DISCUSSION OF RESULTS. 



21 



ined the ash of the injured trees contains a larger percentage of sul- 

 phur trioxid than the ash of the uninjured trees. East of the smelter, 

 in 75 per cent of the cases examined the injured trees contain more 

 sulphur trioxid than the uninjured trees, both in the dried leaves 

 and in the ash, and west of the smelter, in 67 per cent of the groups 

 examined the injured trees contain more sulphur trioxid than the 

 uninjured ones, while in 78 per cent of the groups examined the sul- 

 phur trioxid content of the ash of the injured trees is higher than 

 that of the uninjured trees. It would be expected that more trees in 

 a northerly and southerly direction would be killed by the sulphur 

 dioxid fumes than in an easterly or westerly direction because of 

 the prevailing winds, and this expectation is justified by the above 

 figures. 



TABLE 8. Study of sulphur trioxid content of foliage of trees in California, 

 arranged according to direction from smelter. 



TREES NORTH OF SMELTER. 



TREES EAST OF SMELTER. 



TREES SOUTH OF SMELTER (ALL LOCATIONS EAST OF SHASTA CALLED SOUTH). 



