CONDUCTIVITY AND PERMEABILITY 215 



Tliis harmonizes with the results obtained with Laminaria. 



Direct tests of the sap were made by determin- 

 ing N0 3 , since it was found that the cells normally 

 give tests for Na and Ca. The method employed was not 

 sensitive enough to detect N0 3 in the sap of the control 

 cells under any circumstances, so that if a test was 

 obtained after exposure to a solution containing N0 3 , it 

 must have been due to penetration from without. The 

 sap was tested by placing it on a glass slide, adding a 

 drop of a solution of nitron in 10% acetic acid, and observ- 

 ing it under the microscope. If NO 3 is present, it may be 

 recognized by the formation of characteristic crystals. 



Cells kept for 24 hours in 100 c.c. NaN0 3 0.05 M + 10 

 c.c. Ca (N0 3 ) 2 0.05 M gave no test, which shows conclu- 

 sively that the method is safe as far as contamination by 

 NO 3 on the surface is concerned. After 48 hours a test 

 was obtained. As the cells continued to live in this solu- 

 tion for 3 weeks (at which time the experiment was 

 discontinued) and as they appeared normal in every 

 way, it is evident that the penetration was not the result 

 of injury. 



It is probable that in 24 hours some N0 3 penetrated 

 which was not revealed by the test. This, however, is 

 of no significance in the present investigation which does 

 not aim to determine the absolute amount of penetration, 

 but merely to compare the relative penetration in bal- 

 anced and unbalanced solutions. 



The results of such a comparison are very striking. 

 After 3 hours in NaN0 3 0.05 M a good test was obtained. 

 The cells had lost some of their turgidity ; if left in the 

 the solution of NaN0 3 or if transferred to tap water they 

 subsequently lost all their turgidity, indicating death. 

 It is therefore evident that this rapid penetration was 

 accompanied by injury. Similar results were obtained 

 by Mrs. Brooks (1922) with Li, Ba, and Sr. 



