Simple Permanent Tissues: Sclerenchyma Fibres
- Sclerenchyma is the simple permanent tissue made up of thick-walled, lignified and dead cells.
- They have a secondary wall deposited with lignin which makes them devoid of protoplasm and dead.
- It consists of two types of cells: Fibres and Sclereids
Fibres:
- These are elongated cells with pointed needle like ends called tapering ends.
- They are always dead at maturity.
- These originate from the procambium of apical meristem and from vascular cambium.
- Fibres can be classified on the basis of their position in plant body as follows:
- Intraxylary fibres: present in xylem (wood).
- Extraxylary fibres: present outside xylem, that is, in phloem.
Intraxylary Fibres: these are of following types:
- Libriform fibres: Thick walled wood fibres having simple pits.
- Fibre Tracheids: Thin walled wood-fibres having bordered pits
Extraxylary Fibres: these have simple pits and are of following types:
- Cortical fibres: these are present in cortex
- Perivascular fibres: these are present in the periphery of vascular bundles
- Phloic fibres: these are present in the phloem
Functions of fibres: provide mechanical strength, maintain elasticity and are economically important.
The cells of sclerenchyma are devoid of protoplasm because of lignified secondary cell walls.
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