779 



parenchymatous, short, with wide lumina (x) and perforated by isolated, 

 short, wide ducts (g). The further the new wood lies from the edge of the 

 wound, the more regular, narrow, dense and longer celled it is, the sharper 

 appear the medullary rays (m) and their continuation (m) in the bark. The 

 more gradual the formation of the new wood, the more taut is the tension 

 in the outer cork zone (^ to ^) of the overgrowth edge. This frequently 

 tears apart in places as a result of the inner pressure, so that the bark 

 parenchyma is exposed and pushes out into the torn place. On these out- 

 pushing cells, new cork cells are formed in the shortest possible time, which 

 lie against the surrounding ones and thus close the cork girdle. 



Fig-. 176. Cross-section through a hollow pine trunk in which only the circum- 

 vallation edges, several years old, carry on the nutrition of the trunk. 



In case a scarifying incision is so broad that the overgrowth edge of the 

 first year cannot cover it, the new wood of the following year will overgrow 

 the wound surface like a lip. In this lip-like, convex overgrowth, which is 

 recognized best by the course of the new covering cork zone {k to k, Fig. 

 175) the cambial zone (c) assumes a special curvature, which becomes more 

 marked the deeper the wound surface lies. If it now happens that, in old 

 trunks, a broad longitudinal wound is made, instead of a scarifying one, and 

 the wound body is destroyed by atmospheric influences, together with para- 

 sitic action, so that the trunk becomes hollow, ultimately only the overgrowth 

 edges will remain. Fig. 176 represents such a case. It is a cross-section 

 from a hollow pine trunks Because of the slow rotting away of the 



1 The orig-inal may be found in the Botanical Museum in Berlini, 



