370 JOURNAL OP FORESTRY 



It is well known from researches elsewhere that damage may extend 

 for a distance of 10 or even 20 miles from the source of impurities. 

 It is reasonably certain, therefore, that the large amounts of coal con- 

 sumed at many points in Naugatuck \^alley permit adequate sulphur 

 dioxide to escape into the air to cause more or less damage to all 

 vegetation. This damage, hoivcvcr, is chiefly in reducing the foliage 

 and as a consequence the rate of growth. 



Near the more important centers of coal consumption damage is 

 more or less apparent to the casual observer. It should be emphasized, 

 however, that a vast amount of damage in reduced growth occurs 

 before it is apparent to the average citizen. When the damage from 

 sulphur dioxide poisoning becomes so great it is conspicuous in the 

 vegetation the air has reached a degree of saturation far beyond that 

 of the first degree of damage. 



The injury to vegetation from sulphur poisoning is not only direct 

 through the action of sulphur dioxide on the foliage but is also indirect 

 as appears later in this paper. The indirect damage is due to the action 

 of the sulphur compounds in converting the insoluble gray oxide of 

 zinc which forms the bulk of the ash into the soluble zinc sulphate 

 which when in solution in the soil water is very harmful to surface- 

 rooted plants. Pierce says that "the soluble compounds of zinc are 

 highly poisonous to all plants though some species are better able to 

 withstand them than others.'' PfefTer says that ''zinc sulphate is a 

 very strong poison for all seed plants and when in solution in the soil 

 water it is readily absorbed through the roots." Baumann says that 

 "zinc salts can be presented to the living plant only in extreme dilution. 

 A watery solution containing more than five milligrams of zinc sulphate 

 to one liter of water (one part of zinc sulphate to two hundred thousand 

 parts of water) acts injuriously upon seed plants." 



Recent researches in Europe show that a large part of the damage 

 from fumes and dusts from manufacturing plants is done indirectly 

 through the effect of the chemicals contained therein on the soil and 

 humus. The damage to surface-rooted vegetation like grass and garden 

 truck in the Naugatuck Valley, particularly in the vicinity of brass 

 works appears to be chiefly due to this indirect effect rather than to 

 the direct effect of sulphur dioxide on the foliage. 



The dust which escapes from the stacks is identical with that which 

 remains behind as flue dust only it is more finely divided. It comes to 

 rest at a greater or less distance from the plant on the soil and on 



