Pollination is the process by which pollen grains are transferred from the top of the stamen called the anther(male sex organ) to the top of the pistil called the stigma(female sex organ). This process helps transfer the pollen which contains sperm cells to the stigma. Insects, wind, water, and birds aid in pollination. Once the pollen grains stick to the stigma, they begin to germinate down through the pistil and form a pollen tube. Inside, the sperm cells will eventually travel down to the female ovary, where ovules containing egg cells are located. When a sperm and egg nucleus join, this forms an embryo plant. The other sperm joins to two polar nuclei to form endosperm--the food that nourishes the embryo inside the seed. Therefore, pollination is an important step leading to fertilization.