INJURIES TO SHADE-TREES 143 



fermented odor, as that of cider. Finally, all the foliage 

 of the tree was gone, the sap stopped flowing, and the tree 

 was dead. 



The formation of ulcers and the oozing of sap are not 

 necessary symptoms of gas-poisoning, however, but may 

 follow other diseased or weakened conditions of trees. See 

 page 199. 



The wilting of the foliage of a tree following its attack 

 by borers is sometimes mistaken for gas-poisoning. When a 

 branch of a tree becomes riddled, the exposed wood dries 

 and checks, and in the course of time the draft of sap is 

 interrupted and the end of the branch dies. The wilting of 

 the foliage in such cases makes one suspicious of gas. An 

 examination of the branch, however, will reveal the true 

 source of injury. 



How to Detect Leaks. — The presence of gas can be 

 detected by making a hole in the ground, three or four feet 

 deep, with a crowbar, and applying the nostrils to the open- 

 ing. Unless the leak is extremely slight, the gas can usually 

 be discovered by the above method. A more certain way of 

 proceeding, however, is to insert a piece of gas or other pipe 

 into the hole made by the crowbar, and draw up and inhale 

 through the nostrils or the mouth the gases at the base 

 of the opening. The slightest amount of gas in the soil 

 can be detected in this way. When the gas is present in 

 the soil in large quantities, it can be ignited by applying a 

 match at the opening made with a crowbar. It will burn 

 with a flash. This method, however, should not be used in 

 testing for gas-leaks. It is extremely dangerous, as it is 

 likely to result in an explosion of the gas-main. 



When a slight leak is discovered before the injury pro- 

 ceeds very far, the tree can be saved by quickly repairing 



