﻿1903] CURRENT LITERATURE 373 



salt occurs up to a certain limits and then ceases. The limit of absorption 

 seems to be determined by the concentration of the external solution, more 

 solute being absorbed the more concentrated the latter is; but the process 

 never continues until equality of concentration within and without the cells is 

 even approached. This rule does not hold for sea-water, however, in which 

 the alga accumulates NaNOg to a concentration of 0.02 per cent., although 

 this medium contains only minute traces of the salt. 



Further than this, if the alga be placed for a day in a 5 per cent, solution 

 of NaNOa, and then be transferred to a 3 per cent, solution of the same salt, 

 absorption occurs in the stronger solution until the limit for that solution is 

 reached, but after the transfer NaNO^ is lost by the cells until the internal 

 concentration has fallen to the limit for the weaker solution. Since the limit 

 of absorption, even for the stronger solution, lies far below 3 per cent., this 

 outward passage of the salt takes place from a lower to a higher concentra- 

 tion, and therefore in the direction opposite to that in which it should move 

 according to the principles of diffusion of solutes. 



The cells contain a large amount of NaCl when taken from sea-water. 

 This salt diffuses outward in NaNOs solutions until a certain minimum of 

 internal concentration of NaCl is reached, and this minimum limit is lower, 

 the weaker is the external solution of the other salt. The internal concentra- 

 tion of the chlorid never even approaches its external concentration ; thus 

 this stoppage of outward diffusion of NaCl is parallel with the cessation of 

 absorption in the case of the nitrate. There is no evidence of accumulation 

 of either salt in the protoplasm, neither is the solubility of either salt different 

 in the cell sap from its solubility in sea-water. 



Further, if Codium plants be placed in a solution containing both NaNOa 

 and NaCl (the latter salt being always of the same concentration, while the 

 former is varied in amount), diffusion of the chlorid takes place either out- 

 ward or inward according to the concentration of the nitrate without. Thus, 

 if the concentration of NaNO^ is i per cent, the plant loses chlorid ; if it is 2 or 

 3 per cent., chlorid is absorbed, and this diffusion occurs whether the chlorid 

 is moving with or against its diffusion tension. The usual principles of diffu- 

 sion seem not to apply here at all. 



This is the first unquestionable evidence that the living membrane in 

 plants can overcome the osmotic pressure of a solute and cause its movement 

 from lower to higher concentration. The phenomenon has been known in 

 animals, however. The paper contains a large amount of suggestive theo- 

 retical discussion. — Burton E. Livingston. 



