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.^ 



Geotropic response in nature is illustrated in Figs. 



Fig. 



-Negative geotropism in a fleshy fungus growing on a tree trunk. 



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



posure and the efficient distribution of seeds and spores. 



130. Problems to Solve. — Many interesting questions 



now arise. How does the root, for e.xample, "detect" 



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

 on all sides. 



