Which of the following is an example of dedifferentiation in plants?

Options

A. Formation of interfascicular cambium in dicotyledonous stem from parenchymatous medullary rays
B. Formation of cork cambium from fully differentiated parenchymatous cells
C. Formation of cells by culturing the cells of pith during plant tissue culture
D. All of these

Answer

To determine which of the provided options is an example of dedifferentiation in plants, we need to understand the concept of dedifferentiation and analyze each option accordingly.

### Step-by-Step Solution:

1. **Understanding Dedifferentiation**:
- Dedifferentiation is a process where specialized, differentiated cells lose their specific characteristics and revert to a more primitive, meristematic state. This allows them to regain the ability to divide and form new tissues.

2. **Analyzing the First Option**:
- **Formation of interfascicular cambium and dicot stem from parenchymatous medullary rays**:
- In this process, parenchyma cells from the medullary rays can dedifferentiate to form interfascicular cambium, which is capable of cell division. This is indeed an example of dedifferentiation.

3. **Analyzing the Second Option**:
- **Formation of cork cambium from fully differentiated parenchymatous cells**:
- Cork cambium arises from the dedifferentiation of parenchyma cells. These cells lose their specific functions and regain the ability to divide, which is characteristic of dedifferentiation.

4. **Analyzing the Third Option**:
- **Formation of cells by culturing of cells of pith during plant tissue culture**:
- In tissue culture, differentiated cells can revert to a more meristematic state and proliferate. This process also exemplifies dedifferentiation as the cells regain the ability to divide.

5. **Conclusion**:
- Since all three options describe processes that involve dedifferentiation, the correct answer is that all of these are examples of dedifferentiation in plants.

### Final Answer:
- The answer is **4. All of these**.