The Origin of Species 321 



reproduce themselves from seed if care is taken to 

 prevent crossing. A recently described example of 

 what appears to be the appearance of a new species 

 by mutation, is that of Capsella Heegeri, described 

 by Solms-Laubach, who considers it to be a new 

 species derived by mutation from the common shep- 

 herd's-purse, C. bursa-pastoris. 



De Vries' Studies on the Evening Primrose 



The theory of De Vries is based principally upon 

 a very extensive series of studies of the variation 

 in an American plant, the large flowered evening 

 primrose, (Enothera Lamarckiana. This plant was 

 found growing wild near Amsterdam, where it had 

 evidently escaped from cultivation, and an examina- 

 tion showed that it was in a very variable condition. 

 For a series of years the plant was kept under ob- 

 servation, and many cultures were made, with the 

 result that certain marked variations were found to 

 appear repeatedly, and these varieties, or incipient 

 species, according to De Vries, were nearly always 

 constant, when kept from crossing with other va- 

 rieties, or with the original type. From the behavior 

 of these " mutants," as De Vries called these va- 

 rieties, he came to the conclusion that new species 

 always arise by such discontinuous variations, and 

 their persistence as permanent species depends upon 

 whether or not they survive as the result of natural 

 selection. 



De Vries' Theory of Pangenes. De Vries be- 

 lieves that heredity is to be explained by the assump- 



