Herkogamy is a contrivance for cross pollination. In a bisexual flower, self-pollination can be prevented by presence of a physical barrier between style and stigma. This is herkogamy. It is seen in pansy where there is hood covering the stigma. Heterostyly is the presence of different lengths of styles in different flowers of the same species. This adaptation also helps in cross pollination. Dichogamy is the phenomenon where male and female parts of the flowers mature at different times thus causing cross pollination. Cleistogamy is the phenomenon in which the flowers always stay in bud condition and never bloom. This ensures self pollination