274 



Gates. 



7. Furthermore, in crossing back the Fj with graiidiflora and 

 mbricalyx, the red pigmentation becomes in the first case muclr 

 paler and in the second case decidedly darker, showing that 

 the amount of pigment produced by the indi\-idual cells is 

 quantitatively inherited. This is also supported by microscopic 

 examination of the living cells. 



8. In crossing back tlie F^ with grandiflora there is always an 

 excess of R's, but the excess is much less than in Fg offspring 

 of the same plants. Thus two plants (Nos. IX. 4 and VI. 6) 

 from grandiflora riihricalyx give Fo ratios respectively of 

 4.25 : I and 9.5 : i, but when crossed back with grandiflora 

 they give an average of 1.39 : i. Similarly with the reciprocal 

 cross, in one case (No. VI. i) the Fg ratio is 5.15 : i, while the 

 ratio from crossing back with grandiflora becomes 1.23 : i. 

 Hence grandiflora exerts an inhibiting effect, not only in reducing 

 the quantity of pigment produced in all the R plants, but also 

 in reducing the excess of 7?'s in the whole population. 



9. The pigmentation-character, R. ma\^ be viewed from two 

 aspects, (i) morphological, (2) physiological. Morphologically 

 considered, tlie plants may with very few exceptions be classed 

 as R or r, i. c, the hypanthia are either visibly red throughout 

 or green throughout; but physiologically, the amount of 

 pigment is intermediate between that of the parents, and in 

 crossing back, e. g. grandiflora x rubricalyx with grandiflora, 

 the amount of pigment, as measured by the depth of shade, 

 is again intermediate between these parents. Graiidiflora thus 

 inhibits anthocyanin production in the offspring according to 

 the proportion in which it is represented in the parents of the 

 cross. It is, therefore, probable that some unknown feature 

 in morphogenesis determines that the hypanthium shall be 

 red or green throughout, and therefore gives the appearance 

 of complete dominance to a character which, when present, 

 is actually inherited in a fundamentally quantitative manner. 



10. The inheritance of the recessive imit-character, /, for dwarfing, 

 is compared with that of the dominant character, R. In the 

 cross grandiflora .-. rubricalyx, t was carried in a recessive 

 condition by the rubricalyx parent (see pedigree r). In two 

 of the five Fo families it appeared, the ratio tall : dwarf being 

 in one case nearly 3:1; but in the other case the result was 

 reversed, the ratio being practically i : 2. This result again 



