GROWTH 



185 



Experiments performed under these conditions have 

 proved that the root and the stem may be made to 

 assume any desired position, and generally to keep 

 growing in the direction in which they have been fixed 

 (see fig. 52, B i). 



So far we have supposed the wheel to rotate slowly, 

 but yet quickly enough to prevent the seed from remain- 

 ing a long time in the same position with regard to the 

 horizon : now let us make it rotate more quickly. In 

 this case a centrifugal force will be set up, just as when 

 we quickly twirl in the air a heavy body of some kind at 



FIG. 52. 



the end of a rope. This force acts, as it were, from the 

 centre to the circumference, as is easily seen by the 

 following experiment. A ring is placed on a smooth 

 spoke near the axle of a wheel which rotates horizontally. 

 As soon as the wheel begins to rotate at a moderate rate 

 the ring begins to slide down the spoke until it touches 

 the rim of the wheel. Therefore when this centrifugal 

 force acts upon bodies it compels them to move in the 

 direction away from the centre towards the circumfer- 

 ence of the wheel. It is clear that this force cannot 

 remain without influence upon germinating seeds. In 

 fact if we make the wheel B rotate fairly rapidly we shall 

 observe that rootlets and stems will assume a certain 



