io6 Dominant Whites [ch. v 



stemmed recessive whites, give a white-flowered F^ with a 

 reddish stem. The F^ generation from this cross has 

 contained a small number of plants with coloured flowers, 

 but the ratio has not yet been determined. There is an 

 obvious general agreement between this case and that 

 described in fowls, and we may feel fairly sure that the 

 Primula colours similarly depend on two colour-factors, and 

 that the absence of colour in the dominant whites is due to 

 the super-imposition of a third factor^. 



* The white-flowered variety of Matthiola incana (Stock) is as regards 

 its genetic behaviour, a coloured form. Moreover its flowers tinge on 

 fading and its embryos have the deep green colour characteristic of purple- 

 flowered types. Crossed with a self-coloured type it gives ^jwith purple 

 flowers. Clearly therefore it is not, as some of the tinged forms of Pritmda 

 Sinensis are, a dominant white. Miss Wheldale has suggested with some 

 plausibility that the white M, incana is comparable with the picotee types 

 of Sweet Peas. 



