Both autogamy and geitonogamy are prevented in:

1. Autogamy is self-pollination within the same flower.2. Geitonogamy is pollination between different flowers on the same plant.In dioecious plants like Papaya, male and female flowers are present on different plants. This condition prevents both autogamy and geitonogamy, ensuring xenogamy (cross-pollination). In Maize and Castor (monoecious), autogamy is prevented but geitonogamy can occur.