1899.] PUBLIC DOCUMENT — No. 33. 165 



The death of many trees can be referred to ilhiniinating 

 gas. If a leak occurs in the pipe, the gas escapes very 

 readily into the soil, especially if it is porous, and when it 

 comes in contact with the roots they are asphyxiated, and 

 the result to the tree manifests itself very quickly. The 

 symptoms of gas poisoning are most generally a sudden 

 falling of the leaves, a deadened appearance of the bark, 

 due to the collapse of the cambium or living layer, brought 

 about by the asphyxiation of the roots, which results in the 

 rapid death of the tree. In mild instances of poisoning the 

 effect shows only upon one side of the tree, l)ut in general 

 the tree seldom escapes death. We have observed many 

 single trees killed by gas on the private grounds of city 

 residences, without the owner ever surmising what the 

 trouble was ; and this last summer we had an opportunity 

 to examine whole rows of native trees Avhich had died by gas 

 asphyxiation. Some of the trees which we observed were at 

 a distance of fifty feet from the nearest gas main, while others 

 succumbed when not nearer than one hundred feet to the 

 leak in the pipes. While it is advantageous to all gas com- 

 panies to stop these leaks as soon as they are found, it be- 

 comes practically impossible to do so in every instance, and 

 the death of trees from this source must constantly be ex- 

 pected. As a matter of fact, the death of some fine shade 

 tree is not infrequently the first indication the gas company 

 has of a leak in its main. 



Abnormal respiratory conditions, which usually result in 

 either a sudden or lingering death to trees, occur where they 

 have become submerged in water, or where they have been 

 covered with a foot or move of soil. We have noticed trees 

 growing beside sloping roadsides which had become filled in 

 with earth only on one side of the tree, resulting in that side 

 of the tree becoming dead, while the other side would linger 

 along in an unhealthy condition for years. 



Less often does the death of trees result from steam, as 

 the transmission of this is not so common. Occasionally, 

 however, where steam pipes are laid near trees, they are 

 sometimes injured. 



The various forms of concrete and pavements and the large 



