134 Swedes and Turnips [CH. 



tained that each kind of family was produced with regularity 

 as the consequence of a particular kind of union, the work 

 of bringing all these into one analytical scheme was only a 

 matter of time. Much still remains to be done before the 

 analysis will be complete for Stocks in general^ For 

 example, among the Brompton Stocks races occur which are 

 hoary though devoid of sap- colour, and as yet we are not 

 aware what condition or factor exists which there enables 

 the hoariness-factor to assert itself. 



In cases like these we get glimpses of the strict specific 

 rules which govern the genetics of pigmentation. In the 

 Sweet Pea again we have found that both variation in the 

 pollen-shape and in the structure of the standard petal are 

 closely related with the distribution of the factor which 

 turns the colouring matter purple. There is every hope 

 that in our further analyses these apparently trivial 

 phenomena will serve as indications of the underlying 

 processes. 



Apart however from these curious inter-relations be- 

 tween colours and structural peculiarities, there are several 

 remarkable specific phenomena to be seen in the genetic 

 behaviour of colours. Of these some examples may be 

 given as incentives to future experiment General rules 

 regarding colour-inheritance are scarcely to be expected as 

 yet, for very little is known of the pigments of either 

 animals or plants. Beyond the fact that albinism has always 

 been found to be recessive to colour in both animals and 

 plants no general proposition can be put forward with 

 confidence. We believe also that yellow chromoplast-colour 

 is always recessive to white or colourless chromoplast-colour, 

 though the cases studied are not numerous enough to justify 

 a general assertion. Stocks, Sweet Peas, Swedes and 

 Turnips, Verbascum, may be cited as plants following this 

 rule and no clear exception is yet known. 



Mr Arthur Sutton tells me it is well known that when 

 Swedes are being grown for seed, Turnips must not be 

 allowed to flower near them, but that in growing turnip- 

 seed, no injury is done by the presence of flowering Swedes. 

 The meaning of this is now clear. The Swedes are in 

 general yellow-fleshed, their colour being due to yellow 

 plastids. Turnips as a rule are white. If therefore the 



