DAMAGE TO TREES BY GASES 
171 
ous that where coal smoke and other harmful gases are 
present, tree planting should be confined to the varieties 
which are least damaged by the gases. 
Trees in the vicinity of cement plants suffer from the 
deposit of cement dust on the foliage. Dampness may 
cause the dust to “set” or harden, which results in damage, 
although rain is apt to wash it off. The gases from open- 
air furnaces, used for melting tar and asphalt, and from 
steam rollers sometimes do serious harm. 
There is no remedy for trees affected by atmospheric 
gases. Removal of the cause is the only way to put a stop 
to the trouble. The construction of tall smoke stacks 
helps to overcome the danger. 
Trees weakened from the effect of gases, as from other 
causes, are more subject to insect and disease attacks than 
are healthy trees. 
