Bugs, dirt, plants, pond water, pebbles, worms, and food scraps - think of these as nature's Legos. Throw in a couple of empty two-liter soda bottles and you can begin exploring the ways nature works and the ways humans affect nature.
Like the folks who spend hours designing new Lego kits, Paul Williams has spent hours with soda bottles and things that grow, buzz, drip, and rot to come up with bottle-biology kits.
''In October 1988, I was raking leaves from my garden to put in my compost pile,'' Dr. Williams recalls. (Besides being a model builder, he is also a plant scientist at the University of Wisconsin.) ''I began to wonder what was happening inside that pile. How could I create a transparent core that would let me see what happens? Then I thought of cutting up soda bottles.''
The final result: a book of easy, cheap projects that range from his ''compost column'' to building a model of an entire ecosystem.
In addition to several clear two-liter bottles, the budding bottle biologist needs a tool kit of items readily found around the house: clear tape, a wax pencil or crayon, scissors, a hole punch, an awl, a razor in a safety holder, a darning needle or diaper pin to poke small holes, and some silicone sealant.
The first step in building any of the projects is to remove the bottle's label and, if the design calls for it, its base (if it has one). You can loosen the glue that holds the base by submerging the bottle in warm water.
Then, following the illustrations at the right, cut bottles into sections. Don't be discouraged if the result doesn't look perfect. All it has to do is work, not win beauty contests. Use the tape and silicone sealer to secure and waterproof the joins.
The compost model, for example, can help show how fall is not a season marking the end of a growing cycle, but the beginning. In the woods, the fallen leaves slowly decay and enrich the soil, providing vital nutrients for a new generation of plants. Gardeners use the same process to turn their raked leaves into rich, nutritious soil for next year's garden.
Build several columns, and you can join the ''rot race.'' Put different things in each column to see how they affect the speed of decay. One column might have leaves and soil; another might have leaves, soil, and vegetable scraps; yet another might have leaves that have been finely chopped, soil, and a couple of earth worms. You can also experiment with different amounts of water, which needs to be added to keep decay under way. Or you could add a slight bit of vinegar to the water to see how ''acid rain'' affects the decay process.
Lest you think the compost column is smelly kids' stuff, Williams says that college microbiology classes use them to grow organisms to study.
With the ''terraqua column,'' you can explore the relationship between ponds and the land surrounding them. How does garden fertilizer affect the ''pond'' and the plants in it? What happens if you add salt to the soil, which happens where people use salt on roads to melt ice in the winter?
The full range of projects are contained in a book called ''Bottle Biology,'' available from Kendall/Hunt Publishing Company in Dubuque, Iowa. The book costs $15.95 and can be ordered by calling 1-800-228-0810.
One project, the ''water cycle column,'' can even be adjusted to make rain and snow, Williams says.
For the Pugsley and Wednesday Addams wannabes, you can build a predator column, which raises fruit flies on one level to be pursued by spiders or praying mantises on another.
The granddaddy of all the projects is the ''ecocolumn.'' Sections modeling various parts of an ecosystem can be stacked - from plants, soil, and bugs on top, to a composting section beneath, to a terraqua-like section below that.
Nature in a bottle - not a bad way to ''spend'' a nickel deposit.
* Peter Spotts' e-mail address is firstname.lastname@example.org.