In which of the following the vasuclar cambium is completely secondary meristem?

Options

A. Dicot stem
B. Dicot root
C. Monocot stem
D. Monocot root

Answer

To determine in which of the following options the vascular cambium is completely a secondary meristem, we need to analyze each option provided: dicot stem, dicot root, monocot stem, and monocot root.

### Step-by-Step Solution:

1. **Understanding Vascular Cambium**:
- Vascular cambium is a type of meristematic tissue that is responsible for the secondary growth in plants. It forms between the xylem and phloem and contributes to the formation of secondary xylem (wood) and secondary phloem.

2. **Types of Meristem**:
- **Primary Meristem**: This is the initial meristematic tissue that gives rise to primary growth (lengthening of the plant).
- **Secondary Meristem**: This arises from the differentiation of permanent tissues and is responsible for secondary growth (thickening of the plant).

3. **Analyzing the Options**:
- **Dicot Stem**: In dicot stems, the vascular cambium is partially secondary as it develops from both primary and secondary meristematic tissues.
- **Dicot Root**: In dicot roots, the vascular cambium is completely secondary. It arises from the dedifferentiation of permanent tissues, making it entirely a secondary meristem.
- **Monocot Stem**: Monocots generally do not have a vascular cambium. They exhibit primary growth only, with no secondary growth.
- **Monocot Root**: Similar to monocot stems, monocot roots also lack a vascular cambium.

4. **Conclusion**:
- The only option where the vascular cambium is completely a secondary meristem is the **dicot root**.

### Final Answer:
The correct answer is **B. Dicot Root**.