21 



insulation is insufficient and contact with the tree exists, grounding 

 takes place, and burning due to arcing, results. 



No authentic cases have been observed by us where the alternat- 

 ing current, employed for lighting service, has killed trees, though 

 there are authentic cases, extremely rare, where the direct current, 

 used in operating street railroads, has killed large shade trees. This 

 has been accomplished by reversing the polarity, causing the posi- 

 tive current to traverse the rail, and the return current the feed 

 wire, which usually carries the positive. 



The high resistance offered by trees and plants, in general, serves 

 as a protection against death from an electrical contact. 



The least resistance in trees occurs in the vital layer, (cambium), 

 and those tissues adjacent to it. 



Electric currents of whatever nature, when applied to plants of a 

 certain intensity, act as a stimulus. 



The physiological effect of the direct current on vegetable life 

 differs from that of the alternating : the latter current acts more as 

 a stimulus to the plant than the former. 



There is evidence to support the idea that a current, of not suffi- 

 cient strength to cause burning, may over stimulate the plant and 

 cause a retardation of its activities which will subsequently result 

 in death. 



Earth discharges during thunderstorms are more common than 

 generally supposed, and they are known to disfigure and cause the 

 death of trees. 



