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2a-Meristematic Tissues.pptx

There are two main types of plant tissues: meristematic tissues and permanent tissues. Meristematic tissues are composed of immature, undifferentiated cells that are capable of cell division. They develop into permanent tissues through differentiation. Meristematic tissues are further classified based on their origin, position, and function. The main types include promeristem, primary meristem, secondary meristem, apical meristem, intercalary meristem, lateral meristem, protoderm meristem, procambium meristem, and ground meristem.

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Meristematic Tissues Types of Tissues : There are two basic types of tissues: 1- Meristematic Tissues 2- Permanent Tissues
1- Meristematic Tissues : (meristos= divisible) It is a tissue composed of immature, not well differentiated cells which has the capacity of division.
2- Permanent Tissues : It is a tissue composed of differentiated cells ( in the growth has ceases) which may be living or dead and thin or thick walled. These tissues develop from meristematic tissue by differentiation.
Meristematic Tissues: The term meristem is derived from a Greek word Meristos meaning Divisible. It emphasizes the cell division activity characteristic of the tissue which bears this name.
• Origin: From early stages of development some cells remain embryonic in character and retain the ability to divide in the mature plant body are called meristems. • These are formative tissues i.e they add new cells to the plant body and also increase their own number.
• Some remains meristematic (able to divide) and are called initiating cells. • Others develop into various tissue elements and are known as the Derivatives of the initiating cells. These cells undergo morpho- physiological changes and this process is called differentiation.
Structure of Meristematic Cells: • Thin-walled, isodiametric,spherical,oval or polygonal in shape. • Rich in protoplasm. • Protoplast is without reserve material and crystals. • Plastids are at proplastid stage. • Usually vacuoles are small and scattered throughout the protoplast.
Size: • Size very • Thick walled meristematic cells are found in the meristematic are found in the apical meristems. • Cells of vascular cambium have thick radial walls.
Classification: On the basis of origin 1- Promeristem 2- Primary Meristem 3- Secondary Meristem On the basis of Position 1-Apical Meristem 2- Intercalary Meristem 3- Lateral Meristem
On the basis of their function • 1-Protoderm Meristem • 2-Procambium Meristem • 3-Ground Meristem
On the basis of origin • 1- Promeristem or primordial meristem: • A group of young meristematic cells of a growing organ. It is the early embryonic meristem from which other advanced meristems are derived. In a plant, it occupies a small area at the tip of stem and root. It further divides to form primary meristem.
2-Primary meristem: • These are derived from promeristem. They are present below the promeristem at shoot and root apices. These cells divide and form permanent tissues.
3-Secondary meristem: It is derived from primary permanent tissues which have the capacity of division e.g. Cork-cambium, cambium of roots and inter fascicular cambium of stem.
On the basis of Position 1-Apical Meristem: These are found at the apices or growing points of root and shoot and bring about increase in length. It includes both pro- meristem as well as primary meristem.
2- Intercalary Meristem: • It lies between the region of permanent tissues and is considered| as a part of primary meristem which has become detached due to formation of intermediate permanent tissues. It is found either at the base of leaf e.g. Pinus or at the base of internodes e.g. grasses.
3- Lateral Meristem: These are arranged parallel to the sides of origin and normally divide periclinally or radially and give rise to secondary permanent tissues. These increase the thickness of the plant part.
• 1-Protoderm Meristem : A meristem that is made up of undifferentiated, actively dividing cells. It is the outermost meristematic tissue. It gives rise to epidermis layer.
2-Procambium Meristem: It is composed of narrow, elongated, prosenchymatous, meristematic cells that gives rise to the vascular tissues system.
3-Ground Meristem: It is composed of large, thick-walled cells which develop to form ground tissue system, i.e. hypodermis, cortex and pith.
2a-Meristematic Tissues.pptx