There are some very tough plants in the American desert. They can endure the blinding heat of noonday and thrive in the salty desert soil. And they produce an odd collection of useful substances that scientists are still trying to sort out.
A whole new frontier may exist in the agriculture of arid regions - in water-stingy, energy-stingy crops of ancient but forgotten foods, high-quality rubber, high-quality lubricants, natural insecticides, waxes, medicines, resins, and crude oil.
These hard-boiled plants have yet to produce a commercial crop, but they hold forth some exotic promises for the water-poor Southwest.
The dream of making the desert bloom with conventional crops, like cotton and grains, is fading. The budding notion is to make the desert the desert again, only more and better, growing some ancient crops and products that have never been cultivated before.
The scene has been changing since about 1972. A quarter of the Arizona farmland of more than a decade ago is out of production now. Apart from spreading urban sprawl, the reasons are the growing salinity of the heavily irrigated soil and depletion of ground water.
''It's kind of a silent crisis,'' says Arizona ethnobotanist Gary Nabhan. ''These things aren't needed 100 years down the line. They're needed now.''
Most desert crops need about half as much water as their conventional counterparts do. Jojobas, for example, demand less than 5 inches a year, compared with 4 or 5 feet for cotton.
The real test for desert plant products, of course, is the marketplace. None of the crops have developed yet to the point where a buyer can dependably schedule railroad cars to pick up bulk harvests.
Jojoba (ho-HO-ba), which produces a high-quality oil, may reach that point in a couple of years. Some 25,000 acres have been commercially planted, and the first harvests were just last year. The 1983 harvest should begin to show mature yields, says Demetrios M. Yermanos, a plant scientist at the University of California, Riverside.
''Jojoba to me is a symbol of what can be done,'' Dr. Yermanos says.
On the other hand, Dr. Nabhan cautions: ''When jojoba goes from a shampoo crop using about 10 drops to a bottle to a major auto lubricant, it will put some people out of business who are counting on shampoo prices.''
Guayule, this country's first source of rubber, may be the next crop to reach commercial scale. There are no guayule processing plants now, so farmers don't plant it. But the Department of Defense has contracted with the Gila River Indian tribe of Arizona to farm the plant, which may help the industry begin to sprout.
Plants that produce crude oil, known as biocrude, have drawn private research funds since the energy crunch of the early 1970s. Euphorbia lathyris was once expected to produce 10 to 20 barrels an acre, but test plots have yet to realize that amount.
A gumweed, grindelia, is being now tested at the University of Arizona. It produces resin and a potential fuel oil that can be removed virtually by dipping the flowers in water.
''If we ever get to growing crude oil,'' points out Kenneth Foster, associate director of the Center for Arid Land Studies at the Unviersity of Arizona, ''it's going to take vast acreage.''
For now, some desert food crops would seem more practical. In this field, scientists are following the lead of the Aztecs. In fact, anthropologist Bernardo Ortiz de Montellano of Wayne State University says he thinks the Indians of Mexico ate more and better 500 years ago, before the Spanish conquistadors came, than they do today.
Grain amaranth, which can be popped like corn, ground into flour, or the leaves eaten in a salad (they taste like spinach leaves), was nearly stamped out by Spanish missionaries because it had religious meaning to the Aztecs.
Instead, the continent inherited corn, a less water-efficient Aztec crop.
The Aztecs also ate the pods of the mesquite, which Dr. Ortiz de Ortellano calls ''a nearly perfect food tree.'' Its deep roots pull it through severe droughts. It has strains that grow in areas with only 4 inches of rain a year and strains that grow in soil too salty for other plants. It takes nitrogen from the air, so needs no nitrogen fertilizer.
Its pods are generally ground into a flour with a taste comparable in richness to carob.
The buffalo gourd is a promising source of cooking oil and root starch. Amaranth, tepary beans, and screwbeans (the mesquite pods) are already on the market and sell out as soon as they are harvested.
The markets for these crops are now in health food stores, on a small scale. They are harvested in wild stands and grown by farmers with 20 or 30 acres. ''These crops go through quantum leaps in their careers,'' Dr. Nabhan says. ''Most of them are in their adolescence.''
Significantly, these crops could be grown in dry regions of Africa, Asia, and Latin America where food is short. In this country, Richard Gordon of Arizona State University's Center for New Crop Applied Science and Technology estimates that it will take $12 million to $14 million in research and development to prove out any given plant product.