GROWTH. 83 



pulley to the other end of which is attached a second pan contain- 

 ing a 5-gram weight. Fill the first pan firmly with moist sand, and 

 fasten a seedling of Bean in such position that it touches the sand. 

 It will push downward into the sand and elevate the w.eight-pan. 

 The scale-pan touched by the root may be suspended directly from 

 the horizontal arm by a delicate spiral spring, omitting the pulley 

 and second scale-pan. As the root grows it will push the pan 

 downward as before, and the distance through which the scale- 

 pan moves will indicate the force directly. The strength of the 

 spring can be determined by placing weights on the scale-pan. 

 (Fig. 71.) 



