246 THE MEANING OF EVOLUTION 



observation ran back so short a time that we really 

 have no clear idea of how rapid evolution may have 

 been. Again, it has been answered that transitional 

 geological periods, in which there is much change in 

 the physical geography of a country, will produce 

 more rapid evolution than we at present are experi- 

 encing. 



Hugo DeVries, of Amsterdam, believes he has 

 found the answer to this difficulty. Outside of his 

 botanical garden an American species of Evening 

 Primrose had run wild. In looking over a number 

 of these plants he found, every here and there, cer- 

 tain peculiar members of the species. They differed 

 noticeably to the practiced eye from the rest of the 

 group. When they were planted and crossed with 

 each other, and the resulting seeds were again planted, 

 the peculiarity remained constant in all the members 

 of the collection. Here then we have a true varia- 

 tion, not large in amount, but at the same time quite 

 definite, and which from the first remains true. Here 

 are the beginnings, says DeVries, of new species. 

 They are true from the first; they can live among 

 other members of the species and still come true; 

 they do not need isolation, at least in Wagner's geo- 

 graphical sense. These forms DeVries calls muta- 

 tions. It is his thought that a species may run along 

 uniformly for a long time when, from some cause 



