ELECTRICAL INJURIES TO TREES. 9 



lionally at times to prevent electrolysis as well as unintentionally by 

 various companies, and is responsible in quite a few instances for the 

 death of shade trees near electric railroads. There is much greater 

 opportunity for extensive burning in the case of reversed polarity 

 than in the regular systems employed. The moisture conditions of the 

 soil and bark are such as to reduce the resistance, and in consequence 

 the film of water and water-soaked bark become intensely heated, de- 

 stroying the living tissues and girdling the tree to a considerable dis- 

 tance. The part of the trunk towards the rail is almost invariably 

 the most severely aifeeted. In the cases observed some years ago, where 

 the cuiTcnt was reversed, there were no deep burning effects on the 

 tree either above or below, — the rule when the overhead feed wire is 

 positive (as is usually the case) and in direct contact with the tree. 

 Moreover, the affected areas about the base of the tree are decidedly 

 larger than when a positive overhead feed wire comes into contact with 

 limbs. The entire area between the base of the tree and the overhead 

 wire is not, as a rule, affected, although the extent of injury may vary 

 somewhat. The injury from burning is confined to a space around the 

 overhead wires, and also to the base of the tree. On the elm shown in 

 Fig. 8, Plate IV., the burning was caused by a reversed system, and there 

 was only slight injury at the point of contact with the overhead wire, 

 while at the base about 6 or 7 feet of the tree was affected. This injury 

 takes place when the soil and bark of the tree are moist, and may occur 

 during a single period of excessive moisture, or intermittently. In 

 some instances trees show serious effects a short time after the current 

 has been reversed, when the bark will become loose and later fall off. 

 The writer has obser\'ed both elms and maples — some of them 2 feet 

 or more in diameter — which have been killed in this way. In some 

 cases the trees were not moi'e than 3 feet from the rails, while in others 

 the distance was considerably greater. 



In one well-planted city having extensive street railways, 51 trees 

 were reported killed or so badly injured as to be of no value, 67 had 

 large limbs removed, and many more were saved by removing limbs 

 likely to come into contact with the wires. According to Mr. G. A. 

 Cromie,^ who had these under observation, the injured trees were in 

 some eases located from 200 to 1,000 feet from the track. Some of the 

 injury took place on streets having wires but no electric railways, and 

 it is surmised that the ground connections were made through several 

 pipe lines, located near the trees, Avhich led very close to the electric 

 railway. Mr. Cromie states that the effects on the trees were noted 

 shortly after the street railway had changed its system, i.e., using the 

 rail to carry the positive, and the overhead wire the negative or return 

 current. The trees in contact with the overhead wire became electri- 



1 G. A. Cromie, "Scientific American" supplement, No. 1985, p. 40, Jan. 17, 1914. 



