Simple Tissues

Simple Tissues

Simple tissue are homogeneous -composed of structurally and functionally similar cells. eg., Parenchyma, Collenchyma and Sclerenchyma.

1. Parenchyma

Parenchyma are simple permanent tissue composed of living cells. Parenchyma cells are thin walled, oval, rounded or polygonal in shape with well developed spaces among them. In aquatic plants, Parenchyma possesses intercellular air spaces, and is named as Aerenchyma. When exposed to light, parenchyma cells may develop chloroplasts and are known as Chlorenchyma.

Functions:

Parenchyma may store water in many succulent and xerophytic plants. It also serves the functions of storage of food reserves, absorption, buoyancy, secretion etc.,

2. Collenchyma

Collenchyma is a living tissue found beneath the epidermis. Cells are elongated with unevenly thickened non-lignified walls. Cells have rectangular oblique or tapering ends and persistent protoplast. They possess thick primary non-lignified walls.

Functions:

They provide mechanical support for growing organs.

3. Sclerenchyma

Sclerenchyma consists of thick walled cells which are often lignified. Sclerenchyma cells do not possess living protoplasts at maturity. Sclerenchyma cells are grouped into (i) fibres and (ii) sclereids.

Fibres are elongated sclerenchymatous cells, usually with pointed ends. Their walls are lignified. Fibres are abundantly found in many plants. The average length of fibres is 1 to 3 mm, however in plants like Linum usitatissimum (flax), Cannabis sativa (hemp) and Corchorus capsularis (jute), fibres are extensively longer ranging from 20 mm to 550 mm.

Sclereids

Sclereids are widely distributed in plant body. They are usually broad, may occur in single or in groups. Sclereids are isodiametric, with liginified walls. Pits are prominent and seen along the walls. Lumen is filled with wall materials. Sclereids are also common in fruits and seeds.

Table 7.1 Differences between Parenchyma and Collenchyma

Parenchyma

·           Cell wall is thin and uniform in thickness

·           It serves as storage tissue.

·           It is found in outer and inner parts of plant organs

Collenchyma

·           It possesses well developed extra thickening at places adjacent to intercellular spaces

·           It serves as mechanical tissue

·           It is restricted to sub epidermal parts of plant organs.

Table 7.2 Differences between Collenchyma and Sclerenchyma

Collenchyma

·           It consist of living cells

·           Cells contain protoplasm

·           Cell walls are made of cellulose

·           Thickening of cell wall is not uniform

·           Lumen of the cell is wide

·           Pits are simple straight

·           It provides mechanical support and elasticity to the plant body

Sclerenchyma

·           It consist of dead cells

·           Cells are empty

·           Cell walls are lignified

·           Cell wall thickening is uniform

·           Lumen of the cell is narrow

·           Pits are simple oblique sometimes branched

·           It provides only mechanical support

Table 7.3 Differences between Sclereids and Fibres

Sclereids

·           Usually broad

·           End walls blunt

·           Occur singly

·           Deep pits

Fibres

·           Elongated narrow

·           thread like

·           End walls tapering

·           Occur in bundles

·           Narrow pits