MUTATION THEORY OF DE VRIES 91 



features of animals and plants do not exist between the elements 

 themselves, any more than they do between the elements of the 

 chemist." 



The Case of the Evening Primrose. In 1886, De Vries began 

 hunting about around Amsterdam for a plant which would show 

 hints of being in what we may call a changeful mood. He tried 

 over a hundred species, bringing them under cultivation, but 

 almost all were disappointingly conservative. It seemed as if 

 most of the species around Amsterdam were in a non-mutable 

 state. It is possible, as Weismann suggested in one of his first 

 evolutionary essays (1872), that in the life of species periods of 

 constancy alternate with periods of changefulness. The human 

 historian has often made a similar remark. 



In the course of his wanderings around Amsterdam, De Vries 

 came across a deserted potato-field at Hilversum a field of 

 treasure for him. For there he found his long-looked-for mutable 

 plant, an evening primrose ((Enothera lamarckiana) . Like its 

 nearest relatives, (Enothera biennis and (Enothera muricata, which 

 it excels in size and beauty of flowers, it probably came from 

 America, where it is a native. It had probably " escaped " at 

 Hilversum about 1875, and in the following ten years it had 

 spread in hundreds over the field. It had been extremely prolific 

 in its freedom, but that was not its chief interest. 



Its chief interest was its changefulness. It had, so to speak, 

 frolicked in its freedom. Almost all its organs were varying as 

 if swayed by a restless tide of life. It showed minute fluctuations 

 from generation to generation ; it showed extraordinary freaks like 

 fasciation and pitcher-forming ; it showed hesitancy as to how 

 long it meant to live, for while the majority were biennial, many 

 were annual, and a few were triennial ; it showed what can 

 hardly be otherwise described than as new species in the making. 



It is possible that the prolific multiplication in a new environ- 

 ment may have had something to do with the awakening of the 

 impulsive mutability. 



