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



experiments carried out contemporaneously on discs cut at the same time and 

 thoroughly mixed. 



As it seems almost certain that the rates of absorption and exosmosis 

 must be influenced by temperature, the experiments were all carried out in a 

 thermostat at 20° C, and the conductivity measurements were made at the 

 same temperature by means of Kohlrausch's method. A dipping electrode 

 was used, wliich was placed direct into the experimental solutions. 



A difficulty arises in such work owing to the formation of diffusion 

 gradients between the body of the solution and the absorbing surface. The 

 difficulty is to be overcome by breaking down the diffusion gradients over 

 the absorbing surface. This can be effected by shaking the bottles, and 

 accordingly this was done in our experiments. The shaker was of the usual 

 trolley pattern and was worked by an electric motor. 



Expcrimevital Results. 



(a) Potassium, Sodimn, and Calcium Chlorides {Carrot). — The results 

 obtained with carrot immersed in solutions of these salts in a number of 

 concentrations ranging from IST/SOOO to N/IO are shown in Tables I to III. 

 In each case a control in which the tissue was immersed in distilled water 

 was subjected to the same conditions as the experimental solutions. It will 

 be observed that in all cases, except those of the most dilute solutions used, 

 the conductivity of the external solutions progressively decreases, and 

 in the case of the weakest solutions of the various salts the rise in 

 conductivity is less than in the case of distilled water. The results are 

 shown graphically in fig. 1, where the initial conductivities are taken as zero. 

 We may assume with propriety that the decrease in conductivity represents 

 approximately the diflerence between the absorption of the salt by the tissue 

 and exosmosis from the tissue. Hence the ofdinates between the curves for 

 distilled water and the salt solution can be assumed as approximately pro- 

 portional to the actual amount of salt ions absorbed, or that at any rate they 

 represent minimum values for absorption.* 



* Possible causes making for a fall of conductivity in the external salt solutions not 

 due to absorption and which would therefore make the values obtained greater than the 

 true numbers for absorption : — 



(1) Reactions between the exudate and the external solutions by which non-ionised 



molecules are produced. The possibility of such reactions appears to be ruled 

 out as a serious source of error when we have regard to the dilution of some 

 of the solutions and the magnitude of the decreases with higher concentrations, 

 and further when the results that were obtained when the discs were sub- 

 sequently returned to distilled water are considered. 



(2) The action of sugars and other non-ionised substances in the exudate in reducing 



