Inbreeding depression occurs due to self-pollination. Chasmogamous flowers are open and can be pollinated through autogamy, geitonogamy, and xenogamy. Maize is monoecious and papaya is dioecious; therefore, self-pollination does not occur in these conditions. Cleistogamous flowers, as seen in plants like Commelina, Viola, and Oxalis, are flowers that never open. In these flowers, the anthers and stigma lie in close proximity to each other. When the anthers dehisce within the closed flower, the pollen grains fall directly on the stigma, ensuring self-pollination.