Contact angle of water droplets in relation to leaf water potential

Abstract

The relationship between the contact angle of distilled water droplets and leaf water potential was measured as a function of time of day on three different types of leaf surfaces. Leaves of dry edible beans ( Phaseolus vulgaris L.) were representative of a corrugated, relatively waxless surface; soybean leaves ( Glycine max L.) were representative of dense pubescence superimposed on a corrugated, relatively waxless surface; and alfalfa leaves ( Medicago sativa L.) were representative of a relatively smooth, waxy surface. On alfalfa, the contact angle remained constant at around 140° indicating that the leaf waxes exert the major influence on it. Although the contact angles of the droplets on dry edible beans and soybeans displayed a diurnal trend, these variations were all within one standard deviation of the mean contact angle. The contact angle of water droplets on well watered and stressed dry edible beans was also studied. Again, all contact angles observed were within one standard deviation of each other. These results conflict with those of Fogg (1947) who found a diurnal trend in the contact angle of water droplets on leaf surfaces which he attributed to changes in the cuticular structure of the leaf.