THE EFFECT OF SOOT ON VEGETATION. 9 



tive to the amounts of solid impurities found in the air 

 at a number of stations. They attributed the observed 

 injury on vegetation to the blocking up of stomata, thus 

 impeding the process of transpiration; to the coating of 

 the leaf, thereby reducing the intensity of sunlight and 

 at the same time affecting the diffusion of car'bon dioxide 

 into the leaf; and to the corrosive effect of the acid it con- 

 tains. The injury took the form of a general reduction 

 in the size of the leaves and plants. It was also seen in 

 the narrowing of the annual rings in trees. 



