LAWS OF VARIATION 215 



for an immense period in nearly the same states and thus 

 it has come not to be more variable than any other 

 structure. It is only in those cases in which the modi- 

 fication has been comparatively recent and extraordinarily 

 great that we ought to find the generative variability, as 

 it may be called, still present in a high degree. For 

 in this case the variability will seldom as yet have been 

 fixed by the continued selection of the individuals vary- 

 ing in the required manner and degree, and by the con- 

 tinued rejection of those tending to revert to a former 

 and less-modified condition. 



k^pecific Characters more Variable than Generic Characters 



The principle discussed under the last heading may 

 be applied to our present subject. It is notorious that 

 specific characters are more variable than generic. To 

 explain by a simple example what is meant: if in a large 

 genus of plants some species had blue flowers and some 

 had red, the color would be only a specific character, 

 and no one would be surprised at one of the blue spe- 

 cies varying into red, or conversely; but if all the species 

 had blue flowers, the color would become a generic char- 

 acter, and its variation would be a more unusual circum- 

 stance. I have chosen this example because the explana- 

 tion which most naturalists would advance is not here 

 applicable, namely, that specific characters are more vari- 

 able than generic, because they are taken from parts of 

 less physiological importance than those commonly used 

 for classing genera. I believe this explanation is partly, 

 yet only indirectly, true; I shall, however, have to return 

 to this point in the chapter on Classification. It would 

 be almost superfluous to adduce evidence in support of 



