Simple Tissues
Simple tissue are
homogeneous -composed of structurally and functionally similar cells. eg.,
Parenchyma, Collenchyma and Sclerenchyma.
Parenchyma are simple
permanent tissue composed of living cells. Parenchyma cells are thin walled,
oval, rounded or polygonal in shape with well developed spaces among them. In
aquatic plants, Parenchyma possesses intercellular air spaces, and is named as
Aerenchyma. When exposed to light, parenchyma cells may develop chloroplasts
and are known as Chlorenchyma.
Parenchyma may store
water in many succulent and xerophytic plants. It also serves the functions of
storage of food reserves, absorption, buoyancy, secretion etc.,
Collenchyma is a living
tissue found beneath the epidermis. Cells are elongated with unevenly thickened
non-lignified walls. Cells have rectangular oblique or tapering ends and
persistent protoplast. They possess thick primary non-lignified walls.
They provide mechanical
support for growing organs.
Sclerenchyma consists of
thick walled cells which are often lignified. Sclerenchyma cells do not possess
living protoplasts at maturity. Sclerenchyma cells are grouped into (i) fibres
and (ii) sclereids.
Fibres are elongated
sclerenchymatous cells, usually with pointed ends. Their walls are
lignified. Fibres are abundantly found in many plants. The average length of
fibres is 1 to 3 mm, however in plants like Linum usitatissimum (flax),
Cannabis sativa (hemp) and Corchorus capsularis (jute),
fibres are extensively longer ranging from 20 mm to 550 mm.
Sclereids are widely
distributed in plant body. They are usually broad, may occur in single or in
groups. Sclereids are isodiametric, with liginified walls. Pits are prominent
and seen along the walls. Lumen is filled with wall materials. Sclereids are
also common in fruits and seeds.
·
Cell
wall is thin and uniform in thickness
·
It
serves as storage tissue.
·
It
is found in outer and inner parts of plant organs
·
It
possesses well developed extra thickening at places adjacent to intercellular
spaces
·
It
serves as mechanical tissue
·
It
is restricted to sub epidermal parts of plant organs.
·
It
consist of living cells
·
Cells
contain protoplasm
·
Cell
walls are made of cellulose
·
Thickening
of cell wall is not uniform
·
Lumen
of the cell is wide
·
Pits
are simple straight
·
It
provides mechanical support and elasticity to the plant body
·
It
consist of dead cells
·
Cells
are empty
·
Cell
walls are lignified
·
Cell
wall thickening is uniform
·
Lumen
of the cell is narrow
·
Pits
are simple oblique sometimes branched
·
It
provides only mechanical support
·
Usually
broad
·
End
walls blunt
·
Occur
singly
·
Deep
pits
·
Elongated
narrow
·
thread
like
·
End
walls tapering
·
Occur
in bundles
·
Narrow
pits
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