ldso, S. B., 1983. Stomatal regulation of evaporation from well-watered plant canopies: a new synthesis. Agric. Meteorol., 29: 213--217.
New experimental evidence is presented to resolve a long-standing controversy relative to the existence or non-existence of evaporation control by stomata in situations where the water supply to plant roots is non-limiting. It is shown that both sides of the argument were correct in certain respects, but that the claim for significant stomatal control was the one most representative of reality in the broadest perspective. Some 16 years ago, Lee (1967) published a major paper about the hydrologic importance of transpiration control by stomata. As a result of considerable theoretical and experimental work on diffusion rates through tubes of various size and single-pore and multi-pore non-living membranes, he showed that stomatal characteristics should have considerable impact on plant transpiration rates. Thus, he concluded that plant canopies are not passive evaporating surfaces, but significant regulators of evaporative water loss.
This view prompted me to suggest that although Lee's work indicated that plants should act in such a manner, in reality they may not (Idso, 1968). As evidence, I cited many experiments conducted by C. H. M. van Bavel and his associates which led them to conclude that plant transpiration is not regulated by leaf stomata, except during periods of darkness, low illumination, and water stress, and to state that the response of the plants to the evaporative demand of the atmosphere is "truly that of a wick". Lee (1968a) countered this argument by indicating that the experiments in question were not definitive on this point. That is, he said that they could not prove that stomata were not still acting in a regulatory fashion, even though there was a wick-like response to environmental stimuli. He concluded that if plants are indeed "wicks", they are wicks of a unique kind, having varying hydraulic conductivities and coated with an epidermis that * Contribution from Agricultural Research Service, U.S. Department of Agriculture.