Dicotyledonous Stem 



43 



cells immediately beneath it, more often from the more deeply 

 lying cells. 



On the inner side there is developed a ring of meristem, 

 known as phellogen or cork cambium, whilst within this there 

 is a layer of cells containing chlorophyll, the phelloderma or 

 green layer. Sooner or later all the cells outside the cork 

 tissue dry up and shrivel, forming the outermost layer of the 

 bark. 



^^liMBiarSiSfe,^ 



Fig. 66. —Transverse section of one-year-old stem oi Ailanthtts glandulosits: 

 e, epidermis withered ; k, cork cells, formed by the inner cells with proto- 

 plasm, the cork cambium or phellogen ; r, inner green cells, the phello- 

 derma, (After Prantl.) 



The dicotyledonous stem now consists of the following 

 parts : — 



1. A ring of epidermis and cells with it becoming dried and 

 dead. 



2. A ring of cork tissue, the outer bark or epiphloeum, with 

 the cork cambium within. 



3. A ring of pheiloderma, the middle bark or mesophlceum. 



4. A ring of phloem, interrupted by the passage of the 

 medullary rays, and forming the bast, liber, inner bark, or 

 endophloeuni. 



