THE TEEATMENT OF THE SHOOT 153 



of a looser nature, and contained more and larger vessels 

 (g) than the old wood {aJC), and the latter became still more 

 separated from the old bast (r) by the formation of new bast 

 (w*) on the outside of the cambium. At the point where the 

 cut was inflicted, the cambium (camb) bends down into the 

 original callus and forms there too new wood and bast, which 

 form the closing lips projecting from the healing tissues. 



If we imagine the branch to be cut through transversely, we 

 find this healing tissue starting on all sides as a ringlike out- 

 growth from the cambial and cortical cells, and gradually 

 approaching the centre of the cut surface, until the margins 

 of this circular crest meet in the centre. Here the margins 

 fuse and form a complete cap, covering the stump of the 

 branch. 



This process of covering may be completely successful, but 

 it must be remembered that no fusion ever takes place between 

 the old wood and the cap which covers it. Mature and com- 

 pletely thickened wood cells can never give rise to new cells, 

 nor ever fuse with new tissues. A protective growth of cells 

 may cover in a cut end of old wood as completely and as close 

 as you please ; but it can never nourish the wood nor prevent' 

 it from decaying. This is best seen in the case of stumps on 

 oak-trees which have thus become covered up. The healing 

 tissue may here have formed a complete cap, but if the latter 

 be knocked off, the wood of the former branch will be found to 

 be discoloured and. decayed. 



The quicker a wound is covered in, the smaller is the 

 danger of decay to the woody tissues. 



The rapidity of growth of the healing tissues depends upon 

 the proportion of the cambium layer to the area which has to 

 be covered. Consequently the conditions become more un- 

 favourable the larger the cross-section of the branch. 



Furthermore, of two equally large wounds, the one in which 

 the cambial activity is greater will be the first to heal com- 

 pletely. The rapidity of cell division, however, depends upon 

 the amount of nourishment which the cambium receives, and 

 this again is dependent upon the position and form of the 

 wound. 



The position of the wound is of importance, inasmuch as 



