Primary Structure of Dicot Stem (Sunflower Stem) - PDF

**Primary structure of typical dicot stem (T.S. of young Sunflower stem)** Take a series of transverse sections of young sunflower stem. Add them in watch glass containing water. Select the thin, transparent, floating sections, stain with dilute safranine, wash in water to remove excess of stain an...

**Primary structure of typical dicot stem (T.S. of young Sunflower stem)** Take a series of transverse sections of young sunflower stem. Add them in watch glass containing water. Select the thin, transparent, floating sections, stain with dilute safranine, wash in water to remove excess of stain and mount in glycerine. Place cover-slip and observe under low power of compound microscope. T.S. of sunflower stem shows epidermis, hypodermis, cortex, endodermis and stele having pith in the centre. **Epidermis** It is the outermost most protective layer formed by thin-walled, compactly arranged rectangular cells. The outer walls of the epidermal cells are highly cutinized. Multicellular epidermal outgrowths called trichomes are present sparingly. **Hypodermis** It is made up of two or four layers of collenchyma cells just internal to the epidermis. **Cortex** Cortex is formed by thin walled parenchymatous cells with intercellular spaces. In the young stem the cells often possess chloroplasts. In cortex, oil ducts are present at intervals. **Endodermis** The innermost layer of the cortex forms the endodermis. It is formed by thin walled; barrel shaped cells possessing starch grains and is often called starch sheath. **Stele** Outermost layer of the stele is pericycle which is multi-layered and heterogenous i.e., formed by two types of tissues viz. sclerenchymatous tissue and parenchymatous tissue alternating with each other. The sclerenchymatous tissues are present above the vascular tissues and are often called hard bast. The parenchymatous tissues are present above the medullary rays. The vascular bundles are arranged in a ring with pith in the centre. Thus, the stele is Eustele. The vascular bundles are conjoint, collateral and open. The xylem is endarch. The parenchymatous areas between the vascular bundles are called medullary rays, the cells of which are radially elongated. The rays join the pith. Anatomy and Primary Structure of Dicot stem - sunflower stem