THE HYGROSCOPICITY OF SEEDS 181 



under ordinary air-conditions, the water of vitality ; and there 

 is the water that this air-dried material loses in the oven when 

 exposed to a temperature of 100 C. and subsequently regains 

 from the air, the water of hygroscopicity. Air-dried vegetable 

 material, whether living or dead, contains only the water of 

 hygroscopicity, which in these circumstances is one and the 

 same with the water-percentage. There is no room for any 

 more free water in a plant's economy than that which is 

 included in the water of vitality and the water of hygro- 

 scopicity. It is the water of hygroscopicity that we are 

 here concerned with, and we have just seen that in air-dried 

 vegetable substances this is the water that such materials lose 

 in the oven. Let us then determine how this principle applies 

 to seeds. 



But before we can apply this principle to seeds it is Thecor- 

 requisite to determine the correlative of the seed in its pre- [h^seed'with 

 resting and resting stages with other portions of the plant. othe . r 

 Manifestly the correlative of the living leaf and the living stem the plant, 

 is the large soft seed of the ripe fruit before the drying and 

 shrinking process begins. Manifestly also the correlative of 

 the dried-up leaf and stem is the same seed after it has com- 

 pleted its shrinking process and has entered upon the resting 

 stage. As far as their water-contents are concerned, there is 

 no difference between the resting seed and the dried-up leaf 

 and stem, all of them holding only the water of hygroscopicity, 

 which is driven off in the oven and subsequently regained from 

 the air. As far as vitality is concerned there is also no differ- 

 ence. We term the leaf dead and say that the vitality of the 

 seed is suspended. What is the difference ? There is room 

 for none. 



It is thus clear that the seed's hydratation acquires a new 

 significance when we allow the .discussion to centre around the 

 water of hygroscopicity and apply the principle of Berthelot. The logical 

 This principle raises the whole question of the necessity 

 of water for the resting seed, and the logical issue is the 

 denial of its necessity altogether. From this point of view see" 



