What is the process called when pollen unites with the stigma?

The correct process when pollen unites with the stigma is referred to as pollination. In this context, pollination is the transfer of pollen grains from the male anther of a flower to the female stigma. This is a critical step in the plant reproduction process, as it enables fertilization to occur. The pollen must land on a compatible stigma for successful pollination to take place, leading to subsequent fertilization when the sperm cells within the pollen grains travel down the style to fuse with the ovules.

Understanding the process of pollination is fundamental to grasping how flowering plants reproduce and produce seeds. It is an essential mechanism in the life cycle of flowering plants, affecting plant breeding, biodiversity, and agricultural practices.

The other options refer to different processes: germination pertains to the growth of a seed after it has absorbed water, fertilization involves the actual fusion of the sperm and egg cells after successful pollination, and cross-breeding is a method of sexual reproduction to create hybrids by mating different strains or species. Each of these terms has a specific role in plant biology but is distinct from the act of pollen reaching the stigma.