PRUNING 251 



(80), it follows that when a branch is cut off at some dis- 

 tance from the member that supports it, the wound usually 

 will not heal, unless there are leaves beyond the wound to 

 manufacture food, and thus make a growth current possi- 

 ble (72) . The cut should, therefore, be made close enough 

 to the supporting member so that it can be healed from 

 the cambium of the latter. In woody plants there is 

 usually a more or less distinct swelling about the base of 

 a branch (Fig. 156), produced by the cambium of the 

 supporting member, and just beyond this swelling a more 

 or less distinct line marks the point where the cambium 

 of the branch and of the supporting members unite. In 

 a healthy tree a wound made by a branch of reasonable 

 size, cut off at this line, will usually heal promptly, but 

 if the cut is made much farther out, it will not. 



Wounds so large that they cannot heal promptly should 

 be painted with lead and oil paint to preserve the wood. 



419. Unhealed wounds introduce decay into the 

 heartwood of trees, since the cells of the heartwood 

 form a congenial field for certain destructive fungi (321), 

 that having once gained entrance sooner or later destroy 

 the heartwood of the whole trunk, thus greatly weaken- 

 ing it and preparing the way for the final destruction of 

 the tree. 



420. Objects of pruning. — If intelligently performed, 

 pruning has one of four objects in view, viz. : (a) To change 

 the form of the plant, as to outline or density (formative 

 pruning), (b) To stimulate development in some special 

 part, so as to promote the growth of wood or the formation 

 of flower-buds (stimulative pruning) . (c) To prevent some 

 impending evil to the plant, e.g., to arrest or exclude disease 

 (protective pruning), (d) To hasten or retard maturity 

 (maturative pruning). 



