Sclerenchyma Tissue Characteristics, Types and Functions | Free Biology Notes

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