(a) The strategies adopted by flowering plants to prevent self-pollination are : -
(i) In some plants, pollen release and stigma receptivity are not synchronised. Either the pollen is released much before the stigma is receptive or vice-versa.
(ii) In some plants the anther and stigma are placed at different positions so that the pollen cannot come in contact with the stigma of the same flower.
(iii) The natural pollens fall on the receptive stigva of the same flower are not able to germinate or by retarding the growth of pollen tube.
(iv) Production of unisexual flowers : This pevents autogamy but not geitonogamy Eg. maize.
(b) Geitonogamy : Transfer of pollen grains from the anther to the stigma of another flower of the same plant. Although geitonogamy is functionally cross-pollination involving a pollinating agent, genetically it is similar to autogamy, since the pollen grains come from the same plant.
