Question

Explain internal structure of dicot root in detail with a neat labelled diagram.

Answer 1

A thin transverse section of dicot root shows the following structures.
(i) Epiblema: It is the outermost layer. Cuticle and stomata are absent. Unicellular root hairs are present. It is also known as Rhizodermis or Piliferous layer.
(ii) Cortex: It is a multilayered large zone made of thin-walled parenchymatous cells with intercellular spaces. It stores food and water.
(iii) Endodermis: It is the innermost layer of cortex. The cells are barrel - shaped, closely packed, and show band like thickenings on their radial and inner tangential walls called casparian strips.

• But these casparian strips are absent in the endodermis cells which are located opposite the protoxylem these thin walled cells without casparian strips are called passage cell.
• It helps in the movement of water and dissolved salts from cortex into xylem.

(iv) Stele: All tissues inner to endodermis constitute stele. It includes pericycle and vascular bundle.
(a) Pericycle: Inner to endodermis lies a single layer of pericycle. It is the site of origin of lateral roots.
(b) Vascular bundle: It is radial. Xylem is exarch and tetrach. The tissue present between xylem and phloem is called conjunctive tissue. In dicot root, it is made up of parenchyma.
(c) Pith: Young root contains pith whereas in old root pith is absent.