IF EXTRATERRESTRIAL SCIENTISTS were ever to visit our planet, they might not pay much attention to relatively large, complex creatures like ourselves. Rather I suspect they would notice that the greatest diversity, and indeed most of the biomass, on the earth comes from its simplest residents-protozoans, fungi and algae, for example. By just about any objective measure, these organisms represent the dominant forms of life.

The world of algae is a particularly fascinating realm for amateur exploration. A single drop of pond water can harbor a breathtaking variety of microscopic species, with each algal cell constituting a complete plant. So if you want to view the essential biological underpinnings of all plant life, algae provide the best show in town.

Obviously, you will need a microscope to see the spectacle. An instrument with a magnification of about 120 times should be adequate. But the real secret to exploring this enthralling world successfully is to create small enclosures—"microponds," if you like—in which your specimens can flourish.

Canning jars filled with some water and soil make ideal environments. To let gases in and out, cut a hole one centimeter (about half an inch) in diameter in each lid and plug the opening with a wad of sterile cotton. You will also need a source of light for these diminutive plants. Because direct sunlight can rapidly warm your tiny ponds to temperatures that are lethal to algae, place them in a window with a northern exposure. Or set a full-spectrum bulb on a timer to provide a more controlled source of illumination.

You must sterilize the soil, water, jar and lid before introducing any algae; otherwise stray bacteria could quickly take over. A special apparatus called an autoclave kills bacteria with heat under enough pressure to keep water from boiling. Scientists at a local university or commercial laboratory would probably be delighted to sterilize some materials for your home research using an autoclave. But a pressure cooker will also work.

You should first assemble everything. Add about four centimeters of dirt or mud and distilled water fortified with commercial plant food according to the manufacturer's instructions. Fill the jar to within two centimeters of the top, but do not screw the lids down yet. Place the prepared jars inside a plastic basin that is filled with two centimeters of water to prevent the base of the glass from getting too hot and breaking. Heat the jars for 20 minutes at 120 degrees Celsius (about 250 Fahrenheit).

If you don't have access to a pressure cooker, you can try vigorously boiling the water, jar and lid for at least 20 minutes in a covered pot and baking the soil in your oven at 180 degrees C for one hour. This method requires that you assemble the sterilized parts afterward, a procedure that risks contaminating your cultures with bacteria. If you do use this approach, let your containers sit for at least 10 days to make sure that your ponds are truly sterile; contaminating bacteria will turn the water cloudy as they multiply.

Otherwise, once the microponds have cooled completely, you should inoculate them with algae as soon as possible. A scraping from a piece of seaweed, a smidgen of pond mud, a pinch of garden soil, even a rubbing from the inside of a friend's aquarium are all great sources. Add such samples to a few jars and watch these aquatic gardens grow.

Your first cultures will probably contain a jungle of different single-celled plants. For scientific work, you will need to isolate individual species. You can do so by separating a small group of cells and implanting them in sterile agar, a gelatinous growth medium, which, incidentally, is itself made from algae. (A source of agar is listed at the end.)

This process is not as hard as it sounds. You begin by filling a set of sterilized petri dishes with agar to which you've added a small amount of plant food. Add the food just before setting the agar aside to gel. Next, use a sterile probe to take a tiny piece of the algae from one micropond. Swab the probe rapidly over the surface of the agar in a widely spaced zigzag pattern. Cells transferred onto the nutritious surface will take hold and grow in a few days into a splotchy garden of isolated groups plainly visible to the naked eye. Because cells will tend to shed in clumps from the original grab, most of the second-generation crop will be only slightly less diverse than their parent sample. But by taking a small amount from the center of one of these groups and then repeating the process on a second petri dish, you will create third-generation growths of even fewer species.

Some biologists recommend raising each succeeding generation by transferring a speck from a single petri dish to a sterilized culture jar, waiting for plants to multiply and then separating them again on a fresh agar surface. But I can sometimes get results more quickly by raising multiple generations on enriched agar, without culturing in jars as an intermediary step. Try this shortcut, but don't be surprised if you find you need to use the more laborious procedure.

It usually takes between three and five generations of swabbing and growing, but eventually your microponds will each contain a single algal species. Careful examination of samples under the microscope will reveal whether your cultures are pure. Once you have isolated several strains of algae in this way, the investigations you can make are limited only by your imagination. One useful class of experiments involves seeing how different chemicals affect growth.

Your test results will be much simpler to compare if you begin each trial with samples containing roughly the same number of cells. One way to make up such samples is to dip blotting paper (sterilized with an autoclave or pressure cooker) into a dilute solution of sterile plant food and let it dry. Then soak the paper in molten beeswax for a few seconds until it is thoroughly impregnated. Remove the strips from the wax and return them to the solution of sterile plant food to harden. Transfer the waxed strips quickly to your culture jars. With luck, algal cells will grow uniformly over the treated paper. You can then cut out standardized samples using a sterile metal hole punch.

To start your experiment, set up a rack of 10 test tubes. Place a high concentration of the chemical you wish to evaluate in the first tube and then dilute each succeeding test tube by a factor of 10. That is, add nine parts of distilled water to one part of solution. (An eyedropper makes this task easier.) With 10 test tubes, you'll have a billionfold difference in concentration between the first and last mixtures.

If you want to see whether the chemical in question improves growth, add three standard hole-punched samples and a fixed quantity of each of the dilutions to sterile culture jars. If you want to test whether the chemical can kill algae, you should place three standard samples for a prescribed time in each tube. Then use sterile tweezers to retrieve the samples and wash them gently with distilled water before placing them in the sterile culture jars.

Now monitor how the treated algae grow. Once you know roughly the minimum level at which the test chemical alters the amount of algae seen in the jar after one week, you can conduct a more tightly focused experiment to determine the critical concentration more precisely. A similar procedure lets you explore how algae respond to two separate chemicals (see diagram above). This tactic is useful, for example, if you want to compare the effects of, say, a nitrogen-based fertilizer and a substance such as aspirin, which reduces the surface tension of water and so might make it easier for nutrients to get inside the cells.

This procedure will let you identify the optimal concentrations of two chemicals for growth of a particular species. You might also try to gauge how varying levels of heat and light affect the growth of algae, to learn their method of reproduction by microscopic examination or to identify some of their metabolic products using more sophisticated analytical apparatus (see, for example, the gas chromatograph described in the June 1966 Amateur Scientist). Remember, you can dive into this wondrous aquatic realm as deeply as you like.

For more information about this and other projects from the Amateur Scientist, consult the Society for Amateur Scientists World Wide Web page. Or you may write the society at 5600, Post Road, #114-341, East Greenwich, RI 02818, or call 1-401-823-7800.

NOTE: Powdered agar can be obtained from VWR Scientific Products; call (800) 727-4368 or (847) 459-6625. Ask for catalogue no. WLC 3049R.

The Society for Amateur Scientists (SAS) is a nonprofit research and educational organization dedicated to helping people enrich their lives by following their passion to take part in scientific adventures of all kinds.