DAMAGE TO TREES BY GASES 167 



The presence of a sudden leak of large volume, result- 

 ing from a break in a main, will usually show itself through 

 changes in the appearance of all vegetation within a nearby 

 circle. When the tree is in leaf, a flowing leak of this nature 

 may generally be located by noting where the damage is 

 greatest, for it will be found that the leak is near the center 

 of the area affected, and nearest the particular tree which 

 appears to suffer most seriously. The exact location may 

 then be determined by the sense of smell. 



When the trees are in foliage, gas poisoning which 

 results from a sudden flow of gas makes itself immediately 

 visible by the action of the gas on the leaves. As a result 

 of the poison the leaves turn yellow, wilt, and finally fall. 

 Later, the bark is apt to drop off in small patches, while 

 dark blue stains may be found in the inner bark and in the 

 roots. In the case of a smaller and more gradual leak the 

 leaves turn yellow and droop, foliage is gradually thinned 

 by the falling of some of the leaves, and a general 

 appearance of unhealthiness and loss of vigor shows itself 

 in the entire tree. 



While the signs mentioned may result from other 

 causes, and do not always indicate gas poisoning, their 

 appearance makes it important that an immediate investi- 

 gation should be made for the location of a possible leak. 

 The surest proof of the presence of gas is its odor, which is 

 so pervasive that it cannot be overlooked and is not likely 

 to be confused with any other scent. When there is the 

 slightest suggestion of this odor, steps should be taken at 

 once to locate its origin. Even if the sense of smell does 

 not detect gas when the symptoms of trouble appear, a 

 careful search should quickly be made for the purpose of 

 determining whether or not gas is to blame. In this search, 

 one or more holes should be made in the ground with a 

 crow-bar, to a depth of three feet or more. When the 



