104 



BOTANY FOR BEGINNERS 



CHAP. 



In an old stem of the Sunflower the vascular bundles form a 

 complete ring, and in such an old stem a complete ring of cam- 

 bium passes through the bundles and across the medullary rays. 

 Those parts of this cambium ring which lie between the vascular 

 bundles are spoken of as forming the 

 interfascicular cambium (p. 99). 

 The interfascicular cambium is formed 

 by the cells between the bundles be- 

 coming meristematic, i.e., they begin 

 to divide up and so complete the ring. 

 This portion of the cambium ring forms 



FIG. 129. Transverse section of older stem of Sun- 

 flower, showing the first formation of interfascicular 

 cambium. Ph. and cb, phloem and cambium ; xy> 

 xylem ; Scl, sclerenchyma ; s, spiral vessels ; sf, 

 interfascicular cambium. 



FIG. 130. Transverse sec- 

 tion of part of cylinder of 

 old Sunflower stem ; Ph, 

 phloem ; cb, cambium ; 

 xy, xylem ; WF, wood 

 fibres ; MR, medullary 

 rays \v, vessels of xylem. 



vascular elements which partly fill up the spaces between the 

 bundles. The whole of the cambium during the active period 

 of growth produces xylem on one side and phloem on the other. 

 Thus, in an old stem the vascular cylinder is formed (p. 66). 



EXPT. 95. Cut transverse sections of a young stem of the Wallflower 

 and mount in water. Look for a thin section, and note 



(i) The epidermis, a single row of cells which surrounds the cortex. 



(ii) The cut ends of the vascular bundles. 



(iii) The ground tissue forming the cortex and pith. 



