Epidermis -> Collenchyma -> Parenchyma -> Vascular Bundle
Explanation
The anatomy of a young dicotyledonous stem displays a distinct arrangement of tissues in concentric layers. These layers are organized from the periphery (outer surface) towards the central axis (pith) to perform specific functions such as protection, mechanical support, and transport.
Analysis of Tissue Sequence:
The transverse section of a young stem reveals the following sequence from the exterior to the interior:
- Epidermis: This is the outermost protective layer, typically consisting of a single layer of cells covered with a cuticle.
- Cortex: The region between the epidermis and the vascular cylinder. In dicot stems, it is differentiated into sub-zones:
- Hypodermis (Collenchyma): Located immediately below the epidermis. It consists of collenchyma cells which provide mechanical strength to the young stem.
- General Cortex (Parenchyma): Situated below the hypodermis. It consists of thin-walled parenchyma cells with intercellular spaces.
- Endodermis: The innermost layer of the cortex (rich in starch grains).
- Stele: The central core containing the pericycle, Vascular Bundles (xylem and phloem), and pith.
Therefore, the correct anatomical sequence is Epidermis → Collenchyma → Parenchyma → Vascular Bundle.
Key Takeaway:
In a young dicot stem, the cortex is differentiated into an outer collenchymatous hypodermis (for support) and an inner parenchymatous zone (for storage), positioned between the epidermis and the vascular bundles.