NATURE OF CORK TISSUE 



outer daughter cell act as the cambium cell while the inner cell 

 develops into one of the cells of the cortex. As soon as the 

 cork cells have reached their growth, a substance called suber 



C 



FIG. 46. Cross-section of the outer part of the stem of geranium. 

 The cork cambium, c, originating in the cells immediately below the 

 epidermis. 



begins to be deposited in their walls. This completely changes 

 the properties of the cellulose walls and renders them impervious 

 to fluids and gases. So the cork cells have the same physical 

 properties as the cuticle of the epidermis and owing to the 

 continued activity of the cork cambium they are able to keep 

 pace with the growth of the stem. It is evident that the cork 

 cells must die as soon as they become impervious to fluids, and 

 it must also follow that all cells lying outside of these cork cells 

 will die since no fluids can reach them from the vascular bundles. 

 These dead cork cells give the characteristic aspect to the outer 

 bark of trees and we would naturally come to think of the coarse, 

 dark bark as composed of rather thick cells. As a rule, however, 

 the cork cells are quite delicate and compactly put together (Fig. 

 47) and the dark color is more usually due to the dried remains 



FIG. 47. FIG. 48. 



FIG. 47. Cross-section of cells of bottle cork showing the delicate char- 

 acter of cork cells. 



FIG. 48. Scale bark of pitch pine. The crescent-like lines in the bark 

 show the successive positions of the cork cambium. 



