Law of Proenvironment 



213 



of the sporangiophore in line with the incident rays. So in 

 such an illustration as that of Fig. 5 each individual plots 

 and pursues a proenvironal path that is different in angular 

 relation to every other one. But all execute such movement 

 that the most beneficial result is secured to the species, in 

 resulting growth and dissemination of the spores. The sur- 

 prisingly accurate manner in which the sporangia hit a circum- 

 scribed light-orifice is a striking proof of lines of energy-dis- 

 tribution and of cell tensions in relation thereto. 



Fig. 5. — Growth of the Fungus Piloboliis on horse manure, b, placed under 

 belljar, a, the exterior of which was lined with black paper except for orifice at 

 c. From resultant action of apogeotropic and specially of heliotropic stimuli 

 the black sporangia are discharged accurately against the orifice. 



But the feeding or absorptive threads of this fungus, which 

 are a continuation of the same elongate plant cell that produced 

 the spore masses, exhibit proenvironal responses of a totally 

 opposite kind, though equally beneficial for the species. Thus 

 these grow either directly or obliquely downward into the 

 manure through geotropic action; they at the same time grow 

 away from the light or are apoheliotropic; they also are influ- 

 enced hydrotropically by the moisture of the manure and so 

 grow toward it to absorb food material. All three of these 



