Which of the following is not a component of xylem ?

Options

A. Wood parenchyma
B. Vessels
C. Sieve tube
D. Tracheids

Explanation

To determine which of the following is not a component of xylem, we will analyze each option provided:

1. **Wood Parenchyma**:
- Wood parenchyma is a type of xylem tissue that serves primarily for storage of nutrients and water. It is indeed a component of xylem.

2. **Vessels**:
- Xylem vessels are specialized structures that facilitate the conduction of water and dissolved minerals from the roots to the rest of the plant. They are a crucial part of xylem.

3. **Sieve Tube**:
- Sieve tubes are not part of xylem; they are components of phloem, which is responsible for the transport of carbohydrates and other organic compounds throughout the plant.

4. **Tracheids**:
- Tracheids are elongated cells in the xylem that help in the conduction of water and provide structural support. They are also a component of xylem.

Based on the analysis, the only option that is not a component of xylem is **sieve tube**.

### Final Answer:
The correct answer is **sieve tube**.