That the movement is primarily due to variation of temperature will be demonstrated in two different ways: (_a_) by the change of normal rhythm of movement by artificial transpositions of periods of maximum and minimum temperature, and (_b_) by the abolition of periodic movement through maintenance of constant temperature. That the phenomenon is not nastic, but paratonic will be demonstrated:-- (_a_) by the reversal of closure into opening movement and _vice versâ_, in consequence of inversion of the plant upside down, and (_b_) by the diurnal variation of torsional movement, the direction of which is dependent on the directive action of the stimulus of gravity. I shall now describe the diurnal movement of various geotropically curved plant-organs; the most striking example of this is furnished by the 'Praying' Palm of Faridpore, already described. I shall here recapitulate some of the important features connected with the phenomenon. DIURNAL MOVEMENT OF PALM TREES. Movements similar to that of the Faridpore Palm (p. 12) are found in other Palm trees growing at an inclination from the vertical. I reproduce once more the diurnal curve given by the Sijberia Palm together with the curve of daily thermal variation (Fig. 199). It will be seen that the two curves resemble each other so closely that the curve of movement of the tree is practically a replica of the thermographic record. There can therefore be no doubt of the movement being brought about by variation of temperature; rise of temperature is attended by the movement of fall of the tree and _vice versâ_. The record was commenced at noon; the temperature rose till the maximum was reached at about 3 p.m. and the tree also reached its lowest position at 3-45 p.m., the lag being 45 minutes. The temperature fell continuously after the maximum at 3 p.m., to the minimum at 6 a.m. next morning. In response to the falling temperature, the tree exhibited a movement of erection. The temperature rose after 6 a.m. and the movement of the tree became reversed from ascent to descent. [Illustration: FIG. 199.--Diurnal record of the Sijberia Palm. Upper curve gives variation of temperature, and the lower curve the movement of the tree.]