212 Mineral Nutrition of Plants 



usually migrates more rapidly into roots when supplied with potassium 

 than with calcium. This is shown in Figure 15 from Hoagland (27) 

 (compare Table II and Figures 13 and 14). The relative rates of migra- 

 tion between cations or between anions will no doubt be modified by 

 the relative importance of the various modes of movement in any 

 particular case. 



I 5 10 20 30 40 



CONCENTRATION OF EXTERNAL SOLUTION IN MILLIEQUIV. PER LITER 



Figure 15. Effect of concentration of the culture medium on the absorp- 

 tion of K and Br from KBr and CaBr 2 solutions by abscised barley roots, 

 barley plants grew in one-half strength (standard) nutrient (22 days). 

 Absorption period 8{ hours; culture solution temperature 16.5 C; con- 

 centrations from 1 to 50 milliequivalents per liter. — Hoagland (2j) 



Where more than one inorganic solute is supplied in the medium 

 around the roots, the rates of ion absorption are further complicated. 

 Early studies with intact plants have shown the movements of one 

 cation to be modified (usually reduced) by the presence of another 

 cation (26). Similar effects have been obtained between cations, be- 

 tween anions, and between ions of opposite charge (the latter referred 

 to previously for single inorganic solutes). These results recall to mind 

 early studies on antagonism (5^, 80). The latter, however, were related 

 to amelioration of toxic effects of single inorganic solutes supplied in 

 high concentrations through addition (usually of low concentrations) 



