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Sclerenchyma Characteristics, Types and Functions

This article we will discuss about Sclerenchyma Tissue Characteristics, Types and Functions

Sclerenchyma Tissue Characteristics

Sclerenchyma are dead mechanical tissues occurring in mature organs of plant body
Cells of sclerenchyma are long, narrow, thick walled, lignified without protoplasts
Pits are also found. It may be simple pits or bordered pits
Found in cortex, pericycle, xylem and phloem region
Main function is provides mechanical support to plant organs
Based on size and shape sclerenchyma cells are of two types:- Sclerenchyma fibres and Sclereids

Sclerenchyma fibres

Fibres are longest cell in higher plants. 13mm in angiosperm and 28mm in
gymnosperms i.e. Boehmeria nivea (55cm)
Walls of fibres are lignified, hard, uniformly thickened with pointed ends
They have simple pits as well as bordered pits
Fibres are associated with vascular bundles
Their cell lumen is very narrow
They are present in almost all plant parts
Main function is provide mechanical support in plants

Classification of fibres: based on structure

Libriform Fibres

Mainly obtained from phloem
They are also obtained from pericycle
Libriform Fibres are thick walled and very much long fibres
They are having narrow lumen
They have simple pits

Fibre Tracheids

They are thick walled and short fibres
They are obtained only from xylem
They have bordered pits

Classification of fibres: based on position

Surface fibres

Surface fibres are found on the covering of seed, leaves or fruits
They are economically very important

i) Seed Surface fibre (Cotton fibres)

They are found on surface of seed coats
Cotton fibres are made of cellulose
They are non-lignified fibres and hence they are called false fibres
Cotton fibres two types
Lint – Very long and used in clothing
Fuzz – Small and used in filling

ii) Coir Fibres (coconut)

Obtained from the mesocarp of coconut
They are lignified fibres and hence are true fibres

iii) Leaves Fibre (Pineapple)

The leaves of pineapple are used to make the fibre
The fibre from the leaves is obtained either by manually retting the leaves under water or by mechanically extracting them

Classification of fibres: based on position

Intraxylary fibres / Wood fibres

They are associated with the primary and secondary xylem
They are hard and non flexible
They cannot knitted
Commercially and economically not so much useful
Ex. Saccharum munja

Extraxylary Fibres / Bast Fibres

They are associated with the tissues outside the xylem (like phloem, pericycle and pith of a plant cell)
They are soft fibres and flexible
They can be knitted and economically very useful
Fibres obtained from phloem of
1. Corchorus capsularis (Jute)
2. Crotalaria juncea (Hemp fibre)
3. Fibres obtained from pericycle
4. Cannabis sativa (Hemp)
5. Linum usitatissimum (Flax Fibre)

Sclerenchyma:- sclereids

Sclereids are short, extremely thick walled and their ends are not pointed
Sclereids are various shaped and very small lumen
They generally found in hard parts of the plant
The sclereids provide mechanical support and hardness
Sclereids are classified into five types

Types of sclereids

I. Brachysclereids / Stone Cells / Grit Cells

Appearance: Deeply resemble parenchymatous cells and are roughly isodiametric
Occurrence: It is commonly present in the fleshy portions of fruit
Example: Flesh of pear fruit, sapota & Annona

II. Macrosclereids / Malpighian Cells / Rod Cells

Appearance: Elongated and columnar in shape
Occurrence: Found in the outer epidermal cells of seed
Example: Seed coat of Pisum species

III. Osteosclereids / Bone cells / Pillar Cells / Prop Cells

Appearance: These are bone like sclereids with lobed towards the end
Occurrence: Usually found below the epidermal layer, i.e. hypodermis of seeds and leaves of certain plants belonging to the Xerophytes category.
Example: Leaves of Hakea species.

IV. Astrosclereids / Stellate cells

Appearance: They appear star-like and deeply lobed with the radiating arms from the central body
Occurrence: Extends from the leaves upper epidermis to the lower epidermis.
Example: Leaves of Thea, Olea, Nymphaea etc

V. Trichosclereids (Needle-like cells)

Appearance: They seem hair-like, more elongated, and branched cells stretching towards the intercellular spaces.
Occurrence: Present in specialized tissues of leaves and roots
Example: Aerial roots of Monstera sp, leaves of olive, musa and water-lily etc.

VI. Filiformsclereids (Fibre-like cells)

Appearance: They are much elongated, sparingly-branched & uncommon kind of a cell.
Occurrence: Found in the specialized tissues of leaves.
Example: Leaves of Olea

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