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[1] a very close resemblance between the activities of rhythmic tissue in the plant and in the animal.
EFFECT OF DIFFUSE LIGHT ON PULSATION OF DESMODIUM.
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
- ↑ Boss—Irritability of Plantar—p. 29:3.
