PAIRS OF CHARACTERS 129 



amount of water absorbed by a round pea in twenty- 

 four hours is about 80 per cent, of its weight when 

 dry. In other words its absorptive capacity is 80. It 

 does not absorb its own weight of water in twenty- 

 four hours. A wrinkled pea, on the other hand, 

 absorbs more than its own weight of water in twenty- 

 four hours. Its absorptive capacity is about 120. 



The cause of this difference is probably that, in 

 the case of the wrinkled pea, the whole of the sugar 

 is not converted into starch. In fact, the wrinkling 

 itself, which takes place during the ripening of the 

 seed, is probably due to this incomplete conversion 

 of the sugar into starch. All peas, wrinkled as well 

 as round, are round before they are dry ; that is, 

 in the state in which they are eaten. Cooks think 

 that all peas are round. It is only gardeners, who 

 sow or harvest the dry seed, who know the distinction 

 between round and wrinkled. Wrinkled peas wrinkle 

 because more water escapes from them than from 

 round peas; and more water escapes from them 

 because water can escape from a sugary solution 

 more easily than it can from the grains of starch. 

 The water is, so to speak, locked up in the solid 

 starch grain much more securely than it is in a solu- 

 tion of sugar. 



It is not possible — at any rate it would be very diffi- 

 cult — to measure the relative amounts of water given 

 off by round and by wrinkled peas during the process 

 of ripening. But what can be done is to measure 

 the converse of this process, namely, the relative 

 amounts of water taken up by round and wrinkled 

 J 



