BREEDING AND HEREDITY 5 



course of many generations. According to the 

 former view, species cannot be said to arise by 

 selection. If, when they have once arisen, they 

 have defects which hamper them in the struggle for 

 existence, where this occurs, they will doubtless 

 drop out. But this does not constitute origin by 

 selection. According to the latter view, on the 

 other hand, the character of the new species is only 

 attained by the traversing of the gradational stages 

 between it and the parent one ; and inasmuch as it 

 may be supposed that these gradational forms would 

 not have left offspring if they had any defects which 

 prevented them doing so, it may be said that the 

 new species arises by a process of natural selection. 



The view that species have originated by muta- 

 tion is based on Prof, de Vries' observations on the 

 Evening Primrose {(Enothera Lamarchiana) (Fig. 1). 

 Working with this form, he was able to witness, for 

 the first time, the actual process of the origin of new 

 species. 



For some time he had been searching in the neigh- 

 bourhood of Amsterdam for plants which were 

 giving off new forms ; but as he failed to find any 

 he concluded that they were all in an immutable 

 condition. At last he found a plant which appeared 

 to be in a mutable state. This was (Enothera 

 Lamarchiana. It was growing in a disused potato 

 field near Hilversum, in Holland. This plant had 

 escaped into the field from a bed in a park close by, 

 where some annuals were grown every year. The 

 CEnotheras were thickest at the corner of the field 



