Describe structure of a vessel.

Explanation

**Step-by-Step Text Solution:**

1. **Definition of Vessel**: A vessel is a long cylindrical tube-like structure found in the vascular system of plants, primarily involved in the transport of water and nutrients.

2. **Structure**:
- **Shape**: The vessel is characterized by its elongated, cylindrical shape.
- **Walls**: The walls of the vessel are lignified, meaning they contain lignin, which provides strength and rigidity.
- **Central Cavity**: There is a wide central cavity within the vessel that facilitates the flow of water and dissolved substances.
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