INSECTS, DISEASES, AND INJURIES 163 



with ordinary commercial creosote and the entire shellacked 

 and creosoted surface finally waterproofed with thick coal-tar 

 or asphaltum. Should the color of the tar be objectionable, it 

 may be replaced by a covering of thick bark-colored paint. 

 This will need careful watching, however, for paint has a ten- 

 dency to crack, and such cracks are sufficient to permit the 

 entrance of fungi. 



Removal of bark. 



In many cases, the larger limbs or the trunk of the tree 

 are attacked, either in the living portions or in the heart wood, 

 thus necessitating the local removal of the diseased tissues. 

 The excavation of the heartwood would not in any way interfere 

 with the life processes of the tree, but, as the sapwood and bark 

 are the channels through which water and food materials 

 pass up and down the tree, they must be conserved as far as 

 possible. If the diseased area extends more than two-thirds 

 of the way around the trunk or limb, it is doubtful whether 

 treatment would be possible, for, as has been pointed out above, 

 a portion of healthy tissue must always be removed as a 

 safety zone. 



In peeling off diseased bark, a sharp hook-pointed knife 

 is most useful. The bark is first cut through to the wood 

 around the margin of the area to be removed, making it V- 

 shaped above and below. The bark is then peeled off and the 

 edges trimmed with a sharp knife. As soon as the exposed 

 surface is sufficiently dry, it should be covered with a coating 

 of shellac and waterproofed with thick bark-colored paint, 

 tar, or asphaltum. 



Cavity work. 



Removing diseased wood involves the making of a cavity 

 and requires expert workmanship if the best results are to be 



