STRUCTURAL BOTANY 



contents. This part of the bundle is called the last 

 or phloem (ph in Figs. 20 and 21). 



Between xylem and phloem is a band of very 

 regular cells, which appear oblong in transverse sec- 

 tion, and have very thin walls, showing that active 

 division is going 'on (see Fig. 21, c). This layer is the 

 cambium, which in plants of the Class to which the 



_T." i^lS^T^' ? y 



o o ooooOQ&o e&oooooaooiyv&ooo 0c>a6/oac><yo6>c>0o l y 



FIG. 22. Radial longitudinal section passing through a 

 vascular bundle from a young stem of Wallflower. 

 e, endodermis, containing starch ; pc, pericycle ; ph, 

 phloem ; c, cambium ; xy, xylem ; pxy, protoxylem ; p, 

 pith. Somewhat diagrammatic. Magnified 220. (R. S.) 



Wallflower belongs is constantly undergoing cell- 

 division, and adding new cells to the wood internally, 

 and to the bast externally (see pp. 59 and 90). 



