'Incompatibility is as natural barrier in the fusion of gametes' justify the statement.

Incompatibility many occur due to many reason. sometime the microgamate and sometime the microgamate may be incompatible to each other or one or may be sterile. some time to prevent self pollination flowers adopt some contrivances so that only cross pollination takes place. This contrivances are actually natural barrier which prevents self pollination. Thus the plant create self incompatibility. The natural berries one of various types such as  unisexualities self stability Dichogany,hetecosty,ferkogany etc. Of these  unisexuality is the best adaptation of incompatibility. Because of incompatibility, cross pollination occurs in most bisexual flowers. This leads to exchange of genetic quality. Which causes improvement in the genetic quality of plants and leads to father evolution.