Describe the internal structure of a sunflower root.

(N/A) $\rightarrow$ To understand the tissue organization of roots,stems,and leaves,it is convenient to study the transverse sections of the mature zones of these organs.
$\rightarrow$ Internal structure of a mature sunflower root: Sunflower is a dicotyledonous plant. When a transverse section of the sunflower root is stained with safranin,washed with water,and viewed under a microscope,the following regions are seen from outside to inside:
$(1)$ Epidermis $(2)$ Cortex $(3)$ Endodermis $(4)$ Pericycle $(5)$ Vascular bundles $(6)$ Pith.
$\rightarrow$ Epidermis: It is the outermost layer. Many epidermal cells protrude as unicellular root hairs. The cells are thin-walled and composed of cellulose. Its primary function is the absorption of water and mineral salts.
$\rightarrow$ Cortex: It consists of several layers of thin-walled parenchyma cells with intercellular spaces.
$\rightarrow$ Endodermis: It comprises a single layer of barrel-shaped cells without intercellular spaces. The tangential and radial walls have a deposition of water-impermeable,waxy material called suberin,forming Casparian strips.
$\rightarrow$ Pericycle: Located next to the endodermis,it consists of a few layers of thick-walled parenchymatous cells. Initiation of lateral roots and vascular cambium during secondary growth occurs here.
$\rightarrow$ Vascular Bundles: These are radial,with xylem and phloem arranged in an alternating manner. The number of xylem and phloem patches is usually two to four (diarch to tetrarch).
$\rightarrow$ Conjunctive Tissue: The parenchymatous cells lying between the xylem and phloem are called conjunctive tissue.
$\rightarrow$ Pith: In dicot roots,the pith is small or inconspicuous.