In angiosperms the functional megaspore undergoes mitotic division and forms 8 haploid nuclei. Out of which 3 micropyler cell (nuclei with cell wall) form egg apparatus, 3 chalazal cells form antipodal cells and the two central nuclei (polar nuclei) form central cell. These two polar nuclei fused just before their fertilization by second male gamete to form primary endosperm nucleus which is triploid.