Stomatal Responses to Pressure Changes and Interruptions in the Water Supply of Detached Leaves of Zea mays L.

Stomata of Zea mays L. respond to changes in hydrostatic pressure in the water supply of the leaves almost instantaneously and in all leaf parts simultaneously. Therefore, the leaf is a hydraulic unit. The stomata are part of it and their aperture is controlled by the water potential in the water-conducting system. Stomatal aperture is not uniquely related to the relative water content of a leaf. The relation depends also on the humidity in the air and is different for the upper and the lower epidermis.