Why is bagging of the emasculated flowers essential during hybridisation experiments?

Removal of anthers from the bisexual flowers of female parent during hybridization is called Emasculation. it is meant for to prevent unknown cross pollination. These emasculated flowers are covered by porous polythene bags or paper bags.

Bagging of the emasculated flowers during hybridisation experiments is essential to prevent contamination of its stigma by undesired pollen grains.