The major role in the dehiscence of a fern sporangium is played by its

Options

A. Annulus
B. Indusium
C. Tapetum
D. Sorus

Explanation

To answer the question "The major role in the dehiscence of a fern sporangium is played by its," we need to identify the correct structure involved in this process. Here’s a step-by-step breakdown of the solution:

### Step-by-Step Solution:

1. **Understanding Dehiscence**:
- Dehiscence refers to the process by which a sporangium (a structure that produces spores) opens up to release spores.

2. **Identifying the Structures**:
- The options given are annulus, indusium, tepidum, and sorus. We need to understand the role of each structure in the context of a fern sporangium.

3. **Role of Annulus**:
- The annulus is a specialized structure that is located on the outer rim of the sporangium. It consists of a single row of specialized cells that play a crucial role in the opening of the sporangium.

4. **Function of Annulus in Dehiscence**:
- When the spores mature, the cells in the annulus dry out and contract, causing the sporangium to split open along a predetermined line. This mechanism is essential for the effective release of spores into the environment.

5. **Other Structures**:
- **Indusium**: A membranous outgrowth that covers the sporangium but does not play a direct role in dehiscence.
- **Tepidum**: Provides nutrition to developing spores but is not involved in the opening of the sporangium.
- **Sorus**: A cluster of sporangia but does not directly facilitate dehiscence.

6. **Conclusion**:
- Based on the above information, the major role in the dehiscence of a fern sporangium is played by the **annulus**.

### Final Answer:
The major role in the dehiscence of a fern sporangium is played by its **annulus**.

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