of Rhythm in Plants. 247 
he considered to be an inherent power and named rectipetality. 
Since, as above pointed out, it is by no means clear that 
plants rotating on the klinostat are truly freed from stimula- 
tion, it seemed desirable to test rectipetality with our new 
instrument. 
A . vigorously growing internode was fixed to the inter- 
mittent klinostat with its axis parallel to the spindle. The 
clock-work was ungeared, so that no rotation could occur, and 
the plant was left until a distinct geotropic curvature was 
visible. The plant was now arranged so that the plane of its 
curvature was horizontal, and the clock-work escapement was 
set in action. The plant is now subject to alternate opposite 
geotropic stimuli in the vertical plane, i. e. at right angles to 
the plane of the geotropic curvature which it has already 
undergone. If it were not for these opposing and equal 
stimuli the plant would obviously assume a distorted form 
owing to the superposition of a fresh geotropic curvature in a 
plane at right angles to the first. But since no such distortion 
can occur, the original curvature can be studied. Under these 
circumstances it was found, as in Vochting’s experiments, that 
the curvature flattens out, and the plant becomes straight. 
Since this unbending or straightening occurs in a horizontal 
plane it can be in no way influenced by gravitation. This 
result, confirmed by a series of experiments, convinced us of 
the existence of an inherent regulating power which leads to 
growth in a straight line h 
Rhythm . We have succeeded in inducing a rhythmic 
condition by subjecting plants to alternate and opposite 
stimuli of a geotropic and heliotropic character. The geo- 
tropic curvatures, for which the above described form of the 
intermittent klinostat is employed, will first be considered. 
Vigorously growing shoots of a Valerian, or scapes of 
the dandelion ( Taraxacum dens-leonis ) are fixed in bored 
corks in test-tubes of water which are attached to the 
klinostat so that the axis of the plant is parallel to the 
1 These results were briefly published in the Proceedings of the Cambridge 
Philos. Soc. 1891. 
S 
