THE EFFECT OF SOOT ON VEGETATION. 11 



A. The general opinion is that the injury is due col- 

 lectively to the smoke and gases. 



9. Have you lived in other places where these conditions 

 of smoke and gas do not exist? 



A. They usually had. 



If so, state where, when, and how long, and give the 

 general conditions which existed at this place. 



A. Most had lived in other localities where they did 

 not have to contend with smoke and gases. 



The writer's Observations in the main confirm these 

 replies. The specific causes for these injuries may not be 

 so easily fixed, for it must be recognized that there are 

 a number of factors which must be considered, such as 

 rainfall, temperature, humidity, transpiration, various 

 soots and gases liberated from chimneys and smokestacks, 

 and dust. 



In order to show that plants are injured by various 

 by-products given off into the air by the industrial estab- 

 lishments, specific locations were selected and kept under 

 constant observation during the summer of 1912 and cer- 

 tain data, which will be presented later, were obtained. 



To get some general notion of the climatic conditions 

 of these regions, atmometer cups of the Livingston type 

 were employed and weekly readings were made. In addi- 

 tion to this, The Annual Meteorological Summary of Pitts- 

 burgh for the past four years was consulted. The atmom- 

 eter readings are given in the form of curves. The amount 

 of evaporation is given in cubic centimeters per 25 square 

 centimeters of evaporating area. The time intervals are 

 approximately seven days (Fig. 1). 



By referring to Figure 1, we note, in the first place, 

 that the curves for the most part run low, indicating a 

 comparatively high humidity for all of the districts, and 

 that each curve bears a strong resemblance to the aver- 

 age curve. In the second place, the periods when the trans- 

 piration was excessive were few and short. 



