76 Experiments with Primula sinensis 



horticulture as " Sirdar" (Plate XXX, fig. 4 ; Plate XXXI, figs. 44, 45), 

 (3) pale colours on faintly coloured or green stems. The " Sirdars " have 

 a peculiar distribution of the colour. The pigment of the petals is one 

 of the full colours, but it occurs in separate minute dots and the edges 

 of the petals are white. Associated with flowers of this kind, the stems 

 have pigment at the bases of the petioles and pedicels, the rest of the 

 stem and leaves being green. The inheritance of the " Sirdar " 

 character may be described conveniently if the " Sirdars " be looked 

 upon as belonging to the fully coloured series, while they lack a factor, 

 the presence of which is required to bring about the even distribution 

 of the colour which is found in the full colours. The full colours and 

 " Sirdars " together constitute three-fourths of the total F^ population. 

 The remaining one-fourth consists of pale colours and whites in the 

 ratio 3 : 1. The significance of the ratio 15 pigmented forms : 1 albino, 

 and the relation of the pale colours to the full colours, is discussed in 

 the text (pp. 103, 104). 



The full colours are divisible into three classes, namely, (1) shades 

 of magenta, (2) shades of red or crimson, (3) shades of blue. 



The pale flower-colour is always a shade of pink, never magenta or 

 red. This colour, in its deepest shade, is that of Sutton's " Reading 

 Pink " (Plate XXX, fig. 13). 



Full colours are dominant to pale colour; magentas are dominant to 

 reds, and blue is recessive to all magentas and reds. 



Whites may be dominant or recessive to colours. 



Suppression of colour, partial or complete, by dominant factors is a 

 common phenomenon in Primula sinensis. Some of these factors affect 

 the colour of the flowers only, and one, at least, affects the colour of 

 both flowers and stems. 



When plants, which otherwise would have coloured flowers, are 

 homozygous in the factors which suppress flower-colour, the flowers 

 are quite white (dominant whites) ; when they are heterozygous in the 

 inhibiting factors, the flowers are sometimes white, but are more often 

 tinged with colour, the depth of the tinge varying with the races used 

 and with the temperature of the house. 



As regards the suppression of flower-colour, the evidence reveals a 

 curious complication in that the operation of two inhibiting factors, 

 affecting distinct areas, can be separately traced. Of these factors, one 

 suppresses colour in the peripheral parts of the corolla, the other affects 

 the gynoecium and central part of the corolla. In consequence it follows 

 that in F^ from fully coloured plants with coloured stigmas x dominant 



