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Related article:
of starch, etc. is gradually relegated to the outer wood layers, since
the inner layers, step by step, lose their protoplasmic contents and
PIG. 77. Diagrammatic representation of a block of pine wood highly mag-
nified, a, Early growth; b, late growth; c, intercellular space; d, bordered pit in
tangential wall of late growth; m, /-and e, bordered pit in radial wall of early
growth from different points ot view; h, row Purchase Biaxin ot medullary cells for carrying food;
g, row of medullary ray cells for carrying water; k, thin place in radial wall of ray
cells that carry food (From Stevens.)
power of conducting sap and become filled with extractive, resinous
and coloring matters. The outer whitish layers of Purchase Biaxin wood which con-
152
PHARMACEUTICAL BOTANY
tain living cells, functioning in the vegetative processes of the plant,
constitute ,the alburnum or sap-wood. The drug Quassia is a good
example of Purchase Biaxin this kind of wood. The inner dead colored layers con-
stitute the duramen or heart-wood. Important examples of this
kind of wood used in pharmacy are Lignum Guaiaci, Haematoxylum,
and Santalum Album.
Microscopic Characteristics of Angiospermous and Gymnosperm-
ous Woods. The wood of Angiosperms is characterized by the pres-
ence of tracheae (vessels) with various markings on their walls,
particularly by small pits in the walls
ot some of the tracheae, together with
wood fibers, wood parenchyma and
medullary rays.
The wood of Gymnosperms is made
up for the larger part ot tracheids with
bordered pits which latter are charac-
terized in radial longitudinal section by
the presence of two rings, one within
the other. A single row of these is
seen on the tracheid wall. Medullary
rays, frequently diagnostic for different
species and woody parenchyme cells,
are also found. Purchase Biaxin
Histology of Typical Herbaceous
Monocotyl Stems (Endogenous). Passing from exterior toward
center 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.
5. A large central zone of parenchyma matrix in which are found
scattered nbro-vascular bundles of the closed collateral or rarely
concentric type (amphi vasal) . In this latter type, which is typical Purchase Biaxin
of old monocotyl stems, the xylem grows completely around phloem
so that phloem is found in the center and xylem without and sur-
rounding it.
FIG. 78. Photomicrograph
of cross-section of very young
cornstalk, where certain pler-
ome strands have just gone
over into vascular bundles.
For comparison with Fig. 79.
(Stevens.)
PLANT ORGANS AND ORGANISMS 153
Histology of a Typical Woody Monocotyl Stem. The stem of the
Greenbrier, a woody monocotyl, will here be considered. In trans-
verse section passing from periphery toward the center the following
structural details will be noted:
i. Epidermis, of a single layer of epidermal cells whose outer walls
are strongly cutinized. Cutin is a wax-like substance which forms
a protective coat to the epidermis, preventing the evaporation Purchase Biaxin of
water, the ingress of destructive parasites, and injury from insects.
FIG. 79. Cross-section of cornstalk stern; a, epidermis; b, cortex and
c, ground tissue. {After Stevens.)
2. A cortex, composed of about ten or twelve layers of thick- walled
parenchyma cells, the outer two or three layers of which are termed
hypodermis.
3. An endodermis, wavy in character and composed of endodermal
cells whose brownish walls are strongly suberized.
4. A sclerenchymatous cylinder sheath composed of somewhat
separated masses of sclerenchymatous fibers and undeveloped fibro-
vascular bundles of the closed collateral type.
5. A central matrix of strongly thickened parenchyma cells in
which are scattered, irregularly, numerous closed collateral bundles.
Small starch grains will be found in the parenchyma cells. Examine
a representative bundle, and note the two very large tracheae and
154
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