There are curators in this town who are responsible for some pretty important stuff: the Declaration of Independence, Leonardo da Vinci's picture of Ginevra de'Benci and copies of Shakespeare's First Folio, to name a few. Jack Sustic has his own priceless exhibit to fret over, a Japanese white pine tree that began life circa 1625. The pine is different from the other icons: It's alive, meaning it has the potential not to be alive. Sustic, who is curator of the world-class bonsai collection at the U.S. National Arboretum, is ready for every contingency. 'I've packed a suitcase in the hall. If this died, you wouldn't be able to find me. I would be gone somewhere.' It's a jest, of course; he has no intention of letting this or any of the other 300 specimens fail in the arboretum's National Bonsai and Penjing Museum. Penjing is the Chinese art of dwarfing trees, and it predates the more familiar Japanese bonsai. Both are defined by their haunting paradoxes: How can something as large as a tree be rendered pot size, and how can something so old be so small? The Japanese white pine, started just five years after the Pilgrims arrived on the Mayflower, is now about 3 1/2 feet tall and four feet across. I used to think of bonsai as a freakish avenue of gardening, but I dismissed that notion years ago. A bonsai needs continual care and the artistic skills of its owner; the tree repays the debt by becoming, literally, a model plant _ a grove of beech trees, a stately old maple, or a bleached, writhing juniper on some imagined mountain top. For all the playacting, there is a deep and quiet relationship between the plant and its caretaker, and isn't that what gardening is all about? The tree is kept small not so much by the constriction of the roots, or the periodic out-of-container root pruning and repotting, but by the careful clipping of the branches. It is an art that at first establishes the lowest branch as the largest, then creates a healthy array of scaffold branches and maintains a convincing canopy of tapering stems. Even old specimens need wiring every few years to keep the pint-size boughs in their horizontal planes. The trick is to remove the copper coils before they imprint themselves on the bark. Bonsai growers favor species and varieties with naturally undersized leaves or short needles to keep the diminutive scale, gravitating to such trees as the trident maple, Chinese elm, finer-textured azaleas and bristly conifers. But after 15 or 20 years of constant care, many of the trees do something quite miraculous: They obligingly produce smaller leaves. In your yard this is a sign of stress; in the bonsai pot it's the plant's recognition that it is getting the feeding, watering and light levels it needs and can reduce the effort it puts into making foliage. The trees must grow in a free-draining soil to avoid root rot, a condition that also requires a remarkable degree of attention. In winter dormancy, you might water a deciduous bonsai once or twice a month; in high summer it's once or twice a day, or it will decline quickly. In the pavilion, I am drawn to the deciduous trees: the trident and Japanese maples, the elms, the beeches and one eye-catching Chinese quince. Leafless but not lifeless, they reveal a branch structure at least decades in the making. In a trident maple, the base of the trunk flares to surface roots, with ripples in the smooth bark that suggest an old tree. The 1625 Japanese white pine has a stout trunk with bark made of red-brown plates, each framed by fissures lined with light green lichens. The trunk forms the hub for 14 or so ascending branches, themselves diverging into two or three more. Here, on its turntable base, sits a survivor. It was one of more than 50 museum-quality specimens donated to the United States for the 1976 bicentennial, including a Japanese red pine from the Imperial Household that has been in training since 1795. The white pine was donated by a bonsai master named Masaru Yamaki, whose family could trace its horticultural roots to the 17th century and had cared for the tree for at least five generations. Yamaki lived in Hiroshima, and years after its donation, his family members visited the tree at the arboretum and began to give a fuller picture of this astonishing plant. Of all the daybreaks that this tree has witnessed, none was more ominous than that of Aug. 6, 1945. At 8:15 a.m. an atomic bomb exploded over the city. The Yamakis' walled bonsai nursery was less than two miles from ground zero. The property, the Yamakis and their ancient trees were all just far enough from the blast, just, to survive it relatively unscathed. I don't attach anthropomorphic qualities to vegetation, but just to be alone in the quiet presence of this tree is moving, and one cannot help but feel reverence for a venerable and palpable life force. Sustic, who came to know and love bonsai when he served in the Army in Korea in the early 1980s, says the art form has taught him patience and humility. 'Bonsai isn't for everyone, but it can be transformative to your life. It certainly was in mine.' He and his assistant, Aarin Packard, are mindful that they are merely stewards of plants that have received the care of generations of gardeners before and, it is hoped, generations yet to come. Sustic recounts the story of the late Yamaki coming to the arboretum about five years after the tree was donated. He stood in front of it and began to weep, and the curator at the time was mortified that Yamaki had seen some decline. But through an interpreter, he said, 'Everything's fine. The tree is happy here.' 