This is a diagram of the journey a pollen tube must make in order to deliver sperm to the egg cell that lies inside the ovule inside the ovary. For each egg cell, a separate pollen grain must produce a pollen tube that travels this same route to the ovary. Pollination happened when the pollen grains landed on the stigma. Fertilization takes place later in the ovary. The growth of the single cell of a pollen tube, sometimes over six inches in large flowers like, say is the most remarkable example of directional single cell growth that I know of.