INSECTS, DISEASES, AND INJURIES 149 



Injury from this cause is very difficult to diagnose in the 

 living tree, as the symptoms are very diverse and many of them 

 are also exhibited by trees which are declining for other reasons. 

 A general sickly appearance, with yellowing or browning of 

 the leaves and probably partial defoliation, may first be seen. 

 This usually commences at the top of the tree and progresses 

 downward. The twigs become brittle and lose their bark, and 

 this shedding of the bark may continue until a large portion 

 of the trunk is bare. Unless the trouble is remedied in time, 

 death of the tree results. If a tree is deteriorating and no other 

 cause of injury can be found, the above symptoms would 

 warrant one in suspecting illuminating gases as the causal 

 factor, but no degree of certainty could be felt without a 

 careful examination of the tissues. The wood shows a marked 

 brittleness, while the tissues outside of the wood are dry and 

 brown. The roots, naturally, are the first parts to be affected. 

 The wood of affected trees possesses a characteristic odor for 

 one who is familiar with this trouble. One would also be able 

 to detect the smell of gas in the soil. 



If the injury is very extensive, it is doubtful whether any 

 remedial measures will be effective in saving the trees, although, 

 as mentioned above, conifers may recover after considerable 

 exposure. If only a portion of the roots is affected, they should 

 be removed. After the leak has been repaired, the soil should 

 be dug up and well aerated for several days or, better still, 

 it should be replaced by other soil which is not impregnated 

 with the gases. 



Wood-rots. 



While very serious losses occur in coniferous trees in the 

 forest, due to several destructive wood-rots, these diseases 

 rarely cause much damage to individual ornamental specimens. 



