4. Simple permanent tissue

In the above topic, we learnt about meristematic tissues. But plants can't do their functions with only meristematic tissues.
1. Plants have to store food and water
2. Plants have to get mechanical support

 
To perform such kind of specific functions, plants require permanent tissues.

 

\(\text{Meristematic tissue}\) \(\xrightarrow{\small{\text{Differentiation process}}}\) \(\text{Permanent Tissues}\)

There are two types of permanent tissue.

1. Simple Permanent tissue

2. Complex Permanent tissue

Simple permanent tissue consists of the same cells performing a similar function and occur in homogenous groups. They are not such specialized cells and with thin cell walls made up of cellulose. Cells are loosely spaced in this tissue. So intercellular spaces between these cells are large.

 

Location: Generally found in few layers below epidermis  

 

  

1. Parenchyma
2. Collenchyma
3. Sclerenchyma

Parenchyma word derived from Greek (Para means"beside", enchyma means "in-filling"). The term parenchyma was coined by Grew. It is the simplest, unspecialized, most primitive, most abundant permanent tissue that evolved first; therefore, it is treated as a fundamental tissue. Framework of tissues in cortex, Pith, mesophyll of the leaves and floral parts are provided by parenchyma cells.

The shape of the parenchyma cells ultimately depends on their function.

 

 

1. It is responsible for storage of food, nutrients and water.
2. It provides mechanical support to the plants.

3. As it is a living tissue, metabolic activities occur in it.

4. Secondary tissues, responsible for the secondary growth of a plant is formed by the de-differentiation process of parenchyma.

  

Chlorenchyma: In some cases, parenchyma tissue contains chlorophyll and involves in the process of photosynthesis. This type of Parenchyma tissue is called as chlorenchyma.

 

Aerenchyma: In aquatic plants, parenchyma tissues have large air cavities inside it. These tissues float inside the water because of buoyancy caused by the air cavities. This type of parenchyma tissue is called as aerenchyma.

Collenchyma word derived from Greek (Kolla means glue). The term collenchyma was coined by Schleiden \((1839)\).

 

Location: Leaf Stalks below the epidermis and leaf midrib. It is absent in dicot roots, monocot plants and underground parts.

  

1. It gives flexibility and elasticity to the plant and prevents tearing of leaves.
2. It provides mechanical support for the plant.
3. This tissue enables parts of the plants such as tendrils and stems of climbers to bend easily without any breaking.

Location: In stems, around vascular bundles, in the veins of leaves, in the hard covering of seeds and nuts.

Sclereids: These are also called grit cells or stone cells. These are small cells, where the lumen is so tiny due to higher thickening of the cell wall as in drupe fruit (mango, coconut, walnut).

 

 

Fibres: They are very long, narrow, thick, lignified cells. Lumen is large as compared to the sclereids. In the thick wall, both the sclereids and fibres are present in thin areas called as pits. Pits are narrow and unbranched. These fibres are present in bundles and provide strength and hardness.

  

Functions of sclerenchyma: This tissue gives very rigid mechanical support to plants so that plants are hard and stiff. For example, husk of coconut is made up of sclerenchymatous tissue.

 

  

Importance of fibres and sclereids: It is used to manufacture of ropes, mats and certain textile fibres.