390 BOTANICAL GAZETTE [December 



etc., which have an important bearing on permeability changes, 

 can be detected. 



The electrical conductivity method, while making quantitative 

 measurements possible, is subject to criticism because of the impossi- 

 bility of knowing whether the changes in resistance are actually 

 due to corresponding changes in permeability. There exists the 

 possibility that a change in conductivity may well result from a 

 diffusion of substance from the salt solution into the tissue, bringing 

 about changes in cell content of electrolytes without any change in 

 permeability. That this may be true is indicated by the rapidity 

 with which salts enter a cell in sufficient quantity to produce an 

 immediate change in the relative positions of the cell inclusions. 

 The writer has repeatedly observed a sudden aggregation of chloro- 

 plasts, before plasmolysis takes place, when a dilute solution of 

 KN0 3 i s added to an Elodea leaf. This immediate change in the 

 position of the chloroplasts on the addition of a salt can only mean 

 that there has been a very rapid entrance of the electrolyte into the 

 cell, with no increase in permeability sufficiently great to permit a 

 noticeable exosmosis of water. The whole problem of permeability 

 presents so many difficulties that at present we can only present the 

 data obtained from every possible method of attack. To restrict 

 ourselves to any one theory or any single method of investigation is 

 likely to lead to faulty conceptions. 



Leaves of Elodea served as material. All observations were 

 made on the superficial cells of the upper surface of the leaf. The 

 reagents used were potassium nitrate (KN0 3 ), potassium chloride 

 (KC1), sodium chloride(NaCl), calcium chloride (CaCl 2 ), barium 

 chloride (BaCl 2 ), copper hydroxide (Cu(OH) 2 ), and ethyl alcohol 

 (C 2 H 6 0). Spring water was used, the same in which the Elodea 

 plants were kept growing in the laboratory, and which in Geneva is 

 very pure. 



I. Reaction of protoplasm to some monovalent and 

 bivalent cations 



Experimental data 



Potassium nitrate was used as the plasmolyzing salt. The 

 critical plasmolytic values were determined by ascertaining the 



