Chap. XIL NON-INHEEITANCE. 471 



which form one of the most ancient breeds in the world. 

 "With plants, we have seen that tropical varieties of maize 

 lose their proper character in the course of two or three 

 generations, when cultivated in Europe ; and conversely so 

 it is with Eiiropean varieties cultivated in Brazil. Our 

 cabbages, which here come so true by seed, cannot form heads 

 in hot countries. According to Carrieie,''^ the purple-leafed 

 beech and barberry transmit their character by seed far less 

 truly in certain districts than in others. Under changed 

 circumstances, periodical habits of life soon fail to be trans- 

 mitted, as the period of maturity in summer and winter 

 wheat, barley, and vetches. So it is with animals : for 

 instance, a person, whose statement I can trust, procured eggs 

 of Aylesbury ducks from t4iat town, where they are kept in 

 houses and are reared as early as possible for the London 

 market : the ducks bred from these eggs in a distant part of 

 England, hatched their first brood on January 24th, whilst 

 common ducks, kept in the same yard and treated in the 

 same manner, did not hatch till the end of March ; and this 

 shows that the period of hatching was inherited. But the 

 grandchildren of these Aylesbury ducks completely lost their 

 habit of early incubation, and hatched their eggs at the 

 same time with the common ducks of the same place. 



Many cases of non-inheritance apparently result from the 

 conditions of life continually inducing fresh variability. We 

 have seen that when the seeds of pears, plums, aj^ples, &c., 

 are sown, the seedlings generally inherit some degree of 

 family likeness. Mingled with these seedlings, a few, and 

 sometimes many, worthless, wild-looking plants commonly 

 aj^pear, and their appearance may be attributed to the prin- 

 ciple of reversion. But scarcely a single seedling will be 

 found perfectly to resemble the parent-form ; and this may 

 be accounted for by constantly recurring variability induced 

 by the conditions of life. J believe in this, because it has 

 been observed that certain fruit-trees truly projiagate their 

 kind whilst growing on their own roots ; but when grafted on 

 other stocks, and by this process their natural state is mani- 

 festly aifected, tliey produce seedlings which vary greatly, 



"2 ' Production et Fixation des Varietds,' 18i35, p. 72. 



