47 



injured. There are, however, no authentic cases of an alternating 

 current completely killing a tree, and the injuries caused by this 

 current occur only during periods of moisture, when there is a 

 grounding. Owing to the high resistance of trees it would require 

 an exceptionally high potential to furnish sufficient curient to kill a 

 tree even if wires were inserted into limbs and roots and the current 

 allowed to pass through the tree. In all cases, so far as has been 

 observed, the injury resulting from alternating currents is due to 

 burning. 



When grounding takes place leakage occurs, causing burning and 

 steaming which, if the contact continues, will cause a blaze and burn 

 a deep hole in the limb. Sometimes a tree may be injured a few 

 feet above and below this burning, but it never extends to the base 

 of the tree. Occasionally the grounding is so marked that it is dan- 

 gerous for one to come into contact with a tree, and a person stand- 

 ing on the ground and touching his fingers to the leaves would re- 

 ceive quite a severe shock. 



During periods of damp weather neither rubber nor porcelain in- 

 sulators prevent leakage in high tension wires ; consequently, when 

 even insulated wires are brought into close contact with trees some 

 escape of the current takes place. Injuries to trees often occur 

 when alternating current wires during storms accidentally come in 

 contact with other wires attached to trees. For this reason there is 

 always risk, as has already been pointed out, in allowing any wires 

 to be attached to trees. 



Direct Currents. 



Direct currents of electricity are chiefly employed by electric rail- 

 ways, although occasionally used for lighting purposes. A direct 

 current appears to have a different physiological effect upon, and is 

 more disastrous to protoplasm than an alternating current, since it 

 causes disintegration of the cells, and there is reason to believe that 

 a direct current is capable of killing a tree even if the strength of 

 current is not sufficient to cause burning. 



The direct current, like the alternating, causes injury to trees by 

 burning, and there are instances known where it has killed trees. 

 In some instances the base of a tree has been girdled to a distance 

 of ten feet or more from the effects of direct currents from trolley 

 lines, and in such cases the trees have died from electrocution. 



