chinensi-barbatus were more variable than those raised from this latter hybrid fertilised by the pure D. barbatus. Max Wichura (22/45. 'Die b.a.s.t.a.r.dbefruchtung' s. 56.) insists strongly on an a.n.a.logous result with his hybrid willows. Again Gartner (22/46. 'b.a.s.t.a.r.derzeugung' s. 423.) a.s.serts that the degree of variability sometimes differs in hybrids raised from reciprocal crosses between the same two species; and here the sole difference is, that the one species is first used as the father and then as the mother. On the whole we see that, independently of the appearance of new characters, the variability of successive crossed generations is extremely complex, partly from the offspring partaking unequally of the characters of the two parent- forms, and more especially from their unequal tendency to revert to such characters or to those of more ancient progenitors.]

ON THE MANNER AND ON THE PERIOD OF ACTION OF THE CAUSES WHICH INDUCE VARIABILITY.

This is an extremely obscure subject, and we need here only consider, whether inherited variations are due to certain parts being acted on after they have been formed, or through the reproductive system being affected before their formation; and in the former case at what period of growth or development the effect is produced. We shall see in the two following chapters that various agencies, such as an abundant supply of food, exposure to a different climate, increased use or disuse of parts, etc., prolonged during several generations, certainly modify either the whole organisation or certain organs; and it is clear at least in the case of bud-variation that the action cannot have been through the reproductive system.

[With respect to the part which the reproductive system takes in causing variability, we have seen in the eighteenth chapter that even slight changes in the conditions of life have a remarkable power in causing a greater or less degree of sterility. Hence it seems not improbable that beings generated through a system so easily affected should themselves be affected, or should fail to inherit, or inherit in excess, characters proper to their parents. We know that certain groups of organic beings, but with exceptions in each group, have their reproductive systems much more easily affected by changed conditions than other groups; for instance, carnivorous birds, more readily than carnivorous mammals, and parrots more readily than pigeons; and this fact harmonises with the apparently capricious manner and degree in which various groups of animals and plants vary under domestication.

Kolreuter (22/47. 'Dritte Fortsetzung' etc. 1766 s. 85.) was struck with the parallelism between the excessive variability of hybrids when crossed and recrossed in various ways,--these hybrids having their reproductive powers more or less affected,--and the variability of anciently cultivated plants.

Max Wichura (22/48. 'Die b.a.s.t.a.r.dbefruchtung' etc. 1865 s. 92: see also the Rev. M.J. Berkeley on the same subject in 'Journal of Royal Hort. Soc.' 1866 page 80.) has gone one step farther, and shows that with many of our highly cultivated plants, such as the hyacinth, tulip, auricula, snapdragon, potato, cabbage, etc., which there is no reason to believe have been hybridised, the anthers contain many irregular pollen-grains in the same state as in hybrids.

He finds also in certain wild forms, the same coincidence between the state of the pollen and a high degree of variability, as in many species of Rubus; but in R. caesius and idaeus, which are not highly variable species, the pollen is sound. It is also notorious that many cultivated plants, such as the banana, pineapple, bread-fruit, and others previously mentioned, have their reproductive organs so seriously affected as to be generally quite sterile; and when they do yield seed, the seedlings, judging from the large number of cultivated races which exist, must be variable in an extreme degree. These facts indicate that there is some relation between the state of the reproductive organs and a tendency to variability; but we must not conclude that the relation is strict. Although many of our highly cultivated plants may have their pollen in a deteriorated condition, yet, as we have previously seen, they yield more seeds, and our anciently domesticated animals are more prolific, than the corresponding species in a state of nature. The peac.o.c.k is almost the only bird which is believed to be less fertile under domestication than in its native state, and it has varied in a remarkably small degree. From these considerations it would seem that changes in the conditions of life lead either to sterility or to variability, or to both; and not that sterility induces variability. On the whole it is probable that any cause affecting the organs of reproduction would likewise affect their product,--that is, the offspring thus generated.

The period of life at which the causes that induce variability act, is likewise an obscure subject, which has been discussed by various authors.

(22/49. Dr. P. Lucas has given a history of opinion on this subject 'Hered.

Nat.' 1847 tome 1 page 175.) In some of the cases, to be given in the following chapter, of modifications from the direct action of changed conditions, which are inherited, there can be no doubt that the causes have acted on the mature or nearly mature animal. On the other hand, monstrosities, which cannot be distinctly separated from lesser variations, are often caused by the embryo being injured whilst in the mother's womb or in the egg. Thus I.

Geoffroy Saint-Hilaire (22/50. 'Hist. des Anomalies' tome 3 page 499.) a.s.serts that poor women who work hard during their pregnancy, and the mothers of illegitimate children troubled in their minds and forced to conceal their state, are far more liable to give birth to monsters than women in easy circ.u.mstances. The eggs of the fowl when placed upright or otherwise treated unnaturally frequently produce monstrous chickens. It would, however, appear that complex monstrosities are induced more frequently during a rather late than during a very early period of embryonic life; but this may partly result from some one part, which has been injured during an early period, affecting by its abnormal growth other parts subsequently developed; and this would be less likely to occur with parts injured at a later period. (22/51. Ibid tome 3 pages 392, 502. The several memoirs by M. Dareste hereafter referred to are of special value on this whole subject.) When any part or organ becomes monstrous through abortion, a rudiment is generally left, and this likewise indicates that its development had already commenced.

Insects sometimes have their antennae or legs in a monstrous condition, the larvae of which do not possess either antennae or legs; and in these cases, as Quatref.a.ges (22/52. See his interesting work 'Metamorphoses de l'Homme' etc.

1862 page 129.) believes, we are enabled to see the precise period at which the normal progress of development was troubled. But the nature of the food given to a caterpillar sometimes affects the colours of the moth, without the caterpillar itself being affected; therefore it seems possible that other characters in the mature insect might be indirectly modified through the larvae. There is no reason to suppose that organs which have been rendered monstrous have always been acted on during their development; the cause may have acted on the organisation at a much earlier stage. It is even probable that either the male or female s.e.xual elements, or both, before their union, may be affected in such a manner as to lead to modifications in organs developed at a late period of life; in nearly the same manner as a child may inherit from his father a disease which does not appear until old age.

In accordance with the facts above given, which prove that in many cases a close relation exists between variability and the sterility following from changed conditions, we may conclude that the exciting cause often acts at the earliest possible period, namely, on the s.e.xual elements, before impregnation has taken place. That an affection of the female s.e.xual element may induce variability we may likewise infer as probable from the occurrence of bud- variations; for a bud seems to be the a.n.a.logue of an ovule. But the male element is apparently much oftener affected by changed conditions, at least in a visible manner, than the female element or ovule and we know from Gartner's and Wichura's statements that a hybrid used as the father and crossed with a pure species gives a greater degree of variability to the offspring, than does the same hybrid when used as the mother. Lastly, it is certain that variability may be transmitted through either s.e.xual element, whether or not originally excited in them, for Kolreuter and Gartner (22/53. 'Dritte Fortsetzung' etc. s. 123; 'b.a.s.t.a.r.derzeugung' s. 249.) found that when two species were crossed, if either one was variable, the offspring were rendered variable.]

SUMMARY.

From the facts given in this chapter, we may conclude that the variability of organic beings under domestication, although so general, is not an inevitable contingent on life, but results from the conditions to which the parents have been exposed. Changes of any kind in the conditions of life, even extremely slight changes, often suffice to cause variability. Excess of nutriment is perhaps the most efficient single exciting cause. Animals and plants continue to be variable for an immense period after their first domestication; but the conditions to which they are exposed never long remain quite constant. In the course of time they can be habituated to certain changes, so as to become less variable; and it is possible that when first domesticated they may have been even more variable than at present. There is good evidence that the power of changed conditions acc.u.mulates; so that two, three, or more generations must be exposed to new conditions before any effect is visible. The crossing of distinct forms, which have already become variable, increases in the offspring the tendency to further variability, by the unequal commingling of the characters of the two parents, by the reappearance of long-lost characters, and by the appearance of absolutely new characters. Some variations are induced by the direct action of the surrounding conditions on the whole organisation, or on certain parts alone; other variations appear to be induced indirectly through the reproductive system being affected, as we know is often the case with various beings, which when removed from their natural conditions become sterile. The causes which induce variability act on the mature organism, on the embryo, and, probably, on the s.e.xual elements before impregnation has been effected.

CHAPTER 2.XXIII.

DIRECT AND DEFINITE ACTION OF THE EXTERNAL CONDITIONS OF LIFE.

SLIGHT MODIFICATIONS IN PLANTS FROM THE DEFINITE ACTION OF CHANGED CONDITIONS, IN SIZE, COLOUR, CHEMICAL PROPERTIES, AND IN THE STATE OF THE TISSUES.

LOCAL DISEASES.

CONSPICUOUS MODIFICATIONS FROM CHANGED CLIMATE OR FOOD, ETC.

PLUMAGE OF BIRDS AFFECTED BY PECULIAR NUTRIMENT, AND BY THE INOCULATION OF POISON.

LAND-Sh.e.l.lS.

MODIFICATIONS OF ORGANIC BEINGS IN A STATE OF NATURE THROUGH THE DEFINITE ACTION OF EXTERNAL CONDITIONS.

COMPARISON OF AMERICAN AND EUROPEAN TREES.

GALLS.

EFFECTS OF PARASITIC FUNGI.

CONSIDERATIONS OPPOSED TO THE BELIEF IN THE POTENT INFLUENCE OF CHANGED EXTERNAL CONDITIONS.

PARALLEL SERIES OF VARIETIES.

AMOUNT OF VARIATION DOES NOT CORRESPOND WITH THE DEGREE OF CHANGE IN THE CONDITIONS.

BUD-VARIATION.

MONSTROSITIES PRODUCED BY UNNATURAL TREATMENT.

SUMMARY.

If we ask ourselves why this or that character has been modified under domestication, we are, in most cases, lost in utter darkness. Many naturalists, especially of the French school, attribute every modification to the "monde ambiant," that is, to changed climate, with all its diversities of heat and cold, dampness and dryness, light and electricity, to the nature of the soil, and to varied kinds and amount of food. By the term definite action, as used in this chapter, I mean an action of such a nature that, when many individuals of the same variety are exposed during several generations to any particular change in their conditions of life, all, or nearly all the individuals, are modified in the same manner. The effects of habit, or of the increased use and disuse of various organs, might have been included under this head; but it will be convenient to discuss this subject in a separate chapter. By the term indefinite action I mean an action which causes one individual to vary in one way and another individual in another way, as we often see with plants and animals after they have been subjected for some generations to changed conditions of life. But we know far too little of the causes and laws of variation to make a sound cla.s.sification. The action of changed conditions, whether leading to definite or indefinite results, is a totally distinct consideration from the effects of selection; for selection depends on the preservation by man of certain individuals, or on their survival under various and complex natural circ.u.mstances, and has no relation whatever to the primary cause of each particular variation.

I will first give in detail all the facts which I have been able to collect, rendering it probable that climate, food, etc., have acted so definitely and powerfully on the organisation of our domesticated productions, that new sub- varieties or races have been thus formed without the aid of selection by man or nature. I will then give the facts and considerations opposed to this conclusion, and finally we will weigh, as fairly as we can, the evidence on both sides.

When we reflect that distinct races of almost all our domesticated animals exist in each kingdom of Europe, and formerly even in each district of England, we are at first strongly inclined to attribute their origin to the definite action of the physical conditions of each country; and this has been the conclusion of many authors. But we should bear in mind that man annually has to choose which animals shall be preserved for breeding, and which shall be slaughtered. We have also seen that both methodical and unconscious selection were formerly practised, and are now occasionally practised by the most barbarous races, to a much greater extent than might have been antic.i.p.ated. Hence it is difficult to judge how far differences in the conditions between, for instance, the several districts in England, have sufficed to modify the breeds which have been reared in each. It may be argued that, as numerous wild animals and plants have ranged during many ages throughout Great Britain, and still retain the same character, the difference in conditions between the several districts could not have modified in a marked manner the various native races of cattle, sheep, pigs, and horses. The same difficulty of distinguishing between the effects of natural selection and the definite action of external conditions is encountered in a still higher degree when we compare closely allied species inhabiting two countries, such as North America and Europe, which do not differ greatly in climate, nature of soil, etc., for in this case natural selection will inevitably and rigorously have acted during a long succession of ages.

Prof. Weismann has suggested (23/1. 'Ueber den Einfluss der Isolirung auf die Artbildung' 1872.) that when a variable species enters a new and isolated country, although the variations may be of the same general nature as before, yet it is improbable that they should occur in the same proportional numbers.

After a longer or shorter period, the species will tend to become nearly uniform in character from the incessant crossing of the varying individuals; but owing to the proportion of the individuals varying in different ways not being the same in the two cases, the final result will be the production of two forms somewhat different from one another. In cases of this kind it would falsely appear as if the conditions had induced certain definite modifications, whereas they had only excited indefinite variability, but with the variations in slightly different proportional numbers. This view may throw some light on the fact that the domestic animals which formerly inhabited the several districts in Great Britain, and the half wild cattle lately kept in several British parks, differed slightly from one another; for these animals were prevented from wandering over the whole country and intercrossing, but would have crossed freely within each district or park.

[From the difficulty of judging how far changed conditions have caused definite modifications of structure, it will be advisable to give as large a body of facts as possible, showing that extremely slight differences within the same country, or during different seasons, certainly produce an appreciable effect, at least on varieties which are already in an unstable condition. Ornamental flowers are good for this purpose, as they are highly variable, and are carefully observed. All floriculturists are unanimous that certain varieties are affected by very slight differences in the nature of the artificial compost in which they are grown, and by the natural soil of the district, as well as by the season. Thus, a skilful judge, in writing on Carnations and Picotees (23/2. 'Gardener's Chronicle' 1853 page 183.) asks "where can Admiral Curzon be seen possessing the colour, size, and strength which it has in Derbyshire? Where can Flora's Garland be found equal to those at Slough? Where do high-coloured flowers revel better than at Woolwich and Birmingham? Yet in no two of these districts do the same varieties attain an equal degree of excellence, although each may be receiving the attention of the most skilful cultivators." The same writer then recommends every cultivator to keep five different kinds of soil and manure, "and to endeavour to suit the respective appet.i.tes of the plants you are dealing with, for without such attention all hope of general success will be vain." So it is with the Dahlia (23/3. Mr. Wildman 'Floricultural Soc.' February 7, 1843 reported in 'Gardener's Chronicle' 1843 page 86.): the Lady Cooper rarely succeeds near London, but does admirably in other districts; the reverse holds good with other varieties; and again, there are others which succeed equally well in various situations. A skilful gardener (23/4. Mr. Robson in 'Journal of Horticulture' February 13, 1866 page 122.) states that he procured cuttings of an old and well-known variety (pulch.e.l.la) of Verbena, which from having been propagated in a different situation presented a slightly different shade of colour; the two varieties were afterwards multiplied by cuttings, being carefully kept distinct; but in the second year they could hardly be distinguished, and in the third year no one could distinguish them.

The nature of the season has an especial influence on certain varieties of the Dahlia: in 1841 two varieties were pre-eminently good, and the next year these same two were pre-eminently bad. A famous amateur (23/5. 'Journal of Horticulture' 1861 page 24.) a.s.serts that in 1861 many varieties of the Rose came so untrue in character, "that it was hardly possible to recognise them, and the thought was not seldom entertained that the grower had lost his tally." The same amateur (23/6. Ibid 1862 page 83.) states that in 1862 two- thirds of his Auriculas produced central trusses of flowers, and such trusses are liable not to keep true; and he adds that in some seasons certain varieties of this plant all prove good, and the next season all prove bad; whilst exactly the reverse happens with other varieties. In 1845 the editor of the 'Gardener's Chronicle' (23/7. 'Gardener's Chronicle' 1845 page 660.) remarked how singular it was that this year many Calceolarias tended to a.s.sume a tubular form. With Heartsease (23/8. Ibid 1863 page 628.) the blotched sorts do not acquire their proper character until hot weather sets in; whilst other varieties lose their beautiful marks as soon as this occurs.

a.n.a.logous facts have been observed with leaves: Mr. Beaton a.s.serts (23/9.

'Journal of Hort.' 1861 pages 64, 309.) that he raised at Shrubland, during six years, twenty thousand seedlings from the Punch Pelargonium, and not one had variegated leaves; but at Surbiton, in Surrey, one-third, or even a greater proportion, of the seedlings from this same variety were more or less variegated. The soil of another district in Surrey has a strong tendency to cause variegation, as appears from information given me by Sir F. Pollock.

Verlot (23/10. 'Des Varietes' etc. page 76.) states that the variegated strawberry retains its character as long as grown in a dryish soil, but soon loses it when planted in fresh and humid soil. Mr. Salter, who is well known for his success in cultivating variegated plants, informs me that rows of strawberries were planted in his garden in 1859, in the usual way; and at various distances in one row, several plants simultaneously became variegated; and what made the case more extraordinary, all were variegated in precisely the same manner. These plants were removed, but during the three succeeding years other plants in the same row became variegated, and in no instance were the plants in any adjoining row affected.

The chemical qualities, odours, and tissues of plants are often modified by a change which seems to us slight. The Hemlock is said not to yield conicine in Scotland. The root of the Aconitum napellus becomes innocuous in frigid climates. The medicinal properties of the Digitalis are easily affected by culture. As the Pistacia lentiscus grows abundantly in the South of France, the climate must suit it, but it yields no mastic. The Laurus sa.s.safras in Europe loses the odour proper to it in North America. (23/11. Engel 'Sur les Prop. Medicales des Plantes' 1860 pages 10, 25. On changes in the odours of plants see Dalibert's Experiments quoted by Beckman 'Inventions' volume 2 page 344; and Nees in Ferussac 'Bull. des Sc. Nat.' 1824 tome 1 page 60. With respect to the rhubarb etc. see also 'Gardener's Chronicle' 1849 page 355; 1862 page 1123.) Many similar facts could be given, and they are remarkable because it might have been thought that definite chemical compounds would have been little liable to change either in quality or quant.i.ty.

The wood of the American Locust-tree (Robinia) when grown in England is nearly worthless, as is that of the Oak-tree when grown at the Cape of Good Hope.

(23/12. Hooker 'Flora Indica' page 32.) Hemp and flax, as I hear from Dr.

Falconer, flourish and yield plenty of seed on the plains of India, but their fibres are brittle and useless. Hemp, on the other hand, fails to produce in England that resinous matter which is so largely used in India as an intoxicating drug.

The fruit of the Melon is greatly influenced by slight differences in culture and climate. Hence it is generally a better plan, according to Naudin, to improve an old kind than to introduce a new one into any locality. The seed of the Persian Melon produces near Paris fruit inferior to the poorest market kinds, but at Bordeaux yields delicious fruit. (23/13. Naudin 'Annales des Sc.

Nat.' 4th series, Bot. tome 11 1859 page 81. 'Gardener's Chronicle' 1859 page 464.) Seed is annually brought from Thibet to Kashmir (23/14. Moorcroft 'Travels' etc. volume 2 page 143.) and produces fruit weighing from four to ten pounds, but plants raised next year from seed saved in Kashmir give fruit weighing only from two to three pounds. It is well known that American varieties of the Apple produce in their native land magnificent and brightly- coloured fruit, but these in England are of poor quality and a dull colour. In Hungary there are many varieties of the kidney-bean, remarkable for the beauty of their seeds, but the Rev. M.J. Berkeley (23/15. 'Gardener's Chronicle' 1861 page 1113.) found that their beauty could hardly ever be preserved in England, and in some cases the colour was greatly changed. We have seen in the ninth chapter, with respect to wheat, what a remarkable effect transportal from the north to the south of France, and conversely, produced on the weight of the grain.]

When man can perceive no change in plants or animals which have been exposed to a new climate or to different treatment, insects can sometimes perceive a marked change. A cactus has been imported into India from Canton, Manilla Mauritius, and from the hot-houses of Kew, and there is likewise a so-called native kind which was formerly introduced from South America; all these plants belong to the same species and are alike in appearance, but the cochineal insect flourishes only on the native kind, on which it thrives prodigiously.

(23/16. Royle 'Productive Resources of India' page 59.) Humboldt remarks (23/17. 'Personal Narrative' English translation volume 5 page 101. This statement has been confirmed by Karsten 'Beitrag zur Kenntniss der Rhynchoprion' Moscow 1864 s. 39 and by others.) that white men "born in the torrid zone walk barefoot with impunity in the same apartment where a European, recently landed, is exposed to the attacks of the Pulex penetrans."

This insect, the too well-known chigoe, must therefore be able to perceive what the most delicate chemical a.n.a.lysis fails to discover, namely, a difference between the blood or tissues of a European and those of a white man born in the tropics. But the discernment of the chigoe is not so surprising as it at first appears; for according to Liebig (23/18. 'Organic Chemistry'

English translation 1st edition page 369.) the blood of men with different complexions, though inhabiting the same country, emits a different odour.

[Diseases peculiar to certain localities, heights, or climates, may be here briefly noticed, as showing the influence of external circ.u.mstances on the human body. Diseases confined to certain races of man do not concern us, for the const.i.tution of the race may play the more important part, and this may have been determined by unknown causes. The Plica Polonica stands, in this respect, in a nearly intermediate position; for it rarely affects Germans, who inhabit the neighbourhood of the Vistula, where so many Poles are grievously affected; neither does it affect Russians, who are said to belong to the same original stock as the Poles. (23/19. Prichard 'Phys. Hist. of Mankind' 1851 volume 1 page 155.) The elevation of a district often governs the appearance of diseases; in Mexico the yellow fever does not extend above 924 metres; and in Peru, people are affected with the verugas only between 600 and 1600 metres above the sea; many other such cases could be given. A peculiar cutaneous complaint, called the Bouton d'Alep, affects in Aleppo and some neighbouring districts almost every native infant, and some few strangers; and it seems fairly well established that this singular complaint depends on drinking certain waters. In the healthy little island of St. Helena the scarlet-fever is dreaded like the Plague; a.n.a.logous facts have been observed in Chili and Mexico. (23/20. Darwin 'Journal of Researches' 1845 page 434.) Even in the different departments of France it is found that the various infirmities which render the conscript unfit for serving in the army, prevail with remarkable inequality, revealing, as Boudin observes, that many of them are endemic, which otherwise would never have been suspected. (23/21. These statements on disease are taken from Dr. Boudin 'Geographie et Statistique Medicale' 1857 tome 1 pages 44 and 52; tome 2 page 315.) Any one who will study the distribution of disease will be struck with surprise at what slight differences in the surrounding circ.u.mstances govern the nature and severity of the complaints by which man is at least temporarily affected.

The modifications as yet referred to are extremely slight, and in most cases have been caused, as far as we can judge, by equally slight differences in the conditions. But such conditions acting during a series of generations would perhaps produce a marked effect.

With plants, a considerable change of climate sometimes produces a conspicuous result. I have given in the ninth chapter the most remarkable case known to me, namely, that of varieties of maize, which were greatly modified in the course of only two or three generations when taken from a tropical country to a cooler one, or conversely. Dr. Falconer informs me that he has seen the English Ribston-pippin apple, a Himalayan oak, Prunus and Pyrus, all a.s.sume in the hotter parts of India a fastigiate or pyramidal habit; and this fact is the more interesting, as a Chinese tropical species of Pyrus naturally grows thus. Although in these cases the changed manner of growth seems to have been directly caused by the great heat, we know that many fastigiate trees have originated in their temperate homes. In the Botanic Gardens of Ceylon the apple-tree (23/22. 'Ceylon' by Sir J.E. Tennent volume 1 1859 page 89.) "sends out numerous runners under ground, which continually rise into small stems, and form a growth around the parent-tree.) The varieties of the cabbage which produce heads in Europe fail to do so in certain tropical countries (23/23.

G.o.dron 'De l'Espece' tome 2 page 52.) The Rhododendron ciliatum produced at Kew flowers so much larger and paler-coloured than those which it bears on its native Himalayan mountain, that Dr. Hooker (23/24. 'Journal of Horticultural Soc.' volume 7 1852 page 117.) would hardly have recognised the species by the flowers alone. Many similar facts with respect to the colour and size of flowers could be given.

The experiments of Vilmorin and Buckman on carrots and parsnips prove that abundant nutriment produces a definite and inheritable effect on the roots, with scarcely any change in other parts of the plant. Alum directly influences the colour of the flowers of the Hydrangea. (23/25. 'Journal of Hort. Soc.'

volume 1 page 160.) Dryness seems generally to favour the hairiness or villosity of plants. Gartner found that hybrid Verbasc.u.ms became extremely woolly when grown in pots. Mr. Masters, on the other hand, states that the Opuntia leucotricha "is well clothed with beautiful white hairs when grown in a damp heat, but in a dry heat exhibits none of this peculiarity." (23/26. See Lecoq on the Villosity of Plants 'Geograph. Bot.' tome 3 pages 287, 291; Gartner 'b.a.s.t.a.r.derz.' s. 261; Mr. Masters on the Opuntia in 'Gardener's Chronicle' 1846 page 444.) Slight variations of many kinds, not worth specifying in detail, are retained only as long as plants are grown in certain soils, of which Sageret (23/27. 'Pom. Phys.' page 136.) gives some instances from his own experience. Odart, who insists strongly on the permanence of the varieties of the grape, admits (23/28. 'Ampelographie' 1849 page 19.) that some varieties, when grown under a different climate or treated differently, vary in a slight degree, as in the tint of the fruit and in the period of ripening. Some authors have denied that grafting causes even the slightest difference in the scion; but there is sufficient evidence that the fruit is sometimes slightly affected in size and flavour, the leaves in duration, and the flowers in appearance. (23/29. Gartner 'b.a.s.t.a.r.derz.' s. 606, has collected nearly all recorded facts. Andrew Knight in 'Transact. Hort. Soc.' volume 2 page 160, goes so far as to maintain that few varieties are absolutely permanent in character when propagated by buds or grafts.)

There can be no doubt, from the facts given in the first chapter, that European dogs deteriorate in India, not only in their instincts but in structure; but the changes which they undergo are of such a nature, that they may be partly due to reversion to a primitive form, as in the case of feral animals. In parts of India the turkey becomes reduced in size, "with the pendulous appendage over the beak enormously developed." (23/30. Mr. Blyth 'Annals and Mag of Nat. Hist.' volume 20 1847 page 391.) We have seen how soon the wild duck, when domesticated, loses its true character, from the effects of abundant or changed food, or from taking little exercise. From the direct action of a humid climate and poor pasture the horse rapidly decreases in size in the Falkland Islands. From information which I have received, this seems likewise to be the case to a certain extent with sheep in Australia.

Climate definitely influences the hairy covering of animals; in the West Indies a great change is produced in the fleece of sheep, in about three generations. Dr. Falconer states (23/31. 'Natural History Review' 1862 page 113.) that the Thibet mastiff and goat, when brought down from the Himalaya to Kashmir, lose their fine wool. At Angora not only goats, but shepherd-dogs and cats, have fine fleecy hair, and Mr. Ainsworth (23/32. 'Journal of Roy.

Geographical Soc.' volume 9 1839 page 275.) attributes the thickness of the fleece to the severe winters, and its silky l.u.s.tre to the hot summers. Burnes states positively (23/33. 'Travels in Bokhara' volume 3 page 151.) that the Karakool sheep lose their peculiar black curled fleeces when removed into any other country. Even within the limits of England, I have been a.s.sured that the wool of two breeds of sheep was slightly changed by the flocks being pastured in different localities. (23/34. See also on the influence of marshy pastures on the wool G.o.dron 'L'Espece' tome 2 page 22.) It has been a.s.serted on good authority (23/35. Isidore Geoffroy Saint-Hilaire 'Hist. Nat. Gen.' tome 3 page 438.) that horses kept during several years in the deep coal-mines of Belgium become covered with velvety hair, almost like that on the mole. These cases probably stand in close relation to the natural change of coat in winter and summer. Naked varieties of several domestic animals have occasionally appeared; but there is no reason to believe that this is in any way related to the nature of the climate to which they have been exposed. (23/36. Azara has made some good remarks on this subject 'Quadrupedes du Paraguay' tome 2 page 337. See an account of a family of naked mice produced in England 'Proc.

Zoolog. Soc.' 1856 page 38.)

It appears at first sight probable that the increased size, the tendency to fatten, the early maturity and altered forms of our improved cattle, sheep, and pigs, have directly resulted from their abundant supply of food. This is the opinion of many competent judges, and probably is to a great extent true.

But as far as form is concerned, we must not overlook the more potent influence of lessened use on the limbs and lungs. We see, moreover, as far as size is concerned, that selection is apparently a more powerful agent than a large supply of food, for we can thus only account for the existence, as remarked to me by Mr. Blyth, of the largest and smallest breeds of sheep in the same country, of Cochin-China fowls and Bantams, of small Tumbler and large Runt pigeons, all kept together and supplied with abundant nourishment.

Nevertheless there can be little doubt that our domesticated animals have been modified, independently of the increased or lessened use of parts, by the conditions to which they have been subjected, without the aid of selection.

For instance, Prof. Rutimeyer (23/37. 'Die Fauna der Pfahlbauten' 1861 s. 15.) shows that the bones of domesticated quadrupeds can be distinguished from those of wild animals by the state of their surface and general appearance. It is scarcely possible to read Nathusius's excellent 'Vorstudien' (23/38.

'Schweineschadel' 1864 s. 99.) and doubt that, with the highly improved races of the pig, abundant food has produced a conspicuous effect on the general form of the body, on the breadth of the head and face, and even on the teeth.

Nathusius rests much on the case of a purely bred Berkshire pig, which when two months old became diseased in its digestive organs, and was preserved for observation until nineteen months old; at this age it had lost several characteristic features of the breed, and had acquired a long, narrow head, of large size relatively to its small body, and elongated legs. But in this case and in some others we ought not to a.s.sume that, because certain characters are lost, perhaps through reversion, under one course of treatment, therefore that they were at first directly produced by an opposite treatment.