167 



It must be noted that no growing together, or intimate 

 union, is possible between the living cells of the callus and 

 the dead elements of the wood which were exposed on the 

 wound surface, and, although the callus grows over and is 

 closely adpressed to the wood, the junction between them 

 always remains as a distinct line of separation." This is often 

 well seen in the case of hammer-marks stamped on the 

 exposed wood of a blaze, the latter having been subsequently 

 completely healed over as described above. Years afterwards 

 such a mark may be clearly . distinguished deeply embedded 

 in the trunk, the letters and figures having been merely covered 

 over by the new wood and hence not obliterated. 



145. If, in the above example, Bruises, 

 the outer tissues of the sapling had been crushed and bruised 



by a blow from a hammer, or other means, instead of being 

 removed by a clean cut, rapid healing in the manner describ- 

 ed would have been impossible. The bruised cambium and 

 cortical tissues die, contract, and remain adhering to the wood 

 below, thus obstructing the formation of a callus by the living 

 tissues bordering the wounded patch. Such wounds in conse- 

 quence do not heal easily. 



146. Now, instead of wounding Wounds 



the stem itself, we will suppose a branch to have been aused b 

 cut off. If the cut has been made just above one or more 



leafy shoots, the latter will keep the living tissues of the 

 stump alive and the severed end will eventually be healed 

 over by callus tissue. If the stump carries buds* the 

 wound may stimulate the development of these into leafy 

 shoots and the healing process will be as before. If, on the 

 contrary, such a branch stump bears no buds, or leaves, the 

 tissues will dry up and die. The living cambium and cortical 

 tissues of the stem, at the base of the dead stump, now develop 

 a ring of callus tissue around the stump, but the formation 

 of this callus and its further extension up the stump are much 

 impeded by the dead cortical tissues of the latter, which remain 

 adhering to the dead wood and under which the callus has to 

 force its way. The healing is consequently much delayed and 

 the dead tissues of the stump frequently rot before the' process 

 is complete, the decay then spreading into the sound wood of 

 the trunk and causing a hollow stem. Hence, in all cases of 

 pruning branches, the latter should be cut off close to the 

 stem, the cut surface being parallel to the surface of the stem, 

 the healing process then being similar to that described for a 

 simple stem wound, In order to prevent decay spreading in 



