Changes in diffusion resistance of apple leaves undergoing rapid fluctuations in leaf temperature

Transpiration was measured in apple leaves (Malus sylvestris Mill.) which were enclosed in a leaf chamber and subjected to rapid changes in leaf temperature. Fluctuations in leaf temperature produced parallel fluctuations in transpiration. The change in transpiration rate with change in temperature was found to be less than the theoretical value calculated from the change in water vapour density gradient from leaf to air. The results suggest the presence of a small and rapidly varying resistance to water vapour loss from the leaf. The magnitude of this additional resistance increased to a maximum value of approximately 1.5 s cm^-1 as the magnitude of the temperature change increased to a maximum of approximately 12°C.