60 PHARMACEUTICAL BOTANY 
4. Pericycie (Pericambium), usually of one or two layers of 
thin-walled cells containing protoplasm and large nuclei. This 
region surrounds the single bundle. 
5. Rapiat VascuLar BunpDLe, consisting of two phloem 
patches of phloem cells and sieve tubes on either side of two 
radial xylem arms of scalariform tubes (tracheids) and a few 
xylem cells. : 
6. LaTerAL Root ets, which take origin in the pericambium. 
Hisrotocy or Roor Apex.—Microscopic examination shows 
this region to be composed of soft, pale, growing cells ending in 
the triangular 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 
divide to form three primary meristems. These are (1) the 
dermatogen which, by repeated division of its cells, originates the 
epidermis (outer protective covering of the root), (2) the periblem, 
originating cortex, and (3) the plerome originating the bundle and 
related tissue. 
Continuity or Crupe 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 
the 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. 33): 
1. Epmermis, a single layer of epidermal cells with dark 
brown outer walls. 
2. OUTER CorTEX (hypodermis), a wide band of small cells 
with lignified walls. 
3. INNER CorTEx, similar to inner cortex of stem but devoid 
of leaf-trace bundles. 
4. Piru, of fundamental parenchyma, similar to same region 
of the rhizome, in the outer region of which are embedded a 
number of xylocentric vascular bundles arranged in an interrupted 
