The Vascular Cambium

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The Vascular Cambium
Definitions Cell division related to cambial
activity Axial Along the axis of the organ, or
organism Radial At right angles to the axis,
i.e., along a radius Tangential At right angles
to a radius. Ray Initial Meristematic cambial
cell. Forms a file of cells (one or more wide)
that is composed of parenchyma. Orientated ALONG
a RADIUS. Contributes to the RADIAL transport
system Fusiform Initial Meristematic cambial
cell. Forms new secondary xylem and secondary
phloem and associated cells. Contributes to the
AXIAL transport system.
Notes
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THE VASCULAR CAMBIUM
The vascular cambium is unlike the primary
meristems (root and shoot apex) of the plant, in
that it produces new cells and tissues which add
to the axial system (i.e. the conducting system)
as well as to the radial system (i.e. the lateral
transport pathway). In contrast, apical meristems
of the shoot and root add only to the axial
system. The cells of the vascular cambium do not
fit the regular concept of meristematic cells
(i.e. small, isodiametric shaped cells, with a
dense cytoplasm and containing large nuclei).
Cambial cells are usually highly vacuolate and
occur in two forms, namely fusiform cells and ray
cells. Fusiform cells are prism-shaped with a
distinct wedge-shape at both ends. Ray cells are
short and squat. Tangentially, both cell types
may be wider than they appear in radial section
or longitudinal view. The slides that follow will
assist to orientate you with respect to the
planes of cell division within the cambium. The
two cell types (fusiform and ray cells) have
unique functions. Fusiform cells usually only
produce cells associated with the axial system --
that is, they produce either new elements of the
xylem, or elements of the phloem. Fusiform cells
thus add new cells to the AXIAL conducting
system. Ray cells on the other hand, produce ONLY
ray cells and thus add to the RADIAL system of
the plant
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AXIAL
Axial Longitudinal translocation, xylem phloem
elements.
TANGENTIAL
RADIAL
Radial Lateral translocation. Carbohydrate from
phloem, to parenchymatic (living) tissue, water
from xylem to living tissues as well.
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Fusiform vs. ray initials
radius
Fusiform and ray cells form FILES of cells each
file contains a number of differentiating
elements. Both can divide radially OR
tangentially
tangent
endarch TANGENTIAL face
exarch TANGENTIAL face
exarch TANGENTIAL face
RADIAL face
RADIAL face
plane of cell division
normal plane of cell division
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Development of secondary vascular tissues in stems
Remember a fascicle is a vascular bundle
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1.
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First activity is in the vascular bundle
2.
FCZ fascicular cambial zone
Secondary xylem
Secondary phloem
FC
Secondary xylem and phloem are produced by the
fascicular cambium (FC).
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3
The interfascicular regions begins to
differentiate and a cambium originates here.
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The interfascicular cambial area in herbaceous
stems is not usually active, thus does not
produce new phloem or xylem tissues
3b
3a
A widening band of secondary vascular tissue
results from the cambiums activity.
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The ring of secondary tissue is Complete. The
interfascicular and fascicular cambia together
form a vascular cambium
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Cambial activity in the root
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cambium appears between the metaxylem and the
metaphloem
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(No Transcript)
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filling out
Cambial cells differentiate more rapidly at the
interface between the metaxylem and the
metaphloem.
secondary phloem is produced centrifugally
(outwards) as is secondary xylem. In a
centripetal (inward) direction. Outward pressure
begins to be applied to the primary phloem
strands. These strands are gradually forced
outwards, to make way for the newly-added
secondary vascular tissues.
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filling out
E endodermis P pericycle 2X secondary
xylem 2P secondary phloem P pericycle E
endodermis
1. Outward pressure caused by the addition of new
cells continues effectively rounding out the
ring of secondary vascular tissue
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Remnant of primary phloem strands (located by
orange arrows) become completely crushed, and are
non-functional
E
2P
P
2X
E endodermis P pericycle 2X secondary
xylem 2P secondary phloem P pericycle E
endodermis
The root will retain its primary xylem, which
will be visible and may be functional