DAMAGK BY SMOKK, ASH, AM) I'LMKS 3G9 



sulphuric acid. CMicmical aualysis shows the presence of this acid 

 in the tissui'. W hen the acid hecomes sufificiently concentrated within 

 the tissues it is very toxic. Throu^ihout the valley and particularly 

 near the larger nianufacturint^ plants coniferous leaves die at the ends 

 and hecome reddish lirown. Many are prematurely shed and the foliage 

 is thin and open, as shown in figure 1 . The leaves of many hroadleaved 

 species curl at the margins. Some siiow hright hrown spots which 

 gradually increase in size and run together, giving a characteristic 

 mosaic appearance, as shown in figure I. 



The characteristic appearance of the foliage of both conifers and 

 hroadleaved species due to suljjhur dioxide poisoning is in evidence in 

 many places throughout the valley. The slow growth and thinness of 

 foliage of pines, spruces, firs, and hemlock, together with the browning 

 and casting of the leaves, makes their jjlanting even for decorative 

 purposes unwise near the centers of greatest atmospheric contamina- 

 tion. \\v(\ cedar and larch a])i)ear to be much more resistant than otlier 

 conifers in the vallc}-. The lesions or spots which often appear on the 

 foliage of hroadleaved species due to the destruction of the chloro])hyll, 

 although usually small at first, often in time embrace the entire leaf 

 and all the chlorophyll disappears. When this occurs the leaf ceases 

 to function and soon falls from the tree. . With some species, notably 

 elm and ash, every leaf on the tree may be affected. Birches, elms, 

 cherries, thorns, locusts, ash, and lindens appear to be more sensitive 

 to injury than willow, cottonwood, maple, and beech. 



Although the direct damage to the vegetation from the presence of 

 sulphur dioxide in the air is on the whole large, it is seldom that even 

 conifers quickly succumb. 



Wislicenus states that the injury noted above may begin when the 

 atmospheric contamination reaches one part of sulphur dioxide in one 

 million parts of air. 



It is already evident in Naugatuck Valley that the closer the vege- 

 tation is to the source of air contamination with sulphur dioxide the 

 greater the damage, though much depends upon the direction of the 

 prevailing winds. It is possible to classify the degree of injury by 

 mapping the vegetation in zones or belts of varying widths around each 

 important source of air contamination. As the different species show 

 considerable variation in the degree of sensitiveness to this poison they 

 serve in each of these belts as indicators of the amount of damage. 



