The geo-perceptive layer is experimentally localised by measuring the depth of intrusion of the probe for maximum deflection of galvanometric negativity. The geo-perceptive layer thus determined is found to be the starch sheath which contains a number of large-sized starch grains. The power of geo-perception undergoes seasonal variation. It is also lowered by high temperature. The geo-electric response undergoes decline with growing sub-tonicity of the specimen; such specimens exhibit abnormal positive electric response under the stimulus of prick and feeble curvature under geotropic stimulus. The large-sized starch-grains, normally observed in the endodermis, are found to disappear in specimens which have become geo-electrically insensitive. The electric response of the lower side of the organ to gravitational stimulus is of opposite sign to that of the upper side. The electric distribution on the lower side exhibits variations in different layers, the maximum positivity occurring at the perceptive layer. In vigorous specimens the excitatory negative electric change on the upper side is greater than the positive electric change on the lower side. Depressed condition of the tissue is attended by a relatively greater decline of the negative in comparison with the positive. The induced electric variation on the upper and on the lower side indicates that the layers of tissue contiguous to the upper perceptive layer undergoes contraction, while those contiguous to the lower perceptive layer undergoes expansion. XLIV.--ON GEOTROPIC TORSION _By_ SIR J. C. BOSE, _Assisted by_ GURUPRASANNA DAS. I have explained that in a dorsiventral organ, lateral application of various stimuli induces a responsive torsion by which the less excitable side is made to face the stimulus (p. 403). I shall in this chapter show that the effect of stimulus of gravity is in every respect similar to other forms of stimulation. [Illustration: FIG. 179.--Diagram of arrangement for torsional response under geotropic stimulus. The less excitable upper half of pulvinus is, in the above figure, to the left and the torsional response is clockwise.] The direction of force of gravity is fixed, and we have to arrange matters in such a way that the geotropic stimulus should act on the dorsiventral organ in a lateral direction. In the following experiments the pulvinus of _Mimosa_ is taken as the typical dorsiventral organ. For lateral stimulation, the plant is placed on its side, so that the vertical lines of gravity impinge on one of the two flanks of the organ. In regard to this, I shall distinguish two different positions, _a_ and _b_. In the _a-position_, the apex of the stem and the upper half of the pulvinus are to the left of the observer, and in _b-position_, the apex of the stem and the less excitable upper half of the pulvinus are to the right. The arrangement for obtaining record of the torsional response under _a-position_ is shown in figure 179.