92 EXPERIMENTS WITH 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 I 1 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 1 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 revolving 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 resnlt of in- 

 jury, influence of moisture, 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 



