LIFE HISTORY OF THE. MALE FERN 37 
3. Endodermis, a single layer of cells tangentially-elongated. 
4. Pericambium (Pericycle), usually of two layers of thin-walled 
cells containing protoplasm and large nuclei. This region surrounds 
the 
5. Radial fibro-vascular bundle, consisting of two phloem patches 
of phloem cells and sieve tubes on either side of two radial xylem 
arms of xylem cells, spiral tracheae and scalariform tubes. 
6. Lateral rootlets, which take origin in the pericambium. 
Histology of Root Apex. —Microscopic examination shows this 
region to be composed of soft, pale, growing cells ending in the tri¬ 
angular apex-cell of the root. From the free base of the apex cell 
segment cells are cut off as calyptrogen cells. These by dividing 
form the root cap. The root cap or calyptra consists of a mass of 
loosely attached cells which forms a protective covering around the 
tip of the root. 
From the inner sloping sides of the apex cell the segment cells give 
origin to the dermatogen, which by repeated division of its cells, 
originates the epidermis (outer protective covering of the root), the 
periblem , originating cortex and the plerome originating the bundle 
and related tissue. 
Continuity of Crude Sap Flow. —The crude sap (water with mineral 
salts in solution) penetrates the thin walls of the root hairs by osmosis 
and passes into the interior of hairs, thence into the root xylem and 
through this to stem xylem, thence through stem xylem into the 
leaves. 
Histology of Stipe (Petiole). —This, in transverse section,passing 
from periphery toward the center, presents the following structural 
characteristics: (see Fig. 15). 
1. Epidermis, a single layer of epidermal cells with dark brown 
outer walls. 
2. Outer cortex (hypodermis), a wide band of small cells with ligni- 
fied walls. 
3. Inner cortex, similar to inner cortex of stem but devoid of leaf- 
trace bundle. 
4. Fundamental parenchyma, similar to same region of stem, in 
which are embedded a number of concentric fibro-vascular bundles 
arranged in an interrupted circle. Each of these shows a central 
