1923] SEIFRIZ— SALTS 39I 



concentration of salt which would plasmolyze 50 per cent of the 

 cells of a leaf in one-half hour. Owing to the rapidity with which 

 the salt enters a normal protoplast, as is evident from the immediate 

 aggregation of the chloroplasts, it was deemed best to shorten the 

 time of application of the plasmolyzing salt as much as possible. 

 The concentration of potassium nitrate which is isosmotic with the 

 contents of the average normal epidermal cell of an Elodea leaf, 

 that is, the critical plasmolytic concentration, is 0.3 M. Unless 

 otherwise stated, this value is used for comparison. Since, however, 

 the critical plasmolytic concentration of untreated cells varies con- 

 siderably (it may be as low as 0.2 M and as high as 0.5 M KN0 3 ), it 

 is highly important that the critical plasmolytic concentration of 

 control leaves be determined in every experiment, and that these 

 control leaves come from the same general region of the same shoot 

 of Elodea. 



Isosmotic concentrations of salts were used for treating the 

 Elodea leaves in the case of potassium nitrate, sodium chloride, and 

 calcium chloride. Lower concentrations of strontium chloride and 

 barium chloride were ultimately employed, owing to the greater 

 toxicity of these two salts. The following concentrations of solu- 

 tions were used : KN0 3 , o. 1 28 M, being the maximum concentration 

 of this salt which will not plasmolyze a normal cell, no matter how 

 long the time of treatment; NaCl, 0.128 M; CaCL, 0.128 M; 

 SrCL, 0.064 M; and BaCl 2 , 0.064 M. 



Changes in osmotic value of cell. — Brief treatment, up to 

 eighteen hours, in potassium nitrate, sodium chloride, and calcium 

 chloride produces no change in the osmotic value of the cell which 

 can consistently be determined by changes in the critical concentra- 

 tion of the plasmolyzing salt. Longer treatment in all three salts 

 results in a gradual increase in osmotic pressure of the cell. This 

 increase is much more pronounced in the case of the two monovalent 

 ions, potassium and sodium, than it is in the case of the bivalent 

 ion calcium. Two days in either potassium nitrate or sodium 

 chloride will usually result in a critical plasmolytic concentration 

 of 0.4 M or 0.5 M, as compared with a normal of 0.3 M. In cal- 

 cium chloride prolonged treatment seldom results in a critical 

 plasmolytic concentration of more than 0.4 M, and sometimes there 



