n8 
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 Lycopodiaceoe. 
Fig. 55. —Cross-section through a portion of a root of Acorus calamus. A. 
Cortical parenchyma; B, endodermis; C, pericycle; E, phloem; F, xylem. At 
Y, Y, 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. 
