256 Darwin and Pertz. — On the Production 
The klinostat is stopped between the fourteenth and 
fifteenth half-hours, and the plant curved downwards for 
thirty-one minutes before it reversed and curved upwards. 
Fig. 3 represents the movement of a dandelion-stalk ob- 
served on May 15, 1891 (Exp. VII). It is interesting because 
although the movement is at first very irregular, yet after 
eight to nine hours the half-hourly rhythm is so strongly im- 
pressed that two reversals of movement occur after the klino- 
stat is stopped, at the end of the seventeenth half-hour. 
It will be seen that at the end of the seventeenth half-hour 
the plant was curving 
upwards, and that it 
continued for exactly 
30' to do so. It then 
curved downwards for 
29' before it was again 
reversed and converted 
into a permanent apo- 
geotropic curvature. 
Fig. 4 gives the 
movement of a dande- 
lion observed on May 
22,1891. (Exp. VIII.) 
At the end of the 
sixteenth half-hour 
(when the klinostat 
was stopped) the stalk 
was curving upwards. 
It continued to do so 
until it had been 
moving in this direc- 
tion for 28', when it 
reversed, curved downwards for 29', and then permanently 
bent upwards. 
Fig. 5 gives the movement of a Valerian observed June 2, 
1891. (Exp. IX.) 
At the end of the thirteenth half-hour the plant was curving 
