160 PHARMACEUTICAL BOTANY 
hairs begin to make their appearance in this region. Differences 
in size and shape of the cells also begin to occur here. 
REGION oF MaTurATION.—In this region more differentiation 
takes place, the cells become larger and frequently their walls 
become thicker. Root hairs are usually evident throughout this 
region. 
Mature Recion.—This region is the part of the root between 
the region of maturation and the base of the stem. In its lowest 
part the primary tissues have been laid down by the primary 
meristems. These, in order of their arrangement from the 
periphery to the center, are the epidermis, primary cortex (composed 
of parenchyma), endodermis, pericycle, ycle, radial i vascular bundle composed 
of alternating strands of primary xylem and primary phloem, and 
pith (composed of parenchyma). Root hairs usually occur in this 
lower region as outgrowths of epidermal cells but gradually 
disappear in most roots as we pass further upward, 
DIFFERENCES BETWEEN Root AND STEM 
THe Roor Tue Stem 
1. Descending axis of plant. 1. Ascending axis of plant. 
2. Growing point sub-apical, being 2. Growing point apical, but covered 
covered by the root cap. by protective bud scales or young 
foliage leaves. 
3. Contains no chlorophyll. 3. Chlorophyll sometimes present. 
4. Does not bear leaves or leafrudiments. 4. Bears leaves and modifications. 
5. Branches arranged irregularly, and 5. Branches with mathematical regu- 
arising from deeper tissue. larity, the branches arising at 
surface of stem, in axils of leaves 
and from nodes. 
6. No division into nodes and internodes. 6. Division into nodes and internodes. 
7. Internal structure different. 7. Internal structure different. 
CLAassIFICATION OF Roots AS TO ORDER.—1. Primary or first 
root, a direct downward growth of the radicle (from embryo 
within seed), which, if greatly in excess of the lateral roots, is 
called the main or tap root. 
2. Secondary roots are. lateral branches of the primary root. 
They may, in turn, give rise to finer branches, or rootlets. Both 
primary and secondary roots may be either fibrous or fleshy. 
3. Adventitious roots are such as arise from any part of the 
plant other than the seed embryo or normal root system. Exam- 
ples: Roots developing on Bryophyllum and Begonia leaves when 
