116 Experiments with Primula sinensis 



to this discrepancy, were it not that in some F^%, which contain plants 

 with fully coloured stems, there is again a considerable excess of whites 

 in the red-stemmed class, where the distinction between white and 

 coloured forms can be made with certainty. The numbers which have 

 been obtained are' : 



stems not fully 

 coloured (including 

 Red stem those resembling " Sirdar " *) 



Dominant White ''■ ~ ' ^ 



Parent White Magenta "Sirdar" Pale pink White 



Giant White ' 



(18 5 2 4 



(33 8 3 6 33 



"Primrose Queen" 66 13 5 7 36 



* Without the character of the flower-colour as a guide it is scarcely possible accurately 

 to distinguish the " Sirdar" type of coloured stem from other low grades of stem-colora- 

 tion. 



Before passing to a detailed consideration of these results, it is well 

 to recall the fact that in the F.^ from crosses between plants having 

 coloured flowers and stems x the albino " Snowdrift," oil the red- 

 stemmed oflfspring have coloured flowers, whites being found only in 

 the green-stemmed class. These results, together with the fact that 

 all my red-stemmed whites proved to be dominant whites, suggested 

 that the factors for full colour are common to the whole plant, and 

 that, in general, red-stemmed whites are white in virtue of the 

 suppression of the colour in the flower by inhibiting factors 2. 



Turning now to the results of the crosses between " Giant White" x 

 " Snowdrift," it will be seen that the red-stemmed class consists of 

 whites and colours, in proportions which do not diverge so greatly from 

 the expected ratio (3 : 1) as to exclude the possibility of accounting for 

 all the whites on red stems as resulting from the suppression of colour 

 in the flower. 



In the red-stemmed class of the ^2 from "Primrose Queen" x 

 " Snowdrift," however, the whites are much more than three times 

 as numerous as the plants with coloured flowers. The observed ratio 

 of colours to whites agrees closely with the expectation based on the 

 hypothesis that the production of colour in the flower, even in the 

 red-stemmed offspring of this cross, depends upon two complementary 

 factors, for both of which the ^1 was heterozygous. An F-^ heterozygous 

 for these factors and for inhibition, would give an F^ consisting of 

 9 coloured : 55 white ; the numbers obtained are 13 coloured, 66 white 

 (easpectation : ll'll : 67'89). 



1 The earlier experiments only give qualitative results, as many plants were discarded 

 before the characters of the flower could be accurately determined. 



2 Gregory, Rep. Brit. Assoc., Leicester, 1907, p. 692. 



