420 
Notes. 
in four sets containing three in each, and so every observation was 
checked three times under the same conditions. 
The results of such a series of observations are given in Table I. 
The behaviour of cells receiving io, 45, 55, 60, 100, and 120 seconds 
stimulus is here given, and on the right-hand side the behaviour of 
the corresponding controls are tabulated. It was found that the rate 
of turning through 90° varied somewhat at different periods. During 
the first five minutes the angle turned through was less than that 
turned through during the fifth to the tenth and the tenth to the 
fifteenth minute after stimulation. A decrease then generally occurred 
till the revolution was complete. This slow movement during the 
first five minutes would seem to point to a latent period. 
It is also interesting to note that those cells which received 
a stimulus only just sufficient to turn, took no longer to do so than 
those in continuous light. There is then a maximum limit of time- 
stimulation, and by prolonging its duration no additional visible effect 
is produced. These points could perhaps be better appreciated by 
plotting a curve than by tabulation. 
II. Experiments with strong sunlight ( turning chlorophyll-plate 
from the horizontal to the vertical position). 
Cells were taken in which the chlorophyll-plates were horizontal, 
and by the action of strong sunlight were made to turn into the 
vertical position. Here the times taken by the controls to turn 
through 90° were appreciably greater than in the first case, the 
TABLE II. 
Time of 
stimula- 
tion in 
seconds. 
Angle turned through at end of 
Control. 
Angle turned through at end of 
5 min. 
10 min. 
15 min. 
20 min. 
30 min. 
5 min. 
10 min. 
15 min. 
20 min. 
30 min. 
30 
IO° 
15 ° 
J 5 ° 
15 ° 
15 ° 
IO° 
20° 
6o° 
70 ° 
9 0° 
45 
IO° 
15 ° 
20° 
20° 
20° 
IO° 
15 ° 
45 ° 
8o° 
90 ° 
90 
5 ° 
IO° 
6o° 
6o° 
9 °° 
20° 
40° 
C\ 
0 
0 
70° 
9 °° 
Illustrating stimulation of horizontal plate with strong sunlight. 
