1907.] PUBLIC DOCUMENT — No. 33. 181 



is a very large number of leaks in gas mains at the present 

 time, and the number of cubic feet of gas which annually 

 escape into the soil is quite large. 



There are a great many joints in gas mains from which can 

 be detected only slight leakage, — perhaps from two to three 

 cubic feet a day; whereas there are others from which the 

 leakage is very extensive, and from which thousands of cubic 

 feet of gas escape into the soil in the course of a year. Even 

 these smaller leaks, where the outflow is only from two to three 

 cubic feet a day, are capable of injuring trees in the course of 

 time, since the soil becomes charged with gas to quite an ex- 

 tent in a few years. Should the roots of trees happen to be 

 near these leaks, the trees will become unhealthy, but perhaps 

 will not die. There are hundreds of city trees affected in 

 this manner, and gas is seldom suspected of causing their 

 sickly condition. In the eastern States, at least, there are 

 three kinds of gas used, — water gas, coal gas and oil gas. 

 So far as the effects of these various gases on trees are con- 

 cerned, there is apparently little or no difference, since they 

 all contain similar elements which are poisonous to trees. 



There are two classes of injury which may readily be dis- 

 tinguished as resulting from gas poisoning: first, incipient 

 cases ; and second, pronounced cases. In the first series we 

 have those already alluded to as resulting from small leaks, 

 and the ground in such cases never becomes fully charged 

 for any considerable distance. They may not result in killing 

 the tree directly, but cause it to be unhealthy, and there is 

 likely to be a large amount of dead wood found on such trees 

 annually. Occasionally a large tree may be located near a 

 small leakage, and in such a case only a single root will be 

 affected. Those portions of the trunk of the tree, in direct 

 connection with the leak will, however, show the effects of gas 

 poisoning. Small leaks of this description often produce only 

 local injury. Trees affected in this manner may suffer with 

 what is termed " general debility," — a term often used to 

 cover up a vast amount of ignorance concerning diseases in 

 general. In severe cases of gas poisoning, such as take place 

 where there is a large leak, the effects on a tree are very pro- 

 nounced, and there is absolutely no hope of recovery for a 



