Production of Rhythm in Plants . 95 
in eight of these the stimulated rhyth 7 n was apparent, i. e. the 
periodic movement continued as long as the alternate stimula- 
tion was kept going 1 . In six of the eight, the unstimulated 
rhythm was observed, i. e. the periodic movement continued 
after the stimulus had ceased. This is the really important 
result, namely, that when a stimulated rhythm has been formed 
it passes on to unstimidated rhythm in at least three-quarters 
of the cases. 
In the following short series we begin with the full notes of 
an experiment, because in our former paper such details were 
omitted. No. I happens to be a geotropic experiment, and 
we have not thought it necessary to add full details of 
a heliotropic example, since the principle is identical in the 
two classes. 
Half-hourly Period. (Geotropism.) 
Exp. I (Fig. 11). Mustard Seedling. March 15, 1899. 
The seedling was arranged with its hypocotyl parallel to 
the horizontal axis of rotation, which was perpendicular to the 
plane of the window to avoid alternating heliotropic effects. 
The geotropic curvature of the seedling was observed by 
means of a horizontal microscope ; the readings are given in 
column 3 of Table I. The experiment was begun on March 14, 
1899 ; the readings here given were made on March 1 5 during 
the 97th and following periods of revolution of the klinostat, 
as indicated in column 1, which is headed £ Period.’ 
Beginning at 10.12 a.m. it will be seen that the readings 
(column 3) sink in value, indicating a steady upward curvature 
of the hypocotyl, until 10.22 ; at this point the curvature is 
reversed, as shown by the readings suddenly increasing in 
value. This increase continues steadily until 10.37, and at 
10.38 the klinostat rotates through 180 0 . At this point the 
horizontal microscope has to be readjusted, and the readings 
beginning at 10.39 (Period 98) will be seen to be falling in 
value instead of rising. This is the obvious result of the 
rotation of the horizontal axis of the klinostat ; the act of 
1 Three out of the four failures were on badly grown plants. 
