Pollen, or flower sperm, is a fine powder made up of microspores produced by male plants. Pollen carries the male reproductive cells (gametes) of seed plants, which include conifers (plants whose seeds grow inside cones) and flowering plants. Pollen starts out in the stamen, the male part of the seed plant, and needs to get to the pistil, the female part, in order for the plant to propagate.
There are two ways for a seed plant to be pollinated: self-pollination, in which the pollen from the stamen in one plant pollinates the pistil in that same plant, and cross-pollination, in which the pollen from the stamen in one plant pollinates the pistil in another plant of the same species.
But how does the pollen get from one plant to another? That depends on what kind of plant it is. The pollen of anemophilous ("wind-loving") plants is very lightweight and easily dispersed by the wind. Many kinds of grasses and conifers are anemophilous. Researchers have found that the pollen of anemophilous plants can travel 2,000 feet (610 meters) up in the air and 25 miles (40.2 kilometers) away and still germinate 50 percent of the time.
In contrast, entomophilous ("insect-loving") plants, including many flowers (though not all of them) are pollinated by insects. When insects land on an entomophilous plant to drink its nectar, some its heavy, sticky pollen sticks to the insects. The insects then move along from plant to plant to feed from them, and in the process the pollen from previous plants they landed on rubs off their bodies and onto the plants, pollinating them. The pollen from entomophilous plants doesn't travel nearly as far as the pollen from anemophilous plants because an insect only travels a maximum of around 328 feet (100 meters) during its daily feeding.