14 



those usually of the kind, occurring as a result of the electrical con- 

 tact of live wires with the trees, that it was quite evident something 

 very unusual had taken place in these instances. On electric railroad 

 systems, the positive current almost universally traverses the feed 

 wire, and it is at the point of contact with the feed wire that most 

 injury takes place. In all cases where trees were killed by 

 electricity, this condition of things was reversed, namely, the positive 

 current was conducted through the rail, and the return current 

 through what is usually the feed wire. How common the practice 

 has been of operating on this system, we cannot say. Nevertheless, 

 it has been practiced, unintentionally perhaps, by various companies 

 at one time and another. Such practice is responsible in some 

 instances for die killing of shade trees adjacent to the rails. 

 Undoubtedly the conditions at the base of the tree are much more 

 favorable than near the limbs for extensive burning. The moisture 

 condition of the soil and bark are such that the resistance, would be 

 reduced and cause the current to spread over a large area. It is 

 evident in this case, at any rate, that the current had gained access 

 to a large area of the cambium layer, thus girdling the tree to a con- 

 siderable distance, that portion of the tree trunk towards the rails 

 being more severely affected than that away from the track. There 

 were no deep burning effects on the trunk, either above or below in 

 any of these instances, as is quite customary when the positive wire 

 comes into contact with the tree. The area, however, affected about 

 the ba.se of the tree was decidedly larger than that usually occurring 

 when the positive or feed wires are brought into contact with limbs. 

 Shortly after the trees were injured, the bark could be readily 

 removed from the trunks, and later fell off. The trees killed were 

 elms and maples, i8 in. or more in diameter, and in each case they 

 were in the legitimate tree belt, being about three feet from the rails. 

 These experiments and observations, pertaining to the effects of the 

 direct current on plants, demonstrates that we have a variety of con- 

 ditions to deal with, in considering the effects of electricity on trees. 

 A current can be increased in two ways, namely, by decreasing 

 the resistance or increasing the voltage. If the voltage of the trolley 

 system is increased to 5000, we would obtain a current equal to only 

 250 milliamperes in the experiment where we obtained 25 milliam- 

 peres, through 16^ ft. of the maple trunk; and it will require a 



