Meiosis occurs in the megaspore mother cell and microspore mother cell to generate megaspores and microspores respectively. The microspores then undergo mitosis and develop protective outer layers, forming pollen grains. These grains contain sperm cells that can fertilize the female gametophyte within the pistil. The pollen tube grows through the pistil tissues guided by chemicals from the synergid cells within the embryo sac, and releases its contents including sperm for double fertilization of the egg and central cells.