206 PROTOPLASM 



excess of 6 or 7 atmospheres take up water from very dry soil. 

 Newton put cactus stems in a desiccator with sulphuric acid for 

 six months. In this atmosphere of nearly zero humidity, they 

 lost less than 10 per cent of their water. It is assumed that 

 imbibition forces held the water. Again it is impossible to say 

 with any degree of certainty whether osmotic or imbibition 

 forces are responsible. 



The following experiment is an interesting one in which osmotic 

 forces are pitted against imbibition ones : If a series of cubes of a 

 gel (say, 25 per cent gelatin), all of one size, are placed in sugar 

 solutions of different strengths, water passes from the gel to the 



Fig. 105. — Cubes of gelatin placed in solutions of sugar of different concentra- 

 tions. Left, low concentration; right, high concentration. 



solution, or vice versa, according to the concentration of the 

 surrounding sugar (Fig. 105). One cube in the series may main- 

 tain its original size; the others become larger because of the 

 greater imbibition pressure of the gel, or smaller because of the 

 greater osmotic pressure of the surrounding solutions. 



The imbibition-vs.-osmosis controversy when applied to proto- 

 plasm brings up an old discussion on the miscibility of protoplasm 

 in water. 



Imbibition and Solution. — In attempting to distinguish 

 between osmosis and imbibition as the mechanism by means of 

 which protoplasm takes up water, and therefore at the same time 

 deciding whether protoplasm is miscible or immiscible in water, 

 we may simply be again involving ourselves in a futile polemic 

 similar to the attempt to distinguish between osmosis and imbi- 

 bition. There is, however, one very important and fundamental 

 question involved in the distinction between imbibition and solu- 

 tion; it is a question of structure. All agree that protoplasm 

 takes up water with avidity; but does it do so osmotically. 



