3G8 JOURNAL 01' I'ORESTRY 



the armistice was signed. What effect this rapid increase in manu- 

 facture and the resulting increase in atmospheric contamination has 

 had on a vegetation already suffering from impurities in the air has 

 not been adequately studied to permit of definite conclusions. The 

 writer has spent some time studying the situation and has completed 

 a series of investigations which throws some light on the amount and 

 cause of the damage in specific localities. 



From a general study of the woody vegetation of the valley it is 

 apparent that the coniferous species- are gradually disappearing and 

 their places taken by more resistant broadleaved species. Although the 

 general aspect of the forests on the slopes at either side and the isolated 

 trees on the floor of the valley on the whole exhibit but little change to 

 the casual observer aside from the gradual disappearance of the coni- 

 fers, the experienced observer is impressed by the thinness of the 

 foliage as compared with forests on similar sites out of reach of 

 atmospheric impurities. The growth of all species throughout the 

 valley is slow and increment borings made in a number of localities 

 indicate a marked falling off in growth since iQi.j or since the great 

 increase in atmospheric impurities. Although studies are far too frag- 

 mentary for specific proof, the writer believes from those already made 

 that the annual increment throughout the Naugatuck Valley is reduced 

 somewhere between 25 and 50 per cent from the effect of atmospheric 

 impurities. 



Damage is by no means confined to the trees. Lesser vegetation of 

 all kinds has also been injured and in certain localities near the stacks 

 of large manufacturing plants grass has disappeared from the lawns 

 and vegetable gardens have been ruined. 



The damage throughout the valley has been chiefly due (a) to 

 the large quantities of sulphur dioxide (SO.) emitted with the smoke 

 from all establishments that burn coal; {b) to the large quantities of 

 zinc sulphate (ZnSo^) derived from the flue dust (zinc ash) emitted 

 with the smoke from brass works. In addition lo these most important 

 causes of injury other materials emitted with the smoke may cause 

 minor injury l)ut certainly not sufficient to be detected in the general 

 appearance of the vegetation. For practical purposes, therefore, the 

 damage to vegetation in the Naugatuck Valley can be assigned to the 

 two materials mentioned above. 



It is well known that when sulphur dioxide enters the air and comes 

 in contact with the foliage of plants it is absorbed and oxidized into 



