166 HATCH EXPERIMENT STATION. [Jan. 



surface of the ground covered by them about the city streets 

 are a menace to the health of trees, and the sickly conditions 

 which they present are often due to these. Some of our more 

 modern city streets obviate this matter by leaving- a wide 

 space of turf between the sidewalk and road, for the purpose 

 of planting trees. This gives the roots a chance to develop 

 normally, inasmuch as the respiratory functions are not in- 

 terfered with, as is the case when they are covered with 

 pavements. Many of the streets in Springfield are especially 

 commendable in this direction. 



Not a little of the disfiguration of trees is directly due -to 

 the linemen in lopping limbs, and more especially to the 

 direct effect of electric currents. We have observed no in- 

 stance where electricity has killed a tree outright, but there 

 are many cases where the linibs have been killed by burning. 

 This effect is not only caused by the alternating current of 

 the electric lights, but by the direct current of the trolley 

 system ; the latter current being probably more injurious, 

 provided the same amount of amperes and voltage is em- 

 ployed. The damage done by grounded wires takes place 

 when trees are moist, as at that time the resistance is re- 

 duced, and the current becomes increased and has a better 

 opportunity to become dispersed. We have known of in- 

 stances where trees and the grass for some distance about 

 them have been charged with the escaping current. The 

 damage to the trees, however, is due to the heating eifect 

 of electricity. The wire becomes grounded on a limb, and 

 when moist the current escapes. At first comparatively 

 little current passes through the limb, as the resistance is 

 high ; but, as the heat increases the resistance decreases, 

 with the result that a large amount of current passes through, 

 which gives rise to still more heat, and subsequently develops 

 into a blaze. The action of electricity, as we have already 

 stated, is local in its effects. The injury, while sufficient to 

 kill every portion above the limb or trunk, does not, so far 

 as our observation goes, destroy the tissues very far above 

 the point of grounding. There are reasons for believing, 

 however, that the effects of the direct current are more 

 severe than those of the alternatino; current. In the case of 



