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MERISTEMS TISSUE AND ITS CLASSIFICATION.pdf

Meristematic tissues are composed of immature, dividing cells found at growing tips and edges of roots and shoots. They are classified based on position, origin, function, and growth patterns. Apical meristems at tips increase length, while intercalary and lateral meristems produce leaves/flowers and increase diameter through secondary growth. Primary meristems develop directly from embryos, while secondary meristems resume activity in mature tissues. Meristems function as protoderm, procambium, or ground meristem to form epidermis, vascular tissue, or ground tissues, respectively. They exhibit mass, rib, or plate growth patterns through cell divisions.

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Meristematic Tissues  Introduction of Meristematic Tissue  Structure of Meristematic Cells  Classification of Meristems: 1. On the Base of Position 2. On the Base of Function 3. On the Base of Origin and Development 4. On the Base of Growth Pattern and Planes of Division (KASHIF RAZA)
Meristematic Tissues The term Meristem is derived from a Greek word Meristos=Divisible It is a tissue composed of immature not well differentiated cells which has the capacity of division is called meristematic tissue. It is also called Formative tissues. Loaction: The apices of roots, shoots and their lateral branches have meristem at their tips. It increases length of respective axis.
Structure of Meristematic Cell  The cells in the meristem are thin walled.  Meristematic cells are spherical, polygonal, oval and isodiametric in shape.  Rich in protoplast without reserve material.  The vacuoles are small and are scattered throughout the protoplast.  Thick walled meristematic cells are found in the apical meristems. Types: 1. Initiating cells :These cells retain the meristematic activity throughout the growth of the plant. 2. Derivative cells :These cells derive from meristem into various tissue element 3. Differentiation cells :The derivatives undergo morho-physiology changes and this process is called differentiation.
Classification of Meristems On The Base Of Position Of Meristem: 1. Apical meristem: The meristems present at the tip of roots and shoot are called apical meristems.  They play important role in primary growth. 2. Intercalary meristem: The meristem situated at the bases of internodes is called intercalary meristem.  They important role in the in the production of leaves and flower. 3. Lateral meristem: The longitudinal axis of dividing cells present in the vascular and cork tissue of the plants are called lateral meristem.  They play an important role in the diameter of stem and root.  They are involved in secondary growth.
On The Base Of Origin and Development of Meristem 1. Primary Meristem: The meristem developing from directly from the embryonic cells are called primary meristem.  Fundamental body parts are developed such as epidermis ,cortex and mesophyll and primary vascular tissues. b. Secondary Meristems: The meristem developed from differentiated and mature tissue by resuming the meristematic activity is called secondary meristem.  Secondary vascular tissue and protective tissue develop from secondary meristem.  Its example are phellogen and cork cambium. Terms: Meristematic cells layer that are responsible for the development of the periderm is called phellogen.  Cells that grow inwards from there are termed Phelloderm.  Cells that develop outward are termed Phellem.
On the Basis of Function a. Protoderm: It is the outer layer of meristem which will become epidermal meristem. b. Procambium: This is responsible for the development of the primary vascular which will become the vascular tissue. c. Ground meristem: Which will form the ground tissue.(parenchyma,collenchyma,scl erenchyma tissue).
On The Basis of Growth Pattern and Planes of Division a) Mass Meristem: A meristem in which cell division in all planes results in increase in mass.  For example: growth resulting in the formation of endosperm and takes place in young embryos of some plant. b) Rib Meristem: A meristem in which cell division occur anticlinal (t right angles to the longitudinal axis) in one plane and give rise to vertical rows and column.  This type of growth occurs during the development of cortex of root and pith and the cortex of stem. c) Plate Meristem: A meristem in which cell divides by anticlinal divisions with the result that number of layers do not increase and a platelike structure formed.  Growth shown by flat blades of angiosperm leaves.