Permanent Tissues

Permanent tissues are derived from meristematic tissues. They have lost the power of dividing, having attained their definite form and size. In their earlier stages the cells are more or less similar in structure but slowly they become specialized and form permanent tissues. They can be classified into simple and complex tissues.

Simple Tissues

A simple tissue is made up of one type of cells forming a uniform mass.

There are three types of simple tissues:

• Parenchyma

• Collenchyma

• Sclerenchyma

Parenchyma

Nature

• Cells are isodiametric i.e. equally expanded on all sides

• They may be oval, round, polygonal or elongated

• Nucleus is present and hence living

• The cell walls are thin and made of cellulose

• Cytoplasm is dense with a single large vacuole

• Intercellular spaces may be present

• May contain chlorophyll. Parenchyma which contain chlorophyll are called chlorenchyma.

Occurrence

Found in the cortex of root, ground tissue in stems and mesophyll of leaves.

Function

• Store and assimilate food

• Give mechanical strength by maintaining turgidity

• Prepare food if chlorophyll is present

• Store waste products like tanin, gum, crystals and resins

Collenchyma

Nature

• The cells are elongated and are circular, oval or polygonal in cross-section

• Cell wall is unevenly thickened with cellulose at the corners against the intercellular spaces

• Nucleus is present and hence the tissue is living

• Vacuoles are small

• Intercellular spaces are generally absent

• If they contain chlorophyll they are known as chlorenchyma

Occurrence

Found under the skin i.e. below the epidermis in dicot stems.

Function

• Provide mechanical support to the stem

• Being extensible, these cells readily adapt themselves to the rapid elongation of the stem

Sclerenchyma

Nature

• The cells are long, narrow, thick and lignified, usually pointed at both ends

• The cell wall is evenly thickened with lignin and sometimes is so thick that the cell cavity or lumen is absent

• Nucleus is absent and hence the tissue is made up of dead cells

• They have simple, often oblique pits in the walls

• The middle lamella i.e. the wall between adjacent cells is conspicuous

Occurrence

Found abundantly in stems of plants like hemp, jute and coconut, their length varying from 1 mm to 550 mm.

Function

Gives mechanical support to the plant by giving rigidity, flexibility and elasticity to the plant body.

Sclereids

These are special sclerenchymatous cells found in the cortex, pith, phloem, hard seeds, nuts and stony fruits. The flesh of pear and guava are sometimes gritty due to the presence of sclereids. These cells are thick walled, hard and strongly lignified. They are isodiametric, polyhedral, slightly elongated or irregular in shape.

Their function is to give firmness and hardness to the part concerned.