14 



ILLrNOIS NATURAL HISTORY SURVEY CIRCULAR 46 



Fig. 15. — Leaves of trees sensitive to 2,4-D injury grow long and narrow, 

 and the veins become unusually prominent. The severely injured English 

 elm leaves in this picture have become twisted and rolled. 



Injury to trees from applications of tree food, or fertilizer, 

 has been observed on some trees, especially on oak affected with 

 severe dieback of branches and on trees that have large areas 

 of dead bark on the trunks. Such areas of dead bark, which may 

 not show externally and may therefore be overlooked, usually 

 can be detected if the trunk of an affected tree is tapped with 

 a knife or ax for evidence of hollow areas. Fertilizer injury is 

 indicated by browning and yellowing of leaves, especially along 

 the margins and between the veins (Fig. 16). Young leaves may 

 stop growing and appear dwarfed. Many fibrous roots may die. 

 Loss of these roots greatly reduces the amount of food and water 

 supplied to the foliage. Most mildly injured trees recover; many 

 of them do not even lose their leaves. Most severely injured trees 

 lose their leaves, and some of them die. 



Natural gas is relatively nontoxic to trees. However, in 

 large quantities it will displace the oxygen in the soil and cause 

 suffocation of roots. Illuminating gas is toxic. Injury to trees 

 from illuminating gas varies from mild to severe and is in- 

 fluenced by the amount of gas that reaches the roots from leaks 

 in gas mains. Leaks are most apt to occur in old mains. It has 

 been suggested that injury to the trees is caused by hydrogen 



