A thin cross-section of the stem of a dicotyledonous plant shows the following.
1. Epidermis: Epidermis is single layered and composed of parenchyma cells. Cells are densely packed and cysts are absent. It has multicellular chondroma. Cuticles are present outside the skin.
2. Hypodermis: Below the epidermis lies the hypodermis. It is 5-7 layered and composed of collenchyma cells. It has no budget. Some cells contain chloroplasts.
3. Cortex: It is 2/3 layers below the hypodermis. It is composed of parenchyma cells containing chloroplasts. Cells are large and round with intercellular spaces. It stores food.
4. Endodermis: The inner layer of the cortex is called endodermis. It is composed of single-layered and tubular parenchyma cells. The cells are densely packed and without gaps. It is called starch sheath because there are many white grains deposited in the endodermis.
5. Stele: The portion extending from the bottom to the center of the endothelium is known as the styli. Different regions of Stele are-
(i) Pericycle: Pericycle is 3-4 layered and composed of parenchyma or sclerenchyma cells. At the head of the vascular bundle is a cap-like ring made up of sclerenchyma cells. It is called Bundle cap. Pericycle originates from the connective tissue of the head.
ii) Basal tissue: Basal tissue is composed of multi-layered parenchyma cells below the pericycle. The cells are large and the walls are very thin. Vascular bundles are located within this layer.
(iii) Vascular bundles: Vascular bundles are numerous and arranged in two rows in a ring shape. It is connected, parallel and free. Its components are:
Xylem: Metaxylem towards the periphery and protoxylem towards the center i.e. Endarc. Xylem is located between exocambium and endocambium. It transports water. The xylem breaks down to form lysigenous cavities.
Phloem: Phloem is located on both sides of xylem. The phloem outside the xylem is called exophloem and the phloem inside is called endophloem. It transports food.
Cambium: Cambium is located on both sides of xylem. The cambium outside the xylem is called exocambium and the cambium inside is called endocambium. It creates new cells.