182 Plant-Breeding 



tion of sugar left over after ripening, and, consequently, 

 in the last resort due to the absence of that which completes 

 the conversion of the sugar into starch or, at any rate, 

 to an insufficiency in the quantity of that substance, 

 whatever it is. The round pea has the full share of this 

 substance, the wrinkled pea an insufficient one. Some- 

 thing is absent from the wrinkled which is fully present 

 in the round. 



The same author applies the presence-and-absence 

 hypothesis to another pair of characters in peas, the 

 color of the cotyledons. The two characters which meet 

 the eye are yellow and green. But the matter is ' not 

 so simple as this. Bunyard has shown that there is a 

 yellow and a green pigment both in the yellow and in 

 the green cotyledon. When both are present at' 

 the same time, as in the ripe but still moist pea, 

 the green masks the yellow. All peas, both yellow 

 and green varieties, are green when they are eaten. 

 Just as cooks think that all peas -are round, so they 

 think that all peas are green. It is only gardeners who 

 sow and harvest them who know the distinction between 

 yellow and green. 



The ripe but still moist cotyledons of both yellow- and 

 green-seeded varieties are, therefore, green. The yellow 

 kinds become yellow as they ripen ; the green do not 

 change color during this process. The yellowing of the 

 former is brought about by the gradual fading and dis- 

 appearance of the green pigment, which thus leaves the 

 yellow pigment (which is present in both kinds) exposed. 

 The successive stages in the fading of the green can be 

 easily observed. The simultaneous presence of both 



