DISCUSSION OF RESULTS. 19 



It will be observed that in all groups examined in the above table the 

 percentage of sulphur trioxid in the leaves is higher in the injured than 

 in the uninjured plants, and that the sulphur trioxid content varies 

 inversely with the distance from the smelter, i. e., the farther away 

 from the smelter the less sulphur trioxid in the leaves. It is regretted 

 that the distance from the smelter could not be considered more care- 

 fully in the California investigation, but, unfortunately, on account 

 of the very wild nature of the country the presence of high moun- 

 tains, deep chasms, etc. it was not possible to follow the course of 

 the fumes far in any one direction. Even if it had been possible it is 

 doubtful whether definite results could have been obtained, since the 

 smoke really had no one definite path, but by reason of the mountain- 

 ous nature of the country and the very narrow gorges the fumes fol- 

 lowed a large and variable number of channels. Again the fumes 

 would often drift over a high ledge and remain far above the ground, 

 not touching even the tops of the trees for a considerable distance, so 

 that any figures obtained on this basis would doubtless have been 

 misleading. 



COMPARISON AND DISCUSSION OF RESULTS. 



In Table 7 the results obtained by the author upon pine trees are 

 gathered together and compared with the results obtained upon east- 

 ern pines which had not been subjected to smelter fumes. It will be 

 observed that practically all of the pines, both injured and uninjured, 

 around the smelting works (which we will call the western pines) con- 

 tain more sulphur trioxid than the eastern pines and that the average 

 for the injured western pines is more than twice the average of the 

 eastern, while the average for even the uninjured western pines is 

 nearly twice as much as the average for the eastern. The percentage 

 of sulphur trioxid in the ash is also much larger in the western than 

 in the eastern pines. This must be due to one of two causes : Either 

 the western pines absorbed more sulphur trioxid from the soil than the 

 eastern pines or they absorbed more sulphur dioxid from the air. 

 Analyses of both the eastern and western soils upon which these various 

 trees grew show that the western soil does not contain any more sul- 

 phur trioxid than the eastern soils and therefore this increased sulphur 

 trioxid content in the western trees is almost certainly due to an 

 absorption of sulphur dioxid from the air. As stated above, this 

 absorption might kill some trees and not kill others, but there is little 

 doubt that if this absorption takes place year after year practically 

 all of the trees in this region will be finally killed. 



