216 



POROXYLEAE 



[CH. 



feature. At an early stage in the growth of the stem a deep- 

 seated phellogen forms secondary tissue both externally and 

 internally and decortication ensues. 



FIG. 463. Poroxylon Edwardsii. A. Transverse section of stem. B. The 

 central region of another stem of the same species. (A, * 9; University 

 College Collection; B, from a photograph supplied by Prof. Bertrand of a 

 specimen in the Renault Collection, Paris.) 



The bundle of each leaf-trace is accompanied by an arc of 

 secondary centrifugal xylem as it passes through the secondary 

 wood and this is retained in the leaf except in the finer veins. 

 After entering the petiole the leaf-trace branches and an arc of 



