EXERCISE 72 

 IN WHAT MANNER ARE WOUNDS IN TREES HEALED? 



Materials. Shade and orchard trees" with dead branches and 

 accidental injuries. 



Directions for work. Examine shade trees or neglected fruit 

 trees on which branches have died or broken and note the 

 growth of adjacent tissues over the wound. If possible, collect 

 pieces of wood showing all stages in the closing of a wound, 

 from the early condition, such as is represented in the slight 

 thickening about the base of a newly killed branch, to those 

 cases in which the opening is completely closed on the outside. 

 Split these pieces through the healing wound and describe the 

 process by which the wound is closed. Selecting a wound that 

 appears to be completely healed, note the original diameter of 

 the wound and the number of years required to close it. Note 

 also whether the wound is completely healed or whether there 

 is inclosed within it any partly decayed wood, which may be 

 infected with wood-rotting fungi and thus serve as a source of 

 infection for the heartwood of the tree. Do large or small 

 wounds heal the more perfectly ? 



Examine trees from which large branches have been removed 

 or which have been injured by the removal of relatively large 

 areas of bark, as street trees which have been gnawed by horses. 

 Do any of the wounds appear to be too large to be repaired 

 by natural processes before the wood of the trunk has seriously 

 decayed ? So far as you can determine by superficial examina- 

 tion, how wide an area may be successfully healed by natural 

 processes ? Would painting over the exposed wood with disin- 

 fectant substances assist in any way ? (Note that different 

 kinds of trees may differ widely in respect to ability to- 

 survive injuries.) 



Visit an orchard which has been " trimmed " within the last 

 few years. Note whether the cut surfaces are being healed 

 without decay. If possible, find cases in which the stub has 

 been left too long, thus hindering closure of the wound, and 

 other cases in which it has been cut too close to the trunk, thus 



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