106 Experiments with Primula sinensis 



development of colour in the flower^ It has recently become clear 

 that this inhibition is due to the action of two separate components, 

 each of which has its own localized effect. The one component is 

 present in the majority of the races which have coloured flowers, in the 

 form of a factor which prevents the development of coloured sap in the 

 ovary, style and stigma, and gives the green stigma. The second factor, 

 on the other hand, affects only the peripheral parts of the corolla, and 

 in the absence of its fellow, gives rise, in fully coloured forms, to the 

 characteristic "Duchess" type of flower (Plate XXXI, figs. 27, 28), in 

 which coloured sap occurs only in the gynoecium and in the flushed eye 

 of the corolla^ In the pale colours the stigma is only faintly coloured, 

 and the presence of coloured sap can be most easily detected in the 

 placenta and ovules. The recessive green stigma (which corresponds 

 with the recessive white flower, and is green through the absence of 

 colour and not from its inhibition) has been recognized experimentally 

 in F^ plants fi-om the crosses of "Snowdrift" with "Crimson King." 

 The factors for inhibition may of course be present in plants which are 

 devoid of the factors for colour ; thus the green stigma of " Snowdrift " 

 is of the dominant kind, and other green-stemmed whites have been 

 met with, which possess both the factors for inhibition. 



Plants which contain the factors for colour and are heterozygous for 

 the inhibiting factors have tinged white flowers with green stigmas, the 

 depth of the tinge varying with the intensity of the underlying colour 

 (Plate XXXI, figs. 21, 24—26, 32). A heterozygous form of '•' Duchess " 

 is represented in "Sir Red vers Buller" (Plate XXXI, fig. 29), and various 

 other forms, depending on the presence or absence of the magenta and 

 other factors epistatic to colour, exist (figs. 30, 31). In all of them the 

 peripheral part of the corolla is tinged to a greater or less degree, and 

 the full colour is only developed immediately around the eye. 



One other character of flower-colour should be mentioned here. In 

 certain varieties there occur spots of deep colour on the petals just 

 external to the eye (Plate XXXI, figs. 50, 51). The inheritance of this 

 character is, in itself, simple ; but the full development of the spots is 

 limited by the operation of other factors^. Thus, the deep spots are 



1 In certain races belonging to this class an occasional splash or stripe of colour may 

 often be observed, sometimes in only one or two, sometimes in many of the flowers. 



2 The flush rouud the eye is often only faint, especially in flowers of the stellata 

 variety. The flush is an independent character limited to plants with red stigmas (see 

 p. 120). 



'^ Bateson, Mendel's Principles of Heredity, Camb. Univ. Press, 1909, p. 138. 



