Course of Cation Absorption by Plant Tissue.

The absorption of rubidium by excised barley roots from solutions containing calcium was a strictly linear function of time for 1 hour and was temperature-sensitive throughout; there was no evidence of an initial nonmetabolic exchange phase of uptake. The rubidium absorbed reached concentrations many times the external concentration without any slackening of the rate of absorption-evidence for a high degree of irreversibility of the overall absorption process. This is discussed in terms of the "enzyme-kinetic" model of ion transport by carriers.