Plant Anatomy
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Transcript of Plant Anatomy
SECONDARY GROWTH IN ROOTS
BY PRANJAL DHAKA
2042
CONTENT
• Why we need secondary growth?
• Anatomy of dicot roots.
• Process of secondary growth.
Why need it?
• 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.
ANATOMY OF DICOT ROOT• 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.
ANATOMY OF DICOT ROOT
• 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.
PROCESS OF SECONDARY GROWTH
THE CAMBIAL RING
• It is wavy in the beginning unlike in dicot stems.
• The cambial ring is completely secondary in origin.
SECONDARY VASCULAR TISSUE
FUNCTIONS OF SECONDARY XYLEM
• 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
FUNCTIONS OF SECONDARY PHLOEM
• 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
EXTRA-STELAR SECONDARY GROWTH
• 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.
THANK YOU