THE PROBABLE ORIOIN OI- OENOTHliRA LAMAF^CKIANA SER. 581 



from types of biennis by its floral characters" and "a cross between 

 these types must certainly be regarded as a cross between two 

 very distinct evolutionary lines and its product as a hybrid in which 

 marked modifications of germinal constitution are to be expected."') 

 But, as a matter of fact, the Dutch 0. biennis criiciala differs from 

 0. biennis only in the characters of the petals; in all other respects 

 it is wholly the same and therefore evidently only a subordinate 

 variety of this species. It has not been dealt with in recent taxo- 

 nornic treatments, since it occurs almost exclusively in the sand 

 dunes of Holland, where it is produced from time to time by mutation 

 from the mother form (first observed in 1900), without having 

 been able until recently to multiply in the field so as to produce 

 a persistent local variety. 2) 



On the other hand, 0. cruciata Nutt. is quite a different species, 

 with narrow, brownish green leaves, and a different type of branch- 

 ing, of spikes, and of fruits. It grows wild in New York and Ver- 

 mont, and is well known to all students of the American flora. 

 By some authors it has been considered a variety of 0. biennis, 

 and this probably is the chief cause of Davis' confusion. The 

 character and the behavior of its hybrids with 0. biennis have 

 been amply dealt with in my Gruppenweise Artbildung. 



In the experiment of Stomps the dwarf and semigigas muta- 

 tions were produced by hybrid strains of 0. biennis and 0. biennis 

 cruciata, and it was assumed that such strains would behave as 

 true species in all characters not related to the differentiating marks 

 of the petals. It must be conceded, therefore, that the cross of 

 these two forms may be treated "as though it were the combina- 

 tion of forms within the same species, which have similar germinal 

 constitutions" (Davis, op. cit. p. 117). 



But the most clear and simple way of obviating this whole 

 objection is evidently to sow seeds of 0. biennis of pure descent 

 upon the same large scale as in the former experiment. This has 

 been done, and a dwarf and a semigigas form have been produced 

 by this pure line, besides some other mutations.^) They had the 

 same characters as the former ones, and now provide us with the 

 "strong support" asked for by Davis. Moreover, they show that 

 his choice of 0. biennis for a proof of the assertion that nmtability 



i) Amer. Nat. 47: 117, 1913. 



2) Die Mutations-Theorie 2:599, '903- 



3) Stomps, Th. J., Parallele Mutationen bei Oenothera biennis L. Ber. 

 Deutsch. Bot. Gesells. t^z. Heft 3, 1914. 



