PERMEABILITY OF PLANT CELLS 



139 



except only that when a cell is injured by the salt a, contraction 

 (due to false plasmolysis) may take place. But as the fall in 

 resistance is already great before any such contraction begins 

 and as the contraction is in any case too small to account for 

 more than a small per cent of the decrease in resistance it may be 

 regarded as at best a secondary factor which is absent until the 

 resistance has reached a low point and which is almost negligible 

 beyond that point. 



It might be supposed that the change in resistance is due to 

 causes which operate in the interior of the cell rather than in the 

 plasma membrane, but this is opposed to a variety of evidence 

 which can not be discussed here. 



All of the results which the writer obtained by plasmolysis 

 were corroborated in detail by the use of the electrical method. 

 This complete agreement of the results of the two methods fur- 

 nishes the most conclusive proof of their correctness. 



The objection has been made to the plasmolytic method that 

 the behavdor of the cells in hypertonic' solutions may not be the 

 same as in solutions to which they are accustomed. In order to 

 test this matter experiments were made by the electrical method, 

 employing solutions which were strong enough to produce 

 plasmolysis. The alterations of permeabiUty which are produced 

 by various salts are, of course, more rapid the higher the concen- 

 tration, but the relative penetration of various salts and the action 

 of antagonistic salts remains about the same. There is therefore 

 no essential difference in behavior, and it is clear that this objec- 

 tion to the plasmolytic method is unfounded. Incidentally these 

 experiments proved that breaking the protoplasmic connections 

 between the cells (by plasmolysis) does not alter the character of 

 the results. 



The electrical method enables us to follow from moment to 

 moment the changes in permeability of a given piece of tissue with 

 such accuracy that it gives curves which are comparable in 

 regularity with those obtained in purely physical experiments. 

 In these and other respects it is much superior to the plasmolytic 

 method for quantitative purposes and by its use the writer has 



