Pollen
Pollen grains from a variety of common plants:
sunflower (Helianthus annuus), morning glory (Ipomea purpurea),
hollyhock (Sildalcea malviflora), lily (Lilium auratum), primrose
(Oenothera fruticosa), and castor bean (Ricinus communis).
Pollen is a fine powder consisting of microgametophytes (pollen grains), which carry the male gametes of seed plants. Each pollen grain contains one or two generative cells (the male gametes) and a vegetative cell. The group of three cells is surrounded by a cellulose cell wall and a thick, tough outer wall made of sporopollenin.
Pollen is produced in the microsporangium (anther of an angiosperm flower or male cone of a coniferous plant). Pollen grains come in a wide variety of shapes, sizes, and surface markings characteristic of the species (see photomicrograph at right). Most, but certainly not all, are spherical. Pollen grains of pines, firs, and spruces are winged. The smallest pollen grain, that of the Forget-me-not plant (Myosotis sp.), is around 6 μm (0.006 mm) in diameter. The study of pollen is called Palynology and is highly useful in paleontology, archeology, and forensics.
The transfer of pollen grains to the female reproductive structure (pistil in angiosperms) is called pollination. This transfer can be mediated by the wind, in which case the plant is described as anemophilous (literally wind-loving). Anemophilous plants typically produce great quantities of very lightweight pollen grains, and generally have inconspicuous flowers. Entomophilous (literally insect-loving) plants produce pollen that is relatively heavy and sticky, for dispersal by insect pollinators attracted to their flowers.
Honeybee carrying pellet of pollen in its corbicula
Hay Fever
Allergy to pollen is called hay fever. Generally pollens that cause allergies are those of anemophilous, because the lightweight pollen grains are produced in great quantities for wind dispersal. Breathing air containing these pollen grains brings them into contact with the nasal passages. In the US, people often falsely blame the conspicuous entomophilous goldenrod flower for allergies. Since this pollen does not become airborne, the only way to get goldenrod pollen on the nasal passages would be to stick the flower up your nose. The late summer and fall pollen allergies are usually caused by ragweed, a widespread anemophilous plant. Arizona was once regarded as a haven for people with pollen allergies, since ragweed does not grow in the desert. However, as suburbs grew and people began establishing irrigated lawns and gardens, ragweed gained a foothold and Arizona lost its claim of freedom from hay fever. Anemophilous spring blooming plants such as oak, hickory, pecan, and early summer grasses may also induce pollen allergies. Cultivated flowers are most often entomophilous and do not cause allergies.
Miscellaneous
The "tapping panel dryness disease" of the rubber plant is caused by a virus transmitted on pollen grains.
Pollen is sold as a nutritional supplement, marketed as "bee pollen" (even though it is of course from flowers).
