16 



ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 



Fig. 17. — A tree severely injured by illuminating gas usually shows rapid 

 wilting, browning, and death of leaves, followed by dying of branches and 

 death of the tree. In elms, gas injury may be mistaken for phloem necrosis. 



Mild injury by gas is difficult to differentiate from other 

 injuries, similar in appearance, that may be caused by some in- 

 fectious diseases, nutritional deficiencies, high temperatures, too 

 little or too much water, and internal physiological difficulties 

 within a tree. Mild injury can be caused by leaks of 2 to 5 cubic 

 feet of gas per day. A mildly injured tree shows irregular, yel- 

 low discoloration of many leaves, somewhat similar to that in 

 chlorosis ; discoloration is followed by premature falling of in- 

 jured leaves and also of some green leaves. Later the tree pro- 

 duces another crop of small, light green leaves, and some twigs 

 and branches may die. A gas leak that results in only mild injury 

 to trees may or may not be sufficient to kill the surrounding 

 grass and other plants. 



A tree that is only slightly injured by gas may be saved by 

 prompt treatment. The gas leak must be stopped, and the soil 

 around the tree roots should have air forced into it to replace the 

 gas. The day after aeration the soil should be thoroughly washed. 

 A watering needle or lance may be used to supply sufficient 

 water to saturate the soil and to force large quantities of the 



