Chapter:- TISSUES

PLANT TISSUES.

Types of Tissues.

A permanent tissue is a group of cells, which is derived from the meristematic tissues, but these cells have lost the power of division temporarily or permanently.
Note: The development process by which cells which have been derived from meristematic tissue, take up a permanent shape, size and function is called differentiation.

Permanent tissues are of two types: –

These tissues are composed of cells which are structurally and functionally similar. These tissues are of three types:

Parenchyma:

Derived from Greek word “para= besides & enchein= to pour”.
Parenchyma forms the bulk of plant body. It consists of thin walled living cells.
The cells are isodiametric, i.e., equally expanded on all sides.
The cell wall is thin and encloses a dense cytoplasm which contains a small nucleus and a large central vacuole.
The intercellular spaces are abundant.
The parenchyma is present in all the organs of the plants, i.e., roots, stems, leaves, flowers, fruit and seeds.

Types of Parenchyma:-

1) Storage parenchyma:- These parenchymous cells enlarge to store nutrients and water.

2) Aerenchyma:- These cells consist of large air cavities which store gases and provide buoyancy to aquatic plants.

3) Chlorenchyma:- These cells contain chloroplasts to perform photosynthesis. Eg mesophyll of leaves.

4) Prosenchyma:- Type of Parenchyma where cells are elongated.

5) Medullary Parenchyma:- Found radially arranged in between the vascular bundles in the stem . Meant for storage of reserve food.

6) Conjunctive Parenchyma:- Occurs in the root and meant for storage of water.

7) Armed Parenchyma:- Found in epidermis of leaves of some gymnosperms. The cells have many spiny projections which provide defence to the plant.

The main function of parenchymatous tissue is storage of food, e.g., starch in the parenchyma of cortex of potato tuber.
Parenchyma forms the framework of all the plant organs and tissues like cortex. Pith etc.
Parenchyma serves as packing tissue to fill the spaces between other tissues.
It stores waste materials of plants such as gum, crystals etc.
The intercellular air spaces of parenchyma cells allow gaseous exchange.
If chloroplast is present, the parenchyma tissue is called chlorenchyma and it performs photosynthesis.
In aquatic plants, large air cavities are present in parenchyma to give buoyancy to the plants to help them float. Such a parenchyma type is called aerenchyma.

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The writer is working as a teacher and is currently posted at Central High School Pulwama.