NISUS FORMATIVUS, OR THE CO-ORDINATING POWER OF THE ORGANISATION—ON THE
EFFECTS OF THE INCREASED USE AND DISUSE OF ORGANS—CHANGED HABITS OF
LIFE—ACCLIMATISATION WITH ANIMALS AND PLANTS—VARIOUS METHODS BY WHICH
THIS CAN BE EFFECTED—ARRESTS OF DEVELOPMENT—RUDIMENTARY ORGANS.
In this and the two following chapters I shall discuss, as well as the
difficulty of the subject permits, the several laws which govern
Variability. These may be grouped under the effects of use and disuse,
including changed habits and acclimatisation—arrest of
development—correlated variation—the cohesion of homologous parts-the
variability of multiple parts—compensation of growth—the position of
buds with respect to the axis of the plant—and lastly, analogous
variation. These several subjects so graduate into one another that
their distinction is often arbitrary.
It may be convenient first briefly to discuss that coordinating and
reparative power which is common, in a higher or lower degree, to all
organic beings, and which was formerly designated by physiologists as
_nisus formativus._
Blumenbach and others[1] have insisted that the principle which permits
a Hydra, when cut into fragments, to develop itself into two or more
perfect animals, is the same with that which causes a wound in the
higher animals to heal by a cicatrice. Such cases as that of the Hydra
are evidently analogous to the spontaneous division or fissiparous
generation of the lowest animals, and likewise to the budding of
plants. Between these extreme cases and that of a mere cicatrice we
have every gradation. Spallanzani[2] by cutting off the legs and tail
of a Salamander, got in the course of three months six crops of these
members; so that 687 perfect bones were reproduced by one animal during
one season. At whatever point the limb was cut off, the deficient part,
and no more, was exactly reproduced. When a diseased bone has been
removed, a new one sometimes “gradually assumes the regular form, and
all the attachments of muscles, ligaments, etc., become as complete as
before.”[3]
This power of regrowth does not, however, always act perfectly; the
reproduced tail of a lizard differs in the form of the scales from the
normal tail: with certain Orthopterous insects the large hind legs are
reproduced of smaller size:[4] the white cicatrice which in the higher
animals unites the edges of a deep wound is not formed of perfect skin,
for elastic tissue is not produced till long afterwards.[5] “The
activity of the _nisus formativus,_” says Blumenbach, “is in an inverse
ratio to the age of the organised body.” Its power is also greater with
animals, the lower they stand in the scale of organisation; and animals
low in the scale correspond with the embryos of higher animals
belonging to the same class. Newport’s observations[6] afford a good
illustration of this fact, for he found that “myriapods, whose highest
development scarcely carries them beyond the larva of perfect insects,
can regenerate limbs and antennae up to the time of their last moult;”
and so can the larvae of true insects, but, except in one order, not in
the mature insect. Salamanders correspond in development with the
tadpoles or larvae of the tailless Batrachians, and both possess to a
large extent the power of regrowth; but not so the mature tailless
Batrachians.
Absorption often plays an important part in the repair of injuries.
When a bone is broken and does not unite, the ends are absorbed and
rounded, so that a false joint is formed; or if the ends unite, but
overlap, the projecting parts are removed.[7] A dislocated bone will
form for itself a new socket. Displaced tendons and varicose veins
excavate new channels in the bones against which they press. But
absorption comes into action, as Virchow remarks, during the normal
growth of bones; parts which are solid during youth become hollowed out
for the medullary tissue as the bone increases in size. In trying to
understand the many well-adapted cases of regrowth when aided by
absorption, we should remember that almost all parts of the
organisation, even whilst retaining the same form, undergo constant
renewal; so that a part which is not renewed would be liable to
absorption.
Some cases, usually classed under the so-called _nisus formativus,_ at
first appear to come under a distinct head; for not only are old
structures reproduced, but new structures are formed. Thus, after
inflammation “false membranes,” furnished with blood-vessels,
lymphatics, and nerves, are developed; or a fœtus escapes from the
Fallopian tubes, and falls into the abdomen, “nature pours out a
quantity of plastic lymph, which forms itself into organised membrane,
richly supplied with blood-vessels,” and the fœtus is nourished for a
time. In certain cases of hydrocephalus the open and dangerous spaces
in the skull are filled up with new bones, which interlock by perfect
serrated sutures.[8] But most physiologists, especially on the
Continent, have now given up the belief in plastic lymph or blastema,
and Virchow[9] maintains that every structure, new or old, is formed by
the proliferation of pre-existing cells. On this view false membranes,
like cancerous or other tumours, are merely abnormal developments of
normal growths; and we can thus understand how it is that they resemble
adjoining structures; for instance, that a “false membrane in the
serous cavities acquires a covering of epithelium exactly like that
which covers the original serous membrane; adhesions of the iris may
become black apparently from the production of pigment-cells like those
of the uvea.”[10]
No doubt the power of reparation, though not always perfect, is an
admirable provision, ready for various emergencies, even for such as
occur only at long intervals of time.[11] Yet this power is not more
wonderful than the growth and development of every single creature,
more especially of those which are propagated by fissiparous
generation. This subject has been here noticed, because we may infer
that, when any part or organ is either greatly increased in size or
wholly suppressed through variation and continued selection, the
co-ordinating power of the organisation will continually tend to bring
again all the parts into harmony with one another.
_On the Effects of the Increased Use and Disuse of Organs._
It is notorious, and we shall immediately adduce proofs, that increased
use or action strengthens muscles, glands, sense-organs, etc.; and that
disuse, on the other hand, weakens them. It has been experimentally
proved by Ranke[12] that the flow of blood is greatly increased towards
any part which is performing work, and sinks again when the part is at
rest. Consequently, if the work is frequent, the vessels increase in
size and the part is better nourished. Paget[13] also accounts for the
long, thick, dark-coloured hairs which occasionally grow, even in young
children, near old-standing inflamed surfaces or fractured bones by an
increased flow of blood to the part. When Hunter inserted the spur of a
cock into the comb, which is well supplied with blood-vessels, it grew
in one case spirally to a length of six inches, and in another case
forward, like a horn, so that the bird could not touch the ground with
its beak. According to the interesting observations of M. Sedillot,[14]
when a portion of one of the bones of the leg of an animal is removed,
the associated bone enlarges till it attains a bulk equal to that of
the two bones, of which it has to perform the functions. This is best
exhibited in dogs in which the tibia has been removed; the companion
bone, which is naturally almost filiform and not one-fifth the size of
the other, soon acquires a size equal to or greater than that of the
tibia. Now, it is at first difficult to believe that increased weight
acting on a straight bone could, by alternately increasing and
diminishing the pressure, cause the blood to flow more freely in the
vessels which permeate the periosteum and thus supply more nutriment to
the bone. Nevertheless the observations adduced by Mr. Spencer,[15] on
the strengthening of the bowed bones of rickety children, along their
concave sides, leads to the belief that this is possible.
The rocking of the stem of a tree increases in a marked manner the
growth of the woody tissue in the parts which are strained. Prof. Sachs
believes, from reasons which he assigns, that this is due to the
pressure of the bark being relaxed in such parts, and not as Knight and
H. Spencer maintain, to an increased flow of sap caused by the movement
of the trunk.[16] But hard woody tissue may be developed without the
aid of any movement, as we see with ivy closely attached to an old
wall. In all such cases, it is very difficult to distinguish between
the effects of long-continued selection and those which follow from the
increased action of the part, or directly from some other cause. Mr. H.
Spencer[17] acknowledges this difficulty, and gives as an instance the
thorns on trees and the shells of nuts. Here we have extremely hard
woody tissue without the possibility of any movement, and without, as
far as we can see, any other directly exciting cause; and as the
hardness of these parts is of manifest service to the plant, we may
look at the result as probably due to the selection of so-called
spontaneous variations. Every one knows that hard work thickens the
epidermis on the hands; and when we hear that with infants, long before
birth, the epidermis is thicker on the palms and soles of the feet than
on any other part of the body, as was observed with admiration by
Albinus,[18] we are naturally inclined to attribute this to the
inherited effects of long-continued use or pressure. We are tempted to
extend the same view even to the hoofs of quadrupeds; but who will
pretend to determine how far natural selection may have aided in the
formation of structures of such obvious importance to the animal?
That use strengthens the muscles may be seen in the limbs of artisans
who follow different trades; and when a muscle is strengthened, the
tendons, and the crests of bone to which they are attached, become
enlarged; and this must likewise be the case with the blood-vessels and
nerves. On the other hand, when a limb is not used, as by Eastern
fanatics, or when the nerve supplying it with nervous power is
effectually destroyed, the muscles wither. So again, when the eye is
destroyed the optic nerve becomes atrophied, sometimes even in the
course of a few months.[19] The Proteus is furnished with branchiae as
well as with lungs: and Schreibers[20] found that when the animal was
compelled to live in deep water, the branchiae were developed to thrice
their ordinary size, and the lungs were partially atrophied. When, on
the other hand, the animal was compelled to live in shallow water, the
lungs became larger and more vascular, whilst the branchiae disappeared
in a more or less complete degree. Such modifications as these are,
however, of comparatively little value for us, as we do not actually
know that they tend to be inherited.
In many cases there is reason to believe that the lessened use of
various organs has affected the corresponding parts in the offspring.
But there is no good evidence that this ever follows in the course of a
single generation. It appears, as in the case of general or indefinite
variability, that several generations must be subjected to changed
habits for any appreciable result. Our domestic fowls, ducks, and geese
have almost lost, not only in the individual but in the race, their
power of flight; for we do not see a young fowl, when frightened, take
flight like a young pheasant. Hence I was led carefully to compare the
limb-bones of fowls, ducks, pigeons, and rabbits, with the same bones
in the wild parent-species. As the measurements and weights were fully
given in the earlier chapters I need here only recapitulate the
results. With domestic pigeons, the length of the sternum, the
prominence of its crest, the length of the scapulae and furculum, the
length of the wings as measured from tip to tip of the radii, are all
reduced relatively to the same parts in the wild pigeon. The wing and
tail feathers, however, are increased in length, but this may have as
little connection with the use of the wings or tail, as the lengthened
hair on a dog with the amount of exercise which it has habitually
taken. The feet of pigeons, except in the long-beaked races, are
reduced in size. With fowls the crest of the sternum is less prominent,
and is often distorted or monstrous; the wing-bones have become lighter
relatively to the leg-bones, and are apparently a little shorter in
comparison with those of the parent-form, the _Gallus bankiva._ With
ducks, the crest of the sternum is affected in the same manner as in
the foregoing cases: the furculum, coracoids, and scapulae are all
reduced in weight relatively to the whole skeleton: the bones of the
wings are shorter and lighter, and the bones of the legs longer and
heavier, relatively to each other, and relatively to the whole
skeleton, in comparison with the same bones in the wild-duck. The
decreased weight and size of the bones, in the foregoing cases, is
probably the indirect result of the reaction of the weakened muscles on
the bones. I failed to compare the feathers of the wings of the tame
and wild duck; but Gloger[21] asserts that in the wild duck the tips of
the wing-feathers reach almost to the end of the tail, whilst in the
domestic duck they often hardly reach to its base. He remarks also on
the greater thickness of the legs, and says that the swimming membrane
between the toes is reduced; but I was not able to detect this latter
difference.
With the domesticated rabbit the body, together with the whole
skeleton, is generally larger and heavier than in the wild animal, and
the leg-bones are heavier in due proportion; but whatever standard of
comparison be taken, neither the leg-bones nor the scapulae have
increased in length proportionally with the increased dimensions of the
rest of the skeleton. The skull has become in a marked manner narrower,
and, from the measurements of its capacity formerly given, we may
conclude, that this narrowness results from the decreased size of the
brain, consequent on the mentally inactive life led by these
closely-confined animals.
We have seen in the eighth chapter that silk-moths, which have been
kept during many centuries closely confined, emerge from their cocoons
with their wings distorted, incapable of flight, often greatly reduced
in size, or even, according to Quatrefages, quite rudimentary. This
condition of the wings may be largely owing to the same kind of
monstrosity which often affects wild Lepidoptera when artificially
reared from the cocoon; or it may be in part due to an inherent
tendency, which is common to the females of many Bombycidae, to have
their wings in a more or less rudimentary state; but part of the effect
may be attributed to long-continued disuse.
From the foregoing facts there can be no doubt that with our anciently
domesticated animals, certain bones have increased or decreased in size
and weight owing to increased or decreased use; but they have not been
modified, as shown in the earlier chapters, in shape or structure. With
animals living a free life and occasionally exposed to severe
competition the reduction would tend to be greater, as it would be an
advantage to them to have the development of every superfluous part
saved. With highly-fed domesticated animals, on the other hand, there
seems to be no economy of growth, nor any tendency to the elimination
of superfluous details. But to this subject I shall recur.
Turning now to more general observations, Nathusius has shown that with
the improved races of the pig, the shortened legs and snout, the form
of the articular condyles of the occiput, and the position of the jaws
with the upper canine teeth projecting in a most anomalous manner in
front of the lower canines, may be attributed to these parts not having
been fully exercised. For the highly-cultivated races do not travel in
search of food, nor root up the ground with their ringed muzzles.[22]
These modifications of structure, which are all strictly inherited,
characterise several improved breeds, so that they cannot have been
derived from any single domestic stock. With respect to cattle,
Professor Tanner has remarked that the lungs and liver in the improved
breeds “are found to be considerably reduced in size when compared with
those possessed by animals having perfect liberty”;[23] and the
reduction of these organs affects the general shape of the body. The
cause of the reduced lungs in highly-bred animals which take little
exercise is obvious; and perhaps the liver may be affected by the
nutritious and artificial food on which they largely subsist. Again,
Dr. Wilckens asserts[24] that various parts of the body certainly
differ in Alpine and lowland breeds of several domesticated animals,
owing to their different habits of life; for instance, the neck and
fore-legs in length, and the hoofs in shape.
It is well known that, when an artery is tied, the anastomosing
branches, from being forced to transmit more blood, increase in
diameter; and this increase cannot be accounted for by mere extension,
as their coats gain in strength. With respect to glands, Sir J. Paget
observes that “when one kidney is destroyed the other often becomes
much larger, and does double work.”[25] If we compare the size of the
udders and their power of secretion in cows which have been long
domesticated, and in certain breeds of the goat in which the udders
nearly touch the ground, with these organs in wild or half-domesticated
animals, the difference is great. A good cow with us daily yields more
than five gallons, or forty pints of milk, whilst a first-rate animal,
kept, for instance, by the Damaras of South Africa,[26] “rarely gives
more than two or three pints of milk daily, and, should her calf be
taken from her, she absolutely refuses to give any.” We may attribute
the excellence of our cows and of certain goats, partly to the
continued selection of the best milking animals, and partly to the
inherited effects of the increased action, through man’s art, of the
secreting glands.
It is notorious that short-sight is inherited; and we have seen in the
twelfth chapter from the statistical researches of M. Giraud-Teulon,
that the habit of viewing near objects gives a tendency to short-sight.
Veterinarians are unanimous that horses are affected with spavins,
splints, ringbones, etc., from being shod and from travelling on hard
roads, and they are almost equally unanimous that a tendency to these
malformations is transmitted. Formerly horses were not shod in North
Carolina, and it has been asserted that they did not then suffer from
these diseases of the legs and feet.[27]
Our domesticated quadrupeds are all descended, as far as is known, from
species having erect ears; yet few kinds can be named, of which at
least one race has not drooping ears. Cats in China, horses in parts of
Russia, sheep in Italy and elsewhere, the guinea-pig formerly in
Germany, goats and cattle in India, rabbits, pigs, and dogs in all
long-civilised countries have dependent ears. With wild animals, which
constantly use their ears like funnels to catch every passing sound,
and especially to ascertain the direction whence it comes, there is
not, as Mr. Blyth has remarked, any species with drooping ears except
the elephant. Hence the incapacity to erect the ears is certainly in
some manner the result of domestication; and this incapacity has been
attributed by various authors[28] to disuse, for animals protected by
man are not compelled habitually to use their ears. Col. Hamilton
Smith[29] states that in ancient effigies of the dog, “with the
exception of one Egyptian instance, no sculpture of the earlier Grecian
era produces representations of hounds with completely drooping ears;
those with them half pendulous are missing in the most ancient; and
this character increases, by degrees, in the works of the Roman
period.” Godron also has remarked “that the pigs of the ancient
Egyptians had not their ears enlarged and pendent.”[30] But it is
remarkable that the drooping of the ear is not accompanied by any
decrease in size; on the contrary, animals so different as fancy
rabbits, certain Indian breeds of the goat, our petted spaniels,
blood-hounds, and other dogs, have enormously elongated ears, so that
it would appear as if their weight had caused them to droop, aided
perhaps by disuse. With rabbits, the drooping of the much elongated
ears has affected even the structure of the skull.
The tail of no wild animal, as remarked to me by Mr. Blyth, is curled;
whereas pigs and some races of dogs have their tails much curled. This
deformity, therefore, appears to be the result of domestication, but
whether in any way connected with the lessened use of the tail is
doubtful.
The epidermis on our hands is easily thickened, as every one knows, by
hard work. In a district of Ceylon the sheep have “horny callosities
that defend their knees, and which arise from their habit of kneeling
down to crop the short herbage, and this distinguishes the Jaffna
flocks from those of other portions of the island;” but it is not
stated whether this peculiarity is inherited.[31]
The mucous membrane which lines the stomach is continuous with the
external skin of the body; therefore it is not surprising that its
texture should be affected by the nature of the food consumed, but
other and more interesting changes likewise follow. Hunter long ago
observed that the muscular coat of the stomach of a gull (_Larus
tridactylus_) which had been fed for a year chiefly on grain was
thickened; and, according to Dr. Edmondston, a similar change
periodically occurs in the Shetland Islands in the stomach of the
_Larus argentatus,_ which in the spring frequents the cornfields and
feeds on the seed. The same careful observer has noticed a great change
in the stomach of a raven which had been long fed on vegetable food. In
the case of an owl (_Strix grallaria_), similarly treated, Menetries
states that the form of the stomach was changed, the inner coat became
leathery, and the liver increased in size. Whether these modifications
in the digestive organs would in the course of generations become
inherited is not known.[32]
The increased or diminished length of the intestines, which apparently
results from changed diet, is a more remarkable case, because it is
characteristic of certain animals in their domesticated condition, and
therefore must be inherited. The complex absorbent system, the
blood-vessels, nerves, and muscles, are necessarily all modified
together with the intestines. According to Daubenton, the intestines of
the domestic cat are one-third longer than those of the wild cat of
Europe; and although this species is not the parent-stock of the
domestic animal, yet, as Isidore Geoffroy has remarked, the several
species of cats are so closely allied that the comparison is probably a
fair one. The increased length appears to be due to the domestic cat
being less strictly carnivorous in its diet than any wild feline
species; for instance, I have seen a French kitten eating vegetables as
readily as meat. According to Cuvier, the intestines of the
domesticated pig exceed greatly in proportionate length those of the
wild boar. In the tame and wild rabbit the change is of an opposite
nature, and probably results from the nutritious food given to the tame
rabbit.[33]
_Changed and inherited Habits of Life._—This subject, as far as the
mental powers of animals are concerned, so blends into instinct, that I
will here only remind the reader of such cases as the tameness of our
domesticated animals—the pointing or retrieving of dogs— their not
attacking the smaller animals kept by man—and so forth. How much of
these changes ought to be attributed to mere habit, and how much to the
selection of individuals which have varied in the desired manner,
irrespectively of the special circumstances under which they have been
kept, can seldom be told.
We have already seen that animals may be habituated to a changed diet;
but some additional instances may be given. In the Polynesian Islands
and in China the dog is fed exclusively on vegetable matter, and the
taste for this kind of food is to a certain extent inherited.[34] Our
sporting dogs will not touch the bones of game birds, whilst most other
dogs devour them with greediness. In some parts of the world sheep have
been largely fed on fish. The domestic hog is fond of barley, the wild
boar is said to disdain it; and the disdain is partially inherited, for
some young wild pigs bred in captivity showed an aversion for this
grain, whilst others of the same brood relished it.[35] One of my
relations bred some young pigs from a Chinese sow by a wild Alpine
boar; they lived free in the park, and were so tame that they came to
the house to be fed; but they would not touch swill, which was devoured
by the other pigs. An animal when once accustomed to an unnatural diet,
which can generally be effected only during youth, dislikes its proper
food, as Spallanzani found to be the case with a pigeon which had been
long fed on meat. Individuals of the same species take to new food with
different degrees of readiness; one horse, it is stated, soon learned
to eat meat, whilst another would have perished from hunger rather than
have partaken of it.[36] The caterpillars of the _Bombyx hesperus_ feed
in a state of nature on the leaves of the _Café diable,_ but, after
having been reared on the Ailanthus, they would not touch the _ Café
diable,_ and actually died of hunger.[37]
It has been found possible to accustom marine fish to live in fresh
water; but as such changes in fish and other marine animals have been
chiefly observed in a state of nature, they do not properly belong to
our present subject. The period of gestation and of maturity, as shown
in the earlier chapters,—the season and the frequency of the act of
breeding,—have all been greatly modified under domestication. With the
Egyptian goose the rate of change with respect to the season has been
recorded.[38] The wild drake pairs with one female, the domestic drake
is polygamous. Certain breeds of fowls have lost the habit of
incubation. The paces of the horse, and the manner of flight of certain
breeds of the pigeon, have been modified and are inherited. Cattle,
horses, and pigs have learnt to browse under water in the St. John’s
River, East Florida, where the Vallisneria has been largely
naturalised. The cows were observed by Prof. Wyman to keep their heads
immersed for “a period varying from fifteen to thirty-five
seconds.”[39] The voice differs much in certain kinds of fowls and
pigeons. Some varieties are clamorous and others silent, as the Call
and common duck, or the Spitz and pointer dog. Every one knows how the
breeds of the dog differ from one another in their manner of hunting,
and in their ardour after different kinds of game or vermin.
With plants the period of vegetation is easily changed and is
inherited, as in the case of summer and winter wheat, barley, and
vetches; but to this subject we shall immediately return under
acclimatisation. Annual plants sometimes become perennial under a new
climate, as I hear from Dr. Hooker is the case with the stock and
mignonette in Tasmania. On the other hand, perennials sometimes become
annuals, as with the Ricinus in England, and as, according to Captain
Mangles, with many varieties of the heartsease. Von Berg[40] raised
from seed of _Verbascum phœniceum,_ which is usually a biennial, both
annual and perennial varieties. Some deciduous bushes become evergreen
in hot countries.[41] Rice requires much water, but there is one
variety in India which can be grown without irrigation.[42] Certain
varieties of the oat and of our other cereals are best fitted for
certain soils.[43] Endless similar facts could be given in the animal
and vegetable kingdoms. They are noticed here because they illustrate
analogous differences in closely allied natural species, and because
such changed habits of life, whether due to habit, or to the direct
action of external conditions, or to so-called spontaneous variability,
would be apt to lead to modifications of structure.
_Acclimatisation._—From the previous remarks we are naturally led to
the much disputed subject of acclimatisation. There are two distinct
questions: Do varieties descended from the same species differ in their
power of living under different climates? And secondly, if they so
differ, how have they become thus adapted? We have seen that European
dogs do not succeed well in India, and it is asserted,[44] that no one
has there succeeded in keeping the Newfoundland long alive; but then it
may be argued, and probably with truth, that these northern breeds are
specifically distinct from the native dogs which flourish in India. The
same remark may be made with respect to different breeds of sheep, of
which, according to Youatt,[45] not one brought “from a torrid climate
lasts out the second year,” in the Zoological Gardens. But sheep are
capable of some degree of acclimatisation, for Merino sheep bred at the
Cape of Good Hope have been found far better adapted for India than
those imported from England.[46] It is almost certain that all the
breeds of the fowl are descended from one species; but the Spanish
breed, which there is good reason to believe originated near the
Mediterranean,[47] though so fine and vigorous in England, suffers more
from frost than any other breed. The Arrindy silk moth introduced from
Bengal, and the Ailanthus moth from the temperate province of Shan
Tung, in China, belong to the same species, as we may infer from their
identity in the caterpillar, cocoon, and mature states;[48] yet they
differ much in constitution: the Indian form “will flourish only in
warm latitudes,” the other is quite hardy and withstands cold and rain.
Plants are more strictly adapted to climate than are animals. The
latter when domesticated withstand such great diversities of climate,
that we find nearly the same species in tropical and temperate
countries; whilst the cultivated plants are widely dissimilar. Hence a
larger field is open for inquiry in regard to the acclimatisation of
plants than of animals. It is no exaggeration to say that with almost
every plant which has long been cultivated, varieties exist which are
endowed with constitutions fitted for very different climates; I will
select only a few of the more striking cases, as it would be tedious to
give all. In North America numerous fruit-trees have been raised, and
in horticultural publications,—for instance, in that by Downing,—lists
are given of the varieties which are best able to withstand the severe
climate of the northern States and Canada. Many American varieties of
the pear, plum, and peach are excellent in their own country, but until
recently, hardly one was known that succeeded in England; and with
apples,[49] not one succeeds. Though the American varieties can
withstand a severer winter than ours, the summer here is not hot
enough. Fruit-trees have also originated in Europe with different
constitutions, but they are not much noticed, because nurserymen here
do not supply wide areas. The Forelle pear flowers early, and when the
flowers have just set, and this is the critical period, they have been
observed, both in France and England, to withstand with complete
impunity a frost of 18 deg and even 14° Fahr., which killed the
flowers, whether fully expanded or in bud, of all other kinds of
pears.[50] This power in the flower of resisting cold and afterwards
producing fruit does not invariably depend, as we know on good
authority,[51] on general constitutional vigour. In proceeding
northward, the number of varieties which are found capable of resisting
the climate rapidly decreases, as may be seen in the list of the
varieties of the cherry, apple, and pear, which can be cultivated in
the neighbourhood of Stockholm.[52] Near Moscow, Prince Troubetzkoy
planted for experiment in the open ground several varieties of the
pear, but one alone, the _Poire sans Pepins,_ withstood the cold of
winter.[53] We thus see that our fruit-trees, like distinct species of
the same genus, certainly differ from each other in their
constitutional adaptation to different climates.
With the varieties of many plants, the adaptation to climate is often
very close. Thus it has been proved by repeated trials “that few if any
of the English varieties of wheat are adapted for cultivation in
Scotland”;[54] but the failure in this case is at first only in the
quantity, though ultimately in the quality, of the grain produced. The
Rev. M. J. Berkeley sowed wheat-seed from India, and got “the most
meagre ears,” on land which would certainly have yielded a good crop
from English wheat.[55] In these cases varieties have been carried from
a warmer to a cooler climate; in the reverse case, as “when wheat was
imported directly from France into the West Indian Islands, it produced
either wholly barren spikes or furnished with only two or three
miserable seeds, while West Indian seed by its side yielded an enormous
harvest.”[56] Here is another case of close adaptation to a slightly
cooler climate; a kind of wheat which in England may be used
indifferently either as a winter or summer variety, when sown under the
warmer climate of Grignan, in France, behaved exactly as if it had been
a true winter wheat.[57]
Botanists believe that all the varieties of maize belong to the same
species; and we have seen that in North America, in proceeding
northward, the varieties cultivated in each zone produce their flowers
and ripen their seed within shorter and shorter periods. So that the
tall, slowly maturing southern varieties do not succeed in New England,
and the New English varieties do not succeed in Canada. I have not met
with any statement that the southern varieties are actually injured or
killed by a degree of cold which the northern varieties can withstand
with impunity, though this is probable; but the production of early
flowering and early seeding varieties deserves to be considered as one
form of acclimatisation. Hence it has been found possible, according to
Kalm, to cultivate maize further and further northwards in America. In
Europe, also, as we learn from the evidence given by Alph. De Candolle,
the culture of maize has extended since the end of the last century
thirty leagues north of its former boundary.[58] On the authority of
Linnæus,[59] I may quote an analogous case, namely, that in Sweden
tobacco raised from home-grown seed ripens its seed a month sooner and
is less liable to miscarry than plants raised from foreign seed.
With the Vine, differently from the maize, the line of practical
culture has retreated a little southward since the middle ages;[60] but
this seems due to commerce being now easier, so that it is better to
import wine from the south than to make it in northern districts.
Nevertheless the fact of the vine not having spread northward shows
that acclimatisation has made no progress during several centuries.
There is, however, a marked difference in the constitution of the
several varieties,— some being hardy, whilst others, like the muscat of
Alexandria, require a very high temperature to come to perfection.
According to Labat,[61] vines taken from France to the West Indies
succeed with extreme difficulty, whilst those imported from Madeira or
the Canary Islands thrive admirably.
Gallesio gives a curious account of the naturalisation of the Orange in
Italy. During many centuries the sweet orange was propagated
exclusively by grafts, and so often suffered from frosts, that it
required protection. After the severe frost of 1709, and more
especially after that of 1763, so many trees were destroyed, that
seedlings from the sweet orange were raised, and, to the surprise of
the inhabitants, their fruit was found to be sweet. The trees thus
raised were larger, more productive, and hardier than the old kinds;
and seedlings are now continually raised. Hence Gallesio concludes that
much more was effected for the naturalisation of the orange in Italy by
the accidental production of new kinds during a period of about sixty
years, than had been effected by grafting old varieties during many
ages.[62] I may add that Risso[63] describes some Portuguese varieties
of the orange as extremely sensitive to cold, and as much tenderer than
certain other varieties.
The peach was known to Theophrastus, 322 B.C.[64] According to the
authorities quoted by Dr. F. Rolle,[65] it was tender when first
introduced into Greece, and even in the island of Rhodes only
occasionally bore fruit. If this be correct, the peach, in spreading
during the last two thousand years over the middle parts of Europe,
must have become much hardier. At the present day different varieties
differ much in hardiness: some French varieties will not succeed in
England; and near Paris, the _Pavie de Bonneuil_ does not ripen its
fruit till very late in the season, even when grown on a wall; “it is,
therefore, only fit for a very hot southern climate.”[66]
I will briefly give a few other cases. A variety of _Magnolia
grandiflora,_ raised by M. Roy, withstands a temperature several
degrees lower than that which any other variety can resist. With
camellias there is much difference in hardiness. One particular variety
of the Noisette rose withstood the severe frost of 1860 “untouched and
hale amidst a universal destruction of other Noisettes.” In New York
the “Irish yew is quite hardy, but the common yew is liable to be cut
down.” I may add that there are varieties of the sweet potato
(_Convolvulus batatas_) which are suited for warmer, as well as for
colder, climates.[67]
The plants as yet mentioned have been found capable of resisting an
unusual degree of cold or heat, when fully grown. The following cases
refer to plants whilst young. In a large bed of young Araucarias of the
same age, growing close together and equally exposed, it was
observed,[68] after the unusually severe winter of 1860-61, that, “in
the midst of the dying, numerous individuals remained on which the
frost had absolutely made no kind of impression.” Dr. Lindley, after
alluding to this and other similar cases, remarks, “Among the lessons
which the late formidable winter has taught us, is that, even in their
power of resisting cold, individuals of the same species of plants are
remarkably different.” Near Salisbury, there was a sharp frost on the
night of May 24, 1836, and all the French beans (_Phaseolus vulgaris_)
in a bed were killed except about one in thirty, which completely
escaped.[69] On the same day of the month, but in the year 1864, there
was a severe frost in Kent, and two rows of scarlet-runners (_P.
multiflorus_) in my garden, containing 390 plants of the same age and
equally exposed, were all blackened and killed except about a dozen
plants. In an adjoining row of “Fulmer’s dwarf bean” (_P. vulgaris_),
one single plant escaped. A still more severe frost occurred four days
afterwards, and of the dozen plants which had previously escaped only
three survived; these were not taller or more vigorous than the other
young plants, but they escaped completely, with not even the tips of
their leaves browned. It was impossible to behold these three plants,
with their blackened, withered, and dead brethren all around, and not
see at a glance that they differed widely in constitutional power of
resisting frost.
This work is not the proper place to show that wild plants of the same
species, naturally growing at different altitudes or under different
latitudes, become to a certain extent acclimatised, as is proved by the
different behaviour of their seedlings when raised in another country.
In my ‘Origin of Species’ I have alluded to some cases, and I could add
many others. One instance must suffice: Mr. Grigor, of Forres,[70]
states that seedlings of the Scotch fir (_Pinus sylvestris_), raised
from seed from the Continent and from the forests of Scotland, differ
much. “The difference is perceptible in one-year-old, and more so in
two-year-old seedlings; but the effects of the winter on the second
year’s growth almost uniformly make those from the Continent quite
brown, and so damaged, that by the month of March they are quite
unsaleable, while the plants from the native Scotch pine, under the
same treatment, and standing alongside, although considerably shorter,
are rather stouter and quite green, so that the beds of the one can be
known from the other when seen from the distance of a mile.” Closely
similar facts have been observed with seedling larches.
Hardy varieties would alone be valued or noticed in Europe; whilst
tender varieties, requiring more warmth, would generally be neglected;
but such occasionally arise. Thus Loudon[71] describes a Cornish
variety of the elm which is almost an evergreen, and of which the
shoots are often killed by the autumnal frosts, so that its timber is
of little value. Horticulturists know that some varieties are much more
tender than others: thus all the varieties of the broccoli are more
tender than cabbages; but there is much difference in this respect in
the sub-varieties of the broccoli; the pink and purple kinds are a
little hardier than the white Cape broccoli, “but they are not to be
depended on after the thermometer falls below 24° Fahr.;” the Walcheren
broccoli is less tender than the Cape, and there are several varieties
which will stand much severer cold than the Walcheren.[72] Cauliflowers
seed more freely in India than cabbages.[73] To give one instance with
flowers: eleven plants raised from a hollyhock, called the _Queen of
the Whites,_[74] were found to be much more tender than various other
seedlings. It may be presumed that all tender varieties would succeed
better under a climate warmer than ours. With fruit-trees, it is well
known that certain varieties, for instance of the peach, stand forcing
in a hot-house better than others; and this shows either pliability of
organisation or some constitutional difference. The same individual
cherry-tree, when forced, has been observed during successive years
gradually to change its period of vegetation.[75] Few pelargoniums can
resist the heat of a stove, but _Alba Multiflora_ will, as a most
skilful gardener asserts, “stand pine-apple top and bottom heat the
whole winter; without looking any more drawn than if it had stood in a
common greenhouse; and _ Blanche Fleur_ seems as if it had been made on
purpose for growing in winter, like many bulbs, and to rest all
summer.”[76] There can hardly be a doubt that the _Alba Multiflora_
pelargonium must have a widely different constitution from that of most
other varieties of this plant; it would probably withstand even an
equatorial climate.
We have seen that according to Labat the vine and wheat require
acclimatisation in order to succeed in the West Indies. Similar facts
have been observed at Madras: “two parcels of mignonette-seed, one
direct from Europe, the other saved at Bangalore (of which the mean
temperature is much below that of Madras), were sown at the same time:
they both vegetated equally favourably, but the former all died off a
few days after they appeared above ground; the latter still survive,
and are vigorous, healthy plants.” “So again, turnip and carrot seed
saved at Hyderabad are found to answer better at Madras than seed from
Europe or from the Cape of Good Hope.”[77] Mr. J. Scott of the Calcutta
Botanic Gardens, informs me that seeds of the sweet-pea (_Lathyrus
odoratus_) imported from England produce plants, with thick, rigid
stems and small leaves, which rarely blossom and never yield seed;
plants raised from French seed blossom sparingly, but all the flowers
are sterile; on the other hand, plants raised from sweet-peas grown
near Darjeeling in Upper India, but originally derived from England,
can be successfully cultivated on the plains of India; for they flower
and seed profusely, and their stems are lax and scandent. In some of
the foregoing cases, as Dr. Hooker has remarked to me, the greater
success may perhaps be attributed to the seeds having been more fully
ripened under a more favourable climate; but this view can hardly be
extended to so many cases, including plants, which, from being
cultivated under a climate hotter than their native one, become fitted
for a still hotter climate. We may therefore safely conclude that
plants can to a certain extent become accustomed to a climate either
hotter or colder than their own; although the latter cases have been
more frequently observed.
We will now consider the means by which acclimatisation may be
effected, namely, through the appearance of varieties having a
different constitution, and through the effects of habit. In regard to
new varieties, there is no evidence that a change in the constitution
of the offspring necessarily stands in any direct relation with the
nature of the climate inhabited by the parents. On the contrary, it is
certain that hardy and tender varieties of the same species appear in
the same country. New varieties thus spontaneously arising become
fitted to slightly different climates in two different ways; firstly,
they may have the power, either as seedlings or when full-grown, of
resisting intense cold, as with the Moscow pear, or of resisting
intense heat, as with some kinds of Pelargonium, or the flowers may
withstand severe frost, as with the Forelle pear. Secondly, plants may
become adapted to climates widely different from their own, from
flowering and fruiting either earlier or later in the season. In both
these cases the power of acclimatisation by man consists simply in the
selection and preservation of new varieties. But without any direct
intention on his part of securing a hardier variety, acclimatisation
may be unconsciously effected by merely raising tender plants from
seed, and by occasionally attempting their cultivation further and
further northwards, as in the case of maize, the orange and the peach.
How much influence ought to be attributed to inherited habit or custom
in the acclimatisation of animals and plants is a much more difficult
question. In many cases natural selection can hardly have failed to
have come into play and complicated the result. It is notorious that
mountain sheep resist severe weather and storms of snow which would
destroy lowland breeds; but then mountain sheep have been thus exposed
from time immemorial, and all delicate individuals will have been
destroyed, and the hardiest preserved. So with the Arrindy silk-moths
of China and India; who can tell how far natural selection may have
taken a share in the formation of the two races, which are now fitted
for such widely different climates? It seems at first probable that the
many fruit-trees which are so well fitted for the hot summers and cold
winters of North America, in contrast with their poor success under our
climate, have become adapted through habit; but when we reflect on the
multitude of seedlings annually raised in that country, and that none
would succeed unless born with a fitting constitution, it is possible
that mere habit may have done nothing towards their acclimatisation. On
the other hand, when we hear that Merino sheep, bred during no great
number of generations at the Cape of Good Hope—that some European
plants raised during only a few generations in the cooler parts of
India, withstand the hotter parts of that country much better than the
sheep or seeds imported directly from England, we must attribute some
influence to habit. We are led to the same conclusion when we hear from
Naudin[78] that the races of melons, squashes, and gourds, which have
long been cultivated in Northern Europe, are comparatively more
precocious, and need much less heat for maturing their fruit, than the
varieties of the same species recently brought from tropical regions.
In the reciprocal conversion of summer and winter wheat, barley, and
vetches into each other, habit produces a marked effect in the course
of a very few generations. The same thing apparently occurs with the
varieties of maize, which, when carried from the Southern States of
America, or into Germany, soon became accustomed to their new homes.
With vine-plants taken to the West Indies from Madeira, which are said
to succeed better than plants brought directly from France, we have
some degree of acclimatisation in the individual, independently of the
production of new varieties by seed.
The common experience of agriculturists is of some value, and they
often advise persons to be cautious in trying the productions of one
country in another. The ancient agricultural writers of China recommend
the preservation and cultivation of the varieties peculiar to each
country. During the classical period, Columella wrote, “Vernaculum
pecus peregrino longe præstantius est.”[79]
I am aware that the attempt to acclimatise either animals or plants has
been called a vain chimera. No doubt the attempt in most cases deserves
to be thus called, if made independently of the production of new
varieties endowed with a different constitution. With plants propagated
by buds, habit rarely produces any effect; it apparently acts only
through successive seminal generations. The laurel, bay, laurestinus,
etc., and the Jerusalem artichoke, which are propagated by cuttings or
tubers, are probably now as tender in England as when first introduced;
and this appears to be the case with the potato, which until recently
was seldom multiplied by seed. With plants propagated by seed, and with
animals, there will be little or no acclimatisation unless the hardier
individuals are either intentionally or unconsciously preserved. The
kidney-bean has often been advanced as an instance of a plant which has
not become hardier since its first introduction into Britain. We hear,
however, on excellent authority[80] that some very fine seed, imported
from abroad, produced plants “which blossomed most profusely, but were
nearly all but abortive, whilst plants grown alongside from English
seed podded abundantly;” and this apparently shows some degree of
acclimatisation in our English plants. We have also seen that seedlings
of the kidney-bean occasionally appear with a marked power of resisting
frost; but no one, as far as I can hear, has ever separated such hardy
seedlings, so as to prevent accidental crossing, and then gathered
their seed, and repeated the process year after year. It may, however,
be objected with truth that natural selection ought to have had a
decided effect on the hardiness of our kidney-beans; for the tenderest
individuals must have been killed during every severe spring, and the
hardier preserved. But it should be borne in mind that the result of
increased hardiness would simply be that gardeners, who are always
anxious for as early a crop as possible, would sow their seed a few
days earlier than formerly. Now, as the period of sowing depends much
on the soil and elevation of each district, and varies with the season;
and as new varieties have often been imported from abroad, can we feel
sure that our kidney-beans are not somewhat hardier? I have not been
able, by searching old horticultural works, to answer this question
satisfactorily.
On the whole the facts now given show that, though habit does something
towards acclimatisation, yet that the appearance of constitutionally
different individuals is a far more effective agent. As no single
instance has been recorded either with animals or plants of hardier
individuals having been long and steadily selected, though such
selection is admitted to be indispensable for the improvement of any
other character, it is not surprising that man has done little in the
acclimatisation of domesticated animals and cultivated plants. We need
not, however, doubt that under nature new races and new species would
become adapted to widely different climates, by variation, aided by
habit, and regulated by natural selection.
_Arrests of Development: Rudimentary and Aborted Organs._
Modifications of structure from arrested development, so great or so
serious as to deserve to be called monstrosities, are not infrequent
with domesticated animals, but, as they differ much from any normal
structure, they require only a passing notice. Thus the whole head may
be represented by a soft nipple-like projection, and the limbs by mere
papillae. These rudiments of limbs are sometimes inherited, as has been
observed in a dog.[81]
Many lesser anomalies appear to be due to arrested development. What
the cause of the arrest may be, we seldom know, except in the case of
direct injury to the embryo. That the cause does not generally act at
an extremely early embryonic period we may infer from the affected
organ seldom being wholly aborted,—a rudiment being generally
preserved. The external ears are represented by mere vestiges in a
Chinese breed of sheep; and in another breed, the tail is reduced “to a
little button, suffocated in a manner, by fat.”[82] In tailless dogs
and cats a stump is left. In certain breeds of fowls the comb and
wattles are reduced to rudiments; in the Cochin-China breed scarcely
more than rudiments of spurs exist. With polled Suffolk cattle,
“rudiments of horns can often be felt at an early age”;[83] and with
species in a state of nature, the relatively great development of
rudimentary organs at an early period of life is highly characteristic
of such organs. With hornless breeds of cattle and sheep, another and
singular kind of rudiment has been observed, namely, minute dangling
horns attached to the skin alone, and which are often shed and grow
again. With hornless goats, according to Desmarest,[84] the bony
protuberance which properly supports the horn exists as a mere
rudiment.
With cultivated plants it is far from rare to find the petals, stamens,
and pistils represented by rudiments, like those observed in natural
species. So it is with the whole seed in many fruits; thus, near
Astrakhan there is a grape with mere traces of seeds, “so small and
lying so near the stalk that they are not perceived in eating the
grape.”[85] In certain varieties of the gourd, the tendrils, according
to Naudin, are represented by rudiments or by various monstrous
growths. In the broccoli and cauliflower the greater number of the
flowers are incapable of expansion, and include rudimentary organs. In
the Feather hyacinth (_Muscari comosum_) in its natural state the upper
and central flowers are brightly coloured but rudimentary; under
cultivation the tendency to abortion travels downwards and outwards,
and all the flowers become rudimentary; but the abortive stamens and
pistils are not so small in the lower as in the upper flowers. In the
_Viburnum opulus,_ on the other hand, the outer flowers naturally have
their organs of fructification in a rudimentary state, and the corolla
is of large size; under cultivation, the change spreads to the centre,
and all the flowers become affected. In the compositae, the so-called
doubling of the flowers consists in the greater development of the
corolla of the central florets, generally accompanied with some degree
of sterility; and it has been observed[86] that the progressive
doubling invariably spreads from the circumference to the centre,—that
is, from the ray florets, which so often include rudimentary organs, to
those of the disc. I may add, as bearing on this subject, that with
Asters, seeds taken from the florets of the circumference have been
found to yield the greatest number of double flowers.[87] In the above
cases we have a natural tendency in certain parts to be rudimentary,
and this under culture spreads either to, or from, the axis of the
plant. It deserves notice, as showing how the same laws govern the
changes which natural species and artificial varieties undergo, that in
the species of Carthamus, one of the Compositae, a tendency to the
abortion of the pappus may be traced extending from the circumference
to the centre of the disc as in the so-called doubling of the flowers
in the members of the same family. Thus, according to A. de
Jussieu,[88] the abortion is only partial in _Carthamus creticus,_ but
more extended in _C. lanatus_; for in this species only two or three of
the central seeds are furnished with a pappus, the surrounding seeds
being either quite naked or furnished with a few hairs; and lastly in
_C. tinctorius,_ even the central seeds are destitute of pappus, and
the abortion is complete.
With animals and plants under domestication, when an organ disappears,
leaving only a rudiment, the loss has generally been sudden, as with
hornless and tailless breeds; and such cases may be ranked as inherited
monstrosities. But in some few cases the loss has been gradual, and has
been effected partly by selection, as with the rudimentary combs and
wattles of certain fowls. We have also seen that the wings of some
domesticated birds have been slightly reduced by disuse, and the great
reduction of the wings in certain silk-moths, with mere rudiments left,
has probably been aided by disuse.
With species in a state of nature, rudimentary organs are extremely
common. Such organs are generally variable, as several naturalists have
observed; for, being useless, they are not regulated by natural
selection, and they are more or less liable to reversion. The same rule
certainly holds good with parts which have become rudimentary under
domestication. We do not know through what steps under nature
rudimentary organs have passed in being reduced to their present
condition; but we so incessantly see in species of the same group the
finest gradations between an organ in a rudimentary and perfect state,
that we are led to believe that the passage must have been extremely
gradual. It may be doubted whether a change of structure so abrupt as
the sudden loss of an organ would ever be of service to a species in a
state of nature; for the conditions to which all organisms are closely
adapted usually change very slowly. Even if an organ did suddenly
disappear in some one individual by an arrest of development,
intercrossing with the other individuals of the same species would tend
to cause its partial reappearance; so that its final reduction could
only be effected by some other means. The most probable view is, that a
part which is now rudimentary, was formerly, owing to changed habits of
life, used less and less, being at the same time reduced in size by
disuse, until at last it became quite useless and superfluous. But as
most parts or organs are not brought into action during an early period
of life, disuse or decreased action will not lead to their reduction
until the organism arrives at a somewhat advanced age; and from the
principle of inheritance at corresponding ages the reduction will be
transmitted to the offspring at the same advanced stage of growth. The
part or organ will thus retain its full size in the embryo, as we know
to be the case with most rudiments. As soon as a part becomes useless,
another principle, that of economy of growth, will come into play, as
it would be an advantage to an organism exposed to severe competition
to save the development of any useless part; and individuals having the
part less developed will have a slight advantage over others. But, as
Mr. Mivart has justly remarked, as soon as a part is much reduced, the
saving from its further reduction will be utterly insignificant; so
that this cannot be effected by natural selection. This manifestly
holds good if the part be formed of mere cellular tissue, entailing
little expenditure of nutriment. How then can the further reduction of
an already somewhat reduced part be effected? That this has occurred
repeatedly under Nature is shown by the many gradations which exist
between organs in a perfect state and the merest vestiges of them. Mr.
Romanes[89] has, I think, thrown much light on this difficult problem.
His view, as far as it can be given in a few words, is as follows: all
parts are somewhat variable and fluctuate in size round an average
point. Now, when a part has already begun from any cause to decrease,
it is very improbable that the variations should be as great in the
direction of increase as of diminution; for the previous reduction
shows that circumstances have not been favourable for its development;
whilst there is nothing to check variations in the opposite direction.
If this be so, the long continued crossing of many individuals
furnished with an organ which fluctuates in a greater degree towards
decrease than towards increase, will slowly but steadily lead to its
diminution. With respect to the complete and absolute abortion of a
part, a distinct principle, which will be discussed in the chapter on
pangenesis, probably comes into action.
With animals and plants reared by man there is no severe or recurrent
struggle for existence, and the principle of economy will not come into
action, so that the reduction of an organ will not thus be aided. So
far, indeed, is this from being the case, that in some few instances
organs, which are naturally rudimentary in the parent-species, become
partially redeveloped in the domesticated descendants. Thus cows, like
most other ruminants, properly have four active and two rudimentary
mamma; but in our domesticated animals, the latter occasionally become
considerably developed and yield milk. The atrophied mammae, which, in
male domesticated animals, including man, have in some rare cases grown
to full size and secreted milk, perhaps offer an analogous case. The
hind feet of dogs naturally include rudiments of a fifth toe, and in
certain large breeds these toes, though still rudimentary, become
considerably developed and are furnished with claws. In the common Hen,
the spurs and comb are rudimentary, but in certain breeds these become,
independently of age or disease of the ovaria, well developed. The
stallion has canine teeth, but the mare has only traces of the alveoli,
which, as I am informed by the eminent veterinarian Mr. G. T. Brown,
frequently contain minute irregular nodules of bone. These nodules,
however, sometimes become developed into imperfect teeth, protruding
through the gums and coated with enamel; and occasionally they grow to
a fourth or even a third of the length of the canines in the stallion.
With plants I do not know whether the redevelopment of rudimentary
organs occurs more frequently under culture than under nature. Perhaps
the pear-tree may be a case in point, for when wild it bears thorns,
which consist of branches in a rudimentary condition and serve as a
protection, but, when the tree is cultivated, they are reconverted into
branches.
REFERENCES
[1] ‘An Essay on Generation,’ Eng. translat., p. 18; p.t, ‘Lectures on
Surgical Pathology,’ 1853, vol. i. p. 209.
[2] ‘An Essay on Animal Reproduction,’ Eng. translat., 1769, p. 79.
[3] Carpenter’s ‘Principles of Comp. Physiology,’ 1854, p. 479.
[4] Charlesworth’s ‘Mag. of Nat. Hist.,’ vol. i. 1837, p. 145.
[5] Paget, ‘Lectures on Surgical Pathology,’ vol. i. p. 239.
[6] Quoted by Carpenter, ‘Comp. Phys.,’ p. 479.
[7] Prof. Marey’s discussion on the power of co-adaptation in all
parts of the organisation is excellent. ‘La Machine Animale,’ 1873,
chap. ix. _See also_ Paget, ‘Lectures,’ etc., p. 257.
[8] These cases are given by Blumenbach in his ‘Essay on Generation,’
pp. 52, 54.
[9] ‘Cellular Pathology,’ trans. by Dr. Chance, 1860, pp. 27, 441.
[10] Paget, ‘Lectures on Pathology,’ vol. i. 1853, p. 357.
[11] Paget, ibid., p. 150.
[12] ‘Die Blutvertheilung, etc. der Organe,’ 1871, as quoted by
Jaeger, ‘In Sachen Darwin’s,’ 1874, p. 48. _See also_ H. Spencer ‘The
Principles of Biology,’ vol. ii. 1866, chap. 3-5.
[13] ‘Lectures on Pathology,’ 1853, vol. i. p. 71.
[14] ‘Comptes Rendus,’ Sept. 26th, 1864, p. 539.
[15] H. Spencer, ‘The Principles of Biology,’ vol. ii. p. 243.
[16] Ibid., vol. ii. p. 269. Sachs, ‘Text-book of Botany,’ 1875, p.
734.
[17] Ibid., vol. ii. p. 273.
[18] Paget, ‘Lectures on Pathology,’ vol. ii. p. 209.
[19] Müller’s ‘Phys.,’ Eng. translat., pp. 54, 791. Prof. Reed has
given (‘Physiological and Anat. Researches,’ p. 10) a curious account
of the atrophy of the limbs of rabbits after the destruction of the
nerve.
[20] Quoted by Lecoq, in ‘Géograph. Bot.,’ tom. i. 1854, p. 182.
[21] ‘Das Abändern der Vögel,’ 1833, s. 74.
[22] Nathusius, ‘Die Racen des Schweines,’ 1860, s. 53, 57;
‘Vorstudien . . . Schweineschädel,’ 1864, s. 103, 130, 133. Prof.
Lucae supports and extends the conclusions of Von Nathusius: ‘Der
Schädel des Maskenschweines,’ 1870.
[23] ‘Journal of Agriculture of Highland Soc.,’ July 1860, p. 321.
[24] ‘Landwirth. Wochenblatt,’ No. 10.
[25] ‘Lectures on Surgical Pathology,’ 1853, vol. i. p. 27.
[26] Andersson, ‘Travels in South Africa,’ p. 318. For analogous cases
in South America _see_ Aug. St.-Hilaire ‘Voyage dans la Province de
Goyaz,’ tom. i. p. 71.
[27] Brickell’s ‘Nat. Hist. of North Carolina,’ 1739, p. 53.
[28] Livingstone, quoted by Youatt on Sheep, p. 142. Hodgson in
‘Journal of Asiatic Soc. of Bengal,’ vol. xvi. 1847, p. 1006, etc.
etc. On the other hand, Dr. Wilckens argues strongly against the
belief that the drooping of the ears is the result of disuse:
‘Jahrbuch der deutschen Viehzucht,’ 1866.
[29] ‘Naturalist’s Library,’ Dogs, vol. ii. 1840, p. 104.
[30] ‘De l’Espèce,’ tom. i. 1859, p. 367.
[31] ‘Ceylon,’ by Sir J. E. Tennent, 1859, vol. ii. p. 531.
[32] For the foregoing statements, _see_ Hunter’s ‘Essays and
Observations,’ 1861, vol. ii. p. 329; Dr. Edmondston, as quoted in
Macgillivray’s ‘British Birds,’ vol. v. p. 550: Menetries, as quoted
in Bronn’s ‘Geschichte der Natur,’ B. ii. s. 110.
[33] These statements on the intestines are taken from Isidore
Geoffroy Saint-Hilaire, ‘Hist. Nat. Gén.,’ tom. iii. pp. 427, 441.
[34] Gilbert White, ‘Nat. Hist. Selborne,’ 1825, vol. ii. p. 121.
[35] Burdach, ‘Traité de Phys.,’ tom. ii. p. 267, as quoted by Dr. P.
Lucas, ‘L’Héréd. Nat.,’ tom. i. p. 388.
[36] This and several other cases are given by Colin, ‘Physiologie
Comp. des Animaux Dom.,’ 1854, tom. i. p. 426.
[37] M. Michely de Cayenne, in ‘Bull. Soc. d’Acclimat.,’ tom. viii.
1861, p. 563.
[38] Quatrefages, ‘Unité de l’Espèce Humaine,’ 1861, p. 79.
[39] ‘The American Naturalist,’ April 1874, p. 237.
[40] ‘Flora,’ 1835, B. ii. p. 504.
[41] Alph. de Candolle, ‘Géograph. Bot.,’ tom. ii. p. 1078.
[42] Royle, ‘Illustrations of the Botany of the Himalaya,’ p. 19.
[43] ‘Gardener’s Chronicle,’ 1850, pp. 204, 219.
[44] Rev. R. Everest, ‘Journal As. Soc. of Bengal,’ vol. iii. p. 19.
[45] Youatt on Sheep, 1838, p. 491.
[46] Royle, ‘Prod. Resources of India,’ p. 153.
[47] Tegetmeier, ‘Poultry Book,’ 1866, p. 102.
[48] Dr. R. Paterson, in a paper communicated to Bot. Soc. of Canada
quoted in the ‘Reader,’ 1863, Nov. 13th.
[49] _See_ remarks by Editor in ‘Gardener’s Chronicle,’ 1848, p. 5.
[50] ‘Gardener’s Chronicle,’ 1860, p. 938. Remarks by Editor and
quotation from Decaisne.
[51] J. de Jonghe, of Brussels, in ‘Gardener’s Chronicle,’ 1857, p.
612.
[52] Ch. Martius, ‘Voyage Bot. Côtes Sept. de la Norvège,’ p. 26.
[53] ‘Journal de l’Acad. Hort. de Gand,’ quoted in ‘Gardener’s
Chronicle,’ 1859, p. 7.
[54] ‘Gardener’s Chronicle,’ 1851, p. 396.
[55] Ibid., 1862, p. 235.
[56] On the authority of Labat, quoted in ‘Gardener’s Chronicle,’
1862, p. 235.
[57] MM. Edwards and Colin, ‘Annal. des Sc. Nat.,’ 2nd series, Bot.,
tom. v. p. 22.
[58] ‘Géograph. Bot.,’ p. 337.
[59] ‘Swedish Acts,’ Eng. translat., 1739-40, vol. i. Kalm, in his
‘Travels,’ vol. ii. p. 166, gives an analogous case with cotton-plants
raised in New Jersey from Carolina seed.
[60] De Candolle, ‘Géograph. Bot.,’ p. 339.
[61] ‘Gardener’s Chronicle,’ 1862, p. 235.
[62] Gallesio, ‘Teoria della Riproduzione Veg.,’ 1816, p. 125; and
‘Traité du Citrus,’ 1811, p. 359.
[63] ‘Essai sur l’Hist. des Orangers,’ 1813, p. 20, etc.
[64] Alph. de Candolle, ‘Géograph. Bot.,’ p. 882.
[65] ‘Ch. Darwin’s Lehre von der Entstehung,’ etc., 1862, s. 87.
[66] Decaisne, quoted in ‘Gardener’s Chronicle,’ 1865, p. 271.
[67] For the magnolia, _see_ Loudon’s ‘Gardener’s Mag.,’ vol. xiii.
1837, p. 21. For camellias and roses, _see_ ‘Gardener’s Chronicle,’
1860, p. 384. For the yew, ‘Journal of Hort.,’ March 3rd, 1863, p.
174. For sweet potatoes, _see_ Col. von Siebold, in ‘Gardener’s
Chronicle,’ 1855, p. 822.
[68] The Editor, ‘Gardener’s Chronicle,’ 1861, p. 239.
[69] Loudon’s ‘Gardener’s Mag.,’ vol. xii. 1836, p. 378.
[70] ‘Gardener’s Chronicle,’ 1865, p. 699. Mr. G. Maw gives
(‘Gardener’s Chronicle,’ 1870, p. 895) a number of striking cases; he
brought home from southern Spain and northern Africa several plants,
which he cultivated in England alongside specimens from northern
districts; and he found a great difference not only in their hardiness
during the winter, but in the behaviour of some of them during the
summer.
[71] ‘Arboretum et Fruticetum,’ vol. iii. p. 1376.
[72] Mr. Robson, in ‘Journal of Horticulture,’ 1861, p. 23.
[73] Dr. Bonavia, ‘Report of the Agri.-Hort. Soc. of Oudh,’ 1866.
[74] ‘Cottage Gardener,’ 1860, April 24th, p. 57.
[75] ‘Gardener’s Chronicle,’ 1841, p. 291.
[76] Mr. Beaton, in ‘Cottage Gardener,’ March 20th, 1860, p. 377.
Queen Mab will also stand stove heat. _See_ ‘Gardener’s Chronicle,’
1845, p. 226.
[77] ‘Gardener’s Chronicle,’ 1841, p. 439.
[78] Quoted by Asa Gray, in ‘Am. Journ. of Sc.,’ 2nd series, Jan.
1865, p. 106.
[79] For China, _see_ ‘Mémoire sur les Chinois,’ tom. xi. 1786, p. 60.
Columella is quoted by Carlier, in ‘Journal de Physique,’ tom. xxiv.
1784.
[80] Messrs. Hardy and Son, in ‘Gardener’s Chronicle,’ 1856, p. 589.
[81] Isid. Geoffroy Saint-Hilaire, ‘Hist. Nat. des Anomalies,’ 1836,
tom. ii. pp. 210, 223, 224, 395; ‘Philosoph. Transact.,’ 1775, p. 313.
[82] Pallas, quoted by Youatt on Sheep, p. 25.
[83] Youatt on Cattle, 1834, p. 174.
[84] ‘Encyclop. Méthod.,’ 1820, p. 483: _see_ p. 500, on the Indian
zebu casting its horns. Similar cases in European cattle were given in
the third chapter.
[85] Pallas, ‘Travels,’ Eng. Translat., vol. i. p. 243.
[86] Mr. Beaton, in ‘Journal of Horticulture,’ May 21st, 1861, p. 133.
[87] Lecoq, ‘De la Fécondation,’ 1862, p. 233.
[88] ‘Annales du Muséum,’ tom. vi. p. 319.
[89] I suggested in ‘Nature’ (vol. 8 pp. 432, 505) that with organisms
subjected to unfavourable conditions all the parts would tend towards
reduction, and that under such circumstances any part which was not
kept up to its standard size by natural selection would, owing to
intercrossing, slowly but steadily decrease. In three subsequent
communications to ‘Nature’ (March 12, April 9, and July 2, 1874), Mr.
Romanes gives his improved view.