How is it that the embryo …

Replacement of the normal sexual reproduction 'by asexual reproduction without fertilization is called apomixis. e.g., replacement of the flower by bulbils and replacement of the seed by a plant. Apomitically produced offsprings are genetically identical to the parent plant. In flowering plants, apomixis is used in a restricted sense to mean angiosperm, i.e., asexual reproduction through seeds. In some plant species, it is common, e.g., Asteraceae, Poaceae. In some species, the diploid egg cell is formed without reduction division and develops into an embryo without fertilization. It is asexual reproduction in the absence of pollinators such as in extreme environments. In some species like citrus, some of the nucellar cells surrounding the embryo sac start dividing and develop into embryo. It occurs in the megaspore mother cell does not undergo meiosis, thus produces diploid embryo sac through mitotic divisions. Thus, it explains that, embryo sacs of some apomictic species appear normal, but producediploid cells.