Diffusion of water vapor through single-pore membranes with pores 100 to 800 μ in diameter and multipore membranes with pores 2.5 to 20 μ in diameter was studied as a function of wind velocity. The results of these studies are compared with data obtained with transpiring leaves in wind. It was found that wind had relatively little effect on small pores as compared with large pores and free water surfaces. The primary response of stomates or small, isolated pores to wind was simply an increase in the diffusion gradient. In general, the wind-to-still-air diffusion ratios determined with the use of small pores, either isolated or as a part of a multipore system, were less than 2, while the ratio for open surface evaporation in 1,000 feet per minute wind exceeded 15. The relatively small response of transpiration to wind is tenable, considering the epidermis as a multiperforate septum
