Internal Structure of Dicot Stem Notes | Free Biology Notes

This article we will discuss about Internal Structure of Dicot Stem

The transverse section of a dicot stem reveals the following structures

Epidermis

• Epidermis is a outermost layer and made up of parenchymatous cells
• Cuticle a protective layer, covers this layer
• It possesses stomata and large number of multicellular hairs
• Epidermis has following functions: Minimize the rate of transpiration, protects from mechanical injury, prevents the entry of harmful organisms and helps in the exchange of gases through stomata

Hypodermis

• Present below the epidermis & multilayered of collenchymatous cells
• Hypodermis has following functions: provides mechanical strength, perform photosynthesis and storage of food

Middle cortex

• Present below the hypodermis & made up of oval cells of parenchyma
• In some plants contains oil ducts & Resin canals
• Middle cortex has following functions: Storage of food & perform photosynthesis

Endodermis

• Its separates the cortex from vascular bundles
• Cells are barrel shaped, compactly arranged, having no intercellular spaces and are parenchymatous.
• Due to abundant starch grains, this layer is also known as starch sheath
• Casparian strips are absent in stem
• Endodermis has following functions: serve for storage of food

Pericycle

• Pericycle is present below the endodermis and composed of sclerenchymatous and parenchymatous cells
• Sclerenchyma forming like a cap on the bundle, so called as bundle caps.
• Parenchymatous present between the two bundles
• Pericycle has following functions: mechanical support and serves to store food

Vascular bundles

• These are arranged in a ring and inner to the pericycle
• Vascular bundle is conjoint, collateral, open type
• Vascular bundles are made up of: xylem, phloem and cambium
• Xylem – helps in conduction of sap
• Phloem – conducts the foods
• Cambium – lies in between xylem and phloem and responsible for secondary growth

Pith

• Occupies central portion of the stem
• Composed of thin walled parenchymatous, rounded or polygonal, with or without intercellular spaces
• The extension of pith between vascular bundles are called as pith ray or medullary rays.
• Pith has following functions: food is stored in this region.