Pollen analysis—the application of statistical methods to the study of pollen—is less than a century old. Its basic principles were set forth by German geologist Lennart von Post (1884–1951), who used pollen to study past environments. He noted five key features of pollen. First, many plants produce vast amounts of pollen, which are dispersed by the wind. The average pine tree, for example, produces more than 100 billion pollen grains. Second, pollen has a very durable outer wall, called the exine, which can stay intact for a very long time. Examples have been found that are 250 million years old. Third, the general shape and the surface features of pollen vary between plant species, yet they are the same in all plants within the same species. Fourth, the distribution of pollen-producing plants is governed by such ecological factors as moisture, temperature and soil type; the more favorable the conditions for a particular plant, the more of that plant—and its wind-borne pollen—one would expect to see in that region. Fifth, almost all wind-borne pollen falls back to earth within about 30 miles of the plant that produced it, with the overwhelming majority (95%) found within a mile.

Pollen, in sum, is plentiful, hardy, identifiable and traceable to its point of origin.

Plants can produce a staggering amount of pollen. Swedish scientists estimate that the spruce forests in the southern third of their country release more than 75,000 tons of pollen into the atmosphere each year. Some flowering plants, however, generally those with colorful flowers to attract insects, produce relatively tiny amounts of pollen, relying on insects, birds or bats—rather than the wind—to carry out pollination.

The rate of pollen production is an important factor in palynology. Specialists must first determine the expected amounts and the dispersal patterns (called the pollen rain) of a specific pollen type in a particular region and then compare that to what they find on the item under study. With the Shroud of Turin, for example, we must ask if the types and amounts of pollen on the shroud match the pollen patterns in Jerusalem.

In court cases where pollen evidence is introduced, it is the pattern of pollen types—the “pollen print”—that can link a suspect to a crime scene. For example, in a case that took place in New Zealand in 1995–1996, a young woman was attacked and killed in a botanical garden. The suspect swore that he had never been at the site, but pollen embedded in his sweater came from plants not found in the area—except in the botanical garden. The suspect was convicted.