Forest Preserve District of Cook County, Illinois
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Nature Bulletin No. 80   August 24, 1946
Forest Preserve District of Cook County
Clayton F. Smith, President
Roberts Mann, Superintendent of Conservation

From mid-August until early frost, people are "pollen-conscious" -- particularly those who suffer with hay fever. Millions of flowers are in bloom, including the ragweeds which are heavy producers of pollen. Hay fever is an "allergy" or protein sensitivity to this pollen, carried scores or even hundreds of miles by the wind, which sticks to the thin moist membranes of the eyes, nose, throat and lungs.

Most plants, including trees, have flowers. The stamens of a flower are covered with fine yellow grains called pollen. If there is to be fertilization, these grains must be transferred to the pistil in which the seeds are formed. Some plants, such as peas and beans, are self- fertilized but most kinds are cross-fertilized: the pollen being carried from one plant to another by wind or on the bodies of insects attracted to them by the nectar in the flowers. Under a microscope the pollen grains of one species are distinctively different from those of another in size, shape, markings and color.

Curiously, the tiny fragile pollen grains from trees are more durable than any other part of the tree if they fall upon the surface of a swamp or bog and accumulate under water. Scientists, examining the pollen grains found in deep peat bogs, from bottom to top, read there the story of the changes in climate and vegetation that occurred during and since the Ice Age.

When the last glacier melted away, some 50,000 years ago, large blocks of ice broke off and were left behind. These melted to form lakes and potholes. The decaying remains of aquatic plants slowly filled many of the potholes to form peat bogs.

As the glacier retreated, vegetation followed it, advancing across the vast tundra or barren lands that stretched from its front almost to the Ohio River. The pollen grains in these peat bogs show that the first trees were firs and spruces, in forests that persisted for centuries. Then came the pines and tamarack; after them the birches, linden and elms; and then the oaks, maples and hickories. That is the story as told by the pollen grains in peat bogs.

The earth changes. Things disappear. So will your hay fever.

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