1) One of the two sperm cells coming from the pollen of the inducer is defective, yet is able to fuse with the egg cell. During subsequent cell divisions, the chromosomes of this sperm cell degenerate and are eliminated stepwise from the primordial cells. The second sperm cell, which is functional, fuses with the central cells and leads to the development of a regular triploid endosperm.
2) One sperm cell is not able to fuse with the egg cell, but instead triggers haploid embryogenesis. The second sperm cell, which is functional, fuses with the central cells as under the first hypothesis. However, in the latter case, seed abortion is expected if the functional sperm cell fuses with the egg cell, but the defective one fuses with the central cells or if the central cells remain unfertilized for other reasons.