Centrifttgal Force as Geotropic Stimuli . 
725 
Description of the Intermittent Centrifuge . 1 
The centrifuge itself is composed of a rod RR (Text-fig. 1), with a rider 
5 carrying the growing-box B. The rod is a hollow brass cylindrical tube, 
100 cm. long and 1*9 cm. in diameter. It is fixed by its middle to the axis 
A. The axis of rotation is vertical and the rod horizontal, so that the 
centrifugal force is always exerted in the horizontal plane. The rider .S is 
composed of an oak block 4 cm. broad, 4 cm. high, and 17 cm. long. 
The rod RR passes through a central hole and the rider is clamped by 
a butterfly screw as shown in Text-fig. 1 , BS. At each end of the oak rider is 
a brass upright (KK\ Text-figs. 1 and 3), with a small V cut out at the top. 
The box which contains the seeds is made of cedar wood and is of 
dimensions 11-5x9x4 cm. A glass window is let into the hinged cover 
1 The instrument was constructed by Mr. S. W. Bush of the Electrical Laboratory in Oxford. 
3 d 
