XIV FUNDAMEXTAL TROBLEMS 419 



lieritecl independently of any form of selection or of reversion 

 is exceedingly doubtful, and Darwin nowhere expresses him- 

 self as satisfied vnth. the evidence. The two very strongest 

 cases he mentions are the twenty-nine species of American 

 trees which all diftered in a corresponding way from their 

 nearest European allies ; and the American maize Avhich 

 became changed after three generations in Europe. But in 

 the case of the trees the differences alleged may be partly due 

 to correlation with constitutional peculiarities dependent on 

 climate, especially as regards the deeper tint of the fading leaves 

 and the smaller size of the buds and seeds in America than in 

 Europe ; while the less deeply toothed or serrated leaves in the 

 American species are, in our present complete ignorance of the 

 causes and uses of serration, quite as likely to be due to some 

 form of adaptation as to any direct action of the climate. 

 Again, we are not told how many of the allied species do not 

 vary in this joarticular manner, and this is certainly an im- 

 portant factor in any conclusion we may form on the c^uestion. 



In the case of the maize it appears that one of the more 

 remarkable and highly selected American varieties Avas culti- 

 vated in Germany, and in three years nearly all resem- 

 blance to the original, parent was lost ; and in the sixth year 

 it closely resembled a common European variety, but Avas of 

 somewhat more vigorous growth. In this case no selection 

 appears to have been practised, and the effects may have been 

 due to that " reversion to mediocrity " which invariably occurs, 

 and is more especially marked in the case of varieties which 

 have been rapidly produced by artificial selection. It may be 

 considered as a partial reversion to the aWM or unimproved 

 stock ; and the same thing would probably have occurred, 

 though perhaps less rapidly, in America itself. As this is 

 stated by Darwin to be the most remarkable case kno-«Ti to 

 him "of the direct and prompt action of climate on a plant," 

 we must conclude that such direct effects have not been proved 

 to be accumulated by inheritance, independently of reversion 

 or selection. 



The remaining part of Mr. Spencer's essay is devoted 

 to a consideration of the hypothetical action of the environ- 

 ment on the lower organisms which consist of simple cells or 

 formless masses of protoplasm; and he shows wdth great 



