The root-tip when burrowing its way underground comes in contact with hard substances and moves away from the source of irritation. The irritability of the root-tip is generally regarded as being specially evolved for the advantage of the plant. But reference to experiments that, have been described shows that this reaction is not unique but exhibited by all plant organs, growing and non-growing. Indirect stimulus has been shown to give rise, in both shoot and root, to a _negative_ tropic curvature in contrast to the _positive_ curvature brought about by direct stimulation; the response of the root is therefore in no way different from that of vegetable tissues in general. It will also be seen that an identical stimulus induces two opposite effects, according as the stimulus is applied at the tip or at the growing region itself. In the former case, the stimulus is indirect, and in the latter case it is direct. The results are in strict conformity with the laws of effects of direct and indirect stimulations that have been established regarding plant response in general (p. 231). SUMMARY. In the root, the responsive region is in the zone of growth. The tip of the root is separated from the region of response by a semi-conducting or non-conducting tissue. Direct unilateral stimulus (applied at the region of growth) induces a positive curvature by the contraction of the proximal and expansion of the distal side. The electrical response to direct unilateral stimulus is galvanometric negativity of the proximal, and galvanometric positivity of the distal side. Indirect unilateral stimulus induces expansion of the proximal side resulting in negative curvature and movement away from stimulus. The corresponding electric response induced is galvanometric positivity of the proximal side. The responses of the root, to both direct and indirect stimulations, are precisely similar to those in the shoot. The assumption of specific irritability of the root as differing from that of the shoot, is without any justification. XLII.--GEO-ELECTRIC RESPONSE OF ROOT _By_ SIR J. C. BOSE, _Assisted by_ SATYENDRA CHANDRA GUHA. The effects of various stimuli, direct and indirect, on the response of the root have been described in the last chapter. These responsive reactions have been found to be in no way different from those of the shoot. But the shoot and the root exhibit under the stimulus of gravity, responsive movements which are diametrically opposite to each other. These opposite effects of an identical stimulus have been regarded as due to specific differences of irritability in the two organs, specially evolved for the advantage of the plant. The root is thus supposed to be characterised by "positive" and the shoot by "negative" geotropism.