When the pollen grains are not transferred from anthers to the stigma in a flower due to the barrier or fence it is referred as (or when some natural barrier exists between androecium and gynoecium to check self-pollination, it is known as)

Options

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

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks about a situation where pollen grains are not transferred from the anthers to the stigma due to a barrier, preventing self-pollination.

2. **Identifying Key Terms**: The terms involved are:
- Anther: The part of the stamen that produces pollen.
- Stigma: The part of the pistil where pollen germinates.
- Self-pollination: The transfer of pollen from the anther to the stigma of the same flower.

3. **Exploring Options**: The options given are:
- **Dicogamy**: This refers to the maturation of male and female reproductive organs at different times, preventing self-pollination.
- **Kleistogamy**: This involves self-fertilization occurring within a permanently closed flower.
- **Heterostyly**: This refers to the presence of styles of different lengths, which can help reduce self-pollination.
- **Hercogamy**: This is when there is a physical barrier preventing pollen transfer between the male and female parts of the flower.

4. **Analyzing Each Option**:
- **Dicogamy** does not fit as it refers to timing rather than a physical barrier.
- **Kleistogamy** is incorrect as it involves self-fertilization within a closed flower.
- **Heterostyly** relates to different lengths of styles but does not directly imply a barrier.
- **Hercogamy** is the correct term as it specifically refers to a natural barrier that prevents the transfer of pollen from anther to stigma.

5. **Conclusion**: The correct answer to the question is **Hercogamy**, which describes the situation where a natural barrier exists between the androecium (male part) and gynoecium (female part) of a flower, preventing self-pollination.