The Entrance of Water into Cut Leafy Shoots under Conditions which prevent Transpiration

Potometer experiments prove that cut leafy shoots, when transpiration is prevented by submersion, a covering with vaseline, or their being placed in saturated moist air, continue for days Co take up water through the cut surface, which is contradictory to the observations of Smith, Dustman and Shull. Frequently the shoots, when exposed to the daily changes of light and dark, show a rhythmical Intake of water, as especially observed in Eucalyptus globulus. In the dark the intake is large, in the light it is reduced, or water may even pass out. The entrance of water is caused by a pressure deficit in the intercellular spaces in the leaves, as a result of respiration (Theory of Sen and Blackman). This pressure deficit develops as a result of the difference in solubility of absorbed oxygen and produced carbondioxide, which leads to a reduced quantity of gas. The water which has entered through the cut surface passes into the intercellular spaces. Photosynthesis takes place in the light and the deficit disappears; the sapstream practically stops. Only little water directly enters or passes out through the leaf surface. The theory of Dixon and Bose that the sapstream of submersed shoots is caused by the activity of the leaf cells excreting water, is not confirmed. These investigations were carried out in the Laboratory of Technical Botany of the Technical University at Delft, Netherlands. I should like to express my sincere thanks to Professor Dr. G. van Iterson for his Interest and helpful criticisms.