Describe internal structure of (sunflower stem) of young stem of dicot plant.

$\rightarrow$ Sunflower is an annual plant. It possesses erect stem.

$\rightarrow$ If transverse section of a young stem of sunflower is stained and studied under microscope, following structure is seen.

$(1)$  Endodermis: If is the outermost protective layer of the stem. It is one layered and made up of parenchymatic cell. Outer wall is covered with thin layer of cuticle; It may bear trichomes and a few stomata work for gas exchange.

$(2)$  Cortex : In cortex hypodermis, main cortex and endodermis these 3 parts are included.

$(i)$  Hypodermis: It is located below the epidermis. Hypodermis layer is made up of collenchyma cells. It has 3 to 4 layers. The walls of cells are stained with cellulose and pectin, cells lack intercellular spaces. This tissue provides mechanical support and strength.

$(ii)$  Main Cortex : The part located below hypodermis is called main cortex. It is made up of parenchymatic tissue. If has conspicuous intercellular spaces.

$\Rightarrow$ The wall of cells are thin and made up of cellulose.

$\rightarrow$ Resin ducts are located in this region duct eaciresin is small and surrounded by living secretory cells.

$\rightarrow$ Cells of main cortex store water and food.

$(iii)$  Endodermis : The inner most layer of cortex is called endodermis. It is a single layered, cells are parenchymatous cylindrical or barrel shaped.

$\Rightarrow$ Cells possess starch grains. So this layer is called starch sheath.

$(3)$  Stele : Pericycle, vascular bundles, rays and piths are included.

$(i)$  Pericycle : The part located inside endodermis is called pericycle. It is multilayered and it is made up of sclerenchyma and parenchymatous cells. Sclerenchyma cells are located above vascular bundle. It is called as bundle cap.

$\Rightarrow$ The part consisting of parenchyma cells of pericycle is located above ray.

$(ii)$ Vascular Bundles : In stele of sunflower vascular bundles are in number 20-25. They are arranged in a ring.

$\Rightarrow$ Each vascular bundle is conjoint, open and with endarch protoxylem.

$\Rightarrow$ The development of vessels is endarch.

$\Rightarrow$ Vascular bundle includes phloem, meristematic tissue, cambium and xylem tissue.