Sexual Reproduction In Flowering Plants

The primary endosperm nucleus formation involves a process specific to flowering plants known as double fertilization. During this event, one sperm cell fertilizes the egg forming a diploid zygote, while another sperm cell fuses with two polar nuclei in the central cell of the ovule forming a triploid cell, known as the primary endosperm nucleus. This process is called triple fusion.

In conclusion, the primary endosperm nucleus is the result of triple fusion, which is part of the double fertilization process in angiosperms.