476 COBB AND BARTLETT: INHERITANCE IN OENOTHERA 



(2) The characteristic portion of each kind of gamete consists 

 of a group of chromosomes that remain in association at meiosis. 

 It is possible that the characteristic portion may consist of one 

 chromosome only. 



(3) The a gametes, and probably the ^ gametes also, carry 

 factors in the characteristic portion that are not duplicated in 

 the homologous portion of the complimentary gamete. 



(4) Aside from the chromosomes that determine a and & 

 gametes, the chromosomes of Oenothera are freely segregating, 

 and carry factors for Mendelian characters. 



(5) The a gametes are usually female, but may be male; the & 

 gametes, on the contrary, are usually male, but sometimes female. 



(6) Mutations occurring in the characteristic portion of either 

 a or /3 gametes do not make their appearance by Mendelian 

 segregation, and do not subsequently show Mendelian inheritance. 



Our studies have led us to conclude that the difference be- 

 tween the mass-mutating and nonmass-mutating strains of 

 Oenothera pratincola lies in the freely segregating chromosomes. 

 In Lexington E the factor which determines leaf flatness is 

 associated with the characteristic portion of the a gamete. It is 

 not paired with a similar factor in the /3 gamete. In Lexington 

 C, on the contrary, there is a paired factor for flatness, associated 

 with one of the freely segregating pairs of chromosomes, and 

 therefore carried by both a and /S gametes. In Lexington B, 

 the mutative modification of the unpaired factor for flatness 

 results in the appearance of revolute-leaved mutations, which do 

 not come about as a result of Mendelian segregation. The latter 

 fact is proved by their enormous abundance in certain mass- 

 mutating lines, an abundance far in excess of any Mendelian 

 expectation, and by their matroclinic inheritance in crosses 

 with the parent form. 



The several revolute-leaved mutations differ from f. typica 

 not only in the leaves, but in characters involving other organs 

 also, the degree of the difference depending upon the extent of 

 the mutative modification undergone by the a gamete. Whereas 

 the production of all of the revolute-leaved mutations involves 



