142 SHADE-TREES IN TOWNS AND CITIES 



breaking of gas-pipes, and the resulting leaks sometimes 

 kill a row of trees of an entire block. 



A very small leak does not saturate the soil at once, and 

 may not be the cause of the immediate death of a tree. Its 

 effect is bound to tell in time, however. The tree will assume 

 an unhealthy look, the foliage will become yellow and thin 

 at the top and there will appear a large amount of dead 

 wood that will not be accounted for in any other way. 



Symptoms of Gas-Poisoning. The symptoms of gas- 

 poisoning are characteristic. The effect of a large leak 

 upon a tree is very pronounced. The foliage turns yellow, 

 wilts, and falls from the tree. There is no mistaking the 

 cause. The effect of a small leak is yellowing of the foliage, 

 followed by a greater or less defoliation of the tree, accord- 

 ing to the degree of poisoning. Limbs here and there die, 

 the bark becomes loosened in places, and fungous growths 

 make their appearance on the trunk and the main branches. 

 The poisoned soil generally becomes darker than its natural 

 color. The roots and the sapwood of the lower trunk be- 

 come discolored blue, and have a most offensive odor. 



The writer recalls a case when he very carefully watched 

 a number of street-trees affected by gas-poisoning. There 

 were several varieties among them. The elms died first, 

 and soon afterward the bark began to loosen and drop from 

 the trunk and main branches. The sugar maples died next. 

 The red maples withstood the effects of the gas the longest. 

 One red maple in particular was observed for about three 

 weeks, the ground at the roots of which was badly saturated 

 with gas. The foliage did not dry up at once, but gradually 

 dropped from the tree, beginning at the top. Ulcers were 

 formed on the trunk and main branches, and the sap oozed 

 out from splits in the bark. It was frothy white and had a 



