SHADE TREES AND FORESTS 483 



Miscellaneous injuries. Shade trees are subject to injury 

 from a number of causes due largely to man's carelessness. 

 Chief among these are gas escaping from the mains, the 

 regrading of streets, the hitching of horses to trees, and the 

 trimming of trees to make way for telephone and electric 

 wires. Sometimes whole rows of trees may slowly die be- 

 cause the gas escapes from the pipes and reaches the roots. 

 This may be avoided by requiring the gas company to lay 

 pipes that do not leak. In grading streets oftentimes trees 

 are cut down which could be saved by a little care. If the 

 street is being cut down, the sidewalk may usually be run a 

 little to one side of the tree and the dirt left as a mound around 

 the tree. If the street is being filled in, a well of bricks may 

 be built around the tree to prevent the dirt from filling up 

 the space. When electric and telephone wires are being 

 strung, the tops of trees are often cut out, leaving the tree 

 unsymmetrical and disfigured. Every city and town should 

 have ordinances protecting its shade trees from these and 

 other injuries. 



Insect enemies. Trees are subject to injury from a great 

 variety of insects, which may attack every part of the tree. 

 One group of insects, like the elm beetle and tussock moth, 

 feed on the leaves, another group, called borers, gnaw their 

 way into the bark and wood, destroying the cambium layer ; 

 others, like the scales, suck the sap from the leaves and other 

 soft parts of the tree. Some insects injure the roots and some 

 the flower and fruit. These insects may attack the trees in 

 such numbers that serious harm is done in a short time, or 

 the harm may be extended over several years, the trees 

 gradually becoming weakened, sometimes eventually dying, 

 and in other cases living for many years in this sickly con- 

 dition. Many of these insects may be controlled by spray- 

 ing. For biting insects, like the elm beetle, a poison such as 

 Paris green or lead arsenate is sprayed on the leaves, and the 

 insects are killed by eating the poisoned leaves. For suck- 



