This particular Date Palm, _Phœnix dactylifera_, is a full-grown rigid tree, its trunk being 5 metres in length and 25 cm. in diameter. It must have been displaced by storm from the vertical and is now at an inclination of about 60° to the vertical. In consequence of the diurnal movement, the trunk throughout its entire length is erected in the morning, and depressed in the afternoon. The highest point of the trunk thus moves up and down through one metre; the ‘neck,’ above the trunk, is concave to the sky in the morning; in the afternoon the curvature disappears, or is even slightly reversed. The large leaves which point high up against the sky in the morning are thus swung round in the afternoon through a vertical distance of about five metres. To the popular imagination the tree appears like a living giant, more than twice the height of a human being, which leans forward in the evening from its towering height and bends its neck till the crown of leaves press against the ground in an apparent attitude of devotion (Fig. 1). Two vertical stakes, each one metre high, give a general idea of the size of the tree and movements of the different parts of the trunk. [Illustration: Fig. 1. The Faridpur ‘Praying’ Palm; the upper photograph shows position in the morning; the lower, position in the afternoon. The two fixed stakes are one metre in height. In front is seen erect trunk of a different Palm.] For an investigation in elucidation of this phenomenon it was necessary:-- 1. To obtain an accurate record of the movement of the tree day and night, and determine the time of its maximum erection and fall. 2. To find whether this particular instance of movement was unique, or whether the phenomenon was universal. 3. To discover the cause of the periodic movement of the tree. 4. To find the reason of the remarkable similarity between the diurnal movement of the tree, and the diurnal variation of moto-excitability in _Mimosa pudica_. 5. To determine the relative effects of light and temperature on the movement. 6. To demonstrate the physiological character of the movement of the tree. 7. To discover the physiological factor whose variation determines the directive movement. THE RECORDING APPARATUS.