1913.] PUBLIC DOCUMENT — No. 31. 81 



are now much in use, and wc have observed some injury from 

 this source, when the trees were located close to the highway and 

 the buttresses of the roots were exposed. The roots are much 

 more susceptible to injury from various causes than are the 

 trunks as they are not so well protected by bark, and when oil 

 sprinkled on a roadbed touches some of the exposed roots it kills 

 the tissue. Particles of dust from oiled roads which sometimes 

 alight on the foliage of trees are said to cause injury, but this 

 type of injury is rare with us. Whether the oil ever extends 

 deeply enough into the roadbeds to reach the root system of trees 

 is not known as yet, but if it does it may cause serious injury. 

 Neither are there specific cases of injury to the roots of trees by 

 the dripping of oil and gasoline from automobiles, although if 

 this leakage were sufficient it might reach the roots and cause 

 injury. Not long ago, however, our attention was called to a 

 tree supposed to have been killed by gasoline leakage from a 

 near-by garage. 



Creosote. — This material is used extensively on trees for 

 disinfecting cavities, and mixed with lampblack for painting 

 gypsy moth egg clusters. It does not appear to penetrate to 

 any great extent when combined with lampblack. We have ex- 

 amined a great many trees to discover injuries from its use 

 with no success except in the case of linden roots which had been 

 exposed by regrading, where the underlying tissue was injured. 

 But such instances arc rare and the injury purely local in char- 

 acter. 



In one case a combination of creosote and naphtha applied 

 to a large number of trees for the destruction of gypsy moth 

 caterpillars appeared to soak into the outer bark, apparently 

 killing the cork cambium, which later resulted in a disintegra- 

 tion of the tissue. Whether these substances did further injury 

 to the tree we were not aide to learn. 



Coal Tar. — Coal tar is mucn used for painting wounds and 

 scars caused by pruning, and sometimes injures delicate tissue 

 when first applied. The injury, though, is not serious, as shown 

 by the fact that various saprophytic fungi have been applied 

 over dead, punky wood. Therefore after coal tar has been on 

 for some time it is evidently not injurious to even delicate 

 tissue. 



