All the xylem elements, when mature are dead except

Options

A. tracheids
B. vessels
C. xylem parenchyma
D. xylem fibres

Explanation

**Step-by-Step Solution:**

1. **Understanding Xylem Composition**: Xylem is a type of vascular tissue in plants responsible for the conduction of water and minerals. It consists of four main elements: tracheids, vessels, xylem parenchyma, and xylem fibers.

2. **Identifying the Function of Each Element**:
- **Tracheids**: These are elongated cells that facilitate water transport. They have thick cell walls and are dead at maturity.
- **Vessels**: These are wider tubes that also conduct water. Like tracheids, vessels are dead when mature.
- **Xylem Fibers**: These provide structural support and are also dead at maturity, composed of thick lignified walls.
- **Xylem Parenchyma**: This is the only living component of the xylem. It contains protoplasm, including a nucleus and cytoplasm, and serves in storage and sometimes in the lateral transport of water.

3. **Conclusion**: Since tracheids, vessels, and xylem fibers are all dead at maturity, the only living xylem element is the xylem parenchyma.

4. **Final Answer**: Therefore, the answer to the question "All the xylem elements, when mature are dead except" is **xylem parenchyma**.

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