ELECTRICAL INJURIES TO TREES. 11 



conductor for the current than the roots. The actual injury, therefore, 

 is clone by the current traversing the film of water rather than any of 

 the inner tissues. The maximum heat and the areas most affected are 

 near the base of the trunk. 



In regard to the possibility of injury to large trees by direct currents 

 passing directly through them, experiments show that what holds true 

 for alternating currents is true also to a great extent of direct currents. 

 However, it would require a voltage much higher than that furnished 

 by most electric railways at the present time. 



It might be possible for direct currents to produce a weakening 

 effect on the vital activities of the tree, although not causing any per- 

 ceptible burning. If, for example, a tree was subjected to a strength 

 of current equivalent to that represented between R and MX in Fig. 3, 

 page 2 (retardation current), there might occur a disintegration of 

 the cell contents, causing the tissues to become abnormal and finally 

 die, but the electrical resistance of trees is so great that a quite high 

 IDotential would be necessary. If the potential of the electric raihvay 

 systems were increased ten or twenty times it is possible that some 

 injury might result to trees even under ordinary moisture conditions. 



Probably the amount of ground leakage occurring through imperfect 

 rail connections would not cause any perceptible injury to trees. Xor 

 is there any direct evidence that lightning arresters when placed near 

 trees cause any injury by discharges. However, the guy wires used 

 by electric railway systems are a source of danger from lightning, and 

 we have observed cases where large limbs have been destroyed and 

 the trunks of the tree badly lacerated by electrical discharges from 

 these wires. 



On the whole, the eases of death to trees from electricity are by no 

 means so numei'ous as is generally believed. Because a large number 

 of trees near electric roads, etc., often look sickly it must not be con- 

 cluded that electricity is always the cause. In cities and towns, where 

 most of these unhealthy specimens are found, there are innumerable 

 destructive factors for trees to contend with. It is quite essential in 

 diagnosis work, therefore, that all of these factors be taken into con- 

 sideration before a definite opinion in i-egard to the cause of any 

 abnormal condition is formed. 



Electrolysis. 

 Direct current electricity is frequently responsible for electrolysis of 

 gas and water mains, and lead coverings of underground telegraph 

 circuits are often affected. The trouble is often so serious that the 

 iron gas and water pipes (Fig. 9, Plate III.) become corroded and eaten 

 with holes in a few weeks or months, causing leakage. When gas mains 

 are affected by electrolysis, the gas escapes and permeates the soil, so 



