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Secondary growth in plant roots

This document summarizes secondary growth in dicot roots. It begins by explaining the importance of secondary growth in increasing a plant's ability to absorb and transport water and minerals. It then describes the anatomy of a dicot root, including the epidermis, cortex, endodermis, pericycle, vascular strands, and pith. The document notes that secondary growth in roots occurs through the formation of a cambial ring, unlike in dicot stems. It also provides brief definitions of xylem and phloem tissue and explains that roots can form periderm through a similar process of secondary growth.

Science◦
BY PRANJAL DHAKA 2042
• Why we need secondary growth? • Anatomy of dicot roots. • Process of secondary growth.
• 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.
• 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.
• 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 metaxylem towards the center. • Pith: Not very prominent. Bundle of parenchymatous tissue.
• It is wavy in the beginning unlike in dicot stems. • The cambial ring is completely secondary in origin.
• 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
• 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
• Roots can also form the exact kind of periderm by the process of seconary growth. • The cork cambium cuts off the phelloderm inside of it, composed of living parenchymatous tissue. • It cuts off phellem (cork) on the outside of it.
Secondary growth in plant roots