114 SOME RECENT RESEARCHES IN PLANT PHYSIOLOGY 



The two following experiments are described as typical 

 of a number which were performed to determine the rates 

 of penetration of various ions: 



A cylinder of Laminaria discs was found to maintain a 

 resistance of 1,100 ohms unchanged for four hours when 

 in sea-water. It was then transferred to 0'52 N sodium 

 chloride, which has the same conductivity as sea-water at 

 the same temperature. Each disc was carefully rinsed 

 and replaced in the clamp ; such manipulation, when carried 

 out in sea- water, only altered the reading slightly. 



Immersion for five minutes in 0-52 N sodium chloride 

 sufficed to lower the resistance to 1,000 ohms; after ten 

 minutes it had fallen to 890, after fifteen to 780, after 

 sixty to 420 ohms. This fall continued till a resistance of 

 320 ohms was reached, at which point a constant reading 

 was obtained. Thus at the end the tissue had practically 

 the same conductivity as sea-water. When replaced in 

 sea-water it failed to recover any of its resistance, even 

 when allowed to stand for several days. As the sodium 

 chloride was nearly isotonic with sea-water, none of the 

 observed toxic action could have been due to osmotic 

 effects. 



It was shown, however, that replacement in sea-water, 

 at the stage at which the resistance of the tissue had fallen 

 only about 100 ohms below its original value, always 

 resulted in complete recovery, the resistance rising to the 

 initial figure. 



Thus the rapid alteration in permeability brought about 

 by sodium chloride solutions is reversible when not per- 

 mitted to proceed too far. 



When living tissue is placed in a solution of calcium 

 chloride having the same conductivity as sea-water, instead 

 of decreasing, the resistance rises in a very marked manner. 

 Thus it may increase from 1,100 ohms to a maximum of 



