In this ready-to-eat, Seal-A-Meal, Brown-'n-Serve age, we tend to forget that turkeys don't incubate in supermarket poultry cases or that sweet potatoes don't grow on produce shelves. Thanksgiving, a celebration of the harvest, is losing its roots.

Turkey parts are becoming a staple for all seasons. Still, we eat over 60 percent of the whole birds sold annually on one day of the year. And according to the United Fresh Fruit and Vegetable Association, there are more brussels sprouts, cranberries and sweet potatoes available during the month of November than at any other time of the year.

While the harvest of Thanksgiving fruits and vegetables obviously coincides with the holiday, modern agriculture has manipulated mother nature just enough to make the dinner fit. How do we get all those turkeys together every year on that last Thursday in November?

Our connection to the food chain gets further and further from the Pilgrims' experience. Here then, is how we give thanks, supermarket-style. The Turkey

Dave Goldenberg, director of industry relations at the National Turkey Federation, can tell you everything you always wanted to know about turkey. And more.

Turkey farming has followed the saga of the rest of American agriculture, says Goldenberg. As agriculture has gotten larger, it has been transferred into the hands of fewer, larger producers. Whereas the federation used to have 10,000 members, it now has 2,000, Goldenberg says.

Still, the producers are not large enough to meet the huge Thanksgiving demand with fresh birds, so turkeys are raised in advance of the holiday, slaughtered and frozen. Supermarkets start making claims on turkeys in late August or early September, when they are either stored by the processor or shipped to the market's storage facilities. At the beginning of November, the orders start coming in for fresh birds.

The typical American Thanksgiving turkey starts its life as a fertilized egg on a farm that probably raises about 50,000 birds annually. Hens are induced to lay the eggs by being placed in a controlled environment with artificial light, which is slightly increased each day to simulate the increasing hours of light associated with spring, the birds' natural laying time.

A physiological reaction is triggered in the photo-sensitive birds, and they lay eggs -- at the rate of one per day. The fertilized eggs go into an incubator by April or May. It takes about 27 days for the bird to hatch and from 16 (for a hen) to 19 weeks (for a tom) to reach market size.

Turkey producers must decide, however, whether it is economical to keep their hens after their initial 25-week production cycle and to molt them, a sort of a rest period until their next, slightly less productive laying cycle. Or they may decide to slaughter them instead.

After the toms are finished fertilizing and the hens finished laying, you won't find these breeders sold in the supermarket, says Goldenberg. Most whole turkeys are sold young and breeders may be up to a year old before they are past their prime. Their meat, which becomes tougher as they age, is turned into processed foods, such as soups. (Hens that have surpassed their egg laying prime are called "spent.")

The turkeys sold in supermarkets are both hens and toms, says Goldenberg. According to the Turkey Federation, there is no taste difference between the two birds; their differences are size only.

In fact, throughout the year, tom turkeys are used more than hens for processed items such as turkey ham and turkey hot dogs, says Goldenberg, since they contain more meat. That makes them more cost efficient.

Once the turkey has reached market size, has been slaughtered, stored, frozen or possibly kept fresh, it is shipped to the supermarket. The wholesale price, determined between the buyer and seller or supermarket poultry buyer and the salesman from the processing plant, is reported and verified by two market reporting agencies, the USDA and Urner Barry. This stabilizes wholesale and retail prices and keeps the industry informed. The negotiated price is a result of supply and demand as turkey producers do not receive federal support.

Once in the supermarket, turkeys are considered "loss leaders," as stores intentionally sell them below their costs during Thanksgiving. The turkey is the bait to hook consumers into buying other holiday foods, such as pumpkin pies, and perhaps some of the following side dishes. The Trimmings

What was once a straightforward task of hunting or planting and then gathering and eating food has turned into a complicated production and distribution system. From produce farms to marketing firms to terminal market receivers to brokers to wholesalers to foodservice outlets and finally to the consumer, it's now a multi-layered system. Here's how it all works.

Sweet potatoes: Despite popular confusion, yams and sweet potatoes are as different in species as people and dogs, says L. George Wilson, professor of horticulture at North Carolina State University and chairman of the National Sweet Potatoes Collaborators Group, an organization of scientists who does research on sweet potatoes.

According to Wilson, the confusion arose in the 1920s and '30s when agricultural specialists developed an orange-fleshed, moister and sweeter potato than the whiter, dryer sweet potatoes that had thus far been grown. Since it was a new product, a new name was warranted, says Wilson, and "yam" was adopted. Only problem was, yams are another vegetable, grown in Africa and the Caribbean, that have a woody, bark-colored skin, are slightly fuzzy and have cream or yellow flesh.

As it stands now, according to Wilson, what are grown domestically are sweet potatoes. Although a limited number of yams are raised in this country, most are imported. And because of the possibility of insect infestation from other countries, no sweet potatoes are imported to the U.S.

The life cycle of a Thanksgiving sweet potato begins around April. According to Wilson, the "mother roots" (actually the potato itself, no seeds are planted) are then placed in beds and covered with soil and plastic. By May or June, the plants that grow -- which are actually vines about a foot long -- are harvested and planted in fields. U.S. growers plant about 13,000 plants per acre, says Wilson.

During the next four months or so, the underground vines grow, sprouting new potatoes. Interestingly, there is no termination to their development, says Wilson; it can grow "as big as your head." Farmers simply interrupt the growth cycle by harvesting potatoes at a marketable size. But Wilson says he has seen sweet potatoes in the tropics that are as big as watermelons.

After harvest, the sweet potatoes undergo a curing process for about a week, during which the vegetables are stored at hot and humid temperatures. A new layer of skin is formed, the moisture is trapped inside and the starches are converted to sugar. This curing process allows us to eat sweet potatoes all year round, according to Wilson, because what is not eaten during the fall can be stored and eaten through the winter, or planted as "mother roots" for the next season.

It's been a good year for sweet potatoes, says Wilson; there's a high supply in the marketplace and they should be more economical than usual.

Brussels sprouts: Years ago, there was a brussels sprouts promotion board, according to Vince Rubatzky, extension vegetable specialist at the University of California at Davis, and Thanksgiving was a big "push" time for the "not well known" and "not well appreciated" vegetable. But it was difficult to verify whether consumption really increased, so the association was dissolved.

Nonetheless, the United Fresh Fruit and Vegetable Association reports that more brussels sprouts are available during November than at any other time. Turns out, that's the height of the harvest, according to Rubatzky.

The mini-cabbages grow on the cool coast just south of San Francisco ("they're not happy unless they can see the ocean," Rubatzky says), and take six or seven months to reach maturity.

A typical California brussels sprouts farm ranges from about 100 to 200 acres, according to Rubatzky, and farmers who grow them don't raise much else.

Cranberries: Cranberries grew wild when the Pilgrims got here; in fact, cultivation dates back only about 100 to 150 years, according to Irving Demoranville, director of the Cranberry Station in East Wareham, Mass., a field station of the University of Massachusetts. But it's some of those same cranberry bogs that are providing the fruit for your cranberry bread and cranberry sauce this Thanksgiving.

The berries are perennials, which lie dormant during the winter. The growing season starts in late March, the plants flower by late June and then green berries appear in early to mid-July, says Demoranville. Harvesting begins in mid-September and continues into mid-November, he said.

While Ocean Spray is a 700-member co-op, including growers from five states, most of the fresh cranberries come from either Massachusetts or Wisconsin, says Skip Colcord, manager of consumer affairs at Ocean Spray. In Massachusetts, the bogs are harvested by the dry method; in Wisconsin it is called water-raking. The berries from the bogs that are flooded, or wet harvested, are not sold as fresh fruit, but are frozen for future processing, according to Demoranville.

After harvest, cranberries are delivered to receiving stations, where they are cleaned, sorted, separated and frozen, if not sold as fresh. Throughout the year, they are delivered to processing plants, where they are made into sauces and drinks. Ocean Spray has six processing plants around the country, according to Colcord.

Although the holiday season is the largest consumption period for the fresh berries, cranberry juice drinks and juice combinations comprise the largest segment of our cranberry consumption, says Demoranville. The cranberries made into juice are first frozen for a minimum of 30 days, he says, which permits a better return of juice once they are defrosted. (Cranberries freeze well; just don't wash them before putting the plastic bag in the freezer.)

The cranberries processed into commercial sauces for this Thanksgiving and Christmas most likely have just been harvested, according to Demoranville and Colcord. Refrigerated, fresh cranberries have a shelf life of up to three months.

Cranberry sauce didn't become a major selling item in this country until the early 1950s, says Demoranville, and cranberry drinks didn't come on the scene until the '60s, but both are now consumed in far larger quantities than the fresh fruit -- the way the Pilgrims most often ate them.