the plant is practically continuous with that in the substratum. The absorption of water by the plant, or rather the movement of water from the soil into the plant is influenced by the agencies which affect diffusion, osmosis and adsorption anywhere. In other words, the properties of protoplasm, as a mixture of colloids, cause water to move from the substratum into its body. The further movements of water, such as the ascent of sap, may be taken to result similarly from physical conditions. The uppermost part of the gelatinous mass of the plant ramifies as does the lower, but in this case into flattened organs or leaves. Here, as well as everywhere, on the external surfaces of the plant evaporation of water takes place in a manner modified by the specialized character and structure of the surface as well as by the relative humidity, temperature and movements of the air. This transpiration, or loss of water from the exposed surfaces, is a process of such importance that it is impossible for the plant to maintain growth to any extent, or carry out normal development without it. Consequently it has come in for a great deal of attention during the last century. Much of the work has been of a