246 MASS. EXPERIMENT STATION BULLETIN 170. 



street lighting systems are frequent, attention should be given to this 

 subject by those having the welfare of trees in their charge. 



It would, of course, be possible for injury to be produced directly to 

 the foliage of trees in close proximity to lamps resulting from the intense 

 heat produced by the electric current setting free poisonous gases from 

 the heated carbons used for lighting purposes, the carbons in such in- 

 stances being composed of or containing chemical substances which when 

 volatilized by intense heat and diffused in the atmosphere would be toxic 

 to plants. 



Moreover, it is possible for light itself to affect vegetation detrimentall3^ 

 It is well known that artificial lights differ from sunlight very materially, 

 and in proportion as they are characterized by rays of high refrangibility 

 they produce abnormal conditions on vegetation. However, the in- 

 jurious effects to plants resulting from various artificial lights can be 

 and are eliminated to a large extent by the use of globes and glass screens. 

 We have never observed, however, any detrimental effects upon shade 

 trees from an}' lighting system which could be attril)uted to any peculiaritj' 

 in the nature of the light itself. 



The carbons in the older type of arc lamps which have been extensively 

 used are supposed to be pure, while those used in the flame arc contain 

 certain admixtures, such as fluorides. The older type of arc lamps pro- 

 vided with pure carbons were apparently harmless to street trees and to 

 vegetation in general when the light was properly screened through glass, 

 although more or less delicate, rapid-growing plants became abnormal 

 when subject to the naked arc. 



Apparently the flame arc lamps have not as j^et been extensively em- 

 ploj'-ed on street circuits, and if the trouble to trees resulting from their 

 use is caused by the deposition of the products of combustion of the car- 

 bons on the foliage, which appears to be the most rational explanation, 

 it is not likely that any serious difficulty to street trees will follow their 

 use if ordinary care is given to the handling of the residue which gathers 

 in the globes. 



Injury to Trees from Wires. 

 The constantly increasing use of electricity for various purposes makes 

 necessary a more extensive use of wires, which has become a great menace 

 to shade trees. The appearance of streets is injured by the increased 

 number of poles and wires, and the legal restrictions as to the height, 

 distance apart, etc., of the wires of the telephone, telegraph, trolley and 

 electric light companies make the problem of maintaining shade trees on the 

 same street with public-service 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. Where 40-foot poles must carry the wires of three or four public- 



