82 BOTANICAL GAZETTE [eebeuaky 



and (3) that its habit of throwing off marked germinal variations 

 is paralleled by the behavior of certain interspecific hybrids in the 

 F2 and F3 generations seem to Davis' a sufl5.cient indication that 

 this plant is of comparatively recent hybrid origin, and that its 

 mutations are due to germinal instability resulting from hybridiza- 

 tion. He holds that the germinal variations of 0. Lamarckiana 

 and of various hybrids which he has studied show marked pro- 

 gressive evolution which seemingly caimot be accounted for on a 

 Mendehan basis. Although he does not deny that slight discon- 

 tinuous variations may occur in homozygous strains (and he insists 

 that the term mutation ought to be used only for such variations), 

 he is of the opinion that variations large enough to be of evolu- 

 tionary significance occur rarely if at all except in heterozygous lines. 

 Gates'* does not believe that 0. Lamarckiana is a recent inter- 

 specific hybrid, but does ascribe its mutations to germinal insta- 

 bility caused by occasional random crossing with other types. In 

 their main conclusion, that when germinal variation occurs it 

 usually follows crossing, Davis and Gates appear to agree. Gates, 

 however, is more emphatic than Davis in his conclusion that muta- 

 tion in Oenothera is not merely a result of Mendelian redistribution 

 of unit characters, but is a distinct type of variation. He believes, 

 moreover, that mutation sometimes takes place in pure as well as 

 in hybrid lines. Since the phenomena are identical in the two cases, 

 he has laid especial stress on the fact that there is no excuse for 

 confusing mutation, when it occurs in hybrids, with any tj^e of 

 Mendehan segregation.^ 



3D4VIS, B. M., Genetical studies on Oenothera. II. Amer. Nat. 45:193-233. 

 1911; III. Ibid. 46:377-427. 1912; IV. Ibid. 47:449-476, S47-57I- 1913- 



■•Gates, R. R., Mutation in Oenothera. Amer. Nat. 43:577-606. 1911. 



, A contribution to a knowledge of the mutating Oenotheras. Trans. 



Linn. Soc. Lond. II. Bot. 8:1-67. 1913. 



, Tetraploid mutants and chromosome mechanisms. Biol. Centralbl. 



33:92-99, 113-15°- 1913- 



sin this author's last paper he says: "The cytological evidence shows that 

 germinal changes may and do occur which are independent of all the laws of hybrid 

 combination and hybrid splitting. This generalization is of more fundamental signifi- 

 cance than might at first appear; for it shows that mutation in Oenothera is a process 

 sui generis, and that no amount of hybrid combination and splitting, Mendelian or 

 otherwise, is sufficient to account for it." Gates,_R. R., Breeding experiments which 

 show that hybridization and mutation are independent phenomena. Zeitschr. Ind. 

 Abstammungs- u. Vererbungslehre 11:209-279. 1914. 



