The Theory of Evolution 217 



have temporary effects produced in its somatic cells by the en- 

 vironment must be granted, but such effects should not be con- 

 fused with these permanent mutations brought about in the germ- 

 cells. On some such hypothesis as this it may be possible to 

 harmonize current views. 



De Vries's Results with (Enothera 



Although de Vries's experiments have been made entirely with 

 plants, the results are of so great importance that they must be 

 stated here briefly ; for there can be little doubt that if his con- 

 clusions are established they will apply equally well to animals. 

 His principal work has been with Lamarck's evening primrose, 

 (Enothera Lamarckiana. This American species has been intro- 

 duced into Europe, where it has been cultivated in gardens for a 

 long time. It has also escaped and established itself in a wild 

 condition. De Vries found a field at Hilversam near Amster- 

 dam in which the escaped evening primrose grew, but also several 

 other closely related forms which as subsequent experiment 

 showed had sprung from Lamarck's primrose. These new 

 forms bred true, when self -fertilized, showing that they were 

 fixed types and not local races depending on special conditions. 

 They are new elementary species. 



When the seeds of Lamarck's primrose were sown in de Vries's 

 experimental garden, a small percentage of them gave rise to 

 some of the same types that had been found growing wild. 

 Other types also appeared. In all, de Vries has described seven 

 such elementary forms. The chief character of these mutations 

 is that they breed perfectly true to their type when self-fertilized. 

 Occasionally another new type may appear from the seeds of a 

 mutation itself. These also in most cases breed true to their kind 

 if self -fertilized. The parent type, O. Lamarckiana, has been 

 found to produce year after year its quota of mutations. The 

 percentage of new forms, although small, not much more than 

 about 1.5 per cent, seems to be constant, and the mutants 

 continue to appear year after year. 



De Vries has formulated a theory or rather several theories 



