182 EXPERIMENT STATION. [Jan. 



tree which has once been severely injured by gas; in short, 

 where a tree has been defoliated or even half defoliated from 

 the effects of gas, there is no hope for it, although it might be 

 possible, if one could dig up all the soil around it and expose 

 it to the air, to eliminate much of the gas in the soil, in 

 which case the tree might make some attempt to recover. 



The characteristic symptoms of gas j^oisoning are quite 

 marked to one familiar with them, and can generally be dis- 

 tinguished from other kinds of injury which are likely to 

 ' affect a tree. It requires, however, pretty close observation 

 and thorough understanding of conditions in order to dis- 

 tinguish gas poisoning from some other types of injury which 

 may occur. For example, in the gypsy moth district about 

 Boston the trunks of many trees have been treated with crude 

 oil and various other substances which are exceedingly in- 

 jurious to trees. Crude oil or kerosene, when sprayed on the 

 bark of a tree, will penetrate the wood to some extent. Un- 

 less one is perfectly familiar with the characteristic symptoms 

 of trees poisoned with gas, it would be a very easy matter to 

 confound these two classes of injuries. In both cases the bark 

 becomes loose and falls off the tree very quickly. From care- 

 ful observations of the trunks of trees, however, the effects of 

 crude oil can generally be distinguished from those caused by 

 gas, by one who is familiar with these characteristic injuries. 



In general, however, the symj)toms shown by trees affected 

 with illuminating gas are quite different from those arising 

 from other causes which are likely to be active. Trees affected 

 with gas are very susceptible to rapid disintegration. One of 

 the first effects .of poisoning in summer would be a yellowing 

 and drying up of the foliage, and a greater or less defoliation 

 of the tree, according to the degree of poisoning. The trunk 

 of the tree is generally dark colored, indicating an absence of 

 life ; but this feature is not always present. 



The occurrence of various species of fungi on trees affected 

 by gas is rather conspicuous, since these fungi are often very 

 numerous, and make their appearance soon after a tree has 

 been injured ; whereas on trees dying from other causes it is 

 sometimes many years before the bark becomes covered with 

 fungi. The sap wood is often found to be discolored, and it 



