56 PHARMACEUTICAL BOTANY 
into the roots and others into the leaves. Upon reaching the 
blade of the leaf, they branch in such a way as to form the char- 
acteristic veins of that organ. These are of two kinds, viz.: 
stem bundles and leaf-trace bundles. The leaf trace bundles are 
the smaller of the two kinds seen. Both are of elliptical outline, 
as seen in cross section, and are embedded in the parenchyma 
forming the broad central matrix. The stem bundles are 
comparatively broad and, as viewed in 
longitudinal sections, form a continuous 
network with good-sized meshes, each 
mesh being opposite the point of insertion 
of one. of the leaves (see Fig. 29). In 
transverse section these bundles are seen 
to be usually ten in number and arranged 
in an interrupted circle within the funda- 
mental tissue. The leaf-trace bundles are 
comparatively narrow and are observed 
Fic. 29.—A, Cylindrical t0 Come off of the stem-bundles and pass 
network of vascular bundles Out through the cortex into the leaves 
in the stem of Dryopteris (fronds). When each “bundle” is ex- 
Filix-mas. B, A portion of : ‘ ‘ : 
ihe Tanto witwe Highly dnag: amined under a high-power magnification 
nified. At L are the inter- it is seen to be composed of: (a) an 
stices over which the leaves endodermis or bundle sheath, a single layer 
a ae cae ails © of cells with yellowish walls and granular 
passing into the leaves from COntents enveloping the bundle; (b) a 
the main vascular bundles. pericycle (pericambium) or phloem sheath of 
(Sayrs.) one to three\layers of delicate thin-walled 
cells, rich in protoplasm; (c) a phloem, a broad zone of tissue formed 
of phloem cells, with thin cellulose w ls and protoplasmic contents, 
which convey sugar in solution from \the leaves to the roots, and 
broader steve tubes which appear polygonal in transverse section and 
whose function is that of conveying soluble proteins in the same 
direction; (¢) abroad central zone, the xylem (wood) formed of thin- 
walled xylem cells which conduct sap slowly and store food, and 
scalariform tubes or tracheids which conduct crude sap (water 
with mineral salts in solution) rapidly from the roots to the leaves 
(fronds). The scalariform tubes in lengthwise view have ladder- 
like thickenings in their walls which alternate with thin areas. 
