ADJUSTMENT TO SURROUNDINGS 131 



in a vertical line, growth takes place by equal amounts, 

 in equal periods of time, throughout the entire diameter, 

 thus resulting in growth directly downward. 1 



Geotropic response in nature is illustrated in Figs. 



FIG. 89. Negative geotropism in a fleshy fungus growing on a treetrunk. 



87-89. Its value is evident in insuring good light-ex- 

 posure and the efficient distribution of seeds and spores. 

 130. Problems to Solve. Many interesting questions 

 now arise. How does the root, for example, "detect" 



1 Granting, of course, that all environmental conditions remain uniform 

 on all sides. 



