In most modern samples, for instance, pollen grains generally form more than 95 per cent of the sample. Many coniferous and flowering plants produce vast quantities of pollen as part of their reproductive cycle. Pollen grains carry the male genetic information for fertilization. From this, seeds are formed which ultimately can produce new plants. Pollen grains are dispersed widely over the landscape, mainly by wind, and are a major cause of the hay fever and allergies suffered by many people in the summer months.
Plants produce many more pollen grains than are actually used in reproduction.
Much of the pollen falls to the ground or is washed from the atmosphere by rain and ultimately becomes part of sediments, especially the mud accumulating on the floor of lakes. Because pollen grains are so tiny, less than a teaspoonful of sediment can contain many thousands of them. Most pollen grains are extremely resistant to decay and are preserved in large numbers in many types of sediments. Pollen grains have distinct shapes and surface patterns that allow palynologists to identify them according to the plants that produced them. The walls of pollen grains are made from sporopollenin, one of the most resistant natural chemical substances known.