Describe the internal structure of a young dicot stem (e.g.,sunflower).

(N/A) $\rightarrow$ Sunflower is an annual plant with an erect stem.
$\rightarrow$ $A$ transverse section $(TS)$ of a young sunflower stem reveals the following structures:
$(1)$ Epidermis: The outermost protective layer,one cell thick,composed of parenchyma cells. The outer wall is covered with a thin cuticle. It may bear trichomes and a few stomata for gas exchange.
$(2)$ Cortex: Comprises three parts: hypodermis,main cortex,and endodermis.
$(i)$ Hypodermis: Located just below the epidermis,consisting of $3-4$ layers of collenchyma cells. These cells have thickened walls due to cellulose and pectin deposition and lack intercellular spaces. It provides mechanical support.
$(ii)$ Main Cortex: Located below the hypodermis,made of parenchymatous tissue with conspicuous intercellular spaces. The cell walls are thin and cellulosic. Resin ducts may be present in this region. These cells store water and food.
$(iii)$ Endodermis: The innermost layer of the cortex,single-layered,with barrel-shaped parenchymatous cells. These cells contain starch grains,hence it is often called the starch sheath.
$(3)$ Stele: Includes the pericycle,vascular bundles,medullary rays,and pith.
$(i)$ Pericycle: Located inside the endodermis,it is multilayered and composed of sclerenchyma and parenchyma. Sclerenchyma patches located above the vascular bundles are called bundle caps.
$(ii)$ Vascular Bundles: In a sunflower stem,there are $20-25$ vascular bundles arranged in a ring. Each bundle is conjoint,open (possessing cambium),and endarch (protoxylem towards the center).