246 



Gates. 



This difference in pigment-production extends to every part of the 

 plant, though its external development in the buds affords the best 

 criterion of the relative amount present in other organs. 



Cross-sections of the capsules some time after fertilization showed 

 clearly great differences in the amount of pigment produced. Thus 

 in rubricalyx nearly the whole epidermis of the capsule was composed 

 of cells filled with anthocyanin. There were also patches of red cells 

 in the sub-epidermal parenchyma, and nearly all the cells of the 

 nucellus were red. In the R hybrids with graiidiflora this amount 

 was so reduced that only patches of pink epidermal cells occurred, 

 with scattered pink idioblasts in the sub-epidermal parenchyma, also 

 in the vascular bundles of the capsule wall, and conspicuously in the 

 chalaza. The individual pink cells evidently contained less antho- 

 cyanin than the darker red ones of rubricalyx. 



It is then perfectly clear that, although extent of pigment on the 

 buds behaves, with very few exceptions, as a definite unit-character, 

 showing the phenomena of dominance and absence; yet the amount 

 of pigment produced is very probably reduced to a half in the Fi 

 hybrids, and is certainly diluted very much (probably one-half) again 

 on crossing back with graiidiflora. It is difficult to get definite mea- 

 surements of pigment-production, but it seems certain that this 

 character is quantitatively inherited, and that each successive back- 

 cross with gr audi flora results in dilution while each back-cross with 

 rubricalyx increases the concentration of the pigment. The cause 

 of the definiteness of distribution of the pigment in the buds is a 

 problem in morphogenesis. 



F. Inheritance of the recessive unit-character, /. 



It is most instructive to compare with the behaviour of the 

 dominant character, R, that of the recessive character, t. By reference 

 to pedigrees i and 2, it will be seen that in the cross grandiflora x 

 rubricalyx, dwarfing was brought in through the male parent, rubri- 

 calyx, while in the reciprocal it was also brought in through the male 

 parent, grandiflora. Being recessive, the character only reappeared 

 in Fa in both cases. Out of the 29 Fg families and back-crosses, 

 dwarfs occurred in five as shown in the following table V. 



Several interesting points appear from an examination of table V. 

 In the first place, of the five Fg families from grandiflora x rubri- 

 calyx, two contained dwarfs. This is in accord with the Mendelian 

 expectation that half the families would produce dwarfs. With the 



