Pharmaceutical botany - Lighthouse Survival Blog

PLANT HAIES 29
Periderm.— -Periderm is a name applied to all the tissue, produced
externally by the cork cambium (phellogen). This term appears
often in pharmacognic and materia medica texts.
Histology of Typical Monocotyl Stems (Endogenous).—Passing
from exterior toward centre the following structures are seen:
1 Epidermis whose cells are cutinized in their outer walls.
2. Hypodermis, generally
collenchymatic.
3. Cortex.
4. Endodermis or innermost
layer of cortex generally with
greatly suberized cell walls.
5. A large central zone of
parenchyme matrix in which are
found scattered fibrovascular
bundles of the closed collateral
or rarely concentric t3rpe (am-
phivasal). In this latter type,
which is typical of old monocotyl
stems, the xylem grows
completely around phloem so
that phloem is found in the
centre and xylem without and
surrounding it.
Plant Hairs or Trichomes
These are out-growths of
the epidermal cells which have
become greatly elongated and
Fig. 23. Cinchona calisaya. Cross-section
of bark. A, Cork cells; B, cortical
parenchyma; C, stone cells; D, phloem portion;
E, soft bast; F, phellogen forming
bark; G. medullary rays. (The black line
from G should be extended to the parenchyma
cells between the phloem portions.) H, Bast
fibers. {From Sayre.)
may be unicellular or multicellular. They may be of various forms
simple, consisting of a single row of cells; branching; clavate, or club-
shaped; stellate or star-shaped; barbed, hooked, forked, etc.
The terminal cell is often modified into a secretion sac for gummy,
resinous or odorous products. Such hairs are called glandular. Ex.
Glandular hairs from strobiles of Humulus lupulus.
The cotton of commerce which is the hairs of the seed of the
cotton plant, Gossypium herbaceum, is a good example of simple
hairs.