100 Experiments with Primula sinensis 



" Orange King " characters of stem and flower are however so intimately 

 associated that the fuller consideration of this case may be deferred 

 until the section dealing with flower-colour (p. 114). 



Partial Suppression of Colour. 



The light shades of the colour in the stem are dominant to the 

 intense shades. This fact is well illustrated in the F^s from (" Ivy- 

 leaf" X deep red stem), where the red-stemmed plants fall into two 

 sharply separated categories. The numbers obtained are : 



Light Intense 



3 families ... 157 49 



Expectation ... 154-5 51'5 



Similar sharpl}' divided categories are found in families raised from 

 the cross of a deep red stem with the F^ of (" Snowdrift " x deep red 

 stem). The numbers obtained in these crosses are : 



Light Intense 



9 families ... 198 202 



+ 3 doubtful (occurred in cue family) 

 Expectation ... equality. 



It is clear from these cases that the light class, taken as a whole, 

 may be explained as being due to the presence of a single factor, 

 epistatic to the factors for colour, which diminishes the intensity of 

 the pigmentation (pallifying factor). In the F^'s produced by the self- 

 fertilization of the Fi from the cross ("Snowdrift" x deep red stem) there 

 are forms intermediate between the light and the very dark red stems, 

 and the separation between the classes is by no means sharp. No doubt 

 many of these intermediate forms are the result merely of heterozygosis 

 in the factors for colour and for its partial suppression. In different 

 pure races, however, and in the hybrids produced by their matings, 

 colour is developed to very different degrees, and in order to account 

 for the detailed phenomena it would probably be necessary further to 

 elaborate the simple scheme put forward here, which is intended only 

 to apply to the general outlines of the phenomena of the partial 

 suppression of stem-colour. 



The partial suppression of flower-colour follows, in general, very 

 similar lines to that of stem-colour, but is independent of the latter, 

 at least to the extent that light flowers may occur on deeply coloured 

 stems. 



In the lower grades of steni-eolour the same relation subsists between the light and 

 intense states as in the fully coloured types, but the separation of the categories is 



