How many of the following meristems are completely secondary in origin ?
A. Cork cambium of a dicot stem
B. Vascular cambium of a dicot stem
C. Cork cambium of a dicot root
D. Vascular cambium of a dicot root

Options

A. `4`
B. `3`
C. `2`
D. `1`

Answer

To determine how many of the listed meristems are completely secondary in origin, we need to analyze each option provided in the question.

### Step-by-Step Solution:

1. **Understanding Meristems**:
- Meristems are regions of undifferentiated cells in plants that can divide and differentiate into various types of tissues. They can be classified into primary and secondary meristems.
- Primary meristems are responsible for the primary growth (lengthening) of the plant, while secondary meristems are involved in secondary growth (thickening).

2. **Analyzing Each Option**:
- **A. Cork cambium of a dicot stem**:
- The cork cambium is a secondary meristem that forms during secondary growth. It produces cork cells that replace the epidermis in stems and roots.
- **Conclusion**: This is secondary in origin.

- **B. Vascular cambium of a dicot stem**:
- The vascular cambium is also a secondary meristem responsible for producing secondary xylem (wood) and secondary phloem.
- **Conclusion**: This is secondary in origin.

- **C. Cork cambium of a dicot root**:
- Similar to the cork cambium in stems, the cork cambium in roots is formed during secondary growth and contributes to the protective outer layer.
- **Conclusion**: This is secondary in origin.

- **D. Vascular cambium of a dicot root**:
- The vascular cambium in roots functions similarly to that in stems, facilitating secondary growth by producing additional vascular tissues.
- **Conclusion**: This is secondary in origin.

3. **Final Count**:
- All four options (A, B, C, D) are completely secondary in origin. Therefore, the answer is 4.

### Final Answer:
**4** meristems are completely secondary in origin.