Adaptations for cross-pollination

chemical self-incompatability

pollen won’t germinate stigma of flower from the same plant in many plants

chemical signals produced by stigma do not stimulate pollen from the same flower

ensures that the pollen must come from a different individual and this increases genetic variation

flower structure

arrangement of anthers and stigmas can force cross or self pollination in many flowers

flowers with irregular structures force insects to enter and leave the flower in a certain way - reducing likelihood that pollen from a flower is transferred to its own stigma

Development of anthers and stigmas

anthers mature before stigmas in many plants or vice versa

meaning that pollen and stigmas in the same flower can’t be present at the same time

separate male and female flowers

where male and female flowers are produced on different plants, self-pollination is impossible