Extra stelar secondary growth occurs due to the activity of

Options

A. intrafascicular cambium
B. interfascicular cambium
C. vascular cambium
D. Cork cambium

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks about the activity responsible for extra-stelar secondary growth in plants. Extra-stelar growth refers to growth that occurs outside the vascular bundles.

2. **Identifying the Cambium Types**: There are two types of cambium involved in secondary growth: intrafascicular cambium and interfascicular cambium. The intrafascicular cambium is located between the xylem and phloem within the vascular bundles, while the interfascicular cambium is found between the vascular bundles.

3. **Role of Vascular Cambium**: The vascular cambium, which is formed by the combination of intrafascicular and interfascicular cambium, is responsible for secondary growth. It has two types of divisions: multiplicative and additive.

4. **Understanding Growth Patterns**: The vascular cambium contributes to secondary growth through two growth patterns:
- Centripetal growth (towards the center) produces secondary xylem.
- Centrifugal growth (away from the center) produces secondary phloem.

5. **Extra-stelar Growth**: The question specifically refers to extra-stelar secondary growth, which occurs outside the vascular bundles. This growth is primarily due to the activity of the cork cambium.

6. **Conclusion**: Therefore, the activity responsible for extra-stelar secondary growth is the cork cambium.

**Final Answer**: The activity responsible for extra-stelar secondary growth occurs due to the activity of cork cambium.

---