218 MASS. EXPERIMENT STATION BULLETIN 170. 



Paint. 



Ordinary house paint, although a crude enough treatment, has some- 

 times been used by ignorant persons on smooth bark trees, with, of course, 

 resultant injury. 



Miscibk Oil*. 



Occasionally commercial oils used for spraying fruit trees for the San 

 Jose" scale cause local injury, and some shade trees have been known to be 

 affected by their use. This is especially true of maples, and it is never 

 safe to use oils of any sort on many smooth bark trees. 



Road Oil 



Oils and other materials to keep down the dust in roadbeds are now 

 much in use, and we have observed some injur}- 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 penetrates deeply enough into the road- 

 beds to reach the root systems of trees is not as yet known, 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 sup- 

 posed 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 examined 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 

 are rare and the injury purely local in character. 



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 disintegration of the tissue. Whether these substances 

 did further injury to the tree we were not able to learn. 



Coal Tar. 



Coal tar is much used for painting wounds and scars caused by pruning, 

 and sometimes injures delicate tissue when first applied. The injury, 

 however, is not serious, as shown by the fact that various saprophytic 



