section_path: Pollination
section_name: Pollination
paragraph_text: Pollination
  
  Since the flowers are the reproductive organs of the plant, they mediate the joining of the sperm, contained within pollen, to the ovules — contained in the ovary. Pollination is the movement of pollen from the anthers to the stigma. Normally pollen is moved from one plant to another, known as cross-pollination, but many plants can self-pollinate. Cross-pollination is preferred because it allows for genetic variation, which contributes to the survival of the species. Many flowers depend on external factors for pollination, such as the wind, water, animals, and especially insects. Larger animals such as birds, bats, and even some pygmy possums, however, can also be employed. To accomplish this, flowers have specific designs which encourage the transfer of pollen from one plant to another of the same species. The period during which this process can take place (when the flower is fully expanded and functional) is called anthesis, hence the study of pollination biology is called anthecology.
  
  Flowering plants usually face evolutionary pressure to optimize the transfer of their pollen, and this is typically reflected in the morphology of the flowers and the behavior of the plants. Pollen may be transferred between plants via several 'vectors,' or methods. Around 80% of flowering plants make use of biotic or living vectors. Others use abiotic, or non-living, vectors and some plants make use of multiple vectors, but most are highly specialized.
  
  Though some fit between or outside of these groups, most flowers can be divided between the following two broad groups of pollination methods: