The Ground Tissue
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The ground tissue makes up
a large portion of the primary
body of the plant. It consists
of cortex and pith of the
stem and root as well as the
mesophyll of the leaves. The
cortex lies next to the
epidermis while the pith
occupies the center of many
roots and stems. Three kinds
of cells are present in the
ground tissue: the
parenchyma, sclerenchyma,
and collenchyma.
Sclerenchyma
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The chief strengthening
tissues of plants are called
sclerenchyma. Sclerenchyma
consists of elongated cell with
very thick walls. There are two
kinds of these; the sclereids
and the fibers.
In some mature sclerenchyma
cells, all protoplasm may be
replaced by the encroachment
of the thick cell walls, which
impart mechanical strength to
the tissues.
It is present in some stem,
roots and in some leaves.
Parenchyma
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Parenchyma cells are the
most abundant type of cells
in the plant. They have thin
walls and retain their
protoplasm throughout their
lifetime. They are the least
differentiated among plant
cells so they are able to redifferentiate into other type
of cells.
They also sere as storage
cells and may have starch
granules contained inside
plastids.
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There are also
parenchyma cells which
perform specialized
functions.
Photosynthesis takes
place specifically in
parenchyma cells which
contain chloroplastids.
They are called
chlorenchyma cells and
they make up the
ground tissue of the
leaves and other
photosynthetic parts of
the plant.
Photosynthetic Tissues
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The photosynthetic tissues are
abundant in the leaves and
young stems of the plant.
These are the chlorenchyma
cells which contain the
chloroplasts.
The photosynthetic tissues are
found in the mesophyll layer
of the leaves and young
stems.
Collenchyma

Collenchyma cells are
elongated cells with unevenly
thickened primary cell walls.
Thickenings are usually found
at the corners or on certain
areas of the cell wall like
parenchyma, collenchyma
also retain their protoplasm
throughout their life but
unlike parenchyma,
collenchyma cells hae no
intercellular spaces at the
corners of the cells ecause
such spaces are filled with
cell wall materials.

Collenchyma can
perform the various
metabolic activities
undertaken by
parenchyma cells. The
main function of
collenchyma is to
provide mechanical
strength to herbaceous
and rapidly growing
parts of the plants.
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Mature complex plants are
mainly supported by supporting
tissues located in roots and
stems. Roots anchor the plant
to the ground.
The roots branch even more
profusely than the stem and
frequently, the total root
surface is greater than the stem
with all its branches.
The extensively branching stem
system of the typical land plant
has two primary functions: it
supports the leaves in a
position which assures balance
and to maximize
photosynthesis.
Permanent
Tissues
The Vascular or Conducting Tissues

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Conducting tissues or
vascular tissues are also
present in the plant. They are
concerned with the transport
of material and are the
equivalent of the circulatory
system of the animals.
Vascular tissues are made up
of the xylem and phloem.
Xylem conducts water and
mineral salts from the roots
to the leaves while the
phloem conducts food
materials from the leaves to
the other parts of the plants.
Sieve tubes: The main conducting
cells of the phloem
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Vascular tissues are
composed of the sieve tubes
and ducts. Sieve tubes are
tubular units found in phloem
of stems, roots and leaves.
Each sieve tube represents a
column of elongated
cylindrical cells placed end to
end.
At maturity the end walls of
these become perforated,
forming sieve plates which
give protoplasmic continuity
between the successively
placed cells in the column.
Tracheid and Vessel elements
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Tracheid and vessel elements
are tubular units localized in
the xylem regions of roots,
stems and leaves. Theyare the
two kinds of xylary elements
of the xylem. At first, it
resembles that of the sieve
tube, but later the side walls
become much thicker, and the
end walls are reabsorbed
completely.
They form continuous
channels from roots to stems
and into the leaves.
Secondary Tissues and Secondary Growth
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Vascular tissues which
develop from the
procambium are
referred to as primary
phloem and primary
xylem. In the dicot, a
layer of meristematic
tissue becomes the
vascular cambium and
eventually gives rise to
secondary vascular
tissues and the cork
tissue.
Organs and Organ Systems
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An organ is a group of
tissues that perform a
certain function.
The science of the
arrangement of
tissues to form organs
is called Organology.
The chief functional
cells of an organ are
its parenchyma; the
supporting tissues, its
stroma.
Organ Systems
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An integrated group of organs form systems.
Each system is concerned with one of the basic
functions common to all animals.