The presence of a special organ called obturator stimulates the growth of pollen tube.
In the porogamy the pollen tube enters the ovule through the micropyle. The movement of pollen tube towards the embryo sac is by the chemotactic movement. The growth of the pollen tube aided by the special organ called obturator. It forms as a swelling from the placenta and it functions as a bridge for the pollen tube. In some species the distal cells of the integument dissolved and produce a mucilaginous secretion and it will facilitate the movement of pollen tube.