216 PHARMACEUTICAL BOTANY 
(see Fig. 147) presents the following structural details, passing 
from periphery toward the center: 
1. Epidermis of a layer of epidermal cells whose outer walls are 
covered with a waxy cutin deposit. 
2. Cortex of about 20 rows of ordinary parenchyma cells, some 
of which contain more or less spheroidal starch grains, others 
raphides of calcium oxalate. 
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Fic. 146.—Transverse section through a representative portion of the mono- 
cotyledonous stem of the corn (Zea Mays) (X 50). ep, epidermis; A, hypodermis 
containing lignified fibers; co, cortex (poorly defined in corn); ph, primary phloem 
and x, primary xylem of a closed collateral bundle surrounded by a sclerenchyma 
sheath of lignified fibers (scl); par, parenchyma of pith in which the bundles are 
scattered; sz, sieve tissue; tr, tracheae; a, a ring of an annular trachea bordering a 
large air-space; scl, sclerenchyma fibers. The two large lateral trachez in each 
bundle are pitted tracheae. 
3. Endodermis of usually 2 layers of endodermal cells, the radial 
and inner walls of which are strongly indurated with lignin. 
4. Stele, a broad central region consisting of a matrix of 
starch- and crystal-bearing parenchyma and through which 
region course closed collateral and concentric bundles. 
The closed collateral bundles are arranged in an interrupted 
circle just beneath the endodermis. The concentric phlocentric 
bundles are scattered through the center of the stele. 
