104 



Shull. 



The distribution of the two types of capsule in the several gener- 

 ations of hybrids between Bursa bursa-pastoris and B. Heegeri may 

 be considered now in relation to the foregoing theoretical expectations. 



The original crosses were made reciprocally in March, 1906, and 

 the hybridized seeds were sown as soon as mature, on April 25, 1906. 



In the Fi B. bursa-pastoris X Heegeri (ped. No. 0688) produced 

 about 100 offspring, and B. Heegeri X bursa-pastoris (0689) yielded 23 

 offspring, all of both families having triangular capsules indistinguishable 

 from those of pure B. bursa-pastoris; that is, dominance is complete, 

 and there is no perceptible cumulative effect of the presence of several 

 determiners as compared with but one. 



Six F 2 families have been grown, three of which have been reported 

 in earlier papers. On the assumption that the duplicate determiners, C 

 and D, were involved in these crosses, all of these F 2 families should 

 have given the ratio 15 : 1. The actual ratios ranged from 16 : 1 to 

 36'5 : 1, thus in every instance exceeding the expected ratio to a greater 

 or less extent. The detailed results in the several families are presented 

 in the following table: 



Table I. 



Eighteen families have now been grown from self-fertilized bursa- 

 pastoris individuals in the F 2 , and eleven of these families have been 

 published elsewhere (SHULL 1911). For the sake of completeness the 

 latter are included here with the families more recently grown, in 

 Table II. Owing to the wide range of the ratios and the small number 

 of the families which included both types of capsule, those first eleven 

 families left the question of duplicate genes in doubt, though I believed 

 that the three kinds of families which are expected in the Fa were 

 actually present, their character being obscured by unknown modifying 

 causes, - - possibly selective elimination or selective fertilization. The 



