Unisexuality of flowers prevents

Options

A. Autogamy, but not geitonogamy
B. Both geitonogamy and xenogamy
C. Geitonogamy, but not xenogamy
D. Autogamy and geitonogamy

Explanation

**Step-by-Step Solution:**

1. **Understanding Unisexuality**:
- Unisexuality refers to flowers that contain only one type of reproductive organ, either male (staminate) or female (pistillate). This means that a unisexual flower cannot produce both pollen and ovules.

2. **Defining Autogamy**:
- Autogamy is the process of self-pollination, where pollen from the anther of a flower fertilizes the ovule of the same flower. Since unisexual flowers lack both male and female parts, they cannot undergo autogamy.

3. **Defining Gatenogamy**:
- Gatenogamy (or more commonly referred to as geitonogamy) is the transfer of pollen from the anther of one flower to the stigma of another flower on the same plant. Since unisexual flowers can still have multiple flowers on the same plant, this type of pollination can still occur.

4. **Defining Xenogamy**:
- Xenogamy is cross-pollination, where pollen is transferred from the anther of a flower to the stigma of a flower on a different plant of the same species. Unisexuality does not prevent xenogamy either, as it involves different plants.

5. **Conclusion**:
- Since unisexual flowers prevent autogamy (self-pollination) but do not prevent gatenogamy (pollination between different flowers on the same plant) or xenogamy (cross-pollination), the correct answer is that unisexuality of flowers prevents autogamy but not gatenogamy.

**Final Answer**: Unisexuality of flowers prevents autogamy but not gatenogamy.

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