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TEXTBOOK OF PLANT PHYSIOLOGY 



If a salt with another cation than one connected with the pro- 

 teinate within the osmometer is taken, for instance KC1 instead of 

 NaCl, another correlation will be obtained. The cation of this 

 electrolyte introduced into the surrounding solution, in this case K, 

 will be attracted towards the interior of the membrane by the 

 anion of protein. The anion, on the contrary, will be forced out- 

 wards. Donnan illustrates this correlation by the following table: 



With a great abundance of colloidal ions within the osmometer, if 

 compared to the concentration of salts in the surrounding liquid, 

 for instance 100 : 1 in the last line of our table, the almost com- 

 plete disappearance of K (99 per cent of the original amount) from 

 the surrounding medium and its accumulation within the osmom- 

 eter may be observed. At the same time, the almost complete 

 "expulsion" of the CI ion from the osmometer is observed, in spite 

 of the fact that both ions pass readily through the membrane and 

 enter into no chemical reactions within the osmometer. 



In an analogous way may be explained the accumulation of dif- 

 ferent kinds of ions in the plant cells containing a considerable 

 amount of protein substances which show the properties of ampho- 

 lytes, that is, substances which act as weak acids and weak bases 

 and, therefore, are able to induce the accumulation of cations, as 

 well as of anions. As the composition of the colloidal substances 

 in the cells changes continually, quantitatively as well as quali- 

 tatively, however, the conditions of Donnan's equilibria prove 

 very complicated in them, and are still far from being sufficiently 

 understood. The protoplasm being impermeable not only to 

 colloids but also to many electrolytes, for instance to organic acids, 



