Sclerenchyma is a simple highly thick-walled dead tissue. It is the third type of Permanent tissue. The cell wall is made up of cellulose or lignin or both. It is found in hard parts of plants and helps in mechanical supports and also helps in stiffness to the plant parts.
Characteristics of Sclerenchyma
- Sclerenchyma consists of long, narrow, thick-walled and lignified cells.
- These are dead cells and do no perform any metbolic activities.
- They re usuyally pointed at both ends and re fibre like in appearance and elce called sclerenchymatous fibres or smple fibres. They have simple , often bolique pits in their walls.
Location of sclerenchyma tissue: They are found abundantly in plants and occur in patches or indefinite layers.
Types of Sclerenchyma
Sclerenchyma is two types: Fibre and Sclereids.
Fibres are highly elongated, narrow, and spindle-shaped thick-walled dead cells with pointed end walls. They are found in longitudinal bundles. Fibres constitute the major mechanical tissue of plants because they can bear compression, pull, bending, and shearing forces. They have a narrow lumen and thick secondary walls. The walls may have simple, oblique, or bordered pits. Fibres occur in all parts where mechanical strength is required: leaves, petioles, cortex, pericycle, phloem, and xylem as well and around the vascular bundle(monocot stem).
Types of Fibres: Wood Fibres ( Present in Xylem), Bast fibre (present in phloem) and surface fibres
Location of Fibres: The fibres are present in the xylem of stem and roots, testa of various seeds or forms covering on fruit, etc.
The function of Fibres: The sclerenchymatous fibres function to give mechanical strength. Their position and distribution in plants save them from the various stresses and strains of environmental factors such as strong wind.
They are highly thickened dead sclerenchyma cells with very narrow cavities. Sclereids are broader as compared to fibres. They may be isodiametric, polyhedral or cylindrical. the thick cell wall has branched or unbranched simple pits. Sclereids may occur singly or in groups and provide stiffness to the plant parts.
Location of Sclereids: They are generally found in hard parts of the plant body and sometimes in the pulp of fruits.
Types of sclereids
The important types of sclereids are
- Stone cells or brachysclereids: They are unbranched shor and isodiametric structure with ramiform(branced) pit canals. Gritness of the fruits of guava, apple, pear, etc. is due to brachysclereids.
- Macrosclereids: They are elongated and columar or rod-like structure. They are found in epidermal covering of legume seeds.
- Osteosclereids: They are bone ike columnar shape structure with swollen ends. They are found n subepidermal covering of some legume seeds.
- Astrosclereids: They are star like structure. They are found in tea leaves and petioles of locus.
- Filliform Sclereids: They are fibre-like sparingly branched structure and found in stem of hydrophytes.
The function of Sclereids: They provide local mechanical strength.
Function of Sclerenchyma
The important functions of Sclerenchyma are:
- Fibres type of sclerenchyma help in mechanical support to the various plants.
- Fibres allows the plant organs to tolerate bending, shearing , compression and pull forces caused by environmental factors.
- A number of fibres are commercial exploited e.g. Corchours(jute), Linus (flax) and Cannabis (hemp), Agave, Musa, etc.
- Splitting and coiling of valves druing dehiscence of some frits is due to orientation of sclerenchyma fibres.
- Sclereids form stoney endrocarp of drupes called stone fruits (almond, coconut, etc)
- Sclereinds from protective covering of testa in many legume seeds.
- Grintness of the ffruis of guava, apple, pear, etc. is due of brachysclereids.
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