Which one of the following statements is correct?

Options

A. Cleistogamous flowers are always autogamous
B. Xenogamy occurs only by wind pollination
C. Chasmogamous flowers do not open at all
D. Geitonogamy involves the pollen and stigma of flowers of different plants

Answer

To determine which statement is correct among the options provided, we can analyze each statement one by one based on the definitions and characteristics of the types of pollination and flowers mentioned.

### Step-by-Step Solution:

1. **Understanding Clistogamous Flowers**:
- Clistogamous flowers are those that do not open and are capable of self-pollination. This means that the anthers and stigmas are not exposed, and pollination occurs within the same flower.
- **Conclusion**: Clistogamous flowers are always autogamous (self-pollinating). This statement is correct.

2. **Understanding Xenogamy**:
- Xenogamy refers to the fertilization of a flower by pollen from a genetically different plant. This process can occur through various means, including wind, insects, or water.
- **Conclusion**: The statement claiming that xenogamy occurs only by wind pollination is incorrect.

3. **Understanding Chasmogamous Flowers**:
- Chasmogamous flowers are those that open up, allowing for the exposure of anthers and stigmas. This facilitates cross-pollination.
- **Conclusion**: The statement that chasmogamous flowers do not open at all is incorrect.

4. **Understanding Gytonogamy**:
- Gytonogamy is a form of self-pollination where pollen from the same flower fertilizes its stigma. It does not involve different plants.
- **Conclusion**: The statement claiming that gytonogamy involves pollen and stigma of flowers from different plants is incorrect.

### Final Answer:
The correct statement is: **Clistogamous flowers are always autogamous.**