372 JOURNAI^ OF FORESTRY 



reaches 2j grams per square foot of surface and all vegetation is quickly 

 killed zvhen it reaches 200 grams per square foot of surface. 



The damage to lawns and gardens due to the absorption of zinc 

 sulphate through the roots is conspicuous in many parts of the valley. 

 In some places even in midsummer the sod has been destroyed and the 

 soil covered with dead grass. Even with the best of attention the grass 

 becomes very thin and dies out in large patches giving the lawn a sun- 

 scorched appearance. The total destruction of all surface vegetation 

 is particularly noticeable in depressions, at the base of trees and where 

 the ash collects in more than average amount. Thus large amounts of 

 ash reach the areas immediately around the base of the tree trunks due 

 to its accumulation on the crowns and later being washed by the rains 

 down the trunks. This accumulation causes the death of the grass, 

 as shown in figure 3. It is also noticeable that there is no grass at 

 the corners, as shown in figure 2, and under the eaves of buildings 

 where washings from the roofs flow over the surface, due to the accu- 

 mulation of ash on the roofs being washed at times of rain onto a 

 limited area of surface. In general the grass is likely to disappear 

 in all low places or depressions in lawns and on terraces facing the 

 source of air contamination due to these areas receiving an excessive 

 amount of ash. 



In order to determine the amounts of ash (flue dust from zinc mills) 

 that cause diiferent degrees of injury to grass and other surface-rooted 

 vegetation and in order to ascertain a practical method for overcoming 

 the injury seven series of experiments consisting of twenty-nine sep- 

 arate numbers were planned and executed by the writer in the summer 

 of 1920. 



Ash was collected from the stack of a large brass mill in Naugatuck 

 Valley. In one series of experiments the ash in varying amounts was 

 applied to definite areas of a thrifty grass plot. In another series the 

 ash was mixed with air-slaked lime before being applied. In looking 

 about for a practical method of neutralizing the toxic effect of the zinc, 

 lime suggested itself as a possible remedy. European investigations 

 have shown that lime is especially necessary in soils exposed to acid 

 fumes. In the second series of experiments varying amounts of air- 

 slaked lime were mixed with the ash and applied in different quan- 

 tities to equal areas of a thrifty grass plot. 



The results obtained from two series of experiments permit the 

 following conclusions : 



