_Experiment 110._--A tendril of _Passiflora_ was held in a clamp, as in the diagram (Fig. 106) in which the left is the more excitable side of the organ. The responsive movement of the tendril is observed by focussing a reading microscope on a mark on the upper part of the tendril. Direct mechanical stimulation at the dotted arrow makes the tendril move in the same direction, the response being _positive_. But if stimulus be applied on the same side below the clamp the tendril is found to move away from stimulus, the response being now _negative_. This reversal of response, as previously stated, is due to the fact that the transmitted effect of indirect stimulus induces an acceleration of growth higher up on the same side, which now becomes convex. The result though unexpected, is in every way parallel to the response of the flower bud of _Crinum_, in which the normal positive response was converted into negative by changing the point of application of stimulus, so that it became indirect (p. 216). SUMMARY. The response of tendril is in no way different from that of growing organs in general. Direct stimulus, electrical or mechanical, induces an incipient contraction; the after-effect of a feeble stimulus is an acceleration of growth above the normal. Indirect stimulus induces an enhancement of the rate of growth. Under unilateral mechanical stimulus of short duration the directly excited proximal side undergoes contraction, the indirectly stimulated distal side exhibits the opposite effect of expansion. The induced curvature is thus due to the joint effects of the contraction of one side, and the expansion of the opposite side. As the after-effect of direct stimulus is an acceleration of growth above the normal, the stimulated side undergoes an expansion by which the recovery is hastened. Unilateral application of direct stimulus induces a _positive_ curvature, but the same stimulus applied at a distance from the responding region induces a _negative_ curvature. The tendril of _Passiflora_ is excitable both on the upper and under sides: the excitability of the under side is about seven times greater than that of the upper side. Stimulation of one side of the tendril induces an expansion of the opposite side, even in cases where the contractility of the stimulated side is feeble. The response to stimulation of the more excitable side of the tendril is thus inhibited by the stimulation of the opposite side. This is because of the neutralisation of the effect of direct by that of indirect stimulation. XXVII.--ON GALVANOTROPISM _By_ SIR J. C. BOSE, _Assisted by_ GURUPRASANNA DAS. Before describing the effect of unilateral application of an electrical current in inducing tropic curvature, I shall give an account of the polar effect of anode and cathode on the pulvinated and growing organs. In my previous work[6] on the action of electrical current on sensitive pulvini I have shown that:--