_The normal characters: colour of cotyledons and seed-coats._ Culinary peas (_P. sativum_, omitting purple sorts) can primarily be classified on colour into two groups, yellow and green. In the green certain pigmentary matters persist in the ripe seed which disappear or are decomposed in the yellow as the seed ripens. But it may be observed 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 cotyledon 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 proportions 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 Sutton’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[64]. [64] Knowing my interest in this subject Professor Weldon was so good as to forward to me a series of his peas arranged to form a scale of colours and shapes, 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. There are some varieties which have cotyledons green and intermediate shading to greenish yellow, like _Stratagem_ quoted by Professor Weldon. Others have yellow and intermediate shading to yellowish green, such as McLean’s _Best of all_[65]. I am quite disposed to think there may be truly monomorphic varieties with cotyledons permanently of intermediate colour only, but so far I have not seen one[66]. The variety with greatest _irregularity_ (apart from regular dimorphism) in cotyledon-colour I have seen is a sample of “_mange-tout à rames, à grain vert_,” but it was a good deal injured by weevils (_Bruchus_), which always cause irregularity or change of colour.