2 BOTANICAL GAZETTE [January 



If we should apply the principle of Bartlett concerning mass 

 mutation, and that of Morgan concerning lethal factors to this case, 

 as I have made use of them in explaining the secondary mutability 

 of 0. grandiflora and O. Lamar ckiana,^ we would conclude that 

 O. deserens is a mass mutation of O. rubrinervis, and as such is a 

 repetition of the initial mutation which produced the O. rubrinervis 

 from O. Lamarckiana in my garden. This initial mutation must 

 have occurred in a sexual cell, which, after copulation with a normal 

 gamete of 0. Lamarckiana, gave rise to a half mutant, O. rubrinervis. 

 In other words, O. rubrinervis arose as a half mutant between poten- 

 tial 0. deserens and normal 0. Lamarckiana. This half mutant, after 

 artificial self-fertilization, must have produced a splitting into three 

 types, exactly in the same way as this splitting can be observed in 

 the half mutants of O. gigas nanella. Of these types two must be 

 constant, but the third must repeat the splitting. O. deserens is 

 one of the constant ones, whereas the other is assumed to be hidden 

 in the empty seeds, containing a lethal factor just as in O. grandi- 

 flora and O. Lamarckiana. The third type is the continuance of 

 O. rubrinervis, and repeats the splitting in every generation. 



According to my view O. Lamarckiana produces yearly two 

 kinds of gametes in consequence of a secondary mutability into 

 velutina. These velutina are linked to a lethal factor, which kills 

 them in the young seeds. If we assume that the mutation into 

 deserens took place in the typical gametes, leaving the velutina 

 unchanged, we would conclude that O. rubrinervis consists of two 

 types of gametes, even as O. Lamarckiana, but that both of them 

 are in a mutated condition. One is the new deserens, without lethal 

 factor; the other is the old velutina, linked to a lethal factor. The 

 result of self-fertilization is now easily explained; the copulation 

 of deserens gametes among themselves must produce this form, that 

 of velutina must give empty seeds, and the combination of the two 

 types must repeat the rubrinervis with its splitting capacity. 



On the same basis the occurrence of twin hybrids may be 

 explained, the deserens gametes giving the laeta hybrids; but here 

 we have a considerable advantage over other instances of twin 



^ Mass mutation and twin hybrids of Oenothera grandiflora Ait. Bot. Gaz. 65 : 

 377-422. 1918. 



