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.
I shall now describe the principle and construction of my recording apparatus ([Fig. 2]) seen attached to a horizontally growing stem of Mimosa pudica. When used to trace the movement of the palm tree, a reducing device is employed to keep the record within the plate. A lever, R′, records the movement of the attached tree or plant on a moving plate of smoked glass. The plate is not in contact with the tip of the recording lever, but separated from it by a distance of about 3 mm. A special oscillating device, actuated by clock-work, C, makes the plate move forwards and backwards. The forward movement brings about a momentary contact of the recording tip with the smoked plate inscribing a dot. These single dots are made at intervals of 15 minutes; at the expiration of the hour, however, contact is made three times in rapid succession, printing a thick dot. It is thus easy to determine the movement of the tree at all times of the day and night. A second lever, R, placed above, gives on the same plate, thermographic record of the diurnal variation of temperature. For this I use a differential thermometer, T, made of a compound strip of brass and steel. Curvature is induced by the differential expansion of the two pieces of metal. The up or down movement of the free end of the compound strip is further magnified by the recording lever. This arrangement was extremely sensitive and gave accurate record of variation of temperature. By the forward movement of the oscillating plate two dots are made at the same time,—one for the temperature and the other for the corresponding movement of the tree. As the two recorders do not move vertically up or down, but describe a circle, the dots vertically one above the other may not correspond as regards time. Any possibility of error in calculation is obviated by the fact that the thick dots in both the records are made every hour, and the subsequent thin dots at intervals of 15 minutes.