Anatomy of Dicot Root

Secretory and Excretory Tissue

• Specialized tissues store secretory or excretory products in cavities.
• Products include gums, oils, mucilage, tannins, and resins.
• Glands can be categorized as internal or external.

Anatomy of Dicot Root

• Epiblema (Rhizodermis or Piliferous layer):

  • Outermost layer, consists of thin-walled barrel-shaped parenchyma.
  • Lacks intercellular spaces, cuticle, and stomata.
  • Features unicellular root hairs for absorption of water and minerals.

• Cortex:

  • Multilayered zone of thin-walled parenchymatous cells with intercellular spaces.
  • Functions in the storage of food and water.

• Endodermis:

  • Innermost layer of the cortex with tightly packed barrel-shaped cells.
  • Features Casparian strips (internal bands of suberin/lignin) preventing wall-to-wall movement of substances.
  • Contains thin-walled passage cells opposite xylem, aiding water and dissolved salt movement.

• Pericycle:

  • Located beneath the endodermis, composed of thin-walled parenchyma without intercellular spaces.
  • Responsible for forming vascular cambium and cork.

• Vascular Bundle:

  • Positioned inner to pericycle; arranged radially (alternating xylem and phloem).
  • Typically contains 2-6 bundles; xylem is exarch (protoxylem at periphery, metaxylem towards center).
  • Xylem structure includes vessels, tracheids, parenchyma, and fibers, facilitating water and mineral conduction.
  • Phloem consists of sieve elements, companion cells, parenchyma, and fibers, serving in food conduction.

• Conjunctive Tissue:

  • Located between xylem and phloem bundles, composed of elongated thin-walled parenchyma.
  • Assists in food storage.

• Pith:

  • Generally reduced or absent; if present, made of thin-walled parenchyma (with or without intercellular spaces).
  • Functions primarily in food storage.