In a cellar vault on a picture-book place of orchard, pasture and field known as Heritage Farm, a big slice of America's history is preserved in trays, barrels and shelves housing thousands of white packets containing seeds.

A soup bean believed ferried on the Mayflower, a black pole bean carried by the Cherokee over the Trail of Tears, a variety of tomato collected by Robert E. Lee while at war. In all, a stock of 24,000 varieties of vegetables, herbs and flowers are represented in the 20-by-15-foot room bathed in bright light and icy cold air. Many were staples of life in Colonial America, some originated from Indian tribes and yet others passed through Ellis Island sewn into hatbands and dress hems.

For gardeners, farmers and historians of America's agrarian traditions, the collection maintained by the Seed Savers Exchange is nothing less than a modern-day Noah's ark and a model for similar efforts in 30 other countries by like-minded preservationists concerned that the world's rich tapestry of vegetable and flower varieties, centuries in the making, is unraveling at an alarming rate.

Other seed banks, notably the government's National Center for Genetic Resources Preservation in Fort Collins, Colo., are maintained by scientists looking for better crops or as insurance against future agricultural calamities. But Seed Savers' mission is to place seeds in the hands of tens of thousands of gardeners who grow heirloom varieties not just to preserve genetic diversity but to experience a taste of America before our food went into the melting pot.

"When you begin to grasp the sheer numbers of varieties that are there compared to what we eat on a daily basis, it's shocking and awesome," says Deborah Madison, a cookbook author and board member of Seed Savers, founded in 1975 by a young midwestern couple, Kent and Diane Whealy.

Today, the nonprofit's 8,000 members offer each other 11,000 heirloom varieties of vegetables, fruits and grains. Separately, the seed catalogue is distributed to 150,000 gardeners and farmers in the United States and offers more than 600 selected varieties.

This year's, for example, features Armenian melons sold in Philadelphia markets in the 1840s, a garlic from a Republic of Georgia village and the Opalka paste tomato, brought to New York a century ago by Polish immigrants.

The collection began with the seeds of a morning glory and a tomato that Diane Whealy's grandfather collected and handed her shortly before his death in 1972. His parents had brought them from their German homeland in the 19th century. Each year, Grandpa Ott grew the annual vine on his porch and collected its seeds every fall for the following year.

This is how seeds, unique to one religious sect or a village or even a family, were passed from one generation to the next for centuries. But by the 1970s, decades of hybridization and mail-order marketing, which like the auto industry relied on introducing novel varieties each year, had rendered the heirloom a dinosaur.

Some hybrids are more productive and disease resistant, but many are bred for mechanical harvesting, shipping and durability, all at the expense of flavor. Moreover, hybrids were severing the cultural strands spun by heirlooms. As a rule, hybrids cannot reproduce themselves.

Thanks to the rescue effort and a new interest in heirlooms, the recorded loss of commercially available varieties has slowed, Kent Whealy says. But even his lifetime of seed sleuthing has failed to recover more than a fraction of the varieties once known in America. Among the losses: An apple variety named Taliaferro that Thomas Jefferson called "the best cyder apple existing."

Diane Whealy says that after her grandfather died, she looked at the pillbox containing the morning glory seed and realized "that if I hadn't talked to him about it, they probably would have been ripped out and disappeared. This is the only morning glory of this color growing in the country." Thus started the Whealys' quest, which culminated in the move to Heritage Farm in 1984.

Every summer since then, the distinctive purple and red trumpets of Grandpa Ott's morning glory grow high against the old dairy barn that is the farm's signature building. The two-hour drive from Dubuque, ironically, takes visitors past countless acres of just one crop, corn, most of it genetically modified.

In the bizarre parallel worlds of agriculture in the 21st century, Heritage Farm flourishes as an oasis of diversity and genetic purity. The Whealys, now in their fifties and recently divorced, still work together but for an endeavor far bigger and sophisticated than at the start. Their son, Aaron Whaley (he uses an older spelling of the family name), runs a catalogue, and garden manager Matthew Barthel oversees a crew of 19 gardeners who grow the 10 percent of the stock that's planted each year to renew the seed.

In a way that the Whealys could not have foreseen 30 years ago, the heirloom seed movement has been swept up in the revolution taking place in the nation's food chain. Small local farms have proliferated to serve restaurants, roadside stands, direct sales to subscribers and farmers markets.

Madison, in her book "Local Flavors," says there are almost 3,000 farmers markets nationally compared with just a handful when the Whealys started. There are approximately 70 in metropolitan Washington alone. The Dupont Circle Fresh Farm Market, for example, has 30 vendors who must raise what they sell.

Modern-day truck farming also has been invigorated by regulations that have opened new markets for farmers who are certified organic growers, changes that have increased the demand for heirloom seed. Seed Savers is not only selling to farmers directly but growing heirlooms for other seed companies to sell.

Neil Hamilton, a director of Seed Savers and president of the National Gardening Association, told 180 heirloom gardeners convening recently at Heritage Farm that all these strands are part of a "broad development of food democracy" in America. "I don't think anybody believes we are going to create this separate food system that replaces grocery stores," he said. "The question is broadening the food system."

The Seed Savers catalogue offered 47 certified organic varieties last year, 124 this year, and more will follow. Home gardeners still make up the majority of the catalogue's customers, but the expansion is in supplying commercial growers and other seed companies, including bulk sales to Japan and Europe, ironically from where many of these New World heirlooms came.

Catalogue sales have grown by 125 percent in the past five years, Aaron Whaley says. He has developed Seed Savers' response to the market with a slick, colorful sales catalogue and Web site, replacing a folksy black-and-white flier.

All this has led to a major expansions in operations: The area under intensive cultivation jumped from 14 to 23 acres this year with greater emphasis on bulk production, and two years ago Seed Savers bought a 716-acre neighboring tract to quintuple its size. This will allow heirloom corn and other varieties to be isolated from the pollen of genetically modified crops on other farms, Kent Whealy says.

In spite of the growth of Seed Savers, its homespun origins were clearly evident at its recent convention, camp-out and reunion of the faithful. On a bright summer weekend, members from more than 20 states mingled in the display garden that Diane Whealy tends, filled with the annuals, herbs and vegetables racing to bloom in the short growing season.

Kent Whealy believes that as baby boomers retire, the interest in vegetable gardening will climb again, further broadening the role of heirlooms. About one in four American households grows vegetables, according to the National Gardening Association. Sioux Ammerman, a seed saver from Santa Clara, Calif., who grows heirlooms for "nourishment" of body and soul, is not so sure. "It's so simple" to grow vegetables, she says, "but then I talk to people who cut down all their trees because they make such a mess. It's a little scary."

She points to the Irish potato famine of the 1840s as the prime example of the danger of relying on one crop. Others note the summer of 1970, when 15 percent of America's corn crop was wiped out by a single disease, southern corn leaf blight.

In 2002, 90 percent of Michigan's tart cherry crop was ruined by frost damage because the trees derived from a single variety named Montmorency, says Peter Bretting, national program leader for the Agricultural Research Service's plant germ plasm and genomes banks. Cherries of later-blooming types would have gone on to set fruit.

Bretting's agency, as part of the national system, controls its own ark: 10,000 species, tens of thousands of varieties, 450,000 samples of plants, stored for use by scientists in developing new agricultural crops.

The government's gene banks and those of grass-roots organizations such as Seed Savers complement each other, he says, and are recognized as vital in protecting the food supply for future generations. Paradoxically, advances in genetic engineering have increased scientific interest in heirlooms because their vast genetic wealth can be better tapped today, says Bretting, who is based in Beltsville.

The advent of the Internet has protected heirlooms by establishing new networks of home growers, Whealy says. Early on, he amassed Asian heirlooms brought by refugees from the Vietnam War. With the collapse of the Soviet Union, Whealy returned from Eastern Europe with 4,000 newly discovered varieties. "We are getting material now from Mexico, Cuba and Haiti," he says.

After a tour of the seed vault the other day, Whealy takes his visitors past a herd of ghostly white cows and their calves -- rare Ancient White Park cattle from Britain -- and on to a remote apple orchard where 700 pre-1900 heirloom varieties grow in neat grids. A century ago, America had more than 7,000 regional apple types. "This," he says, "is what's left."

Seed Savers Exchange gardeners Amy Fortman, Jason Skoda, Marissa Knehans and Linda Drackley harvest garlic at Heritage Farm in Iowa.Seed Savers Exchange co-founder Kent Whealy: Preserving heirloom crops for posterity.