XIV 
FUNDAMENTAL PROBLEMS 
419 
herited independently of any form of selection or of reversion 
is exceedingly doubtful, and Darwin nowhere expresses him¬ 
self as satisfied with the evidence. The two very strongest 
cases he mentions are the twenty-nine species of American 
trees which all differed in a corresponding way from their 
nearest European allies; and the American maize which 
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, cpiite 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 particular manner, and this is certainly an im¬ 
portant factor in any conclusion we may form on the question. 
In the case of the maize it appears that one of the more 
remarkable and highly selected American varieties was culti¬ 
vated in Germany, and in three years nearly all resem¬ 
blance to the original parent Avas lost; and in the sixth year 
it closely resembled a common European variety, but was of 
someAvhat more vigorous groAvth. In this case no selection 
appears to have been practised, and the effects may have been 
due to that “ reversion to mediocrity ” Avhich invariably occurs, 
and is more especially marked in the case of varieties Avhich 
have been rapidly produced by artificial selection. It may be 
considered as a partial reversion to the wild or unimproved 
stock ; and the same thing Avould probably have occurred, 
though perhaps less rapidly, in America itself. As this is 
stated by Darwin to be the most remarkable case known to 
him “ of the direct and prompt action of climate on a plant,” 
Ave 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 deA r oted 
to a consideration of the hypothetical action of the environ¬ 
ment on the loAver organisms which consist of simple cells or 
formless masses of protoplasm; and he shows with great 
