What is the term used for later formed primary xylem?

Explanation

**Step-by-Step Solution:**

1. **Understanding Primary Xylem**: The primary xylem is the first xylem formed during the growth of a plant. It is responsible for the transport of water and nutrients from the roots to the rest of the plant.

2. **Components of Primary Xylem**: The primary xylem differentiates into two main components: protoxylem and metaxylem.

3. **Differentiation of Protoxylem and Metaxylem**:
- **Protoxylem**: This is the first formed xylem tissue. It is characterized by narrower vessels and tracheids.
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