Question

Pistil of a flower does not accept pollen from any plant other than from its own kind. how does it happen? explain

Answer 1

in these the stigma is quite more down the the anther so the pollen grains can go easily

Answer 2

This process is called Self pollination.

In self pollination, flowers exchange pollen with same flower or another flower on the same plant. Any foreign pollen that lands on a flower from a different flower is rejected.

Self pollination does not always ensure genetic variation since genetic material between same plants  is exchanged.