Il8 PHARMACEUTICAL BOTANY 



between the xylem and outer phloem mass. Seen chiefly in stems 

 and leaves of the Cucurbitacece and Solanacece. 



IV. Concentric, characterized by a central xylem mass surrounded 

 by a phloem mass or vice versa. No cambium present. 



(a) Concentric, with xylem central in bundle. Seen in stems and 

 leaves of nearly all ferns and- the Lycopodiaceos. 



FIG. 55. Cross-section through a portion of a root of A corns calamus. A. 

 Cortical parenchyma; B, endodermis; C, pericycle; E, phloem; F, xylem. At 

 F, F, are large tracheal tubes, which were formed last, the narrow tubes near 

 the periphery of the xylem being formed first. At the center of the root, within 

 the circle of the radial vascular bundle, occur thin-walled parenchymatous pith 

 cells. (From Sayre after Frank.} 



(b) Concentric, with phloem central in bundle. Seen in stems and 

 leaves of some Monocotyledons. Examples'. Calamus and Conval- 

 laria rhizomes. 



V. Radial, characterized by a number of xylem and phloem masses 

 alternating with one another. Seen in the roots of all Spermato- 

 phytes and Pteridophytes. 



