T.S. of monocot root shows the following anatomical features:

Epidermis/Epiblema/Rhizodermis:

• It is the outermost layer composed of compact parenchymatous cells having no intercellular spaces and stomata.
• The tubular unicellular root hairs are also present on this layer
• Both epiblema and root hairs are without cuticle.
• In older parts, epiblema either becomes impervious or is shed.
• Epiblema and root hairs absorb water and mineral salts.

Cortex:

• It lies just below the epidermis.
• Cortex consists of thin walled multilayered parenchyma cells having sufficiently developed intercellular spaces among them.
• Usually in an old root of Zea mays, a few layers of cortex undergo suberization and give rise to a single or multi-layered zone- the exodermis.
• This is a protective layer which protects internal tissues from outer injurious agencies.
• The starch grains are abundantly present in the cortical cells.
• Cortex functions as:
  • a) conduction of water and mineral salts from root hairs to inner tissues
  • b) storage of food
  • c) protection when exodermis is formed in older parts.

Endodermis:

• The innermost layer of the cortex is termed as endodermis.
• It is composed of barrel-shaped compact cells that lacks intercellular spaces among them.
• Young endodermal cells have an internal strip of suberin and lignin which is called casparian strip.
• The strip is located close to the inner tangential wall.
• There are some unthickened cells opposite to the protoxylem vessels known as passage cells which serve for conducting of fluids.
• The function of endodermis is to regulate the flow of both inward as well as outward.

Pericycle:

• It lies just below the endodermis and is composed of single layered sclerenchymatous cells intermixed with parenchyma.

Vascular tissue:

• The vascular tissue contains alternating strands of xylem and phloem.
• The phloem is visualized in the form of strands near the periphery of the vascular cylinder, beneath the pericycle.
• The xylem forms discrete strands, alternating with phloem strands.
• The center is occupied by large pith which maybe parenchymatous or sclerenchymatous.
• The number of vascular bundles is more than six, hence called as polyarch.
• Xylem is exarch i.e. the protoxylem is located towards the periphery and the metaxylem towards the center.
• Vessels of protoxylem are narrow and the walls possess annular and spiral thickenings in contrast, metaxylem are broad and the walls have reticulate and pitted thickenings.
• Phloem strands consist of sieve tubes, companion cells and phloem parenchyma.
• The phloem strands are also exarch having protophloem towards the periphery and metaphloem towards the center.

Conjunctive tissues:

• In between the xylem and phloem bundles, there is the presence of many layered parenchymatous or sclerenchymatous tissue.
• These help in storage of food and help in mechanical support.

Pith:

• It is the central portion usually composed of thin-walled parenchymatous cells which appear polygonal or rounded in T.S.
• Intercellular spaces may or may not be present amongst pith cells.
• In some cases pith becomes thick walled and lignified.
• Pith cells serve to store food.

Internal structure of Monocot root

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