466 Mr. W. Stiles and Dr. F. Kidd. Position of the 



Discussion. 



From the experiments recorded in this paper, we may conclude that all the 

 salts, or one or other of their constituent ions, readily enter cells of potato 

 and carrot in all the concentrations employed. These two tissues show 

 markedly different properties, exosmosis of electrolytes taking place in potato 

 to such an extent as to mask the absorption when the electrical conductivity 

 method is used, whereas in carrot this exosmosis is apparently negligible. 

 For this reason, carrot is a much more suitable object for studying absorp- 

 tion of salts by the method employed than potato. Differences in regard to 

 the water relations of these two tissues have been previously recorded (13), 

 but it remains to be determined how far these different properties of the two 

 tissues in regard to water absorption and salt exosmosis are correlated. 



The substances employed fall broadly into two classes : those where the 

 absorption does not produce any obvious injurious effect in the concentra- 

 tions used, as in the case of sodium and potassium and calcium chlorides, and 

 those where toxic action results as with copper sulphate. This division is, 

 no doubt, arbitrary, for it is reasonable to suppose that these two classes are 

 connected by a whole series of substances intermediate in their toxic action. 



When toxic action takes place, this is accompanied by exosmosis in both 

 potato and carrot, the initial rate of exosmosis being greater the greater the 

 concentration of the external solution, as has previously been recorded (11). 



In the case of carrot tissue immersed in solutions of potassium, sodium, 

 and calcium chlorides, it is possible to follow the course of absorption by the 

 electrical conductivity method. It may be said, in general, that the absorp- 

 tion is more rapid at first, especially for the first hour or two, and then 

 gradually slows down until after 40 or 50 hours or more a condition of 

 equilibrium is approached. The rapid absorption during the first minutes is 

 particularly noticeable with the higher strengths of solutions (see the curves 

 for N/10 solutions in fig. 1). In some recent work, ritting(2) has concluded 

 that the permeability of the epidermal cells of the leaf of Bhoeo discolor as 

 measured by the rate of entrance of potassium nitrate diminishes with time, 

 or, in other words, that the rate of absorption of the salt decreases with time. 

 His method of measurement of salt intake is based on the rate of deplasmo- 

 lysis of the cells in solutions of the salt in question, so that only strong con- 

 centrations of the salt were employed. In a communication published while 

 this paper was being written, Troendle(14} has recorded the results of some 

 experiments on the absoiption by bean roots and epidermal cells of Acer 

 platanoides and Salix habylonica of salts in strong (hypertonic) solutions, the 

 plasmolytic method being employed also here. Troendle's results are similar 



