240 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 
