In the midst of the winter doldrums, there is one bright spot for thousands of homeowners: the promise of spring that arrives in the mail with the myriad of seed and nursery catalogues.

Timed to take advantage of the winter blues, the catalogues are carefully written to convey a folksy image of a small family business handed down through generations.

For example, the 183-page catalogue from W. Atlee Burpee Co., one of the nation's largest mail-order gardening concerns, begins with a letter from Jonathan Burpee, the grandson of the company's founder: "My grandfather, W. Atlee Burpee, first trumpeted the famous slogan 'Burpee's Seeds Grow' more than 80 years ago. Since then the phrase has been recognized and trusted by four generations of gardeners all over America."

At the back of the catalogue is a picture of the current Burpee--the only company official to be featured--along with a brief biography that shows he grew up on Burpee's Pennsylvania farm and "has spent all his life in the Burpee Seed business."

Nowhere in the catalogue is there mention of International Telephone & Telegraph Corp., which has owned Burpee since 1979.

Burpee is only one of a growing number of mail-order gardening firms taken over by conglomerates. In recent years, several of the larger and more well-known gardening concerns have been bought by major corporations seeking to diversify into what has traditionally been a low-cost operation with large growth potential, in both good and bad economic times.

Within the past two years, Gurney Seed & Nursery Co. Inc., and Henry Field Seed & Nursery Co. were bought by AMFAC, a Hawaiian-based conglomerate that specializes in food and hotels. To expand its agricultural research, the Celanese Corp. purchased Joseph Harris Co. in 1979.

Meanwhile, Jackson & Perkins Co., the nation's largest rose grower, is a subsidiary of the Oregon-based Bear Creek Corp., which also owns Harry & David, another mail order company that specializes in food. Large corporations also run the gardening firms of Northrup-King and Ferry-Morse.

"When I look around at my friends in the business, I realize I'm the last of the privately owned major mail-order gardening seed companies," comments William J. Park, head of 114-year-old George W. Park Seed Co. Inc., one of the six largest mail-order gardening firms in the country.

"It used to be a very strong, close-knit business" whose executives would meet at gardening conventions and freely discuss one another's problems, he says. But today, the 56-year-old Park laments, conventions are "much more impersonal, attended by lieutenants of the big conglomerates that are scared to say something. . . . I used to have the feeling that if I had a calamity, I could have called on my friends in the industry and they would have knocked themselves out to handle their business and help me from losing mine. Today, I think the industry leaders would just chuckle and say 'We'll beat him.' "

The son of the company's founder, Park says he has no intention of selling his firm. Although his two children are not interested in the business, two nephews and a niece are. "We intend to stay privately owned, and we still anticpate another 114 years of business," he says.

But other companies may not be able to remain viable as small family concerns in an increasingly sophisticated and competitive industry, says Maxwell Sroge, the head of a Colorado Springs publishing company that specializes in the mail-order industry.

"We predict there will be many more mergers and acquisitions happening in the gardening business, especially for the small firms," says Sroge. "They will be able to operate a lot more efficiently by merging together. They will be able to afford more sophisticated computer systems and advanced marketing campaigns."

For large companies, mail-order gardening firms appear to be attractive merger candidates. "They are cash cows," says an official of a large company that just bought a seed operation. For one thing, he points out, cash orders begin to pour in almost immediately after the catalogues are sent out in the winter, even though the requested products may not be shipped for several months. Then, too, "there are no middle men and you can get very, very large margins on many of the products," he adds.

What's more, says Park, larger companies may be looking "further down the road" when they buy companies specializing in vegetable seeds and fruit trees, because food supplies "may be a real problem in this country 30 to 40 years from now. It is a basic industry," in which many firms now want a part, he says.

A Burpee official agrees: "Gardening companies are very attractive businesses because one thing is for sure: we all have to eat."

Additionally, with more and more consumers shopping through the mail, the old, well-established gardening firms are all the more attractive.

Although statistics on the size of the industry are sketchy--almost all firms refuse to reveal their financial figures--it's clear the industry's revenues have been growing at healthy rates for the past decade, usually faster than inflation and even during recessions. According to Sroge's figures, the business had sales of $475 million in 1981, up nearly 15 percent from 1980 sales of $414 million.

However, some industry experts say the figures are far higher because Sroge's figures only include sales of plants, seeds and other live products, and not the gardening supplies many firms now are promoting heavily. With the costs of processing each order practically constant--whether the order is for $10 of seeds or for hundreds of dollars of equipment--companies are trying to push big-ticket items to gain more profits.

Including the gardening equipment, the Mailorder Association of Nurserymen estimates, industry sales totaled nearly $850 million in 1981.

The vigorous growth has brought many changes to the industry, which until recently operated on a relatively small scale.

With the increased demand for their stock, most large and small firms have stopped growing on their premises all the plants they sell. Instead, they buy most of their stock under contract from specialized growers. "At one time, nurseries probably produced everything they sold, from chrysanthemums to rhubarb," says John E. Miller, president of the 50-year-old family-held J. E. Miller Nurseries in upstate New York. "Now, some nurseries only grow strawberries."

There are other changes as well. Fred Van Bourgondien, president of K. Van Bourgondien, a 65-year-old New York firm begun by his forebears, recalls having file cards on all of his customers. "Now, everything is on computer, making the business much more impersonal," he observes.

What's more, he says, his small company, which employs 35 people in the off season and as many as 175 in the spring when orders are being processed, has had to acquire special expertise in publishing--to make sure the colors in the catalogue precisely match the flowers--and in marketing. "We no longer just mail catalogues out. We carefully select potential buyers, targeting zip codes that appear to give us the most likely results."

Even the date of mailing has become a science. "Psychologically, spring arrives about Jan. 9," says Miller, explaining why the catalogues seem to suddenly appear in mailboxes just after Christmas.

"A lot of smaller mail order operations are just now discovering the sophistication they need to be successful," says David E. Schroeder, general sales manager for Stark Brothers Nurseries, the nation's largest merchandizer of fruit trees.

That realization may force many of the old small firms to sell out to larger companies, frets Schroeder, whose company has been run by the same family for 166 years. "It is a major concern of our business."