4 FRIEDA COBB 



concerned in the cross is normal; but mut. formosa (aftff) pollinated by 

 strain C (afiFF) gives a flat-leaved progeny (a'pFf) (flat-leaved, notwith- 

 standing the mutated condition of a, because of the presence of one Men- 

 delian factor for flatness, inherited from the pistillate parent) which shows 

 in the next generation a Mendelian segregation of flat-leaved plants (a$FF 

 and a.'&Ff) and revolute-leaved plants (a$ff). Thee/ gamete concerned 

 in the cross has lost the factor for flatness, and so those F 2 individuals 

 that are recessive for the Mendelian factors for flatness show the revolute- 

 ness determined by a '. This new synthetic f. typica (a&FF or afiFf), 

 differing in genetic composition from both f . typica C and f. typica E, carry- 

 ing the factor for revoluteness masked by at least one of the Mendelian 

 pair of factors for flatness, will be called f. typica M (homozygous or hete- 

 rozygous, as the case may be). 



The hypothesis of the genetic constitution of the plants, and the results 

 of crossing, may be stated in brief as follows: 



Strain C, apFF, flat, and, with respect to this char- 



acter, immutable. 



Strain E, aftff, flat, mutable. 



Mut. formosa, a 'Pff, revolute-leaved. 



Strain E X formosa, aflff, flat, mutable. 



Formosa X strain E, a'pff revolute, breeding true with respect to 



this character. 



Strain C X formosa, a(3Ff flat, segregating with respect to muta- 



bility. 



1 a0FF flat, immutable, breeding true. 



2 a0Ff flat, continuing the segregation of the 



Fi generation. 



1 apff flat, mutable, otherwise breeding true. 

 Formosa X strain C, a'&Ff flat, segregating with respect to revo- 

 luteness. 

 1 a&FF flat, non-segregating. 



(Formosa X strain C) FJ 2 'W^< continuing the segregation of the 



FI generation. 

 1 o'jSjfjT revolute, breeding true. 



EQUIVALENCE, WITHIN STRAIN C, OF POLLEN OF OENOTHERA PRATINCOLA 

 F. TYPICA AND MUT. LATIFOLIA 



The former paper (COBB and BARTLETT 1919) gave data of the F, and 

 F 2 generations of the cross mut. formosa E X mut. latifolia C. At the 

 time the original crosses between mut. formosa and strain C were made, 



(Strain C X formosa) F 2 



