WHEN Mary, the heroine in Frances Burnett's "The Secret Garden," opened the door to that secret garden, her young readers were enchanted by what she saw: "The high walls were covered with the leafless stems of climbing roses, which were so thick they were matted together. ... It was this hazy tangle from tree to tree which made it so mysterious." That garden filled a need that all of us have, for a place secret and private, and filled with green growing things.When I was a child, my own secret garden was the green leafy room beneath the drooping branches of a live oak tree that stood at the edge of the lawn, just beyond the garden. It was a Southern garden filled with old-fashioned scented flowers with old-fashioned names: snapdragons, sweet peas, candy tuft, larkspur, pinks, love-in-a-mist, and bachelor's buttons, flowers spoken of as "old-fashioned" when our mothers, aunts, and grandmothers were planting gardens. Describing something as "old-fashioned" is no t to impart some out-of-date virtue or the "old times there are not forgotten" school of Southern gardening, but simply to describe flowers that colored our lives in a simpler time. Southern gardens are as unique and elusive as the Southern mystique. And the memorable ones are old-fashioned with scented flowers that bring summer to our hearts. At the heart of each garden is scent, what someone has described as a power without a name - a mystery, a sacredness. People who are anosmic, who have no sense of smell, do not garden in the same way as those of us who are hyperosmic. They must miss the sense of d vu on suddenly being assailed by the fragrance of wet acacia, or the wild fragrance of early hyacinths brought into a warm, winter room, or the tender sweetness of wisteria blooming in lavender panoply in the branches of old trees. Louise Beebe Wilder, a gifted gardener writing about scented plants, said in "The Fragrant Path" that fragrance "speaks more clearly to age than to youth... . With the young it may not pass much beyond the olfactory nerve, but with those who have started down the far side of the hill it reaches into the heart." It is memory created by the older for the young that holds and brings us back, time after time, to that precious place. Years after the death of her beloved mother "Sido," Colette would write about her childhood years in her mother's garden in France. Remembering a packet of love-in-the-mist seeds in a twist of paper in the bottom of Sido's pocket that "made a sound like rain and fingernails scratching silk as she walked." Colette, who may write of flowers and gardens better than any other writer, tells us, "Many a garden has left its memory with me." Each garden is marked by the personality of its gardener. A year or so ago, a friend and I had driven to a nursery not far from where we lived. We'd spent the best part of the morning, going up and down the rows of beds, admiring the plants, pinching leaves of herbs, discovering treasures. When it was time to go and we'd each chosen our plants, she suddenly looked at the wagon filled with my choices: rosemary, dianthus, lemon thyme, lamb's ears, scented geraniums. "Good grief," she said. "Does everything you plant have to sprawl?" Her plants, neat and tidy, mirrored her personality while mine, I saw with some dismay, mirrored mine. There is something intimate and private about each garden which, as Colette said, "Everyone creates in his own image." For me, a garden without scent is a hollow heart. We can't really describe scent, but only the emotion it engenders. Helen Keller wrote of her days in the South, "Even as I think of smells, my nose is full of scents that start awake sweet memories of summer gone and ripening fields far away." She has called this sense of smell "the fallen angel." Memory is triggered by smells: The scent of night-blooming lilies, faintly decadent and languorous, recalls hidden courtyards of New Orleans; the intense creami ness of lotus blossoms conjures up a hidden pond and a dress of pale blue organdy fashioned by my grandmother, a seamstress with an Alabama softness and a quicksilver needle. A Catherine Mermet rose takes me back to summer afternoons when as children we used to color in the garden, the smell of crayons waxy and warm in the sun. Remembered gardens are not the formal, carefully tended beds attached to fine plantations of the South. But gardens with wildings that sprawled, tangled, and had no place in formal beds. Old-fashioned gardens where honeysuckle perfumed hot summer nights and gardenias with buds like tightly furled green fairy umbrellas bloomed suddenly, their waxen, creamy fragrance sensuous and compelling. These flowers never bear the onerous description "improved" in a gardening catalog because they aren't. Geo. Parks' catalog, the Southern gardener's testament, still offers these old flowers to its customers along with poetry and a bit of philosophy. I remember one issue showing gypsophila in clouds of pink and white and offering a poem by Emerson All my hurts/My garden spade can heal." At some point, annuals imported from the tropics and subtropics of Mexico and South America became fashionable in this country. Marigolds, red salvia, ageratum, coleus, and showier scentless flowers took the place of the less showy sweet peas, stocks, and pinks. These flowers that border well-tended suburban lawns have nothing that in later years will evoke a particular quality of moonlight, a mockingbird's call at dawn, or the poignancy of something lost and not returning. The heart, the mystery of a garden, is held in its fragrance, in the way that a tiny seed holds the promise of the flower to come. Judy Collins has a wonderful song about "secret gardens of the heart," which is what we carry into adulthood if we were fortunate enough to have known gardens and their bordering fields of wildflowers. Primroses, whose pale pink-veined petals drifted along roadsides; a haze of blue larkspur, shimmering in the sun, dotted with yellow Monarch butterflies, and phlox, the petals like crimson velvet, picked in ragged bouquets by children. Southern gardens were planted primarily by women and were works of art in the same sense that a quilt, handmade with love, is a work of art. The Sweetbriar was the first rose to bloom in spring; it grew up the side of the chimney and smelled of fresh apples. The Marechal Neil, with its haunting scent of orris root and tea, was brought as a cutting by a new bride from the "old home place," and nurtured to shade Southern verandas. The Lady Banksia, thornless, its white or yellow blossoms drifted over balco nies and porches and climbed into flowering trees. While the Cherokee rose, with a faint scent of gardenia, was already native to our land when discovered by new settlers. These flowers are memory's bouquets, held in time. Summer is windows opened onto dark rooms, sheer curtains puffed outward by the breeze that carried on it the fragrance of Southern gardens. Remembrance of those gardens drifts in memory in a vespertine stillness, waiting to be recalled.