When a non-animal vector is responsible for moving the pollen, the term abiotic pollination is used. There are two primary abiotic vectors: wind, and in aquatic environments, water. Wind pollination is chancy. Pollen is released and carried airborne by the wind until it reaches a stigma of the same species. Consider the likelihood of the process being very accurate; yet, consider that all grasses and many tree species are exclusively wind-pollinated. Do you think that wind pollination is very accurate? Is it very effective?

(1) Pollen grains on the wind, an improbable venture.

In order for wind pollination to work, consider what must happen to the pollen grains. They must be released when the wind is blowing, there must be a stigma somewhere downwind, and somehow the pollen grain must hit its target without the aid of any animal. While this process may appear to be inefficient, it obviously works well enough in some species. In addition, certain aspects of the system have evolved to enhance the likelihood of wind pollination. For example, wind-pollinated species generally produce relatively large amounts of pollen compared to the number of ovules (high pollen/ovule ratio). Ask yourself (and answer, too) why a high pollen/ovule ratio is an advantage in wind pollination. Another common adaptation seen in many wind-pollinated species is a very large stigma one the gynoecium. A third adaptation involved in this system is the loss of a corolla. Describe the collective advantage of this wind-pollination syndrome.