Sclerenchyma Tissue Types of Fibers Sclereids and Fibers Functions of Sclerenchyma Development of fibers

Definition


The lignified tissues which lack protoplast at maturity. These tissues are known as sclerenchyma tissues.


Explanation


Thick secondary wall is present in them. These tissues provide strength to the plants.

Occurrence


Sclerenchyma cells are present in all parts of the plant. They are present in both ground tissues and vascular tissues i.e. Xylem and Phloem tissues.

Types




Sclerenchyma tissue has two important types

1. Fibers. 2. Sclereids


Fibro~sclereids


In some cases, it becomes very difficult to differentiate between fibers and sclereids. In these cases, term fibers~sclereids is used.

1. Fibers


Definition


Very long and narrow sclerenchymatous cells with tapering ends are called fibers.

For example


Sugar cane

Explanation


Fibers exists almost in all parts of the plant. They exists in stems, roots and leaves. Fibers are also found in Xylem and Phloem. They may present outside and inside the vascular tissues.

Types of fibers


Fibers have three basic types

1. Xylary fibers. 2. Bast fibers. 3. Septate fibers.


1. Xylary fibers or wood fibers


They are found in Xylem and they form majority of xylem .

Xylary fibers have three main types

--> Libiform fibers.


-->Fibro~tracheids.


-->Mucilaginous fibers.


2. Bast or extraxylary/Phloem fibers


These fibers are found in phloem and cortex tissues. In phloem, they form fiber sheath.

Monocots


Bast fibers occurs in the form of a continuous cylinder in monocot stem.

Dicots or Pericycle fibers


Bast fibers are present on the innermost layer of cortex and on the periphery of central cylinder in dicot plants. These fibers are called pericycle fibers.

Types of bast fibers


1. Cortical fibers


These fibers present in cortex.

2. Phloem fibers


These fibers exits in phloem.

3. Perivascular fibers


They are present inside the innermost cortical layer.

3. Septate fibers


These fibers are present in both Xylem and Phloem tissues. They are found in septate wood fibers.

Development of fibers


Fibers are developed from different meristems like cambium (wood or growing part) , procambium, and ground meristem. Fibers are also develop from parenchyma cells.

Commercial Fibers


Bast or phloem fibers are economically very important. Commercial fibers are obtained from these fibers. These fibers are used in cloth making. Commercial fibers are obtained from some important plants i.e. Flax, Kenaf, Hemp, Jute etc. The leaf of monocot plants are also gives commercial fibers. These plants are: Manila hemp, Pineapple fiber, New Zealand hemp.

Types


There are two types of commercial fibers.

Hard fibers


These fibers are stiff in nature. They have high lignin contents in the walls. They are found in monocots.

Soft fibers


They are flexible and elastic.

They may or may not contains lignin.

Uses of fibers


They have different uses. They also have different types on the basis of its uses.

Textile fibers


Cotton fibers are main textile fibers. These fibers are commonly used in manufacturing of fabrics.

Cordage fibers


These fibers are obtained from Abaca, Sisal spp. These are hard fibers. They are used in making ropes.

Filling fibers


These fibers are obtained from cotton etc. They are used as mattresses.

Brush fibers


These fibers are obtained from Agave, Palmae, Sorghum vulgare.

They are used in making brushes & brooms.

2. Sclereids


Definition


The variable shape sclerenchymatous cells with strongly lignified wall having simple pits are called sclereids.

Explanation


Any non-fibrous sclerenchymatous cell is sclereid. They have thick lignified secondary walls. They may or may not retain protoplast at maturity. In some cases, they become dead.

Types of Sclereids


They have 4 types

1. Stone cells


Isodiametric shape. They found in fruits, bark of leaves, Phloem and cortex.

2. Macrosclereids


Rod shaped. Found in testa of seed.

3. Astrosclereids


Star shaped. They are found in leaves.

4. Osteosclereids


Bone shaped. They are present in seed coat.

5. Trichosclereids


They are thin walled branched.

6. Filiform sclereids


They look like fibers.

Development of Sclereids


Coordinated development


Uniformly cell wall grows. This uniform growth on all sides without separation from neighbouring cells is called coordinated growth.

Intrusive development


Later, the growth becomes localized at certain points. So they produces several processes. These processes grow outward form branches. These outwardly grown branches penetrate into the middle lamella of the neighboring cells . This type of growth is called intrusive growth.

Functions of Sclereids


Sclereids performs following functions

1. They are present in ground and vascular tissues.

2. Present in the form of hard mass of cells.

3. Seed coat of many seeds is made up of Sclereids e.g. Nuts

4. Sclereids are also common in fruits.

5. Sclereids are also found in the leaves of many plants.

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