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Biology
Megasporogenesis Near the micropyle being nourished in the nucellus of an ovule, a cell starts to become larger. Its protoplasm is dense and the nucleus is comparatively larger. The cell divides into four haploid cells through meiotic division. Every cell except the smallest one, gets disintegrated. Growing gradually the larger cell matures into an embryo sac. The nucleus of the cell is haploid. The nuclei are evolved as the nucleus divides. These two nuclei take position in two opposing poles. Next, these two nuclei consecutively divide twice and result in four nuclei. In the next stage, two nuclei form the two poles coming at the middle of the cell get fused and cause the emergence of two haploid secondary nuclei. The nuclei in the two poles turn into cells with some amount of cytoplasm. Collectively, the combined structure of the three cells near the micropyle is called egg apparatus. In between the cells, the one occupying the middle place is the ovum, which is little larger. This is called an egg cell and the other two are called synargid cells. The cells in the opposite pole to the egg apparatus are called antipodal cells. This way the process of developing embryo sac is ultimately done. Fertilization: Trough pollination, mature pollen lands on the stigma of a carpel. Then pollen tube grows penetrating the style and becomes little flatulent absorbing some liquid. Once the tips of the extended pollen tube entering into the embryo ejects two male gametes in the embryo sac. One of them meeting with the egg causes the emergence of a zygote. Another male gamete mixing with the secondary nuclei develop triploid endosperm cells. The two fusions, mixing of a male gamete with an egg and mixing of another male gamete with secondary nuclei, take place at about the same time. This phenomenon is called double fertilization.