the production of unisexual flowers is an outbreeding device used to prevent self-pollination. In monoecious plants (where male and female flowers are separate but located on the same plant, such as castor and maize), unisexuality prevents autogamy—the transfer of pollen within the same flower. However, it does not prevent geitonogamy, which is the transfer of pollen between different flowers on the same plant . Prevention of both autogamy and geitonogamy only occurs in dioecious plants like papaya, where male and female flowers are on entirely separate plants .