524 



VARIATION 



of plants, many of which he brought under experimental cul- 

 tivation. He obtained the best results with the Evening Prim- 

 rose, Oenothera Lamarckiana, (Fig. 4-7^), a large group of which 

 he found growing in an abandoned potato field in the suburbs of 

 Amsterdam. This Evening Primrose, commonly known as 

 Lamarck's Evening Primrose, reaches a height of four or five feet, 

 branches freely, and has attractive yellow flowers. This particu- 

 lar Primrose is not found in our country, but we have others and 

 the one known as the Common Evening Primrose is a common 



weed in fields where weeds are al- 

 lowed to grow. In this group of 

 Lamarck's Evening Primroses, con- 

 sisting of several thousand individ- 

 uals, De Vries found two forms 

 strikingly different from the normal 

 type. They differed from the nor- 

 mal type in a number of ways. One 

 differed from the normal type 

 chiefly in having smooth leaves and 

 the other in having a short style. 

 The discovery of these new forms 

 suggested to him that new species 

 were being formed in this group of 

 plants and that a careful study of 

 this species of Evening Primroses 

 might result in valuable information 

 as to how new species are produced. 

 From some of the Lamarckiana 

 plants he gathered seeds from which 

 he started a series of generations in 

 his experimental garden. He also 

 transplanted to the garden a num- 

 ber of young plants. His purpose in growing the plants in the 

 garden was to have them under experimental control. Here 

 he controlled their pollination and kept careful records and de- 

 scriptions of the plants throughout a number of generations, 

 so as to know the exact hneage or pedigree of each new form 

 that might appear. He demonstrated the value of the pedigree 

 method in the study of variations and this is one of the valuable 

 contributions of his work. 



Fig. 472. — Lamarck's Even- 

 ing Primrose (Oenothera La- 

 marckiana), a mutating species. 

 After De Vries. 



