8 FRIEDA COBB 



THE FI AND F 2 GENERATIONS OF VARIOUS CROSSES BETWEEN F. TYPICA M 



(THE NEW, MENDELIAN STRAIN) AND F. TYPICA OF STRAIN c, 



F. TYPICA OF STRAIN E, AND MUT. FORMOSA 



The data recorded in this paper concerning the FI and F 2 generations 

 of crosses of eighteen different kinds between f . typica M (the new Men- 

 delian strain from the cross mut. formosa X strain C) as one parent, and 

 f. typica C, f. typica E, or mut. formosa, as the other parent, confirm the 

 hypotheses of non-equivalent gametes and the presence of a pair of inde- 

 pendent Mendelian factors in Oenothera pratincola. 



All f. typica M plants used in the crosses were self -pollinated to deter- 

 mine whether they were homozygous or heterozygous. 



All of the flat-leaved types other than f. typica which occurred in the 

 progenies of crosses are mutations regularly thrown by f. typica C, and 

 some of them by f. typica E also. All of the revolute-leaved types which 

 occurred, are regularly thrown by f . typica E and by mut. formosa. 



The cross mut. formosa X f . typica M (homozygous) (afrff X a$FF) 

 gave in the Fi generation (see table 11) only flat-leaved plants (a'(3Ff), 

 and in the F 2 generation (see table 12) a segregation of 3 flat-leaved plants 

 (a'QFF and a'QFf) to 1 revolute-leaved plant (a'fff). 



The reciprocal cross, f . typica M (homozygous) X mut. formosa (a' 

 X afiff), gave the same results (see tables 13 and 14). 



The cross mut. formosa X f . typica M (heterozygous) (aftff X a 

 gave in the Fi generation (see table 15) progenies consisting of flat-leaved 

 plants (a&Ff) and revolute-leaved plants (aftff) in approximately equal 

 numbers, and in the F 2 generation from flat-leaved plants (see table 16) a 

 segregation of 3 flat-leaved plants (a'pFF and a'flFf) to 1 revolute-leaved 

 plant (a'fff). 



The reciprocal cross, f. typica M (heterozygous) X mut. formosa (a'ftFJ 

 X a r pff) gave the same results (see tables 17 and 18). 



The cross f . typica E X f . typica M (homozygous) (a/3// X a'QFF) gave 

 in both the Fi and the F 2 generations (see tables 19 and 20) only flat-leaved 

 plants. It is known that the a of strain E frequently mutates to a', and a 

 few revolute-leaved plants would therefore be expected in the F 2 progenies, 

 by a combination of a and the recessive Mendelian factors. One-fourth 

 of the plants of the F 2 generation, those with the constitution aftff, would 

 be expected to become revolute-leaved by mutation with the frequency 

 of mutation in pure strain E. But this did not occur. The only explana- 

 tion that can be suggested is that because the germination percentage was 

 much higher than was expected, the seedlings were very much crowded in 



