440 



MOSSES AND FERNS 



CHAP. 



Shortly after this first indication of the vascular bundle of the 

 leaf can be seen, the cells of the cortex immediately outside the 

 central pith begin to divide rapidly by longitudinal walls and form 



A. 



Fig. 229. — Transverse section of a young vegetative shoot just below the apex, X260; B, outer part 

 of a section lower down, X 260 ; pr, procambial zone ; C, young vascular bundle, X 520 ; t, 

 primary tracheids. 



a zone of cambiform cells completely surrounding the medulla. 

 In the primary central row of cells in the leaves similar divisions 

 occur, and a very evident procambium cylinder is formed, bending 



