The relation between the angle of inclination and the resulting geotropic action has already been determined by the Method of Axial Rotation. The ratio between the geotropic effects at 90° and 45° was thus found to be 1·49, which is nearly the same as Sin 90°/Sin 45°. I was next desirous of determining the relative excitations at the two angles by the Method of Vertical Rotation. It is necessary here to refer to certain differences of condition in the two methods. In the Axial Method, the hypothetical statoliths are distributed uniformly through the length of the cell, and rotation round the long axis causes displacement of the statoliths, the resulting pressure thus increasing with the sine of the angle of inclination. But in the case of vertical rotation through 45° to the right, the statoliths originally at the base of the cell accumulate to the right hand corner of the cell; a portion of the basal side of the cell is thus subjected to pressure. When the angle is increased to 90° the statoliths pass along the whole length including the basal and apical sides of the cell; but the excitability of the apical half may prove to be greater than that of the basal half. Hence excitatory geotropic effect is not likely to vary strictly as in sine of angle of inclination. Whatever the reason may be, I find as a result of experiments with 12 different specimens that the mean ratio of the effects at 90° and 45°, obtained by the Method of Vertical Rotation, is 1·8:1 which is greater than 1·49:1 obtained by the Method of Axial Rotation, this latter value being practically the same as Sin 90°/Sin 45°. SUMMARY. It is shown that the state of excitation under direct stimulus is exhibited by an electrical change of galvanometric negativity; the effect of indirect stimulus induces, on the other hand, an electrical change of galvanometric positivity. The negative electric change corresponds to contraction and diminution of turgor; the positive electric change indicates, on the other hand, an expansion and increase of turgor. The electric response to geotropic stimulus is studied by the two methods of Axial and Vertical Rotation. The upper side of a horizontally laid shoot is found to undergo an excitatory change of galvanometric negativity. In quick reacting organs the latent period of geo-electric response is about 5 seconds, and the maximum excitation is induced in the course of 2 minutes. The geo-electric response is due to physiological reaction. The intensity of response declines with age and is abolished at the death of the plant. Under symmetrical conditions, the intensity of geotropic reaction is found proportional to the sine of the angle of inclination. Electric investigation shows that the lower half of the pulvinus of _Mimosa_ is geotropically more excitable than the upper half. XLI.--THE MECHANICAL AND ELECTRICAL RESPONSE OF ROOT TO VARIOUS STIMULI _By_ SIR J. C. BOSE.