Describe the common mode of reproduction in Angiosperms.
Stamens and pistils are the two reproductive parts of a flower. The stamen consists of a slender filament with anthers at the tip. Each pistil is made of three parts- ovary, style and stigma. The ovary contains one to many ovules. Each ovule contains a megaspore mother cell it produces four haploid megaspores after meiosis of them three degenerate and the remaining one is a functional megaspore. It divides by meiosis forming a megagametophyte. It consists of 8 haploid nuclei embedded in the cytoplasm of which 3 cells lie at the micropylar end and 3 antipodal lies at the chalazal end. The two remaining nuclei move to the centre to make a diploid nucleus. The anthers have a pollen sac and contain many microspore mother cells. Each of them produces four haploid microspores after meiosis and each becomes a microgametophyte. It contains two nuclei generative nucleus and the tube nucleus. The pollen is carried away by air and other agencies and reaches the stigma of the pistil of the same or different plants. This process is called pollination. Pollen grains germinate and produce a pollen tube it grows within the style and reaches the ovule of the ovary. The generative nucleus divides pollen tubes producing two male gametes.On reaching the ovule, the pollen tube burst to release male gametes. One of the two gametes fertilise the egg and forms a diploid zygote. The other male gamete fertilizes with polar nuclei to form triploid endosperm. This is known as double fertilization.
