MUTATION 317 



mentary species, while others are to be considered as 

 retrograde varieties." 



The last statement requires a few explanations. 

 De Vries takes great pains to define the word species 

 and to delimit the notion of species. Species as com- 

 monly understood in classification (the Linnasan spe- 

 cies) is, he thinks, too inclusive a unit, correspond- 

 ing as it does to a complex group of forms. In the 

 majority of cases it can be subdivided into a certain 

 number of secondary units called varieties, but which 

 it would be more fitting to call elementary species, 

 reserving the word variety for lesser subdivisions. 



Every new species which De Vries obtained in the 

 course of his experiments on Oenothera constituted 

 therefore an "elementary species" and its "varieties" 

 were only subvarieties. This is not for De Vries a 

 mere question of conventional nomenclature; to him 

 the definition of species corresponds to something 

 very real, for he belongs, as we stated elsewhere, to 

 the school of biologists who believe that characters 

 originate and are contained in material particles. Ac- 

 cording to whether those particles, which he desig- 

 nates as "specific units" are active or passive, the cor- 

 responding character may either appear or remain 

 latent. 



"Latency, from this point of view, must be one of 

 the most common things in nature. All organisms 



