16 INJURY TO VEGETATION BY SMELTER FUMES. 



A glance at Table 4 shows that of the 25 groups of trees examined 

 20 groups, or 80 per cent, contained more sulphur trioxid in the 

 leaves of the injured trees than in the leaves of the uninjured, while 

 only 5 groups (E, I, J, L, R), or 20 per cent, showed the reverse. It 

 is further shown that 80 per cent of the injured trees contained a 

 larger percentage of sulphur trioxid in the ash than the uninjured 

 trees, while only 20 per cent (C, E, L, R, X) showed the reverse. 



It will be noted in groups I and J that although the uninjured tree 

 contains slightly more sulphur trioxid than the injured one, yet 

 the percentage of sulphur trioxid in the ash in both cases is much 

 lower in the uninjured tree than in the injured. It would appear 

 from this that the injured trees in these groups were undoubtedly 

 killed by sulphur dioxid, but that the whole ash content of the unin- 

 jured trees, and consequently their sulphur trioxid content, was so 

 much greater than that of the injured trees that even when the latter 

 absorbed sulphur trioxid not enough was taken up to increase its 

 percentage in the foliage over that naturally contained in the unin- 

 jured tree. For groups C and X the opposite is true; so that although 

 in these groups the sulphur trioxid content of the injured tree is 

 greater than that of the uninjured, it would appear that they were 

 not killed by sulphur dioxid fumes. 



Such an increase of the sulphur trioxid content of the injured trees 

 over that of the uninjured trees in so large a number of cases must 

 have some significance. It means either (1) that the injured trees 

 grew in soils containing more sulphur trioxid than the uninjured 

 trees; (2) that the injured were of a more vigorous growth than the 

 uninjured trees, or (3) that the former absorbed more sulphur dioxid 

 from the air than the uninjured trees. The first can not be the true 

 cause, because the different groups of trees (one injured and the 

 other uninjured) were taken near each other from the same soil, 

 which on the average would give approximately the same amount of 

 sulphur trioxid in both trees. The second can not be the true cause, 

 for if the injured trees had been more vigorous the} 7 would have been 

 the ones to live under the same conditions. The third, then, must be 

 the true Cause for this increased sulphur trioxid content in the 

 injured trees. 



It might be asked why all of the injured trees did not show a higher 

 sulphur trioxid figure than the uninjured ones. It must be remem- 

 bered in this connection that trees sometimes die of natural causes, 

 and that in taking a large number of samples it was impossible for 

 the chemist to tell which trees died from natural causes and which 

 from sulphur dioxid fumes. The whole investigation is not intended 

 to show that all injured and dead trees were affected by sulphur 

 dioxid, but to show whether or not the large majority were. 



Again it might be asked why one tree should be killed by sulphur 

 dioxid and one close by not killed. This might be caused by several 



