THE EFFECT OF SOOT ON VEGETATION. 25 



5. It is a well established fact, based upon results 

 of other studies, that fumes containing sulphur dioxide and 

 sulphur trioxide do considerable injury to vegetation. It 

 is also known that the gases, ethylene, a constituent of il- 

 luminating gas; carbon monoxide, benzene, hydrogen sul- 

 phide, and carbon bisulphide are injurious to plants. 



