348 BOTANICAL GAZETTE [may 



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 saine 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 hne, 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 mutability 

 might be produced by crossing immutable species was a most 

 unhappy one. 



The second condition for success in this kind of work is, as has 

 been stated, the purity of the types to be crossed. As already 

 quoted, Davis assumes that a cross between two very distinct 

 evolutionary lines may give a hybrid with marked modifications of 

 germinal constitution. This may be appKed to his choice of the 

 type which he calls 0. grandiflora, and which he has made the 

 other parent of his initial cross. He got his seeds from Dixie 

 Landing, Alabama, a locahty where Bartram had discovered 

 0. grandiflora about a century ago. He assumed them to be of the 

 pure species, but a culture which I made in my garden from seeds 

 kindly suppHed to me by Mr. Davis proved to be a mixture, and 

 thereby threw a distinct doubt upon the purity of the station. 

 For this reason I visited Dixie Landing in September 191 2, and had 

 the good fortune to be accompanied by Mr. H. H. Bartlett, 

 of Washington, well known for his systematic researches among 

 the wild species of this group. We found the station in a most 

 desolate condition. A small-flowered species, 0. Tracyi, in almost 

 all respects different from 0. grandiflora, had migrated into the same 

 old cotton fields and mixed everywhere with the species of Bar- 



' Stomps, Th. J., Parallele Mutationen be! den Oenotheren. Ber. Deutsch. Bot. 

 Gesells. 30: Heft 3, 1914. 



