58 TREE PR UNING. 



pruned, with the exception perhaps of trees growing 

 on very poor and barren soil. These, as a general rule, 

 can produce nothing more valuable than fuel, and 

 hardly justify the cost and labor of pruning. 



The Use of Coal-tar. Coal-tar, a waste product of 

 gas works, is a dark-brown imperishable substance 

 with the odor of creosote. It can be applied with an 

 ordinary painter's-brush, and may be used cold, except 

 in very cold weather, when it should be slightly 

 warmed before application. Coal-tar has remarkable 

 preservative properties, and may be used with equal 

 advantage on living and dead wood. A single appli- 

 cation without penetrating deeper than ordinary paint 

 forms an impervious coating to the wood cells, which 

 would without such covering, under external influ- 

 ences, soon become channels of decay. This simple 

 application then produces a sort of instanta- 

 neous cauterization, and preserves from decay wounds 

 caused either in pruning or by accident. The odor of 

 coal-tar drives away insects, or prevents them, by 

 complete adherence to the wood, from injuring it. 

 After long and expensive experiments the director of 

 the Parks of the City of Paris finally, in 1863, adopted 

 coal-tar in preference to other preparations used for 

 covering tree wounds, as may be seen in all the prin- 

 cipal streets of the capital. 



Objections to other Preparations. Efforts have been 

 made for a long time to discover some method of 

 covering the wounds inflicted on trees, either acciden- 

 tally or by the hands of man. The remedy usually 



