGES IN THE CONDITIONS OF LIFE.

STERILITY FROM CHANGED CONDITIONS, IN ANIMALS, IN THEIR NATIVE COUNTRY AND IN

MENAGERIES.

MAMMALS, BIRDS, AND INSECTS.

LOSS OF SECONDARY SEXUAL CHARACTERS AND OF INSTINCTS.

CAUSES OF STERILITY.

STERILITY OF DOMESTICATED ANIMALS FROM CHANGED CONDITIONS.

SEXUAL INCOMPATIBILITY OF INDIVIDUAL ANIMALS.

STERILITY OF PLANTS FROM CHANGED CONDITIONS OF LIFE.

CONTABESCENCE OF THE ANTHERS.

MONSTROSITIES AS A CAUSE OF STERILITY.

DOUBLE FLOWERS.

SEEDLESS FRUIT.

STERILITY FROM THE EXCESSIVE DEVELOPMENT OF THE ORGANS OF VEGETATION.

FROM LONG-CONTINUED PROPAGATION BY BUDS.

INCIPIENT STERILITY THE PRIMARY CAUSE OF DOUBLE FLOWERS AND SEEDLESS FRUIT.

ON THE GOOD DERIVED FROM SLIGHT CHANGES IN THE CONDITIONS OF LIFE.

In considering whether any facts were known which might throw light on the

conclusion arrived at in the last chapter, namely, that benefits ensue from

crossing, and that it is a law of nature that all organic beings should

occasionally cross, it appeared to me probable that the good derived from

slight changes in the conditions of life, from being an analogous phenomenon,

might serve this purpose. No two individuals, and still less no two varieties,

are absolutely alike in constitution and structure; and when the germ of one

is fertilised by the male element of another, we may believe that it is acted

on in a somewhat similar manner as an individual when exposed to slightly

changed conditions. Now, every one must have observed the remarkable influence

on convalescents of a change of residence, and no medical man doubts the truth

of this fact. Small farmers who hold but little land are convinced that their

cattle derive great benefit from a change of pasture. In the case of plants,

the evidence is strong that a great advantage is derived from exchanging

seeds, tubers, bulbs, and cuttings from one soil or place to another as

different as possible.

[The belief that plants are thus benefited, whether or not well founded, has

been firmly maintained from the time of Columella, who wrote shortly after the

Christian era, to the present day; and it now prevails in England, France, and

Germany. (18/1. For England see below. For Germany see Metzger 'Getreidearten'

1841 s. 63. For France Loiseleur-Deslongchamps ('Consid. sur les Cereales'

1843 page 200) gives numerous references on this subject. For Southern France

see Godron 'Florula Juvenalis' 1854 page 28.) A sagacious observer, Bradley,

writing in 1724 (18/2. 'A General Treatise of Husbandry' volume 3 page 58.),

says, "When we once become Masters of a good Sort of Seed, we should at least

put it into Two or Three Hands, where the Soils and Situations are as

different as possible; and every Year the Parties should change with one

another; by which Means, I find the Goodness of the Seed will be maintained

for several Years. For Want of this Use many Farmers have failed in their

Crops and been great Losers." He then gives his own practical experience on

this head. A modern writer (18/3. 'Gardener's Chronicle and Agricult. Gazette'

1858 page 247; and for the second statement, Ibid 1850 page 702. On this same

subject see also Rev. D. Walker 'Prize Essay of Highland Agricult. Soc.'

volume 2 page 200. Also Marshall 'Minutes of Agriculture' November 1775.)

asserts, "Nothing can be more clearly established in agriculture than that the

continual growth of any one variety in the same district makes it liable to

deterioration either in quality or quantity." Another writer states that he

sowed close together in the same field two lots of wheat-seed, the product of

the same original stock, one of which had been grown on the same land and the

other at a distance, and the difference in favour of the crop from the latter

seed was remarkable. A gentleman in Surrey who has long made it his business

to raise wheat to sell for seed, and who has constantly realised in the market

higher prices than others, assures me that he finds it indispensable

continually to change his seed; and that for this purpose he keeps two farms

differing much in soil and elevation.

With respect to the tubers of the potato, I find that at the present day the

practice of exchanging sets is almost everywhere followed. The great growers

of potatoes in Lancashire formerly used to get tubers from Scotland, but they

found that "a change from the moss-lands, and vice versa, was generally

sufficient." In former times in France the crop of potatoes in the Vosges had

become reduced in the course of fifty or sixty years in the proportion from

120-150 to 30-40 bushels; and the famous Oberlin attributed the surprising

good which he effected in large part to changing the sets. (18/4. Oberlin

'Memoirs' English translation page 73. For Lancashire see Marshall 'Review of

Reports' 1808 page 295.)

A well-known practical gardener, Mr. Robson (18/5. 'Cottage Gardener' 1856

page 186. For Mr. Robson's subsequent statements see 'Journal of Horticulture'

February 18, 1866 page 121. For Mr. Abbey's remarks on grafting etc. Ibid July

18, 1865 page 44.) positively states that he has himself witnessed decided

advantage from obtaining bulbs of the onion, tubers of the potato, and various

seeds, all of the same kind, from different soils and distant parts of

England. He further states that with plants propagated by cuttings, as with

the Pelargonium, and especially the Dahlia, manifest advantage is derived from

getting plants of the same variety, which have been cultivated in another

place; or, "where the extent of the place allows, to take cuttings from one

description of soil to plant on another, so as to afford the change that seems

so necessary to the well-being of the plants." He maintains that after a time

an exchange of this nature is "forced on the grower, whether he be prepared

for it or not." Similar remarks have been made by another excellent gardener,

Mr. Fish, namely, that cuttings of the same variety of Calceolaria, which he

obtained from a neighbour, "showed much greater vigour than some of his own

that were "treated in exactly the same manner," and he attributed this solely

to his own plants having become "to a certain extent worn out or tired of

their quarters." Something of this kind apparently occurs in grafting and

budding fruit-trees; for, according to Mr. Abbey, grafts or buds generally

take with greater facility on a distinct variety or even species, or on a

stock previously grafted, than on stocks raised from seeds of the variety

which is to be grafted; and he believes this cannot be altogether explained by

the stocks in question being better adapted to the soil and climate of the

place. It should, however, be added, that varieties grafted or budded on very

distinct kinds, though they may take more readily and grow at first more

vigorously than when grafted on closely allied stocks, afterwards often become

unhealthy.

I have studied M. Tessier's careful and elaborate experiments (18/6. 'Mem. de

l'Acad. des Sciences' 1790 page 209.) made to disprove the common belief that

good is derived from a change of seed; and he certainly shows that the same

seed may with care be cultivated on the same farm (it is not stated whether on

exactly the same soil) for ten consecutive years without loss. Another

excellent observer, Colonel Le Couteur (18/7. 'On the Varieties of Wheat' page

52.) has come to the same conclusion; but then he expressly adds, if the same

seed be used, "that which is grown on land manured from the mixen one year

becomes seed for land prepared with lime, and that again becomes seed for land

dressed with ashes, then for land dressed with mixed manure, and so on." But

this in effect is a systematic exchange of seed, within the limits of the same

farm.]

On the whole the belief, which has long been held by many cultivators, that

good follows from exchanging seed, tubers, etc., seems to be fairly well

founded. It seems hardly credible that the advantage thus derived can be due

to the seeds, especially if very small ones, obtaining in one soil some

chemical element deficient in the other and in sufficient quantity to

influence the whole after-growth of the plant. As plants after once

germinating are fixed to the same spot, it might have been anticipated that

they would show the good effects of a change more plainly than do animals

which continually wander about; and this apparently is the case. Life

depending on, or consisting in, an incessant play of the most complex forces,

it would appear that their action is in some way stimulated by slight changes

in the circumstances to which each organism is exposed. All forces throughout

nature, as Mr. Herbert Spencer (18/8. Mr. Spencer has fully and ably discussed

this whole subject in his 'Principles of Biology' 1864 volume 2 chapter 10. In

the first edition of my 'Origin of Species' 1859 page 267, I spoke of the good

effects from slight changes in the conditions of life and from cross-breeding,

and of the evil effects from great changes in the conditions and from crossing

widely distinct forms, as a series of facts "connected together by some common

but unknown bond, which is essentially related to the principle of life.)

remarks, tend towards an equilibrium, and for the life of each organism it is

necessary that this tendency should be checked. These views and the foregoing

facts probably throw light, on the one hand, on the good effects of crossing

the breed, for the germ will be thus slightly modified or acted on by new

forces; and on the other hand, on the evil effects of close interbreeding

prolonged during many generations, during which the germ will be acted on by a

male having almost identically the same constitution.

STERILITY FROM CHANGED CONDITIONS OF LIFE.

I will now attempt to show that animals and plants, when removed from their

natural conditions, are often rendered in some degree infertile or completely

barren; and this occurs even when the conditions have not been greatly

changed. This conclusion is not necessarily opposed to that at which we have

just arrived, namely, that lesser changes of other kinds are advantageous to

organic beings. Our present subject is of some importance, from having an

intimate connection with the causes of variability. Indirectly it perhaps

bears on the sterility of species when crossed: for as, on the one hand,

slight changes in the conditions of life are favourable to plants and animals,

and the crossing of varieties adds to the size, vigour, and fertility of their

offspring; so, on the other hand, certain other changes in the conditions of

life cause sterility; and as this likewise ensues from crossing much-modified

forms or species, we have a parallel and double series of facts, which

apparently stand in close relation to each other.

It is notorious that many animals, though perfectly tamed, refuse to breed in

captivity. Isidore Geoffroy St.-Hilaire (18/9. 'Essais de Zoologie Generale'

1841 page 256. ) consequently has drawn a broad distinction between tamed

animals which will not breed under captivity, and truly domesticated animals

which breed freely--generally more freely, as shown in the sixteenth chapter,

than in a state of nature. It is possible and generally easy to tame most

animals; but experience has shown that it is difficult to get them to breed

regularly, or even at all. I shall discuss this subject in detail; but will

give only those cases which seem most illustrative. My materials are derived

from notices scattered through various works, and especially from a Report,

kindly drawn up for me by the officers of the Zoological Society of London,

which has especial value, as it records all the cases, during nine years from

1838-46, in which the animals were seen to couple but produced no offspring,

as well as the cases in which they never, as far as known, coupled. This MS.

Report I have corrected by the annual Reports subsequently published up to the

year 1865. (18/10. Since the appearance of the first edition of this work, Mr.

Sclater has published ('Proc. Zoolog. Soc.' 1868 page 623) a list of the

species of mammals which have bred in the gardens from 1848 to 1867 inclusive.

Of the Artiodactyla 85 species have been kept, and of these 1 species in 1.9

have bred at least once during the 20 years; of 28 Marsupialia, 1 in 2.5 have

bred; of 74 Carnivora, 1 in 3.0 have bred; of 52 Rodentia, 1 in 4.7 have bred;

and of Quadrumana 75 species have been kept, and 1 in 6.2 have bred.) Many

facts are given on the breeding of the animals in that magnificent work,

'Gleanings from the Menageries of Knowsley Hall' by Dr. Gray. I made, also,

particular inquiries from the experienced keeper of the birds in the old

Surrey Zoological Gardens. I should premise that a slight change in the

treatment of animals sometimes makes a great difference in their fertility;

and it is probable that the results observed in different menageries would

differ. Indeed, some animals in our Zoological Gardens have become more

productive since the year 1846. It is, also, manifest from F. Cuvier's account

of the Jardin des Plantes (18/11. Du Rut 'Annales du Museum' 1807 tome 9 page

120.) that the animals formerly bred much less freely there than with us; for

instance, in the Duck tribe, which is highly prolific, only one species had at

that period produced young.

[The most remarkable cases, however, are afforded by animals kept in their

native country, which, though perfectly tamed, quite healthy, and allowed some

freedom, are absolutely incapable of breeding. Rengger (18/12. 'Saugethiere

von Paraguay' 1830 s. 49, 106, 118, 124, 201, 208, 249, 265, 327.), who in

Paraguay particularly attended to this subject, specifies six quadrupeds in

this condition; and he mentions two or three others which most rarely breed.

Mr. Bates, in his admirable work on the Amazons, strongly insists on similar

cases (18/13. 'The Naturalist on the Amazons' 1863 volume 1 pages 99, 193;

volume 2 page 113.); and he remarks, that the fact of thoroughly tamed native

mammals and birds not breeding when kept by the Indians, cannot be wholly

accounted for by their negligence or indifference, for the turkey and fowl are

kept and bred by various remote tribes. In almost every part of the world--for

instance, in the interior of Africa, and in several of the Polynesian islands

--the natives are extremely fond of taming the indigenous quadrupeds and

birds; but they rarely or never succeed in getting them to breed.

The most notorious case of an animal not breeding in captivity is that of the

elephant. Elephants are kept in large numbers in their native Indian home,

live to old age, and are vigorous enough for the severest labour; yet, with a

very few exceptions, they have never been known even to couple, though both

males and females have their proper periodical seasons. If, however, we

proceed a little eastward to Ava, we hear from Mr. Crawfurd (18/14. 'Embassy

to the Court of Ava' volume 1 page 534.) that their "breeding in the domestic

state, or at least in the half-domestic state in which the female elephants

are generally kept, is of everyday occurrence;" and Mr. Crawfurd informs me

that he believes that the difference must be attributed solely to the females

being allowed to roam the forest with some degree of freedom. The captive

rhinoceros, on the other hand, seems from Bishop Heber's account (18/15.

'Journal' volume 1 page 213.) to breed in India far more readily than the

elephant. Four wild species of the horse genus have bred in Europe, though

here exposed to a great change in their natural habits of life; but the

species have generally been crossed one with another. Most of the members of

the pig family breed readily in our menageries; even the Red River hog

(Potamochoerus penicillatus), from the sweltering plains of West Africa, has

bred twice in the Zoological Gardens. Here also the Peccary (Dicotyles

torquatus) has bred several times; but another species, the D. labiatus,

though rendered so tame as to be half-domesticated, is said to breed so rarely

in its native country of Paraguay, that according to Rengger (18/16.

'Saugethiere' s. 327.) the fact requires confirmation. Mr. Bates remarks that

the tapir, though often kept tame in Amazonia by the Indians, never breeds.

Ruminants generally breed quite freely in England, though brought from widely

different climates, as may be seen in the Annual Reports of the Zoological

Gardens, and in the Gleanings from Lord Derby's menagerie.

The Carnivora, with the exception of the Plantigrade division, breed (though

with capricious exceptions) about half as freely as ruminants. Many species of

Felidae have bred in various menageries, although imported from diverse

climates and closely confined. Mr. Bartlett, the present superintendent of the

Zoological Gardens (18/17. On the Breeding of the Larger Felidae 'Proc.

Zoolog. Soc.' 1861 page 140.) remarks that the lion appears to breed more

frequently and to bring forth more young at a birth than any other species of

the family. He adds that the tiger has rarely bred; "but there are several

well-authenticated instances of the female tiger breeding with the lion."

Strange as the fact may appear, many animals under confinement unite with

distinct species and produce hybrids quite as freely as, or even more freely

than, with their own species. On inquiring from Dr. Falconer and others, it

appears that the tiger when confined in India does not breed, though it has

been known to couple. The chetah (Felis jubata) has never been known by Mr.

Bartlett to breed in England, but it has bred at Frankfort; nor does it breed

in India, where it is kept in large numbers for hunting; but no pains would be

taken to make them breed, as only those animals which have hunted for

themselves in a state of nature are serviceable and worth training. (18/18.

Sleeman's 'Rambles in India' volume 2 page 10.) According to Rengger, two

species of wild cats in Paraguay, though thoroughly tamed, have never bred.

Although so many of the Felidae breed readily in the Zoological Gardens, yet

conception by no means always follows union: in the nine-year Report, various

species are specified which were observed to couple seventy-three times, and

no doubt this must have passed many times unnoticed; yet from the seventy-

three unions only fifteen births ensued. The Carnivora in the Zoological

Gardens were formerly less freely exposed to the air and cold than at present,

and this change of treatment, as I was assured by the former superintendent,

Mr. Miller, greatly increased their fertility. Mr. Bartlett, and there cannot

be a more capable judge, says, "it is remarkable that lions breed more freely

in travelling collections than in the Zoological Gardens; probably the

constant excitement and irritation produced by moving from place to place, or

change of air, may have considerable influence in the matter."

Many members of the Dog family breed readily when confined. The Dhole is one

of the most untamable animals in India, yet a pair kept there by Dr. Falconer

produced young. Foxes, on the other hand, rarely breed, and I have never heard

of such an occurrence with the European fox: the silver fox of North America

(Canis argentatus), however, has bred several times in the Zoological Gardens.

Even the otter has bred there. Every one knows how readily the semi-

domesticated ferret breeds, though shut up in miserably small cages; but other

species of Viverra and Paradoxurus absolutely refuse to breed in the

Zoological Gardens. The Genetta has bred both here and in the Jardin des

Plantes, and produced hybrids. The Herpestes fasciatus has likewise bred; but

I was formerly assured that the H. griseus, though many were kept in the

Gardens, never bred.

The Plantigrade Carnivora breed under confinement much less freely than other

Carnivora, although no reason can be assigned for this fact. In the nine-year

Report it is stated that the bears had been seen in the Zoological Gardens to

couple freely, but previously to 1848 had most rarely conceived. In the

Reports published since this date three species have produced young (hybrids

in one case), and, wonderful to relate, the white Polar bear has produced

young. The badger (Meles taxus) has bred several times in the Gardens; but I

have not heard of this occurring elsewhere in England, and the event must be

very rare, for an instance in Germany has been thought worth recording.

(18/19. Wiegmann 'Archiv. fur Naturgesch.' 1837 s. 162.) In Paraguay the

native Nasua, though kept in pairs during many years and perfectly tamed, has

never been known, according to Rengger, to breed or show any sexual passion;

nor, as I hear from Mr. Bates, does this animal, or the Cercoleptes, breed in

Amazonia. Two other plantigrade genera, Procyon and Gulo, though often kept

tame in Paraguay, never breed there. In the Zoological Gardens species of

Nasua and Procyon have been seen to couple; but they did not produce young.

As domesticated rabbits, guinea-pigs, and white mice breed so abundantly when

closely confined under various climates, it might have been thought that most

other members of the Rodent order would have bred in captivity, but this is

not the case. It deserves notice, as showing how the capacity to breed

sometimes goes by affinity, that the one native rodent of Paraguay, which

there breeds FREELY and has yielded successive generations, is the Cavia

aperea; and this animal is so closely allied to the guinea-pig, that it has

been erroneously thought to be the parent form. (18/20. Rengger 'Saugethiere'

etc. s. 276. On the parentage of the guinea-pig, see also Isid. Geoffroy St.-

Hilaire 'Hist. Nat. Gen.' I sent to Mr. H. Denny of Leeds the lice which I

collected from the wild aperea in La Plata, and he informs me that they belong

to a genus distinct from those found on the guinea-pig. This is important

evidence that the aperea is not the parent of the guinea-pig; and is worth

giving, as some authors erroneously suppose that the guinea-pig since being

domesticated has become sterile when crossed with the aperea.) In the

Zoological Gardens, some rodents have coupled, but have never produced young;

some have neither coupled nor bred; but a few have bred, as the porcupine more

than once, the Barbary mouse, lemming, chinchilla, and agouti (Dasyprocta

aguti) several times. This latter animal has also produced young in Paraguay,

though they were born dead and ill-formed; but in Amazonia, according to Mr.

Bates, it never breeds, though often kept tame about the houses. Nor does the

paca (Coelogenys paca) breed there. The common hare when confined has, I

believe, never bred in Europe; though, according to a recent statement, it has

crossed with the rabbit. (18/21. Although the existence of the Leporides, as

described by Dr. Broca ('Journal de Phys.' tome 2 page 370), has been

positively denied, yet Dr. Pigeaux ('Annals and Mag. of Nat. Hist.' volume 20

1867 page 75) affirms that the hare and rabbit have produced hybrids.) I have

never heard of the dormouse breeding in confinement. But squirrels offer a

more curious case: with one exception, no species has bred in the Zoological

Gardens, yet as many as fourteen individuals of S. palmarum were kept together

during several years. The S. cinera has been seen to couple, but it did not

produce young; nor has this species, when rendered extremely tame in its

native country, North America, been ever known to breed. (18/22. 'Quadrupeds

of North America' by Audubon and Bachman 1846 page 268.) At Lord Derby's

menagerie squirrels of many kinds were kept in numbers, but Mr. Thompson, the

superintendent, told me that none had ever bred there, or elsewhere as far as

he knew. I have never heard of the English squirrel breeding in confinement.

But the species which has bred more than once in the Zoological Gardens is the

one which perhaps might have been least expected, namely, the flying squirrel

(Sciuropterus volucella): it has, also, bred several times near Birmingham;

but the female never produced more than two young at a birth, whereas in its

native American home she bears from three to six young. (18/23. Loudon's 'Mag.

of Nat. Hist.' volume 9 1836 page 571; Audubon and Bachman 'Quadrupeds of

North America' page 221.)

Monkeys, in the nine-year Report from the Zoological Gardens, are stated to

unite most freely, but during this period, though many individuals were kept,

there were only seven births. I have heard of only one American monkey, the

Ouistiti, breeding in Europe. (18/24. Flourens 'De l'Instinct' etc. 1845 page

88.) A Macacus, according to Flourens, bred in Paris; and more than one

species of this genus has produced young in London, especially the Macacus

rhesus, which everywhere shows a special capacity to breed under confinement.

Hybrids have been produced both in Paris and London from this same genus. The

Arabian baboon, or Cynocephalus hamadryas (18/25. See 'Annual Reports Zoolog.

Soc.' 1855, 1858, 1863, 1864; 'Times' newspaper August 10, 1847; Flourens 'De

l'Instinct' page 85.), and a Cercopithecus have bred in the Zoological

Gardens, and the latter species at the Duke of Northumberland's. Several

members of the family of Lemurs have produced hybrids in the Zoological

Gardens. It is much more remarkable that monkeys very rarely breed when

confined in their native country; thus the Cay (Cebus azara) is frequently and

completely tamed in Paraguay, but Rengger (18/26. 'Saugethiere' etc. s. 34,

49.) says that it breeds so rarely, that he never saw more than two females

which had produced young. A similar observation has been made with respect to

the monkeys which are frequently tamed by the aborigines in Brazil. (18/27.

Art. Brazil 'Penny Cyclop.' page 363.) In Amazonia, these animals are so often

kept in a tame state, that Mr. Bates in walking through the streets of Para

counted thirteen species; but, as he asserts, they have never been known to

breed in captivity. (18/28. 'The Naturalist on the Amazons' volume 1 page 99.)

BIRDS.

Birds offer in some respects better evidence than quadrupeds, from their

breeding more rapidly and being kept in greater numbers. (18/29. A list of the

species of birds which have bred in the Zoological Gardens from 1848 to 1867

inclusive has been published by Mr. Sclater in 'Proc. Zoolog. Soc.' 1869 page

626, since the first edition of this work appeared. Of Columbae 51 species

have been kept, and of Anseres 80 species, and in both these families 1

species in 2.6 have bred at least once in the 20 years. Of Gallinae 83 species

have been kept and 1 in 27 have bred; of 57 Grallae 1 in 9 have bred; of 110

Prehensores 1 in 22 have bred; of 178 Passeres 1 in 25.4 have bred; of 94

Accipitres 1 in 47 have bred; of 25 Picariae and of 35 Herodiones not one

species in either group has bred.) We have seen that carnivorous animals are

more fertile under confinement than most other mammals. The reverse holds good

with carnivorous birds. It is said (18/30. 'Encyclop. of Rural Sports' page

691.) that as many as eighteen species have been used in Europe for hawking,

and several others in Persia and India (18/31. According to Sir A. Burnes

'Cabool' etc. page 51, eight species are used for hawking in Sinde.); they

have been kept in their native country in the finest condition, and have been

flown during six, eight, or nine years (18/32. Loudon's 'Mag. of Nat. Hist.'

volume 6 1833 page 110.); yet there is no record of their having ever produced

young. As these birds were formerly caught whilst young, at great expense,

being imported from Iceland, Norway, and Sweden, there can be little doubt

that, if possible, they would have been propagated. In the Jardin des Plantes,

no bird of prey has been known to couple. (18/33. F. Cuvier 'Annal. du Museum'

tome 9 page 128.) No hawk, vulture, or owl has ever produced fertile eggs in

the Zoological Gardens, or in the old Surrey Gardens, with the exception, in

the former place on one occasion, of a condor and a kite (Milvus niger). Yet

several species, namely, the Aquila fusca, Haliaetus leucocephalus, Falco

tinnunculus, F. subbuteo, and Buteo vulgaris, have been seen to couple in the

Zoological Gardens. Mr. Morris (18/34. 'The Zoologist' volume 7-8 1849-50 page

2648.) mentions as a unique fact that a kestrel (Falco tinnunculus) bred in an

aviary. The one kind of owl which has been known to couple in the Zoological

Gardens was the Eagle Owl (Bubo maximus); and this species shows a special

inclination to breed in captivity; for a pair at Arundel Castle, kept more

nearly in a state of nature "than ever fell to the lot of an animal deprived

of its liberty" (18/35. Knox 'Ornithological Rambles in Sussex' page 91.),

actually reared their young. Mr. Gurney has given another instance of this

same owl breeding in confinement; and he records the case of a second species

of owl, the Strix passerina, breeding in captivity. (18/36. 'The Zoologist'

volume 7-8 1849-50 page 2566; volume 9-10 1851-2 page 3207.)

Of the smaller graminivorous birds, many kinds have been kept tame in their

native countries, and have lived long; yet, as the highest authority on cage-

birds (18/37. Bechstein 'Naturgesch. der Stubenvogel' 1840 s. 20.) remarks,

their propagation is "uncommonly difficult." The canary-bird shows that there

is no inherent difficulty in these birds breeding freely in confinement; and

Audubon says (18/38. 'Ornithological Biography' volume 5 page 517.) that the

Fringilla (Spiza) ciris of North America breeds as perfectly as the canary.

The difficulty with the many finches which have been kept in confinement is

all the more remarkable as more than a dozen species could be named which have

yielded hybrids with the canary; but hardly any of these, with the exception

of the siskin (Fringilla spinus), have reproduced their own kind. Even the

bullfinch (Loxia pyrrhula) has bred as frequently with the canary, though

belonging to a distinct genus, as with its own species. (18/39. A case is

recorded in 'The Zoologist' volume 1-2 1843-45 page 453. For the siskin

breeding, volume 3-4 1845-46 page 1075. Bechstein 'Stubenvogel' s. 139 speaks

of bullfinches making nests, but rarely producing young.) With respect to the

skylark (Alauda arvensis), I have heard of birds living for seven years in an

aviary, which never produced young; and a great London bird-fancier assured me

that he had never known an instance of their breeding; nevertheless one case

has been recorded. (18/40. Yarrell 'Hist. British Birds' 1839 volume 1 page

412.) In the nine-year Report from the Zoological Society, twenty-four

insessorial species are enumerated which had not bred, and of these only four

were known to have coupled.

Parrots are singularly long-lived birds; and Humboldt mentions the curious

fact of a parrot in South America, which spoke the language of an extinct

Indian tribe, so that this bird preserved the sole relic of a lost language.

Even in this country there is reason to believe (18/41. Loudon's 'Mag. of Nat.

History' volume 19 1836 page 347.) that parrots have lived to the age of

nearly one hundred years; yet they breed so rarely, though many have been kept

in Europe, that the event has been thought worth recording in the gravest

publications. (18/42. 'Memoires du Museum d'Hist. Nat.' tome 10 page 314: five

cases of parrots breeding in France are here recorded. See also 'Report Brit.

Assoc. Zoolog.' 1843.) Nevertheless, when Mr. Buxton turned out a large number

of parrots in Norfolk, three pairs bred and reared ten young birds in the

course of two seasons; and this success may be attributed to their free life.

(18/43. 'Annals and Mag. of Nat. Hist.' November 1868 page 311.) According to

Bechstein (18/44. 'Stubenvogel' s. 105, 83.) the African Psittacus erithacus

breeds oftener than any other species in Germany: the P. macoa occasionally

lays fertile eggs, but rarely succeeds in hatching them; this bird, however,

has the instinct of incubation sometimes so strongly developed, that it will

hatch the eggs of fowls or pigeons. In the Zoological Gardens and in the old

Surrey Gardens some few species have coupled, but, with the exception of three

species of parakeets, none have bred. It is a much more remarkable fact that

in Guiana parrots of two kinds, as I am informed by Sir R. Schomburgk, are

often taken from the nests by the Indians and reared in large numbers; they

are so tame that they fly freely about the houses, and come when called to be

fed, like pigeons; yet he has never heard of a single instance of their

breeding. (18/45. Dr. Hancock remarks ('Charlesworth's Mag. of Nat. Hist.'

volume 2 1838 page 492) "it is singular that, amongst the numerous useful

birds that are indigenous to Guiana, none are found to propagate among the

Indians; yet the common fowl is reared in abundance throughout the country.")

In Jamaica, a resident naturalist, Mr. R. Hill (18/46. 'A Week at Pert Royal'

1855 page 7.), says, "no birds more readily submit to human dependence than

the parrot-tribe, but no instance of a parrot breeding in this tame life has

been known yet." Mr. Hill specifies a number of other native birds kept tame

in the West Indies, which never breed in this state.

The great pigeon family offers a striking contrast with the parrots: in the

nine-year Report thirteen species are recorded as having bred, and, what is

more noticeable, only two were seen to couple without any result. Since the

above date every annual Report gives many cases of various pigeons breeding.

The two magnificent crowned pigeons (Goura coronata and victoriae) produced

hybrids; nevertheless, of the former species more than a dozen birds were

kept, as I am informed by Mr. Crawfurd, in a park at Penang, under a perfectly

well-adapted climate, but never once bred. The Columba migratoria in its

native country, North America, invariably lays two eggs, but in Lord Derby's

menagerie never more than one. The same fact has been observed with the C.

leucocephala. (18/47. Audubon 'American Ornithology' volume 5 pages 552, 557.)

Gallinaceous birds of many genera likewise show an eminent capacity for

breeding under captivity. This is particularly the case with pheasants, yet

our English species seldom lays more than ten eggs in confinement; whilst from

eighteen to twenty is the usual number in the wild state. (18/48. Mowbray on

'Poultry' 7th edition page 133.) With the Gallinaceae, as with all other

orders, there are marked and inexplicable exceptions in regard to the

fertility of certain species and genera under confinement. Although many

trials have been made with the common partridge, it has rarely bred, even when

reared in large aviaries; and the hen will never hatch her own eggs. (18/49.

Temminck 'Hist. Nat. Gen. des Pigeons' etc. 1813 tome 3 pages 288, 382;

'Annals and Mag. of Nat. Hist.' volume 12 1843 page 453. Other species of

partridge have occasionally bred; as the red-legged (P. rubra), when kept in a

large court in France (see Journal de Physique' tome 25 page 294), and in the

Zoological Gardens in 1856.) The American tribe of Guans or Cracidae are tamed

with remarkable ease, but are very shy breeders in this country (18/50. Rev.

E.S. Dixon 'The Dovecote' 1851 pages 243-252.); but with care various species

were formerly made to breed rather freely in Holland. (18/51. Temminck 'Hist.

Nat. Gen. des Pigeons' etc. tome 2 pages 456, 458; tome 3 pages 2, 13, 47.)

Birds of this tribe are often kept in a perfectly tamed condition in their

native country by the Indians, but they never breed. (18/52. Bates 'The

Naturalist on the Amazons' volume 1 page 193; volume 2 page 112.) It might

have been expected that grouse from their habits of life would not have bred

in captivity, more especially as they are said soon to languish and die.

(18/53. Temminck 'Hist. Nat. Gen.' etc. tome 2 page 125. For Tetrao urogallus

see L. Lloyd 'Field Sports of North of Europe' volume 1 pages 287, 314; and

Bull. de la Soc. d'Acclimat.' tome 7 1860 page 600. For T. scoticus Thompson

'Nat. Hist. of Ireland' volume 2 1850 page 49. For T. cupido 'Boston Journal

of Nat. Hist.' volume 3 page 199.) But many cases are recorded of their

breeding: the capercailzie (Tetrao urogallus) has bred in the Zoological

Gardens; it breeds without much difficulty when confined in Norway, and in

Russia five successive generations have been reared: Tetrao tetrix has

likewise bred in Norway; T. scoticus in Ireland; T. umbellus at Lord Derby's;

and T. cupido in North America.

It is scarcely possible to imagine a greater change in habits than that which

the members of the ostrich family must suffer, when cooped up in small

enclosures under a temperate climate, after freely roaming over desert and

tropical plains or entangled forests; yet almost all the kinds have frequently

produced young in the various European menageries, even the mooruk (Casuarius

bennetii) from New Ireland. The African ostrich, though perfectly healthy and

living long in the South of France, never lays more than from twelve to

fifteen eggs, though in its native country it lays from twenty-five to thirty.

(18/54. Marcel de Serres 'Annales des Sc. Nat.' 2nd series Zoolog. tome 13

page 175.) Here we have another instance of fertility impaired, but not lost,

under confinement, as with the flying squirrel, the hen-pheasant, and two

species of American pigeons.

Most Waders can be tamed, as the Rev. E.S. Dixon informs me, with remarkable

facility; but several of them are short-lived under confinement, so that their

sterility in this state is not surprising. The cranes breed more readily than

other genera: Grus montigresia has bred several times in Paris and in the

Zoological Gardens, as has G. cinerea at the latter place, and G. antigone at

Calcutta. Of other members of this great order, Tetrapteryx paradisea has bred

at Knowsley, a Porphyrio in Sicily, and the Gallinula chloropus in the

Zoological Gardens. On the other hand, several birds belonging to this order

will not breed in their native country, Jamaica; and the Psophia, though often

kept by the Indians of Guiana about their houses, "is seldom or never known to

breed." (18/55. Dr. Hancock in 'Charlesworth's Mag. of Nat. Hist.' volume 2

1838 page 491; R. Hill 'A Week at Port Royal' page 8; 'Guide to the Zoological

Gardens' by P.L. Sclater 1859 pages 11, 12; 'The Knowsley Menagerie' by D.

Gray 1846 p1. 14; E. Blyth 'Report Asiatic Soc. of Bengal' May 1855.)

The members of the great Duck family breed as readily in confinement as do the

Columbae and Gallinae and this, considering their aquatic and wandering

habits, and the nature of their food, could not have been anticipated. Even

some time ago above two dozen species had bred in the Zoological Gardens; and

M. Selys-Longchamps has recorded the production of hybrids from forty-four

different members of the family; and to these Professor Newton has added a few

more cases. (18/56. Prof. Newton in 'Proc. Zoolog. Soc.' 1860 page 336.)

"There is not," says Mr. Dixon (18/57. 'The Dovecote and Aviary' page 428.),

"in the wide world, a goose which is not in the strict sense of the word

domesticable;" that is, capable of breeding under confinement; but this

statement is probably too bold. The capacity to breed sometimes varies in

individuals of the same species; thus Audubon (18/58. 'Ornithological

Biography' volume 3 page 9.) kept for more than eight years some wild geese

(Anser canadensis), but they would not mate; whilst other individuals of the

same species produced young during the second year. I know of but one instance

in the whole family of a species which absolutely refuses to breed in

captivity, namely, the Dendrocygna viduata, although, according to Sir R.

Schomburgk (18/59. 'Geograph. Journal' volume 13 1844 page 32.), it is easily

tamed, and is frequently kept by the Indians of Guiana. Lastly, with respect

to Gulls, though many have been kept in the Zoological Gardens and in the old

Surrey Gardens, no instance was known before the year 1848 of their coupling

or breeding; but since that period the herring gull (Larus argentatus) has

bred many times in the Zoological Gardens and at Knowsley.

There is reason to believe that insects are affected by confinement like the

higher animals. It is well known that the Sphingidae rarely breed when thus

treated. An entomologist (18/60. Loudon's 'Mag. of Nat. Hist.' volume 5 1832

page 153.) in Paris kept twenty-five specimens of Saturnia pyri, but did not

succeed in getting a single fertile egg. A number of females of Orthosia munda

and of Mamestra suasa reared in confinement were unattractive to the males.

(18/61. 'Zoologist' volumes 5-6 1847-48 page 1660.) Mr. Newport kept nearly a

hundred individuals of two species of Vanessa, but not one paired; this,

however, might have been due to their habit of coupling on the wing. (18/62.

'Transact. Entomolog. Soc.' volume 4 1845 page 60.) Mr. Atkinson could never

succeed in India in making the Tarroo silk-moth breed in confinement. (18/63.

'Transact. Linn. Soc.' volume 7 page 40.) It appears that a number of moths,

especially the Sphingidae, when hatched in the autumn out of their proper

season, are completely barren; but this latter case is still involved in some

obscurity. (18/64. See an interesting paper by Mr. Newman in the 'Zoologist'

1857 page 5764; and Dr. Wallace in 'Proc. Entomolog. Soc.' June 4, 1860 page

119.)]

Independently of the fact of many animals under confinement not coupling, or,

if they couple, not producing young, there is evidence of another kind that

their sexual functions are disturbed. For many cases have been recorded of the

loss by male birds when confined of their characteristic plumage. Thus the

common linnet (Linota cannabina) when caged does not acquire the fine crimson

colour on its breast, and one of the buntings (Emberiza passerina) loses the

black on its head. A Pyrrhula and an Oriolus have been observed to assume the

quiet plumage of the hen-bird; and the Falco albidus returned to the dress of

an earlier age. (18/65. Yarrell 'British Birds' volume 1 page 506; Bechstein

'Stubenvogel' s. 185; 'Philosoph. Transact.' 1772 page 271. Bronn 'Geschichte

der Natur' b. 2 s. 96 has collected a number of cases. For the case of the

deer see 'Penny Cyclop.' volume 8 page 350.) Mr. Thompson, the superintendent

of the Knowsley menagerie, informed me that he had often observed analogous

facts. The horns of a male deer (Cervus canadensis) during the voyage from

America were badly developed; but subsequently in Paris perfect horns were

produced.

When conception takes place under confinement, the young are often born dead,

or die soon, or are ill-formed. This frequently occurs in the Zoological

Gardens, and, according to Rengger, with native animals confined in Paraguay.

The mother's milk often fails. We may also attribute to the disturbance of the

sexual functions the frequent occurrence of that monstrous instinct which

leads the mother to devour her own offspring,--a mysterious case of

perversion, as it at first appears.

Sufficient evidence has now been advanced to prove that animals when first

confined are eminently liable to suffer in their reproductive systems. We feel

at first naturally inclined to attribute the result to loss of health, or at

least to loss of vigour; but this view can hardly be admitted when we reflect

how healthy, long-lived, and vigorous many animals are under captivity, such

as parrots, and hawks when used for hawking, cheetahs when used for hunting,

and elephants. The reproductive organs themselves are not diseased; and the

diseases, from which animals in menageries usually perish, are not those which

in any way affect their fertility. No domestic animal is more subject to

disease than the sheep, yet it is remarkably prolific. The failure of animals

to breed under confinement has been sometimes attributed exclusively to a

failure in their sexual instincts: this may occasionally come into play, but

there is no obvious reason why this instinct should be especially liable to be

affected with perfectly tamed animals, except, indeed, indirectly through the

reproductive system itself being disturbed. Moreover, numerous cases have been

given of various animals which couple freely under confinement, but never

conceive; or, if they conceive and produce young, these are fewer in number

than is natural to the species. In the vegetable kingdom instinct of course

can play no part; and we shall presently see that plants when removed from

their natural conditions are affected in nearly the same manner as animals.

Change of climate cannot be the cause of the loss of fertility, for, whilst

many animals imported into Europe from extremely different climates breed

freely, many others when confined in their native land are completely sterile.

Change of food cannot be the chief cause; for ostriches, ducks, and many other

animals, which must have undergone a great change in this respect, breed

freely. Carnivorous birds when confined are extremely sterile, whilst most

carnivorous mammals, except plantigrades, are moderately fertile. Nor can the

amount of food be the cause; for a sufficient supply will certainly be given

to valuable animals; and there is no reason to suppose that much more food

would be given to them than to our choice domestic productions which retain

their full fertility. Lastly, we may infer from the case of the elephant,

cheetah, various hawks, and of many animals which are allowed to lead an

almost free life in their native land, that want of exercise is not the sole

cause.

It would appear that any change in the habits of life, whatever these habits

may be, if great enough, tends to affect in an inexplicable manner the powers

of reproduction. The result depends more on the constitution of the species

than on the nature of the change; for certain whole groups are affected more

than others; but exceptions always occur, for some species in the most fertile

groups refuse to breed, and some in the most sterile groups breed freely.

Those animals which usually breed freely under confinement, rarely breed, as I

was assured, in the Zoological Gardens, within a year or two after their first

importation. When an animal which is generally sterile under confinement

happens to breed, the young apparently do not inherit this power: for had this

been the case, various quadrupeds and birds, which are valuable for

exhibition, would have become common. Dr. Broca even affirms (18/66. 'Journal

de Physiologie' tome 2 page 347.) that many animals in the Jardin des Plantes,

after having produced young for three or four successive generations, become

sterile; but this may be the result of too close interbreeding. It is a

remarkable circumstance that many mammals and birds have produced hybrids

under confinement quite as readily as, or even more readily than, they have

procreated their own kind. Of this fact many instances have been given (18/67.

For additional evidence on this subject see F. Cuvier in 'Annales du Museum'

tome 12 page 119.); and we are thus reminded of those plants which when

cultivated refuse to be fertilised by their own pollen, but can easily be

fertilised by that of a distinct species. Finally, we must conclude, limited

as the conclusion is, that changed conditions of life have an especial power

of acting injuriously on the reproductive system. The whole case is quite

peculiar, for these organs, though not diseased, are thus rendered incapable

of performing their proper functions, or perform them imperfectly.

[STERILITY OF DOMESTICATED ANIMALS FROM CHANGED CONDITIONS.

With respect to domesticated animals, as their domestication mainly depends on

the accident of their breeding freely under captivity, we ought not to expect

that their reproductive system would be affected by any moderate degree of

change. Those orders of quadrupeds and birds, of which the wild species breed

most readily in our menageries, have afforded us the greatest number of

domesticated productions. Savages in most parts of the world are fond of

taming animals (18/68. Numerous instances could be given. Thus Livingstone

('Travels' page 217) states that the King of the Barotse, an inland tribe

which never had any communication with white men, was extremely fond of taming

animals, and every young antelope was brought to him. Mr. Galton informs me

that the Damaras are likewise fond of keeping pets. The Indians of South

America follow the same habit. Capt. Wilkes states that the Polynesians of the

Samoan Islands tamed pigeons; and the New Zealanders, as Mr. Mantell informs

me, kept various kinds of birds.); and if any of these regularly produced

young, and were at the same time useful, they would be at once domesticated.

If, when their masters migrated into other countries, they were in addition

found capable of withstanding various climates, they would be still more

valuable; and it appears that the animals which breed readily in captivity can

generally withstand different climates. Some few domesticated animals, such as

the reindeer and camel, offer an exception to this rule. Many of our

domesticated animals can bear with undiminished fertility the most unnatural

conditions; for instance, rabbits, guinea-pigs, and ferrets breed in miserably

confined hutches. Few European dogs of any kind withstand the climate of India

without degenerating, but as long as they survive, they retain, as I hear from

Dr. Falconer, their fertility; so it is, according to Dr. Daniell, with

English dogs taken to Sierra Leone. The fowl, a native of the hot jungles of

India, becomes more fertile than its parent-stock in every quarter of the

world, until we advance as far north as Greenland and Northern Siberia, where

this bird will not breed. Both fowls and pigeons, which I received during the

autumn direct from Sierra Leone, were at once ready to couple. (18/69. For

analogous cases with the fowl see Reaumur 'L'Art de faire Eclore' etc. 1749

page 243; and Col. Sykes in 'Proc. Zoolog. Soc.' 1832 etc. With respect to the

fowl not breeding in northern regions see Latham 'Hist. of Birds' volume 8

1823 page 169.) I have, also, seen pigeons breeding as freely as the common

kinds within a year after their importation from the upper Nile. The guinea-

fowl, an aboriginal of the hot and dry deserts of Africa, whilst living under

our damp and cool climate, produces a large supply of eggs.

Nevertheless, our domesticated animals under new conditions occasionally show

signs of lessened fertility. Roulin asserts that in the hot valleys of the

equatorial Cordillera sheep are not fully fecund (18/70. "Mem. par divers

Savans" 'Acad. des Sciences' tome 6 1835 page 347.); and according to Lord

Somerville (18/71. 'Youatt on Sheep' page 181.) the merino-sheep which he

imported from Spain were not at first perfectly fertile, it is said (18/72. J.

Mills 'Treatise on Cattle' 1776 page 72.) that mares brought up on dry food in

the stable, and turned out to grass, do not at first breed. The peahen, as we

have seen, is said not to lay so many eggs in England as in India. It was long

before the canary-bird was fully fertile, and even now first-rate breeding

birds are not common. (18/73. Bechstein 'Stubenvogel' s. 242.) In the hot and

dry province of Delhi, as I hear from Dr. Falconer, the eggs of the turkey,

though placed under a hen, are extremely liable to fail. According to Roulin,

geese taken to the lofty plateau of Bogota, at first laid seldom, and then

only a few eggs; of these scarcely a fourth were hatched, and half the young

birds died; in the second generation they were more fertile; and when Roulin

wrote they were becoming as fertile as our geese in Europe. With respect to

the valley of Quito, Mr. Orton says (18/74. 'The Andes and the Amazon' 1870

page 107.) "the only geese in the valley are a few imported from Europe, and

these refuse to propagate." In the Philippine Archipelago the goose, it is

asserted, will not breed or even lay eggs. (18/75. Crawford 'Descriptive Dict.

of the Indian Islands' 1856 page 145.) A more curious case is that of the

fowl, which, according to Roulin, when first introduced would not breed at

Cusco in Bolivia, but subsequently became quite fertile; and the English Game

fowl, lately introduced, had not as yet arrived at its full fertility, for to

raise two or three chickens from a nest of eggs was thought fortunate. In

Europe close confinement has a marked effect on the fertility of the fowl: it

has been found in France that with fowls allowed considerable freedom only

twenty per cent of the eggs failed; when allowed less freedom forty per cent

failed; and in close confinement sixty out of the hundred were not hatched.

(18/76. 'Bull. de la Soc. d'Acclimat.' tome 9 1862 pages 380, 384.) So we see

that unnatural and changed conditions of life produce some effect on the

fertility of our most thoroughly domesticated animals, in the same manner,

though in a far less degree, as with captive wild animals.

It is by no means rare to find certain males and females which will not breed

together, though both are known to be perfectly fertile with other males and

females. We have no reason to suppose that this is caused by these animals

having been subjected to any change in their habits of life; therefore such

cases are hardly related to our present subject. The cause apparently lies in

an innate sexual incompatibility of the pair which are matched. Several

instances have been communicated to me by Mr. W.C. Spooner (well known for his

essay on Cross-breeding), by Mr. Eyton of Eyton, by Mr. Wicksted and other

breeders, and especially by Mr. Waring of Chelsfield, in relation to horses,

cattle, pigs, foxhounds, other dogs, and pigeons. (18/77. For pigeons see Dr.

Chapuis 'Le Pigeon Voyageur Belge' 1865 page 66.) In these cases, females,

which either previously or subsequently were proved to be fertile, failed to

breed with certain males, with whom it was particularly desired to match them.

A change in the constitution of the female may sometimes have occurred before

she was put to the second male; but in other cases this explanation is hardly

tenable, for a female, known not to be barren, has been unsuccessfully paired

seven or eight times with the same male likewise known to be perfectly

fertile. With cart-mares, which sometimes will not breed with stallions of

pure blood, but subsequently have bred with cart-stallions, Mr. Spooner is

inclined to attribute the failure to the lesser sexual power of the racehorse.

But I have heard from the greatest breeder of racehorses at the present day,

through Mr. Waring, that "it frequently occurs with a mare to be put several

times during one or two seasons to a particular stallion of acknowledged

power, and yet prove barren; the mare afterwards breeding at once with some

other horse." These facts are worth recording, as they show, like so many

previous facts, on what slight constitutional differences the fertility of an

animal often depends.]

STERILITY OF PLANTS FROM CHANGED CONDITIONS OF LIFE, AND FROM OTHER CAUSES.

In the vegetable kingdom cases of sterility frequently occur, analogous with

those previously given in the animal kingdom. But the subject is obscured by

several circumstances, presently to be discussed, namely, the contabescence of

the anthers, as Gartner has named a certain affection--monstrosities--

doubleness of the flower--much-enlarged fruit--and long-continued or excessive

propagation by buds.

[It is notorious that many plants in our gardens and hot-houses, though

preserved in the most perfect health, rarely or never produce seed. I do not

allude to plants which run to leaves, from being kept too damp, or too warm,

or too much manured; for these do not flower, and the case may be wholly

different. Nor do I allude to fruit not ripening from want of heat or rotting

from too much moisture. But many exotic plants, with their ovules and pollen

appearing perfectly sound, will not set any seed. The sterility in many cases,

as I know from my own observation, is simply due to the absence of the proper

insects for carrying the pollen to the stigma. But after excluding the several

cases just specified, there are many plants in which the reproductive system

has been seriously affected by the altered conditions of life to which they

have been subjected.

It would be tedious to enter on many details. Linnaeus long ago observed

(18/78. 'Swedish Acts' volume 1 1739 page 3. Pallas makes the same remark in

his 'Travels' English translation volume 1 page 292.) that Alpine plants,

although naturally loaded with seed, produce either few or none when

cultivated in gardens. But exceptions often occur: the Draba sylvestris, one

of our most thoroughly Alpine plants, multiplies itself by seed in Mr. H.C.

Watson's garden, near London; and Kerner, who has particularly attended to the

cultivation of Alpine plants, found that various kinds, when cultivated,

spontaneously sowed themselves. (18/79. A. Kerner 'Die Cultur der

Alpenpflanzen' 1864 s. 139; Watson 'Cybele Britannica' volume 1 page 131; Mr.

D. Cameron also has written on the culture of Alpine plants in 'Gard.

Chronicle' 1848 pages 253, 268, and mentions a few which seed.) Many plants

which naturally grow in peat-earth are entirely sterile in our gardens. I have

noticed the same fact with several liliaceous plants, which nevertheless grew

vigorously.

Too much manure renders some kinds utterly sterile, as I have myself observed.

The tendency to sterility from this cause runs in families; thus, according to

Gartner (18/80. 'Beitrage zur Kenntniss der Befruchtung' 1844 s. 333.), it is

hardly possible to give too much manure to most Gramineae, Cruciferae, and

Leguminosae, whilst succulent and bulbous-rooted plants are easily affected.

Extreme poverty of soil is less apt to induce sterility; but dwarfed plants of

Trifolium minus and repens, growing on a lawn often mown and never manured,

were found by me not to produce any seed. The temperature of the soil, and the

season at which plants are watered, often have a marked effect on their

fertility, as was observed by Kolreuter in the case of Mirabilis. (18/81.

'Nova Acta Petrop.' 1793 page 391.) Mr. Scott, in the Botanic Gardens of

Edinburgh, observed that Oncidium divaricatum would not set seed when grown in

a basket in which it throve, but was capable of fertilisation in a pot where

it was a little damper. Pelargonium fulgidum, for many years after its

introduction, seeded freely; it then became sterile; now it is fertile (18/82.

'Cottage Gardener' 1856 pages 44, 109.) if kept in a dry stove during the

winter. Other varieties of pelargonium are sterile and others fertile without

our being able to assign any cause. Very slight changes in the position of a

plant, whether planted on a bank or at its base, sometimes make all the

difference in its producing seed. Temperature apparently has a much more

powerful influence on the fertility of plants than on that of animals.

Nevertheless it is wonderful what changes some few plants will withstand with

undiminished fertility: thus the Zephyranthes candida, a native of the

moderately warm banks of the Plata, sows itself in the hot dry country near

Lima, and in Yorkshire resists the severest frosts, and I have seen seeds

gathered from pods which had been covered with snow during three weeks.

(18/83. Dr. Herbert 'Amaryllidaceae' page 176.) Berberis wallichii, from the

hot Khasia range in India, is uninjured by our sharpest frosts, and ripens its

fruit under our cool summers. Nevertheless, I presume we must attribute to

change of climate the sterility of many foreign plants; thus, the Persian and

Chinese lilacs (Syringa persica and chinensis), though perfectly hardy here,

never produce a seed; the common lilac (S. vulgaris) seeds with us moderately

well, but in parts of Germany the capsules never contain seed. (18/84. Gartner

'Beitrage zur Kenntniss' etc. s. 560, 564.) Some few of the cases, given in

the last chapter, of self-impotent plants, might have been here introduced, as

their state seems due to the conditions to which they have been subjected.

The liability of plants to be affected in their fertility by slightly changed

conditions is the more remarkable, as the pollen when once in process of

formation is not easily injured; a plant may be transplanted, or a branch with

flower-buds be cut off and placed in water, and the pollen will be matured.

Pollen, also, when once mature, may be kept for weeks or even months. (18/85.

'Gardener's Chronicle' 1844 page 215; 1850 page 470. Faivre gives a good

resume on this subject in his 'La Variabilite des Especes' 1868 page 155.) The

female organs are more sensitive, for Gartner (18/86. 'Beitrage zur Kenntniss'

etc. s. 252, 338.) found that dicotyledonous plants, when carefully removed so

that they did not in the least flag, could seldom be fertilised; this occurred

even with potted plants if the roots had grown out of the hole at the bottom.

In some few cases, however, as with Digitalis, transplantation did not prevent

fertilisation; and according to the testimony of Mawz, Brassica rapa, when

pulled up by its roots and placed in water, ripened its seed. Flower-stems of

several monocotyledonous plants when cut off and placed in water likewise

produce seed. But in these cases I presume that the flowers had been already

fertilised, for Herbert (18/87. 'Journal of Hort. Soc.' volume 2 1847 page

83.) found with the Crocus that the plants might be removed or mutilated after

the act of fertilisation, and would still perfect their seeds; but that, if

transplanted before being fertilised, the application of pollen was powerless.

Plants which have been long cultivated can generally endure with undiminished

fertility various and great changes; but not in most cases so great a change

of climate as domesticated animals. It is remarkable that many plants under

these circumstances are so much affected that the proportion and the nature of

their chemical ingredients are modified, yet their fertility is unimpaired.

Thus, as Dr. Falconer informs me, there is a great difference in the character

of the fibre in hemp, in the quantity of oil in the seed of the Linum, in the

proportion of narcotin to morphine in the poppy, in gluten to starch in wheat,

when these plants are cultivated on the plains and on the mountains of India;

nevertheless, they all remain fully fertile.

CONTABESCENCE.

Gartner has designated by this term a peculiar condition of the anthers in

certain plants, in which they are shrivelled, or become brown and tough, and

contain no good pollen. When in this state they exactly resemble the anthers

of the most sterile hybrids. Gartner (18/88. 'Beitrage zur Kenntniss' etc. s.

117 et seq.; Kolreuter 'Zweite Fortsetzung' s. 10, 121; 'Dritte Fortsetzung'

s. 57. Herbert 'Amaryllidaceae' page 355. Wiegmann 'Ueber die

Bastarderzeugung' s. 27.), in his discussion on this subject, has shown that

plants of many orders are occasionally thus affected; but the Caryophyllaceae

and Liliaceae suffer most, and to these orders, I think, the Ericaceae may be

added. Contabescence varies in degree, but on the same plant all the flowers

are generally affected to nearly the same extent. The anthers are affected at

a very early period in the flower-bud, and remain in the same state (with one

recorded exception) during the life of the plant. The affection cannot be

cured by any change of treatment, and is propagated by layers, cuttings, etc.,

and perhaps even by seed. In contabescent plants the female organs are seldom

affected, or merely become precocious in their development. The cause of this

affection is doubtful, and is different in different cases. Until I read

Gartner's discussion I attributed it, as apparently did Herbert, to the

unnatural treatment of the plants; but its permanence under changed

conditions, and the female organs not being affected, seem incompatible with

this view. The fact of several endemic plants becoming contabescent in our

gardens seems, at first sight, equally incompatible with this view; but

Kolreuter believes that this is the result of their transplantation. The

contabescent plants of Dianthus and Verbascum, found wild by Wiegmann, grew on

a dry and sterile bank. The fact that exotic plants are eminently liable to

this affection also seems to show that it is in some manner caused by their

unnatural treatment. In some instances, as with Silene, Gartner's view seems

the most probable, namely, that it is caused by an inherent tendency in the

species to become dioecious. I can add another cause, namely, the illegitimate

unions of heterostyled plants, for I have observed seedlings of three species

of Primula and of Lythrum salicaria, which had been raised from plants

illegitimately fertilised by their own-form pollen, with some or all their

anthers in a contabescent state. There is perhaps an additional cause, namely,

self-fertilisation; for many plants of Dianthus and Lobelia, which had been

raised from self-fertilised seeds, had their anthers in this state; but these

instances are not conclusive, as both genera are liable from other causes to

this affection.

Cases of an opposite nature likewise occur, namely, plants with the female

organs struck with sterility, whilst the male organs remain perfect. Dianthus

japonicus, a Passiflora, and Nicotiana, have been described by Gartner (18/89.

'Bastarderzengung' s. 356.) as being in this unusual condition.

MONSTROSITIES AS A CAUSE OF STERILITY.

Great deviations of structure, even when the reproductive organs themselves

are not seriously affected, sometimes cause plants to become sterile. But in

other cases plants may become monstrous to an extreme degree and yet retain

their full fertility. Gallesio, who certainly had great experience (18/90.

'Teoria della Riproduzione' 1816 page 84; 'Traite du Citrus' 1811 page 67.),

often attributes sterility to this cause; but it may be suspected that in some

of his cases sterility was the cause, and not the result, of the monstrous

growths. The curious St. Valery apple, although it bears fruit, rarely

produces seed. The wonderfully anomalous flowers of Begonia frigida, formerly

described, though they appear fit for fructification, are sterile. (18/91. Mr.

C.W. Crocker in 'Gardener's Chronicle' 1861 page 1092.) Species of Primula in

which the calyx is brightly coloured are said (18/92. Verlot 'Des Varietes'

1865 page 80.) to be often sterile, though I have known them to be fertile. On

the other hand, Verlot gives several cases of proliferous flowers which can be

propagated by seed. This was the case with a poppy, which had become

monopetalous by the union of its petals. (18/93. Verlot ibid page 88.) Another

extraordinary poppy, with the stamens replaced by numerous small supplementary

capsules, likewise reproduces itself by seed. This has also occurred with a

plant of Saxifraga geum, in which a series of adventitious carpels, bearing

ovules on their margins, had been developed between the stamens and the normal

carpels (18/94. Prof. Allman, Brit. Assoc., quoted in the 'Phytologist' volume

2 page 483. Prof. Harvey, on the authority of Mr. Andrews, who discovered the

plant, informed me that this monstrosity could be propagated by seed. With

respect to the poppy see Prof. Goeppert as quoted in 'Journal of Horticulture'

July 1, 1863 page 171.) Lastly, with respect to peloric flowers, which depart

wonderfully from the natural structure,--those of Linaria vulgaris seem

generally to be more or less sterile, whilst those before described of

Antirrhinum majus, when artificially fertilised with their own pollen, are

perfectly fertile, though sterile when left to themselves, for bees are unable

to crawl into the narrow tubular flower. The peloric flowers of Corydalis

solida, according to Godron (18/95. 'Comptes Rendus' December 19, 1864 page

1039.), are sometimes barren and sometimes fertile; whilst those of Gloxinia

are well known to yield plenty of seed. In our greenhouse Pelargoniums, the

central flower of the truss is often peloric, and Mr. Masters informs me that

he tried in vain during several years to get seed from these flowers. I

likewise made many vain attempts, but sometimes succeeded in fertilising them

with pollen from a normal flower of another variety; and conversely I several

times fertilised ordinary flowers with peloric pollen. Only once I succeeded

in raising a plant from a peloric flower fertilised by pollen from a peloric

flower borne by another variety; but the plant, it may be added, presented

nothing particular in its structure. Hence we may conclude that no general

rule can be laid down; but any great deviation from the normal structure, even

when the reproductive organs themselves are not seriously affected, certainly

often leads to sexual impotence.

DOUBLE FLOWERS.

When the stamens are converted into petals, the plant becomes on the male side

sterile; when both stamens and pistils are thus changed, the plant becomes

completely barren. Symmetrical flowers having numerous stamens and petals are

the most liable to become double, as perhaps follows from all multiple organs

being the most subject to variability. But flowers furnished with only a few

stamens, and others which are asymmetrical in structure, sometimes become

double, as we see with the double gorse or Ulex, and Antirrhinum. The

Compositae bear what are called double flowers by the abnormal development of

the corolla of their central florets. Doubleness is sometimes connected with

prolification (18/96. 'Gardener's Chronicle' 1866 page 681.), or the continued

growth of the axis of the flower. Doubleness is strongly inherited. No one has

produced, as Lindley remarks (18/97. 'Theory of Horticulture' page 333.),

double flowers by promoting the perfect health of the plant. On the contrary,

unnatural conditions of life favour their production. There is some reason to

believe that seeds kept during many years, and seeds believed to be

imperfectly fertilised, yield double flowers more freely than fresh and

perfectly fertilised seed. (18/98. Mr. Fairweather 'Transact. Hort. Soc.'

volume 3 page 406: Bosse quoted by Bronn 'Geschichte der Natur' b. 2 s. 77. On

the effects of the removal of the anthers see Mr. Leitner in Silliman's 'North

American Journ. of Science' volume 23 page 47; and Verlot 'Des Varietes' 1865

page 84.) Long-continued cultivation in rich soil seems to be the commonest

exciting cause. A double narcissus and a double Anthemis nobilis, transplanted

into very poor soil, has been observed to become single (18/99. Lindley's

'Theory of Horticulture' page 3?3.); and I have seen a completely double white

primrose rendered permanently single by being divided and transplanted whilst

in full flower. It has been observed by Professor E. Morren that doubleness of

the flowers and variegation of the leaves are antagonistic states; but so many

exceptions to the rule have lately been recorded (18/100. 'Gardener's

Chronicle' 1865 page 626; 1866 pages 290, 730; and Verlot 'Des Varietes' page

75.), that, though general, it cannot be looked at as invariable. Variegation

seems generally to result from a feeble or atrophied condition of the plant,

and a large proportion of the seedlings raised from parents, if both are

variegated, usually perish at an early age; hence we may perhaps infer that

doubleness, which is the antagonistic state, commonly arises from a plethoric

condition. On the other hand, extremely poor soil sometimes, though rarely,

appears to cause doubleness: I formerly described (18/101. 'Gardener's

Chronicle' 1843 page 628. In this article I suggested the theory above given

on the doubleness of flowers. This view is adopted by Carriere 'Production et

Fix. des Varietes' 1865 page 67.) some completely double, bud-like, flowers

produced in large numbers by stunted wild plants of Gentiana amarella growing

on a poor chalky bank. I have also noticed a distinct tendency to doubleness

in the flowers of a Ranunculus, Horse-chestnut, and Bladder-nut (Ranunculus

repens, Aesculus pavia, and Staphylea), growing under very unfavourable

conditions. Professor Lehmann (18/102. Quoted by Gartner 'Bastarderzeugung' s.

567.) found several wild plants growing near a hot spring with double flowers.

With respect to the cause of doubleness, which arises, as we see, under widely

different circumstances, I shall presently attempt to show that the most

probable view is that unnatural conditions first give a tendency to sterility,

and that then, on the principle of compensation, as the reproductive organs do

not perform their proper functions, they either become developed into petals,

or additional petals are formed. This view has lately been supported by Mr.

Laxton (18/103. 'Gardener's Chronicle' 1866 page 901.) who advances the case

of some common peas, which, after long-continued heavy rain, flowered a second

time, and produced double flowers.

SEEDLESS FRUIT.

Many of our most valuable fruits, although consisting in a homological sense

of widely different organs, are either quite sterile, or produce extremely few

seeds. This is notoriously the case with our best pears, grapes, and figs,

with the pine-apple, banana, bread-fruit, pomegranate, azarole, date-palms,

and some members of the orange-tribe. Poorer varieties of these same fruits

either habitually or occasionally yield seed. (18/104. Lindley 'Theory of

Horticulture' pages 175-179; Godron 'De l'Espece' tome 2 page 106; Pickering

'Races of Man;' Gallesio 'Teoria della Riproduzione' l816 pages 101-110. Meyen

'Reise um Erde' Th. 2 s. 214 states that at Manilla one variety of the banana

is full of seeds: and Chamisso (Hooker's 'Bot. Misc.' volume 1 page 310)

describes a variety of the bread-fruit in the Mariana Islands with small

fruit, containing seeds which are frequently perfect. Burnes in his 'Travels

in Bokhara' remarks on the pomegranate seeding in Mazenderan, as a remarkable

peculiarity.) Most horticulturists look at the great size and anomalous

development of the fruit as the cause, and sterility as the result; but the

opposite view, as we shall presently see, is more probable.

STERILITY FROM THE EXCESSIVE DEVELOPMENT OF THE ORGANS OF GROWTH OR

VEGETATION.

Plants which from any cause grow too luxuriantly, and produce leaves, stems,

runners, suckers, tubers, bulbs, etc., in excess, sometimes do not flower, or

if they flower do not yield seed. To make European vegetables under the hot

climate of India yield seed, it is necessary to check their growth; and, when

one-third grown, they are taken up, and their stems and tap-roots are cut or

mutilated. (18/105. Ingledew in 'Transact. of Agricult. and Hort. Soc. of

India' volume 2.) So it is with hybrids; for instance, Prof. Lecoq (18/106.

'De la Fecondation' 1862 page 308.) had three plants of Mirabilis, which,

though they grew luxuriantly and flowered, were quite sterile; but after

beating one with a stick until a few branches alone were left, these at once

yielded good seed. The sugar-cane, which grows vigorously and produces a large

supply of succulent stems, never, according to various observers, bears seed

in the West Indies, Malaga, India, Cochin China, Mauritius, or the Malay

Archipelago. (18/107. Hooker 'Bot. Misc.' volume 1 page 99; Gallesio 'Teoria

della Riproduzione' page 110. Dr. J. de Cordemoy in 'Transact. of the R. Soc.

of Mauritius' new series volume 6 1873 pages 60-67, gives a large number of

cases of plants which never seed, including several species indigenous in

Mauritius.) Plants which produce a large number of tubers are apt to be

sterile, as occurs, to a certain extent, with the common potato; and Mr.

Fortune informs me that the sweet potato (Convolvulus batatas) in China never,

as far as he has seen, yields seed. Dr. Royle remarks (18/108. 'Transact.

Linn. Soc.' volume 17 page 563.) that in India the Agave vivipara, when grown

in rich soil, invariably produces bulbs, but no seeds; whilst a poor soil and

dry climate lead to an opposite result. In China, according to Mr. Fortune, an

extraordinary number of little bulbs are developed in the axils of the leaves

of the yam, and this plant does not bear seed. Whether in these cases, as in

those of double flowers and seedless fruit, sexual sterility from changed

conditions of life is the primary cause which leads to the excessive

development of the organs of vegetation, is doubtful; though some evidence

might be advanced in favour of this view. It is perhaps a more probable view

that plants which propagate themselves largely by one method, namely by buds,

have not sufficient vital power or organised matter for the other method of

sexual generation.

Several distinguished botanists and good practical judges believe that long-

continued propagation by cuttings, runners, tubers, bulbs, etc., independently

of any excessive development of these parts, is the cause of many plants

failing to produce flowers, or producing only barren flowers,--it is as if

they had lost the habit of sexual generation. (18/109. Godron 'De l'Espece'

tome 2 page 106; Herbert on Crocus in 'Journal of Hort. Soc.' volume 1 1846

page 254: Dr. Wight, from what he has seen in India, believes in this view;

'Madras Journal of Lit. and Science' volume 4 1836 page 61.) That many plants

when thus propagated are sterile there can be no doubt, but as to whether the

long continuance of this form of propagation is the actual cause of their

sterility, I will not venture, from the want of sufficient evidence, to

express an opinion.

That plants may be propagated for long periods by buds, without the aid of

sexual generation, we may safely infer from this being the case with many

plants which must have long survived in a state of nature. As I have had

occasion before to allude to this subject, I will here give such cases as I

have collected. Many alpine plants ascend mountains beyond the height at which

they can produce seed. (18/110. Wahlenberg specifies eight species in this

state on the Lapland Alps: see Appendix to Linnaeus 'Tour in Lapland'

translated by Sir J.E. Smith volume 2 pages 274-280.) Certain species of Poa

and Festuca, when growing on mountain-pastures, propagate themselves, as I

hear from Mr. Bentham, almost exclusively by bulblets. Kalm gives a more

curious instance (18/111. 'Travels in North America' English translation

volume 3 page 175.) of several American trees, which grow so plentifully in

marshes or in thick woods, that they are certainly well adapted for these

stations, yet scarcely ever produce seeds; but when accidentally growing on

the outside of the marsh or wood, are loaded with seed. The common ivy is

found in Northern Sweden and Russia, but flowers and fruits only in the

southern provinces. The Acorus calamus extends over a large portion of the

globe, but so rarely perfects fruit that this has been seen only by a few

botanists; according to Caspary, all its pollen-grains are in a worthless

condition. (18/112. With respect to the ivy and Acorus see Dr. Broomfield in

the 'Phytologist' volume 3 page 376. Also Lindley and Vaucher on the Acorus

and see Caspary as below.) The Hypericum calycinum, which propagates itself so

freely in our shrubberies by rhizomes, and is naturalised in Ireland, blossoms

profusely, but rarely sets any seed, and this only during certain years; nor

did it set any when fertilised in my garden by pollen from plants growing at a

distance. The Lysimachia nummularia, which is furnished with long runners, so

seldom produces seed-capsules, that Prof. Decaisne (18/113. 'Annal. des Sc.

Nat.' 3rd series Zool. tome 4 page 280. Prof. Decaisne refers also to

analogous cases with mosses and lichens near Paris.), who has especially

attended to this plant, has never seen it in fruit. The Carex rigida often

fails to perfect its seed in Scotland, Lapland, Greenland, Germany, and New

Hampshire in the United States. (18/114. Mr. Tuckermann in Silliman's

'American Journal of Science' volume 65 page 1.) The periwinkle (Vinca minor),

which spreads largely by runners, is said scarcely ever to produce fruit in

England (18/115. Sir J.E. Smith 'English Flora' volume 1 page 339.); but this

plant requires insect-aid for its fertilisation, and the proper insects may be

absent or rare. The Jussiaea grandiflora has become naturalised in Southern

France, and has spread by its rhizomes so extensively as to impede the

navigation of the waters, but never produces fertile seed. (18/116. G.

Planchon 'Flora de Montpellier' 1864 page 20.) The horse-radish (Cochleria

armoracia) spreads pertinaciously and is naturalised in various parts of

Europe; though it bears flowers, these rarely produce capsules: Professor

Caspary informs me that he has watched this plant since 1851, but has never

seen its fruit; 65 per cent of its pollen-grains are bad. The common

Ranunculus ficaria rarely bears seed in England, France, or Switzerland; but

in 1863 I observed seeds on several plants growing near my house. (18/117. On

the non-production of seeds in England see Mr. Crocker in 'Gardener's Weekly

Magazine' 1852 page 70; Vaucher 'Hist. Phys. Plantes d'Europe' tome 1 page 33;

Lecoq 'Geograph. Bot. d'Europe' tome 4 page 466; Dr. D. Clos in 'Annal. des

Sc. Nat.' 3rd series Bot. tome 17 1852 page 129: this latter author refers to

other analogous cases. See more especially on this plant and on other allied

cases Prof. Caspary "Die Nuphar" 'Abhand. Naturw. Gesellsch. zu Halle' b. 11

1870 page 40, 78.) Other cases analogous with the foregoing could be given;

for instance, some kinds of mosses and lichens have never been seen to

fructify in France.

Some of these endemic and naturalised plants are probably rendered sterile

from excessive multiplication by buds, and their consequent incapacity to

produce and nourish seed. But the sterility of others more probably depends on

the peculiar conditions under which they live, as in the case of the ivy in

the northern part of Europe, and of the trees in the swamps of the United

States; yet these plants must be in some respects eminently well adapted for

the stations which they occupy, for they hold their places against a host of

competitors.]

Finally, the high degree of sterility which often accompanies the doubling of

flowers, or an excessive development of fruit, seldom supervenes at once. An

incipient tendency is observed, and continued selection completes the result.

The view which seems the most probable, and which connects together all the

foregoing facts and brings them within our present subject, is, that changed

and unnatural conditions of life first give a tendency to sterility; and in

consequence of this, the organs of reproduction being no longer able fully to

perform their proper functions, a supply of organised matter, not required for

the development of the seed, flows either into these organs and renders them

foliaceous, or into the fruit, stems, tubers, etc., increasing their size and

succulency. But it is probable that there exists, independently of any

incipient sterility, an antagonism between the two forms of reproduction,

namely, by seed and buds, when either is carried to an extreme degree. That

incipient sterility plays an important part in the doubling of flowers, and in

the other cases just specified, I infer chiefly from the following facts. When

fertility is lost from a wholly different cause, namely, from hybridism, there

is a strong tendency, as Gartner (18/118. 'Bastarderzeugung' s. 565. Kolreuter

'Dritte Fortsetzung' s. 73, 87, 119) also shows that when two species, one

single and the other double, are crossed, the hybrids are apt to be extremely

double.) affirms, for flowers to become double, and this tendency is

inherited. Moreover, it is notorious that with hybrids the male organs become

sterile before the female organs, and with double flowers the stamens first

become foliaceous. This latter fact is well shown by the male flowers of

dioecious plants, which, according to Gallesio (18/119. 'Teoria della

Riproduzione Veg.' 1816 page 73.) first become double. Again, Gartner (18/120.

'Bastarderzeugung' s. 573.) often insists that the flowers of even utterly

sterile hybrids, which do not produce any seed, generally yield perfect

capsules or fruit,--a fact which has likewise been repeatedly observed by

Naudin with the Cucurbitaceae; so that the production of fruit by plants

rendered sterile through any cause is intelligible. Kolreuter has also

expressed his unbounded astonishment at the size and development of the tubers

in certain hybrids; and all experimentalists (18/121. Ibid s. 527.) have

remarked on the strong tendency in hybrids to increase by roots, runners, and

suckers. Seeing that hybrid plants, which from their nature are more or less

sterile, thus tend to produce double flowers; that they have the parts

including the seed, that is the fruit, perfectly developed, even when

containing no seed; that they sometimes yield gigantic roots; that they almost

invariably tend to increase largely by suckers and other such means;--seeing

this, and knowing, from the many facts given in the earlier parts of this

chapter, that almost all organic beings when exposed to unnatural conditions

tend to become more or less sterile, it seems much the most probable view that

with cultivated plants sterility is the exciting cause, and double flowers,

rich seedless fruit, and in some cases largely-developed organs of vegetation,

etc., are the indirect results--these results having been in most cases

largely increased through continued selection by man.