Principles of Heredity 121 



that the "green" class itself is treated as of two 

 divisions, green and blue. In the seedsmen's lists the 

 classification is made on the external appearance of the 

 seed, without regard to whether the colour is due to the 

 seed-coat, the cotyledons, or both. As a rule perhaps 

 yellow coats contain yellow cotyledons, and green coats 

 green cotyledons, though yellow cotyledons in green coats 

 are common, e.g. Gradus, of which the cotyledons are yellow 

 while the seed-coats are about as often green as yellow (or 

 " white," as it is called technically). Those called "blue" 

 consist mostly of seeds which have green cotyledons seen 

 through transparent skins, or yellow cotyledons combined 

 with green skins. The skins may be roughly classified into 

 thin and transparent, or thick and generally at some stage 

 pigmented. In numerous varieties the colour of the coty- 

 ledon is wholly yellow, or wholly green. Next there are 

 many varieties which are constant in habit and other 

 properties but have seeds belonging to these two colour 

 categories in various proportions. How far these pro- 

 portions are known to be constant I cannot ascertain. 



Of such varieties showing mixture of cotyledon-colours 

 nearly all can be described as dimorphic in colour. For 

 example in Button's Nonpareil Marrowfat the cotyledons 

 are almost always either yellow or green, with some piebalds, 

 and the colours of the seed-coats are scarcely less distinctly 

 dimorphic. In some varieties which exist in both colours 

 intermediates are so common that one cannot assert any 

 regular dimorphism*. 



* Knowing my interest in this subject Professor Weldon was 

 so good as to forward to me a series of bis peas arranged to 

 form a scale of colours and sbapes, as represented in his Plate I. 

 I have no doubt that the use of such colour-scales will much facilitate 

 future study of these problems. 



