PRUNING SHADE TREES 145 



surface with a coat of shellac. This should be applied 



with a brush to the edges of the wound, covering the bark 



and at least half an inch of the wood. This should be done 



as soon as the cut is dry enough to hold the shellac, and 



within three or four minutes at the most after the 



cutting. The shellac serves to prevent loss of moisture, 



and since the cambium, or inner bark, will die if it is 



allowed to dry out, the coating is an essential step. 



Wounds more than half an inch in diameter require 



artificial protection during the process of healing. This 



protection is given by painting with shellac and following 



this by coating the center of the wound with coal tar, 



creosote or lead paint. The shellac forms one of the best 



protecting covers for the sensitive tissue between the 



bark and the wood where growth takes place, and which 



is called cambium layer or cambium. It is the least 



injurious to this vital but sensitive part of the tree of all 



of the substances now known. As it is not permanent 



when exposed to weather, especially moisture, it needs 



to be coated with one of the other substances mentioned. 



The shellac need not be applied to the whole wound if the 



cambium is thoroughly covered, including an inch of the 



adjacent wood. 



If the wound is large, it' should be sterilized by applying 



antiseptic after the application of the shellac. There are 



several preparations of this nature, and among these one 



of the best is creosote, which has a particular value in 



destroying the germs of decay and preventing destruction. 



The creosote is applied with a brush and should cover all 



of the exposed wood not covered by the shellac. On top 



of the shellac and creosote the surface should then be 



covered with a thick coating of coal tar to keep out 



water. This waterproof coating should be renewed from 



year to year, whenever there is a tendency to crack or 

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