Evidence that the inner and outer protoplasmic surfaces in Valonia are unlike is found in the high P.D. across the protoplasm when the external solution has the same composition as the vacuolar sap. Earlier experiments with artificial sap have been repeated, using natural as well as artificial sap. Good agreement between the data with the natural and the artificial solution was found both in the magnitude of the P.D.'s observed and in the shape of the P.D.-time curves. The P.D.'s, however, were considerably higher than the values formerly reported as usual, while the cells proved much less liable to alteration produced by exposure to sap. It is suggested that the cells used in the recent experiments were in a more vigorous condition, perhaps as a result of exposure to stronger illumination.
The interpretation of the shape of the P.D.-time curves, proposed in an earlier report, and based on the theory of protoplasmic layers, is further discussed. It is assumed that the fluctuations in P.D. are due to an increase in the concentration of K in the main body of the protoplasm.
