Why should a bisexual flower be emasculated and then bagged prior to artificial pollination in hybridisation programmes?

Emasculation of the flower is the removal of anthers from the plant. It is done by the use of a sterilized pair of forceps and then it is covered by polythene or any kind of bag which is known as bagging. This process is very necessary for the hybridisation as it stops the fall or different pollen of species..