Download - Secondary growth in plant roots
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BY
PRANJAL DHAKA
2042
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• Why we need secondary growth?
• Anatomy of dicot roots.
• Process of secondary growth.
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• It increases the ability of plants to absorb water and facilitates transport of water and minerals in bulk quantities.
• Helps in mechanical support and anchoring when the tree grows big.
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• Epiblema: Consists of the outermost epidermal layer with root hair arising from it.
• Cortex: Thin layer of parenchymatous layer. Main function is storage.
• Endodermis: Barrel shaped, rich in Starch and have radial and tangential thickenings called casparian bands due to lignin depositions.
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• Pericycle: Made up of thin walled parenchyma cells. It gives rise to cork cambium, part of vascular cambium and all lateral roots.
• Vascular Strands: They are alternate bands of xylem and phloem. Protoxylem towards the periphery and metaxylemtowards the center.
• Pith: Not very prominent. Bundle of parenchymatous tissue.
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• It is wavy in the beginning unlike in dicot stems.
• The cambial ring is completely secondary in origin.
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• principle water-conducting tissue
• combination of vessels and tracheids
• primary xylem derived from procambium
• secondary xylem formed by vascular cambium
• wood made of accumulated secondary xylem
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• principle food-conducting tissue in vascular plants, located toward the outer part of roots and stems
• carried out through sieve cells and sieve-tube members
• some sieve areas (pores) have larger pores called sieve plates
• each sieve-tube member associated with companion cell
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• Roots can also form the exact kind of periderm by the process of seconary growth.
• The cork cambium cuts off the phelloderminside of it, composed of living parenchymatous tissue.
• It cuts off phellem (cork) on the outside of it.
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