18 MASS. EXPERIMENT STATION BULLETIN 156. 



in Fig. 14, No. 2, is cumbersome and unsightly, but is one of the most 

 effective. The principle of the porcelain and dowel insulator is good, 

 but it has a tendency to slide on the wires and become displaced. If it 

 were provided with larger dowels, and the danger of displacement on 

 the wires done away with, it would prove much more satisfactory. 



Wires often accidentally come into contact with trees by the dis- 

 placement of poles, particularly on curves, where the strain is very 

 great, but much of this injury may be prevented by imbedding the 

 poles in Portland cement. It should be pointed out that the necessity 

 for guying poles to trees may be obviated in this way. 



Better methods of handling this vexatious question of wires and 

 shade trees should be forthcoming in the future, and even at present 

 there must be a compromise between the tree warden or city forester 

 and the companies as to the best method of wiring through tree belts 

 and the amount of pruning allowed. Conditions at present favor the 

 corporations, as they are furnishing valuable and necessary facilities 

 for business, etc., and in towns they obtain their franchises and loca- 

 tion of poles from the selectmen with little difficulty. The selectmen 

 notify the abutters of any contemplated installations of poles and wires 

 or of changes to occur in the systems, and the abutters are given a 

 hearing. However, they usually wake up to their duty only after the 

 installation of the lines, when the tree warden must assume all respon- 

 sibility for injury to the trees. He has to choose between two courses, 

 — prevent the pruning or permit it. In either case the comi^anies can 

 erect the poles and install the wires, allowing the wires to burn their 

 way through the trees, although this, of course, often causes trouble 

 to the corporation as well as to the consumer. In case of injury to 

 trees the warden has access to the courts, but most companies are will- 

 ing to put up with a few moderate fines for the sake of the right of 

 way through a tree belt. 



Summary. 



Electricity acts as a stimulus to plants. The minimum and optimum 

 current strengths probably differ little in different plants. The maxi- 

 mum current, or that necessary to kill a plant, is quite variable. 



Outside of the disfiguration to trees from pruning necessitated by 

 wires, the greatest injury consists in the local burning and often partial 

 destruction of the tree caused by high-tension line wires. 



There is practically little or no leakage from wires during dry 

 weather. In wet weather, however, when a film of water is formed on 

 the bark, more or less leakage occurs, and if the insulation is insuffi- 

 cient, grounding takes place and burning, due to " arcing," results. 



No authentic cases have been observed by us where the alternating 

 or direct currents as ordinarily employed have killed trees; but in- 

 stances are known in which the death of trees has taken place when 



