when pollen grains are not transferred from anthers to stigma in a flower due to the barrier it is called

1. cleistogamy
2. herkogamy
3. dichogamy
4. heterogamy

Herkogamyis a common strategy employed by hermaphroditicangiospermsto reduce sexual interference between male (anthers) and female (stigma) function. Herkogamy differs from other such strategies (e.g.dichogamy) by supplying a spatial separation of the anthers and stigma.
Two forms of herkogamy are most common:
1.Approach Herkogamy- (pin) is the presentation of the stigma above the level of the anthers. This arrangement of sex organs causes floral visitors to first contact the stigma, before removing pollen from the anthers. This form of herkogamy is considered to be common, and is associated with a large, diverse fauna of floral visitors/pollinators.
2.Reverse Herkogamy- (thrum) is displayed when the stigma is recessed below the level of the anthers. This arrangement causes floral visitors to first contact the anthers before the stigma. For this reason, reverse herkogamy is believed to facilitate greater pollen export than approach herkogamy. This type of sex-organ arrangement is typically associated with Lepidopteran (moth or butterfly) pollination.