K.— BOTANY 225 



solution of sodium chloride is replaced by ions of calcium, potassium and 

 magnesium which diffuse out of the tissue. Although to be regarded as 

 only preliminary in character, they indicate that an exchange of ions 

 between tissue and external solution can occur in connection with excess 

 absorption of one ion of a salt. 



Even more strikingly at variance with the earlier view of solute 

 absorption by plant cells is the phenomenon which is now generally 

 described, not altogether happily, I think, as accumulation. In 1919 

 F. Kidd and I showed that when thin slices of storage tissues, carrot and 

 potato, were placed in solutions of various salts in different concentrations, 

 absorption took place towards a condition of equilibrium which is not 

 that of equality of concentration inside and outside the cell, but which 

 depends on the concentration of the salt. With dilute solutions the 

 concentration attained inside the cell may be many times that of the 

 solution outside, while in concentrated solutions the reverse is the case 

 and the concentration of the salt inside, even after 48 hours' immersion 

 of the tissue in the solution, may be very much less than that outside. 

 Thus, while more salt is actually absorbed from a stronger solution than 

 from a weaker one, the absorption relative to the concentration is less, 

 both as regards rate and total amount, from a stronger than from a weaker 

 solution. 



These observations by Kidd and myself, though definitely establishing 

 on broad lines the relationship between concentration of salt and absorp- 

 tion, did not pretend to provide more than approximate quantitative 

 data. Thus we found that the relationship between concentration of 

 salt and absorption was much the same as it would have been if the salt 

 were adsorbed by an adsorbent within the cell. It is easy to suggest 

 that a first stage in the absorption of salts by plant cells is the adsorption 

 of the ions of the salt by some constituent or constituents of the proto- 

 plasm. While I have pointed out the similarity of the absorption of 

 salts by plant cells with an adsorption phenomenon, I have more than 

 once stressed the point that this similarity is in itself not sufficient to 

 justify the advocacy of an adsorption theory of salt absorption. Yet it 

 must be admitted that later work by more exact methods has only served 

 to confirm the approximate similarity of the relationship between salt 

 absorption and adsorption. Reference in this connection may be made 

 to the work of Laine on the absorption of manganese and thallium by 

 roots of Phaseolus multiflorus, as well as to observations of my own on 

 the absorption of sodium chloride by carrot root. Further, if the proto- 

 plasm contains adsorbents of the ions presented to it, then adsorption 

 must take place if conditions demand it. 



Before leaving this question for the moment I would like to point out 

 that it is obvious that if the similarity between the relationship of salt 

 absorption to concentration and the adsorption equation is more than a 

 coincidence, then adsorption can only be the first stage in this absorption, 

 at any rate by actively growing tissues in which the absorbed ions must 

 be transferred elsewhere. Again, the adsorbing material one would 

 expect to be present in the protoplasm, whereas a number of more recent 

 observations by various investigators indicate that there is actually an 



