Right Before Your Eyes - Mixed Blessing

RIGHT BEFORE YOUR EYES - The Nose Knows

Some hayfever sufferers have probably tossed around the term "pollen" for years without really understanding what that stuff is that causes their discomfort. The name "pollen" means dust. That's a good description; there are literally hundreds of thousands of microscopic pollen grains in the least smudge of pollen. Each species of plant has its own distinctive pollen grain. The study of the various shapes is a specialized branch of botany and is particularly helpful for identifying fossilized pollen grains. If botanists can identify the pollen grains in a prehistoric site, they can use that information to identify the very species which were growing in the area at that time.

The earliest form of pollination was wind pollination. Most pollen grains are small enough to float for long periods in the air and enough are produced that some eventually reach their goal. The most primitive seed-producing plants, as one would expect, are all wind pollinated (cycads, maidenhair trees, and conifers).

Later in the history of the earth, some plants developed true flowers. For flowering plants to reproduce, pollen from one flower must reach the pistil, or female part, of another, and to this end many varied and beautiful pollen grains have evolved. Some of the particular shapes and compositions of pollen bother some particular noses. You may be allergic to some conifer pollen but not to grasses, for instance.

Insects found pollen to be a good food source, and as plants developed flowers, they used the insects' affinity for pollen to their own advantage. Through evolution, plants have actually encouraged visits by insects; uneaten pollen sticks to the insects' bodies and can be carried to other plants of the same species, where pollination can occur. Taking this a step further, over a very long time plants developed nectar supplies which were highly attractive to insects. As insects were attracted to flowers for the nectar, they picked up pollen incidentally and transferred it to the next flower on which they landed. As you might guess, the development of flowers has been in the direction of obtaining the maximum pollination with the minimum expenditure of energy (in the form of pollen). Some flowers even deliver tidy packets of pollen to the bodies of their pollinating insects, so that less is lost en route.

But despite the specializations that some plants have developed, some insects can subvert those specialized structures for their own benefit. Bumblebees are known to bite into Squirrel-corn flowers to get nectar, and they don't pollinate the plant in doing so. There is almost a cat-and-mouse game of evolution between plant and insect that has gone on for millions of years and is still continuing.

Despite the close association between flowering plants and insects, many plants such as the grasses, sedges, and many flowering trees, have "regressed" once again to a wind pollination strategy and no longer rely on insects for reproduction. In these plants, true flowers are still produced, but they are small, drab, pared down, and inconspicuous. The transfer of pollen from one plant to another is carried out - as it was eons ago - by the wind.

Audubon Nature Encyclopedia. 1965. Curtis Publishing Co. Philadelphia Woodhouse, R. 1935. Pollen Grains. McGraw Hill Book Co., NY.

C. 1988 John Wiessinger Box 453 Etna, NY 13062