40 



for any considerable distance. Such leaks may not result in killing 



the tree directly but cause it to be un- 

 healthy and shorten its life, and there 

 is likely to be an unusual amount of dead 

 wood annually found on such trees. 

 Occasionally a large tree may be located 

 near a small leak, when only a single root 

 will be affected, but those portions of 

 the trunk of the tree in direct connec- 

 tion with that root will show the effects 

 of gas poisoning. Small leaks of this 

 description often produce only local in- 

 jury but trees affected in this manner 

 may suffer with what is termed "general 

 debility," a term often used to conceal 

 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 pronounced, 

 and there is absolutely no hope of recov- 

 ery for a tree which has once been severely 

 injured. If a tree has been defoliated, 

 or even half defoliated, from the effects 

 of gas there is little or no hope for it. 

 There appears to be little difference in 

 the susceptibility of different species 

 to gas poisoning, but trees with a large 

 spread of loots are more likely to be 

 affected than those witli a limited spread. 



The characteristic symptoms of gas 

 poisoning are quite distinct to one 

 familiar with them, and can generally 

 be distinguished from other troubles 

 which are likely to affect a tree. 



One of the first effects in sum- 

 mer is a yellowing of the foliage, 

 followed by a greater or less defoliation 

 of the tree, according to the degree of poisoning. The trunk of the 



Fig. 20. Showing effects of 

 illuminating gas on elm tree 

 one and one-half years after 

 leakage occurred. From "Park 

 and Cemetery." 



