Presence of mechanical barrier between stamen and carpel which prevents self pollination , is known as :

Options

A. Protandry
B. Protogyny
C. Homogamy
D. Herkogamy

Answer

To solve the question regarding the presence of a mechanical barrier between stamen and carpel that prevents self-pollination, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Terms**:
- The question asks for a specific term that describes a mechanical barrier between the stamen (male reproductive part) and carpel (female reproductive part) of a flower.

2. **Identifying the Mechanism**:
- The mechanism that prevents self-pollination is crucial for promoting genetic diversity through cross-pollination.

3. **Recognizing the Correct Term**:
- The term that describes this mechanical barrier is **hercogamy**. Hercogamy is a type of outbreeding device that ensures that the pollen from the stamen does not easily reach the stigma of the same flower, thus preventing self-pollination.

4. **Examples of Hercogamy**:
- In flowers like **pansy**, the stigma is enclosed in a flap, preventing self-pollination.
- In **calamia**, the anthers are hidden inside a corolla pocket.
- In **cypripedium**, the stigma is positioned to allow insect entry while the anthers are near the exit, further promoting cross-pollination.

5. **Differentiating from Other Terms**:
- **Homogamy**: This refers to the maturation of anthers and stigma at the same time, promoting self-pollination.
- **Protandry**: This is when anthers mature before the stigma.
- **Protogyny**: This is when the stigma matures before the anthers.

6. **Conclusion**:
- Based on the definitions and examples, the correct answer to the question is **hercogamy**.

### Final Answer:
The presence of a mechanical barrier between stamen and carpel which prevents self-pollination is known as **hercogamy**.

---