THE EFFECT OF SOOT ON VEGETATION. 13 



By referring to the Annual Meteorological Summary 

 of Pittsburgh we find that the annual rainfall has 

 amounted to approximately 36 inches during the year and 

 that this has been uniformly distributed throughout the 

 year, and has not varied a great deal from year to year. 



In like manner, the monthly temperature reported 

 shows the same general uniformity as the other records. 

 Therefore these records will not account for the variations 

 noted below. 



THE REGIONS SELECTED. 



The following places were selected in Pittsburgh: 

 (a) Allegheny Cemetery, which is almost in the center of 

 the, town and nearly surrounded by large mills which 

 emit considerable quantities of smoke. This locality was 

 selected because it was believed that an idea could be 

 gleaned concerning the effect of smoke upon introduced 

 plants. Here no special injury to these plants was noted, 

 save a general impoverished condition, (b) Homewood 

 Cemetery, which is in the eastern part of the city about 

 midway between the Allegheny and Monongahela rivers 

 and almost two miles from any large mills. Here it was 

 found that native conditions were fairly well maintained 

 and the plants presented approximately normal condi- 

 tions, (c) Munhall Run is located where the smoke has 

 'been spread over the region from the large blast furnaces 

 and steel mills in Homestead for several years. Here it 

 was found that the vegetation and particularly the trees 

 were almost entirely killed for a distance of almost a mile 

 (Fig. 3). Across the river from these mills and near the 

 river is the Baltimore and Ohio Railroad, the smoke from 

 the trains of which, together with that from the mills, has 

 killed practically all the trees on the hillside and hilltop 

 (Fig. 4). Neither of these places enabled one to fix the 

 cause for the trouble quite so well as that of Aliquippa 

 and the nearby vicinity, about twenty miles down the 

 Ohio river from Pittsburgh. By referring to the map 

 the topography as well as the direction of the prevailing 



