54 MENDELISM CHAP. 



and yet the visible result will be nothing but albinos. 

 Under the mask of albinism is all the while occurring that 

 segregation of the different colour factors which would 

 result in all the varieties of coloured forms, if only the 

 essential factor for colour development were present. 

 But put in the developer by crossing with a pure coloured 

 form and their variety of constitution can then at last 

 become manifest. 



So far we have dealt with cases in which the production 

 of a character is dependent upon the interaction of two 

 factors. But it may be that some characters require the 

 simultaneous presence of a greater number of factors for 

 their manifestation, and the experiments of Miss Saunders 

 have shown that there is a character in stocks which is un- 

 able to appear except through the interaction of three 

 distinct factors. Coloured stocks may be either hoary, 

 with the leaves and stem covered by small hairs, or they 

 may lack the hairy covering, in which case they are 

 termed glabrous. Hoariness is dominant to glabrousness ; 

 that is to say, there is a definite factor which can turn the 

 glabrous into a hoary plant when it is present. But in 

 families where coloured and white stocks occur the white 

 are always glabrous, while the coloured plants may or may 

 not be hoary. Now colour in the stock as in the sweet 

 pea has been proved to be dependent upon the interaction 

 of two separate factors. Hence hoariness depends upon 

 three separate factors, and a stock cannot be hoary unless 



