Jonathan wrote; " It doesn't really make sense, as I think about it, and I suspect you'll agree, that the sun's heat would lead to increased chilling of the leaf under where the waterdrop was located--it wouldn't evaporate any more rapidly than the sun's heat caused it to vaporize." I am a bit on shaky ground since I am not a physical chemist, but as I understand the phenomenon. Sunlight can increase evaporation and although there is a direct relationship between light and evaporation, calories may be drawn from the surrounding micro-environment and not just the sunlight as the water changes state. Since there is a proportionally huge consumption of calories required some of these may be drawn from the leaf. The sunlight may not be the only source of heat for the evaporation and may facillitate the process by affecting surface tension and other factors. Thus the immediate area of the leaf may be chilled because of its donation of heat to the process. Perhaps we are both saying the same thing.