142 PHARMACEUTICAL BOTANY 
VI. Radial, characterized by two or more xylem and phloem 
masses arranged in alternate manner usually around a central 
pith. The terms diarch, triarch, tetrarch, pentarch, hexarch, 
heptarch and polyarch are respectively employed to designate 
radial bundles having 2, 3, 4, 5, 6, 7 or many xylem strands and 
ss a 
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Fic. 80.—Vascular bundles. A, the concentric-monocotyl or phlocentric 
type, with xylem, k, surrounding the phloem, h. B, the collateral type, with 
phloem, h, standing in front of the xylem,k. C,a portion of the radial type (under- 
going transition) shown complete in D, where the part outlined at a corresponds 
toC. c, xylem, b, phloem, f, cambium ring; e, pericycle; d, endodermis. Pericycle 
and endodermis are not parts of the bundle. (From Stevens after Haberlandt.) 
a like number of phloem strands. Seen in the primary roots 
of all Spermatophytes and Pteridophytes. 
XYLEM! is that part of a conducting or vascular bundle that 
usually contains wood parenchyma cells, tracheze and tracheids. 
It frequently contains, in addition, wood fibers. The tracheid 
is the fundamental cell type in the xylem. The xylem of most 
Gymunosperms is devoid of trachez. 
* The conducting elements of the xylem comprising trachez, tracheids and 
wood parenchyma constitute the hadrome. : 
