Jan. 3,1921 Amount of Unfree Water Caused by Seeds 593 



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it is considered that this relatively large depression is obtained in a ratio 

 of 1 of seeds to 2 of water (10 gm. of seeds and 20 cc. of water), then it can 

 be imagined what the depression must be at a very low moisture content. 

 It really must be large. In the ratio given here it varies from 3.375 at- 

 mospheres in wheat to 13.336 in speckled wax beans. The great attrac- 

 tion that seeds possess for water and their ability to abstract it from soils 

 even down to the point of air-dryness must be due, therefore, partly, if 

 not largely, to their great osmotic pressure caused by their high content 

 of easily water-soluble material. 



No experimental work was performed to prove definitely the nature of 

 the material in the seeds which went into solution to cause such great 

 depression. But it appears to be largely water-soluble proteins such as 

 albumins and probably also some of the mineral bases. It can not be 

 starch, which is the most abundant constituent in the seeds, because 

 that is very insoluble in water. A test showed, for instance, that 10 

 gm. of starch in the pure form in 20 cc. of water had a depression of only 

 0.025 ° C. Sugar, of course, which is soluble, is not supposed to be found 

 in dry seeds. Furthermore, to give the high depression obtained, there 

 has to be present a very large amount of sugar, because as it is well known 

 that this class of material does not dissociate. All evidences, therefore, 

 point to the proteins as the main class of constituents in the seeds which 

 produced such high depressions in the freezing point when dry seeds in 

 the powdered form were mixed with water. 



SUMMARY 



Seeds cause part of the water which they absorb to become unfree, as 

 is indicated by its refusal to freeze. 



The dilatometer method is a convenient and appropriate method for 

 measuring the magnitude of this unfree water in seeds. 



The amount of water that seeds cause to become unfree is very large, 

 varying from 25.05 per cent in broom corn to 76.76 per cent in black 

 soybeans, based on the air-dry weight of seeds. Repeated freezing and 

 thawing tends to diminish considerably the amount of unfree water, espe- 

 cially in some seeds. 



Dry seeds contain a large amount of water-soluble material, as is evi- 

 denced by the high freezing-point depression. When 10-gm. portions of 

 seed flour are mixed with 20 cc. of water and the mixture is allowed to 

 stand for about 40 minutes or less, the freezing-point depression varies 

 from 0.280 C. in wheat to i'.i8o° in speckled wax beans. At very low 

 moisture content the magnitude of this depression must be very great. 

 The magnitude of the osmotic pressure must also be correspondingly very 

 great. 



The great power that seeds possess to absorb water and to abstract 

 it from the soil is partly if not largely due to their tremendous internal 

 osmotic pressure. 



