Bruce Mccaib, Age 12, Of North Vancouver, B.C., Canada, for his question:

What is spirogyra?

Once in a while it is fun to go on a leisurely safari through the world of nature. One of the most surprising places to investigate is a quiet pond, and the big surprises appear when you examine small items under a hand lens or a microscope. One of these items is likely to be a scrap of slippery, slimy spirogyra.

We all have seen wads of spirogyra on the surface of quiet ponds or clinging to the edges of lazy creeks. The tangled mass of slippery threads is a weed of fresh waters and a member of the alga plant family. Like all its alga relatives, it is a simple plant constructed from cells that are all alike. It has no ce11s that act only as roots, no special ce11s that do the work of leaves and nothing e1se. Each spirogyra cell is a single plant in its own right, able to multiply and support itself using sunlight to manufacture its own food.

In everyday language, the floating wad of slippery spirogyra has been ca11ed green silk, pond scum or frog spittle. Actually it is a colony of longish alga ce118 linked together like sausages. The single cells show up when a strip of the thread is examined under a microscope. When properly prepared with dyes to bring out the structure of the plant, each cell seems to be stuffed with a winding spiral that coils from side to side along the cell walls.

Thete are seyeral varieties of this water weed, each with slight differences. They are named spirogyra from the spirals stuffed inside the cells that form those long matted threads of floating greenery. When the time comes to multiply, the spirogyra has two methods for handing on life to a new generation. Like marry single celled plants and animals, each cell of spirogyra can multiply by dividing into a pair of twins. Like many more sophisticated plants it can produce a batch of seeds, or rather seedlets.

The seedlets of the spirogyra are actually spores. They start to form when two of the green threads arrange themselves side by side. The nuclei or vital cores from two ce11s migrate together through the cell walls and merge. Each nucleus carries the magic chemicals to order a ce11 to make a reproduction of its parents. The pair of merged nuclei develops into dozens of spores, each ab1e to make a reproduction of its parent spirogyra cells.

Ponds and lazy creeks tend to dry up during droughts and long spells of dry weather. Plants which make their homes in these waters must be able to cope with hard times. The spirogyra can survive long droughts because it can produce spores. These tiny seedlets wear tough shells to preserve their moisture, and they can remain in their spore stage until the rains bring supplies of fresh water to their private swimming pools.