USE OF CORK IN HEALING WOUNDS 



71 



general terms from our experience with cork stoppers, namely that 

 fluids in a state of vapor are practically unable to penetrate them. 



Use of Cork in Healing Wounds.— In case of injury to stems 

 and roots, as when the bark is gnawed or branches are broken 

 off by storms or pruned away, the 

 parenchyma cells of the cortex and peri- 

 cycle in the region of the wound form 

 secondary meristems by cell division, 

 which build the various tissues of the 

 bark until the wound is closed over and 

 form a new cambium layer where that 

 has been torn away, and a phellogen 

 which generates an exterior covering of 

 cork. When leaves ripen and fall away 

 the cells at the surface of the wound 

 become suberized and are in effect cork 

 cells. 



The relative dependence of the differ- 

 ent parts of a plant on epidermis and 

 cork is shown dia^rammatically in Fig. 

 35. The fact that a waterproofed epi- 

 dermis does not occur at the growing 

 apex is indicated by a very thin line. 

 As the epidermis becomes better devel- 

 oped on the successively older leaves 

 and portions of stem and root the line 

 is thickened. The evanescent flower 

 does not demand as effective an epi- 

 dermis as the leaves and stem, and this 

 is here indicated by its thin outline. The pistil persists, and 

 as it develops into the fruit it perfects its epidermis as a 

 waterproof covering, as indicated by the thick outline of the 

 fruit in the diagram. Finally on the older portions of stem and 

 root cork appears (the barred zone in the diagram) and gradu- 

 ally increases until it bursts the epidermis, and after a time takes 

 its place altogether. 



Fig. 35. — Diagram illustrat- 

 ing the relative development of 

 the protective tissues in differ- 

 ent parts of a plant. Descrip- 

 tion in the text. 



