I2 4 Mineral Nutrition of Plants 



centration as the carbon dioxide-saturated supernatant liquid of the 

 rubidium-hydrogen sol. In spite of possible contact depletion by hydro- 

 gen clay, the roots secure more rubidium from the clay sol than from the 

 artificial intermicellar liquid. As roots were in contact with solution 

 and suspension for only one second, ion accumulation inside the root 

 was largely excluded. We are probably dealing here with an exchange 

 involving outer root surfaces only. 



Figure 7 portrays the sorption of radioactive sodium by groups of 

 21 intact barley plants during a period of 10 minutes as a function of 



120 



100- 



80 



§ 



<0~ 60 



k 40 



ki 20 



3 



Na-Clay 

 suspension 



% 







Intermicellar liquid 

 C0 2 saturated 



10 20 30 40 50 



ME Na-CLAYPER LITER 



Figure 7. Demonstration of direct 

 utilization of adsorbed ions by roots. 



sodium clay concentration. The upper curve shows the uptake of sodium 

 from a large volume of sodium clay suspension. The lower curve indi- 

 cates the sodium sorption from a large volume of the corresponding 

 intermicellar liquid, saturated with carbon dioxide prior to separation. 

 During the process of ion accumulation by roots, clay sols, as well as 

 sodium bicarbonate solutions, were continually aerated. In our opinion, 

 the difference in the two curves demonstrates direct utilization by roots 

 of adsorbed sodium. 



