Describe internal structure of sunflower root.

$\rightarrow$ For a better understanding of tissue organisation of roots, stems and leaves, it is convenient to study the transverse sections of the mature zones of these organs.

$\rightarrow$ Internal structure of mature root of sunflowers : Sunflower is a dicot and an annual plant. This transverse section of the sunflower root is taken and it is stained with safranin washed with water, viewed under microscope from outside to inside following three regions are seen clearly.

$(1)$ epidermis $(2)$ cortex $(3)$ endodermis.

$\rightarrow$ Epidermis : It is the outermost layer. Many of the epidermal cells protrude in the form of unicellular root hairs. The cells of this layer are thin walled and made up of cellulose. The primary function of this layer to absorb water and mineral salts.

$\rightarrow$ Cortex : The cortex consists of several layers of thin-walled parenchyma cells with intercellular spaces.

$\rightarrow$ Endodermis : It comprises a single layer of barrel-shaped cells without any intercellular spaces. The tangential as well as radial walls of the endodermal cells have a deposition of water impermeable, waxy material-suberin-in the form of casparian strips.

$\rightarrow$ Pericycle : Next to endodermis lies a few layers of thick-walled parenchyomatous cells referred to as pericycle. Initiation of lateral roots and vascular cambium during the secondary growth takes place in these cells.

$\rightarrow$ Pith : The pith is small or inconspicuous.

$\rightarrow$ "Conjuctive Tissue : The parenchymatous cells which lie between the xylem and the phloem are called conjuctive tissue.