Question

How is pollen from other flowers prevented from reaching the stigma of a self pollination flower

Answer 1

by petals or usually it is not prevented it is natural

Answer 2

The way pollen from other flowers is prevented from reaching the stigma of a self pollination flower  is as follows:

• Before or after the period when the stigmas on the same plant are receptive, having the pollen shed is a very way of preventing fertilization.

• There is existence of a mechanical barrier between the compatible stigma and pollen in some flowers. This resists the self pollination.
• In some flowers, the stigma is covered by a hood.
• This is thy way how floral barriers prevents self pollination in herkogamy.