The Initial Uptake of Ions by Barley Roots: II. APPLICATION OF MEASUREMENTS ON SORPTION OF ANIONS TO ELUCIDATE THE STRUCTURE OF THE FREE SPACE

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Abstract
In previous experiments on excised barley roots, results were presented showing the effect of varying the concentration of the uptake solution on the amount of anion which could subsequently be extracted in water. It was concluded that the system could be more satisfactorily analysed by means of the Goüy–Chapman electrical double-layer theory than by the Donnan theory. On the basis that ions diffuse into a system of negatively charged pores within the root, the relationship between the quantity of water-extractable anion and its concentration in the uptake solution has been examined in the light of the electrical double-layer theory. For potassium iodide and sulphate the experimental results conformed reasonably well with a structural model for the Free Space of parallel, charged surfaces separated by a mean distance of about 200 A. The internal surface area of the free space was estimated as 2×106 cm2/g dry weight. The uptake of iodide from calcium iodide was somewhat greater than that predicted by the theory; this may be ascribed to interaction between the anions and divalent cations within the double layer.

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