46 STUDIES IN SEEDS AND FRUITS 



after their weight has been increased threefold, and seeds that fail 

 to germinate sometimes acquire 3^ times their original weight. 

 When we come to deal with the hygroscopicity of seeds 

 we shall be able to state precisely the lower value of the seed's 

 hydratation, that is to say, below the minimum required for 

 germination. This is the " hygroscopic maximum " (see 

 Chapter VII). 



Second, to Coming to the second kind of excessive swelling, we deal 



^enSg^r 6 ner e with seeds abnormally shrunken, when the excess of 

 abnormally water absorbed in the swelling process compensates for the 

 permeable excess lost in the shrinking stage. But it should be noted 

 that we are not here concerned with seeds so much shrunken 

 that they have lost their vitality, a fate that may befall 

 permeable and impermeable seeds alike, but with seeds that 

 still retain their germinating powers. Thus it comes about 

 that permeable seeds alone illustrate this type of excessive 

 absorption, since defective shrinking acts in different ways on 

 the swelling capacity of seeds, according to their permeable or 

 impermeable character in the resting state. If permeable, the 

 shrinking is too great, and the swelling is also excessive. If 

 impermeable, the shrinking is deficient and the swelling ratio 

 is much reduced. This is in accord with the compensatory 

 principle before established, that what the shrinking seed loses 

 the swelling seed gains. But it is important to notice that we 

 are here again brought face to face with the distinction between 

 permeable and impermeable seeds. 



Permeable seeds that are allowed to dry when detached 

 from the plant in the full-sized moist condition generally 

 shrink too much ; and as a rule they fail to germinate, absorb- 

 ing much more water in proportion to their weight than in 

 the case of the normal resting seed. Greatly shrivelled seeds 

 are, as is manifest, imperfectly developed, so that they scarcely 

 call for our attention. However, to illustrate this subject, 

 I give below my observations on the seeds of Canavalia 

 ensiformis in three conditions : excessively shrivelled, moderately 

 shrivelled, and normal. 



