The Relationship Between Adsorption and Absorption of Cations

Steady‐state analysis was applied to the absorption of cations by excised barley roots. The results indicate that ions are adsorbed and absorbed by specific ion‐binding compounds of the root. Only negligible amounts of the cations tested were adsorbed nonspecifically. The intercept of the uptake time curves equals the amount of cation adsorbed to the specific binding compound. The concentration of these ion‐binding compounds was the order of magnitude of 2 me. per 100 g. of dry barley roots for Na, K, and Rb and 4 me. for Sr. The specific reaction‐rate constants for both sites of ion uptake for each of the cations appeared to be the same order of magnitude. This was approximately 1 × 10 ‐3 moles of cation per mole of combined site per second for Na, K, and Rb and 6 × 10 ‐5 moles per mole of combined site per second for Sr.