ICSE Class 9 Answered

In self-pollination, the flowers never open to ensure that pollen grains pollinate the stigma of the same flower. This mechanism is called cleistogamy. In cleistogamous flowers, the pollens are shed within the closed flowers so that self-pollination is obligatory.

In self-pollination, the stamens and carpels of a flower mature at the same time. So, there is a greater chance of self- pollination although that is not obligatory. This mechanism is called homogamy.