248 ENTOMOLOGY 



De Vries has produced new species by experimental means 

 and without the aid of selection. Moreover, he has produced 

 them at once, showing that a species does not necessarily re- 

 quire hundreds of years to develop, by means of a long-con- 

 tinued process of selection. 



It has long been customary to draw a distinction between 

 individual variations and sports. Darwin recognized the dis- 

 tinction and was one of the first to notice the extraordinary 

 persistence with which sports are transmitted, as compared 

 with the relative instability of individual variations. Not a 

 few dominant races of plants and animals are known to have 

 arisen from sports, and the belief has been gaining ground 

 with Bateson and others that species also have to some extent 

 arisen from sports, rather than from individual variations; 

 though the rarity of sports as compared with individual varia- 

 tions is the strongest objection to this theory as a theory of 

 the origin of species in general. 



De Vries, however, was the first to make extensive experi- 

 ments on sports, or unit at ions, as he calls them, and to formu- 

 late a definite theory of the subject from a considerable body 

 of evidence. He regards the qualities of organisms as being 

 built up of definite but sharply separated units, or elements, 

 which combine in groups. The addition of a new unit means 

 a mutation, a sudden departure from the normal specific form ; 

 in other words, a new species may arise from the parent form 

 without any evident gradation. The mutable condition exists 

 only at times, and some species are more mutable than others. 

 Acting upon this as a hypothesis, De Vries made a preliminary 

 study of a great number of plants in order to find one in its 

 period of mutation, and at length selected (Enothera Larnarck- 

 iana (probably a variety of our E. biennis, introduced into 

 Holland from America), because of its exceptionally vigorous 

 multiplication, dispersion and variation. By careful cultivation 

 and by means of artificial pollination, he succeeded in obtaining 

 seven or more new species. Most of these remained con- 

 stant from year to year in spite of intercrossing. Moreover, 



