Variation of animals and plants under domestication, v.2

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312 LAWS OF YAlUATlO~. CHAI'. XXIV. spring necessarily stands in any direct relation with the nature of the climate inhabited by the pare1~ts. On the contra~·y, it is certain that hardy and tender varieties of the same species app~ar in the same country. New vari~ties thus .spontan~­ously arising become fitted to slightly different chm.ates m two different ways; firstly, they may have the power, either. as seedlings or when full-grown, of resisting intense. cold, as '~'Ith the Moscow pear, or of resisting intense heat, as w1th som.e lnnJs of Pelargonium, or the flowers may withstand severe frost, as with the Fore1le pear. Secondly, plants may become ~dapted to climates widely different from their own, from flowermg and fruiting either earlier or later in the season. In both these cases the power of acdimatisation by man consists simply in the selection and preservation of new varieties. But without any direct intention on his part of securing a hardier variety, accli­rnatisation may be unconsciously effected by merely raising tender plants from seed, and by occasionally attempting their cultivation further and further northwards, as in the case of maize, the orange, and the peach. How much influence ought to be attributed to inherited habit or custom in the acclimatisation of animals and plants is a much more difficult question. In many cases natural selection can hardly have failed to have come into play and complicated the result. It is notorious that mountain sheep resist severe weather and storms of snow which would destroy lowland breeds; but then mountain sheep have been thus exposed from time immemorial, and all delicate individuals will hnse been destroyed, and the hardiest preserved. So with the An·indy silk-moths of China and India; who can tell how far natural selection may have taken a share in the formation of the two races, which are now fitted for such widely different climates? It seems at first probable that the many fruit-trees, whjch are so well fitted for the hot summers and cold winters of North America, in contrast with their poor success under our climate, have become adapted through habit; but when we reflect on the multitude of seedlings annually raised in that country, and that none would succeed unless born with a fitting con­stitution, it is possible that mere habit may have done nothing towards their acclimatisation. On the other hand, when we CHAP. XXIV. ACCLIMATISATIOii. 313 hear that lVIeriuo sheep, bred during no great number of genera­tions at the Cape of Good Hope-that some European plants raised during only a few generations in the cooler parts of India, withstand the hotter parts of that country much better than the sheep or seeds imported directly from England, we must attribute some influence to habit. We are led to the ~:;arne conclusion when we hear from N audin 78 that the races of melons, squashes, and gourds, which have long been cultivated in Northern Europe, are comparatively more precocious, and need much less heat for maturing their fruit, than the varieties of the same species recently brought from tropical regions. In the reciprocal conversion of summer and winter wheat, barley, and vetches into each other, habit produces a marked effect in the course of a very few generations. The same thing ap­parently occurs with the varieties of maize, which, when carried from the Southern to the Northern States of America, or into Germany, soon become accustomed to their new homes. 'Vith vine-plants taken to the West Indies from Madeira, which are said to succeed better than plants brought directly from France, we have some degree of acclimatisation in ihe individual, inde­pendently of the production of new varieties by seed. 'fhe common experience of agriculturists is of some value, and they often advise persons to be cautious in trying in one country the productions of another. The ancient agricultural writers of China recommend the preservation and cultivation of the varieties peculiar to each country. During the classical period, Columella wrote, "Vernaculum pecus peregrino longe " prrestantius est." 79 I am aware that the attempt to acclimatise either animals or plants has been called a vain chimrera. No doubt the attempt in most cases deserves to be thus called, if made independ­ently of the production of new varieties endowed with a dif­ferent constitution. Habit, however · much prolonged, rarely produces any effect on a plant propagated by buds; it ap­parently acts only through successive seminal generations. 78 Quoted by Asa Gray, in 'Am. Journ. of Sci.,' 2nd series, Jan. 1865, p. 106. i~ 1!'or China, see ' Memoire sur los Chinois,' tom. xi., 1786, p. 60. Columella is quoted by Curlier, iu 'Journal de Physique,' tom. xxiv. 1784.