Page:Life Movements in Plants.djvu/265

Rh The petiole carrying the leaﬂet is mounted water-tight in the short arm of an U-tube tilled with water; for pro- ducing internal hydrostatic pressure in the plant. the height of water in the longer arm is suitably raised. The U-tube holding the specimen may be adjusted up and down, and laterally. A hinged support also allows the specimen to be placed at any inclination. The movement of the leaflet, it is to be remembered, does not always take place in a vertical direction. The obj 'ct ot' the mechanical adjustments is to place the specimen at such an angle that its up and down movements when in a straight. line should be vertical, or have its long axis vertical when the movement. is elliptical. It is important that the specimen should be illuminated equally from all sides; for one-sided illumina- tion causes a bending over of the leatlet towards light.

The pulvinule of the leatlet acts like the. pulvinus of .llt'nzusa, that is to say, the leaflet. undergoes a sudden fall to down position by the contraction of the more etlective low'er half of the pulvinule; the ‘up’ position denotes re.- covery and expansion of the more. ell'ective halt'. The up-and-down movements of the leaﬂet correspond to the diastolic and systolic mow-merits of the animal heart. There is, indeed, as l have shown elsewhere a very close resemblance between the activities of rhythmic tissue in the plant and in the animal.

19'.rpari7mnt. {RA—For the study of effect of light on Des- modium, I ﬁrst obtained record in darkness. A horizontal beam of divergent light from an arc lamp placed at a dis- tance of 200 cm. was made to act ditl'usely on the leaf from all sides. This was done by means of three inclined mir- rors, the first throwing the light vertically downwards, the