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| Meristematic Tissue (Meristem) |
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| The meristematic tissue is formed exclusively by undifferentiated or embryonic cells. These cells, known as meristematic cells, are responsible for bringing about growth of the plant body due to their capacity to undergo continuous mitotic divisions. |
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| Meristematic Tissue |
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 The cells are relatively smaller in size compared to mature cells. They are either rectangular or isodiametric in shape. |
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 The cells are always compactly arranged, without any intercellular spaces. |
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 The cells have a thin cell wall, which is composed of only cellulose. |
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 The cells enclose a large amount of clear and transparent cytoplasm. |
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 Every cell has a single, conspicuous nucleus, which is situated in the center of the cell. |
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 The chromosomes are always found in some phase of mitotic division. |
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 Except mitochondria, other cell organelles are either absent or present in a nonfunctional state. For example, the plastids may be present in a non-functional state called proplastids. |
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 Vacuoles are absent. |
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 Ergastic substances such as reserve food materials or secretory products or excretory products are completely absent. |
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 The cells are capable of undergoing regular, continuous mitotic divisions. |
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| The meristematic tissue is classified on the basis of origin, location in the plant body and differentiation. |
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| A. Based on Origin |
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| Based on origin, meristem can be classified into the following two types: |
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| Primary Meristem |
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| It is the meristem that is present right from the embryonic stage and continues to be active throughout the life of a plant. It is responsible for primary growth in the plant body. It gives rise to the primary permanent tissues of the plant body. |
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| Example: |
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| Meristem found at the tip of the stem and root. |
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| Secondary Meristem |
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| It is the meristem that appears later in the life cycle of a plant. It develops by a process called dedifferentiation in the permanent tissues. It is responsible for secondary growth in the plant body. It gives rise to secondary permanent tissues such as secondary cortex and secondary xylem. |
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| Example: |
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| Cork cambium and vascular cambium. |
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| B. Based on Location (or Position) in the Plant Body |
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| Based on location in the plant body, meristem can be classified into the following three types |
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| Apical Meristem |
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| It is the meristem present at the tip of the root and stem, commonly called as root apex and shoot apex respectively. Such meristems constitute the actively growing regions in the plant body. Due to the activity of apical meristem the plant body keeps increasing in its length. |
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| Apical Meristem |
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| Intercalary Meristem |
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| It is the meristem that occurs between permanent tissues. It represents the remnant of the apical meristem. It is particularly common at the nodal regions. It may also occur at the base of the leaves. The intercalary meristem also contributes towards the increase in length as it brings about elongation of the internodal regions. It is also responsible for the formation of branches at the nodal regions. |
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| The apical and intercalary meristems are examples of primary meristem. |
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| Intercalary Meristem |
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| Lateral Meristem |
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| It is the meristem that occurs laterally, parallel to the long axis of plant body. Cambium strips formed in the vascular bundles and in the cortex are common examples of lateral meristem. It is responsible for an increase in the girth (circumference) of the plant body as it brings about the formation of secondary permanent tissues. |
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| The lateral meristem is an example of secondary meristem. |
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| C. Based on Differentiation |
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| Based on the type of permanent tissue that differentiates from meristem, following three types of meristem can be recognised. |
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| Protoderm |
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| It is the meristem that always differentiates into protective structures like epidermis. |
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| Ground Meristem |
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| It is the meristem that always differentiates into ground tissue components such as cortex, endodermis and pith. |
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| Procambium |
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| It is the meristem that always differentiates into the vascular tissues like xylem and phloem. |
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| Meristematic Cells |
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| L.S. of a Shoot |
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| T.S. Through Shoot Apex |
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