In roots, the primary xylem is called exarch. because -

Options

A. The protoxylem lies towards the centre and the metaxylem lies towards the periphery
B. The protoxylem lies towards the periphery and the metaxylem lies towards the centre
C. Both the protoxylem and the metaxylem lies towards the centre
D. The protoxylem is surrounded by the metaxylem.

Answer

### Step-by-Step Solution

1. **Understanding Primary Xylem**: The primary xylem is a type of vascular tissue responsible for the transport of water and minerals in plants. It is formed during the primary growth of the plant.

2. **Definition of Exarch Condition**: The term "exarch" refers to the arrangement of xylem in which the protoxylem (the first-formed xylem) is located towards the periphery (outer part) of the root, while the metaxylem (the later-formed xylem) is situated towards the center.

3. **Arrangement of Xylem in Roots**: In roots, the primary xylem exhibits an exarch condition. This means that:
- The protoxylem is positioned closer to the outer edge of the root.
- The metaxylem is positioned closer to the center of the root.

4. **Significance of Exarch Arrangement**: This arrangement is significant for the plant's growth and development. It allows the plant to efficiently transport water and nutrients from the soil while providing structural support.

5. **Contrast with Endarch Condition**: In contrast, an "endarch" condition would have the protoxylem located towards the center and the metaxylem towards the periphery. This is not the case in roots, hence the term exarch is used.

6. **Conclusion**: Therefore, the primary xylem in roots is called exarch because the protoxylem is located towards the periphery and the metaxylem is located towards the center.