Studies in Stomatal Behavior. I. Effects of Moving and Still Air on Stomata of Eupatorium and Mentha

Williams (6, 7) was the first to observe that epidermal strips taken from the area of leaf enclosed by an unswept porometer cup show much wider stomatal pores than elsewhere. Heath's experiments with Pelargonium and wheat (4, 5) showed that sweeping the porometer cup with dry or humid air caused considerable closure of the stomata as compared with the areas in still air. In a repetition of Knight's experiment on the changes in transpiration rate in relation to the leaf water content, Gregory et al (1) showed that the higher transpiration rate following a period of still air was due to wider stomatal pores and not to a higher leaf water content as suggested by Knight. They attributed the observed wide opening of stomata, possibly, to a reduction in the carbon dioxide concentration of the enclosed still air as a result of photosynthesis. In a previous investigation (2), the author has shown that when the air stream circulating through a porometer cup attached to an illuminated cherry laurel leaf was stopped for given periods, the stomata of the enclosed leaf portion opened gradually and considerably with time. When ventilation of the porometer was renewed, the stomata showed a rapid closing movement. The present investigation is an attempt to add to the information on the response of stomata to moving and still air.