254 Darwin and Pertz. — On the Production 
head travels obliquely towards the D side showing that the 
plant was curving downwards for the final 24' of the second 
half-hour. Now the klinostat makes 
half-a-turn, which is shown by the 
D and U changing sides. The line 
representing the movement travels 
on in approximately the same direc- 
tion although it now represents an 
upward curvature. In the middle 
of the third period the direction 
changes and the plant curves down- 
wards. 
Observation was continued at the 
end of the ninth period ; and the 
plant is seen to curve downwards 
during the last nine minutes. The 
clock is now stopped so that the 
klinostat is not alloived to turn . 
This is shown in the diagram by 
the symbols D, D, D for the ninth, 
tenth, and eleventh periods being 
all on the left, while the corre- 
sponding U, U, U are on the right. 
It will be seen that, in spite of the 
absence of the usual change of 
stimulus, the plant curves down- 
wards for half-an-hour before it 
curves upwards permanently. 
The diagram shows clearly enough that a rhythmic con- 
dition was set up during the fourth, fifth, and sixth periods. 
Owing to the difficulty of manipulation mentioned above 
(p. 248), the graphic method probably gives a truer record of 
the movement than the tabular summary. The change in 
direction of curvature occurs in the middle of the half-hour, 
and not at the end or beginning. This has already been shown 
in Exp. IV and V, and is a general feature of the rhythm. 
But the most interesting point shown in Fig. 1 is that after 
