FACTORS AFFECTING SALT ABSORPTION 



59 



total salt concentration and may therefore enhance rubidium 

 absorption, thus offsetting some or all of the depressive effect of the 

 competing cation. (Sutchffe, 1959). 



Alkali cations do not compete with one another on equal terms 

 and potassium absorption, for example, is not usually as strongly 



3-Or 



2-0 



(m equiv.L) 

 25 



0-2 0-4 



l/[Rb*] 



0-6 



3-0 



> 2-0 



0-2 0-4 



i/[Rb*] 



0-6 



Fig. 19. Competition between alkali cations (redrawn from Epstein and 

 Hagen, 1952). (For explanation, see text). 



inhibited by the presence of sodium, as sodium uptake is reduced 

 by potassium. This is shown very clearly in the case of seaweeds, 

 which absorb potassium more rapidly than sodium, in spite of the 

 much larger amount of sodium in sea- water (see Fig. 2, p. 11). 

 G. T. Scott (1943) showed that the sodium content of Chlorella cells 

 increases when they are grown in potassium-deficient media, 

 indicating that sodium absorption is normally restricted by the 



