The effect induced by stimulus of light is transmitted to a distance, in a manner precisely the same as in other modes of stimulation. In the Paniceae, the local unilateral stimulation of the tip of the cotyledon induces positive curvature in the growing hypocotyl, at some distance from the tip. This is due to transmitted excitatory effect of indirect stimulation; the earlier positive impulse induces a preliminary negative curvature, which is reversed later by the excitatory negative impulse into positive curvature. Contrary to generally accepted view the hypocotyl not only perceives but responds to light. The positive curvature induced by direct stimulation is, however, neutralised by transverse conduction of excitation. The effects of direct and indirect stimulus are independent of each other; the final effect is determined by their algebraical summation. XXXIV.--ON PHOTONASTIC CURVATURES _By_ SIR J. C. BOSE, _Assisted by_ GURUPRASANNA DAS. Phototropic response, positive or negative, is determined by the directive action of light. But photonastic reaction is supposed to belong to a different class of phenomenon, where the movement is independent of the directive action of light. I shall, however, be able to establish a continuity between the tropic response of a radial and the nastic movement of a dorsiventral organ. The intermediate link is supplied by organs originally radial, but subsequently rendered anisotropic by the unilateral action of stimulus of the environment. In a dorsiventral organ, owing to anatomico-physiological differentiation, the responsive movement is constrained to take place in a direction perpendicular to the plane of separation of the two unequally excitable halves of the organ. Even in such a case, it will be shown, that light does exert a directive action; the direction of movement will further be shown to be distorted by the lateral action of light. PHOTOTROPIC RESPONSE OF ANISOTROPIC ORGANS. The different sides of a radial organ, such as the young stem of _Mimosa_, are equally excitable. The response to unilateral light of moderate intensity is therefore positive; owing to equal excitabilities of the two sides the response of the opposite sides are alike. Diffuse stimulation therefore induces no resultant curvature. If, however, the plant is allowed to form a creeping habit, the excitabilities of the dorsal and ventral sides will no longer remain the same. Thus in the creeping stem of _Mimosa_ the lower or the shaded side is, generally speaking, found to be the more excitable. In fact such anisotropic stem of _Mimosa_ acts somewhat like the pulvinus of the same plant. Diffuse stimulation induces, in both, a concavity of the more excitable lower half with the down movement of the leaf or the stem.