134 



THE VEGETATIVE FUNCTIONS OF PLANTS 



then placed inside a covered box, to which the Kght is ad- 

 mitted only through a narrow sht in one side, the stimulus 

 of the one-sided illumination will be followed by a curva- 

 ture of the root away from the light, and of the stem 

 toward the light, as shown in Fig. 90. 



Fig. gj.- Mountain palm {Gaiissia sp.), growing on a steep, west-facing 

 cliff. The stems show a phototropic curvature toward the source of 

 most abundant light. 



The result of the simultaneous stimulation of root and 

 shoot by light and gravity is illustrated in Fig. 91. 



132. Phototropism. — The property of an organ by virtue 

 of which it may detect the direction of the source of incident 

 light rays is phototropism. Organs which respond by a 



