Treating Cankers ' 297 



the work must be done with great care in order to insure 

 that all trace of the fungus is eliminated. Whenever the 

 cankers occur on limbs that can be removed without 

 detriment to the tree, it is best to remove them while 

 pruning; care being taken to cut several inches below any 

 visible injury, as the living fungus in the brown-rot canker 

 extends back beyond any external evidence of the dis- 

 ease, and if allowed to remain will continue to infect 

 healthy wood. If the cankers occur on limbs that it is 

 desirable to save, they should be cleaned out by removing 

 all the diseased wood a short distance back of any visible 

 evidence of the disease. The diseased wood and bark can 

 be readily detected by its brown color. In the brown-rot 

 cankers it is very important to remove all this discolored 

 tissue, as it is in this tissue that the fungus lives and if it is 

 not removed the disease will spread. The amount of bark 

 that it is necessary to remove depends on the extent of 

 the diseased part. Sometimes the fungus has extended so 

 far beyond the healthy callus that it is necessary to remove 

 it entirely; while at other times the fungus may have 

 extended but slightly into the upper and lower extremities 

 of the callus and it is necessary only to remove a small 

 part. It is always well to leave as much of the callus as 

 possible, to facilitate healing. All the dead bark and twigs 

 should be removed. It is not necessary to remove any of 

 the solid wood except to smooth the treated part. The 

 wound should be pointed at the upper and lower extremi- 

 ties and the bark should be cut at right angles to the 

 wood. As soon as the wound has dried out it should be 

 coated with gas-tar. The gas-tar acts as a disinfectant 

 and preservative, and no other treatment is necessary. 

 Trials have been made in order to determine this point, 

 and it is now evident that the use of corrosive sub- 



