What is pollination and what is the importance of pollination? What are the types of pollination? Learn about the definition of pollination, the importance of pollinators, and the different types of pollination, including self-pollination and cross-pollination.
Pollination; is the transfer of pollen from the stamens of a higher plant to the ovule-bearing organs or to the ovules themselves. In conifers and cycads the pollen is caught in a liquid drop secreted by the micropyle of the ovule. In flowering plants the ovules are borne within a hollow organ, the carpel, which receives the pollen grains on a special surface called the stigma. In either case the result of a successful union of pollen and ovules is fertilization and seed formation.
The pollen that participates in a given event of pollination may come from a stamen on the same individual plant as the ovule with which it unites, or even from within the same flower, or it may come from a different individual. Thus self-pollination can be distinguished from cross-pollination. Though both methods are common, cross-pollination possesses certain advantages for the plant species that deserve special consideration. For example, cross-pollination leads to seed set as well as to the formation of seeds in which different heredities are combined; it leads not merely to reproduction, but to sexual recombination. The progeny resulting from this process are more variable and flexible and have a better chance of surviving in a changing world than the offspring produced by long-continued self-pollination.
Since plants are sedentary organisms, they can bring about cross-pollination only by committing their pollen to some external agent which possesses the power of movement. The most commonly exploited agents of pollination are insects, birds, wind, and water currents. By adapting their flowers, or in the case of conifers and cycads their cones, to the characteristics of these agents, the plants have made it advantageous or inevitable for them to carry the pollen.
Some flowers are cross-pollinated by bees; they are adapted in their form, color, and odor to the characteristics of bees. Other flowers which are pollinated by moths possess a different set of adaptations. Still other flowers possess special characteristics which fit them for wind pollination. The tremendous diversity of flowers in the world consists, therefore, not of an un-orderly and random array of types, but of various groups, such as bee flowers, moth flowers, and wind flowers, which to a certain extent overlap with the natural families. The attributes which the members of each pollination class possess in common comprise parallel adaptations, attained through natural selection, for similar methods of pollination.