THEORIES OF WEISMANN AND DE VRIES 493 
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 Iced naturalists to 
Fic. 115.—Huco pe VRiEs. 
realize that the method of evolution is not a subject for 
argumentative discussion, but for experimental investigation. 
This is most commendable. 
De Vrics’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 
