What is the term for the union of pollen and the stigma?

The correct term for the union of pollen and the stigma is pollination. In the process of pollination, pollen grains, which contain the male gametes, are transferred from the male part of a flower (the anther) to the female part (the stigma). This key plant reproductive process is essential for fertilization to occur, as it allows the sperm cells within the pollen to fertilize the ovules in the ovary, leading to seed formation.

Understanding this concept is fundamental in the study of plant biology and agriculture, as pollination is critical for the production of many crops and subsequent agricultural yield. This process can be facilitated by various agents, including wind, water, and animals, particularly bees and other pollinators.

The other terms relate to different aspects of plant reproduction: fertilization follows pollination, where the actual fusion of gametes occurs; germination refers to the process by which a seed develops into a new plant; and hybridization involves the crossing of different plant varieties or species to produce a hybrid. Each of these processes plays a distinct role in the life cycle of plants but does not define the initial event of pollen transfer to the stigma, which is specifically termed pollination.