THEORIES OF WEISMANN AND DE VRIES 409 



and that it has given a great stimulus to experimental studies. 

 Experiment was likewise a dominant feature in Darwin's 

 work, but that seems to have been almost overlooked in 

 the discussions aroused by his conclusions; De Vries, by 

 building upon experimental evidence, has led naturalists to 



Fig. 115. — Hugo de Vries. 



realize that the method of evolution is not a subject for 

 argumentative discussion, but for experimental investigation. 

 This is most commendable. 



De Vries's theory tends also to widen the field of explo- 

 ration. Davenport, Tower, and others have made it clear 

 that species may arise by slow accumulations of trivial varia- 

 tions, and that, while the formation of species by mutation 



