54 STUDIES IN SEEDS AND FRUITS 



seeds, such as distinctions in size and weight (p. 39), the albuminous 

 or exalbuminous character of seeds (p. 39), differences in the propor- 

 tional weight of the seed-coats (p. 40), the difference in the types of 

 fruits, as between berries and legumes (p. 41), etc., it is inferred that 

 there is much which theSe distinctions will not explain (p. 41). 



(17) Appeal is then made to the unusual deviations in the swelling 

 capacity of seeds of the same species, with the hope of finding a clue to 

 the origin of the great contrasts in this respect presented by the seeds 

 of different plants (p. 42). 



(18) In the first place, cases of excessive swelling in normal resting 

 seeds are discussed, both of the permeable and impermeable types ; and 

 it is pointed out that it is possible to distinguish between 



(a) The minimum amount of water required for germination as 



shown in laboratory experiments ; 



(b) The average amount of water that under natural conditions 



seeds absorb when swelling for germination ; 



(c) The maximum amount of water that seeds can absorb to 



produce saturation, the seed continuing to take up water 

 long after it has failed to germinate (pp. 43-45). 



(19) In the next place, reference is made to the case of excessive swell- 

 ing in abnormally shrunken resting seeds where the absorbing process 

 is compensatory, the unusual loss of water in the shrinking process 

 being thus supplied. But such seeds, whether in the normal condition 

 permeable or impermeable, have lost their germinative powers, and as 

 such have no concern for us here. Seeds that shrivel much, absorb 

 much, but do not as a rule propagate the species. This is usually the 

 fate of seeds that are removed from the green pod in the soft, full- 

 grown pre-resting state before shrinking has begun. But with imper- 

 meable seeds it sometimes happens that such seeds shrink less when 

 allowed to go through the shrinking process detached from the plant 

 than when left undisturbed in the pod. If we wait until shrinking 

 has just begun before detaching the seed from the plant, this deficiency 

 in the shrinkage is the rule. Such seeds retain their germinative 

 powers, but their shrinking has been deficient ; and, according to the 

 compensatory principle that what the shrinking 'seed loses the swelling 

 seed gains, their capacity of absorbing water for germination is propor- 

 tionately reduced. They are larger and heavier than the normal 

 impermeable seeds, and take up water easily (p. 46). 



(20) When, therefore, we come to appeal to cases of unusual diminu- 

 tion of the swelling capacity in resting seeds, we find that examples are 

 only supplied by abnormal impermeable seeds. Here the shrinking 

 process is incomplete, and in consequence less water is required for 

 germination than in the normal resting seed. This unexpected 

 contrast between the behaviour of permeable and impermeable seeds when 



