THE STEM 217 
Longitudinal-radial sections show that the trachez are of the 
spiral, scalariform, and pitted types. 
HistoLocy or A TypicAL Woopy Monocoty.L StemM.—The 
stem of the Greenbrier, a woody monocotyl, will here be con- 
sidered. In transverse section passing from periphery toward the 
center the following structural details will be noted: 
ep 
nt ; 
eR 
Fic. 147.—Transverse section of the rhizome of Convallaria majalis, a mono- 
cotyledon. X 40. ep, epidermis; co, cortex; end, endodermis; p, phloem and x, 
xylem of a closed collateral fibrovascular bundle; p’, phloem and x’, xylem of a 
concentric bundle; m, pith, in which the concentric bundles are imbedded. 
1. Epidermis, of a single layer of epidermal cells whose outer 
walls are strongly cutinized. Cutin is a wax-like substance which 
forms a protective coat to the epidermis, preventing the evapora- 
tion of water, the ingress of destructive parasites, and injury 
from insects. 
2. A cortex, composed of about ten or twelve layers of thick- 
walled parenchyma cells, the outer two or three layers of which 
are termed hypodermis. 
