118 



VIII. THE MONOCOTYLEDONOUS STEM. 



rounded cells (m), the conjunctive parenchyma of the stele, in 

 which are irregularly scattered isolated circular or elliptic vascular 

 bundles (/'). Outside a definite position (the inner /") the 

 bundles are more numerous, elongated in radial direction, and 



crowded so closely to- 

 gether that they appear 

 separated only by com- 

 paratively thin streaks of 

 ground-tissue. In these 

 latter the cells are more 

 strongly thickened, 

 coarsely pitted, more or 

 less elongated in the di- 

 rection of the radius, and 

 clearly arranged in radial, 

 often wavy, rows. At 

 the outer /" this ceases, 

 and then we come to the 

 boundary (c) between the 

 yellowish central cylinder 

 and the green cortex. We 

 find here a zone composed 

 of flattened thin-walled 

 cells, strictly arranged in 

 radial rows. It is the 

 Cambium - ring, which 

 provides for the increase 

 in thickness of the stem. 

 It belongs in origin to the 

 peripheral ground-tissue 

 of the central cylinder, 

 FIG. H. Dracaena (Gordyline) rubra. Cross-sec- Or stele ; to 



m 



tion through the stem. /, vascular bundles, /' being 



primary, /" secondary, and/'" leaf-bundles; m, 



undignified elements of the ground-tissue ; s, ligni- perlcVCle. 



tied elements of the ground-tissue, sheathing the 



the region 



ac: fVio 

 as tne 



Its cells are 



..... 



vascular bundles ; t, tracheides ; c, cambium-ring ; m active division, and 



produce on their inner, 

 and to a much smaller 

 extent their outer, side new elements. These divisions result from 

 the formation of tangential walls, and produce therefore radially 

 arranged cell-rows, which from time to time are made double by 

 the formation of radially-directed walls. Embedded in the young 



