Monthly Archives: March 2004

The Descent Of Man

Chapter XVII

 

SECONDARY SEXUAL CHARACTERS OF MAMMALS.

The law of battle–Special weapons, confined to the males–Cause of absence
of weapons in the female–Weapons common to both sexes, yet primarily
acquired by the male–Other uses of such weapons–Their high importance–
Greater size of the male–Means of defence–On the preference shown by
either sex in the pairing of quadrupeds.

With mammals the male appears to win the female much more through the law
of battle than through the display of his charms. The most timid animals,
not provided with any special weapons for fighting, engage in desperate
conflicts during the season of love. Two male hares have been seen to
fight together until one was killed; male moles often fight, and sometimes
with fatal results; male squirrels engage in frequent contests, “and often
wound each other severely”; as do male beavers, so that “hardly a skin is
without scars.” (1. See Waterton’s account of two hares fighting,
‘Zoologist,’ vol. i. 1843, p. 211. On moles, Bell, ‘Hist. of British
Quadrupeds,’ 1st ed., p. 100. On squirrels, Audubon and Bachman,
Viviparous Quadrupeds of N. America, 1846, p. 269. On beavers, Mr. A.H.
Green, in ‘Journal of Linnean Society, Zoology,’ vol. x. 1869, p. 362.) I
observed the same fact with the hides of the guanacoes in Patagonia; and on
one occasion several were so absorbed in fighting that they fearlessly
rushed close by me. Livingstone speaks of the males of the many animals in
Southern Africa as almost invariably shewing the scars received in former
contests.

The law of battle prevails with aquatic as with terrestrial mammals. It is
notorious how desperately male seals fight, both with their teeth and
claws, during the breeding-season; and their hides are likewise often
covered with scars. Male sperm-whales are very jealous at this season; and
in their battles “they often lock their jaws together, and turn on their
sides and twist about”; so that their lower jaws often become distorted.
(2. On the battles of seals, see Capt. C. Abbott in ‘Proc. Zool. Soc.’
1868, p. 191; Mr. R. Brown, ibid. 1868, p. 436; also L. Lloyd, ‘Game Birds
of Sweden,’ 1867, p. 412; also Pennant. On the sperm-whale see Mr. J.H.
Thompson, in ‘Proc. Zool. Soc.’ 1867, p. 246.)

All male animals which are furnished with special weapons for fighting, are
well known to engage in fierce battles. The courage and the desperate
conflicts of stags have often been described; their skeletons have been
found in various parts of the world, with the horns inextricably locked
together, shewing how miserably the victor and vanquished had perished.
(3. See Scrope (‘Art of Deer-stalking,’ p. 17) on the locking of the horns
with the Cervus elaphus. Richardson, in ‘Fauna Bor. Americana,’ 1829, p.
252, says that the wapiti, moose, and reindeer have been found thus locked
together. Sir. A. Smith found at the Cape of Good Hope the skeletons of
two gnus in the same condition.) No animal in the world is so dangerous as
an elephant in must. Lord Tankerville has given me a graphic description
of the battles between the wild bulls in Chillingham Park, the descendants,
degenerated in size but not in courage, of the gigantic Bos primigenius.
In 1861 several contended for mastery; and it was observed that two of the
younger bulls attacked in concert the old leader of the herd, overthrew and
disabled him, so that he was believed by the keepers to be lying mortally
wounded in a neighbouring wood. But a few days afterwards one of the young
bulls approached the wood alone; and then the “monarch of the chase,” who
had been lashing himself up for vengeance, came out and, in a short time,
killed his antagonist. He then quietly joined the herd, and long held
undisputed sway. Admiral Sir B.J. Sulivan informs me that, when he lived
in the Falkland Islands, he imported a young English stallion, which
frequented the hills near Port William with eight mares. On these hills
there were two wild stallions, each with a small troop of mares; “and it is
certain that these stallions would never have approached each other without
fighting. Both had tried singly to fight the English horse and drive away
his mares, but had failed. One day they came in TOGETHER and attacked him.
This was seen by the capitan who had charge of the horses, and who, on
riding to the spot, found one of the two stallions engaged with the English
horse, whilst the other was driving away the mares, and had already
separated four from the rest. The capitan settled the matter by driving
the whole party into the corral, for the wild stallions would not leave the
mares.”

Male animals which are provided with efficient cutting or tearing teeth for
the ordinary purposes of life, such as the carnivora, insectivora, and
rodents, are seldom furnished with weapons especially adapted for fighting
with their rivals. The case is very different with the males of many other
animals. We see this in the horns of stags and of certain kinds of
antelopes in which the females are hornless. With many animals the canine
teeth in the upper or lower jaw, or in both, are much larger in the males
than in the females, or are absent in the latter, with the exception
sometimes of a hidden rudiment. Certain antelopes, the musk-deer, camel,
horse, boar, various apes, seals, and the walrus, offer instances. In the
females of the walrus the tusks are sometimes quite absent. (4. Mr.
Lamont (‘Seasons with the Sea-Horses,’ 1861, p. 143) says that a good tusk
of the male walrus weighs 4 pounds, and is longer than that of the female,
which weighs about 3 pounds. The males are described as fighting
ferociously. On the occasional absence of the tusks in the female, see Mr.
R. Brown, ‘Proceedings, Zoological Society,’ 1868, p. 429.) In the male
elephant of India and in the male dugong (5. Owen, ‘Anatomy of
Vertebrates,’ vol. iii. p. 283.) the upper incisors form offensive weapons.
In the male narwhal the left canine alone is developed into the well-known,
spirally-twisted, so-called horn, which is sometimes from nine to ten feet
in length. It is believed that the males use these horns for fighting
together; for “an unbroken one can rarely be got, and occasionally one may
be found with the point of another jammed into the broken place.” (6. Mr.
R. Brown, in ‘Proc. Zool. Soc.’ 1869, p. 553. See Prof. Turner, in
‘Journal of Anat. and Phys.’ 1872, p. 76, on the homological nature of
these tusks. Also Mr. J.W. Clarke on two tusks being developed in the
males, in ‘Proceedings of the Zoological Society,’ 1871, p. 42.) The tooth
on the opposite side of the head in the male consists of a rudiment about
ten inches in length, which is embedded in the jaw; but sometimes, though
rarely, both are equally developed on the two sides. In the female both
are always rudimentary. The male cachalot has a larger head than that of
the female, and it no doubt aids him in his aquatic battles. Lastly, the
adult male ornithorhynchus is provided with a remarkable apparatus, namely
a spur on the foreleg, closely resembling the poison-fang of a venomous
snake; but according to Harting, the secretion from the gland is not
poisonous; and on the leg of the female there is a hollow, apparently for
the reception of the spur. (7. Owen on the cachalot and Ornithorhynchus,
ibid. vol. iii. pp. 638, 641. Harting is quoted by Dr. Zouteveen in the
Dutch translation of this work, vol. ii. p. 292.)

When the males are provided with weapons which in the females are absent,
there can be hardly a doubt that these serve for fighting with other males;
and that they were acquired through sexual selection, and were transmitted
to the male sex alone. It is not probable, at least in most cases, that
the females have been prevented from acquiring such weapons, on account of
their being useless, superfluous, or in some way injurious. On the
contrary, as they are often used by the males for various purposes, more
especially as a defence against their enemies, it is a surprising fact that
they are so poorly developed, or quite absent, in the females of so many
animals. With female deer the development during each recurrent season of
great branching horns, and with female elephants the development of immense
tusks, would be a great waste of vital power, supposing that they were of
no use to the females. Consequently, they would have tended to be
eliminated in the female through natural selection; that is, if the
successive variations were limited in their transmission to the female sex,
for otherwise the weapons of the males would have been injuriously
affected, and this would have been a greater evil. On the whole, and from
the consideration of the following facts, it seems probable that when the
various weapons differ in the two sexes, this has generally depended on the
kind of transmission which has prevailed.

As the reindeer is the one species in the whole family of Deer, in which
the female is furnished with horns, though they are somewhat smaller,
thinner, and less branched than in the male, it might naturally be thought
that, at least in this case, they must be of some special service to her.
The female retains her horns from the time when they are fully developed,
namely, in September, throughout the winter until April or May, when she
brings forth her young. Mr. Crotch made particular enquiries for me in
Norway, and it appears that the females at this season conceal themselves
for about a fortnight in order to bring forth their young, and then
reappear, generally hornless. In Nova Scotia, however, as I hear from Mr.
H. Reeks, the female sometimes retains her horns longer. The male on the
other hand casts his horns much earlier, towards the end of November. As
both sexes have the same requirements and follow the same habits of life,
and as the male is destitute of horns during the winter, it is improbable
that they can be of any special service to the female during this season,
which includes the larger part of the time during which she is horned. Nor
is it probable that she can have inherited horns from some ancient
progenitor of the family of deer, for, from the fact of the females of so
many species in all quarters of the globe not having horns, we may conclude
that this was the primordial character of the group. (8. On the structure
and shedding of the horns of the reindeer, Hoffberg, ‘Amoenitates Acad.’
vol. iv. 1788, p. 149. See Richardson, ‘Fauna Bor. Americana,’ p. 241, in
regard to the American variety or species: also Major W. Ross King, ‘The
Sportsman in Canada,’ 1866, p. 80.

The horns of the reindeer are developed at a most unusually early age; but
what the cause of this may be is not known. The effect has apparently been
the transference of the horns to both sexes. We should bear in mind that
horns are always transmitted through the female, and that she has a latent
capacity for their development, as we see in old or diseased females. (9.
Isidore Geoffroy St.-Hilaire, ‘Essais de Zoolog. Generale,’ 1841, p. 513.
Other masculine characters, besides the horns, are sometimes similarly
transferred to the female; thus Mr. Boner, in speaking of an old female
chamois (‘Chamois Hunting in the Mountains of Bavaria,’ 1860, 2nd ed., p.
363), says, “not only was the head very male-looking, but along the back
there was a ridge of long hair, usually to be found only in bucks.”)
Moreover the females of some other species of deer exhibit, either normally
or occasionally, rudiments of horns; thus the female of Cervulus moschatus
has “bristly tufts, ending in a knob, instead of a horn”; and “in most
specimens of the female wapiti (Cervus canadensis) there is a sharp bony
protuberance in the place of the horn.” (10. On the Cervulus, Dr. Gray,
‘Catalogue of Mammalia in the British Museum,’ part iii. p. 220. On the
Cervus canadensis or wapiti, see Hon. J.D. Caton, ‘Ottawa Academy of Nat.
Sciences,’ May 1868, p. 9.) From these several considerations we may
conclude that the possession of fairly well-developed horns by the female
reindeer, is due to the males having first acquired them as weapons for
fighting with other males; and secondarily to their development from some
unknown cause at an unusually early age in the males, and their consequent
transference to both sexes.

Turning to the sheath-horned ruminants: with antelopes a graduated series
can be formed, beginning with species, the females of which are completely
destitute of horns–passing on to those which have horns so small as to be
almost rudimentary (as with the Antilocapra americana, in which species
they are present in only one out of four or five females (11. I am
indebted to Dr. Canfield for this information; see also his paper in the
‘Proceedings of the Zoological Society,’ 1866, p. 105.))–to those which
have fairly developed horns, but manifestly smaller and thinner than in the
male and sometimes of a different shape (12. For instance the horns of the
female Ant. euchore resemble those of a distinct species, viz. the Ant.
dorcas var. Corine, see Desmarest, ‘Mammalogie,’ p. 455.),–and ending with
those in which both sexes have horns of equal size. As with the reindeer,
so with antelopes, there exists, as previously shewn, a relation between
the period of the development of the horns and their transmission to one or
both sexes; it is therefore probable that their presence or absence in the
females of some species, and their more or less perfect condition in the
females of other species, depends, not on their being of any special use,
but simply on inheritance. It accords with this view that even in the same
restricted genus both sexes of some species, and the males alone of others,
are thus provided. It is also a remarkable fact that, although the females
of Antilope bezoartica are normally destitute of horns, Mr. Blyth has seen
no less than three females thus furnished; and there was no reason to
suppose that they were old or diseased.

In all the wild species of goats and sheep the horns are larger in the male
than in the female, and are sometimes quite absent in the latter. (13.
Gray, ‘Catalogue of Mammalia, the British Museum,’ part iii. 1852, p. 160.)
In several domestic breeds of these two animals, the males alone are
furnished with horns; and in some breeds, for instance, in the sheep of
North Wales, though both sexes are properly horned, the ewes are very
liable to be hornless. I have been informed by a trustworthy witness, who
purposely inspected a flock of these same sheep during the lambing season,
that the horns at birth are generally more fully developed in the male than
in the female. Mr. J. Peel crossed his Lonk sheep, both sexes of which
always bear horns, with hornless Leicesters and hornless Shropshire Downs;
and the result was that the male offspring had their horns considerably
reduced, whilst the females were wholly destitute of them. These several
facts indicate that, with sheep, the horns are a much less firmly fixed
character in the females than in the males; and this leads us to look at
the horns as properly of masculine origin.

With the adult musk-ox (Ovibos moschatus) the horns of the male are larger
than those of the female, and in the latter the bases do not touch. (14.
Richardson, ‘Fauna Bor. Americana,’ p. 278.) In regard to ordinary cattle
Mr. Blyth remarks: “In most of the wild bovine animals the horns are both
longer and thicker in the bull than in the cow, and in the cow-banteng (Bos
sondaicus) the horns are remarkably small, and inclined much backwards. In
the domestic races of cattle, both of the humped and humpless types, the
horns are short and thick in the bull, longer and more slender in the cow
and ox; and in the Indian buffalo, they are shorter and thicker in the
bull, longer and more slender in the cow. In the wild gaour (B. gaurus)
the horns are mostly both longer and thicker in the bull than in the cow.”
(15. ‘Land and Water,’ 1867, p. 346.) Dr. Forsyth Major also informs me
that a fossil skull, believed to be that of the female Bos etruscus, has
been found in Val d’Arno, which is wholly without horns. In the Rhinoceros
simus, as I may add, the horns of the female are generally longer but less
powerful than in the male; and in some other species of rhinoceros they are
said to be shorter in the female. (16. Sir Andrew Smith, ‘Zoology of S.
Africa,’ pl. xix. Owen, ‘Anatomy of Vertebrates,’ vol. iii. p. 624.) From
these various facts we may infer as probable that horns of all kinds, even
when they are equally developed in the two sexes, were primarily acquired
by the male in order to conquer other males, and have been transferred more
or less completely to the female.

The effects of castration deserve notice, as throwing light on this same
point. Stags after the operation never renew their horns. The male
reindeer, however, must be excepted, as after castration he does renew
them. This fact, as well as the possession of horns by both sexes, seems
at first to prove that the horns in this species do not constitute a sexual
character (17. This is the conclusion of Seidlitz, ‘Die Darwinsche
Theorie,’ 1871, p. 47.); but as they are developed at a very early age,
before the sexes differ in constitution, it is not surprising that they
should be unaffected by castration, even if they were aboriginally acquired
by the male. With sheep both sexes properly bear horns; and I am informed
that with Welch sheep the horns of the males are considerably reduced by
castration; but the degree depends much on the age at which the operation
is performed, as is likewise the case with other animals. Merino rams have
large horns, whilst the ewes “generally speaking are without horns”; and in
this breed castration seems to produce a somewhat greater effect, so that
if performed at an early age the horns “remain almost undeveloped.” (18.
I am much obliged to Prof. Victor Carus, for having made enquiries for me
in Saxony on this subject. H. von Nathusius (‘Viehzucht,’ 1872, p. 64)
says that the horns of sheep castrated at an early period, either
altogether disappear or remain as mere rudiments; but I do not know whether
he refers to merinos or to ordinary breeds.) On the Guinea coast there is
a breed in which the females never bear horns, and, as Mr. Winwood Reade
informs me, the rams after castration are quite destitute of them. With
cattle, the horns of the males are much altered by castration; for instead
of being short and thick, they become longer than those of the cow, but
otherwise resemble them. The Antilope bezoartica offers a somewhat
analogous case: the males have long straight spiral horns, nearly parallel
to each other, and directed backwards; the females occasionally bear horns,
but these when present are of a very different shape, for they are not
spiral, and spreading widely, bend round with the points forwards. Now it
is a remarkable fact that, in the castrated male, as Mr. Blyth informs me,
the horns are of the same peculiar shape as in the female, but longer and
thicker. If we may judge from analogy, the female probably shews us, in
these two cases of cattle and the antelope, the former condition of the
horns in some early progenitor of each species. But why castration should
lead to the reappearance of an early condition of the horns cannot be
explained with any certainty. Nevertheless, it seems probable, that in
nearly the same manner as the constitutional disturbance in the offspring,
caused by a cross between two distinct species or races, often leads to the
reappearance of long-lost characters (19. I have given various experiments
and other evidence proving that this is the case, in my ‘Variation of
Animals and Plants under Domestication,’ vol. ii. 1868, pp. 39-47.); so
here, the disturbance in the constitution of the individual, resulting from
castration, produces the same effect.

The tusks of the elephant, in the different species or races, differ
according to sex, nearly as do the horns of ruminants. In India and
Malacca the males alone are provided with well-developed tusks. The
elephant of Ceylon is considered by most naturalists as a distinct race,
but by some as a distinct species, and here “not one in a hundred is found
with tusks, the few that possess them being exclusively males.” (20. Sir
J. Emerson Tennent, ‘Ceylon,’ 1859, vol. ii. p. 274. For Malacca, ‘Journal
of Indian Archipelago,’ vol. iv. p. 357.) The African elephant is
undoubtedly distinct, and the female has large well-developed tusks, though
not so large as those of the male.

These differences in the tusks of the several races and species of
elephants–the great variability of the horns of deer, as notably in the
wild reindeer–the occasional presence of horns in the female Antilope
Bezoartica, and their frequent absence in the female of Antilocapra
americana–the presence of two tusks in some few male narwhals–the
complete absence of tusks in some female walruses–are all instances of the
extreme variability of secondary sexual characters, and of their liability
to differ in closely-allied forms.

Although tusks and horns appear in all cases to have been primarily
developed as sexual weapons, they often serve other purposes. The elephant
uses his tusks in attacking the tiger; according to Bruce, he scores the
trunks of trees until they can be thrown down easily, and he likewise thus
extracts the farinaceous cores of palms; in Africa he often uses one tusk,
always the same, to probe the ground and thus ascertain whether it will
bear his weight. The common bull defends the herd with his horns; and the
elk in Sweden has been known, according to Lloyd, to strike a wolf dead
with a single blow of his great horns. Many similar facts could be given.
One of the most curious secondary uses to which the horns of an animal may
be occasionally put is that observed by Captain Hutton (21. ‘Calcutta
Journal of Natural History,’ vol. ii, 1843, p. 526.) with the wild goat
(Capra aegagrus) of the Himalayas and, as it is also said with the ibex,
namely that when the male accidentally falls from a height he bends inwards
his head, and by alighting on his massive horns, breaks the shock. The
female cannot thus use her horns, which are smaller, but from her more
quiet disposition she does not need this strange kind of shield so much.

Each male animal uses his weapons in his own peculiar fashion. The common
ram makes a charge and butts with such force with the bases of his horns,
that I have seen a powerful man knocked over like a child. Goats and
certain species of sheep, for instance the Ovis cycloceros of Afghanistan
(22. Mr. Blyth, in ‘Land and Water,’ March, 1867, p. 134, on the authority
of Capt. Hutton and others. For the wild Pembrokeshire goats, see the
‘Field,’ 1869, p. 150.), rear on their hind legs, and then not only butt,
but “make a cut down and a jerk up, with the ribbed front of their
scimitar-shaped horn, as with a sabre. When the O. cycloceros attacked a
large domestic ram, who was a noted bruiser, he conquered him by the sheer
novelty of his mode of fighting, always closing at once with his adversary,
and catching him across the face and nose with a sharp drawing jerk of the
head, and then bounding out of the way before the blow could be returned.”
In Pembrokeshire a male goat, the master of a flock which during several
generations had run wild, was known to have killed several males in single
combat; this goat possessed enormous horns, measuring thirty-nine inches in
a straight line from tip to tip. The common bull, as every one knows,
gores and tosses his opponent; but the Italian buffalo is said never to use
his horns: he gives a tremendous blow with his convex forehead, and then
tramples on his fallen enemy with his knees–an instinct which the common
bull does not possess. (23. M. E.M. Bailly, “Sur l’usage des cornes,”
etc., .Annal des Sciences Nat.’ tom. ii. 1824, p. 369.) Hence a dog who
pins a buffalo by the nose is immediately crushed. We must, however,
remember that the Italian buffalo has been long domesticated, and it is by
no means certain that the wild parent-form had similar horns. Mr. Bartlett
informs me that when a female Cape buffalo (Bubalus caffer) was turned into
an enclosure with a bull of the same species, she attacked him, and he in
return pushed her about with great violence. But it was manifest to Mr.
Bartlett that, had not the bull shewn dignified forbearance, he could
easily have killed her by a single lateral thrust with his immense horns.
The giraffe uses his short, hair-covered horns, which are rather longer in
the male than in the female, in a curious manner; for, with his long neck,
he swings his head to either side, almost upside down, with such force that
I have seen a hard plank deeply indented by a single blow.

[Fig. 63. Oryx leucoryx, male (from the Knowsley Menagerie).]

With antelopes it is sometimes difficult to imagine how they can possibly
use their curiously-shaped horns; thus the springboc (Ant. euchore) has
rather short upright horns, with the sharp points bent inwards almost at
right angles, so as to face each other; Mr. Bartlett does not know how they
are used, but suggests that they would inflict a fearful wound down each
side of the face of an antagonist. The slightly-curved horns of the Oryx
leucoryx (Fig. 63) are directed backwards, and are of such length that
their points reach beyond the middle of the back, over which they extend in
almost parallel lines. Thus they seem singularly ill-fitted for fighting;
but Mr. Bartlett informs me that when two of these animals prepare for
battle, they kneel down, with their beads between their fore legs, and in
this attitude the horns stand nearly parallel and close to the ground, with
the points directed forwards and a little upwards. The combatants then
gradually approach each other, and each endeavours to get the upturned
points under the body of the other; if one succeeds in doing this, he
suddenly springs up, throwing up his head at the same time, and can thus
wound or perhaps even transfix his antagonist. Both animals always kneel
down, so as to guard as far as possible against this manoeuvre. It has
been recorded that one of these antelopes has used his horn with effect
even against a lion; yet from being forced to place his head between the
forelegs in order to bring the points of the horns forward, he would
generally be under a great disadvantage when attacked by any other animal.
It is, therefore, not probable that the horns have been modified into their
present great length and peculiar position, as a protection against beasts
of prey. We can however see that, as soon as some ancient male progenitor
of the Oryx acquired moderately long horns, directed a little backwards, he
would be compelled, in his battles with rival males, to bend his head
somewhat inwards or downwards, as is now done by certain stags; and it is
not improbable that he might have acquired the habit of at first
occasionally and afterwards of regularly kneeling down. In this case it is
almost certain that the males which possessed the longest horns would have
had a great advantage over others with shorter horns; and then the horns
would gradually have been rendered longer and longer, through sexual
selection, until they acquired their present extraordinary length and
position.

With stags of many kinds the branches of the horns offer a curious case of
difficulty; for certainly a single straight point would inflict a much more
serious wound than several diverging ones. In Sir Philip Egerton’s museum
there is a horn of the red-deer (Cervus elaphus), thirty inches in length,
with “not fewer than fifteen snags or branches”; and at Moritzburg there is
still preserved a pair of antlers of a red-deer, shot in 1699 by Frederick
I., one of which bears the astonishing number of thirty-three branches and
the other twenty-seven, making altogether sixty branches. Richardson
figures a pair of antlers of the wild reindeer with twenty-nine points.
(24. On the horns of red-deer, Owen, ‘British Fossil Mammals,’ 1846, p.
478; Richardson on the horns of the reindeer, ‘Fauna Bor. Americana,’ 1829,
p. 240. I am indebted to Prof. Victor Carus, for the Moritzburg case.)
From the manner in which the horns are branched, and more especially from
deer being known occasionally to fight together by kicking with their fore-
feet (25. Hon. J.D. Caton (‘Ottawa Acad. of Nat. Science,’ May 1868, p. 9)
says that the American deer fight with their fore-feet, after “the question
of superiority has been once settled and acknowledged in the herd.”
Bailly, ‘Sur l’Usage des cornes,’ ‘Annales des Sciences Nat.’ tom. ii.
1824, p. 371.), M. Bailly actually comes to the conclusion that their horns
are more injurious than useful to them. But this author overlooks the
pitched battles between rival males. As I felt much perplexed about the
use or advantage of the branches, I applied to Mr. McNeill of Colonsay, who
has long and carefully observed the habits of red-deer, and he informs me
that he has never seen some of the branches brought into use, but that the
brow antlers, from inclining downwards, are a great protection to the
forehead, and their points are likewise used in attack. Sir Philip Egerton
also informs me both as to red-deer and fallow-deer that, in fighting, they
suddenly dash together, and getting their horns fixed against each other’s
bodies, a desperate struggle ensues. When one is at last forced to yield
and turn round, the victor endeavours to plunge his brow antlers into his
defeated foe. It thus appears that the upper branches are used chiefly or
exclusively for pushing and fencing. Nevertheless in some species the
upper branches are used as weapons of offence; when a man was attacked by a
wapiti deer (Cervus canadensis) in Judge Caton’s park in Ottawa, and
several men tried to rescue him, the stag “never raised his head from the
ground; in fact he kept his face almost flat on the ground, with his nose
nearly between his fore feet, except when he rolled his head to one side to
take a new observation preparatory to a plunge.” In this position the ends
of the horns were directed against his adversaries. “In rolling his head
he necessarily raised it somewhat, because his antlers were so long that he
could not roll his head without raising them on one side, while, on the
other side they touched the ground.” The stag by this procedure gradually
drove the party of rescuers backwards to a distance of 150 or 200 feet; and
the attacked man was killed. (26. See a most interesting account in the
Appendix to Hon. J.D. Caton’s paper, as above quoted.)

[Fig. 64. Strepsiceros Kudu (from Sir Andrew Smith’s ‘Zoology of South
Africa.’]

Although the horns of stags are efficient weapons, there can, I think be no
doubt that a single point would have been much more dangerous than a
branched antler; and Judge Caton, who has had large experience with deer,
fully concurs in this conclusion. Nor do the branching horns, though
highly important as a means of defence against rival stags, appear
perfectly well adapted for this purpose, as they are liable to become
interlocked. The suspicion has therefore crossed my mind that they may
serve in part as ornaments. That the branched antlers of stags as well as
the elegant lyrated horns of certain antelopes, with their graceful double
curvature (Fig. 64), are ornamental in our eyes, no one will dispute. If,
then, the horns, like the splendid accoutrements of the knights of old, add
to the noble appearance of stags and antelopes, they may have been modified
partly for this purpose, though mainly for actual service in battle; but I
have no evidence in favour of this belief.

An interesting case has lately been published, from which it appears that
the horns of a deer in one district in the United States are now being
modified through sexual and natural selection. A writer in an excellent
American Journal (27. The ‘American Naturalist,’ Dec. 1869, p. 552.) says,
that he has hunted for the last twenty-one years in the Adirondacks, where
the Cervus virginianus abounds. About fourteen years ago he first heard of
SPIKE-HORN BUCKS. These became from year to year more common; about five
years ago he shot one, and afterwards another, and now they are frequently
killed. “The spike-horn differs greatly from the common antler of the C.
virginianus. It consists of a single spike, more slender than the antler,
and scarcely half so long, projecting forward from the brow, and
terminating in a very sharp point. It gives a considerable advantage to
its possessor over the common buck. Besides enabling him to run more
swiftly through the thick woods and underbrush (every hunter knows that
does and yearling bucks run much more rapidly than the large bucks when
armed with their cumbrous antlers), the spike-horn is a more effective
weapon than the common antler. With this advantage the spike-horn bucks
are gaining upon the common bucks, and may, in time, entirely supersede
them in the Adirondacks. Undoubtedly, the first spike-horn buck was merely
an accidental freak of nature. But his spike-horns gave him an advantage,
and enabled him to propagate his peculiarity. His descendants having a
like advantage, have propagated the peculiarity in a constantly increasing
ratio, till they are slowly crowding the antlered deer from the region they
inhabit.” A critic has well objected to this account by asking, why, if
the simple horns are now so advantageous, were the branched antlers of the
parent-form ever developed? To this I can only answer by remarking, that a
new mode of attack with new weapons might be a great advantage, as shewn by
the case of the Ovis cycloceros, who thus conquered a domestic ram famous
for his fighting power. Though the branched antlers of a stag are well
adapted for fighting with his rivals, and though it might be an advantage
to the prong-horned variety slowly to acquire long and branched horns, if
he had to fight only with others of the same kind, yet it by no means
follows that branched horns would be the best fitted for conquering a foe
differently armed. In the foregoing case of the Oryx leucoryx, it is
almost certain that the victory would rest with an antelope having short
horns, and who therefore did not need to kneel down, though an oryx might
profit by having still longer horns, if he fought only with his proper
rivals.

Male quadrupeds, which are furnished with tusks, use them in various ways,
as in the case of horns. The boar strikes laterally and upwards; the musk-
deer downwards with serious effect. (28. Pallas, ‘Spicilegia Zoologica,’
fasc. xiii. 1779, p. 18.) The walrus, though having so short a neck and so
unwieldy a body, “can strike either upwards, or downwards, or sideways,
with equal dexterity.” (29. Lamont, ‘Seasons with the Sea-Horses,’ 1861,
p. 141.) I was informed by the late Dr. Falconer, that the Indian elephant
fights in a different manner according to the position and curvature of his
tusks. When they are directed forwards and upwards he is able to fling a
tiger to a great distance–it is said to even thirty feet; when they are
short and turned downwards he endeavours suddenly to pin the tiger to the
ground and, in consequence, is dangerous to the rider, who is liable to be
jerked off the howdah. (30. See also Corse (‘Philosophical Transactions,’
1799, p. 212) on the manner in which the short-tusked Mooknah variety
attacks other elephants.)

Very few male quadrupeds possess weapons of two distinct kinds specially
adapted for fighting with rival males. The male muntjac-deer (Cervulus),
however, offers an exception, as he is provided with horns and exserted
canine teeth. But we may infer from what follows that one form of weapon
has often been replaced in the course of ages by another. With ruminants
the development of horns generally stands in an inverse relation with that
of even moderately developed canine teeth. Thus camels, guanacoes,
chevrotains, and musk-deer, are hornless, and they have efficient canines;
these teeth being “always of smaller size in the females than in the
males.” The Camelidae have, in addition to their true canines, a pair of
canine-shaped incisors in their upper jaws. (31. Owen, ‘Anatomy of
Vertebrates,’ vol. iii. p. 349.) Male deer and antelopes, on the other
hand, possess horns, and they rarely have canine teeth; and these, when
present, are always of small size, so that it is doubtful whether they are
of any service in their battles. In Antilope montana they exist only as
rudiments in the young male, disappearing as he grows old; and they are
absent in the female at all ages; but the females of certain other
antelopes and of certain deer have been known occasionally to exhibit
rudiments of these teeth. (32. See Ruppell (in ‘Proc. Zoolog. Soc.’ Jan.
12, 1836, p. 3) on the canines in deer and antelopes, with a note by Mr.
Martin on a female American deer. See also Falconer (‘Palaeont. Memoirs
and Notes,’ vol. i. 1868, p. 576) on canines in an adult female deer. In
old males of the musk-deer the canines (Pallas, ‘Spic. Zoolog.’ fasc. xiii.
1779, p. 18) sometimes grow to the length of three inches, whilst in old
females a rudiment projects scarcely half an inch above the gums.)
Stallions have small canine teeth, which are either quite absent or
rudimentary in the mare; but they do not appear to be used in fighting, for
stallions bite with their incisors, and do not open their mouths wide like
camels and guanacoes. Whenever the adult male possesses canines, now
inefficient, whilst the female has either none or mere rudiments, we may
conclude that the early male progenitor of the species was provided with
efficient canines, which have been partially transferred to the females.
The reduction of these teeth in the males seems to have followed from some
change in their manner of fighting, often (but not in the horse) caused by
the development of new weapons.

Tusks and horns are manifestly of high importance to their possessors, for
their development consumes much organised matter. A single tusk of the
Asiatic elephant–one of the extinct woolly species–and of the African
elephant, have been known to weigh respectively 150, 160, and 180 pounds;
and even greater weights have been given by some authors. (33. Emerson
Tennent, ‘Ceylon,’ 1859, vol. ii. p. 275; Owen, ‘British Fossil Mammals,’
1846, p. 245.) With deer, in which the horns are periodically renewed, the
drain on the constitution must be greater; the horns, for instance, of the
moose weigh from fifty to sixty pounds, and those of the extinct Irish elk
from sixty to seventy pounds–the skull of the latter weighing on an
average only five pounds and a quarter. Although the horns are not
periodically renewed in sheep, yet their development, in the opinion of
many agriculturists, entails a sensible loss to the breeder. Stags,
moreover, in escaping from beasts of prey are loaded with an additional
weight for the race, and are greatly retarded in passing through a woody
country. The moose, for instance, with horns extending five and a half
feet from tip to tip, although so skilful in their use that he will not
touch or break a twig when walking quietly, cannot act so dexterously
whilst rushing away from a pack of wolves. “During his progress he holds
his nose up, so as to lay the horns horizontally back; and in this attitude
cannot see the ground distinctly.” (34. Richardson, ‘Fauna Bor.
Americana,’ on the moose, Alces palmata, pp. 236, 237; on the expanse of
the horns, ‘Land and Water,’ 1869, p. 143. See also Owen, ‘British Fossil
Mammals,’ on the Irish elk, pp. 447, 455.) The tips of the horns of the
great Irish elk were actually eight feet apart! Whilst the horns are
covered with velvet, which lasts with red-deer for about twelve weeks, they
are extremely sensitive to a blow; so that in Germany the stags at this
time somewhat change their habits, and avoiding dense forests, frequent
young woods and low thickets. (35. ‘Forest Creatures,’ by C. Boner, 1861,
p. 60.) These facts remind us that male birds have acquired ornamental
plumes at the cost of retarded flight, and other ornaments at the cost of
some loss of power in their battles with rival males.

With mammals, when, as is often the case, the sexes differ in size, the
males are almost always larger and stronger. I am informed by Mr. Gould
that this holds good in a marked manner with the marsupials of Australia,
the males of which appear to continue growing until an unusually late age.
But the most extraordinary case is that of one of the seals (Callorhinus
ursinus), a full-grown female weighing less than one-sixth of a full-grown
male. (36. See the very interesting paper by Mr. J.A. Allen in ‘Bull.
Mus. Comp. Zoology of Cambridge, United States,’ vol. ii. No. 1, p. 82.
The weights were ascertained by a careful observer, Capt. Bryant. Dr. Gill
in ‘The American Naturalist,’ January, 1871, Prof. Shaler on the relative
size of the sexes of whales, ‘American Naturalist,’ January, 1873.) Dr.
Gill remarks that it is with the polygamous seals, the males of which are
well known to fight savagely together, that the sexes differ much in size;
the monogamous species differing but little. Whales also afford evidence
of the relation existing between the pugnacity of the males and their large
size compared with that of the female; the males of the right-whales do not
fight together, and they are not larger, but rather smaller, than their
females; on the other hand, male sperm-whales fight much together, and
their bodies are “often found scarred with the imprint of their rival’s
teeth,” and they are double the size of the females. The greater strength
of the male, as Hunter long ago remarked (37. ‘Animal Economy,’ p. 45.),
is invariably displayed in those parts of the body which are brought into
action in fighting with rival males–for instance, in the massive neck of
the bull. Male quadrupeds are also more courageous and pugnacious than the
females. There can be little doubt that these characters have been gained,
partly through sexual selection, owing to a long series of victories, by
the stronger and more courageous males over the weaker, and partly through
the inherited effects of use. It is probable that the successive
variations in strength, size, and courage, whether due to mere variability
or to the effects of use, by the accumulation of which male quadrupeds have
acquired these characteristic qualities, occurred rather late in life, and
were consequently to a large extent limited in their transmission to the
same sex.

From these considerations I was anxious to obtain information as to the
Scotch deer-hound, the sexes of which differ more in size than those of any
other breed (though blood-hounds differ considerably), or than in any wild
canine species known to me. Accordingly, I applied to Mr. Cupples, well
known for his success with this breed, who has weighed and measured many of
his own dogs, and who has with great kindness collected for me the
following facts from various sources. Fine male dogs, measured at the
shoulder, range from 28 inches, which is low, to 33 or even 34 inches in
height; and in weight from 80 pounds, which is light, to 120 pounds, or
even more. The females range in height from 23 to 27, or even to 28
inches; and in weight from 50 to 70, or even 80 pounds. (38. See also
Richardson’s ‘Manual on the Dog,’ p. 59. Much valuable information on the
Scottish deer-hound is given by Mr. McNeill, who first called attention to
the inequality in size between the sexes, in Scrope’s ‘Art of Deer-
Stalking.’ I hope that Mr. Cupples will keep to his intention of
publishing a full account and history of this famous breed.) Mr. Cupples
concludes that from 95 to 100 pounds for the male, and 70 for the female,
would be a safe average; but there is reason to believe that formerly both
sexes attained a greater weight. Mr. Cupples has weighed puppies when a
fortnight old; in one litter the average weight of four males exceeded that
of two females by six and a half ounces; in another litter the average
weight of four males exceeded that of one female by less than one ounce;
the same males when three weeks old, exceeded the female by seven and a
half ounces, and at the age of six weeks by nearly fourteen ounces. Mr.
Wright of Yeldersley House, in a letter to Mr. Cupples, says: “I have
taken notes on the sizes and weights of puppies of many litters, and as far
as my experience goes, dog-puppies as a rule differ very little from
bitches till they arrive at about five or six months old; and then the dogs
begin to increase, gaining upon the bitches both in weight and size. At
birth, and for several weeks afterwards, a bitch-puppy will occasionally be
larger than any of the dogs, but they are invariably beaten by them later.”
Mr. McNeill, of Colonsay, concludes that “the males do not attain their
full growth till over two years old, though the females attain it sooner.”
According to Mr. Cupples’ experience, male dogs go on growing in stature
till they are from twelve to eighteen months old, and in weight till from
eighteen to twenty-four months old; whilst the females cease increasing in
stature at the age of from nine to fourteen or fifteen months, and in
weight at the age of from twelve to fifteen months. From these various
statements it is clear that the full difference in size between the male
and female Scotch deer-hound is not acquired until rather late in life.
The males almost exclusively are used for coursing, for, as Mr. McNeill
informs me, the females have not sufficient strength and weight to pull
down a full-grown deer. From the names used in old legends, it appears, as
I hear from Mr. Cupples, that, at a very ancient period, the males were the
most celebrated, the females being mentioned only as the mothers of famous
dogs. Hence, during many generations, it is the male which has been
chiefly tested for strength, size, speed, and courage, and the best will
have been bred from. As, however, the males do not attain their full
dimensions until rather late in life, they will have tended, in accordance
with the law often indicated, to transmit their characters to their male
offspring alone; and thus the great inequality in size between the sexes of
the Scotch deer-hound may probably be accounted for.

[Fig. 65. Head of Common wild boar, in prime of life (from Brehm).]

The males of some few quadrupeds possess organs or parts developed solely
as a means of defence against the attacks of other males. Some kinds of
deer use, as we have seen, the upper branches of their horns chiefly or
exclusively for defending themselves; and the Oryx antelope, as I am
informed by Mr. Bartlett, fences most skilfully with his long, gently
curved horns; but these are likewise used as organs of offence. The same
observer remarks that rhinoceroses in fighting, parry each other’s sidelong
blows with their horns, which clatter loudly together, as do the tusks of
boars. Although wild boars fight desperately, they seldom, according to
Brehm, receive fatal wounds, as the blows fall on each other’s tusks, or on
the layer of gristly skin covering the shoulder, called by the German
hunters, the shield; and here we have a part specially modified for
defence. With boars in the prime of life (Fig. 65) the tusks in the lower
jaw are used for fighting, but they become in old age, as Brehm states, so
much curved inwards and upwards over the snout that they can no longer be
used in this way. They may, however, still serve, and even more
effectively, as a means of defence. In compensation for the loss of the
lower tusks as weapons of offence, those in the upper jaw, which always
project a little laterally, increase in old age so much in length and curve
so much upwards that they can be used for attack. Nevertheless, an old
boar is not so dangerous to man as one at the age of six or seven years.
(39. Brehm, ‘Thierleben,’ B. ii. ss. 729-732.)

[Fig. 66. Skull of the Babirusa Pig (from Wallace’s ‘Malay Archipelago’).]

In the full-grown male Babirusa pig of Celebes (Fig. 66), the lower tusks
are formidable weapons, like those of the European boar in the prime of
life, whilst the upper tusks are so long and have their points so much
curled inwards, sometimes even touching the forehead, that they are utterly
useless as weapons of attack. They more nearly resemble horns than teeth,
and are so manifestly useless as teeth that the animal was formerly
supposed to rest his head by hooking them on to a branch! Their convex
surfaces, however, if the head were held a little laterally, would serve as
an excellent guard; and hence, perhaps, it is that in old animals they “are
generally broken off, as if by fighting.” (40. See Mr. Wallace’s
interesting account of this animal, ‘The Malay Archipelago,’ 1869, vol. i.
p. 435.) Here, then, we have the curious case of the upper tusks of the
Babirusa regularly assuming during the prime of life a structure which
apparently renders them fitted only for defence; whilst in the European
boar the lower tusks assume in a less degree and only during old age nearly
the same form, and then serve in like manner solely for defence.

[Fig. 67. Head of female Aethopian wart-hog, from ‘Proc. Zool. Soc.’ 1869,
shewing the same characters as the male, though on a reduced scale.
N.B. When the engraving was first made, I was under the impression that it
represented the male.]

In the wart-hog (see Phacochoerus aethiopicus, Fig. 67) the tusks in the
upper jaw of the male curve upwards during the prime of life, and from
being pointed serve as formidable weapons. The tusks in the lower jaw are
sharper than those in the upper, but from their shortness it seems hardly
possible that they can be used as weapons of attack. They must, however,
greatly strengthen those in the upper jaw, from being ground so as to fit
closely against their bases. Neither the upper nor the lower tusks appear
to have been specially modified to act as guards, though no doubt they are
to a certain extent used for this purpose. But the wart-hog is not
destitute of other special means of protection, for it has, on each side of
the face, beneath the eyes, a rather stiff, yet flexible, cartilaginous,
oblong pad (Fig. 67), which projects two or three inches outwards; and it
appeared to Mr. Bartlett and myself, when viewing the living animal, that
these pads, when struck from beneath by the tusks of an opponent, would be
turned upwards, and would thus admirably protect the somewhat prominent
eyes. I may add, on the authority of Mr. Bartlett, that these boars when
fighting stand directly face to face.

Lastly, the African river-hog (Potomochoerus penicillatus) has a hard
cartilaginous knob on each side of the face beneath the eyes, which answers
to the flexible pad of the wart-hog; it has also two bony prominences on
the upper jaw above the nostrils. A boar of this species in the Zoological
Gardens recently broke into the cage of the wart-hog. They fought all
night long, and were found in the morning much exhausted, but not seriously
wounded. It is a significant fact, as shewing the purposes of the above-
described projections and excrescences, that these were covered with blood,
and were scored and abraded in an extraordinary manner.

Although the males of so many members of the pig family are provided with
weapons, and as we have just seen with means of defence, these weapons seem
to have been acquired within a rather late geological period. Dr. Forsyth
Major specifies (41. ‘Atti della Soc. Italiana di Sc. Nat.’ 1873, vol. xv.
fasc. iv.) several miocene species, in none of which do the tusks appear to
have been largely developed in the males; and Professor Rutimeyer was
formerly struck with this same fact.

The mane of the lion forms a good defence against the attacks of rival
lions, the one danger to which he is liable; for the males, as Sir A. Smith
informs me, engage in terrible battles, and a young lion dares not approach
an old one. In 1857 a tiger at Bromwich broke into the cage of a lion and
a fearful scene ensued: “the lion’s mane saved his neck and head from
being much injured, but the tiger at last succeeded in ripping up his
belly, and in a few minutes he was dead.” (42. ‘The Times,’ Nov. 10,
1857. In regard to the Canada lynx, see Audubon and Bachman, ‘Quadrupeds
of North America,’ 1846, p. 139.) The broad ruff round the throat and chin
of the Canadian lynx (Felis canadensis) is much longer in the male than in
the female; but whether it serves as a defence I do not know. Male seals
are well known to fight desperately together, and the males of certain
kinds (Otaria jubata) (43. Dr. Murie, on Otaria, ‘Proc. Zoolog. Soc.’
1869, p. 109. Mr. J.A. Allen, in the paper above quoted (p. 75), doubts
whether the hair, which is longer on the neck in the male than in the
female, deserves to be called a mane.) have great manes, whilst the females
have small ones or none. The male baboon of the Cape of Good Hope
(Cynocephalus porcarius) has a much longer mane and larger canine teeth
than the female; and the mane probably serves as a protection, for, on
asking the keepers in the Zoological Gardens, without giving them any clue
to my object, whether any of the monkeys especially attacked each other by
the nape of the neck, I was answered that this was not the case, except
with the above baboon. In the Hamadryas baboon, Ehrenberg compares the
mane of the adult male to that of a young lion, whilst in the young of both
sexes and in the female the mane is almost absent.

It appeared to me probable that the immense woolly mane of the male
American bison, which reaches almost to the ground, and is much more
developed in the males than in the females, served as a protection to them
in their terrible battles; but an experienced hunter told Judge Caton that
he had never observed anything which favoured this belief. The stallion
has a thicker and fuller mane than the mare; and I have made particular
inquiries of two great trainers and breeders, who have had charge of many
entire horses, and am assured that they “invariably endeavour to seize one
another by the neck.” It does not, however, follow from the foregoing
statements, that when the hair on the neck serves as a defence, that it was
originally developed for this purpose, though this is probable in some
cases, as in that of the lion. I am informed by Mr. McNeill that the long
hairs on the throat of the stag (Cervus elaphus) serve as a great
protection to him when hunted, for the dogs generally endeavour to seize
him by the throat; but it is not probable that these hairs were specially
developed for this purpose; otherwise the young and the females would have
been equally protected.

CHOICE IN PAIRING BY EITHER SEX OF QUADRUPEDS.

Before describing in the next chapter, the differences between the sexes in
voice, odours emitted, and ornaments, it will be convenient here to
consider whether the sexes exert any choice in their unions. Does the
female prefer any particular male, either before or after the males may
have fought together for supremacy; or does the male, when not a
polygamist, select any particular female? The general impression amongst
breeders seems to be that the male accepts any female; and this owing to
his eagerness, is, in most cases, probably the truth. Whether the female
as a general rule indifferently accepts any male is much more doubtful. In
the fourteenth chapter, on Birds, a considerable body of direct and
indirect evidence was advanced, shewing that the female selects her
partner; and it would be a strange anomaly if female quadrupeds, which
stand higher in the scale and have higher mental powers, did not generally,
or at least often, exert some choice. The female could in most cases
escape, if wooed by a male that did not please or excite her; and when
pursued by several males, as commonly occurs, she would often have the
opportunity, whilst they were fighting together, of escaping with some one
male, or at least of temporarily pairing with him. This latter contingency
has often been observed in Scotland with female red-deer, as I am informed
by Sir Philip Egerton and others. (44. Mr. Boner, in his excellent
description of the habits of the red-deer in Germany (‘Forest Creatures,’
1861, p. 81) says, “while the stag is defending his rights against one
intruder, another invades the sanctuary of his harem, and carries off
trophy after trophy.” Exactly the same thing occurs with seals; see Mr.
J.A. Allen, ibid. p. 100.)

It is scarcely possible that much should be known about female quadrupeds
in a state of nature making any choice in their marriage unions. The
following curious details on the courtship of one of the eared seals
(Callorhinus ursinus) are given (45. Mr. J.A. Allen in ‘Bull. Mus. Comp.
Zoolog. of Cambridge, United States,’ vol. ii. No. 1, p. 99.) on the
authority of Capt. Bryant, who had ample opportunities for observation. He
says, “Many of the females on their arrival at the island where they breed
appear desirous of returning to some particular male, and frequently climb
the outlying rocks to overlook the rookeries, calling out and listening as
if for a familiar voice. Then changing to another place they do the same
again…As soon as a female reaches the shore, the nearest male goes down
to meet her, making meanwhile a noise like the clucking of a hen to her
chickens. He bows to her and coaxes her until he gets between her and the
water so that she cannot escape him. Then his manner changes, and with a
harsh growl he drives her to a place in his harem. This continues until
the lower row of harems is nearly full. Then the males higher up select
the time when their more fortunate neighbours are off their guard to steal
their wives. This they do by taking them in their mouths and lifting them
over the heads of the other females, and carefully placing them in their
own harem, carrying them as cats do their kittens. Those still higher up
pursue the same method until the whole space is occupied. Frequently a
struggle ensues between two males for the possession of the same female,
and both seizing her at once pull her in two or terribly lacerate her with
their teeth. When the space is all filled, the old male walks around
complacently reviewing his family, scolding those who crowd or disturb the
others, and fiercely driving off all intruders. This surveillance always
keeps him actively occupied.”

As so little is known about the courtship of animals in a state of nature,
I have endeavoured to discover how far our domesticated quadrupeds evince
any choice in their unions. Dogs offer the best opportunity for
observation, as they are carefully attended to and well understood. Many
breeders have expressed a strong opinion on this head. Thus, Mr. Mayhew
remarks, “The females are able to bestow their affections; and tender
recollections are as potent over them as they are known to be in other
cases, where higher animals are concerned. Bitches are not always prudent
in their loves, but are apt to fling themselves away on curs of low degree.
If reared with a companion of vulgar appearance, there often springs up
between the pair a devotion which no time can afterwards subdue. The
passion, for such it really is, becomes of a more than romantic endurance.”
Mr. Mayhew, who attended chiefly to the smaller breeds, is convinced that
the females are strongly attracted by males of a large size. (46. ‘Dogs:
their Management,’ by E. Mayhew, M.R.C.V.S., 2nd ed., 1864, pp. 187-192.)
The well-known veterinary Blaine states (47. Quoted by Alex. Walker, ‘On
Intermarriage,’ 1838, p. 276; see also p. 244.) that his own female pug dog
became so attached to a spaniel, and a female setter to a cur, that in
neither case would they pair with a dog of their own breed until several
weeks had elapsed. Two similar and trustworthy accounts have been given me
in regard to a female retriever and a spaniel, both of which became
enamoured with terrier-dogs.

Mr. Cupples informs me that he can personally vouch for the accuracy of the
following more remarkable case, in which a valuable and wonderfully-
intelligent female terrier loved a retriever belonging to a neighbour to
such a degree, that she had often to be dragged away from him. After their
permanent separation, although repeatedly shewing milk in her teats, she
would never acknowledge the courtship of any other dog, and to the regret
of her owner never bore puppies. Mr. Cupples also states, that in 1868, a
female deerhound in his kennel thrice produced puppies, and on each
occasion shewed a marked preference for one of the largest and handsomest,
but not the most eager, of four deerhounds living with her, all in the
prime of life. Mr. Cupples has observed that the female generally favours a
dog whom she has associated with and knows; her shyness and timidity at
first incline her against a strange dog. The male, on the contrary, seems
rather inclined towards strange females. It appears to be rare when the
male refuses any particular female, but Mr. Wright, of Yeldersley House, a
great breeder of dogs, informs me that he has known some instances; he
cites the case of one of his own deerhounds, who would not take any notice
of a particular female mastiff, so that another deerhound had to be
employed. It would be superfluous to give, as I could, other instances,
and I will only add that Mr. Barr, who has carefully bred many bloodhounds,
states that in almost every instance particular individuals of opposite
sexes shew a decided prefered.

The Autobiography of Charles Darwin

Written May 1st, 1881.

 

‘The Effects of Cross and Self-Fertilisation’ was published in
the autumn of 1876; and the results there arrived at explain, as
I believe, the endless and wonderful contrivances for the
transportal of pollen from one plant to another of the same
species. I now believe, however, chiefly from the observations
of Hermann Muller, that I ought to have insisted more strongly
than I did on the many adaptations for self-fertilisation; though
I was well aware of many such adaptations. A much enlarged
edition of my ‘Fertilisation of Orchids’,
English naturalist Charles Darwin wrote the book ‘Fertilization of Orchid’ in 1862. It took ten years to complete this book, this book explains about the how insects take part in the fertilization of British and foreign orchids and good effects of intercrossing. The observations presented in the book was slowly collected for many years. Click Learn More Here to know about the book. was published in 1877.

In this same year ‘The Different Forms of Flowers, etc.,’
appeared, and in 1880 a second edition. This book consists
chiefly of the several papers on Heterostyled flowers originally
published by the Linnean Society, corrected, with much new matter
added, together with observations on some other cases in which
the same plant bears two kinds of flowers. As before remarked,
no little discovery of mine ever gave me so much pleasure as the
making out the meaning of heterostyled flowers. The results of
crossing such flowers in an illegitimate manner, I believe to be
very important, as bearing on the sterility of hybrids; although
these results have been noticed by only a few persons.

In 1879, I had a translation of Dr. Ernst Krause’s ‘Life of
Erasmus Darwin’ published, and I added a sketch of his character
and habits from material in my possession. Many persons have
been much interested by this little life, and I am surprised that
only 800 or 900 copies were sold.

In 1880 I published, with [my son] Frank’s assistance, our ‘Power
of Movement in Plants.’ This was a tough piece of work. The
book bears somewhat the same relation to my little book on
‘Climbing Plants,’ which ‘Cross-Fertilisation’ did to the
‘Fertilisation of Orchids;’ for in accordance with the principle
of evolution it was impossible to account for climbing plants
having been developed in so many widely different groups unless
all kinds of plants possess some slight power of movement of an
analogous kind. This I proved to be the case; and I was further
led to a rather wide generalisation, viz. that the great and
important classes of movements, excited by light, the attraction
of gravity, etc., are all modified forms of the fundamental
movement of circumnutation. It has always pleased me to exalt
plants in the scale of organised beings; and I therefore felt an
especial pleasure in showing how many and what admirably well
adapted movements the tip of a root possesses.

I have now (May 1, 1881) sent to the printers the MS. of a little
book on ‘The Formation of Vegetable Mould, through the Action of
Worms.’ This is a subject of but small importance; and I know
not whether it will interest any readers (Between November 1881
and February 1884, 8500 copies have been sold.), but it has
interested me. It is the completion of a short paper read before
the Geological Society more than forty years ago, and has revived
old geological thoughts.

I have now mentioned all the books which I have published, and
these have been the milestones in my life, so that little remains
to be said. I am not conscious of any change in my mind during
the last thirty years, excepting in one point presently to be
mentioned; nor, indeed, could any change have been expected
unless one of general deterioration. But my father lived to his
eighty-third year with his mind as lively as ever it was, and all
his faculties undimmed; and I hope that I may die before my mind
fails to a sensible extent. I think that I have become a little
more skilful in guessing right explanations and in devising
experimental tests; but this may probably be the result of mere
practice, and of a larger store of knowledge. I have as much
difficulty as ever in expressing myself clearly and concisely;
and this difficulty has caused me a very great loss of time; but
it has had the compensating advantage of forcing me to think long
and intently about every sentence, and thus I have been led to
see errors in reasoning and in my own observations or those of
others.

There seems to be a sort of fatality in my mind leading me to put
at first my statement or proposition in a wrong or awkward form.
Formerly I used to think about my sentences before writing them
down; but for several years I have found that it saves time to
scribble in a vile hand whole pages as quickly as I possibly can,
contracting half the words; and then correct deliberately.
Sentences thus scribbled down are often better ones than I could
have written deliberately.

Having said thus much about my manner of writing, I will add that
with my large books I spend a good deal of time over the general
arrangement of the matter. I first make the rudest outline in
two or three pages, and then a larger one in several pages, a few
words or one word standing for a whole discussion or series of
facts. Each one of these headings is again enlarged and often
transferred before I begin to write in extenso. As in several of
my books facts observed by others have been very extensively
used, and as I have always had several quite distinct subjects in
hand at the same time, I may mention that I keep from thirty to
forty large portfolios, in cabinets with labelled shelves, into
which I can at once put a detached reference or memorandum. I
have bought many books, and at their ends I make an index of all
the facts that concern my work; or, if the book is not my own,
write out a separate abstract, and of such abstracts I have a
large drawer full. Before beginning on any subject I look to all
the short indexes and make a general and classified index, and by
taking the one or more proper portfolios I have all the
information collected during my life ready for use.

I have said that in one respect my mind has changed during the
last twenty or thirty years. Up to the age of thirty, or beyond
it, poetry of many kinds, such as the works of Milton, Gray,
Byron, Wordsworth, Coleridge, and Shelley, gave me great
pleasure, and even as a schoolboy I took intense delight in
Shakespeare, especially in the historical plays. I have also
said that formerly pictures gave me considerable, and music very
great delight. But now for many years I cannot endure to read a
line of poetry: I have tried lately to read Shakespeare, and
found it so intolerably dull that it nauseated me. I have also
almost lost my taste for pictures or music. Music generally sets
me thinking too energetically on what I have been at work on,
instead of giving me pleasure. I retain some taste for fine
scenery, but it does not cause me the exquisite delight which it
formerly did. On the other hand, novels which are works of the
imagination, though not of a very high order, have been for years
a wonderful relief and pleasure to me, and I often bless all
novelists. A surprising number have been read aloud to me, and I
like all if moderately good, and if they do not end unhappily–
against which a law ought to be passed. A novel, according to my
taste, does not come into the first class unless it contains some
person whom one can thoroughly love, and if a pretty woman all
the better.

This curious and lamentable loss of the higher aesthetic tastes
is all the odder, as books on history, biographies, and travels
(independently of any scientific facts which they may contain),
and essays on all sorts of subjects interest me as much as ever
they did. My mind seems to have become a kind of machine for
grinding general laws out of large collections of facts, but why
this should have caused the atrophy of that part of the brain
alone, on which the higher tastes depend, I cannot conceive. A
man with a mind more highly organised or better constituted than
mine, would not, I suppose, have thus suffered; and if I had to
live my life again, I would have made a rule to read some poetry
and listen to some music at least once every week; for perhaps
the parts of my brain now atrophied would thus have been kept
active through use. The loss of these tastes is a loss of
happiness, and may possibly be injurious to the intellect, and
more probably to the moral character, by enfeebling the emotional
part of our nature.

My books have sold largely in England, have been translated into
many languages, and passed through several editions in foreign
countries. I have heard it said that the success of a work
abroad is the best test of its enduring value. I doubt whether
this is at all trustworthy; but judged by this standard my name
ought to last for a few years. Therefore it may be worth while
to try to analyse the mental qualities and the conditions on
which my success has depended; though I am aware that no man can
do this correctly.

I have no great quickness of apprehension or wit which is so
remarkable in some clever men, for instance, Huxley. I am
therefore a poor critic: a paper or book, when first read,
generally excites my admiration, and it is only after
considerable reflection that I perceive the weak points. My
power to follow a long and purely abstract train of thought is
very limited; and therefore I could never have succeeded with
metaphysics or mathematics. My memory is extensive, yet hazy:
it suffices to make me cautious by vaguely telling me that I have
observed or read something opposed to the conclusion which I am
drawing, or on the other hand in favour of it; and after a time I
can generally recollect where to search for my authority. So
poor in one sense is my memory, that I have never been able to
remember for more than a few days a single date or a line of
poetry.

Some of my critics have said, “Oh, he is a good observer, but he
has no power of reasoning!” I do not think that this can be
true, for the ‘Origin of Species’ is one long argument from the
beginning to the end, and it has convinced not a few able men.
No one could have written it without having some power of
reasoning. I have a fair share of invention, and of common sense
or judgment, such as every fairly successful lawyer or doctor
must have, but not, I believe, in any higher degree.

On the favourable side of the balance, I think that I am superior
to the common run of men in noticing things which easily escape
attention, and in observing them carefully. My industry has been
nearly as great as it could have been in the observation and
collection of facts. What is far more important, my love of
natural science has been steady and ardent.

This pure love has, however, been much aided by the ambition to
be esteemed by my fellow naturalists. From my early youth I have
had the strongest desire to understand or explain whatever I
observed,–that is, to group all facts under some general laws.
These causes combined have given me the patience to reflect or
ponder for any number of years over any unexplained problem. As
far as I can judge, I am not apt to follow blindly the lead of
other men. I have steadily endeavoured to keep my mind free so
as to give up any hypothesis, however much beloved (and I cannot
resist forming one on every subject), as soon as facts are shown
to be opposed to it. Indeed, I have had no choice but to act in
this manner, for with the exception of the Coral Reefs, I cannot
remember a single first-formed hypothesis which had not after a
time to be given up or greatly modified. This has naturally led
me to distrust greatly deductive reasoning in the mixed sciences.
On the other hand, I am not very sceptical,–a frame of mind
which I believe to be injurious to the progress of science. A
good deal of scepticism in a scientific man is advisable to avoid
much loss of time, but I have met with not a few men, who, I feel
sure, have often thus been deterred from experiment or
observations, which would have proved directly or indirectly
serviceable.

In illustration, I will give the oddest case which I have known.
A gentleman (who, as I afterwards heard, is a good local
botanist) wrote to me from the Eastern counties that the seed or
beans of the common field-bean had this year everywhere grown on
the wrong side of the pod. I wrote back, asking for further
information, as I did not understand what was meant; but I did
not receive any answer for a very long time. I then saw in two
newspapers, one published in Kent and the other in Yorkshire,
paragraphs stating that it was a most remarkable fact that “the
beans this year had all grown on the wrong side.” So I thought
there must be some foundation for so general a statement.
Accordingly, I went to my gardener, an old Kentish man, and asked
him whether he had heard anything about it, and he answered, “Oh,
no, sir, it must be a mistake, for the beans grow on the wrong
side only on leap-year, and this is not leap-year.” I then asked
him how they grew in common years and how on leap-years, but soon
found that he knew absolutely nothing of how they grew at any
time, but he stuck to his belief.

After a time I heard from my first informant, who, with many
apologies, said that he should not have written to me had he not
heard the statement from several intelligent farmers; but that he
had since spoken again to every one of them, and not one knew in
the least what he had himself meant. So that here a belief–if
indeed a statement with no definite idea attached to it can be
called a belief–had spread over almost the whole of England
without any vestige of evidence.

I have known in the course of my life only three intentionally
falsified statements, and one of these may have been a hoax (and
there have been several scientific hoaxes) which, however, took
in an American Agricultural Journal. It related to the formation
in Holland of a new breed of oxen by the crossing of distinct
species of Bos (some of which I happen to know are sterile
together), and the author had the impudence to state that he had
corresponded with me, and that I had been deeply impressed with
the importance of his result. The article was sent to me by the
editor of an English Agricultural Journal, asking for my opinion
before republishing it.

A second case was an account of several varieties, raised by the
author from several species of Primula, which had spontaneously
yielded a full complement of seed, although the parent plants had
been carefully protected from the access of insects. This
account was published before I had discovered the meaning of
heterostylism, and the whole statement must have been fraudulent,
or there was neglect in excluding insects so gross as to be
scarcely credible.

The third case was more curious: Mr. Huth published in his book
on ‘Consanguineous Marriage’ some long extracts from a Belgian
author, who stated that he had interbred rabbits in the closest
manner for very many generations, without the least injurious
effects. The account was published in a most respectable
Journal, that of the Royal Society of Belgium; but I could not
avoid feeling doubts–I hardly know why, except that there were
no accidents of any kind, and my experience in breeding animals
made me think this very improbable.

So with much hesitation I wrote to Professor Van Beneden, asking
him whether the author was a trustworthy man. I soon heard in
answer that the Society had been greatly shocked by discovering
that the whole account was a fraud. (The falseness of the
published statements on which Mr. Huth relied has been pointed
out by himself in a slip inserted in all the copies of his book
which then remained unsold.) The writer had been publicly
challenged in the Journal to say where he had resided and kept
his large stock of rabbits while carrying on his experiments,
which must have consumed several years, and no answer could be
extracted from him.

My habits are methodical, and this has been of not a little use
for my particular line of work. Lastly, I have had ample leisure
from not having to earn my own bread. Even ill-health, though it
has annihilated several years of my life, has saved me from the
distractions of society and amusement.

Therefore my success as a man of science, whatever this may have
amounted to, has been determined, as far as I can judge, by
complex and diversified mental qualities and conditions. Of
these, the most important have been–the love of science–
unbounded patience in long reflecting over any subject–industry
in observing and collecting facts–and a fair share of invention
as well as of common sense. With such moderate abilities as I
possess, it is truly surprising that I should have influenced to
a considerable extent the belief of scientific men on some
important points.

Effects Of Cross And Self Fertilisation In The Vegetable Kingdom

Chapter VII

 

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

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

The details which have been given under the head of each species are so
numerous and so intricate, that it is necessary to tabulate the results.
In Table 7/A, the number of plants of each kind which were raised from a
cross between two individuals of the same stock and from self-fertilised
seeds, together with their mean or average heights, are given. In the
right hand column, the mean height of the crossed to that of the
self-fertilised plants, the former being taken as 100, is shown. To make
this clear, it may be advisable to give an example. In the first
generation of Ipomoea, six plants derived from a cross between two
plants were measured, and their mean height is 86.00 inches; six plants
derived from flowers on the same parent-plant fertilised with their own
pollen were measured, and their mean height is 65.66 inches. From this
it follows, as shown in the right hand column, that if the mean height
of the crossed plants be taken as 100, that of the self-fertilised
plants is 76. The same plan is followed with all the other species.

The crossed and self-fertilised plants were generally grown in pots in
competition with one another, and always under as closely similar
conditions as could be attained. They were, however, sometimes grown in
separate rows in the open ground. With several of the species, the
crossed plants were again crossed, and the self-fertilised plants again
self-fertilised, and thus successive generations were raised and
measured, as may be seen in Table 7/A. Owing to this manner of
proceeding, the crossed plants became in the later generations more or
less closely inter-related.

Self-fertilisation is thus complex and self-sufficient. This is considered complicated because it happens by itself. This is similar to the auto trading robots that assist in trading, eventually helping us to gain experience by ourselves and master in trading in the long run. Reference various inputs to know more.

In Table 7/B the relative weights of the crossed and self-fertilised
plants, after they had flowered and had been cut down, are given in the
few cases in which they were ascertained. The results are, I think, more
striking and of greater value as evidence of constitutional vigour than
those deduced from the relative heights of the plants.

The most important table is Table 7/C, as it includes the relative
heights, weights, and fertility of plants raised from parents crossed by
a fresh stock (that is, by non-related plants grown under different
conditions), or by a distinct sub-variety, in comparison with
self-fertilised plants, or in a few cases with plants of the same old
stock intercrossed during several generations. The relative fertility of
the plants in this and the other tables will be more fully considered in
a future chapter.

TABLE 7/A. Relative heights of plants from parents crossed with pollen
from other plants of the same stock, and self-fertilised.

Heights of plants measured in inches.

Column 1: Name of Plant.

Column 2: Number of Crossed Plants measured.

Column 3: Average Height of Crossed Plants.

Column 4: Number of Self-fertilised Plants measured.

Column 5: Average Height of Self-fertilised Plants.

Column 6: x, where the ratio of the Average Height of the Crossed to the
Self-fertilised Plants is expressed as 100 to x.

Ipomoea purpurea–first generation:
6 : 86.00 : 6 : 65.66 : 76.

Ipomoea purpurea–second generation:
6 : 84.16 : 6 : 66.33 : 79.

Ipomoea purpurea–third generation:
6 : 77.41 : 6 : 52.83 : 68.

Ipomoea purpurea–fourth generation:
7 : 69.78 : 7 : 60.14 : 86.

Ipomoea purpurea–fifth generation:
6 : 82.54 : 6 : 62.33 : 75.

Ipomoea purpurea–sixth generation:
6 : 87.50 : 6 : 63.16 : 72.

Ipomoea purpurea–seventh generation:
9 : 83.94 : 9 : 68.25 : 81.

Ipomoea purpurea–eighth generation:
8 : 113.25 : 8 : 96.65 : 85.

Ipomoea purpurea–ninth generation:
14 : 81.39 : 14 : 64.07 : 79.

Ipomoea purpurea–tenth generation:
5 : 93.70 : 5 : 50.40 : 54.

Ipomoea purpurea–Number and average height of all the plants of the ten
generations:
73 : 85.84 : 73 : 66.02 : 77.

Mimulus luteus–three first generations, before the new and taller
self-fertilised variety appeared:
10 : 8.19 : 10 : 5.29 : 65.

Digitalis purpurea:
16 : 51.33 : 8 : 35.87 : 70.

Calceolaria–(common greenhouse variety):
1 : 19.50 : 1 : 15.00 : 77.

Linaria vulgaris:
3 : 7.08 : 3 : 5.75 : 81.

Verbascum thapsus:
6 : 65.34 : 6 : 56.50 : 86.

Vandellia nummularifolia–crossed and self-fertilised plants, raised
from perfect flowers:
20 : 4.30 : 20 : 4.27 : 99.

Vandellia nummularifolia–crossed and self-fertilised plants, raised
from perfect flowers: second trial, plants crowded:
24 : 3.60 : 24 : 3.38 : 94.

Vandellia nummularifolia–crossed plants raised from perfect flowers,
and self-fertilised plants from cleistogene flowers:
20 : 4.30 : 20 : 4.06 : 94.

Gesneria pendulina:
8 : 32.06 : 8 : 29.14 : 90.

Salvia coccinea:
6 : 27.85 : 6 : 21.16 : 76.

Origanum vulgare:
4 : 20.00 : 4 : 17.12 : 86.

Thunbergia alata:
6 : 60.00 : 6 : 65.00 : 108.

Brassica oleracea:
9 : 41.08 : 9 : 39.00 : 95.

Iberis umbellata–the self-fertilised plants of the third generation:
7 : 19.12 : 7 : 16.39 : 86.

Papaver vagum:
15 : 21.91 : 15 : 19.54 : 89.

Eschscholtzia californica–English stock, first generation:
4 : 29.68 : 4 : 25.56 : 86.

Eschscholtzia californica–English stock, second generation:
11 : 32.47 : 11 : 32.81 : 101.

Eschscholtzia californica–Brazilian stock, first generation:
14 : 44.64 : 14 : 45.12 : 101.

Eschscholtzia californica–Brazilian stock, second generation:
18 : 43.38 : 19 : 50.30 : 116.

Eschscholtzia californica–average height and number of all the plants
of Eschscholtzia:
47 : 40.03 : 48 : 42.72 : 107.

Reseda lutea–grown in pots:
24 : 17.17 : 24 : 14.61 : 85.

Reseda lutea–grown in open ground :
8 : 28.09 : 8 : 23.14 : 82.

Reseda odorata–self-fertilised seeds from a highly self-fertile plant,
grown in pots:
19 : 27.48 : 19 : 22.55 : 82.

Reseda odorata–self-fertilised seeds from a highly self-fertile plant,
grown in open ground:
8 : 25.76 : 8 : 27.09 : 105.

Reseda odorata–self-fertilised seeds from a semi-self-fertile plant,
grown in pots:
20 : 29.98 : 20 : 27.71 : 92.

Reseda odorata–self-fertilised seeds from a semi-self-fertile plant,
grown in open ground:
8 : 25.92 : 8 : 23.54 : 90.

Viola tricolor:
14 : 5.58 : 14 : 2.37 : 42.

Adonis aestivalis:
4 : 14.25 : 4 : 14.31 : 100.

Delphinium consolida:
6 : 14.95 : 6 : 12.50 : 84.

Viscaria oculata:
15 : 34.50 : 15 : 33.55 : 97.

Dianthus caryophyllus–open ground, about :
6?: 28? : 6?: 24? : 86.

Dianthus caryophyllus–second generation, in pots, crowded:
2 : 16.75 : 2 : 9.75 : 58.

Dianthus caryophyllus–third generation, in pots:
8 : 28.39 : 8 : 28.21 : 99.

Dianthus caryophyllus–offspring from plants of the third
self-fertilised generation crossed by intercrossed plants of the third
generation, compared with plants of fourth self-fertilised generation:
15 : 28.00 : 10 : 26.55 : 95.

Dianthus caryophyllus–number and average height of all the plants of
Dianthus:
31 : 27.37 : 26 : 25.18 : 92.

Hibiscus africanus:
4 : 13.25 : 4 : 14.43 : 109.

Pelargonium zonale:
7 : 22.35 : 7 : 16.62 : 74.

Tropaeolum minus:
8 : 58.43 : 8 : 46.00 : 79.

Limnanthes douglasii:
16 : 17.46 : 16 : 13.85 : 79.

Lupinus luteus–second generation:
8 : 30.78 : 8 : 25.21 : 82.

Lupinus pilosus–plants of two generations:
2 : 35.50 : 3 : 30.50 : 86.

Phaseolus multiflorus:
5 : 86.00 : 5 : 82.35 : 96.

Pisum sativum:
4 : 34.62 : 4 : 39.68 : 115.

Sarothamnus scoparius–small seedlings:
6 : 2.91 : 6 : 1.33 : 46.

Sarothamnus scoparius–the three survivors on each side after three
years’ growth:
: 18.91 :     : 11.83 : 63.

Ononis minutissima:
2 : 19.81 : 2 : 17.37 : 88.

Clarkia elegans:
4 : 33.50 : 4 : 27.62 : 82.

Bartonia aurea:
8 : 24.62 : 8 : 26.31 : 107.

Passiflora gracilis:
2 : 49.00 : 2 : 51.00 : 104.

Apium petroselinum:
* :        : * :        : 100.
*not measured.

Scabiosa atro-purpurea:
4 : 17.12 : 4 : 15.37 : 90.

Lactuca sativa–plants of two generations:
7 : 19.43 : 6 : 16.00 : 82.

Specularia speculum:
4 : 19.28 : 4 : 18.93 : 98.

Lobelia ramosa–first generation:
4 : 22.25 : 4 : 18.37 : 82.

Lobelia ramosa–second generation:
3 : 23.33 : 3 : 19.00 : 81.

Lobelia fulgens–first generation:
2 : 34.75 : 2 : 44.25 : 127.

Lobelia fulgens–second generation:
23 : 29.82 : 23 : 27.10 : 91.

Nemophila insignis–half-grown:
12 : 11.10 : 12 : 5.45 : 49.

Nemophila insignis–the same fully-grown:
: 33.28 :     : 19.90 : 60.

Borago officinalis:
4 : 20.68 : 4 : 21.18 : 102.

Nolana prostrata:
5 : 12.75 : 5 : 13.40 : 105.

Petunia violacea–first generation:
5 : 30.80 : 5 : 26.00 : 84.

Petunia violacea–second generation:
4 : 40.50 : 6 : 26.25 : 65.

Petunia violacea–third generation:
8 : 40.96 : 8 : 53.87 : 131.

Petunia violacea–fourth generation:
15 : 46.79 : 14 : 32.39 : 69.

Petunia violacea–fourth generation, from a distinct parent:
13 : 44.74 : 13 : 26.87 : 60.

Petunia violacea–fifth generation:
22 : 54.11 : 21 : 33.23 : 61.

Petunia violacea–fifth generation, in open ground:
10 : 38.27 : 10 : 23.31 : 61.

Petunia violacea–Number and average height of all the plants in pots of
Petunia:
67 : 46.53 : 67 : 33.12 : 71.

Nicotiana tabacum–first generation:
4 : 18.50 : 4 : 32.75 : 178.

Nicotiana tabacum–second generation:
9 : 53.84 : 7 : 51.78 : 96.

Nicotiana tabacum–third generation:
7 : 95.25 : 7 : 79.60 : 83.

Nicotiana tabacum–third generation but raised from a distinct plant:
7 : 70.78 : 9 : 71.30 : 101.

Nicotiana tabacum–Number and average height of all the plants of
Nicotiana:
27 : 63.73 : 27 : 61.31 : 96.

Cyclamen persicum:
8 : 9.49 : 8?: 7.50 : 79.

Anagallis collina:
6 : 42.20 : 6 : 33.35 : 69.

Primula sinensis–a dimorphic species:
8 : 9.01 : 8 : 9.03 : 100.

Fagopyrum esculentum–a dimorphic species:
15 : 38.06 : 15 : 26.13 : 69.

Beta vulgaris–in pots:
8 : 34.09 : 8 : 29.81 : 87.

Beta vulgaris–in open ground:
8 : 30.92 : 8 : 30.70 : 99.

Canna warscewiczi–plants of three generations:
34 : 35.98 : 34 : 36.39 : 101.

Zea mays–in pots, whilst young, measured to tips of leaves:
15 : 20.19 : 15 : 17.57 : 87.

Zea mays–when full-grown, after the death of some, measured to tips of
leaves:
: 68.10 :     : 62.34 : 91.

Zea mays–when full-grown, after the death of some, measured to tips of
flowers:
: 66.51 :     : 61.59 : 93.

Zea mays–grown in open ground, measured to tips of leaves:
10 : 54.00 : 10 : 44.55 : 83.

Zea mays–grown in open ground, measured to tips of flowers:
: 53.96 :     : 43.45 : 80.

Phalaris canariensis–in pots.
11 : 38.90 : 11 : 35.69 : 92.

Phalaris canariensis–in open ground:
12 : 35.78 : 12 : 33.50 : 93.

TABLE 7/B.–Relative weights of plants from parents crossed with pollen
from distinct plants of the same stock, and self-fertilised.

Column 1: Names of plants.

Column 2: Number of crossed plants.

Column 3: Number of self-fertilised plants.

Column 4: x, where the ratio of the Weight of the Crossed to the
Self-fertilised Plants is expressed as 100 to x.

Ipomoea purpurea–plants of the tenth generation:
6 : 6 : 44.

Vandellia nummularifolia–first generation:
41 : 41 : 97.

Brassica oleracea–first generation:
9 : 9 : 37.

Eschscholtzia californica–plants of the second generation:
19 : 19 : 118.

Reseda lutea–first generation, grown in pots:
24 : 24 : 21.

Reseda lutea–first generation, grown in open ground:
8 : 8 : 40.

Reseda odorata–first generation, descended from a highly self-fertile
plant, grown in pots:
19 : 19 : 67.

Reseda odorata–first generation, descended from a semi-self-fertile
plant, grown in pots:
20 : 20 : 99.

Dianthus caryophyllus–plants of the third generation:
8 : 8 : 49.

Petunia violacea–plants of the fifth generation, in pots:
22 : 21 : 22.

Petunia violacea–plants of the fifth generation, in open ground:
10 : 10 : 36.

TABLE 7/C.–Relative heights, weights, and fertility of plants from
parents crossed by a fresh stock, and from parents either
self-fertilised or intercrossed with plants of the same stock.

Column 1: Names of the plants and nature of the experiments.

Column 2: Number of plants from a cross with a fresh stock.

Column 3: Average height in inches and weight.

Column 4: Number of the plants from self-fertilised or intercrossed
parents of the same stock.

Column 5: Average height in inches and weight.

Column 4: x, where the ratio of the Height, Weight and Fertility of the
plants from the Cross with a fresh stock is expressed as 100 to x.

Ipomoea purpurea–offspring of plants intercrossed for nine generations
and then crossed by a fresh stock, compared with plants of the tenth
intercrossed generation:
19 : 84.03 : 19 : 65.78 : 78.

Ipomoea purpurea–offspring of plants intercrossed for nine generations
and then crossed by a fresh stock, compared with plants of the tenth
intercrossed generation, in fertility:
.. :     .. : .. :     .. : 51.

Mimulus luteus–offspring of plants self-fertilised for eight
generations and then crossed by a fresh stock, compared with plants of
the ninth self-fertilised generation:
28 : 21.62 : 19 : 10.44 : 52.

Mimulus luteus–offspring of plants self-fertilised for eight
generations and then crossed by a fresh stock, compared with plants of
the ninth self-fertilised generation, in fertility:
.. :     .. : .. :     .. : 3.

Mimulus luteus–offspring of plants self-fertilised for eight
generations and then crossed by a fresh stock, compared with the
offspring of a plant self-fertilised for eight generations, and then
intercrossed with another self-fertilised plant of the same generation:
28 : 21.62 : 27 : 12.20 : 56.

Mimulus luteus–offspring of plants self-fertilised for eight
generations and then crossed by a fresh stock, compared with the
offspring of a plant self-fertilised for eight generations, and then
intercrossed with another self-fertilised plant of the same generation,
in fertility:
.. :     .. : .. :     .. : 4.

Brassica oleracea–offspring of plants self-fertilised for two
generations and then crossed by a fresh stock, compared with plants of
the third self-fertilised generation, by weight:
6 :        :    6 :        : 22.

Iberis umbellata–offspring from English variety crossed by slightly
different Algerine variety, compared with the self-fertilised offspring
of the English variety:
30 : 17.34 : 29 : 15.51 : 89.

Iberis umbellata–offspring from English variety crossed by slightly
different Algerine variety, compared with the self-fertilised offspring
of the English variety, in fertility:
.. :     .. : .. :     .. : 75.

Eschscholtzia californica–offspring of a Brazilian stock crossed by an
English stock, compared with plants of the Brazilian stock of the second
self-fertilised generation:
19 : 45.92 : 19 : 50.30 : 109.

Eschscholtzia californica–offspring of a Brazilian stock crossed by an
English stock, compared with plants of the Brazilian stock of the second
self-fertilised generation, in weight:
.. :     .. : .. :     .. : 118.

Eschscholtzia californica–offspring of a Brazilian stock crossed by an
English stock, compared with plants of the Brazilian stock of the second
self-fertilised generation, in fertility:
.. :     .. : .. :     .. : 40.

Eschscholtzia californica–offspring of a Brazilian stock crossed by an
English stock, compared with plants of the Brazilian stock of the second
intercrossed generation, in height:
19 : 45.92 : 18 : 43.38 : 94.

Eschscholtzia californica–offspring of a Brazilian stock crossed by an
English stock, compared with plants of the Brazilian stock of the second
intercrossed generation, in weight:
.. :     .. : .. :     .. : 100.

Eschscholtzia californica–offspring of a Brazilian stock crossed by an
English stock, compared with plants of the Brazilian stock of the second
intercrossed generation, in fertility:
.. :     .. : .. :     .. : 45.

Dianthus caryophyllus–offspring of plants self-fertilised for three
generations and then crossed by a fresh stock, compared with plants of
the fourth self-fertilised generation:
16 : 32.82 : 10 : 26.55 : 81.

Dianthus caryophyllus–offspring of plants self-fertilised for three
generations and then crossed by a fresh stock, compared with plants of
the fourth self-fertilised generation, in fertility:
.. :     .. : .. :     .. : 33.

Dianthus caryophyllus–offspring of plants self-fertilised for three
generations and then crossed by a fresh stock, compared with the
offspring of plants self-fertilised for three generations and then
crossed by plants of the third intercrossed generation:
16 : 32.82 : 15 : 28.00 : 85.

Dianthus caryophyllus–offspring of plants self-fertilised for three
generations and then crossed by a fresh stock, compared with the
offspring of plants self-fertilised for three generations and then
crossed by plants of the third intercrossed generation, in fertility:
.. :     .. : .. :     .. : 45.

Pisum sativum–offspring from a cross between two closely allied
varieties, compared with the self-fertilised offspring of one of the
varieties, or with intercrossed plants of the same stock:
? :        : ? :        : 60 to 75.

Lathyrus odoratus–offspring from two varieties, differing only in
colour of their flowers, compared with the self-fertilised offspring of
one of the varieties: in first generation:
2 : 79.25 :    2 : 63.75 : 80.

Lathyrus odoratus–offspring from two varieties, differing only in
colour of their flowers, compared with the self-fertilised offspring of
one of the varieties: in second generation:
6 : 62.91 :    6 : 55.31 : 88.

Petunia violacea–offspring of plants self-fertilised for four
generations and then crossed by a fresh stock, compared with plants of
the fifth self-fertilised generation, in height:
21 : 50.05 : 21 : 33.23 : 66.

Petunia violacea–offspring of plants self-fertilised for four
generations and then crossed by a fresh stock, compared with plants of
the fifth self-fertilised generation, in weight:
.. :     .. : .. :     .. : 23.

Petunia violacea–offspring of plants self-fertilised for four
generations and then crossed by a fresh stock, compared with plants of
the fifth self-fertilised generation, grown in open ground, in height:
10 : 36.67 : 10 : 23.31 : 63.

Petunia violacea–offspring of plants self-fertilised for four
generations and then crossed by a fresh stock, compared with plants of
the fifth self-fertilised generation, grown in open ground, in weight:
.. :     .. : .. :     .. : 53.

Petunia violacea–offspring of plants self-fertilised for four
generations and then crossed by a fresh stock, compared with plants of
the fifth self-fertilised generation, grown in open ground, in
fertility:
.. :     .. : .. :     .. : 46.

Petunia violacea–offspring of plants self-fertilised for four
generations and then crossed by a fresh stock, compared with plants of
the fifth intercrossed generation, in height:
21 : 50.05 : 22 : 54.11 : 108.

Petunia violacea–offspring of plants self-fertilised for four
generations and then crossed by a fresh stock, compared with plants of
the fifth intercrossed generation, in weight:
.. :     .. : .. :     .. : 101.

Petunia violacea–offspring of plants self-fertilised for four
generations and then crossed by a fresh stock, compared with plants of
the fifth intercrossed generation, grown in open ground, in height:
10 : 36.67 : 10 : 38.27 : 104.

Petunia violacea–offspring of plants self-fertilised for four
generations and then crossed by a fresh stock, compared with plants of
the fifth intercrossed generation, grown in open ground, in weight:
.. :     .. : .. :     .. : 146.

Petunia violacea–offspring of plants self-fertilised for four
generations and then crossed by a fresh stock, compared with plants of
the fifth intercrossed generation, grown in open ground, in fertility:
.. :     .. : .. :     .. : 54.

Nicotiana tabacum–offspring of plants self-fertilised for three
generations and then crossed by a slightly different variety, compared
with plants of the fourth self-fertilised generation, grown not much
crowded in pots, in height:
26 : 63.29 : 26 : 41.67 : 66.

Nicotiana tabacum–offspring of plants self-fertilised for three
generations and then crossed by a slightly different variety, compared
with plants of the fourth self-fertilised generation, grown much crowded
in pots, in height:
12 : 31.53 : 12 : 17.21 : 54.

Nicotiana tabacum–offspring of plants self-fertilised for three
generations and then crossed by a slightly different variety, compared
with plants of the fourth self-fertilised generation, grown much crowded
in pots, in weight:
.. :     .. : .. :     .. : 37.

Nicotiana tabacum–offspring of plants self-fertilised for three
generations and then crossed by a slightly different variety, compared
with plants of the fourth self-fertilised generation, grown in open
ground, in height:
20 : 48.74 : 20 : 35.20 : 72.

Nicotiana tabacum–offspring of plants self-fertilised for three
generations and then crossed by a slightly different variety, compared
with plants of the fourth self-fertilised generation, grown in open
ground, in weight:
.. :     .. : .. :     .. : 63.

Anagallis collina–offspring from a red variety crossed by a blue
variety, compared with the self-fertilised offspring of the red variety:
3 : 27.62 :    3 : 18.21 : 66.

Anagallis collina–offspring from a red variety crossed by a blue
variety, compared with the self-fertilised offspring of the red variety,
in fertility:
.. :     .. : .. :     .. : 6.

Primula veris–offspring from long-styled plants of the third
illegitimate generation, crossed by a fresh stock, compared with plants
of the fourth illegitimate and self-fertilised generation:
8 : 7.03 :    8 : 3.21 : 46.

Primula veris–offspring from long-styled plants of the third
illegitimate generation, crossed by a fresh stock, compared with plants
of the fourth illegitimate and self-fertilised generation, in fertility:
.. :     .. : .. :     .. : 5.

Primula veris–offspring from long-styled plants of the third
illegitimate generation, crossed by a fresh stock, compared with plants
of the fourth illegitimate and self-fertilised generation, in fertility
in following year:
.. :     .. : .. :     .. : 3.5.

Primula veris–(equal-styled, red-flowered variety)–offspring from
plants self-fertilised for two generations and then crossed by a
different variety, compared with plants of the third self-fertilised
generation:
3 : 8.66 :    3 : 7.33 : 85.

Primula veris–(equal-styled, red-flowered variety)–offspring from
plants self-fertilised for two generations and then crossed by a
different variety, compared with plants of the third self-fertilised
generation, in fertility:
.. :     .. : .. :     .. : 11.

In these three tables the measurements of fifty-seven species, belonging
to fifty-two genera and to thirty great natural families, are given. The
species are natives of various parts of the world. The number of crossed
plants, including those derived from a cross between plants of the same
stock and of two different stocks, amounts to 1,101; and the number of
self-fertilised plants (including a few in Table 7/C derived from a
cross between plants of the same old stock) is 1,076. Their growth was
observed from the germination of the seeds to maturity; and most of them
were measured twice and some thrice. The various precautions taken to
prevent either lot being unduly favoured, have been described in the
introductory chapter. Bearing all these circumstances in mind, it may be
admitted that we have a fair basis for judging of the comparative
effects of cross-fertilisation and of self-fertilisation on the growth
of the offspring.

It will be the most convenient plan first to consider the results given
in Table 7/C, as an opportunity will thus be afforded of incidentally
discussing some important points. If the reader will look down the right
hand column of this table, he will see at a glance what an extraordinary
advantage in height, weight, and fertility the plants derived from a
cross with a fresh stock or with another sub-variety have over the
self-fertilised plants, as well as over the intercrossed plants of the
same old stock. There are only two exceptions to this rule, and these
are hardly real ones. In the case of Eschscholtzia, the advantage is
confined to fertility. In that of Petunia, though the plants derived
from a cross with a fresh stock had an immense superiority in height,
weight, and fertility over the self-fertilised plants, they were
conquered by the intercrossed plants of the same old stock in height and
weight, but not in fertility. It has, however, been shown that the
superiority of these intercrossed plants in height and weight was in all
probability not real; for if the two sets had been allowed to grow for
another month, it is almost certain that those from a cross with the
fresh stock would have been victorious in every way over the
intercrossed plants.

Before we consider in detail the several cases given in Table 7/C, some
preliminary remarks must be made. There is the clearest evidence, as we
shall presently see, that the advantage of a cross depends wholly on the
plants differing somewhat in constitution; and that the disadvantages of
self-fertilisation depend on the two parents, which are combined in the
same hermaphrodite flower, having a closely similar constitution. A
certain amount of differentiation in the sexual elements seems
indispensable for the full fertility of the parents, and for the full
vigour of the offspring. All the individuals of the same species, even
those produced in a state of nature, differ somewhat, though often very
slightly, from one another in external characters and probably in
constitution. This obviously holds good between the varieties of the
same species, as far as external characters are concerned; and much
evidence could be advanced with respect to their generally differing
somewhat in constitution. There can hardly be a doubt that the
differences of all kinds between the individuals and varieties of the
same species depend largely, and as I believe exclusively, on their
progenitors having been subjected to different conditions; though the
conditions to which the individuals of the same species are exposed in a
state of nature often falsely appear to us the same. For instance, the
individuals growing together are necessarily exposed to the same
climate, and they seem to us at first sight to be subjected to
identically the same conditions; but this can hardly be the case, except
under the unusual contingency of each individual being surrounded by
other kinds of plants in exactly the same proportional numbers. For the
surrounding plants absorb different amounts of various substances from
the soil, and thus greatly affect the nourishment and even the life of
the individuals of any particular species. These will also be shaded and
otherwise affected by the nature of the surrounding plants. Moreover,
seeds often lie dormant in the ground, and those which germinate during
any one year will often have been matured during very different seasons.
Seeds are widely dispersed by various means, and some will occasionally
be brought from distant stations, where their parents have grown under
somewhat different conditions, and the plants produced from such seeds
will intercross with the old residents, thus mingling their
constitutional peculiarities in all sorts of proportions.

Plants when first subjected to culture, even in their native country,
cannot fail to be exposed to greatly changed conditions of life, more
especially from growing in cleared ground, and from not having to
compete with many or any surrounding plants. They are thus enabled to
absorb whatever they require which the soil may contain. Fresh seeds are
often brought from distant gardens, where the parent-plants have been
subjected to different conditions. Cultivated plants like those in a
state of nature frequently intercross, and will thus mingle their
constitutional peculiarities. On the other hand, as long as the
individuals of any species are cultivated in the same garden, they will
apparently be subjected to more uniform conditions than plants in a
state of nature, as the individuals have not to compete with various
surrounding species. The seeds sown at the same time in a garden have
generally been matured during the same season and in the same place; and
in this respect they differ much from the seeds sown by the hand of
nature. Some exotic plants are not frequented by the native insects in
their new home, and therefore are not intercrossed; and this appears to
be a highly important factor in the individuals acquiring uniformity of
constitution.

In my experiments the greatest care was taken that in each generation
all the crossed and self-fertilised plants should be subjected to the
same conditions. Not that the conditions were absolutely the same, for
the more vigorous individuals will have robbed the weaker ones of
nutriment, and likewise of water when the soil in the pots was becoming
dry; and both lots at one end of the pot will have received a little
more light than those at the other end. In the successive generations,
the plants were subjected to somewhat different conditions, for the
seasons necessarily varied, and they were sometimes raised at different
periods of the year. But as they were all kept under glass, they were
exposed to far less abrupt and great changes of temperature and moisture
than are plants growing out of doors. With respect to the intercrossed
plants, their first parents, which were not related, would almost
certainly have differed somewhat in constitution; and such
constitutional peculiarities would be variously mingled in each
succeeding intercrossed generation, being sometimes augmented, but more
commonly neutralised in a greater or less degree, and sometimes revived
through reversion; just as we know to be the case with the external
characters of crossed species and varieties. With the plants which were
self-fertilised during the successive generations, this latter important
source of some diversity of constitution will have been wholly
eliminated; and the sexual elements produced by the same flower must
have been developed under as nearly the same conditions as it is
possible to conceive.

In Table 7/C the crossed plants are the offspring of a cross with a
fresh stock, or with a distinct variety; and they were put into
competition either with self-fertilised plants, or with intercrossed
plants of the same old stock. By the term fresh stock I mean a
non-related plant, the progenitors of which have been raised during some
generations in another garden, and have consequently been exposed to
somewhat different conditions. In the case of Nicotiana, Iberis, the red
variety of Primula, the common Pea, and perhaps Anagallis, the plants
which were crossed may be ranked as distinct varieties or sub-varieties
of the same species; but with Ipomoea, Mimulus, Dianthus, and Petunia,
the plants which were crossed differed exclusively in the tint of their
flowers; and as a large proportion of the plants raised from the same
lot of purchased seeds thus varied, the differences may be estimated as
merely individual. Having made these preliminary remarks, we will now
consider in detail the several cases given in Table 7/C, and they are
well worthy of full consideration.

1. Ipomoea purpurea.

Plants growing in the same pots, and subjected in each generation to the
same conditions, were intercrossed for nine consecutive generations.
These intercrossed plants thus became in the later generations more or
less closely inter-related. Flowers on the plants of the ninth
intercrossed generation were fertilised with pollen taken from a fresh
stock, and seedlings thus raised. Other flowers on the same intercrossed
plants were fertilised with pollen from another intercrossed plant,
producing seedlings of the tenth intercrossed generation. These two sets
of seedlings were grown in competition with one another, and differed
greatly in height and fertility. For the offspring from the cross with a
fresh stock exceeded in height the intercrossed plants in the ratio of
100 to 78; and this is nearly the same excess which the intercrossed had
over the self-fertilised plants in all ten generations taken together,
namely, as 100 to 77. The plants raised from the cross with a fresh
stock were also greatly superior in fertility to the intercrossed,
namely, in the ratio of 100 to 51, as judged by the relative weight of
the seed-capsules produced by an equal number of plants of the two sets,
both having been left to be naturally fertilised. It should be
especially observed that none of the plants of either lot were the
product of self-fertilisation. On the contrary, the intercrossed plants
had certainly been crossed for the last ten generations, and probably,
during all previous generations, as we may infer from the structure of
the flowers and from the frequency of the visits of humble-bees. And so
it will have been with the parent-plants of the fresh stock. The whole
great difference in height and fertility between the two lots must be
attributed to the one being the product of a cross with pollen from a
fresh stock, and the other of a cross between plants of the same old
stock.

This species offers another interesting case. In the five first
generations in which intercrossed and self-fertilised plants were put
into competition with one another, every single intercrossed plant beat
its self-fertilised antagonist, except in one instance, in which they
were equal in height. But in the sixth generation a plant appeared,
named by me the Hero, remarkable for its tallness and increased
self-fertility, and which transmitted its characters to the next three
generations. The children of Hero were again self-fertilised, forming
the eighth self-fertilised generation, and were likewise intercrossed
one with another; but this cross between plants which had been subjected
to the same conditions and had been self-fertilised during the seven
previous generations, did not effect the least good; for the
intercrossed grandchildren were actually shorter than the
self-fertilised grandchildren, in the ratio of 100 to 107. We here see
that the mere act of crossing two distinct plants does not by itself
benefit the offspring. This case is almost the converse of that in the
last paragraph, on which the offspring profited so greatly by a cross
with a fresh stock. A similar trial was made with the descendants of
Hero in the following generation, and with the same result. But the
trial cannot be fully trusted, owing to the extremely unhealthy
condition of the plants. Subject to this same serious cause of doubt,
even a cross with a fresh stock did not benefit the great-grandchildren
of Hero; and if this were really the case, it is the greatest anomaly
observed by me in all my experiments.

2. Mimulus luteus.

During the three first generations the intercrossed plants taken
together exceeded in height the self-fertilised taken together, in the
ratio of 100 to 65, and in fertility in a still higher degree. In the
fourth generation a new variety, which grew taller and had whiter and
larger flowers than the old varieties, began to prevail, especially
amongst the self-fertilised plants. This variety transmitted its
characters with remarkable fidelity, so that all the plants in the later
self-fertilised generations belonged to it. These consequently exceeded
the intercrossed plants considerably in height. Thus in the seventh
generation the intercrossed plants were to the self-fertilised in height
as 100 to 137. It is a more remarkable fact that the self-fertilised
plants of the sixth generation had become much more fertile than the
intercrossed plants, judging by the number of capsules spontaneously
produced, in the ratio of 147 to 100. This variety, which as we have
seen appeared amongst the plants of the fourth self-fertilised
generation, resembles in almost all its constitutional peculiarities the
variety called Hero which appeared in the sixth self-fertilised
generation of Ipomoea. No other such case, with the partial exception of
that of Nicotiana, occurred in my experiments, carried on during eleven
years.

Two plants of this variety of Mimulus, belonging to the sixth
self-fertilised generation, and growing in separate pots, were
intercrossed; and some flowers on the same plants were again
self-fertilised. From the seeds thus obtained, plants derived from a
cross between the self-fertilised plants, and others of the seventh
self-fertilised generation, were raised. But this cross did not do the
least good, the intercrossed plants being inferior in height to the
self-fertilised, in the ratio of 100 to 110. This case is exactly
parallel with that given under Ipomoea, of the grandchildren of Hero,
and apparently of its great-grandchildren; for the seedlings raised by
intercrossing these plants were not in any way superior to those of the
corresponding generation raised from the self-fertilised flowers.
Therefore in these several cases the crossing of plants, which had been
self-fertilised for several generations and which had been cultivated
all the time under as nearly as possible the same conditions, was not in
the least beneficial.

Another experiment was now tried. Firstly, plants of the eighth
self-fertilised generation were again self-fertilised, producing plants
of the ninth self-fertilised generation. Secondly, two of the plants of
the eighth self-fertilised generation were intercrossed one with
another, as in the experiment above referred to; but this was now
effected on plants which had been subjected to two additional
generations of self-fertilisation. Thirdly, the same plants of the
eighth self-fertilised generation were crossed with pollen from plants
of a fresh stock brought from a distant garden. Numerous plants were
raised from these three sets of seeds, and grown in competition with one
another. The plants derived from a cross between the self-fertilised
plants exceeded in height by a little the self-fertilised, namely, as
100 to 92; and in fertility in a greater degree, namely, as 100 to 73. I
do not know whether this difference in the result, compared with that in
the previous case, can be accounted for by the increased deterioration
of the self-fertilised plants from two additional generations of
self-fertilisation, and the consequent advantage of any cross whatever,
along merely between the self-fertilised plants. But however this may
be, the effects of crossing the self-fertilised plants of the eighth
generation with a fresh stock were extremely striking; for the seedlings
thus raised were to the self-fertilised of the ninth generation as 100
to 52 in height, and as 100 to 3 in fertility! They were also to the
intercrossed plants (derived from crossing two of the self-fertilised
plants of the eighth generation) in height as 100 to 56, and in
fertility as 100 to 4. Better evidence could hardly be desired of the
potent influence of a cross with a fresh stock on plants which had been
self-fertilised for eight generations, and had been cultivated all the
time under nearly uniform conditions, in comparison with plants
self-fertilised for nine generations continuously, or then once
intercrossed, namely in the last generation.

3. Brassica oleracea.

Some flowers on cabbage plants of the second self-fertilised generation
were crossed with pollen from a plant of the same variety brought from a
distant garden, and other flowers were again self-fertilised. Plants
derived from a cross with a fresh stock and plants of the third
self-fertilised generation were thus raised. The former were to the
self-fertilised in weight as 100 to 22; and this enormous difference
must be attributed in part to the beneficial effects of a cross with a
fresh stock, and in part to the deteriorating effects of
self-fertilisation continued during three generations.

4. Iberis umbellata.

Seedlings from a crimson English variety crossed by a pale-coloured
variety which had been grown for some generations in Algiers, were to
the self-fertilised seedlings from the crimson variety in height as 100
to 89, and as 100 to 75 in fertility. I am surprised that this cross
with another variety did not produce a still more strongly marked
beneficial effect; for some intercrossed plants of the crimson English
variety, put into competition with plants of the same variety
self-fertilised during three generations, were in height as 100 to 86,
and in fertility as 100 to 75. The slightly greater difference in height
in this latter case, may possibly be attributed to the deteriorating
effects of self-fertilisation carried on for two additional generations.

5. Eschscholtzia californica.

This plant offers an almost unique case, inasmuch as the good effects of
a cross are confined to the reproductive system. Intercrossed and
self-fertilised plants of the English stock did not differ in height
(nor in weight, as far as was ascertained) in any constant manner; the
self-fertilised plants usually having the advantage. So it was with the
offspring of plants of the Brazilian stock, tried in the same manner.
The parent-plants, however, of the English stock produced many more
seeds when fertilised with pollen from another plant than when
self-fertilised; and in Brazil the parent-plants were absolutely sterile
unless they were fertilised with pollen from another plant. Intercrossed
seedlings, raised in England from the Brazilian stock, compared with
self-fertilised seedlings of the corresponding second generation,
yielded seeds in number as 100 to 89; both lots of plants being left
freely exposed to the visits of insects. If we now turn to the effects
of crossing plants of the Brazilian stock with pollen from the English
stock,–so that plants which had been long exposed to very different
conditions were intercrossed,–we find that the offspring were, as
before, inferior in height and weight to the plants of the Brazilian
stock after two generations of self-fertilisation, but were superior to
them in the most marked manner in the number of seeds produced, namely,
as 100 to 40; both lots of plants being left freely exposed to the
visits of insects.

In the case of Ipomoea, we have seen that the plants derived from a
cross with a fresh stock were superior in height as 100 to 78, and in
fertility as 100 to 51, to the plants of the old stock, although these
had been intercrossed during the last ten generations. With
Eschscholtzia we have a nearly parallel case, but only as far as
fertility is concerned, for the plants derived from a cross with a fresh
stock were superior in fertility in the ratio of 100 to 45 to the
Brazilian plants, which had been artificially intercrossed in England
for the two last generations, and which must have been naturally
intercrossed by insects during all previous generations in Brazil, where
otherwise they are quite sterile.

6. Dianthus caryophyllus.

Plants self-fertilised for three generations were crossed with pollen
from a fresh stock, and their offspring were grown in competition with
plants of the fourth self-fertilised generation. The crossed plants thus
obtained were to the self-fertilised in height as 100 to 81, and in
fertility (both lots being left to be naturally fertilised by insects)
as 100 to 33.

These same crossed plants were also to the offspring from the plants of
the third generation crossed by the intercrossed plants of the
corresponding generation, in height as 100 to 85, and in fertility as
100 to 45.

We thus see what a great advantage the offspring from a cross with a
fresh stock had, not only over the self-fertilised plants of the fourth
generation, but over the offspring from the self-fertilised plants of
the third generation, when crossed by the intercrossed plants of the old
stock.

7. Pisum sativum.

It has been shown under the head of this species, that the several
varieties in this country almost invariably fertilise themselves, owing
to insects rarely visiting the flowers; and as the plants have been long
cultivated under nearly similar conditions, we can understand why a
cross between two individuals of the same variety does not do the least
good to the offspring either in height or fertility. This case is almost
exactly parallel with that of Mimulus, or that of the Ipomoea named
Hero; for in these two instances, crossing plants which had been
self-fertilised for seven generations did not at all benefit the
offspring. On the other hand, a cross between two varieties of the pea
causes a marked superiority in the growth and vigour of the offspring,
over the self-fertilised plants of the same varieties, as shown by two
excellent observers. From my own observations (not made with great care)
the offspring from crossed varieties were to self-fertilised plants in
height, in one case as 100 to about 75, and in a second case as 100 to
60.

8. Lathyrus odoratus.

The sweet-pea is in the same state in regard to self-fertilisation as
the common pea; and we have seen that seedlings from a cross between two
varieties, which differed in no respect except in the colour of their
flowers, were to the self-fertilised seedlings from the same
mother-plant in height as 100 to 80; and in the second generation as 100
to 88. Unfortunately I did not ascertain whether crossing two plants of
the same variety failed to produce any beneficial effect, but I venture
to predict such would be the result.

9. Petunia violacea.

The intercrossed plants of the same stock in four out of the five
successive generations plainly exceeded in height the self-fertilised
plants. The latter in the fourth generation were crossed by a fresh
stock, and the seedlings thus obtained were put into competition with
the self-fertilised plants of the fifth generation. The crossed plants
exceeded the self-fertilised in height in the ratio of 100 to 66, and in
weight as 100 to 23; but this difference, though so great, is not much
greater than that between the intercrossed plants of the same stock in
comparison with the self-fertilised plants of the corresponding
generation. This case, therefore, seems at first sight opposed to the
rule that a cross with a fresh stock is much more beneficial than a
cross between individuals of the same stock. But as with Eschscholtzia,
the reproductive system was here chiefly benefited; for the plants
raised from the cross with the fresh stock were to the self-fertilised
plants in fertility, both lots being naturally fertilised, as 100 to 46,
whereas the intercrossed plants of the same stock were to the
self-fertilised plants of the corresponding fifth generation in
fertility only as 100 to 86.

Although at the time of measurement the plants raised from the cross
with the fresh stock did not exceed in height or weight the intercrossed
plants of the old stock (owing to the growth of the former not having
been completed, as explained under the head of this species), yet they
exceeded the intercrossed plants in fertility in the ratio of 100 to 54.
This fact is interesting, as it shows that plants self-fertilised for
four generations and then crossed by a fresh stock, yielded seedlings
which were nearly twice as fertile as those from plants of the same
stock which had been intercrossed for the five previous generations. We
here see, as with Eschscholtzia and Dianthus, that the mere act of
crossing, independently of the state of the crossed plants, has little
efficacy in giving increased fertility to the offspring. The same
conclusion holds good, as we have already seen, in the analogous cases
of Ipomoea, Mimulus, and Dianthus, with respect to height.

10. Nicotiana tabacum.

My plants were remarkably self-fertile, and the capsules from the
self-fertilised flowers apparently yielded more seeds than those which
were cross-fertilised. No insects were seen to visit the flowers in the
hothouse, and I suspect that the stock on which I experimented had been
raised under glass, and had been self-fertilised during several previous
generations; if so, we can understand why, in the course of three
generations, the crossed seedlings of the same stock did not uniformly
exceed in height the self-fertilised seedlings. But the case is
complicated by individual plants having different constitutions, so that
some of the crossed and self-fertilised seedlings raised at the same
time from the same parents behaved differently. However this may be,
plants raised from self-fertilised plants of the third generation
crossed by a slightly different sub-variety, exceeded greatly in height
and weight the self-fertilised plants of the fourth generation; and the
trial was made on a large scale. They exceeded them in height when grown
in pots, and not much crowded, in the ratio of 100 to 66; and when much
crowded, as 100 to 54. These crossed plants, when thus subjected to
severe competition, also exceeded the self-fertilised in weight in the
ratio of 100 to 37. So it was, but in a less degree (as may be seen in
Table 7/C), when the two lots were grown out of doors and not subjected
to any mutual competition. Nevertheless, strange as is the fact, the
flowers on the mother-plants of the third self-fertilised generation did
not yield more seed when they were crossed with pollen from plants of
the fresh stock than when they were self-fertilised.

11. Anagallis collina.

Plants raised from a red variety crossed by another plant of the same
variety were in height to the self-fertilised plants from the red
variety as 100 to 73. When the flowers on the red variety were
fertilised with pollen from a closely similar blue-flowered variety,
they yielded double the number of seeds to what they did when crossed by
pollen from another individual of the same red variety, and the seeds
were much finer. The plants raised from this cross between the two
varieties were to the self-fertilised seedlings from the red variety, in
height as 100 to 66, and in fertility as 100 to 6.

12. Primula veris.

Some flowers on long-styled plants of the third illegitimate generation
were legitimately crossed with pollen from a fresh stock, and others
were fertilised with their own pollen. From the seeds thus produced
crossed plants, and self-fertilised plants of the fourth illegitimate
generation, were raised. The former were to the latter in height as 100
to 46, and in fertility during one year as 100 to 5, and as 100 to 3.5
during the next year. In this case, however, we have no means of
distinguishing between the evil effects of illegitimate fertilisation
continued during four generations (that is, by pollen of the same form,
but taken from a distinct plant) and strict self-fertilisation. But it
is probable that these two processes do not differ so essentially as at
first appears to be the case. In the following experiment any doubt
arising from illegitimate fertilisation was completely eliminated.

13. Primula veris. (Equal-styled, red-flowered variety.)

Flowers on plants of the second self-fertilised generation were crossed
with pollen from a distinct variety or fresh stock, and others were
again self-fertilised. Crossed plants and plants of the third
self-fertilised generation, all of legitimate origin, were thus raised;
and the former was to the latter in height as 100 to 85, and in
fertility (as judged by the number of capsules produced, together with
the average number of seeds) as 100 to 11.

SUMMARY OF THE MEASUREMENTS IN TABLE 7/C.

This table includes the heights and often the weights of 292 plants
derived from a cross with a fresh stock, and of 305 plants, either of
self-fertilised origin, or derived from an intercross between plants of
the same stock. These 597 plants belong to thirteen species and twelve
genera. The various precautions which were taken to ensure a fair
comparison have already been stated. If we now look down the right hand
column, in which the mean height, weight, and fertility of the plants
derived from a cross with a fresh stock are represented by 100, we shall
see by the other figures how wonderfully superior they are both to the
self-fertilised and to the intercrossed plants of the same stock. With
respect to height and weight, there are only two exceptions to the rule,
namely, with Eschscholtzia and Petunia, and the latter is probably no
real exception. Nor do these two species offer an exception in regard to
fertility, for the plants derived from the cross with a fresh stock were
much more fertile than the self-fertilised plants. The difference
between the two sets of plants in the table is generally much greater in
fertility than in height or weight. On the other hand, with some of the
species, as with Nicotiana, there was no difference in fertility between
the two sets, although a great difference in height and weight.
Considering all the cases in this table, there can be no doubt that
plants profit immensely, though in different ways, by a cross with a
fresh stock or with a distinct sub-variety. It cannot be maintained that
the benefit thus derived is due merely to the plants of the fresh stock
being perfectly healthy, whilst those which had been long intercrossed
or self-fertilised had become unhealthy; for in most cases there was no
appearance of such unhealthiness, and we shall see under Table 7/A that
the intercrossed plants of the same stock are generally superior to a
certain extent to the self-fertilised,–both lots having been subjected
to exactly the same conditions and being equally healthy or unhealthy.

We further learn from Table 7/C, that a cross between plants that have
been self-fertilised during several successive generations and kept all
the time under nearly uniform conditions, does not benefit the offspring
in the least or only in a very slight degree. Mimulus and the
descendants of Ipomoea named Hero offer instances of this rule. Again,
plants self-fertilised during several generations profit only to a small
extent by a cross with intercrossed plants of the same stock (as in the
case of Dianthus), in comparison with the effects of a cross by a fresh
stock. Plants of the same stock intercrossed during several generations
(as with Petunia) were inferior in a marked manner in fertility to those
derived from the corresponding self-fertilised plants crossed by a fresh
stock. Lastly, certain plants which are regularly intercrossed by
insects in a state of nature, and which were artificially crossed in
each succeeding generation in the course of my experiments, so that they
can never or most rarely have suffered any evil from self-fertilisation
(as with Eschscholtzia and Ipomoea), nevertheless profited greatly by a
cross with a fresh stock. These several cases taken together show us in
the clearest manner that it is not the mere crossing of any two
individuals which is beneficial to the offspring. The benefit thus
derived depends on the plants which are united differing in some manner,
and there can hardly be a doubt that it is in the constitution or nature
of the sexual elements. Anyhow, it is certain that the differences are
not of an external nature, for two plants which resemble each other as
closely as the individuals of the same species ever do, profit in the
plainest manner when intercrossed, if their progenitors have been
exposed during several generations to different conditions. But to this
latter subject I shall have to recur in a future chapter.

TABLE 7/A.

We will now turn to our first table, which relates to crossed and
self-fertilised plants of the same stock. These consist of fifty-four
species belonging to thirty natural orders. The total number of crossed
plants of which measurements are given is 796, and of self-fertilised
809; that is altogether 1,605 plants. Some of the species were
experimented on during several successive generations; and it should be
borne in mind that in such cases the crossed plants in each generation
were crossed with pollen from another crossed plant, and the flowers on
the self-fertilised plants were almost always fertilised with their own
pollen, though sometimes with pollen from other flowers on the same
plant. The crossed plants thus became more or less closely inter-related
in the later generations; and both lots were subjected in each
generation to almost absolutely the same conditions, and to nearly the
same conditions in the successive generations. It would have been a
better plan in some respects if I had always crossed some flowers either
on the self-fertilised or intercrossed plants of each generation with
pollen from a non-related plant, grown under different conditions, as
was done with the plants in Table 7/C; for by this procedure I should
have learnt how much the offspring became deteriorated through continued
self-fertilisation in the successive generations. As the case stands,
the self-fertilised plants of the successive generations in Table 7/A
were put into competition with and compared with intercrossed plants,
which were probably deteriorated in some degree by being more or less
inter-related and grown under similar conditions. Nevertheless, had I
always followed the plan in Table 7/C, I should not have discovered the
important fact that, although a cross between plants which are rather
closely related and which had been subjected to closely similar
conditions, gives during several generations some advantage to the
offspring, yet that after a time they may be intercrossed with no
advantage whatever to the offspring. Nor should I have learnt that the
self-fertilised plants of the later generations might be crossed with
intercrossed plants of the same stock with little or no advantage,
although they profited to an extraordinary degree by a cross with a
fresh stock.

With respect to the greater number of the plants in Table 7/A, nothing
special need here be said; full particulars may be found under the head
of each species by the aid of the Index. The figures in the right-hand
column show the mean height of the self-fertilised plants, that of the
crossed plants with which they competed being represented by 100. No
notice is here taken of the few cases in which crossed and
self-fertilised plants were grown in the open ground, so as not to
compete together. The table includes, as we have seen, plants belonging
to fifty-four species, but as some of these were measured during several
successive generations, there are eighty-three cases in which crossed
and self-fertilised plants were compared. As in each generation the
number of plants which were measured (given in the table) was never very
large and sometimes small, whenever in the right hand column the mean
height of the crossed and self-fertilised plants is the same within five
per cent, their heights may be considered as practically equal. Of such
cases, that is, of self-fertilised plants of which the mean height is
expressed by figures between 95 and 105, there are eighteen.