178 Alfred J. Ewart : 



is under compression. The maximal total contraction will be 

 given at some intermediate point between commencing absorp- 

 tion and complete absorption and swelling. 



There may be two reasons for the greater contraction of 

 volume with swelling seeds as compared with the gelatine. Using; 

 equal volumes of barley, haricot beans and peas, the maximal 

 contraction obtained varied from 2.5 to 6 c.c, but in all cases 

 were greater than with gelatine. This would indicate absorption 

 pressures of 50 to 120 atmospheres. An organised colloid, like- 

 cellulose, may be capable of showing a higher absorption pres- 

 sure than an unorganised one like gelatine. In addition a certain, 

 amount of solution may take place in the seed as water is ab- 

 sorbed. Tamman^ has shown that a volume of a solution under 

 one atmosphere pressure expands when heated like a similar 

 volume of water under a constantly higher pressure, i.e., a solu- 

 tion has a high internal pressure due to the solute. This action 

 is a general one, independently of whether the solute is an- 

 electrolyte or a non-electrolyte. In other words, the minimum 

 volume temperature of water is lowered by the presence of a^ 

 solute. It follows, therefore, that as some of the food consti- 

 tuents of the seed begin to dissolve, the total volume may tend 

 to undergo a slight decrease as the result of the action of the 

 solute. There are, however, certain exceptions to this rule. For 

 instance, a mixture of ammonium chloride and water expands 

 on solution, so that a 6.85 per cent, solution has an increased' 

 volume of 0.266 c.c. (100.266 c.c. instead of 100 c.c.).^ Hence 

 it is impossible to say exactly what part may be played by dis- 

 solving solids in producing a contraction of the total volume. 



In addition, if cellulose obtained from a colloidal solution has- 

 the same composition as that in the cell-wall, the fact that it has- 

 a higher density may indicate that in penetrating the cell-wall' 

 the water molecules may partly enter empty intermicellar spaces,, 

 thus producing a contraction of total volume. It is at least evi- 

 dent that the changes of volume in a mixture of dry seeds and' 

 water are by no means simple phenomena, but are due to vari- 

 ous interacting, and in some cases antagonistic factors. 



I G. Tainnian, Ueber die Beziehunjren Zwischen den inueren Krafteri and Eigenshaften der 

 Losnnffen, Voss, Hamburg: and Leipzijr, 1907. 

 2.Happart, Bulletin Inst. Liejfe, 1903. 



