The Uptake of Metallic Ions by Leaves of Apple Trees. IV. The Uptake of Coppei by Leaves of Cox’S Orange Pippin Momentarily Dipped in Solutions of Copper Sulphate

Abstract

Leaves of Cox’s Orange Pippin apple momentarily dipped in solutions of copper sulphate showed a similar pattern of uptake to that previously described for leaves which were immersed in similar solutions for much longer periods.From weak solutions retained on the leaf surface, copper was taken up initially at a rapidly declining rate (phase I), then at a linear rate proportional to the applied concentration (phase II). With stronger solutions, phases I and II were followed by further linear-with-time phases (III and IV). The rate and amount of uptake in phase I were similar in dipped and immersed leaves, but the rates of uptake in the other phases were lower in the dipped leaves.Copper ceased to be taken up from weak solutions at a fixed time after dipping the leaves ; this was taken to be the time at which the surface deposit dried out, though any visible moisture had already disappeared. Strong solutions induced a further phase (IV), in which uptake persisted long after the surface deposit had apparently dried out ; this is tentatively explained in terms of a diffusion of water out of the leaf during phase IV, thus maintaining a supply of copper ions in solution.Leaves treated on the tree behaved like detached ones, but the time taken for the surface deposit to dry out was shorter, presumably because of differences in the environmental conditions.The final amount of copper taken up by leaves treated with solutions containing 0.04M copper sulphate, or less, could be related to the applied concentration by means of a Freundlich adsorption isotherm. It follows, and was confirmed, that proportionate more copper was taken up from the weaker solutions, and the following expression was derived and shown to be in agreement with the experimental data :