An annual ring is formed by

Options

A. Two consecutive rings of spring wood
B. Two alternate rings of spring wood and autumn wood.
C. Two consecutive rings of autumn wood
D. Two alternate rings of sapwood and heartwood

Answer

**Step-by-Step Solution:**

1. **Understanding Annual Rings**: Annual rings are growth rings found in the cross-section of a tree trunk. They represent one year of growth.

2. **Formation of Annual Rings**: Annual rings are formed by the activity of the cambium layer in the tree, which is responsible for secondary growth.

3. **Seasons of Growth**: The cambium layer is more active during certain seasons:
- **Spring Season**: During spring, the cambium is highly active, leading to the formation of larger xylem vessels. This wood is referred to as **spring wood** or **early wood**.
- **Autumn Season**: In contrast, during the autumn (or winter) season, the cambium activity decreases, resulting in the formation of smaller, narrower xylem vessels. This wood is known as **autumn wood** or **late wood**.

4. **Composition of Annual Rings**: Each annual ring is composed of one layer of spring wood and one layer of autumn wood. Therefore, an annual ring consists of two alternating types of wood.

5. **Conclusion**: The correct answer to the question "An annual ring is formed by" is "two alternate rings of spring wood and autumn wood."

---