717 



normal. The part hp. passes over gradually into the regular wood much 

 more distinctly divided by medullary rays (m). The transformation of the 

 bark elements, taking place parallel to the change of the wood elements, will 

 be described more in detail in the callus rolls due to girdling. 



When the trunk grows further, the cambial zone (c) always deposits 

 new normal wood and new bark with hard bast {hh') above the wound sur- 

 face and when finally the old parts of the bark {ar) , separated by the pre- 

 vious incision, with their cork zone (^) and the dead wound edges of the 

 bark formation {t) which have been separated by the cork zone of living 

 tissue, die and scale off, the wounded place externally becomes smooth and 

 even. 



We will have to consider Fig. 175, if we wish to go somewhat more in 

 detail into the beginnings of the process of healing. This represents a cross- 

 section through a single wound edge of a place of scarification (Fig. 173 6) 



^ 7c 



Fig:. 173. Scarification wound. 



Fig-. 174. Healed scarification wound. 



in the sweet cherry at a time when this edge had not yet united with the 

 opposite one, growing from the other side of the wound. The wound sur- 

 face (Fig. 175 w) has not yet been covered, h indicates here also the old 

 wood which at w has been exposed by the incision. At the time the incision 

 was made, the knife passed from j to zv. The old bark {ar) was drawn 

 back towards the sides from this plane of incision. This part corresponds 

 to that similarly indicated in Fig. 174. The upper part of this old piece of 

 the bark, as well as the edge, which has dried out because of the incision 

 (Fig. 174 t), is indicated in Fig. 175 by the contours marked t and only one 

 hard bast bundle {hh) has been sketched in the bark parenchyma {ar). At 

 the time the incision was made, the cambial zones {c) and the young inner 

 bark (fr) lay close to the old wood {h). The cells which bounded the plane 

 of the wound incision {s to w) reacted differently to the wound stimulus. 

 The parenchyma of the older bark dried backward, for a certain distance, 



