Law of Proenvironment 



215 



in nature, but at different angles with each other, the pro- 

 environal course pursued is an exact resultant between the 

 lines of action and the intensity of stimulation of the different 

 stimuli applied. 



But even the same quality of stimulus, when applied at 

 varying distances, may cause proenvironal deviations that are 

 liighly suggestive. Thus the writer had under observation for 

 nearly two years a plant of the screw pine, Pandanus caricosus. 

 The strong thick aerial roots descended (Fig. 6) from parts 



Fig. 6. — Stem with branches of Pandanus caricosus that bear aerial roots. 

 The root to the right has bent, hydrotropically, so as to reach and penetrate 

 the soil of the pot. 



of branches that had spread out considerably beyond the cir- 

 cumference of the large flower-pot below. These roots grew 

 almost vertically do^\Tiward in virtue of geotropic, apohelio- 

 tropic, and weak hydrotropic action. Somewhat subdued 

 light reached the roots through a mass of vegetation, and 

 faintly but perceptibly caused uniform growth of all away from 

 that side. But when three and a half inches above the level 

 of and outside the circumferential range of the pot, and fully 

 fifteen inches above the cinder-covered soil below, the hydro- 



