Assertion: Secondary growth usually occurs in dicotyledonous stems.
Reason: The vascular cambium present between xylem and phloem possesses the ability to form secondary xylem and secondary phloem respectively.

Options

A. If both assertion and reason are true and reason is the correct explanantion of assertion
B. if both assertion and reason are true but reason is not the correct explanation of assertion.
C. if assertion is true but reason is false.
D. if both assertion and reason are false.

Explanation

### Step-by-Step Solution:

1. **Understanding the Assertion**: The assertion states that "Secondary growth usually occurs in dicotyledonous stems."
- **Explanation**: In dicotyledonous plants (dicots), secondary growth is common due to the presence of vascular cambium, which allows for the increase in girth of the stem.

2. **Understanding the Reason**: The reason provided is that "The vascular cambium present between xylem and phloem possesses the ability to form secondary xylem and secondary phloem respectively."
- **Explanation**: The vascular cambium is a layer of meristematic tissue that is responsible for the production of secondary xylem (wood) and secondary phloem (inner bark). This cambium is located between the xylem and phloem tissues.

3. **Analyzing the Relationship**: We need to determine if the reason correctly explains the assertion.
- **Explanation**: The presence of vascular cambium is indeed what allows for secondary growth in dicots. The cambium divides to produce new xylem and phloem, which contributes to the thickening of the stem.

4. **Conclusion**: Both the assertion and the reason are true, and the reason provides a correct explanation for the assertion.
- **Final Statement**: Therefore, both the assertion and the reason are correct, and the reason is the correct explanation for the assertion.