R. P. Gregory 117 



Other experiments made with " Primrose Queen " definitely support 

 the view as to its constitution which is entailed by this hypothesis. 

 The results of Keeble and Pellew's experiments with the red-stemmed 

 "Snow King"' indicate that in certain cases the factors for colour may 

 be absent from the flower, though present in the stem, and consequently 

 that certain red-stemmed plants may have white flowers in the absence 

 of inhibition. On the other hand, the mode of inheritance of the full 

 colour in my crosses between coloured, red stem x " Snowdrift " suggests 

 that in certain other cases the factors for colour are common to the 

 whole plant, both stems and flowers. 



Doviinant white x Coloured, green stigma. The simplest cases illus- 

 trative of the operation of the factors which inhibit the development of 

 colour in the flower are those in which a dominant white is crossed 

 with a coloured form having green stigmas. The Fi in these cases is 

 white or tinged-white, the depth of the tinge depending, under uniform 

 conditions-, upon the intensity of the colour of the coloured parent, and 

 to some extent upon the particular race of dominant white used. The 

 F„ from this cross consists of whites, tinged whites and colours, all with 

 green stigmas. The numbers obtained are : 



Fi X coloured, 

 Fi X Self green stigma 



Number of White and 



F2 families Tinged white Coloured 



3 59 58 



Equality 



The experiment has been repeated iu a slightly different form by 

 crossing coloured plants with the F^ of (Dominant white x Recessive 

 white). The numbers obtained from these crosses are : 



1 Journ. Genetics, Vol. i. 1910, p. 1. 



2 The depth of the tinge is dependent upon the conditions under which the F^ is 

 grown, and its maximum development is only obtained by keeping the house as cold as 

 is possible without injury to the plants. At higher temperatures very little tinge is 

 developed, and the Fj from the cross of such an intense colour as " Crimson King " with 

 a dominant white is scarcely tinged. 



