Growth rings are formed by the activity of
(a) Extrasteral cambium
(b) Intrasteler cambium
(c) Interstelar cambium
(d) Both b and c

Options

A. Extrasteral cambium
B. Intrasteler cambium
C. Interstelar cambium
D. Both 2 and 3

Answer

To solve the question regarding the formation of growth rings, we need to analyze the options provided and understand the role of different types of cambium in the growth of plants.

### Step-by-Step Solution:

1. **Understanding Cambium**: Cambium is a type of meristematic tissue in plants that is responsible for secondary growth. It produces new cells that contribute to the thickness of the plant.

2. **Types of Cambium**:
- **Extrastelar Cambium**: This term is not commonly used in the context of growth rings.
- **Intrastelar Cambium**: This is also known as **Intrafascicular Cambium**. It is located between the xylem and phloem in vascular bundles and is responsible for the formation of secondary xylem (wood) and phloem.
- **Interstelar Cambium**: This term is not standard in plant anatomy and does not refer to a recognized type of cambium.

3. **Formation of Growth Rings**: Growth rings are formed due to the activity of the cambium during different seasons. The cambium produces more xylem in the spring (spring wood) and less in the autumn (autumn wood), leading to the formation of distinct rings.

4. **Identifying the Correct Option**: Since the intrastelar cambium (or intrafascicular cambium) is responsible for the formation of growth rings, we can conclude that:
- Option (a) is incorrect.
- Option (b) is correct as it refers to intrastelar (or intrafascicular) cambium.
- Option (c) is not a recognized term in this context.
- Option (d) is incorrect since only option (b) is valid.

5. **Final Answer**: The correct answer is **(b) Intrastelar cambium**.