Page:Life Movements in Plants.djvu/37

Rh 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.

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.

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