Hydraulic conductances of leaf tissues of Hedera helix and Tradescantia virginiana leaves were measured. It was found that water could flow most easily through the veins, but that the cell walls of at least the ventral epidermis were more efficient at resupplying water lost from the epidermal tissue than was the mesophyll at rehydrating itself. Vein and bundle-sheath extensions, which are characteristic of mesomorphic leaves (e.g. T. virginiana), seem to be important in maintaining a close hydraulic connection between the epidermis and the vascular tissue. In leaves not containing vein and bundle-sheath extensions, typically xeromorphic leaves (e.g. H. helix), there is not such a close connection between the epidermis and vascular tissue. This was shown in experiments involving the sudden application of a reduced pressure potential to either the epidermis or the other tissues of leaves, and the measurement of transient stomatal opening.