Summary.A method has been developed in which a chloroplast suspension is placed between electrodes to which a variable AC potential is applied. The dielectric constant of the suspension varies inversely as the square root of frequency within the range 0.5 to 50 MHz. Results are consistent with the view that this dielectric dispersion is due to ion movement across the chloroplast internal membranes, under the influence of the applied potential. The slope of the dispersion depends on the permeability of the membranes, and thus enables the mobility of externally added ions to be calculated. Results imply that the internal membranes of sugar cane chloroplasts are more permeable to K + than Na +, and more permeable to CI-than CH3COO-. Results also confirm the view that Triton X-100 increases the ionic permeability of membranes.

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Short pulse excitation is investigated of SnOxZnSCuxJZnS(Mn)Al electroluminescent thin film structures. The phenomenon of time delay of the electroluminescence maximum is observed. A model of the growth and decay of the electroluminescence curve is proposed on the assumption that energy transfer takes place from Cu centres to Mn centres. Good agreement between the theoretical and experimental curves is obtained. The three parameters used in the fitting, the lifetimes of the sensitizer and activator and the electroluminescence maximum delay time are in good agreement with the experimental results and the literature data.

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