i6 
PHARMACEUTICAL BOTANY 
Upon removing the extreme apex of the apical cone with a sharp 
razor, mounting in dilute glycerine or water and examining under 
low power, it will be noted that a large pyramidal cell occupies the 
center of the apical cone. This is the apical cell. The cells sur- 
rounding it have been derived by segmentation (cell-division) from 
it, by means of walls parallel to its three sides; they are termed seg- 
ment cells and in turn undergo further division and redivision to 
originate the entire stem tissue and leaf tissue. Step by step the 
tissue cells become modified into epidermal, cortical, bundle and 
fundamental cells. 
Histology of Mature Root. -Transverse sections cut some distance 
above the apex will present the following structures for examination: 
1. Epidermis, of epidermal cells whose outer walls are brown. 
Some of these cells have grown out as root hairs which surround soil 
particles and absorb water with mineral salts in solution. 
2. Cortex, of many layers of cortical parenchyme cells with brown 
walls. The outer layers of cells of this region are thin- walled while 
the extreme inner ones are lignified and form a sclerenchymatous 
ring which surrounds the 
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 origi- 
nates the epidermis (outer protective covering of the root), the peri- 
