Allogamy is also known as cross-pollination. In this type of pollination, pollen is transferred from the anther to the stigma of another plant of the same or different species.
There are various mechanisms that facilitate cross-pollination and resist self-pollination.
These are dicliny (unisexuality), dichogamy, herkogamy, heterostyly, etc. Dicliny is the condition where the flowers are either male (staminate) or female (pistillate).
The dicliny may be monoecy or dioecy. In monoecy, males and females occur on the same plant. For example, strawberries, grapes, etc. In dioecy, male and female flowers are present on different plants i.e. plants in such species are either male or female. For example, papaya, date, etc.