154 



PHARMACEUTICAL BOTANY 



several smaller ones in the xylem portion of the bundle which faces 

 toward the center of the section, In the outer or phloem portion 

 of the bundle will be seen an area of soft, small-celled sieve tubes and 

 phloem parenchyme. The entire bundle is enclosed by_a several 



FIG. 80. Photomicrograph of a representative portion of Greenbrier stem 

 showing epidermis (e.p.), cortex (c), endodermis (e.n.d.), cylinder sheath (c.s.) 

 sclerenchyma fibers of closed collateral bundle (&), fundamental parenchyma 

 (/..), trachea (t). X 22. 



layered ring of sclerenchyma fibers, which on the inner face are 

 called wood fibers, on the outer, bast fibers. The wood fibers con- 

 stitute the supporting elements of the xylem, while the bast fibers 

 are the supporting elements of the phloem. 



