2- Collenchyma tissue: - Defination:- They are living cells with irregularly thick walls and acts as first supporting tissue in the plant. in young growing organs of the plant, and the old organs of herbaceous stems. Collenchyma are often
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Presentation Transcript
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2- Collenchyma tissue: -
Defination:-
They are living cells with irregularly thick walls and acts as first supporting tissue in the plant.
in young growing organs of the plant, and the old organs of herbaceous stems.
Collenchyma are often found under the epidermis<br>
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Classification of Collenchyma tissue: -
On the basis of distribution of wall thickening chlorenchyma can be classified into: -
1-Angular collenchyma
In this type the wall thickening (deposition of cellulose & pectin) are localized in the corners
2- Lamellar collenchyma
Cells arranged into ordered rows and the wall thickening is mainly found on the tangential wall of cells<br>
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3-Lacunar or (tubular) collenchyma
Collenchyma with intercellular spaces, in which the wall thickening is restricted to the walls that facing the intercellular spaces.
3) Sclerenchyma tissues
Definition: -
They are dead cells with very thick lignified walls and considering as the principal mechanical support of fully grown parts of the plant.<br>
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Sclerenchyma tissues are Characterized by:-
Composed of dead cells with extremely thick cell walls.
Their cell walls consist of cellulose, hemicellulose and lignin.
Cells are closely packed without inter-cellular spaces between them.<br>
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Classification of sclerenchyma tissues: -
The sclerenchyma cells are classified into two types they are:
A- Fibers b- Sclereids
A-Fibers: - Definition: -
Fibers are long, spindle shaped cells with thick secondary wall and occur as strands in plant.
Fibers characterized by the following: -
Very much elongated cells with tapering or pointed ends and very thick walls.<br>
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Sclereids .Definition: -
They are short sclerenchyma cells having thick and strongly lignified secondary walls.
Its function:- Protects soft plant tissue from herbivores or mechanical damage.
Sclerides are characterized by the following: -
A thick-walled lignified plant cell with narrow lumen.
Often branched in shape.
Shorter than fibers.
Vary widely in shape and size.<br>
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Classification of sclerides
According to different shapes and size it is classified :
1-Brachysclereid (Stone cell):
Brachysclereids are also known as stone cells.
These are isodiametric or elongated cells
and are distributed widely in cells of cortex, phloem and pith of stem
and are also found in the flesh of food.<br>
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2- Astrosclereid (Stellate):
It is star shape. It is found in intercellular spaces of leaf and stems of hydrophytes.<br>
