No. 572] SHORTER ARTICLES AND DISCUSSION 495 



ably a mutant from 0. biennis itself. Therefore, hybrids between 

 these two forms can be looked upon as pure 0. hu nnis except for 

 floral characters. 



With this conception Bradley Moore Davis docs nol agree. 1 

 He thinks that the 0. biennis and O. biennis eruciata of our dunes 

 are not so closely related types, that a cross between them can 

 be treated "as though it were the combination of forms within 

 the same species which have similar terminal emistitutions." He 



nized in the more recent taxonomic treatments as a true species sharply 

 distinguished from types of biennis by its floral characters. ... 0. 

 eruciata is found wild in certain regions of New England and New 

 York and is consequently a native American species. . . . Whatever 

 may have been the origin of 0. eruciata or its possible relationship to 

 0. biennis, a cross between these types must certainly be regarded as a 

 cross between two very distinct evolutionary lines and its product a 



be expected. 



From Davis's point of view I "really made a cross between 

 two rather closely related species" and obtained in the second 

 generation "two marked variants due to some germinal modifica- 

 tion! as the result of the cross. " In so far as my observations bear 

 upon the problem of mutation Davis's interpretation is exactly 

 the reverse of mine. To him they further illustrate the same 

 phenomenon which he is obtaining through his "hybrids of 

 biennis and grancliflora, namely, that behavior by which these 

 hybrids in the F 2 generation throw off variants that in taxonomic 

 practise would be considered new species readily distinguished 

 from the parents of the cross and from the F 1 hybrid." 



It will be shown in the following lines that the objections made 

 by Davis are not sufficiently justified. My argument consists of 



In the first place, Davis is mistaken as to the nature of the 0. 

 biennis eruciata de Vr. of our dunes. This strain is in reality 

 quite another type than the different forms of the American 0. 

 eruciata Nutt, called by some authors 0. biennis eruciata. With 

 this species it has in common only the character of the narrow 



» Bradley Moore Davis, "Mutation in (Enothera biennis L.f " The Ameri- 

 can Naturalist, Vol. XLVII, 1913, pp. 116-121; "Genetical Studies on 

 CEnothera," IV, The American Naturalist, Vol. XLVII, 1913, pp. 



