Properties of Internal Water Exchange in Leaves ofIlex opacaAit. andCornus floridaL.

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Abstract
Resistances, capacitances, and time constants for internal water transfer were estimated in leaves from naturally-occurring individuals of Ilex opaca Ait. and Cornus florida L., both common under-story tree species in the North Carolina piedmont deciduous forest. The water exchange properties depended strongly on the current water status of the leaf tissue. Resistance to water transfer from leaf storage sites, capacitance of storage sites, and the time constant for transfer of water out of storage sites all increased as tissue water deficits developed. The exchange properties were determined over a range of leaf water potentials which the plants typically experienced in the field. The measured responses are viewed as properties integrally associated with other aspects of water transfer elsewhere in the plant and in the soil and atmosphere, and may be significant in determining leaf water deficits under a fluctuating environment.