26 MANUAL OF TREE DISEASES 



vicinity of Indianapolis, Indiana, it was computed that 1200 

 tons of soot to the square mile were deposited in a year, which 

 means ten and a quarter pounds to the acre every day. 



Other toxic substances which may accompany smoke are 

 carbon-monoxide, acetylene, ethylene, arsenic and various 

 toxic organic compounds found in the particles of tar accom- 

 panying soot. The action of all these substances, where they 

 accumulate in the soil, may cause direct or indirect injury to 

 plants. It is thought that the elimination of the lower forms 

 of plant and animal life in the soil may be the most important 

 injurious factor, although the substances may be directly 

 responsible for damage to growing, trees by being taken in 

 through the roots into the sap of the tree. 



Control. 



The prevention of smoke-injury is largely outside the power 

 of the individual. However, it should not be difficult for an 

 energetic community to secure relief from smoke conditions by 

 establishing some sort of city control of the smoke nuisance. 

 When the total elimination of smoke cannot be accomplished, 

 smoke-resistant trees should be planted where conditions are 

 worst. A careful study of the condition of those trees which 

 remain in the vicinity of the source of the smoke will show what 

 species should be chosen for replanting. 



Repeeences 



Bakke, A. L. The effect of city smoke on vegetation. Iowa Agr. 

 Exp. Sta. Bui: 145 : 383-409, figs. 1-22, map 1. 1913. 



Stone, G. E. Effects of atmospheric gases on vegetation. In Shade 

 trees, characteristics, adaptation, diseases and care. Massa- 

 chusetts Agr. Exp. Sta. Bui. 170 : 228-232. 1916. 



Buckhout, W. A. The effect of smoke and gas upon vegetation. Penn- 

 sylvania Agr. Exp. Sta. Ann. Rept. 1900-1901 : 297-324. 1902. 



Clevenger, J. F. The effect of the soot in smoke on vegetation. 

 Mellon Inst. Indus. Res. and School Spec. Indus. Bui. 7 : 1-26, 

 pis. 1-8, figs. 1-2. 1913. 



