Growth rings are formed due to activity of

Options

A. extrastellar cambium
B. intrastellar cambium
C. interstellar cambium
D. both (ii) and (i)

Answer

To answer the question "Growth rings are formed due to activity of:", we need to analyze the types of cambium involved in the formation of growth rings in plants.

### Step-by-Step Solution:

1. **Understanding Cambium**: Cambium is a type of meristematic tissue responsible for the secondary growth in plants. It is crucial for the formation of new xylem and phloem.

2. **Types of Cambium**:
- **Intrastellar Cambium**: Also known as intrafascicular cambium, it is located between the xylem and phloem within the vascular bundles.
- **Interstellar Cambium**: This is found between the vascular bundles and is also referred to as interfascicular cambium.

3. **Formation of Vascular Cambium**: The intrastellar (intrafascicular) cambium and interstellar (interfascicular) cambium together form a complete cambium ring known as the vascular cambium. This is essential for secondary growth.

4. **Growth Ring Formation**: The vascular cambium is responsible for producing secondary xylem (wood) on the inner side and secondary phloem (bark) on the outer side. The activity of the cambium varies with seasons, leading to the formation of growth rings. During spring, the cambium is more active, producing wider xylem cells, while in autumn, it produces narrower cells. This seasonal variation results in the visible growth rings.

5. **Conclusion**: Based on the explanation, the correct answer to the question is that growth rings are formed due to the activity of the **intrastellar cambium**.

### Final Answer:
Growth rings are formed due to the activity of **intrastellar cambium**.

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