SHADE TREES. 



217 



the trunks with this oil to kill clusters of gypsy moth eggs, it being used 

 without any knowledge of its adaptability to this purpose. (Fig. 91.) 

 The oil quickly soaked into 

 the bark, cortical tissue and 

 cambium, and in some cases 

 extended into the sapwood 

 for one-half to three-fourths 

 of an inch. This injury 

 occurred even on trees with 

 fairly thick bark, killing all 

 the living tissue wherever 

 the oil was applied. While 

 in some instances the trees 

 did not show extensive in- 

 jury, in others the trunks 

 were 50 to 90 per cent, 

 girdled, and many of the 

 trees died from complete 

 girdUng. The most striking 

 feature of this case was the 

 ability of the trees to pro- 

 duce perfect foliage even 

 after serious injury had 



Fig. 91. — Effects of spraying heavy oil on trees. 

 The oil penetrated tlie bark and killed the 



tissue. 



taken place. One tree was examined whose trunk 

 was girdled for a height of 15 to 20 feet, but this 

 tree persisted in producing foliage for two years after 

 the bark had fallen off. An explanation of this 

 remarkable case consists in the fact that the heavy 

 oil soaking into the sapwood prevented it from 

 checking or cracking, therefore the supply of water 

 from the roots was uninterrupted. The trees treated 

 were elms, different species of maples, which are 

 especially susceptible to injury, and others. The 

 presence of oil in the sapwood in the cases cited above 

 was of the greatest aid in preventing cracking and 

 in helping to maintain the transpiration current and 

 normal foUage, and this bears out the recommenda- 

 tion that tree wounds, very soon after they are 

 formed, should be painted or treated in some way to 

 prevent cracking. It is sometimes necessary to 

 scrape the wound before applying the paint. 



Fig. 92. — Maple in- 

 jured by burning 

 leaves near the base 

 of the tree. 



