Question

Give the origin, structure, function and fate of the pollen tube and PEN

Answer 1

Primary Endosperm Nucleus.Primary endosperm nucleus is formed as a result of triple fusion in the embryo sac.Two polar nuclei and one male gamete fuse to form triploid primary endosperm nucleus.It divides by mitosis to give rise a large number of nuclei in the central cell which ultimately transformed into endosperm.
Pollen Tube.Following the phase of mutual recognition, the pollen grain germinates on the stigma giving rise one or several germ tubes or pollen tubes. The tube nucleus migrates into the pollen tube and reaches the extreme end.The pollen tube grows between the cells of stigma and transmitting tissue of the style.The wall of pollen tube grows between the cells of stigma and transmitting tissue of the style.The wall of pollen tube is the extension on intine. The pollen tube grows towards embryosac chemotropically due to the concentration gradient of calcium-born-inositol sugar complex.Pollen tube acts as a carrier of male gametes up to the embryo sac and enters into the ovule either through the micropylar end, chalazal end or laterally.
Rest is out of my bio knowledge.

Answer 2

PEN
The triploid nucleus which results from the fusion of the two polar nuclei of the embryo sac with a sperm nucleus, and which (usually) divides to form the endosperm tissue.
POLLEN TUBE
A hollow tube which develops from a pollen grain when deposited on the stigma of a flower. It penetrates the style and conveys the male gametes to the ovule.