Chap. XXIY. ACCLIMATISATION. 303 



these cases tiie power of acclimatisation by man consists 

 simply in the selection and preservation of new varieties. 

 But without any direct intention on his part of securing 

 a hardier variety, acclimatisation may be unconsciously 

 effected by merely raising tender plants from seed, and by 

 occasionally attempting their cultivation further and further 

 northwards, as in the case of maize, the orange and the 

 peach. 



How much influence ought to be attributed to inherited 

 habit or custom in the acclimatisation of animals and plants 

 is a much more difficult question. In many cases natural 

 selection can hardly have failed to have come into play and 

 complicated the result. It is notorious that mountain sheep 

 resist severe weather and storms of snow which would destroy 

 lowland breeds ; but then mountain sheep have been thus 

 exposed from time immemorial, and all delicate individuals 

 will have been destroyed, and the hardiest preserved. So 

 with the Arrindy silk-moths of China and India ; who can 

 tell how far natural selection may have taken a share in the 

 formation of the two races, which are now fitted for such 

 widely different climates ? It seems at first probable that the 

 many fruit-trees which are so well fitted for the hot summers 

 and cold winters of North America, in contrast with their 

 poor success under our climate, have become adapted through 

 habit ; but when we reflect on the multitude of seedlings 

 annually raised in that country, and that none would succeed 

 unless born with a fitting constitution, it is possible that 

 mere habit may have done nothing towards their acclima- 

 tisation. On the other hand, when we hear that Merino 

 sheep, bred during no great number of generations at the 

 Cape of Good Hope — that some European plants raised 

 during only a few generations in the cooler parts of India, 

 withstand the hotter parts of that country much better than 

 the sheep or seeds imported directly from England, we must 

 attribute some influence to habit. We are led to the same 

 conclusion when we hear from Naudin 78 that the races of 

 melons, squashes, and gourds, which have long been cultivated 



78 Quoted by Asa Gray, in * Am. Juurn. of Sci.,' 2nd series, Jan. 1 865, 

 p. 106. 



