In which of the following order, an exarch xylem develops

Options

A. (a) Centripetal
B. (b) Centrifugal
C. (c) Both centripetal and centrifugal
D. (d) Irregular

Answer

To determine the order in which exarch xylem develops, we need to understand the characteristics of exarch and endarch xylem.

### Step-by-Step Solution:

1. **Definition of Exarch Xylem**: Exarch xylem is characterized by the arrangement where the protoxylem (the first formed xylem) is located towards the periphery, and the metaxylem (the later formed xylem) is situated towards the center. This indicates that the development of xylem is directed towards the inner side.

2. **Understanding Protoxylem and Metaxylem**:
- **Protoxylem**: This is the first xylem to develop and is typically formed in a way that allows for growth and elongation of the plant.
- **Metaxylem**: This is formed after protoxylem and is responsible for the bulk of water transport in mature plants.

3. **Centripetal Development**: In exarch xylem, the development is centripetal, meaning that as the plant grows, the protoxylem is formed on the outer side, and the metaxylem is formed inwardly. This is opposite to endarch xylem, where the protoxylem is located centrally and metaxylem is towards the periphery, indicating centrifugal development.

4. **Conclusion**: Based on the characteristics of exarch xylem, we can conclude that the correct order of development is centripetal. Therefore, the answer to the question is that exarch xylem develops in a centripetal manner.

### Final Answer:
The exarch xylem develops in a **centripetal** order.