| Abstract: | In previous experiments on excised barley roots, results werepresented showing the effect of varying the concentration ofthe uptake solution on the amount of anion which could subsequentlybe extracted in water. It was concluded that the system couldbe more satisfactorily analysed by means of the GoüyChapmanelectrical double-layer theory than by the Donnan theory. Onthe basis that ions diffuse into a system of negatively chargedpores within the root, the relationship between the quantityof water-extractable anion and its concentration in the uptakesolution has been examined in the light of the electrical double-layertheory. For potassium iodide and sulphate the experimental resultsconformed reasonably well with a structural model for the FreeSpace of parallel, charged surfaces separated by a mean distanceof about 200 A. The internal surface area of the free spacewas estimated as 2x106 cm2/g dry weight. The uptake of iodidefrom calcium iodide was somewhat greater than that predictedby the theory; this may be ascribed to interaction between theanions and divalent cations within the double layer. |
