TREATMENT OF WOUNDS 47 



certainly die and permit the entrance of fungi and 

 borers, no matter how effectively these may have 

 been excluded from the upper part. The de- 

 tached wood must be chopped or sawed away, so 

 as to make a good water-shed, and so as to make 

 it certain that there is healthy bark, in connection 

 with the rest of the bark of the trunk, around 

 every part of the wound, ready to start a callus 

 over it. Of course it is not to be supposed that 

 so large a surface will be grown over, at least for 

 a very long period of years. The covering given 

 the exposed surface should therefore be a thorough 

 one, of metal or reinforced asphalt. Large sur- 

 faces of metal on bending trees have a tendency 

 to tear out at the nails, a tendency, however, 

 which can be partly remedied by putting the metal 

 on in vertical strips overlapping each other. 



Frost cracks and the effects of lightning will 

 also be included in this discussion of mechanical 

 injuries, for they are like the truly mechanical 

 ones in result if not in cause. Frost cracks are 

 fairly common, but their origin is not generally 

 understood. The cracks first come to the notice 

 as long but very narrow openings lengthwise of 

 the trunk or main branches. After one or two 

 seasons they usually develop long, narrow, light- 

 colored projecting lip-like calluses on each side of 

 the crack. These calluses grow and project 

 farther and farther from the trunk as the years 



