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. 



