ROOTS 



91 



81. ROOTS 

 Object. Same as in Experiment 76. 



Method. To show how a root obeys both gravity and 

 water in its direction of growth, place a triangular piece of 

 wood small end down- 

 ward. Cover it with sev- 

 eral layers of filter paper 

 and saturate it with water. 

 Fix a young seedling as 

 in Figure 31 so that its 

 roots hang down. 



Leave it standing for a 

 few hours and note change 

 of direction. 



Make a sketch to show 

 original position and with 

 a dotted line indicate any 

 change in direction of the 

 root. 



Note. See also Experi- 

 ments 42 and 64. 



FIG. 31. a, root in original position: 

 b, root in new position ; c, wood ; d, water. 



Geotropism 



It has been demonstrated in several experiments that 

 roots of a plant have a more or less definite tendency to 

 grow downward. This property is known as geotropism. 



We say that roots are positively geotropic when they grow 

 downward towards the earth's center. 



Stems may be negatively geotropic when they grow up- 

 ward or away from the earth. Stems which creep or lie 



