250 Darwin and Pertz. — On the Production 
In this experiment it is clear that downward movement at 
the beginning of the half-hourly periods (absent in Period 4), 
is a physical effect. We may assume that but for the physical 
droop, the movement would have been continuous from one 
period to the next. We can therefore get an approximate 
idea of the growth of the shoot if we add each of these short 
periods of ‘ sagging ’ to the figures immediately below them. 
In this way we obtain the following figures, representing the 
times during which the shoot curved, first in one direction (A) 
then in (B) the opposite. Beginning at period 3, we see that 
it curved up for fifteen minutes, adding in the previous 
three minutes of sag, and calling this curvature A, we get — 
A = 18, B = 35, A = 14, B = 29, A = 31. 
Here we see the beginning of a half-hourly rhythm at the 
end of the fifth half-hourly period, that is after about three 
hours. This is shown by the fact that the shoot curved for 
twenty-nine minutes in direction B, then reversed the move- 
ment, and after thirty-one minutes again curved in direction B. 
Exp. III. May 21, 1889. Dandelion . 
p. 
Minutes. 
Movement. 
I 
28 
D 
II 
30 
D 1 
j- 46 '= A 
III 
16 
13 
U J 
D ; 
IV 
5 
5 
D ( 
u ] 
! 2 3 '= B 
20 
D i 
j- 3 V'= A 
1 . 
V 
i 7 
1 1 
u j 
D 
VI 
3 
9 
13 
5 
D 2 $ — B 
u ) 
D 
not observed 
