90 THE ANNUAL GROWTH 



of the bundles (Fig. 54). Consequently new cells are now added 

 not alone to the vascular bundles but also along the entire extent 



ph 



FIG. 53. Cross-section of a stem of castor bean showing the formation of 

 the cambium between two vascular bundles: x, xylem; ph, phloem; c, cam. 

 bium of the bundle. The faint lines, ic, are the first divisions of the parenchyma 

 cells between the bundles that result in the formation of the cambium cylinder. 



of the cambium cylinder. This growth results in the formation 

 of a layer of xylem on the inside of the cambium cylinder and a 

 layer of phloem on the outside, and so brings about the principal 



cam 



FIG. 54. Cross-section of a stem of castor bean in which the formation of 

 the cambium cylinder, cam, as a ring of regular cells, has been completed; 

 p, pith; v, vascular bundles; st, stereome; c, cortex. Compare Fig. 40. 

 H. O. Hanson. 



