86 



HEALING < >K \V< lUNDS 



or b) a cut into the truk that removes the tissues as far as the 

 xylem it will be noticed that the exposed cambium is stimulated 

 to form a mass of large cells, the callus, that gradually extend 

 over the wound if this is not too large. While the callus is still 

 in process of forming an outer protective layer of cork tissue is 

 developed and also a new cambium layer is formed on the inner 



side of the callus which finally unites the old camhium. thus 

 continuing the camhium of the stem over the surface of the wound 

 (Fig. '>4. ./). In this way wounds are covered or healed and 

 the tissue exposed by the cut is gradually buried deeper by the 

 annual addition of new tissue derived from the camhium ( Fig. 

 04, />', (.'). Grafting is made possible owing to the formation of 

 callus that unites the tissues of the scion and stock 1 Fig. 65). 

 While grafting is performed in a variety of ways the pri 

 consists essentially in all cases of bringing the camhium and 

 cortex of the cutting or scion in contact with the corresponding 



Ik, 1.5 A common method of grafting: ./. insertion of t\\" scions into 

 cleft of stock .it cambium region. B, wound protected with wax to prevent 

 drying out of ti .u<r I.. II. Bailey. 



>n of the stock. The junction of the scion with the stock is 

 sealed with grafting wax to prevent decay and the drying oul 

 of the exposed cells while the callus is joining together the corres- 

 ponding tissues in the two parts. When the wound is h< 

 only a slighl ring or swelling indicates the point where the scion 



inserted so complete is the union of the vascular and cor- 

 tical regions. Strang* , although the organic union i> 

 complete, each part, with ver) rare exceptions, continues a sepa- 

 rate and distinct 1 pie, a scion from a plum 



