OTHER THEORIES OF SPECIES-FORMING. 345 



period within the life-time of the species, and probably it is 

 only a small part of it." 



The following paragraphs and diagram quoted from 

 Morgan 21 give an admirably concise statement of the actual 

 details of the primrose mutations observed by de Vries. 



"We may now proceed to examine the evidence from 

 which de Vries has been led to the general conclusions given 

 in the preceding pages. De Vries found at 

 Hilversum, near Amsterdam, a locality where 



Vries's experi- a number of plants of the evening primrose, 

 (Enothera lamarckiana, grow in large numbers. 

 This plant is an American form [native to the Southern 

 United States] that has been imported into Europe. It 

 often escapes from cultivation, as is the case at Hilversum,. 

 where for ten years it has been growing wild. Its rapid 

 increase in numbers in the course of a few years may be one 

 of the causes that have led to the appearance of a mutation 

 period. The escaped plants showed fluctuating variations 

 in nearly all of their organs. They also had produced a 

 number of abnormal forms. Some of the plants came to 

 maturity in one year, others in two, or in rare cases in 

 three, years. 



"A year after the first finding of these plants de Vries 

 observed two well-characterised forms, which he at once 

 recognised as new elementary species. One of these was 

 O. brevistylis, which occurred only as female plants. The 

 other new species was a smooth-leafed form with a more 

 beautiful foliage than 0. lamarckiana. This is O. lavifolia* 

 It was found that both of these new forms bred true from 

 self-fertilised seeds. At first only a few specimens were 

 found, each form in a particular part of the field, which 

 looks as though each might have come from the seeds of a 

 single plant. 



"These two new forms, as well as the common O. la- 

 marckiana, were collected, and from these plants there have 



