When conditions are favorable for relatively rapid transpiration the rate of water loss is often determined by the rate of absorption. If soil moisture is not limiting this rate depends largely on the extent and efficiency of the absorbing surface, that is, the root system. Variation in the ratio of root surface might therefore be expected to affect the rate of transpiration. Fowells and Kirk (2) found that removal of part of the root system of pine seedlings reduced transpiration, and Marshall and Maki (5) believed that transpiration of pine seedlings might be related to size of the root system. Bialoglowski (1) was able to demonstrate a quantitative relationship between root-leaf ratio and the water loss per unit of leaf surface with rooted lemon cuttings. In order to obtain further information on this relationship for various woody species, the following experiments were carried out.