128 HISTORY OF BOTANY 



propagation was controlled by reason, although, in his 

 case also, the same limitations were existent and active, 

 and these he proceeded to enumerate and illustrate from 

 the histories of different nations. " The necessary 

 result of unrestricted multiplication," said Huxley, " is 

 competition for the means of existence. The success of 

 one competitor involves the failure of the rest, that is, 

 their extinction ; and this selection is dependent on the 

 better adaptation of the successful competitors to the 

 conditions of the competition. Variation occurs under 

 natural no less than under artificial conditions. Un- 

 restricted multiplication implies the competition of 

 varieties and the selection of these which are relatively 

 best adapted to the conditions. An individual which 

 varies, ipso facto diverges .from the type of its species ; 

 and its progeny, in which the variation becomes intensified 

 by selection, must diverge still more, not only from the 

 parent stock, but from any other race of that stock 

 starting from a variation of a different character. The 

 selective process could not take place unless the selected 

 variety was either better adapted to the conditions than 

 the original stock, or adapted to other conditions than 

 the original stock. In the first case, the original stock 

 would be sooner or later extirpated ; in the second, the 

 type, as represented by the original stock and the variety, 

 would occupy more diversified stations than it did 

 before." 



Darwin wrote out his theory in 1844, but instead of 

 publishing it at once he spent the next fifteen years 

 gathering new data bearing on the various aspects of 

 the subject, conducting experiments, and, so to speak, 

 polishing the rough-hewn marble into the perfect statue. 

 During this period also Darwin was busily engaged in 

 working out other problems suggested by or connected 

 with his main thesis, the gist of which latter was known 

 only to a few intimate friends. At length in 1856, at 

 LyelTs instigation, Darwin began to expand the pre- 



