The record of the diurnal movement showed that the head was erected to the highest position between 7 and 8 in the morning, after which there was a continuous fall which reached its climax at 3-15 P.M.; after this the movement was reversed and the maximum erection was again reached next morning. This phenomenon is not unique, but is found exhibited, more or less, by all trees and their branches and leaves. Diurnal records of temperature, and movement of the tree showed, that the two curves closely resembled each other. Rise of temperature was attended by a fall of the tree, and _vice versâ_. The movement is brought about by the physiological action of temperature; it may be arrested by artificially induced physiological depression, and is permanently abolished at death. The movement is primarily determined by the modifying influence of temperature on geotropic curvature. Rise of temperature is found to oppose or neutralise geotropic curvature, the fall of temperature inducing the opposite effect. The ever present tendency of upwards geotropic movement is opposed or helped by the effects of rise and fall of temperature respectively. The movement of the ‘Praying’ Palm is a thermonastic phenomenon. The tree, apparently so rigid, responds as a gigantic pulvinoid to the changes of its environment. III.--ACTION OF STIMULUS ON VEGETABLE TISSUES _By_ SIR J. C. BOSE, _Assisted by_ NARENDRA NATH SEN GUPTA. The leaf of _Mimosa pudica_ undergoes a rapid fall when subjected to any kind of shock. This plant has, therefore, been regarded as “sensitive,” in contradistinction to ordinary plants which remain apparently immobile under external stimulus. I shall, however, show in course of this Paper that there is no justification in regarding ordinary plants as insensitive. Let us first take any radial organ of a plant and subject it to an electric shock. It will be found that the organ undergoes a contraction in length in response to the stimulus. On the cessation of excitation the specimen gradually recovers its original length. Different organs of plant may be employed for the experiment, for example, the tendril of _Cucurbita_, the pistil of _Datura_, or the flower bud of _Crinum_. The shortening may be observed by means of a low power microscope. Greater importance is, however, attached to the detailed study of response and its time relations. The pull exerted by a delicate organ during its excitatory contraction is slight; hence arises the necessity of devising a very sensitive apparatus, which would give records magnified from ten to a hundred times. RESPONSE RECORDERS.