CHAPTER XVII. ON THE GOOD EFFECTS OF CROSSING, AND ON THE EVIL EFFECTS

OF CLOSE INTERBREEDING.

DEFINITION OF CLOSE INTERBREEDING—AUGMENTATION OF MORBID

TENDENCIES—GENERAL EVIDENCE OF THE GOOD EFFECTS DERIVED FROM CROSSING,

AND ON THE EVIL EFFECTS FROM CLOSE INTERBREEDING—CATTLE, CLOSELY

INTERBRED; HALF-WILD CATTLE LONG KEPT IN THE SAME

PARKS—SHEEP—FALLOW-DEER—DOGS, RABBITS, PIGS—MAN, ORIGIN OF HIS

ABHORRENCE OF INCESTUOUS MARRIAGES—FOWLS—PIGEONS—HIVE-BEES—PLANTS,

GENERAL CONSIDERATIONS ON THE BENEFITS DERIVED FROM CROSSING—MELONS,

FRUIT-TREES, PEAS, CABBAGES, WHEAT, AND FOREST-TREES—ON THE INCREASED

SIZE OF HYBRID PLANTS, NOT EXCLUSIVELY DUE TO THEIR STERILITY—ON

CERTAIN PLANTS WHICH EITHER NORMALLY OR ABNORMALLY ARE SELF-IMPOTENT,

BUT ARE FERTILE, BOTH ON THE MALE AND FEMALE SIDE, WHEN CROSSED WITH

DISTINCT INDIVIDUALS EITHER OF THE SAME OR ANOTHER SPECIES—CONCLUSION.

The gain in constitutional vigour, derived from an occasional cross

between individuals of the same variety, but belonging to distinct

families, or between distinct varieties, has not been so largely or so

frequently discussed, as have the evil effects of too close

interbreeding. But the former point is the more important of the two,

inasmuch as the evidence is more decisive. The evil results from close

interbreeding are difficult to detect, for they accumulate slowly, and

differ much in degree with different species; whilst the good effects

which almost invariably follow a cross are from the first manifest. It

should, however, be clearly understood that the advantage of close

interbreeding, as far as the retention of character is concerned, is

indisputable, and often outweighs the evil of a slight loss of

constitutional vigour. In relation to the subject of domestication, the

whole question is of some importance, as too close interbreeding

interferes with the improvement of old races. It is important as

indirectly bearing on Hybridism; and possibly on the extinction of

species, when any form has become so rare that only a few individuals

remain within a confined area. It bears in an important manner on the

influence of free intercrossing, in obliterating individual

differences, and thus giving uniformity of character to the individuals

of the same race or species; for if additional vigour and fertility be

thus gained, the crossed offspring will multiply and prevail, and the

ultimate result will be far greater than otherwise would have occurred.

Lastly, the question is of high interest, as bearing on mankind. I

shall therefore discuss this subject at full length. As the facts which

prove the evil effects of close interbreeding are more copious, though

less decisive, than those on the good effects of crossing, I shall,

under each group of beings, begin with the former.

There is no difficulty in defining what is meant by a cross; but this

is by no means easy in regard to “breeding in and in” or “too close

interbreeding,” because, as we shall see, different species of animals

are differently affected by the same degree of interbreeding. The

pairing of a father and daughter, or mother and son, or brothers and

sisters, if carried on during several generations, is the closest

possible form of interbreeding. But some good judges, for instance Sir

J. Sebright, believe that the pairing of a brother and sister is much

closer than that of parents and children; for when the father is

matched with his daughter he crosses, as is said, with only half his

own blood. The consequences of close interbreeding carried on for too

long a time, are, as is generally believed, loss of size,

constitutional vigour, and fertility, sometimes accompanied by a

tendency to malformation. Manifest evil does not usually follow from

pairing the nearest relations for two, three, or even four generations;

but several causes interfere with our detecting the evil—such as the

deterioration being very gradual, and the difficulty of distinguishing

between such direct evil and the inevitable augmentation of any morbid

tendencies which may be latent or apparent in the related parents. On

the other hand, the benefit from a cross, even when there has not been

any very close interbreeding, is almost invariably at once conspicuous.

There is good reason to believe, and this was the opinion of that most

experienced observer Sir J. Sebright,[1] that the evil effects of close

interbreeding may be checked or quite prevented by the related

individuals being separated for a few generations and exposed to

different conditions of life. This conclusion is now held by many

breeders; for instance Mr. Carr[2] remarks, it is a well-known “fact

that a change of soil and climate effects perhaps almost as great a

change in the constitution as would result from an infusion of fresh

blood.” I hope to show in a future work that consanguinity by itself

counts for nothing, but acts solely from related organisms generally

having a similar constitution, and having been exposed in most cases to

similar conditions.

That any evil directly follows from the closest interbreeding has been

denied by many persons; but rarely by any practical breeder; and never,

as far as I know, by one who has largely bred animals which propagate

their kind quickly. Many physiologists attribute the evil exclusively

to the combination and consequent increase of morbid tendencies common

to both parents; and that this is an active source of mischief there

can be no doubt. It is unfortunately too notorious that men and various

domestic animals endowed with a wretched constitution, and with a

strong hereditary disposition to disease, if not actually ill, are

fully capable of procreating their kind. Close interbreeding, on the

other hand, often induces sterility; and this indicates something quite

distinct from the augmentation of morbid tendencies common to both

parents. The evidence immediately to be given convinces me that it is a

great law of nature, that all organic beings profit from an occasional

cross with individuals not closely related to them in blood; and that,

on the other hand, long-continued close interbreeding is injurious.

Various general considerations have had much influence in leading me to

this conclusion; but the reader will probably rely more on special

facts and opinions. The authority of experienced observers, even when

they do not advance the grounds of their belief, is of some little

value. Now almost all men who have bred many kinds of animals and have

written on the subject, such as Sir J. Sebright, Andrew Knight,

etc.,[3] have expressed the strongest conviction on the impossibility

of long-continued close interbreeding. Those who have compiled works on

agriculture, and have associated much with breeders, such as the

sagacious Youatt, Low, etc., have strongly declared their opinion to

the same effect. Prosper Lucas, trusting largely to French authorities,

has come to a similar conclusion. The distinguished German

agriculturist Hermann von Nathusius, who has written the most able

treatise on this subject which I have met with, concurs; and as I shall

have to quote from this treatise, I may state that Nathusius is not

only intimately acquainted with works on agriculture in all languages,

and knows the pedigrees of our British breeds better than most

Englishmen, but has imported many of our improved animals, and is

himself an experienced breeder.

Evidence of the evil effects of close interbreeding can most readily be

acquired in the case of animals, such as fowls, pigeons, etc., which

propagate quickly, and, from being kept in the same place, are exposed

to the same conditions. Now I have inquired of very many breeders of

these birds, and I have hitherto not met with a single man who was not

thoroughly convinced that an occasional cross with another strain of

the same sub-variety was absolutely necessary. Most breeders of highly

improved or fancy birds value their own strain, and are most unwilling,

at the risk, in their opinion, of deterioration, to make a cross. The

purchase of a first-rate bird of another strain is expensive, and

exchanges are troublesome; yet all breeders, as far as I can hear,

excepting those who keep large stocks at different places for the sake

of crossing, are driven after a time to take this step.

Another general consideration which has had great influence on my mind

is, that with all hermaphrodite animals and plants, which it might have

been thought would have perpetually fertilised themselves and been thus

subjected for long ages to the closest interbreeding, there is not a

single species, as far as I can discover, in which the structure

ensures self-fertilisation. On the contrary, there are in a multitude

of cases, as briefly stated in the fifteenth chapter, manifest

adaptations which favour or inevitably lead to an occasional cross

between one hermaphrodite and another of the same species; and these

adaptive structures are utterly purposeless, as far as we can see, for

any other end.

With _Cattle_ there can be no doubt that extremely close interbreeding

may be long carried on advantageously with respect to external

characters, and with no manifest evil as far as constitution is

concerned. The case of Bakewell’s Longhorns, which were closely

interbred for a long period, has often been quoted; yet Youatt says[4]

the breed “had acquired a delicacy of constitution inconsistent with

common management,” and “the propagation of the species was not always

certain.” But the Shorthorns offer the most striking case of close

interbreeding; for instance, the famous bull Favourite (who was himself

the offspring of a half-brother and sister from Foljambe) was matched

with his own daughter, granddaughter, and great-granddaughter; so that

the produce of this last union, or the great-great-granddaughter, had

15-16ths, or 93·75 per cent of the blood of Favourite in her veins.

This cow was matched with the bull Wellington, having 62·5 per cent of

Favourite blood in his veins, and produced Clarissa; Clarissa was

matched with the bull Lancaster, having 68·75 of the same blood, and

she yielded valuable offspring.[5] Nevertheless Collings, who reared

these animals, and was a strong advocate for close breeding, once

crossed his stock with a Galloway, and the cows from this cross

realised the highest prices. Bates’s herd was esteemed the most

celebrated in the world. For thirteen years he bred most closely in and

in; but during the next seventeen years, though he had the most exalted

notion of the value of his own stock, he thrice infused fresh blood

into his herd: it is said that he did this, not to improve the form of

his animals, but on account of their lessened fertility. Mr. Bates’s

own view, as given by a celebrated breeder,[6] was, that “to breed

in-and-in from a bad stock was ruin and devastation; yet that the

practice may be safely followed within certain limits when the parents

so related are descended from first-rate animals.” We thus see that

there has been much close interbreeding with Shorthorns; but Nathusius,

after the most careful study of their pedigrees, says that he can find

no instance of a breeder who has strictly followed this practice during

his whole life. From this study and his own experience, he concludes

that close interbreeding is necessary to ennoble the stock; but that in

effecting this the greatest care is necessary, on account of the

tendency to infertility and weakness. It may be added, that another

high authority[7] asserts that many more calves are born cripples from

Shorthorns than from other and less closely interbred races of cattle.

Although by carefully selecting the best animals (as Nature effectually

does by the law of battle) close interbreeding may be long carried on

with cattle, yet the good effects of a cross between almost any two

breeds is at once shown by the greater size and vigour of the

offspring; as Mr. Spooner writes to me, “crossing distinct breeds

certainly improves cattle for the butcher.” Such crossed animals are of

course of no value to the breeder; but they have been raised during

many years in several parts of England to be slaughtered;[8] and their

merit is now so fully recognised, that at fat-cattle shows a separate

class has been formed for their reception. The best fat ox at the great

show at Islington in 1862 was a crossed animal.

The half-wild cattle, which have been kept in British parks probably

for 400 or 500 years, or even for a longer period, have been advanced

by Culley and others as a case of long-continued interbreeding within

the limits of the same herd without any consequent injury. With respect

to the cattle at Chillingham, the late Lord Tankerville owned that they

were bad breeders.[9] The agent, Mr. Hardy, estimates (in a letter to

me, dated May, 1861) that in the herd of about fifty the average number

annually slaughtered, killed by fighting, and dying, is about ten, or

one in five. As the herd is kept up to nearly the same average number,

the annual rate of increase must be likewise about one in five. The

bulls, I may add, engage in furious battles, of which battles the

present Lord Tankerville has given me a graphic description, so that

there will always be rigorous selection of the most vigorous males. I

procured in 1855 from Mr. D. Gardner, agent to the Duke of Hamilton,

the following account of the wild cattle kept in the Duke’s park in

Lanarkshire, which is about 200 acres in extent. The number of cattle

varies from sixty-five to eighty; and the number annually killed (I

presume by all causes) is from eight to ten; so that the annual rate of

increase can hardly be more than one in six. Now in South America,

where the herds are half-wild, and therefore offer a nearly fair

standard of comparison, according to Azara the natural increase of the

cattle on an estancia is from one-third to one-fourth of the total

number, or one in between three and four and this, no doubt, applies

exclusively to adult animals fit for consumption. Hence the half-wild

British cattle which have long interbred within the limits of the same

herd are relatively far less fertile. Although in an unenclosed country

like Paraguay there must be some crossing between the different herds,

yet even there the inhabitants believe that the occasional introduction

of animals from distant localities is necessary to prevent

“degeneration in size and diminution of fertility.”[10] The decrease in

size from ancient times in the Chillingham and Hamilton cattle must

have been prodigious, for Professor Rütimeyer has shown that they are

almost certainly the descendants of the gigantic _Bos primigenius._ No

doubt this decrease in size may be largely attributed to less

favourable conditions of life; yet animals roaming over large parks,

and fed during severe winters, can hardly be considered as placed under

very unfavourable conditions.

With _Sheep_ there has often been long-continued interbreeding within

the limits of the same flock; but whether the nearest relations have

been matched so frequently as in the case of Shorthorn cattle, I do not

know. The Messrs. Brown during fifty years have never infused fresh

blood into their excellent flock of Leicesters. Since 1810 Mr. Barford

has acted on the same principle with the Foscote flock. He asserts that

half a century of experience has convinced him that when two nearly

related animals are quite sound in constitution, in-and-in breeding

does not induce degeneracy; but he adds that he “does not pride himself

on breeding from the nearest affinities.” In France the Naz flock has

been bred for sixty years without the introduction of a single strange

ram.[11] Nevertheless, most great breeders of sheep have protested

against close interbreeding prolonged for too great a length of

time.[12] The most celebrated of recent breeders, Jonas Webb, kept five

separate families to work on, thus “retaining the requisite distance of

relationship between the sexes”;[13] and what is probably of greater

importance, the separate flocks will have been exposed to somewhat

different conditions.

Although by the aid of careful selection the near interbreeding of

sheep may be long continued without any manifest evil, yet it has often

been the practice with farmers to cross distinct breeds to obtain

animals for the butcher, which plainly shows that good of some kind is

derived from this practice. We have excellent evidence on this head

from Mr. S. Druce,[14] who gives in detail the comparative numbers of

four pure breeds and of a cross-breed which can be supported on the

same ground, and he gives their produce in fleece and carcase. A high

authority, Mr. Pusey, sums up the result in money value during an equal

length of time, namely (neglecting shillings), for Cotswolds 248_l_.,

for Leicesters 223_l_., for Southdowns 204_l_., for Hampshire Downs

264_l_., and for the crossbred 293_l_. A former celebrated breeder,

Lord Somerville, states that his half-breeds from Ryelands and Spanish

sheep were larger animals than either the pure Ryelands or pure Spanish

sheep. Mr. Spooner concludes his excellent Essay on Crossing by

asserting that there is a pecuniary advantage in judicious

cross-breeding, especially when the male is larger than the female.[15]

As some of our British parks are ancient, it occurred to me that there

must have been long-continued close interbreeding with the fallow-deer

(_Cervus dama_) kept in them; but on inquiry I find that it is a common

practice to infuse new blood by procuring bucks from other parks. Mr.

Shirley,[16] who has carefully studied the management of deer, admits

that in some parks there has been no admixture of foreign blood from a

time beyond the memory of man. But he concludes “that in the end the

constant breeding in-and-in is sure to tell to the disadvantage of the

whole herd, though it may take a very long time to prove it; moreover,

when we find, as is very constantly the case, that the introduction of

fresh blood has been of the very greatest use to deer, both by

improving their size and appearance, and particularly by being of

service in removing the taint of ‘rickback,’ if not of other diseases,

to which deer are sometimes subject when the blood has not been

changed, there can, I think, be no doubt but that a judicious cross

with a good stock is of the greatest consequence, and is indeed

essential, sooner or later, to the prosperity of every well-ordered

park.”

Mr. Meynell’s famous foxhounds have been adduced, as showing that no

ill effects follow from close interbreeding; and Sir J. Sebright

ascertained from him that he frequently bred from father and daughter,

mother and son, and sometimes even from brothers and sisters. With

greyhounds also there has been much close interbreeding, but the best

breeders agree that it may be carried too far.[17] But Sir J. Sebright

declares,[18] that by breeding in-and-in, by which he means matching

brothers and sisters, he has actually seen the offspring of strong

spaniels degenerate into weak and diminutive lapdogs. The Rev. W. D.

Fox has communicated to me the case of a small lot of bloodhounds, long

kept in the same family, which had become very bad breeders, and nearly

all had a bony enlargement in the tail. A single cross with a distinct

strain of bloodhounds restored their fertility, and drove away the

tendency to malformation in the tail. I have heard the particulars of

another case with bloodhounds, in which the female had to be held to

the male. Considering how rapid is the natural increase of the dog, it

is difficult to understand the large price of all highly improved

breeds, which almost implies long-continued close interbreeding, except

on the belief that this process lessens fertility and increases

liability to distemper and other diseases. A high authority, Mr.

Scrope, attributes the rarity and deterioration in size of the Scotch

deerhound (the few individuals formerly existing throughout the country

being all related) in large part to close interbreeding.

With all highly-bred animals there is more or less difficulty in

getting them to procreate quickly, and all suffer much from delicacy of

constitution. A great judge of rabbits[19] says, “the long-eared does

are often too highly bred or forced in their youth to be of much value

as breeders, often turning out barren or bad mothers.” They often

desert their young, so that it is necessary to have nurse-rabbits, but

I do not pretend to attribute all these evil results to close

interbreeding.[20]

With respect to _Pigs_ there is more unanimity amongst breeders on the

evil effects of close interbreeding than, perhaps, with any other large

animal. Mr. Druce, a great and successful breeder of the Improved

Oxfordshires (a crossed race), writes, “without a change of boars of a

different tribe, but of the same breed, constitution cannot be

preserved.” Mr. Fisher Hobbs, the raiser of the celebrated Improved

Essex breed, divided his stock into three separate families, by which

means he maintained the breed for more than twenty years, “by judicious

selection from the _three distinct families._”[21] Lord Western was the

first importer of a Neapolitan boar and sow. “From this pair he bred

in-and-in, until the breed was in danger of becoming extinct, a sure

result (as Mr. Sidney remarks) of in-and-in breeding.” Lord Western

then crossed his Neapolitan pigs with the old Essex, and made the first

great step towards the Improved Essex breed. Here is a more interesting

case. Mr. J. Wright, well known as a breeder, crossed[22] the same boar

with the daughter, granddaughter, and great-granddaughter, and so on

for seven generations. The result was, that in many instances the

offspring failed to breed; in others they produced few that lived; and

of the latter many were idiotic, without sense, even to suck, and when

attempting to move could not walk straight. Now it deserves especial

notice, that the two last sows produced by this long course of

interbreeding were sent to other boars, and they bore several litters

of healthy pigs. The best sow in external appearance produced during

the whole seven generations was one in the last stage of descent; but

the litter consisted of this one sow. She would not breed to her sire,

yet bred at the first trial to a stranger in blood. So that, in Mr.

Wright’s case, long-continued and extremely close interbreeding did not

affect the external form or merit of the young; but with many of them

the general constitution and mental powers, and especially the

reproductive functions, were seriously affected.

Nathusius gives[23] an analogous and even more striking case: he

imported from England a pregnant sow of the large Yorkshire breed, and

bred the product closely in-and-in for three generations: the result

was unfavourable, as the young were weak in constitution, with impaired

fertility. One of the latest sows, which he esteemed a good animal,

produced, when paired with her own uncle (who was known to be

productive with sows of other breeds), a litter of six, and a second

time a litter of only five weak young pigs. He then paired this sow

with a boar of a small black breed, which he had likewise imported from

England; this boar, when matched with sows of his own breed, produced

from seven to nine young. Now, the sow of the large breed, which was so

unproductive when paired with her own uncle, yielded to the small black

boar, in the first litter twenty-one, and in the second litter eighteen

young pigs; so that in one year she produced thirty-nine fine young

animals!

As in the case of several other animals already mentioned, even when no

injury is perceptible from moderately close interbreeding, yet, to

quote the words of Mr. Coate (who five times won the annual gold medal

of the Smithfield Club Show for the best pen of pigs), “Crosses answer

well for profit to the farmer, as you get more constitution and quicker

growth; but for me, who sell a great number of pigs for breeding

purposes, I find it will not do, as it requires many years to get

anything like purity of blood again.”[24]

Almost all the animals as yet mentioned are gregarious, and the males

must frequently pair with their own daughters, for they expel the young

males as well as all intruders, until forced by old age and loss of

strength to yield to some stronger male. It is therefore not improbable

that gregarious animals may have been rendered less susceptible than

non-social species to the evil consequences of close interbreeding, so

that they may be enabled to live in herds without injury to their

offspring. Unfortunately we do not know whether an animal like the cat,

which is not gregarious, would suffer from close interbreeding in a

greater degree than our other domesticated animals. But the pig is not,

as far as I can discover, strictly gregarious, and we have seen that it

appears eminently liable to the evil effects of close interbreeding.

Mr. Huth, in the case of the pig, attributes (Chapter XXIV) these

effects to their having been “cultivated most for their fat,” or to the

selected individuals having had a weak constitution; but we must

remember that it is great breeders who have brought forward the above

cases, and who are far more familiar than ordinary men can be, with the

causes which are likely to interfere with the fertility of their

animals.

The effects of close interbreeding in the case of man is a difficult

subject, on which I will say but little. It has been discussed by

various authors under many points of view.[25] Mr. Tylor[26] has shown

that with widely different races in the most distant quarters of the

world, marriages between relations—even between distant relations—have

been strictly prohibited. There are, however, many exceptions to the

rule, which are fully given by Mr. Huth.[27] It is a curious problem

how these prohibitions arose during early and barbarous times. Mr.

Tylor is inclined to attribute them to the evil effects of

consanguineous marriages having been observed; and he ingeniously

attempts to explain some apparent anomalies in the prohibition not

extending equally to the relations on the male and female side. He

admits, however, that other causes, such as the extension of friendly

alliances, may have come into play. Mr. W. Adam, on the other hand,

concludes that related marriages are prohibited and viewed with

repugnance, from the confusion which would thus arise in the descent of

property, and from other still more recondite reasons. But I cannot

accept these views, seeing that incest is held in abhorrence by savages

such as those of Australia and South America,[28] who have no property

to bequeath, or fine moral feelings to confuse, and who are not likely

to reflect on distant evils to their progeny. According to Mr. Huth the

feeling is the indirect result of exogamy, inasmuch as when this

practice ceased in any tribe and it became endogamous, so that

marriages were strictly confined to the same tribe, it is not unlikely

that a vestige of the former practice would still be retained, so that

closely-related marriages would be prohibited. With respect to exogamy

itself Mr. MacLennan believes that it arose from a scarcity of women,

owing to female infanticide, aided perhaps by other causes.

It has been clearly shown by Mr. Huth that there is no instinctive

feeling in man against incest any more than in gregarious animals. We

know also how readily any prejudice or feeling may rise to abhorrence,

as shown by Hindus in regard to objects causing defilement. Although

there seems to be no strong inherited feeling in mankind against

incest, it seems possible that men during primeval times may have been

more excited by strange females than by those with whom they habitually

lived; in the same manner as according to Mr. Cupples,[29] male

deerhounds are inclined towards strange females, while the females

prefer dogs with whom they have associated. If any such feeling

formerly existed in man, this would have led to a preference for

marriages beyond the nearest kin, and might have been strengthened by

the offspring of such marriages surviving in greater numbers, as

analogy would lead us to believe would have occurred.

Whether consanguineous marriages, such as are permitted in civilised

nations, and which would not be considered as close interbreeding in

the case of our domesticated animals, cause any injury will never be

known with certainty until a census is taken with this object in view.

My son, George Darwin, has done what is possible at present by a

statistical investigation,[30] and he has come to the conclusion, from

his own researches and those of Dr. Mitchell, that the evidence as to

any evil thus caused is conflicting, but on the whole points to the

evil being very small.

_Birds._—In the case of the _Fowl_ a whole array of authorities could

be given against too close interbreeding. Sir J. Sebright positively

asserts that he made many trials, and that his fowls, when thus

treated, became long in the legs, small in the body, and bad

breeders.[31] He produced the famous Sebright Bantams by complicated

crosses, and by breeding in-and-in; and since his time there has been

much close interbreeding with these animals; and they are now

notoriously bad breeders. I have seen Silver Bantams, directly

descended from his stock, which had become almost as barren as hybrids;

for not a single chicken had been that year hatched from two full nests

of eggs. Mr. Hewitt says that with these Bantams the sterility of the

male stands, with rare exceptions, in the closest relation with their

loss of certain secondary male characters: he adds, “I have noticed, as

a general rule, that even the slightest deviation from feminine

character in the tail of the male Sebright—say the elongation by only

half an inch of the two principal tail feathers—brings with it improved

probability of increased fertility.”[32]

Mr. Wright states[33] that Mr. Clark, “whose fighting-cocks were so

notorious, continued to breed from his own kind till they lost their

disposition to fight, but stood to be cut up without making any

resistance, and were so reduced in size as to be under those weights

required for the best prizes; but on obtaining a cross from Mr.

Leighton, they again resumed their former courage and weight.” It

should be borne in mind that game-cocks before they fought were always

weighed, so that nothing was left to the imagination about any

reduction or increase of weight. Mr. Clark does not seem to have bred

from brothers and sisters, which is the most injurious kind of union;

and he found, after repeated trials, that there was a greater reduction

in weight in the young from a father paired with his daughter, than

from a mother with her son. I may add that Mr. Eyton of Eyton, the

well-known ornithologist, who is a large breeder of Grey Dorkings,

informs me that they certainly diminish in size, and become less

prolific, unless a cross with another strain is occasionally obtained.

So it is with Malays, according to Mr. Hewitt, as far as size is

concerned.[34]

An experienced writer[35] remarks that the same amateur, as is well

known, seldom long maintains the superiority of his birds; and this, he

adds, undoubtedly is due to all his stock “being of the same blood;”

hence it is indispensable that he should occasionally procure a bird of

another strain. But this is not necessary with those who keep a stock

of fowls at different stations. Thus, Mr. Ballance, who has bred Malays

for thirty years, and has won more prizes with these birds than any

other fancier in England, says that breeding in-and-in does not

necessarily cause deterioration; “but all depends upon how this is

managed. My plan has been to keep about five or six distinct runs, and

to rear about two hundred or three hundred chickens each year, and

select the best birds from each run for crossing. I thus secure

sufficient crossing to prevent deterioration.”[36]

We thus see that there is almost complete unanimity with

poultry-breeders that, when fowls are kept at the same place, evil

quickly follows from interbreeding carried on to an extent which would

be disregarded in the case of most quadrupeds. Moreover, it is a

generally received opinion that cross-bred chickens are the hardiest

and most easily reared.[37] Mr. Tegetmeier, who has carefully attended

to poultry of all breeds, says[38] that Dorking hens, allowed to run

with Houdan or Crevecœur cocks, “produce in the early spring chickens

that for size, hardihood, early maturity, and fitness for the market,

surpass those of any pure breed that we have ever raised.” Mr. Hewitt

gives it as a general rule with fowls, that crossing the breed

increases their size. He makes this remark after stating that hybrids

from the pheasant and fowl are considerably larger than either

progenitor: so again, hybrids from the male golden pheasant and female

common pheasant “are of far larger size than either parent-bird.”[39]

To this subject of the increased size of hybrids I shall presently

return.

With _Pigeons,_ breeders are unanimous, as previously stated, that it

is absolutely indispensable, notwithstanding the trouble and expense

thus caused, occasionally to cross their much-prized birds with

individuals of another strain, but belonging, of course, to the same

variety. It deserves notice that, when size is one of the desired

characters, as with pouters[40] the evil effects of close interbreeding

are much sooner perceived than when small birds, such as short-faced

tumblers, are valued. The extreme delicacy of the high fancy breeds,

such as these tumblers and improved English carriers, is remarkable;

they are liable to many diseases, and often die in the egg or during

the first moult; and their eggs have generally to be hatched under

foster-mothers. Although these highly-prized birds have invariably been

subjected to much close interbreeding, yet their extreme delicacy of

constitution cannot perhaps be thus fully explained. Mr. Yarrell

informed me that Sir J. Sebright continued closely interbreeding some

owl-pigeons, until from their extreme sterility he as nearly as

possible lost the whole family. Mr. Brent[41] tried to raise a breed of

trumpeters, by crossing a common pigeon, and recrossing the daughter,

granddaughter, great-granddaughter, and great-great-granddaughter, with

the same male trumpeter, until he obtained a bird with 15/16 of

trumpeter’s blood; but then the experiment failed, for “breeding so

close stopped reproduction.” The experienced Neumeister[42] also

asserts that the offspring from dovecotes and various other breeds are

“generally very fertile and hardy birds:” so again MM. Boitard and

Corbié,[43] after forty-five years’ experience, recommend persons to

cross their breeds for amusement; for, if they fail to make interesting

birds, they will succeed under an economical point of view, “as it is

found that mongrels are more fertile than pigeons of pure race.”

I will refer only to one other animal, namely, the Hive-bee, because a

distinguished entomologist has advanced this as a case of inevitable

close interbreeding. As the hive is tenanted by a single female, it

might have been thought that her male and female offspring would always

have bred together, more especially as bees of different hives are

hostile to each other; a strange worker being almost always attacked

when trying to enter another hive. But Mr. Tegetmeier has shown[44]

that this instinct does not apply to drones, which are permitted to

enter any hive; so that there is no _à priori_ improbability of a queen

receiving a foreign drone. The fact of the union invariably and

necessarily taking place on the wing, during the queen’s nuptial

flight, seems to be a special provision against continued

interbreeding. However this may be, experience has shown, since the

introduction of the yellow-banded Ligurian race into Germany and

England, that bees freely cross: Mr. Woodbury, who introduced Ligurian

bees into Devonshire, found during a single season that three stocks,

at distances of from one to two miles from his hives, were crossed by

his drones. In one case the Ligurian drones must have flown over the

city of Exeter, and over several intermediate hives. On another

occasion several common black queens were crossed by Ligurian drones at

a distance of from one to three and a half miles.[45]

_Plants._

When a single plant of a new species is introduced into any country, if

propagated by seed, many individuals will soon be raised, so that if

the proper insects be present there will be crossing. With

newly-introduced trees or other plants not propagated by seed we are

not here concerned. With old-established plants it is an almost

universal practice occasionally to make exchanges of seed, by which

means individuals which have been exposed to different conditions of

life,—and this, as we have seen with animals, diminishes the evil from

close interbreeding,—will occasionally be introduced into each

district.

With respect to individuals belonging to the same sub-variety, Gärtner,

whose accuracy and experience exceeded that of all other observers,

states[46] that he has many times observed good effects from this step,

especially with exotic genera, of which the fertility is somewhat

impaired, such as Passiflora, Lobelia, Fuchsia. Herbert also says,[47]

“I am inclined to think that I have derived advantage from impregnating

the flower from which I wished to obtain seed with pollen from another

individual of the same variety, or at least from another flower, rather

than with its own.” Again, Professor Lecoq ascertained that crossed

offspring are more vigorous and robust than their parents.[48]

General statements of this kind, however, can seldom be fully trusted:

I therefore began a long series of experiments, continued for about ten

years, which will I think conclusively show the good effects of

crossing two distinct plants of the same variety, and the evil effects

of long-continued self-fertilisation. A clear light will thus be thrown

on such questions, as why flowers are almost invariably constructed so

as to permit, or favour, or necessitate the union of two individuals.

We shall clearly understand why monœcious and dioecious,—why

dichogamous, dimorphic and trimorphic plants exist, and many other such

cases. I intend soon to publish an account of these experiments, and I

can here give only a few cases in illustration. The plan which I

followed was to grow plants in the same pot, or in pots of the same

size, or close together in the open ground; carefully to exclude

insects; and then to fertilise some of the flowers with pollen from the

same flower, and others on the same plant with pollen from a distinct

but adjoining plant. In many of these experiments, the crossed plants

yielded much more seed than the self-fertilised plants; and I have

never seen the reversed case. The self-fertilised and crossed seeds

thus obtained were allowed to germinate in the same glass vessel on

damp sand; and as the seeds germinated, they were planted in pairs on

opposite sides of the same pot, with a superficial partition between

them, and were placed so as to be equally exposed to the light. In

other cases the self-fertilised and crossed seeds were simply sown on

opposite sides of the same small pot. I have, in short, followed

different plans, but in every case have taken all the precautions which

I could think of, so that the two lots should be equally favoured. The

growth of the plants raised from the crossed and self-fertilised seed,

were carefully observed from their germination to maturity, in species

belonging to fifty-two genera; and the difference in their growth, and

in withstanding unfavourable conditions, was in most cases manifest and

strongly marked. It is of importance that the two lots of seed should

be sown or planted on opposite sides of the same pot, so that the

seedlings may struggle against each other; for if sown separately in

ample and good soil, there is often but little difference in their

growth.

I will briefly describe two of the first cases observed by me. Six

crossed and six self-fertilised seeds of _Ipomoea purpurea,_ from

plants treated in the manner above described, were planted as soon as

they had germinated, in pairs on opposite sides of two pots, and rods

of equal thickness were given them to twine up. Five of the crossed

plants grew from the first more quickly than the opposed

self-fertilised plants; the sixth, however, was weakly and was for a

time beaten, but at last its sounder constitution prevailed and it shot

ahead of its antagonist. As soon as each crossed plant reached the top

of its seven-foot rod its fellow was measured, and the result was that,

when the crossed plants were seven feet high the self-fertilised had

attained the average height of only five feet four and a half inches.

The crossed plants flowered a little before, and more profusely than

the self-fertilised plants. On opposite sides of another _ small_ pot a

large number of crossed and self-fertilised seeds were sown, so that

they had to struggle for bare existence; a single rod was given to each

lot: here again the crossed plants showed from the first their

advantage; they never quite reached the summit of the seven-foot rod,

but relatively to the self-fertilised plants their average height was

as seven feet to five feet two inches. The experiment was repeated

during several succeeding generations, treated in exactly the same

manner, and with nearly the same result. In the second generation, the

crossed plants, which were again crossed, produced 121 seed-capsules,

whilst the self-fertilised, again self-fertilised, produced only 84

capsules.

Some flowers of the _Mimulus luteus_ were fertilised with their own

pollen, and others were crossed with pollen from distinct plants

growing in the same pot. The seeds were thickly sown on opposite sides

of a pot. The seedlings were at first equal in height; but when the

young crossed plants were half an inch, the self-fertilised plants were

only a quarter of an inch high. But this degree of inequality did not

last, for, when the crossed plants were four and a half inches high,

the self-fertilised were three inches, and they retained the same

relative difference till their growth was complete. The crossed plants

looked far more vigorous than the uncrossed, and flowered before them;

they produced also a far greater number of capsules. As in the former

case, the experiment was repeated during several succeeding

generations. Had I not watched these plants of Mimulus and Ipomoea

during their whole growth, I could not have believed it possible, that

a difference apparently so slight as that of the pollen being taken

from the same flower, or from a distinct plant growing in the same pot,

could have made so wonderful a difference in the growth and vigour of

the plants thus produced. This, under a physiological point of view, is

a most remarkable phenomenon.

With respect to the benefit derived from crossing distinct varieties,

plenty of evidence has been published. Sageret[49] repeatedly speaks in

strong terms of the vigour of melons raised by crossing different

varieties, and adds that they are more easily fertilised than common

melons, and produce numerous good seed. Here follows the evidence of an

English gardener:[50] “I have this summer met with better success in my

cultivation of melons, in an unprotected state, from the seeds of

hybrids (_i.e._ mongrels) obtained by cross impregnation, than with old

varieties. The offspring of three different hybridisations (one more

especially, of which the parents were the two most dissimilar varieties

I could select) each yielded more ample and finer produce than any one

of between twenty and thirty established varieties.”

Andrew Knight[51] believed that his seedlings from crossed varieties of

the apple exhibited increased vigour and luxuriance; and M.

Chevreul[52] alludes to the extreme vigour of some of the crossed

fruit-trees raised by Sageret.

By crossing reciprocally the tallest and shortest peas, Knight[53]

says: “I had in this experiment a striking instance of the stimulative

effects of crossing the breeds; for the smallest variety, whose height

rarely exceeded two feet, was increased to six feet: whilst the height

of the large and luxuriant kind was very little diminished.” Mr. Laxton

gave me seed-peas produced from crosses between four distinct kinds;

and the plants thus raised were extraordinarily vigorous, being in each

case from one to two or three feet taller than the parent-forms growing

close alongside them.

Wiegmann[54] made many crosses between several varieties of cabbage;

and he speaks with astonishment of the vigour and height of the

mongrels, which excited the amazement of all the gardeners who beheld

them. Mr. Chaundy raised a great number of mongrels by planting

together six distinct varieties of cabbage. These mongrels displayed an

infinite diversity of character; “But the most remarkable circumstance

was, that, while all the other cabbages and borecoles in the nursery

were destroyed by a severe winter, these hybrids were little injured,

and supplied the kitchen when there was no other cabbage to be had.”

Mr. Maund exhibited before the Royal Agricultural Society[55] specimens

of crossed wheat, together with their parent varieties; and the editor

states that they were intermediate in character, “united with that

greater vigour of growth, which it appears, in the vegetable as in the

animal world, is the result of a first cross.” Knight also crossed

several varieties of wheat,[56] and he says “that in the years 1795 and

1796, when almost the whole crop of corn in the island was blighted,

the varieties thus obtained, and these only, escaped in this

neighbourhood, though sown in several different soils and situations.”

Here is a remarkable case: M. Clotzsch[57] crossed _Pinus sylvestris_

and _nigricans, Quercus robur_ and _pedunculata, Alnus glutinosa_ and

_incana, Ulmus campestris_ and _ effusa_; and the cross-fertilised

seeds, as well as seeds of the pure parent-trees, were all sown at the

same time and in the same place. The result was, that after an interval

of eight years, the hybrids were one-third taller than the pure trees!

The facts above given refer to undoubted varieties, excepting the trees

crossed by Clotzsch, which are ranked by various botanists as

strongly-marked races, sub-species, or species. That true hybrids

raised from entirely distinct species, though they lose in fertility,

often gain in size and constitutional vigour, is certain. It would be

superfluous to quote any facts; for all experimenters, Kolreuter,

Gärtner, Herbert, Sageret, Lecoq, and Naudin, have been struck with the

wonderful vigour, height, size, tenacity of life, precocity, and

hardiness of their hybrid productions. Gärtner[58] sums up his

conviction on this head in the strongest terms. Kölreuter[59] gives

numerous precise measurements of the weight and height of his hybrids

in his comparison with measurements of both parent-forms; and speaks

with astonishment of their “_statura portentosa,_” their “_ambitus

vastissimus ac altitudo valde conspicua._” Some exceptions to the rule

in the case of very sterile hybrids have, however, been noticed by

Gärtner and Herbert; but the most striking exceptions are given by Max

Wichura[60] who found that hybrid willows were generally tender in

constitution, dwarf, and short-lived.

Kolreuter explains the vast increase in the size of the roots, stems,

etc., of his hybrids, as the result of a sort of compensation due to

their sterility, in the same way as many emasculated animals are larger

than the perfect males. This view seems at first sight extremely

probable, and has been accepted by various authors;[61] but Gärtner[62]

has well remarked that there is much difficulty in fully admitting it;

for with many hybrids there is no parallelism between the degree of

their sterility and their increased size and vigour. The most striking

instances of luxuriant growth have been observed with hybrids which

were not sterile in any extreme degree. In the genus Mirabilis, certain

hybrids are unusually fertile, and their extraordinary luxuriance of

growth, together with their enormous roots[63] have been transmitted to

their progeny. The result in all cases is probably in part due to the

saving of nutriment and vital force through the sexual organs acting

imperfectly or not at all, but more especially to the general law of

good being derived from a cross. For it deserves especial attention

that mongrel animals and plants, which are so far from being sterile

that their fertility is often actually augmented, have, as previously

shown, their size, hardiness, and constitutional vigour generally

increased. It is not a little remarkable that an accession of vigour

and size should thus arise under the opposite contingencies of

increased and diminished fertility.

It is a perfectly well ascertained fact[64] that hybrids invariably

breed with either pure parent, and not rarely with a distinct species,

more readily than with one another. Herbert is inclined to explain even

this fact by the advantage derived from a cross; but Gärtner more

justly accounts for it by the pollen of the hybrid, and probably its

ovules, being in some degree vitiated, whereas the pollen and ovules of

both pure parents and of any third species are sound. Nevertheless,

there are some well-ascertained and remarkable facts, which, as we

shall presently see, show that a cross by itself undoubtedly tends to

increase or re-establish the fertility of hybrids.

The same law, namely, that the crossed offspring both of varieties and

species are larger than the parent-forms, holds good in the most

striking manner with hybrid animals as well as with mongrels. Mr.

Bartlett, who has had such large experience says, “Among all hybrids of

vertebrated animals there is a marked increase of size.” He then

enumerates many cases with mammals, including monkeys, and with various

families of birds.[65]

_On certain Hermaphrodite Plants which, either normally or

abnormally, require to be fertilised by pollen from a distinct

individual or species._

The facts now to be given differ from the foregoing, as self-sterility

is not here the result of long-continued close interbreeding. These

facts are, however, connected with our present subject, because a cross

with a distinct individual is shown to be either necessary or

advantageous. Dimorphic and trimorphic plants, though they are

hermaphrodites, must be reciprocally crossed, one set of forms by the

other, in order to be fully fertile, and in some cases to be fertile in

any degree. But I should not have noticed these plants, had it not been

for the following cases given by Dr. Hildebrand:—[66]

_Primula sinensis_ is a reciprocally dimorphic species: Dr. Hildebrand

fertilised twenty-eight flowers of both forms, each by pollen of the

other form, and obtained the full number of capsules containing on an

average 42·7 seed per capsule; here we have complete and normal

fertility. He then fertilised forty-two flowers of both forms with

pollen of the same form, but taken from a distinct plant, and all

produced capsules containing on an average only 19·6 seed. Lastly, and

here we come to our more immediate point, he fertilised forty-eight

flowers of both forms with pollen of the same form and taken from the

same flower, and now he obtained only thirty-two capsules, and these

contained on an average 18·6 seed, or one less per capsule than in the

former case. So that, with these illegitimate unions, the act of

impregnation is less assured, and the fertility slightly less, when the

pollen and ovules belong to the same flower, than when belonging to two

distinct individuals of the same form. Dr. Hildebrand has recently made

analogous experiments on the long-styled form of _Oxalis rosea,_ with

the same result.[67]

It has recently been discovered that certain plants, whilst growing in

their native country under natural conditions, cannot be fertilised

with pollen from the same plant. They are sometimes so utterly

self-impotent, that, though they can readily be fertilised by the

pollen of a distinct species or even distinct genus, yet, wonderful as

is the fact, they never produce a single seed by their own pollen. In

some cases, moreover, the plant’s own pollen and stigma mutually act on

each other in a deleterious manner. Most of the facts to be given

relate to orchids, but I will commence with a plant belonging to a

widely different family.

Sixty-three flowers of _Corydalis cava,_ borne on distinct plants, were

fertilised by Dr. Hildebrand[68] with pollen from other plants of the

same species; and fifty-eight capsules were obtained, including on an

average 4.5 seed in each. He then fertilised sixteen flowers produced

by the same raceme, one with another, but obtained only three capsules,

one of which alone contained any good seeds, namely, two in number.

Lastly, he fertilised twenty-seven flowers, each with its own pollen;

he left also fifty-seven flowers to be spontaneously fertilised, and

this would certainly have ensued if it had been possible, for the

anthers not only touch the stigma, but the pollen-tubes were seen by

Dr. Hildebrand to penetrate it; nevertheless these eighty-four flowers

did not produce a single seed-capsule! This whole case is highly

instructive, as it shows how widely different the action of the same

pollen is, according as it is placed on the stigma of the same flower,

or on that of another flower on the same raceme, or on that of a

distinct plant.

With exotic Orchids several analogous cases have been observed, chiefly

by Mr. John Scott.[69] _Oncidium sphacelatum_ has effective pollen, for

Mr. Scott fertilised two distinct species with it; the ovules are

likewise capable of impregnation, for they were readily fertilised by

the pollen of _O. divaricatum_; nevertheless, between one and two

hundred flowers fertilised by their own pollen did not produce a single

capsule, though the stigmas were penetrated by the pollen-tubes. Mr.

Robertson Munro, of the Royal Botanic Gardens of Edinburgh, also

informs me (1864) that a hundred and twenty flowers of this same

species were fertilised by him with their own pollen, and did not

produce a capsule, but eight flowers, fertilised by the pollen of _O.

divaricatum,_ produced four fine capsules: again, between two and three

hundred flowers of _O. divaricatum,_ fertilised by their own pollen,

did not set a capsule, but twelve flowers fertilised by _O. flexuosum_

produced eight fine capsules: so that here we have three utterly

self-impotent species, with their male and female organs perfect, as

shown by their mutual fertilisation. In these cases fertilisation was

effected only by the aid of a distinct species. But, as we shall

presently see, distinct plants, raised from seed, of _Oncidium

flexuosum,_ and probably of the other species, would have been

perfectly capable of fertilising each other, for this is the natural

process. Again, Mr. Scott found that the pollen of a plant of _O.

microchilum_ was effective, for with it he fertilised two distinct

species; he found its ovules good, for they could be fertilised by the

pollen of one of these species, and by the pollen of a distinct plant

of _O. microchilum_; but they could not be fertilised by pollen of the

same plant, though the pollen-tubes penetrated the stigma. An analogous

case has been recorded by M. Rivière[70] with two plants of _O.

cavendishianum,_ which were both self-sterile, but reciprocally

fertilised each other. All these cases refer to the genus Oncidium, but

Mr. Scott found that _Maxillaria atro-rubens_ was “totally

insusceptible of fertilisation with its own pollen,” but fertilised,

and was fertilised by, a widely distinct species, viz. _M. squalens._

As these orchids had been grown under unnatural conditions in

hot-houses, I concluded that their self-sterility was due to this

cause. But Fritz Müller informs me that at Desterro, in Brazil, he

fertilised above one hundred flowers of the above-mentioned _Oncidium

flexuosum,_ which is there endemic, with its own pollen, and with that

taken from distinct plants: all the former were sterile, whilst those

fertilised by pollen from any _other plant_ of the same species were

fertile. During the first three days there was no difference in the

action of the two kinds of pollen: that placed on stigma of the same

plant separated in the usual manner into grains, and emitted tubes

which penetrated the column, and the stigmatic chamber shut itself; but

only those flowers which had been fertilised by pollen taken from a

distinct plant produced seed-capsules. On a subsequent occasion these

experiments were repeated on a large scale with the same result. Fritz

Müller found that four other endemic species of Oncidium were in like

manner utterly sterile with their own pollen, but fertile with that

from any other plant: some of them likewise produced seed-capsules when

impregnated with pollen of widely distinct genera, such as Cyrtopodium,

and Rodriguezia. _Oncidium crispum,_ however, differs from the

foregoing species in varying much in its self-sterility; some plants

producing fine pods with their own pollen, others failing to do so in

two or three instances, Fritz Müller observed that the pods produced by

pollen taken from a distinct flower on the same plant, were larger than

those produced by the flower’s own pollen. In _Epidendrum

cinnabarinum,_ an orchid belonging to another division of the family,

fine pods were produced by the plant’s own pollen, but they contained

by weight only about half as much seed as the capsules which had been

fertilised by pollen from a distinct plant, and in one instance from a

distinct species; moreover, a very large proportion, and in some cases

nearly all the seeds produced by the plant’s own pollen, were destitute

of an embryo. Some self-fertilised capsules of a Maxillaria were in a

similar state.

Another observation made by Fritz Müller is highly remarkable, namely,

that with various orchids the plant’s own pollen not only fails to

impregnate the flower, but acts on the stigma, and is acted on, in an

injurious or poisonous manner. This is shown by the surface of the

stigma in contact with the pollen, and by the pollen itself becoming in

from three to five days dark brown, and then decaying. The

discoloration and decay are not caused by parasitic cryptograms, which

were observed by Fritz Müller in only a single instance. These changes

are well shown by placing on the same stigma, at the same time, the

plant’s own pollen and that from a distinct plant of the same species,

or of another species, or even of another and widely remote genus.

Thus, on the stigma of _Oncidium flexuosum,_ the plant’s own pollen and

that from a distinct plant were placed side by side, and in five days’

time the latter was perfectly fresh, whilst the plant’s own pollen was

brown. On the other hand, when the pollen of a distinct plant of the

_Oncidium flexuosum_ and of the _ Epidendrum zebra (nov. spec.?)_ were

placed together on the same stigma, they behaved in exactly the same

manner, the grains separating, emitting tubes, and penetrating the

stigma, so that the two pollen-masses, after an interval of eleven

days, could not be distinguished except by the difference of their

caudicles, which, of course, undergo no change. Fritz Müller has,

moreover, made a large number of crosses between orchids belonging to

distinct species and genera, and he finds that in all cases when the

flowers are not fertilised their footstalks first begin to wither; and

the withering slowly spreads upwards until the germens fall off, after

an interval of one or two weeks, and in one instance of between six and

seven weeks; but even in this latter case, and in most other cases, the

pollen and stigma remained in appearance fresh. Occasionally, however,

the pollen becomes brownish, generally on the external surface, and not

in contact with the stigma, as is invariably the case when the plant’s

own pollen is applied.

Fritz Müller observed the poisonous action of the plant’s own pollen in

the above-mentioned _Oncidium flexuosum, O. unicorne, pubes (?),_ and

in two other unnamed species. Also in two species of Rodriguezia, in

two of Notylia, in one of Burlingtonia, and of a fourth genus in the

same group. In all these cases, except the last, it was proved that the

flowers were, as might have been expected, fertile with pollen from a

distinct plant of the same species. Numerous flowers of one species of

Notylia were fertilised with pollen from the same raceme; in two days’

time they all withered, the germens began to shrink, the pollen-masses

became dark brown, and not one pollen-grain emitted a tube. So that in

this orchid the injurious action of the plant’s own pollen is more

rapid than with _Oncidium flexuosum._ Eight other flowers on the same

raceme were fertilised with pollen from a distinct plant of the same

species: two of these were dissected, and their stigmas were found to

be penetrated by numberless pollen-tubes; and the germens of the other

six flowers became well developed. On a subsequent occasion many other

flowers were fertilised with their own pollen, and all fell off dead in

a few days; whilst some flowers on the same raceme which had been left

simply unfertilised adhered and long remained fresh. We have seen that

in cross-unions between extremely distinct orchids the pollen long

remains undecayed; but Notylia behaved in this respect differently; for

when its pollen was placed on the stigma of _ Oncidium flexuosum,_ both

the stigma and pollen quickly became dark brown, in the same manner as

if the plant’s own pollen had been applied.

Fritz Müller suggests that, as in all these cases the plant’s own

pollen is not only impotent (thus effectually preventing

self-fertilisation), but likewise prevents, as was ascertained in the

case of the Notylia and _Oncidium flexuosum,_ the action of

subsequently applied pollen from a distinct individual, it would be an

advantage to the plant to have its own pollen rendered more and more

deleterious; for the germens would thus quickly be killed, and dropping

off, there would be no further waste in nourishing a part which

ultimately could be of no avail.

The same naturalist found in Brazil three plants of a Bignonia growing

near together. He fertilised twenty-nine flowerets on one of them with

their own pollen, and they did not set a single capsule. Thirty flowers

were then fertilised with pollen from a distinct plant, one of the

three, and they yielded only two capsules. Lastly, five flowers were

fertilised with pollen from a fourth plant growing at a distance, and

all five produced capsules. Fritz Müller thinks that the three plants

which grew near one another were probably seedlings from the same

parent, and that from being closely related, they acted very feebly on

one another. This view is extremely probable, for he has since shown in

a remarkable paper,[71] that in the case of some Brazilian species of

Abutilon, which are self-sterile, and between which he raised some

complex hybrids, that these, if near relatives, were much less fertile

_inter se,_ than when not closely related.

We now come to cases closely analogous with those just given, but

different in so far that only certain individuals of the species are

self-sterile. This self-impotence does not depend on the pollen or

ovules being in an unfit state for fertilisation, for both have been

found effective in union with other plants of the same or of a distinct

species. The fact of plants having acquired so peculiar a constitution,

that they can be fertilised more readily by the pollen of a distinct

species than by their own, is exactly the reverse of what occurs with

all ordinary species. For in the latter the two sexual elements of the

same individual plant are of course capable of freely acting on each

other; but are so constituted that they are more or less impotent when

brought into union with the sexual elements of a distinct species, and

produce more or less sterile hybrids.

Gärtner experimented on two plants of _Lobelia fulgens,_ brought from

separate places, and found[72] that their pollen was good, for he

fertilised with it _L. cardinalis_ and _ syphilitica_; their ovules

were likewise good, for they were fertilised by the pollen of these

same two species; but these two plants of _L. fulgens_ could not be

fertilised by their own pollen, as can generally be effected with

perfect ease with this species. Again, the pollen of a plant of

_Verbascum nigrum_ grown in a pot was found by Gärtner[73] capable of

fertilising _V. lychnitis_ and _V. austriacum_; the ovules could be

fertilised by the pollen of _V. thapsus_; but the flowers could not be

fertilised by their own pollen. Kölreuter, also,[74] gives the case of

three garden plants of _Verbascum phœniceum,_ which bore during two

years many flowers; these he fertilised successfully with the pollen of

no less than four distinct species, but they produced not a seed with

their own apparently good pollen; subsequently these same plants, and

others raised from seed, assumed a strangely fluctuating condition,

being temporarily sterile on the male or female side, or on both sides,

and sometimes fertile on both sides; but two of the plants were

perfectly fertile throughout the summer.

With _Reseda odorata_ I have found certain individuals quite sterile

with their own pollen, and so it is with the indigenous _Reseda lutea._

The self-sterile plants of both species were perfectly fertile when

crossed with pollen from any other individual of the same species.

These observations will hereafter be published in another work, in

which I shall also show that seeds sent to me by Fritz Müller produced

by plants of _Eschscholtzia californica_ which were quite self-sterile

in Brazil, yielded in this country plants which were only slightly

self-sterile.

It appears[75] that certain flowers on certain plants of _Lilium

candidum_ can be fertilised more freely by pollen from a distinct

individual than by their own. So, again, with the varieties of the

potato. Tinzmann,[76] who made many trials with this plant, says that

pollen from another variety sometimes “exerts a powerful influence, and

I have found sorts of potatoes which would not bear seed from

impregnation with the pollen of their own flowers would bear it when

impregnated with other pollen.” It does not, however, appear to have

been proved that the pollen which failed to act on the flower’s own

stigma was in itself good.

In the genus Passiflora it has long been known that several species do

not produce fruit, unless fertilised by pollen taken from distinct

species: thus, Mr. Mowbray[77] found that he could not get fruit from

_P. alata_ and _racemosa_ except by reciprocally fertilising them with

each other’s pollen; and similar facts have been observed in Germany

and France.[78] I have received two accounts of _P. quadrangularis_

never producing fruit from its own pollen, but doing so freely when

fertilised in one case with the pollen of _ P. cœrulea,_ and in another

case with that of _P. edulis._ But in three other cases this species

fruited freely when fertilised with its own pollen; and the writer in

one case attributed the favourable result to the temperature of the

house having been raised from 5° to 10° Fahr. above the former

temperature, after the flowers were fertilised.[79] With respect to _P.

laurifolia,_ a cultivator of much experience has recently remarked[80]

that the flowers “must be fertilised with the pollen of _P. cœrulea,_

or of some other common kind, as their own pollen will not fertilise

them.” But the fullest details on this subject have been given by

Messrs. Scott and Robertson Munro:[81] plants of _ Passiflora racemosa,

cœrulea,_ and _alata_ flowered profusely during many years in the

Botanic Gardens of Edinburgh, and, though repeatedly fertilised with

their own pollen, never produced any seed; yet this occurred at once

with all three species when they were crossed together in various ways.

In the case of _ P. cœrulea_ three plants, two of which grew in the

Botanic Gardens, were all rendered fertile, merely by impregnating each

with pollen of one of the others. The same result was attained in the

same manner with _P. alata,_ but with only one plant out of three. As

so many self-sterile species of Passiflora have been mentioned, it

should be stated that the flowers of the annual _P. gracilis_ are

nearly as fertile with their own pollen as with that from a distinct

plant; thus sixteen flowers spontaneously self-fertilised produced

fruit, each containing on an average 21·3 seed, whilst fruit from

fourteen crossed flowers contained 24·1 seed.

Returning to _P. alata,_ I have received (1866) some interesting

details from Mr. Robertson Munro. Three plants, including one in

England, have already been mentioned which were inveterately

self-sterile, and Mr. Munro informs me of several others which, after

repeated trials during many years, have been found in the same

predicament. At some other places, however, this species fruits readily

when fertilised with its own pollen. At Taymouth Castle there is a

plant which was formerly grafted by Mr. Donaldson on a distinct

species, name unknown, and ever since the operation it has produced

fruit in abundance by its own pollen; so that this small and unnatural

change in the state of this plant has restored its self-fertility! Some

of the seedlings from the Taymouth Castle plant were found to be not

only sterile with their own pollen, but with each other’s pollen, and

with the pollen of distinct species. Pollen from the Taymouth plant

failed to fertilise certain plants of the same species, but was

successful on one plant in the Edinburgh Botanic Gardens. Seedlings

were raised from this latter union, and some of their flowers were

fertilised by Mr. Munro with their own pollen; but they were found to

be as self-impotent as the mother-plant had always proved, except when

fertilised by the grafted Taymouth plant, and except, as we shall see,

when fertilised by her own seedlings. For Mr. Munro fertilised eighteen

flowers on the self-impotent mother-plant with pollen from these her

own self-impotent seedlings, and obtained, remarkable as the fact is,

eighteen fine capsules full of excellent seed! I have met with no case

in regard to plants which shows so well as this of _P. alata,_ on what

small and mysterious causes complete fertility or complete sterility

depends.

The facts hitherto given relate to the much-lessened or completely

destroyed fertility of pure species when impregnated with their own

pollen, in comparison with their fertility when impregnated by distinct

individuals or distinct species; but closely analogous facts have been

observed with hybrids.

Herbert states[82] that having in flower at the same time nine hybrid

Hippeastrums, of complicated origin, descended from several species, he

found that “almost every flower touched with pollen from another cross

produced seed abundantly, and those which were touched with their own

pollen either failed entirely, or formed slowly a pod of inferior size,

with fewer seeds.” In the ‘Horticultural Journal’ he adds that “the

admission of the pollen of another cross-bred Hippeastrum (however

complicated the cross) to any one flower of the number, is almost sure

to check the fructification of the others.” In a letter written to me

in 1839, Dr. Herbert says that he had already tried these experiments

during five consecutive years, and he subsequently repeated them, with

the same invariable result. He was thus led to make an analogous trial

on a pure species, namely, on the _Hippeastrum aulicum,_ which he had

lately imported from Brazil: this bulb produced four flowers, three of

which were fertilised by their own pollen, and the fourth by the pollen

of a triple cross between _H. bulbulosum, reginæ,_ and _vittatum_; the

result was, that “the ovaries of the three first flowers soon ceased to

grow, and after a few days perished entirely: whereas the pod

impregnated by the hybrid made vigorous and rapid progress to maturity,

and bore good seed, which vegetated freely.” This is, indeed, as

Herbert remarks, “a strange truth,” but not so strange as it then

appeared.

As a confirmation of these statements, I may add that Mr. M. Mayes[83]

after much experience in crossing the species of Amaryllis

(Hippeastrum), says, “neither the species nor the hybrids will, we are

well aware, produce seed so abundantly from their own pollen as from

that of others.” So, again, Mr. Bidwell, in New South Wales[84] asserts

that _Amaryllis belladonna_ bears many more seeds when fertilised by

the pollen of _ Brunswigia_ (_Amaryllis_ of some authors) _ josephinæ_

or of _B. multiflora,_ than when fertilised by its own pollen. Mr.

Beaton dusted four flowers of a Cyrtanthus with their own pollen, and

four with the pollen of _Vallota (Amaryllis) purpurea_; on the seventh

day “those which received their own pollen slackened their growth, and

ultimately perished; those which were crossed with the Vallota held

on.”[85] These latter cases, however, relate to uncrossed species, like

those before given with respect to Passiflora, Orchids, etc., and are

here referred to only because the plants belong to the same group of

Amaryllidaceæ.

In the experiments on the hybrid Hippeastrums, if Herbert had found

that the pollen of two or three kinds alone had been more efficient on

certain kinds than their own pollen, it might have been argued that

these, from their mixed parentage, had a closer mutual affinity than

the others; but this explanation is inadmissible, for the trials were

made reciprocally backwards and forwards on nine different hybrids; and

a cross, whichever way taken, always proved highly beneficial. I can

add a striking and analogous case from experiments made by the Rev. A.

Rawson, of Bromley Common, with some complex hybrids of Gladiolus. This

skilful horticulturist possessed a number of French varieties,

differing from each other only in the colour and size of the flowers,

all descended from Gandavensis, a well-known old hybrid, said to be

descended from _G. natalensis_ by the pollen of _ G.

oppositiflorus._[86] Mr. Rawson, after repeated trials, found that none

of the varieties would set seed with their own pollen, although taken

from distinct plants of the same variety (which had, of course, been

propagated by bulbs), but that they all seeded freely with pollen from

any other variety. To give two examples: Ophir did not produce a

capsule with its own pollen, but when fertilised with that of Janire,

Brenchleyensis, Vulcain and Linné, it produced ten fine capsules; but

the pollen of Ophir was good, for when Linné was fertilised by it seven

capsules were produced. This latter variety, on the other hand, was

utterly barren with its own pollen, which we have seen was perfectly

efficient on Ophir. Altogether, Mr. Rawson, in the year 1861 fertilised

twenty-six flowers borne by four varieties with pollen taken from other

varieties, and every single flower produced a fine seed-capsule;

whereas fifty-two flowers on the same plants, fertilised at the same

time with their own pollen, did not yield a single seed-capsule. Mr.

Rawson fertilised, in some cases, the alternate flowers, and in other

cases all those down one side of the spike, with pollen of other

varieties, and the remaining flowers with their own pollen. I saw these

plants when the capsules were nearly mature, and their curious

arrangement at once brought full conviction to the mind that an immense

advantage had been derived from crossing these hybrids.

Lastly, I have heard from Dr. E. Bornet, of Antibes, who has made

numerous experiments in crossing the species of Cistus, but has not yet

published the results, that, when any of these hybrids are fertile,

they may be said to be, in regard to function, dioecious; “for the

flowers are always sterile when the pistil is fertilised by pollen

taken from the same flower or from flowers on the same plant. But they

are often fertile if pollen be employed from a distinct individual of

the same hybrid nature, or from a hybrid made by a reciprocal cross.”

_Conclusion._—That plants should be self-sterile, although both sexual

elements are in a fit state for reproduction, appears at first sight

opposed to all analogy. With respect to the species, all the

individuals of which are in this state, although living under their

natural conditions, we may conclude that their self-sterility has been

acquired for the sake of effectually preventing self-fertilisation. The

case is closely analogous with that of dimorphic and trimorphic or

heterostyled plants, which can be fully fertilised only by plants

belonging to a different form, and not, as in the foregoing cases,

indifferently by any other individual of the species. Some of these

hetero-styled plants are completely sterile with pollen taken from the

same plant or from the same form. With respect to species living under

their natural conditions, of which only certain individuals are

self-sterile (as with _Reseda lutea_), it is probable that these have

been rendered self-sterile to ensure occasional cross-fertilisation,

whilst other individuals have remained self-fertile to ensure the

propagation of the species. The case seems to be parallel with that of

plants which produce, as Hermann Müller has discovered, two forms—one

bearing more conspicuous flowers with their structure adapted for

cross-fertilisation by insects, and the other form with less

conspicuous flowers adapted for self-fertilisation. The self-sterility,

however, of some of the foregoing plants is incidental on the

conditions to which they have been subjected, as with the

Eschscholtzia, the _Verbascum phœniceum_ (the sterility of which varied

according to the season), and with the _Passiflora alata,_ which

recovered its self-fertility when grafted on a different stock.

It is interesting to observe in the above several cases the graduated

series from plants which, when fertilised by their own pollen, yield

the full number of seeds, but with the seedlings a little dwarfed in

stature—to plants which when self-fertilised yield few seeds—to those

which yield none, but have their ovaria somewhat developed—and, lastly,

to those in which the plant’s own pollen and stigma mutually act on one

another like poison. It is also interesting to observe on how slight a

difference in the nature of the pollen or of the ovules complete

self-sterility or complete self-fertility must depend in some of the

above cases. Every individual of the self-sterile species appears to be

capable of producing the full complement of seed when fertilised by the

pollen of any other individual (though judging from the facts given

with respect to Abutilon the nearest kin must be excepted); but not one

individual can be fertilised by its own pollen. As every organism

differs in some slight degree from every other individual of the same

species, so no doubt it is with their pollen and ovules; and in the

above cases we must believe that complete self-sterility and complete

self-fertility depend on such slight differences in the ovules and

pollen, and not their having been differentiated in some special manner

in relation to one another; for it is impossible that the sexual

elements of many thousand individuals should have been specialised in

relation to every other individual. In some, however, of the above

cases, as with certain Passifloras, an amount of differentiation

between the pollen and ovules sufficient for fertilisation is gained

only by employing pollen from a distinct species; but this is probably

the result of such plants having been rendered somewhat sterile from

the unnatural conditions to which they have been exposed.

Exotic animals confined in menageries are sometimes in nearly the same

state as the above-described self-impotent plants; for, as we shall see

in the following chapter, certain monkeys, the larger carnivora,

several finches, geese, and pheasants, cross together, quite as freely

as, or even more freely than the individuals of the same species breed

together. Cases will, also, be given of sexual incompatibility between

certain, male and female domesticated animals, which, nevertheless, are

fertile when matched with any other individual of the same kind.

In the early part of this chapter it was shown that the crossing of

individuals belonging to distinct families of the same race, or to

different races or species, gives increased size and constitutional

vigour to the offspring, and, except in the case of crossed species,

increased fertility. The evidence rests on the universal testimony of

breeders (for it should be observed that I am not here speaking of the

evil results of close interbreeding), and is practically exemplified in

the higher value of cross-bred animals for immediate consumption. The

good results of crossing have also been demonstrated with some animals

and with numerous plants, by actual weight and measurement. Although

animals of pure blood will obviously be deteriorated by crossing, as

far as their characteristic qualities are concerned, there seems to be

no exception to the rule that advantages of the kind just mentioned are

thus gained, even when there has not been any previous close

interbreeding; and the rule applies to such animals as cattle and

sheep, which can long resist breeding in-and-in between the nearest

blood-relations.

In the case of crossed species, although size, vigour, precocity, and

hardiness are, with rare exceptions, gained, fertility, in a greater or

less degree, is lost; but the gain in the above respects can hardly be

attributed to the principle of compensation; for there is no close

parallelism between the increased size and vigour of hybrid offspring

and their sterility. Moreover, it has been clearly proved that mongrels

which are perfectly fertile gain these same advantages as well as

sterile hybrids.

With the higher animals no special adaptations for ensuring occasional

crosses between distinct families seem to exist. The eagerness of the

males, leading to severe competition between them, is sufficient; for

even with gregarious animals, the old and dominant males will be

dispossessed after a time and it would be a mere chance if a closely

related member of the same family were to be the victorious successor.

The structure of many of the lower animals, when they are

hermaphrodites, is such as to prevent the ovules being fertilised by

the male element of the same individual; so that the concourse of two

individuals is necessary. In other cases the access of the male element

of a distinct individual is at least possible. With plants, which are

affixed to the ground and cannot wander from place to place like

animals, the numerous adaptations for cross-fertilisation are

wonderfully perfect, as has been admitted by every one who has studied

the subject.

The evil consequences of long-continued close interbreeding are not so

easily recognised as the good effects from crossing, for the

deterioration is gradual. Nevertheless, it is the general opinion of

those who have had most experience, especially with animals which

propagate quickly, that evil does inevitably follow sooner or later,

but at different rates with different animals. No doubt a false belief

may, like a superstition, prevail widely; yet it is difficult to

suppose that so many acute observers have all been deceived at the

expense of much cost and trouble. A male animal may sometimes be paired

with his daughter, granddaughter, and so on, even for seven

generations, without any manifest bad result: but the experiment has

never been tried of matching brothers and sisters, which is considered

the closest form of interbreeding, for an equal number of generations.

There is good reason to believe that by keeping the members of the same

family in distinct bodies, especially if exposed to somewhat different

conditions of life, and by occasionally crossing these families, the

evil results of interbreeding may be much diminished or quite

eliminated. These results are loss of constitutional vigour, size, and

fertility; but there is no necessary deterioration in the general form

of the body, or in other good qualities. We have seen that with pigs

first-rate animals have been produced after long-continued close

interbreeding, though they had become extremely infertile when paired

with their near relations. The loss of fertility, when it occurs, seems

never to be absolute, but only relative to animals of the same blood;

so that this sterility is to a certain extent analogous with that of

self-impotent plants which cannot be fertilised by their own pollen,

but are perfectly fertile with pollen of any other individual of the

same species. The fact of infertility of this peculiar nature being one

of the results of long-continued interbreeding, shows that

interbreeding does not act merely by combining and augmenting various

morbid tendencies common to both parents; for animals with such

tendencies, if not at the time actually ill, can generally propagate

their kind. Although offspring descended from the nearest

blood-relations are not necessarily deteriorated in structure, yet some

authors believe that they are eminently liable to malformations; and

this is not improbable, as everything which lessens the vital powers

acts in this manner. Instances of this kind have been recorded in the

case of pigs, bloodhounds, and some other animals.

Finally, when we consider the various facts now given which plainly

show that good follows from crossing, and less plainly that evil

follows from close interbreeding, and when we bear in mind that with

very many organisms elaborate provisions have been made for the

occasional union of distinct individuals, the existence of a great law

of nature is almost proved; namely, that the crossing of animals and

plants which are not closely related to each other is highly beneficial

or even necessary, and that interbreeding prolonged during many

generations is injurious.

REFERENCES

[1] ‘The Art of Improving the Breed, etc.,’ 1809, p. 16.

[2] ‘The History of the Rise and Progress of the Killerby, etc.

Herds,’ p. 41.

[3] For Andrew Knight, _see_ A. Walker, on ‘Intermarriage,’ 1838, p.

227. Sir J. Sebright’s Treatise has just been quoted.

[4] ‘Cattle,’ p. 199.

[5] I give this on the authority of Nathusius, ‘Ueber Shorthorn

Rindvieh,’ 1857, s. 71, (_see also_ ‘Gardener’s Chronicle,’ 1860, p.

270). But Mr. J. Storer, a large breeder of cattle, informs me that

the parentage of Clarissa is not well authenticated. In the first vol.

of the ‘Herd Book,’ she was entered as having six descents from

Favourite, “which was a palpable mistake,” and in all subsequent

editions she was spoken of as having only four descents. Mr. Storer

doubts even about the four, as no names of the dams are given.

Moreover, Clarissa bore “only two bulls and one heifer, and in the

next generation her progeny became extinct.” Analogous cases of close

interbreeding are given in a pamphlet published by Mr. C. Macknight

and Dr. H. Madden, ‘On the True Principles of Breeding;’ Melbourne,

Australia, 1865.

[6] Mr. Willoughby Wood, in ‘Gardener’s Chronicle,’ 1855, p. 411; and

1860, p. 270. _See_ the very clear tables and pedigrees given in

Nathusius’ ‘Rindvieh,’ s. 72-77.

[7] Mr. Wright, ‘Journal of Royal Agricult. Soc.,’ vol. vii., 1846, p.

204. Mr. J. Downing (a successful breeder of Shorthorns in Ireland)

informs me that the raisers of the great families of Shorthorns

carefully conceal their sterility and want of constitution. He adds

that Mr. Bates, after he had bred his herd in-and-in for some years,

“lost in one season twenty-eight calves solely from want of

constitution.”

[8] Youatt on Cattle, p. 202.

[9] ‘Report British Assoc., Zoolog. Sect.,’ 1838.

[10] Azara, ‘Quadrupèdes du Paraguay,’ tom. ii. pp. 354, 368.

[11] For the case of the Messrs. Brown, _see_ ‘Gardener’s Chronicle,’

1855, p. 26. For the Foscote flock, ‘Gardener’s Chronicle,’ 1860, p.

416. For the Naz flock, ‘Bull. de la Soc. d’Acclimat.,’ 1860, p. 477.

[12] Nathusius, ‘Rindvieh,’ s. 65; Youatt on Sheep, p. 495.

[13] ‘Gardener’s Chronicle,’ 1861, p. 631.

[14] ‘Journal R. Agricult. Soc.,’ vol. xiv., 1853, p. 212.

[15] Lord Somerville, ‘Facts on Sheep and Husbandry,’ p. 6. Mr.

Spooner in ‘Journal of Royal Agricult. Soc. of England,’ vol. xx. part

ii. _See also_ an excellent paper on the same subject in ‘Gardener’s

Chronicle,’ 1860, p. 321, by Mr. Charles Howard.

[16] ‘Some Account of English Deer Parks,’ by Evelyn P. Shirley, 1867.

[17] Stonehenge, ‘The Dog,’ 1867, pp. 175-178.

[18] ‘The Art of Improving the Breed,’ etc., p. 13. With respect to

Scotch deerhounds, _see_ Scrope’s ‘Art of Deer Stalking,’ pp. 350-353.

[19] ‘Cottage Gardener,’ 1861, p. 327.

[20] Mr. Huth gives (‘The Marriage of Near Kin,’ 1875, p. 302) from

the ‘Bulletin de l’Acad. R. de Méd. de Belgique’ (vol. ix., 1866, pp.

287, 305), several statements made by a M. Legrain with respect to

crossing brother and sister rabbits for five or six successive

generations with no consequent evil results. I was so much surprised

at this account, and at M. Legrain’s invariable success in his

experiments, that I wrote to a distinguished naturalist in Belgium to

inquire whether M. Legrain was a trustworthy observer. In answer, I

have heard that, as doubts were expressed about the authenticity of

these experiments, a commission of inquiry was appointed, and that at

a succeeding meeting of the Society (‘Bull. de l’Acad. R. de Méd. de

Belgique,’ 1867, 3rd series, Tome 1, No. 1 to 5), Dr. Crocq reported

“qu’il était matériellement impossible que M. Legrain ait fait les

expériences qu’il annonce.” To this public accusation no satisfactory

answer was made.

[21] Sidney’s edit. of ‘Youatt on the Pig,’ 1860, p. 30; p. 33

quotation from Mr. Druce; p. 29 on Lord Western’s case.

[22] ‘Journal of Royal Agricult. Soc. of England,’ 1846, vol. vii. p.

205.

[23] ‘Ueber Rindvieh,’ etc., s. 78. Col. Le Couteur, who has done so

much for the agriculture of Jersey, writes to me that from possessing

a fine breed of pigs he bred them very closely, twice pairing brothers

and sisters, but nearly all the young had fits and died suddenly.

[24] Sidney on the Pig, p. 36. _See also_ note p. 34. Also Richardson

on the Pig, 1847, p. 26.

[25] Dr. Dally has published an excellent article (translated in the

‘Anthropolog. Review,’ May, 1864, p. 65), criticising all writers who

have maintained that evil follows from consanguineous marriages. No

doubt on this side of the question many advocates have injured their

cause by inaccuracies: thus it has been stated (Devay, ‘Du Danger des

Mariages,’ etc., 1862, p. 141) that the marriages of cousins have been

prohibited by the legislature of Ohio; but I have been assured, in

answer to inquiries made in the United States, that this statement is

a mere fable.

[26] _See_ his interesting work on the ‘Early History of Man,’ 1865,

chap. x.

[27] ‘The Marriage of Near Kin,’ 1875. The evidence given by Mr. Huth

would, I think, have been even more valuable than it is on this and

some other points, if he had referred solely to the works of men who

had long resided in each country referred to, and who showed that they

possessed judgment and caution. _See also_ Mr. W. Adam, ‘On

Consanguinity in Marriage’ in the ‘Fortnightly Review,’ 1865, p. 710.

Also Hofacker, ‘Ueber die Eigenschaften,’ etc., 1828.

[28] Sir G. Grey’s ‘Journal of Expeditions into Australia,’ vol. ii.

p. 243; and Dobrizhoffer, ‘On the Abipones of South America.’

[29] ‘Descent of Man,’ 2nd. edit. p. 524.

[30] ‘Journal of Statistical Soc.’ June, 1875, p. 153; and

‘Fortnightly Review,’ June, 1875.

[31] ‘The Art of Improving the Breed,’ p. 13.

[32] ‘The Poultry Book,’ by W. B. Tegetmeier, 1866, p. 245.

[33] ‘Journal Royal Agricult. Soc.,’ 1846, vol. vii. p. 205; _ see

also_ Ferguson on the Fowl, pp. 83, 317; _see also_ ‘The Poultry

Book,’ by Tegetmeier, 1866, p. 135, with respect to the extent to

which cock-fighters found that they could venture to breed in-and-in,

viz., occasionally a hen with her own son; “but they were cautious not

to repeat the in-and-in breeding.”

[34] ‘The Poultry Book,’ by W. B. Tegetmeier, 1866, p. 79.

[35] ‘The Poultry Chronicle,’ 1854, vol. i. p. 43.

[36] ‘The Poultry Book,’ by W. B. Tegetmeier, 1866, p. 79.

[37] ‘The Poultry Chronicle,’ vol. i. p. 89.

[38] ‘The Poultry Book,’ 1866, p. 210.

[39] Ibid. 1866, p. 167; and ‘Poultry Chronicle,’ vol. iii., 1855, p.

15.

[40] ‘A Treatise on Fancy Pigeons,’ by J. M. Eaton, p. 56.

[41] ‘The Pigeon Book,’ p. 46.

[42] ‘Das Ganze der Taubenzucht,’ 1837, s. 18.

[43] ‘Les Pigeons,’ 1824, p. 35.

[44] ‘Proc. Entomolog. Soc.,’ Aug. 6th, 1860, p. 126.

[45] ‘Journal of Horticulture,’ 1861, pp. 39, 77, 158; and 1864, p.

206.

[46] ‘Beiträge zur Kenntniss der Befruchtung,’ 1844, s. 366.

[47] ‘Amaryllidaceæ,’ p. 371.

[48] ‘De la Fécondation,’ 2nd edit., 1862, p. 79.

[49] ‘Mémoire sur les Cucurbitacées,’ pp. 36, 28, 30.

[50] Loudon’s ‘Gard. Mag.,’ vol. viii., 1832, p. 52.

[51] ‘Transact. Hort. Soc.,’ vol. i. p. 25.

[52] ‘Annal. des Sc. Nat.,’ 3rd series, Bot., tom. vi. p. 189.

[53] ‘Philosophical Transactions,’ 1799, p. 200.

[54] ‘Ueber die Bastarderzeugung,’ 1828, s. 32, 33. For Mr. Chaundy’s

case, _see_ Loudon’s ‘Gard. Mag.’ vol. vii. 1831, p. 696.

[55] ‘Gardener’s Chron.,’ 1846, p. 601.

[56] ‘Philosoph. Transact.,’ 1799, p. 201.

[57] Quoted in ‘Bull. Bot. Soc. France,’ vol. ii., 1855, p. 327.

[58] Gärtner, ‘Bastarderzeugung,’ s. 259, 518, 526 _et seq._

[59] ‘Fortsetzung,’ 1763, s. 29; ‘Dritte Fortsetzung,’ s. 44, 96;

‘Act. Acad. St. Petersburg,’ 1782, part ii., p. 251; ‘Nova Acta,’

1793, pp. 391, 394; ‘Nova Acta,’ 1795, pp. 316, 323.

[60] ‘Die Bastardbefruchtung,’ etc., 1865, s. 31, 41, 42.

[61] Max Wichura fully accepts this view (‘Bastardbefruchtung,’ s.

43), as does the Rev. M. J. Berkeley, in ‘Journal of Hort. Soc.,’ Jan.

1866, p. 70.

[62] ‘Bastarderzeugung,’ s. 394, 526, 528.

[63] Kölreuter, ‘Nova Acta,’ 1795, p. 316.

[64] Gärtner, ‘Bastarderzeugung,’ s. 430.

[65] Quoted by Dr. Murie, in ‘Proc. Zoolog. Soc.,’ 1870, p. 40.

[66] ‘Botanische Zeitung,’ Jan. 1864, s. 3.

[67] ‘Monatsbericht Akad. Wissen.’ Berlin, 1866, s. 372.

[68] International Hort. Congress, London, 1866.

[69] ‘Proc. Bot. Soc. of Edinburgh,’ May, 1863: these observations are

given in abstract, and others are added, in the ‘Journal of Proc. of

Linn. Soc.,’ vol. viii. Bot., 1864, p. 162.

[70] Prof. Lecoq, ‘De la Fécondation,’ 2nd edit., 1862, p. 76.

[71] ‘Jenaische Zeitschrift fur Naturwiss.’ B. vii. p. 22, 1872, and

p. 441, 1873. A large part of this paper has been translated in the

‘American Naturalist,’ 1874, p. 223.

[72] ‘Bastarderzeugung,’ s. 64, 357.

[73] Ibid., s. 357.

[74] ‘Zweite Fortsetzung,’ s. 10; ‘Dritte Forts.,’ s. 40. Mr. Scott

likewise fertilised fifty-four flowers of _Verbascum phœniceum,_

including two varieties, with their own pollen, and not a single

capsule was produced. Many of the pollen-grains emitted their tubes,

but only a few of them penetrated the stigmas; some slight effect

however was produced, as many of the ovaries became somewhat

developed: ‘Journal Asiatic Soc. Bengal,’ 1867, p. 150.

[75] Duvernoy, quoted by Gärtner, ‘Bastarderzeugung,’ s. 334.

[76] ‘Gardener’s Chronicle,’ 1846, p. 183.

[77] ‘Transact. Hort. Soc.,’ vol. vii., 1830, p. 95.

[78] Prof. Lecoq ‘De la Fécondation,’ 1845, p. 70; Gärtner,

‘Bastarderzeugung,’ s. 64.

[79] ‘Gardener’s Chronicle,’ 1868, p. 1341.

[80] ‘Gardener’s Chronicle,’ 1866, p. 1068.

[81] ‘Journal of Proc. of Linn. Soc.,’ vol. viii., 1864, p. 1168. Mr.

Robertson Munro, in ‘Trans. Bot. Soc.’ of Edinburgh, vol. ix. p. 399.

[82] ‘Amaryllidaceæ,’ 1837, p. 371; ‘Journal of Hort. Soc.,’ vol. ii.,

1847, p. 19.

[83] Loudon’s ‘Gardener’s Magazine,’ vol. xi., 1835, p. 260.

[84] ‘Gardener’s Chronicle,’ 1850, p. 470.

[85] ‘Journal Hort. Soc.,’ vol. v. p. 135. The seedlings thus raised

were given to the Hort. Soc.; but I find, on inquiry, that they

unfortunately died the following winter.

[86] Mr. D. Beaton, in ‘Journal of Hort.,’ 1861, p. 453. Lecoq however

(‘De la Fécond.,’ 1862, p. 369), states that this hybrid is descended

from _G. psittacinus_ and _ cardinalis_; but this is opposed to

Herbert’s experience, who found that the former species could not be

crossed.