1309 
V at the beginning of period 1 in the mercury-contact O,, in conse - 
quence of which the solenoid S, (at the clockwork) works and 
makes T, catch into T, — while at the beginning of period 2 in C, 
circuit IV is closed, which by means of S, pulls down the cog- 
wheel T,. 
Thursday May 13 1920. Friday May 14. 
ONE BeOne ah ae IS neder he SOF. ew 4s wih ea eS 
BANNER Ch reek Ca 
i) 
ast mi he 
Fig. 2. Course of the stomatal aperture in a leaf of Ficus elastica for 
nearly 24 hours. The lengths of the lines denote the time, in which the 
pressure in the porometer was increased from 5 to 1 cms. of water below 
the height of the barometer. 
Fig. 2 is a reproduction of a diagram, obtained with the aid of 
the described arrangement. It is hardly necessary to point out, that the 
distance between the lines is the smaller, the shorter the periods 1 
are. If period 1 lasts longer than 16 minutes, the pencil goes no 
farther, so that the line is, as it were cut off. There is however no 
objection to this, because in such long periods the length may be 
accurately read from the time-axis down to half-minutes. 
The picture given by fig. 2 clearly shows how on May 13th at 
5.30 p.m. a slow closure of the stomata had already set in, between 7 
and 8 o’clock the closure went quicker and quicker, at 8.30 the 
period was 5 times longer than at 5.30. Next the stomata remained 
in the strongly-narrowed condition, till about midnight, then they 
began to re-open, first very slowly, but between 4 and 6 o’clock 
in the morning very fast. 
From 7 to 9 o'clock they were more open than the previous 
afternoon at 5.30. Between 9 and 2 the degree of aperture showed 
fairly strong oscillations, which, in connection with observations | 
shall no further discuss here, should probably be attributed more 
to the influence of temperature than the light. At the maximal 
aperture at 2 o'clock, period 1 was 16 times shorter than at the 
greatest closure at 10 o’clock in the previous night. After 4 hours 
