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Related article:
Il6 RHARMACEUTICAL BOTANY
Tracheids are undeveloped ducts having bordered pores and fre-
quently scalariform thickenings. Like tracheae their walls give the
characteristic lignin reaction with phloroglucin and HC1. The
bordered pores of coniferous tracheids (Fig. 77) exhibit a wall
surrounding the pore which forms a dome shaped protrusion into
the cell. Like tracheae, also, tracheids convey water with mineral
salts in solution. Tracheids and medullary rays make up most of
the wood of Conifers.
PIG. 53. Transverse section Order Avodart of a concentric bundle from the rhizome of Iris
(a monocotyledon). Xylem surrounding the phloem. /, Tracheae; f 1 , proto-
xylem; s, sieve. tubes; g, companion cells of the internal phloem portion. (From
Sayre after Vines.)
MEDULLARY RAYS
These are bands of parenchyma cells which extend radially from
the cortex to the pith (primary medullary rays) or from a part of the
xylem to & part of the phloem (secondary medullary rays). In
tangential-longitudinal sections they usually Order Avodart appear spindle shaped
'while in radial-longitudinal sections they are seen Order Avodart crossing the other
elements. Their primary function is to supply the cambium and
wood with elaborated sap formed in the leaves and conveyed away
by the sieve tubes, Order Avodart and phloem parenchyma and to supply the cam-
PLANT TISSUES
117
bium and phloem with crude sap which passes up ma inly through the
tracheae and tracheids from the absorptive regions of the roots.
They furthermore serve as storage places for starch, alkaloids, resins,
and other substances.
Fibro-vascular Bundles are groups of fibers, vessels and cells cours-
ing through the various organs of a plant and serving for conduction
PIG. 54. Diagrams illustrating the arrangement of the regions in different
types of nbrovascular bundles. In each diagram x represents xylem; P, phloem
and C, cambium. A, Radial bundle; B, concentric bundle of fern stem type;
C, concentric bundle of monocotyl type; D, closed collateral bundle; E, open
collateral bundle; F, bi-collateral bundle.
and support. According to the relative structural arrangement of
their xylem and phloem Order Avodart masses they may be classed as follows:
I. Closed collateral, consisting of a mass of xylern lying alongside
of a mass of phloem, the xylem facing toward the center, the phloem
facing toward the exterior. Order Avodart Stems of most Monocotyledons and
Horsetails.
II. Open collateral, consisting of a mass of xylem facing toward
the pith and a mass of phloem facing toward the exterior and sepa-
rated from each other by a cambium. Stems and leaves of Dicoty-
ledons and roots of Dicotyls and Gymnosperms of secondary growth.
III. Bicollateral, characterized by a xylem mass being between
an inner and an outer phloem mass. There are two layers of cam-
bium cells, one between the xylem and inner phloem mass, the other
Il8 PHARMACEUTICAL BOTANY
between the xylem and outer phloem mass. Seen chiefly in stems
and leaves of the Cucurbitacece and Solanacece.
IV. Concentric, characterized by a central xylem mass surrounded
by a phloem mass or vice versa. No cambium present.
(a) Concentric, with xylem central in bundle. Seen in stems and
leaves of nearly all ferns and- the Lycopodiaceos.
FIG. 55. Cross-section through a portion of a root of A corns calamus. A.
Cortical parenchyma; B, endodermis; C, pericycle; E, phloem; F, xylem. At
F, F, are large tracheal tubes, which were formed last, the narrow tubes near
the periphery of the xylem being formed first. At the center of the root, within
the circle of the radial vascular bundle, occur thin-walled parenchymatous pith
cells. (From Sayre after Frank.}
(b) Concentric, with phloem central in bundle. Seen in stems and
leaves of some Monocotyledons. Examples'. Calamus and Conval-
laria rhizomes.
V. Radial, characterized by a number of xylem and phloem masses
alternating with one another. Seen in the roots of all Spermato-
phytes and Pteridophytes.
PLANT TISSUES IIQ
Xylem is that part of a fibro-vascular bundle that contains wood
cells and fibers. It may also contain tracheae, tracheids, Order Avodart seldom
sieve tubes.
Phloem is that part of a fibro-vascular bundle that contains sieve
tubes, phloem cells, and often bast fibers.
SECRETION SACS (SECRETION CELLS)
These were formerly parenchyma cells which sooner or later lost
their protoplasm and nucleus and became receptacles for oil, resin,
oleoresin, mucilage or some other secretory substance. They are
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