Dicotyledonous Stem 



47 



4. Outside the xylem there is the interrupted ring of cam- 

 bium, consisting of prosenchymatous cells dormant during the 

 winter, and in full activity on the return of spring. After the 

 first year cambium is formed between the fibro-vascular bundles 



Fig. 69.— Diagrammatic viewof the structure of a dicotyledonous stem with 

 circumferential growth as seen in transverse section. ^— m, r, ground 

 tissue forming pith (m) and cortex (r), the external ring representing the 

 epidermis. Six fibro-vascular bundles separate — jx the xylem, and p the 

 phloem of each bundle. i>'— older stem : the bundlesnow united bycam- 

 bium ring of fascicular (yr) and interfascicular {id) cambium ; b^ b, the pri- 

 mary bast fibres of the phloem. C— still older stem. By the activity of 

 the cambium new wood and bast have beenformed. fk, wood formed by 

 fascicular cambium ; if It, wood formed by interfascicular cambium ; ifp^ 

 interfascicular phloem ; x, j', medullary sheath. The shaded upper part 

 shows medullary rays. (After Sachs.) 



(interfascicular cambizun), thus making the cambium ring com- 

 plete (see figs. 65 and 69, b). By means of this interfascicular 

 cambium, not only are the medullary rays lengthened as the 



