Simple Permanent Tissues: Parenchyma, Collenchyma, Sclerenchyma

The Permanent tissues develop from apical meristem. They lose the power of cell division either permanently or temporarily. They are classified into two types:

1. Simple permanent tissues.

2. Complex permanent tissues.

Simple Permanent Tissues

Simple tissues are composed of one type of cells only. The cells are structurally and functionally similar. It is of three types.

1. Parenchyma

2. Collenchyma

3. Sclerenchyma

1. Parenchyma (Gk: Para-beside; enehein- to pour)

Parenchyma is generally present in all organs of the plant. It forms the ground tissue in a plant. Parenchyma is a living tissue and made up of thin walled cells. The cell wall is made up of cellulose. Parenchyma cells may be oval, polyhedral, cylindrical, irregular, elongated or armed. Parenchyma tissue normally has prominent intercellular spaces. Parenchyma may store various types of materials like, water, air, ergastic substances. It is usually colourless. The turgid parenchyma cells help in giving rigidity to the plant body. Partial conduction of water is also maintained through parenchymatous cells.

Occsionally Parenchyma cells which store resin, tannins, crystals of calcium carbonate, calcium oxalate are called idioblasts. Parenchyma is of different types and some of them are discussed as follows.

Types of Parenchyma

2. Collenchyma (Gk. Colla-glue; enchyma – an infusion)

Collenchyma is a simple, living mechanical tissue. Collenchyma generally occurs in hypodermis of dicot stem. It is absent in the roots and also occurs in petioles and pedicels. The cells are elongated and appear polygonal in cross section. The cell wall is unevenly thickened. It contains more of hemicellulose and pectin besides cellulose. It provides mechanical support and elasticity to the growing parts of the plant. Collenchyma consists of narrow cells. It has only a few small chloroplast or none. Tannin maybe present in collenchyma.Based on pattern of pectinisation of the cell wall, there are three types of collenchymas.

Types of Collenchyma

1. Angular collenchyma

It is the most common type of collenchyma with irregular arrangement and thickening at the angles where cells meets. Example:Hypodermis of Datura and Nicotiana

2. Lacunar collenchyma

The collenchyma cells are irregularly arranged. Cell wall is thickening on the walls bordering intercellular spaces. Example:Hypodermis of Ipomoea

3. Lamellar collenchyma

The collenchyma cells are arranged compactly in layers(rows). The Cell wall is thickening is at tangential walls.These thickening appear as successsive tangential layers. Example:Hypodermis of Helianthus

Diagramatic structures

Annular Collenchyma: Duchaigne (1955) reported another type called Annular collenchyma in petiole of Nerium. The lumen is more or less circular in shape.

3. Sclerenchyma (Gk. Sclerous- hard: enchyma-an infusion)

The sclerenchyma is dead cell and lacks protoplasm. The cells are long or short, narrow thick walled and lignified secondary walls. The cell walls of these cells are uniformly and strongly thickened. The sclerenchymatous cells are of two types: 

1.     Sclereids

2.     Fibres

Sclereids (Stone Cells)

Sclereids are dead cells, usually these are isodiametric but some are elongated too. The cell wall is very thick due to lignification. Lumen is very much reduced. The pits may simple or branched. Sclereids are mechanical in function. They give hard texture to the seed coats, endosperms etc., Sclereids are classified into the following types.

Types of Sclereids

1. Branchysclereids or Stone cells:

Isodiametric sclereids, with hard cell wall. It is found in bark, pith cortex, hard endosperm and fleshy portion of some fruits. Example: - Pulp of Pyrus.

2. Macrosclereids:

Elongated and rod shaped cells, found in the outer seed coat of leguminous plants. Example: Crotalaria and Pisum sativum.

3. Osteosclereids (Bone cells):

Rod shaped with dilated ends. They occur in leaves and seed coats. Example: seed coat of Pisum and Hakea

4. Astrosclereids:

Star cells with lobes or arms diverging form a central body. They occur in petioles and leaves. Example: Tea, Nymphae and Trochodendron.

5. Trichosclereids:

Hair like thin walled sclereids. Numerous small angular crystals are embedded in the wall of these sclereids, present in stems and leaves of hydrophytes. Example: Nymphaea leaf and Aerial roots of Monstera.

Filiform Sclereids: The sclereids are present in the leaf lamina of Olea europaea. They are very much elongated fibre like and about 1m.m length.

Sclerenchyma Found in Some Fruits

Fibres

Fibres are very much elongated sclerenchyma cells with pointed tips. Fibres are dead cells and have lignified walls with narrow lumen. They have simple pits. They provide mechanical strength and protect them from the strong wind. It is also called supporting tissues. Fibres have a great commercial value in cottage and textile industries.

Fibres are of five types

Wood Fibres or Xylary Fibres

These fibres are associated with the secondary xylem tissue. They are also called xylary fibres. These fibres are derived from the vascular cambium. These are of four types.

a. Libriform fibres b. Fibre tracheids c. Septate fibres d. Gelatinous fibres.

a.  Libriform fibres: These fibres have slightly lignified secondary walls with simple pits. These fibres are long and narrow.

b. Fibre tracheids: These are shorter than the libriform fibres with moderate secondary thickenings in the cell walls. Pits are simple or bordered.

c. Septate fibres: Fibres that have thin septa separating the lumen into distinct chambers. Eg. Teak

d. Gelatinous fibres: Fibres in which lignin is less in amount and cellulose is more in this cell walls.

These fibres are characteristic of tension wood which is formed in the underside of leaning stems and branches.

Bastfibres or Extra Xylary Fibres

These fibres are present in the phloem. Natural Bast fibres are strong and cellulosic. Fibres obtaining from the phloem or outer bark of jute, kenaf, flax and hemp plants. The so called pericyclic fibres are actually phloem fibres.

Surface Fibres

These fibres are produced from the surface of the plant organs. Cotton and silk cotton are the examples.They occur in the testa of seeds.

Mesocarp Fibres

Fibres obtained from the mesocarp of drupes like Coconut.

Leaf Fibres

Fibres obtained from the leaf of Musa, Agave and Sensciveria.

Fibres in Our Daily Life

Economically fibres may be grouped as follows

1)    Textile Fibres: Fibres utilized for the manufacture of fabrics, netting and cordage etc.

a)           Surface Fibres: Example: Cotton.

b)          Soft Fibres: Example: Flax, Jute and Ramie

c)           Hard fibres: Example: Sisal, Coconut, Pineapple, Abaca etc.

2)    Brush fibre: Fibres utilized for the manufacture of brushes and brooms.

3)    Rough weaving fibres: Fibres utilized in making baskets, chairs, mats etc.

4)    Paper making fibres: Wood fibres utilized for paper making.

5)    Filling fibres: Fibres used for stuffing cushions, mattresses, pillows, furniture etc. Example: Bombax and Silk cotton.