402 PRINCIPLES AND PRACTICE OF PRUNING 



within five minutes after the final trimming cut is made. (4) All 

 cut and shellacked surfaces shall be painted with commercial 

 creosote, followed by thick coal tar. (5) All diseased, rotten, dis- 

 colored, water-soaked, or insect-eaten wood shall be removed in 

 cavity work and the cavity inspected by the owner or his agent be- 

 fore it is filled. (6) Only a good grade of Portland cement and 

 clean, sharp sand in no weaker mixture than one to three shall be 

 used to fill cavities. (7) The contractor shall repair, free of ex- 

 pense, any defects that may appear in the work within one year. 



Tree owners are urged to remember at all times the axiom : The 

 need of tree surgery 15 or 20 years hence may be very, largely 

 obviated by promptly attending to the fresh injuries of today. 



312. Electrical injuries to trees. According to G. E. Stone* most 

 of the injury to trees from trolley or electric light currents is local ; 

 i. e., the injury takes place at or near the point of contact of the 

 wire with the tree. This injury is done in wet weather when the 

 tree is covered with a film of water, which provides favorable con- 

 ditions for leakage, the current traversing the film of water on the 

 tree to the ground. The result of contact of a wire with a limb 

 under these conditions is grounding of the current and burning <>f 

 the limb due to "arcing." The vital layer and wood become in- 

 jured at the point of contact, resulting in an ugly scar and some- 

 times the destruction of the limb or leader. In a large number of 

 tests made by the aid of sensitive instruments with guy wire and 

 other connections of wires to trees we have never found any leakage 

 during fair weather, or when the surface of the tree is dry. 



313. Preventing injury to tress from wires. The constantly in- 

 creasing use of electricity for various purposes makes necessary a 

 more extensive use of wires. These have become a great menace 

 to shade trees. The appearance of streets is also hardly improved 

 by the increased number of poles and wires, and the legal restric- 

 tions as to the height, distance apart, etc., of the wires of the tele- 

 phone, telegraph, trolley and electric light companies make the prob- 

 lem of maintaining shade trees on the same street with public serv- 

 ice corporations a serious one. 



Of all the troubles with which tree wardens have to contend the 

 wire problem is often regarded as the worst. Notwithstanding the 

 strict laws which some states have adopted in regard to injuring 

 shade trees, the agents of some public service corporations often 

 have little regard for trees or the laws respecting them. \Yhere 

 40-foot poles must carry the wires of three or four public service 

 corporations there can be little or no opportunity to preserve the 

 natural symmetry of shade trees, especially when low-branching 

 trees are planted on the same side of the street with the wires. 



The best solution of the wire problem lies in burying the wires. 

 This has been done a good deal in large cities, especially in the busi- 

 ness sections. It is an expensive system, however, and those who 



* Massachusetts Agricultural Experiment Station, Bulletin 165. 



