VI.] GENESIS OF VARIATIONS. 167 



or modifications which are acquired from the direct or 

 indirect effects of environment in the lifetime of the 

 individual may become hereditary. 



In recent years, however, it has been strenuously 

 denied that any such incidental or adaptive characters 

 can be hereditary, and that all new forms come as a 

 result of sexual union. This is the hypothesis of Weis- 

 mann; but, inasmuch as Weismann's conception sup- 

 poses that evolution takes place as a result of natural 

 selection or survival of the fittest amongst the forms 

 so originating, his theory is generally known as Neo- 

 Darwinism, or the new Darwinism. The fundamental 

 concepts of Weismann are too recondite for presen- 

 tation here, but I have already said enough, I think, to 

 bring the general trend of the three leading hypotheses 

 of evolution before your minds. (Consult Essay II.) 



The chief points in these hypotheses, it will be 

 noticed, are the means of accounting for the origin of 

 variations, and it is upon this general question that 

 philosophical naturalists are at present most divided. 

 It is plain that there can be no evolution without varia- 

 tions or initial differences between individuals; and here 

 is the first and most important direct lesson which the 

 evolution theories bring to the agriculturist, — the im- 

 portance of individual differences and the means of 

 securing them. You all know that no two plants are 

 alike. Why ? 



It is not doubted, even by the adherents of Weis- 

 mann, that environment may cause immediate variation 

 of organisms, but these writers declare that such varia- 

 tions are not transmitted, that is, that they are lost with 

 the death of the individual in which they occur. It is 

 only when any variation is a part of the germ or sex 



