Full description is given of the new method of physiological exploration by means of the electric probe, by which the particular layer which perceives the stimulus of gravity is definitely localised. The method of electric probe is also found to be of extended application in the detection of physiological changes in the interior of an organ. An important factor of nyctitropic movements, hitherto unsuspected, is the effect of variation of temperature on geotropic curvature. This and other co-operative factors have been fully analysed, and a satisfactory explanation has been offered of various types of diurnal movement. A generalisation has been obtained which explains all the diverse movements of plants, under all modes of stimulation: _it has been shown that direct stimulation induces contraction and retardation of growth, and that indirect stimulation induces an expansion and acceleration of growth._ Another generalisation of still greater importance is the establishment of identical nature of physiological reaction in the plant and the animal, leading to advances in general physiology. Thus the discovery of a method for immediate enhancement or inhibition of nervous impulse in the plant led to my success in the control of nervous impulse in the animal. Another important discovery was the dual nervous impulses in plants, and I have very recently been able to establish, that the nervous impulse generated in the animal nerve by stimulus is not single, but double. The study of the responsive phenomena in plants must thus form an integral part of physiological investigation into various problems relating to the irritability of all living tissues, and without such study the investigation must in future remain incomplete. _October 1919._ J. C. BOSE. CONTENTS. PART III. TROPISM IN PLANTS. XXII.--THE BALANCED CRESCOGRAPH. PAGE. Principle of the Method of Balance--Compensating movement-- Growth-scale--Sensitiveness of the Crescographic Balance-- Effect of CO_{2}--Effect of anæsthetics 255 XXIII.--ON TROPIC MOVEMENTS. Complexity of the problem--Contradictory nature of responses--Two classes of tropic responses--Longitudinal transmission of effect of stimulus--Transverse transmission of effect of stimulus--Modification of tropic curvature by conducting power of tissues and differential excitability of the organ 268 XXIV.--TROPIC CURVATURE WITH LONGITUDINAL TRANSMISSION OF EFFECT OF STIMULUS. Dual impulses, positive and negative, caused by stimulus-- Direct and Indirect stimulus--Tropic effect of Indirect stimulation 271 XXV.--TROPIC CURVATURE WITH TRANSVERSE TRANSMISSION OF EFFECT OF STIMULUS.