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. 
