I have explained the complex effect of rise of temperature on phototropic curvature. Rise of temperature, within limits, enhances the excitability, and therefore the positive curvature under light. Its expansive reaction, on the other hand, opposes the contraction of the proximal side, which produces the normal positive curvature. Rise of temperature, as previously stated, introduces another element of variation by its effect on conductivity. Transverse conduction favoured by rise of temperature promotes neutralisation and reversal; the resultant effect will thus be very complicated. I give below account of an experiment where the induced positive curvature under light underwent a reversal during rise of temperature. _Reversal of tropic curvature under rise of temperature: Experiment 146._--The specimen employed for this experiment was a seedling of pea, enclosed in a glass chamber, the temperature of which could be gradually raised by means of an electric heater. Provisions were made to maintain the chamber in a humid condition. The temperature of the chamber was originally at 29°C., and application of light on one side of the organ gave rise to positive curvature, followed by complete recovery on the cessation of light (Fig. 146a). The next experiment was carried out with the same specimen; while the plant was undergoing increasing positive curvature under the continued action of light, the temperature of the chamber was gradually raised from 29° to 33°C. at the point marked with arrow. It will be seen that the positive curvature became arrested, neutralised, and finally reversed into negative (Fig. 146b). [Illustration: FIG. 146.--Effect of rise of temperature on phototropic curvature. (_a_) normal positive curvature followed by recovery, (_b_) reversal of positive into negative curvature by rise of temperature at (H). (Pea seedling).] _After-effect of rise of temperature: Experiment 147._--The after-effect of rise of temperature exhibited by this specimen was extremely curious. The temperature of the chamber was allowed to return to the normal, and the experiment repeated after an hour; the response was now found to be negative (Fig. 147a). It appeared probable that the temperature in the interior of the tissue had not yet returned to the normal, and an interval of four hours was therefore allowed for the restoration of the tissue to the normal temperature of the room. The response still persisted to be negative, as seen in the series of records obtained under successive stimulations of light of short duration; these negative responses exhibited recovery on the cessation of light (Fig. 147b). This reversal of response as an after-effect of rise of temperature was in this case found to persist for several hours. I experimented with the same specimen next day when the response was found restored to the normal positive.