Effects of Phenyl‐mercuric Acetate on Stomatal and Cuticular Resistance to Transpiration

SUMMARY Phenyl mercuric acetate applied to both sides of the leaves of sunflower plants growing in both wet and dry soil caused a greater closure of the stomates on the upper than on the lower side of the leaves. By contrast, application of PMA increased cuticular resistance to gas diffusion only in the case of leaves of plants growing in dry soil, suggesting that soil moisture stress as well as PMA decreases the permeability of non‐stomatal epidermal cells.