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Mystery Plant: The powdery cloud that's making you sneeze plays an important role

It’s spring! Everything is turning green. And yellow.

Just about everywhere you look these days in my neighborhood, and maybe yours, too, there is a distinct yellow, grainy film settling down on just about all surfaces, living and non-living. Of course, it is pollen, and it’s one of our favorite things to complain about.

Pollen is an important fact of botanical life, and it is vital to the reproduction of all land-based, seed-producing plants. (Recall that there are land-based mosses and ferns, but they don’t produce pollen.) Pollination is the process of the actual movement of pollen grains into relatively close proximity to the ovules of a plant, and, if all goes well, fertilization of the ovules will result. Without pollination, there can be no fertilizations. And, of course, without fertilizations, seeds are not formed, and thus no reproduction. Very clearly, successful pollination is a requirement for most plants grown in cultivation from which we harvest fruits.

Flowering plants, as well as conifers, produce pollen in the form of tiny grains. (The word “pollen” comes from a Latin word meaning “flour.”) Each grain is a tiny individual plant and contains one or several cells within, some of which are ultimately capable of acting as sperm cells. The grains themselves tend to be characteristic, and recognizable, within various plant groups, and it is usually easy to differentiate such groups, based upon the appearance of a pollen grain under a microscope.

Aside from a dirty car, pollen indeed may be a serious matter to cope with, as certain plant species produce pollen that is highly allergenic (that is, inducing allergies). For humans, allergic responses are extremely variable from one person to another, but these allergies are nearly always caused by a physiologic response to proteins in the wall of the pollen grain. Some plant species are rather improperly accused of producing allergies; the worst culprits are, as a rule, those species that are “wind-pollinated,” rather than those whose flowers attract insect visitors for this purpose. Goldenrods and asters in the fall are commonly accused as culprits, but actually their pollen is not particularly problematic. On the other hand, the wind-pollinated ragweeds, oaks and hickories may be the guilty parties.

The pollen pictured here is that of a very common pine, viewed with about 20X magnification. Each grain is about 3/1,000 of an inch long. The main body of the grain bears a couple of bulbous, rounded wings, and thus an intact grain somewhat resembles a Mickey Mouse face.

The very sight of a cloud of yellow pollen falling from trees in the spring can send some of us running for the antihistamines. Our complaints should be tempered with the knowledge of the importance of pollen in the biology of the plants around us, and the realization that, eventually, it will largely go away.

On the other hand, the folks at the car washes aren’t complaining too much.


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