392 BOTANICAL GAZETTE [December 



is no increase at all. Three days in potassium or sodium will result 

 in an extraordinarily high critical plasmolytic concentration, which 

 will reach 0.5 M for a few cells, 0.6 M for the majority, and over 

 1.0M KNO3 for some of the cells. The critical plasmolytic con- 

 centration of calcium treated cells never exceeds 0.5 M. 



According to work on the permeability of protoplasm by the 

 electrical conductivity method, one would expect the two bivalent 

 elements strontium and barium to produce an effect on protoplasm 

 similar to that produced by the bivalent element calcium, if, as is 

 stated by Osterhout (6), all bivalent cations (Ca, Ba, Sr, etc.) 

 decrease permeability to a marked degree. Results obtained with 

 the bivalent ions strontium and barium, however, are contrary to 

 those of calcium. After twenty-four hours' treatment in 0.064 M. 

 SrCl 2 , there is a slight reduction in critical concentration of salt. 

 After forty-eight hours this reduction becomes pronounced, being 

 then 0.2 M as compared with a normal of 0.3 M KN0 3 . 



Critical concentration values expressed in figures do not impress 

 one with the change in osmotic value of the cell so forcibly as does 

 a visual demonstration. If leaves treated for about two days 

 (forty hours) in a 0.064 M SrCl 2 solution are plasmolyzed, together 

 with untreated leaves, with 0.3 M KN0 3 , and examined in half an 

 hour, numerous cells will be slightly plasmolyzed in the control 

 leaves, while in the strontium-treated leaves nearly every cell will 

 be prominently plasmolyzed. Although these results were obtained 

 in the great majority of cases, it is not always true that the decrease 

 in osmotic value of strontium-treated leaves is so evident. Cells of 

 different leaves, and especially of different lots of Elodea collected 

 at different times and in different localities, vary greatly in their 

 reaction to strontium. 



The most startling reduction in critical plasmolytic concentration 

 was observed in the case of barium chloride. A critical concentra- 

 tion value of plasmolyzing salt of o.n M was obtained with barium- 

 treated cells, a value far below the average normal and considerably 

 below the minimum value of 0.18 M ever found for a control leaf. 



More highly toxic to protoplasm than any of the ions so far 

 considered is copper. The copper ion was used in the form of 



