2 FRIEDA COBB 



The present paper is a contribution to the genetic analysis of Oenothera 

 pratincola. It deals exhaustively with the first case in which simple 

 Mendelian inheritance has been recognized and conclusively demonstrated 

 when complicated by phenomena peculiar to the Oenotheras. 



The strains of Oenothera pratincola used in this investigation were those of 

 which the history has already been published (BARTLETT 1915 a, b; COBB 

 and BARTLETT 1919). Although morphologically alike, one of them, desig- 

 nated as strain E, is genetically different from the other seven, of which 

 strain C, the strain used in the experiments recorded in this paper, is a 

 typical example. 



Strain C produces in every generation a small number of mutations of 

 several kinds (BARTLETT 1915 a). Some of these kinds appear also in 

 strain E, but much more conspicuous in strain E are numerous mutations, 

 of a strikingly distinct series, which do not occur in the other strains. 

 These mutations occur in such numbers as to merit the term mass muta- 

 tion (BARTLETT 1915 b) as a designation of the phenomenon. The series 

 consists of four distinct types, all alike in having narrow, strongly revolute 

 leaves, and in producing nothing butrevolute-leaved plants in their progenies. 

 Of these revolute-leaved mutations, mut. formosa (BARTLETT 1915 b), the 

 strongest and most fertile of the series, was crossed with f . typica of strain 

 E, and with strain C. 



In a former paper (COBB and BARTLETT 1919) it has been stated that in 

 reciprocal crosses between mut. formosa and f . typica E, from which mut. 

 formosa arises, inheritance is matroclinic. Strain C pollinated by mut. 

 formosa gives a matroclinic progeny; but the reciprocal cross, mut. formosa 

 pollinated by strain C, gives in the FI generation only f. typica, in the F 2 

 generation a Mendelian segregation of 3 f. typica: 1 mut. formosa. 



HYPOTHESIS OF HETEROGAMETISM 



The hypothesis of heterogametism offered (COBB and BARTLETT 1919) 

 in explanation of these phenomena, assumes that two types of gametes 

 occur in Oenothera pratincola, a gametes (usually female) and gametes 

 (usually male), the a gametes carrying some factors not represented in the 

 gametes. Each zygote is formed by the union of an a and a /3 gamete, 

 and so gets (except in rare cases of metacliny) the a determiners of its 

 pistillate parent and the determiners of its staminate parent. It, in 

 turn, produces a (female) and (male) gametes. In the case of a cross, 

 the zygote is quite unaffected by the nature of the a of its staminate parent 

 and the /3 of its pistillate parent. 



