THE HYGROSCOPICITY OF SEEDS 185 



of several physicists show, it can retain its germinative powers 

 after being long in conditions completely water-free. I would 

 assume that in all experiments where vital processes have been 

 detected in resting seeds the drying process was incomplete. 

 The indications of the balance are that the permeable resting 

 seed, when it has attained a stable weight varying only about 

 a mean in response to the hygrometric changes of the air, 

 has no use for the water it contains ; and we may infer the 

 same for the impermeable seed with its diminished water- 

 contents. ,The water of hygroscopicity which the resting 

 seed alone retains is, as we have seen in the previous chapter, 

 quite insufficient to induce germination. That it is^ necessary 

 for the preservation of the germinative powers is negatived 

 by the fact that when we have exposed the seed for hours 

 in a broken condition to a temperature of 100° to 110° C. it 

 gains back from the air in the course of a week or two all 

 the water it lost in the oven, and in the case of impermeable 

 seeds considerably more. As a dead seed, therefore, it holds 

 at least as much water as it does when preserving its germin- 

 ative capacity. The water of hygroscopicity belongs to a 

 plant-tissue, whether living or dead, and this is the only free 

 water that the resting seed contains. 



SUMMARY 



(i) The water of hygroscopicity becomes the central point of the 

 discussion, and it is shown that there is no room for any more water 

 in a plant's economy than that which is included in the water which 

 the living tissue loses during natural drying, the water of vitalityj and 

 the water which such air-dried material loses in the oven and subse- 

 quently regains from the air, the water of hygroscopicity. Such are 

 the indications of the balance as interpreted by the principle of 

 Berthelot. 



(2) In comparing the water-contents of the leaf, the fruit, and the 

 seed, it is pointed out that just as they are all comparable in the living 

 condition, so they can be compared in the natural air-dried state, the 

 withered leaf with the dried-up fruit-case, and both of them with the 

 normal resting seed. All of them are inert and lifeless, and if we wish 



