92 



ROOTS 



prostrate, and secondary roots which extend outward from 

 the main root, are said to be neutral, since they show neither 

 positive nor negative geotropism. 



Many interesting experiments may be devised by the use 

 of an apparatus called a clinostat. This is a revolving sup- 

 port run by clockwork, and cap- 

 7/ able of being made to rotate at 

 any angle. 



Glass, 



Thistle 

 tube.... 



Water. 



82. ROOTS 



Object. To measure the ra- 

 pidity of growth. 



Method. Arrange a thistle tube 

 or funnel as in Figure 32 and place 

 a seedling in position. 



...Cork. 

 Thumb tacKS 



.....Threads 

 ;'...,, Seedlings 



...,,-MarKed root 



Jar 



.....water 



FIG. 32. 



FIG. 33. 



As the sprout pushes downward, mark its termination 

 from time to time by thread or mucilaged markers. 



If conditions of heat, light, etc., are varied, the effects of 

 these agencies upon rapidity of growth can be noted and 

 measured. 



