Plant Tissues are stationary or fixed and most of them are dead. Dead cells provide mechanical strength and needs less maintenance. Some plant tissues divide through out the life while others not. So based on their dividing capacity, plant tissues are classified into: Meristematic Tissues and Permanent Tissues.
- The dividing tissues are known as Meristematic Tissues.
- They are located at specific regions only.
- The characteristics of cells changes as they grow and mature.
- They have dense cytoplasm, thin cellulose walls and prominent nuclei.
- They lack vacuoles.
- Based on the location, meristematic cells are classified into: apical, lateral and intercalary.
- Apical meristem – Found at the tips of stem and roots and increases their length .
- Lateral meristem – Increases the girth of stem and roots.
- Intercalary meristem – Present at the base of leaves or internodes.
- They perform specific functions.
- They don’t divide.
- Their ability to take up permanent shape, size and a function is known as “Differentiation“.
- There are two types of Permanent Tissues: Simple Permanent Tissues and Complex Permanent Tissues.
Simple Permanent Tissue:
- They are made up of only one type of cell.
- They have same structures.
- The Simple Permanent Tissues are further classified into:
- They have large intercellular spaces between them as they are loosely packed.
- They consist of relatively unspecialised cells with thin cell walls.
- It supports the plant and stores food.
- Sometimes, it contains chlorophyll and performs photosynthesis. Then, such cells are called “Chlorenchyma“.
- In aquatic plants, a type of parenchyma tissue called “Aerenchyma“, gives buoyancy to plants.
- It is responsible for the plant’s flexibility.
- It allows easy bending of plant parts.
- It provides mechanical support to plants.
- They are present in the leaf stalks below the epidermis.
- The cells of this tissue are elongated and living.
- They are irregularly thickened at the corners.
- They have very little intercellular space.
- It makes plant hard and stiff.
- The cells of this tissue are dead.
- The cell walls are thick due to the presence of lignin.
- It is found in stems, around vascular bundles, in the veins of leaves and in the hard covering of seeds and nuts.
Complex Permanent Tissue:
- They are made up of more than one type of cells.
- These cells coordinate to perform a single function.
- The two types of Complex Permanent Tissues are:
- It consists of tracheids, vessels, xylem parenchyma and xylem fibres.
- Their cell walls are thick and made up of mostly dead cells.
- Tracheids and vessels allow the transportation of water and minerals.
- Parenchyma stores food and helps in sideway conduction of water.
- It consists of sieve tubes, companion cells, phloem fibres and phloem parenchyma.
- Phloem cells are living cells except phloem fibres.
- It transports food from leaves to other parts of the plant.
- Transportation in phloem is in both directions (up and down).
Xylem and Phloem constitute a vascular bundle and are known as conducting tissues.