io6 Dominant Whites [CH. v 



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

 reddish stem. The F z 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*. 



* In Stocks we have an unexpected result which has not yet been 

 reconciled with the conclusions based on the behaviour of these white 

 Primulas. Matthiola incana has flowers almost white, though on fading 

 they take on a purplish tinge. Undoubtedly the plant contains all the 

 elements of colour, for its embryos have the deep green colour characteristic 

 of purple-flowered types. We should therefore suppose that the white 

 flower was due to some factor suppressing the development of colour. In 

 that case it should be a dominant white, and when crossed with coloured 

 types we should expect J\ to have flowers white or nearly so. As a matter 

 of fact however J^ in all such crosses is coloured. At present no suggestion 

 has been made which accounts for the anomaly. 



