PAIRS OF CHARACTERS 131 



substance ; the wrinkled pea an insufficient dose. 

 Something is absent from the wrinkled pea which is 

 present to the full in the round. 



It will be gathered from the above that the 

 object of our inquiries is not merely to analyse an 

 organism into its component characters and to leave 

 the matter there, but to push deeper and obtain 

 some insight into the fundamental nature of these 

 characters. The reader will do well to lay it to heart 

 that in the case of the pair of characters, roundness 

 and wrinkledness, which Mendel placed first on his 

 list of the seven with which he experimented, we are 

 at present only on the threshold of an investigation 

 of the true nature of the characters themselves. 



The application of the presence and absence 

 hypothesis to the other pair of cotyledon characters 

 will now be considered. The two characters which 

 meet the eye are yellow and green. But the matter 

 is not so simple as this. Mr. 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 kind become yellow as they ripen ; the green 



