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SUMMARY

The rate of rehydration of sunflower (Helianthus annuus L.) leaves was measured after dehydration (in air or in a pressure bomb) down to a relative water content of about 89 %. The results, when plotted as the log of the rate of rehydration (mg min-1) against time, displayed an unusual shoulder in which a phase with a long half time was succeeded by a phase with a short half time. The rehydration kinetics can be explained by two cellular compartments in series in which the bulk elastic modulus increases substantially during rehydration. The first compartment might be associated with the phloem and bundle sheath cells. Water rehydrating the second compartment, consisting of the remainder of the leaf cells, must pass through the first compartment by a transcellular pathway.