Annual growth rings are formed due to activity

Options

A. extrastelar cambium
B. intrastelar cambium
C. interstelar cambium
D. both B and C

Answer

### Step-by-Step Solution:

1. **Understanding Cambium**:
- Cambium is a layer of tissue in plants that is responsible for secondary growth. It is a type of meristematic tissue that produces new cells.

2. **Types of Cambium**:
- There are different types of cambium, including intrafascicular cambium (also known as intrastellar cambium) and extrafascicular cambium. The intrafascicular cambium is located between the xylem and phloem within the vascular bundles.

3. **Formation of Annual Growth Rings**:
- Annual growth rings are formed due to the activity of the vascular cambium. This cambium produces secondary xylem (wood) on the inner side and secondary phloem on the outer side.

4. **Differential Cambial Activity**:
- The formation of growth rings is influenced by seasonal changes. In spring, the cambium is more active, leading to the production of wider secondary xylem rings. In autumn, the activity decreases, resulting in narrower secondary xylem rings.

5. **Resulting Structure**:
- The alternating patterns of wide and narrow rings due to the cambial activity in different seasons create the visible annual growth rings in trees.

6. **Conclusion**:
- Therefore, the correct answer to the question is that annual growth rings are formed due to the activity of the intrastellar cambium (or intrafascicular cambium).

### Final Answer:
Annual growth rings are formed due to the activity of **Intrastellar Cambium**.

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