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.[1] A sagacious observer,
Bradley, writing in 1724,[2] 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[3] 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.[4]
A well-known practical gardener, Mr. Robson[5] 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[6] 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[7] 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[8] 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[9] 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.[10] 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[11] 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,[12] 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;[13] 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[14] 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[15] 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 (_Potamochœrus 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[16] 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[17] 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] 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.[19] 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.[20] 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 (_Cœlogenys 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.[21] 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.[22] 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.[23]
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.[24] 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,_[25] 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
azaræ_) is frequently and completely tamed in Paraguay, but Rengger[26]
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.[27] 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.[28]
_Birds._
Birds offer in some respects better evidence than quadrupeds, from
their breeding more rapidly and being kept in greater numbers.[29] 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[30] that as many as eighteen species have been used in
Europe for hawking, and several others in Persia and India;[31] they
have been kept in their native country in the finest condition, and
have been flown during six, eight, or nine years;[32] 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.[33] 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[34] 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,”[35] 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.[36]
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[37] 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[38]
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.[39] 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.[40] 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[41]
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.[42]
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.[43]
According to Bechstein[44] 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.[45] In Jamaica, a resident naturalist, Mr. R. Hill,[46] 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 _ victoriæ_) 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._[47]
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.[48] With the Gallinaceæ, 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.[49] The American tribe of Guans or Cracidæ are tamed with
remarkable ease, but are very shy breeders in this country;[50] but
with care various species were formerly made to breed rather freely in
Holland.[51] Birds of this tribe are often kept in a perfectly tamed
condition in their native country by the Indians, but they never
breed.[52] 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.[53] 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.[54]
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.”[55]
The members of the great Duck family breed as readily in confinement as
do the Columbæ and Gallinæ 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.[56] “There is not,”
says Mr. Dixon,[57] “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[58] 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,[59] 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[60] 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.[61] 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.[62] Mr. Atkinson could never succeed in India
in making the Tarroo silk-moth breed in confinement.[63] 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.[64]
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.[65] 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[66] 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;[67] 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;[68] 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.[69] 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;[70] and according to Lord Somerville[71] the merino-sheep which
he imported from Spain were not at first perfectly fertile, it is
said[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.[73] 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[74] “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.[75] 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.[76] 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.[77] 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 Gärtner 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. Linnæus long ago
observed[78] 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.[79] 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 Gärtner,[80] it is hardly possible to give too much
manure to most Gramineæ, Cruciferæ, and Leguminosæ, 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 Kölreuter in the case of
Mirabilis.[81] 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[82] 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.[83] _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.[84] 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.[85] The female organs are more
sensitive, for Gärtner[86] 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[87] 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._—Gärtner 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. Gärtner,[88] in his discussion on this subject, has shown that
plants of many orders are occasionally thus affected; but the
Caryophyllaceæ and Liliaceæ suffer most, and to these orders, I think,
the Ericaceæ 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 Gärtner’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 Kölreuter 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, Gärtner’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 Gärtner[89] 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,[90] 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.[91] Species of Primula in which the calyx
is brightly coloured are said[92] 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.[93] 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[94] 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,[95] 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
Compositæ bear what are called double flowers by the abnormal
development of the corolla of their central florets. Doubleness is
sometimes connected with prolification,[96] or the continued growth of
the axis of the flower. Doubleness is strongly inherited. No one has
produced, as Lindley remarks,[97] 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.[98] 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;[99] 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,[100] 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[101] 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[102] 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[103] 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.[104] 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.[105]
So it is with hybrids; for instance, Prof. Lecoq[106] 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.[107] 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[108] 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.[109]
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.[110] 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[111] 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.[112] 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,[113] 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.[114] The periwinkle (_Vinca minor_), which spreads
largely by runners, is said scarcely ever to produce fruit in
England;[115] 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.[116] 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.[117] 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 Gärtner[118] 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[119] first become double. Again, Gärtner[120] 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 Cucurbitaceæ; so
that the production of fruit by plants rendered sterile through any
cause is intelligible. Kölreuter has also expressed his unbounded
astonishment at the size and development of the tubers in certain
hybrids; and all experimentalists[121] 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.
REFERENCES
[1] For England, _see_ below. For Germany, _see_ Metzger,
‘Getreidearten,’ 1841, s. 63. For France, Loiseleur-Deslongchamps
(‘Consid. sur les Céréales,’ 1843, p. 200) gives numerous references
on this subject. For Southern France, _see_ Godron, ‘Florula
Juvenalis,’ 1854, p. 28.
[2] ‘A General Treatise of Husbandry,’ vol. 3 p. 58.
[3] ‘Gardener’s Chronicle and Agricult. Gazette,’ 1858, p. 247; and
for the second statement, Ibid., 1850, p. 702. On this same subject
_see also_ Rev. D. Walker’s ‘Prize Essay of Highland Agricult. Soc.’
vol. ii. p. 200. Also Marshall ‘Minutes of Agriculture,’ November,
1775.
[4] Oberlin’s ‘Memoirs,’ Eng. translat., p. 73. For Lancashire _see_
Marshall’s ‘Review of Reports,’ 1808, p. 295.
[5] ‘Cottage Gardener,’ 1856, p. 186. For Mr. Robson’s subsequent
statements, _see_ ‘Journal of Horticulture,’ Feb. 18, 1866, p. 121.
For Mr. Abbey’s remarks on grafting, etc., Ibid., July 18, 1865, p.
44.
[6] ‘Mém. de l’Acad. des Sciences,’ 1790, p. 209.
[7] ‘On the Varieties of Wheat,’ p. 52.
[8] Mr. Spencer has fully and ably discussed this whole subject in his
‘Principles of Biology,’ 1864, vol. ii. ch. x. In the first edition of
my ‘Origin of Species,’ 1859, p. 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.”
[9] ‘Essais de Zoologie Générale,’ 1841, p. 256.
[10] Since the appearance of the first edition of this work, Mr.
Sclater has published (‘Proc. Zoolog. Soc.,’ 1868, p. 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.
[11] Du Rut, ‘Annales du Muséum,’ 1807, tom. ix. p. 120.
[12] ‘Saugethiere von Paraguay,’ 1830, s. 49, 106, 118, 124, 201, 208,
249, 265, 327.
[13] ‘The Naturalist on the Amazons,’ 1863, vol. i. pp. 99, 193; vol.
ii. p. 113.
[14] ‘Embassy to the Court of Ava,’ vol. i. p. 534.
[15] ‘Journal,’ vol. i. p. 213.
[16] ‘Säugethiere,’ s. 327.
[17] On the Breeding of the Larger Felidæ, ‘Proc. Zoolog. Soc.,’ 1861,
p. 140.
[18] Sleeman’s ‘Rambles in India,’ vol. ii. p. 10.
[19] Wiegmann’s ‘Archiv. fur Naturgesch.,’ 1837, s. 162.
[20] Rengger ‘Säugethiere,’ 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.
[21] Although the existence of the _Leporides,_ as described by Dr.
Broca (‘Journal de Phys.,’ tom. ii. p. 370), has been positively
denied, yet Dr. Pigeaux (‘Annals and Mag. of Nat. Hist.,’ vol. xx.,
1867, p. 75) affirms that the hare and rabbit have produced hybrids.
[22] ‘Quadrupeds of North America,’ by Audubon and Bachman, 1846, p.
268.
[23] Loudon’s ‘Mag. of Nat. Hist.,’ vol. ix., 1836, p. 571; Audubon
and Bachman’s ‘Quadrupeds of North America,’ p. 221.
[24] Flourens, ‘De l’Instinct,’ etc., 1845, p. 88.
[25] _See_ ‘Annual Reports Zoolog. Soc.,’ 1855, 1858, 1863, 1864;
‘Times’ newspaper, Aug. 10th, 1847; Flourens, ‘De l’Instinct,’ p. 85.
[26] ‘Säugethiere,’ etc., s. 34, 49.
[27] Art. Brazil, ‘Penny Cyclop.,’ p. 363.
[28] ‘The Naturalist on the Amazons,’ vol. i. p. 99.
[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, p. 626, since the first edition of this
work appeared. Of Columbæ 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 Gallinæ 83 species have been kept and 1
in 27 have bred; of 57 Grallæ 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 Picariæ and of 35 Herodiones not one species
in either group has bred.
[30] ‘Encyclop. of Rural Sports,’ p. 691.
[31] According to Sir A. Burnes (‘Cabool,’ etc., p. 51), eight species
are used for hawking in Sinde.
[32] Loudon’s ‘Mag. of Nat. Hist.,’ vol. vi., 1833, p. 110.
[33] F. Cuvier, ‘Annal. du Muséum,’ tom. ix. p. 128.
[34] ‘The Zoologist,’ vol. vii.-viii., 1849-50, p. 2648.
[35] Knox, ‘Ornithological Rambles in Sussex,’ p. 91.
[36] ‘The Zoologist,’ vol. vii.-viii., 1849-50, p. 2566; vol. ix.-x.,
1851-2, p. 3207.
[37] Bechstein, ‘Naturgesch. der Stubenvögel,’ 1840, s. 20.
[38] ‘Ornithological Biography,’ vol. v. p. 517.
[39] A case is recorded in ‘The Zoologist,’ vol. i.-ii., 1843-45, p.
453. For the siskin breeding, vol. iii.-iv., 1845-46, p. 1075.
Bechstein ‘Stubenvögel,’ s. 139, speaks of bullfinches making nests,
but rarely producing young.
[40] Yarrell’s ‘Hist. British Birds,’ 1839, vol. i. p. 412.
[41] Loudon’s ‘Mag. of Nat. History,’ vol. xix., 1836, p. 347.
[42] ‘Mémoires du Muséum d’Hist. Nat.,’ tom. x. p. 314: five cases of
parrots breeding in France are here recorded. _ See also_ ‘Report
Brit. Assoc. Zoolog.,’ 1843.
[43] ‘Annals and Mag. of Nat. Hist.,’ Nov. 1868, p. 311.
[44] ‘Stubenvögel,’ s. 105, 83.
[45] Dr. Hancock remarks (‘Charlesworth’s Mag. of Nat. Hist.’ vol.
ii., 1838, p. 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.”
[46] ‘A Week at Pert Royal,’ 1855, p. 7.
[47] Audubon, ‘American Ornithology,’ vol. v. pp. 552, 557.
[48] Mowbray on Poultry, 7th edit., p. 133.
[49] Temminck, ‘Hist. Nat. Gén. des Pigeons,’ etc., 1813, tom. iii.
pp. 288, 382; ‘Annals and Mag. of Nat. Hist.,’ vol. xii., 1843, p.
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,’ tom. xxv. p. 294), and in the Zoological
Gardens in 1856.
[50] Rev. E. S. Dixon, ‘The Dovecote,’ 1851, pp. 243-252.
[51] Temminck, ‘Hist. Nat. Gén. des Pigeons,’ etc., tom. ii. pp. 456,
458; tom. iii. pp. 2, 13, 47.
[52] Bates, ‘The Naturalist on the Amazons,’ vol. i. p. 193; vol. ii.
p. 112.
[53] Temminck, ‘Hist. Nat. Gén.,’ etc., tom. ii. p. 125. For _Tetrao
urogallus, see_ L. Lloyd, ‘Field Sports of North of Europe,’ vol. i.
pp. 287, 314; and ‘Bull. de la Soc. d’Acclimat.,’ tom. vii., 1860, p.
600. For _T. scoticus,_ Thompson, ‘Nat. Hist. of Ireland,’ vol. ii.
1850, p. 49. For _ T. cupido,_ ‘Boston Journal of Nat. Hist.,’ vol.
iii. p. 199.
[54] Marcel de Serres, ‘Annales des Sc. Nat.,’ 2nd series, Zoolog.,
tom. xiii. p. 175.
[55] Dr. Hancock, in ‘Charlesworth’s Mag. of Nat. Hist.,’ vol. ii.,
1838, p. 491; R. Hill, ‘A Week at Port Royal,’ p. 8; ‘Guide to the
Zoological Gardens,’ by P. L. Sclater, 1859, pp. 11, 12; ‘The Knowsley
Menagerie,’ by D. Gray, 1846, pl. xiv.; E. Blyth, ‘Report Asiatic Soc.
of Bengal,’ May 1855.
[56] Prof. Newton, in ‘Proc. Zoolog. Soc.,’ 1860, p. 336.
[57] ‘The Dovecote and Aviary,’ p. 428.
[58] ‘Ornithological Biography,’ vol. iii. p. 9.
[59] ‘Geograph. Journal,’ vol. xiii., 1844, p. 32.
[60] Loudon’s ‘Mag. of Nat. Hist.,’ vol. v., 1832, p. 153.
[61] ‘Zoologist,’ vols. v.-vi., 1847-48, p. 1660.
[62] ‘Transact. Entomolog. Soc.,’ vol. iv., 1845, p. 60.
[63] ‘Transact. Linn. Soc.,’ vol. vii. p. 40.
[64] _See_ an interesting paper by Mr. Newman in the ‘Zoologist,’
1857, p. 5764; and Dr. Wallace, in ‘Proc. Entomolog. Soc.,’ June 4th,
1860, p. 119.
[65] Yarrell’s ‘British Birds,’ vol. i. p. 506; Bechstein
‘Stubenvögel,’ s. 185; ‘Philosoph. Transact.,’ 1772, p. 271. Bronn
(‘Geschichte der Natur,’ Band ii. s. 96) has collected a number of
cases. For the case of the deer, _see_ ‘Penny Cyclop.,’ vol. viii. p.
350.
[66] ‘Journal de Physiologie,’ tom. ii. p. 347.
[67] For additional evidence on this subject, _see_ F. Cuvier in
‘Annales du Muséum,’ tom. xii. p. 119.
[68] Numerous instances could be given. Thus Livingstone (‘Travels,’
p. 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.
[69] For analogous cases with the fowl, _see_ Réaumur, ‘L’Art de faire
Eclore,’ etc., 1749, p. 243; and Col. Sykes, in ‘Proc. Zoolog. Soc.,’
1832, etc. With respect to the fowl not breeding in northern regions,
_see_ Latham’s ‘Hist. of Birds,’ vol. viii., 1823, p. 169.
[70] “Mém. par divers Savans,” ‘Acad. des Sciences,’ tom. vi., 1835,
p. 347.
[71] Youatt on Sheep, p. 181.
[72] J. Mills, ‘Treatise on Cattle,’ 1776, p. 72.
[73] Bechstein, ‘Stubenvögel,’ s. 242.
[74] ‘The Andes and the Amazon,’ 1870, p. 107.
[75] Crawfurd’s ‘Descriptive Dict. of the Indian Islands,’ 1856, p.
145.
[76] ‘Bull. de la Soc. d’Acclimat.,’ tom. ix., 1862, pp. 380, 384.
[77] For pigeons, _see_ Dr. Chapuis, ‘Le Pigeon Voyageur Belge,’ 1865,
p. 66.
[78] ‘Swedish Acts,’ vol. i., 1739, p. 3. Pallas makes the same remark
in his ‘Travels’ (Eng. translat.), vol. i. p. 292.
[79] A. Kerner, ‘Die Cultur der Alpenpflanzen,’ 1864, s. 139; Watson’s
‘Cybele Britannica,’ vol. i. p. 131; Mr. D. Cameron, also, has written
on the culture of Alpine plants in ‘Gard. Chronicle,’ 1848, pp. 253,
268, and mentions a few which seed.
[80] ‘Beiträge zur Kenntniss der Befruchtung,’ 1844 s. 333.
[81] ‘Nova Acta Petrop.,’ 1793, p. 391.
[82] ‘Cottage Gardener,’ 1856, pp. 44, 109.
[83] Dr. Herbert, ‘Amaryllidaceæ,’ p. 176.
[84] Gärtner, ‘Beiträge zur Kenntniss,’ etc., s. 560, 564.
[85] ‘Gardener’s Chronicle,’ 1844, p. 215; 1850, p. 470. Faivre gives
a good résumé on this subject in his ‘La Variabilité des Espèces,’
1868, p. 155.
[86] ‘Beiträge zur Kenntniss,’ etc., s. 252, 338.
[87] ‘Journal of Hort. Soc.,’ vol. ii., 1847, p. 83.
[88] ‘Beiträge zur Kenntniss,’ etc., s. 117 _et seq._; Kölreuter,
‘Zweite Fortsetzung,’ s. 10, 121; ‘Dritte Fortsetzung,’ s. 57.
Herbert, ‘Amaryllidaceæ,’ p. 355. Wiegmann ‘Ueber die
Bastarderzeugung,’ s. 27.
[89] ‘Bastarderzengung,’ s. 356.
[90] ‘Teoria della Riproduzione,’ 1816, p. 84; ‘Traité du Citrus,’
1811, p. 67.
[91] Mr. C. W. Crocker, in ‘Gardener’s Chronicle,’ 1861, p. 1092.
[92] Verlot, ‘Des Variétés,’ 1865, p. 80.
[93] Verlot, ibid., p. 88.
[94] Prof. Allman, Brit. Assoc., quoted in the ‘Phytologist,’ vol. ii.
p. 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 1st, 1863, p. 171.
[95] ‘Comptes Rendus,’ Dec. 19th, 1864, p. 1039.
[96] ‘Gardener’s Chronicle,’ 1866, p. 681.
[97] ‘Theory of Horticulture,’ p. 333.
[98] Mr. Fairweather, in ‘Transact. Hort. Soc.,’ vol. iii. p. 406:
Bosse, quoted by Bronn, ‘Geschichte der Natur,’ B. ii. s. 77. On the
effects of the removal of the anthers, _see_ Mr. Leitner, in
Silliman’s ‘North American Journ. of Science,’ vol. xxiii. p. 47; and
Verlot, ‘Des Variétés,’ 1865, p. 84.
[99] Lindley’s ‘Theory of Horticulture,’ p. 3?3.
[100] ‘Gardener’s Chronicle,’ 1865, p. 626; 1866, pp. 290, 730; and
Verlot, ‘Des Variétés,’ p. 75.
[101] ‘Gardener’s Chronicle,’ 1843, p. 628. In this article I
suggested the theory above given on the doubleness of flowers. This
view is adopted by Carrière, ‘Production et Fix. des Variétés,’ 1865,
p. 67.
[102] Quoted by Gärtner, ‘Bastarderzeugung,’ s. 567.
[103] ‘Gardener’s Chronicle,’ 1866, p. 901.
[104] Lindley, ‘Theory of Horticulture,’ pp. 175-179; Godron, ‘De
l’Espèce,’ tom. ii. p. 106; Pickering, ‘Races of Man;’ Gallesio,
‘Teoria della Riproduzione,’ l816, pp. 101-110. Meyen, (‘Reise um
Erde,’ Th. ii. s. 214) states that at Manilla one variety of the
banana is full of seeds: and Chamisso (Hooker’s ‘Bot. Misc.,’ vol. i.
p. 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.
[105] Ingledew, in ‘Transact. of Agricult. and Hort. Soc. of India,’
vol. ii.
[106] ‘De la Fécondation,’ 1862, p. 308.
[107] Hooker’s ‘Bot. Misc.,’ vol. i. p. 99; Gallesio, ‘Teoria della
Riproduzione,’ p. 110. Dr. J. de Cordemoy, in ‘Transact. of the R.
Soc. of Mauritius’ (new series), vol. vi. 1873, pp. 60-67, gives a
large number of cases of plants which never seed, including several
species indigenous in Mauritius.
[108] ‘Transact. Linn. Soc.,’ vol. xvii. p. 563.
[109] Godron, ‘De l’Espèce,’ tom. ii. p. 106; Herbert on Crocus, in
‘Journal of Hort. Soc.,’ vol. i., 1846, p. 254: Dr. Wight, from what
he has seen in India, believes in this view; ‘Madras Journal of Lit.
and Science,’ vol. iv., 1836, p. 61.
[110] Wahlenberg specifies eight species in this state on the Lapland
Alps: _see_ Appendix to Linnæus’ ‘Tour in Lapland,’ translated by Sir
J. E. Smith, vol. ii. pp. 274-280.
[111] ‘Travels in North America,’ Eng. translat., vol. iii. p. 175.
[112] With respect to the ivy and Acorus, _see_ Dr. Broomfield in the
‘Phytologist,’ vol. iii. p. 376. Also Lindley and Vaucher on the
Acorus, and _see_ Caspary as below.
[113] ‘Annal. des Sc. Nat.,’ 3rd series, Zool., tom. iv. p. 280. Prof.
Decaisne refers also to analogous cases with mosses and lichens near
Paris.
[114] Mr. Tuckermann, in Silliman’s ‘American Journal of Science,’
vol. xlv. p. 1.
[115] Sir J. E. Smith, ‘English Flora,’ vol. i. p. 339.
[116] G. Planchon, ‘Flora de Montpellier,’ 1864, p. 20.
[117] On the non-production of seeds in England, _see_ Mr. Crocker, in
‘Gardener’s Weekly Magazine,’ 1852, p. 70; Vaucher, ‘Hist. Phys.
Plantes d’Europe,’ tom. i. p. 33; Lecoq, ‘Géograph. Bot. d’Europe,’
tom. iv. p. 466; Dr. D. Clos, in ‘Annal. des Sc. Nat.,’ 3rd series,
Bot., tom. xvii. 1852, p. 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. xi. 1870, p. 40, 78.
[118] ‘Bastarderzeugung,’ s. 565. Kölreuter (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.
[119] ‘Teoria della Riproduzione Veg.,’ 1816, p. 73.
[120] ‘Bastarderzeugung,’ s. 573.
[121] Ibid., s. 527.