Which of the following is secondary meristem ?

Options

A. Procambium
B. Cork cambium
C. Protoderm
D. All of these

Explanation

To determine which of the following is a secondary meristem, we need to understand the definitions and functions of different types of meristems.

### Step-by-Step Solution:

1. **Understand Meristems**:
- Meristems are regions of undifferentiated cells in plants that are capable of cell division. They are classified into primary and secondary meristems based on their function and location.

2. **Identify Primary Meristems**:
- Primary meristems are responsible for the primary growth of the plant, which includes elongation of stems and roots. Examples include:
- **Apical meristem**: Found at the tips of roots and shoots.
- **Procambium**: Responsible for the formation of primary vascular tissues.

3. **Identify Secondary Meristems**:
- Secondary meristems contribute to the lateral growth of plants, which increases the thickness of stems and roots. They are involved in secondary growth. Examples include:
- **Vascular cambium**: Produces secondary xylem and phloem.
- **Cork cambium (Phellogen)**: Produces cork cells, which replace the epidermis in older stems and roots.

4. **Analyze the Options**:
- **Procambium**: This is a primary meristem, not a secondary meristem.
- **Cork cambium**: This is a secondary meristem and is responsible for secondary growth.
- **Protoderm**: This is also a primary meristem, forming the outer layer of the plant.
- **All of the above**: This option cannot be correct as only cork cambium is a secondary meristem.

5. **Conclusion**:
- The correct answer is **cork cambium**, as it is the only option listed that qualifies as a secondary meristem.

### Final Answer:
The secondary meristem is **cork cambium**.

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