6oo 



THE STRUCTURE OF ECONOMIC PLANTS 



Fig. 313. Vascular transition. Seriesof transections showing: ^,root; B, differentiation 

 of pith ; C, enlargement of pith area with metaxylem in peripheral position ; D, differentia- 

 tion of inner phloem; E, tangential divergence of each primary xylem strand; F, establish- 

 ment of dissected siphonostele of four, tangential, transition bundles; G, formation of eight 

 bundles, each with protoxylem in tangential position ; H, abrupt enlargement of axis at peg, 



