Barrier to avoid self pollination between stamens and pistils is

Options

A. Heterostyly
B. Herkogamy
C. Dichogamy
D. Dicliny.

Explanation

To solve the question regarding the barrier to avoid self-pollination between stamens and pistils, we will analyze the provided options step by step.

### Step-by-Step Solution:

1. **Understanding Self-Pollination**: Self-pollination occurs when pollen from the stamens of a flower fertilizes the ovules of the same flower or another flower on the same plant. To prevent this, plants have developed various mechanisms.

2. **Analyzing the Options**:
- **Option 1: Heterostyling**: This refers to the presence of different types of flowers within the same plant, which have varying lengths of styles and stamens. While this can promote cross-pollination, it does not directly create a barrier to self-pollination.
- **Option 2: Hercogamy**: This is a condition where the flower structure prevents pollen from reaching the stigma, even though the flower is bisexual. This can involve mechanical barriers, such as a covering over the stigma, which effectively prevents self-pollination.
- **Option 3: Dichogamy**: This refers to the maturation of anthers and stigmas at different times. While this can reduce the chances of self-pollination, it does not create a physical barrier.
- **Option 4: Diclinae**: This term describes flowers that have only one type of reproductive organ (either male or female). This does not create a barrier to self-pollination since it leads to unisexuality.

3. **Identifying the Correct Answer**: Based on the analysis, the option that describes a barrier to avoid self-pollination is **Option 2: Hercogamy**. This option highlights the mechanical barriers that prevent pollen from reaching the stigma, thus avoiding self-pollination.

### Final Answer:
The barrier to avoid self-pollination between stamens and pistils is **Hercogamy**.