92 EXPERIMENTS WIIH PLANTS 



clock going. The roots grow well under these con- 

 ditions; do they continue to grow in different direc- 

 tions, or do all assume the same direction?^ Does this 

 (in connection with the previous experiments) indicate 

 that it is gravity which causes all roots, under ordi- 

 nary circumstances, to assume the same direction? 

 How do the stems behave ? It seems at first rather 

 puzzling to conclude that gravity, which causes roots 

 to grow downward, also causes stems to grow upward; 

 but there seems to be no escape from such a conclusion. 

 We may now go a step further and substitute an- 

 other force for that of gravity. This we may do by 

 making the wheel revolve more rapidly. If a piece 

 of wire is bent around the spoke of a wheel, so as to 

 form a loose ring, and one spins the wheel, the ring 

 will be hurled to the rim by a force commonly called 

 centrifugal force. If the wheel be turned rapidly 

 enough, the centrifugal force will be much greater than 

 the force of gravity. Will a seed ]'evolving rapidly 

 on such a wheel direct its roots in accordance with 

 the centrifugal force? To test this, we may construct 

 a water-wheel as shown in Fig. 76. Cut out of thin 

 sheet zinc a circular piece six inches in diameter. 

 Have this cut to allow the insertion of corks, as shown 



1 It may happen that the root will grow on perfectly straight in the direc- 

 tion given to it when fastened to the cork, or it may bend as the result of in- 

 jury, influence of moiiture, light, etc. If such bendings do not occur in the 

 control experiment (which should be made) it indicates that the directive force 

 ■which prevents such bendings, and causes all the roots to grow in the same 

 direction in the control experiment, has been nullified by the revolving wheel 



