CHAPTER VIII 



HEREDITY OF COLOUR— continued. 



Various Specific Phenomena in Colour-Inheritance. Re- 

 lation of Colour to Hoariness in Stocks. Miscellaneous 

 Cases. Colottr of a Special Part controlling that of 

 other Parts. — Sum7na7y and Discussion. — Subtraction- 

 Stages. 



Again and again in tracing the genetic properties of 

 colours in animals and plants we encounter the phenomenon 

 of a specific connection between certain colours and their 

 modes of hereditary transmission on the one hand, and 

 various apparently distinct physiological properties on the 

 other. Colour, which S3^stematists have often spoken of as 

 one of the superficial or impermanent properties of organ- 

 isms, seems thus to be bound up with fundamental pheno- 

 mena of chemical economy. To treat this part of genetics 

 with any fulness is not yet possible. As an illustration may 

 be mentioned the curious result discovered by Miss Saunders 

 in Mat thio la, using the varieties known as ''ten-week Stocks." 

 These may be either ''hoary," viz. covered with branching 

 hairs forming a tomentum, or glabrous and destitute of 

 hairs. When the hoary are crossed with the glabrous, 

 hoariness is an ordinary dominant, giving 3 hoary : i 

 glabrous in /^. 



But when certain glabrous strains are crossed together 

 the P^ form is hoa^y, reverting to the primitive type. This 

 reversion never occurs when any of the many red or purple 

 varieties are crossed together, but is universal when any of 

 them are crossed with either the white or the cream-coloured 

 glabrous strains. The purples and reds owe their colours 

 to the presence of coloured sap. This coloured sap is not 

 present in the whites, nor in the creams, whose colour is 

 due to the existence of yellow plastids in the cells of their 

 petals. 



