ELECTRICAL INJURIES TO TREES. 19 



the polarity in electric railway systems have become reversed; i.e., the 

 rail becoming positive and the feed wire negative. 



The burning is more pronounced at the positive electrode than at the 

 negative, and when the current is reversed a larger area of tissue is 

 affected. The burning arises from the heating of the film of water on 

 the bark, which destroys the live tissue underneath. 



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

 a protection against severe injury from lightning and contact with high- 

 tension line wires. 



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

 adjacent tissues. 



The electrical resistance of trees is influenced materially by tempera- 

 ture and moisture. 



The physiological effect of the direct current on vegetable life differs 

 from that of the alternating. 



There is evidence to support the idea that a direct current of not 

 sufficient strength to cause burning may electrolize the cell contents and 

 later result in the death of the tree. 



Earth discharges during thunder storms are more common than gen- 

 erally supposed, and are known to disfigure and cause the death of 

 trees. 



