He leads me on a tour of his world, which like the greater world, having grown from a simple beginning, has evolved into some wonderful forms. The garden is both terrestrial and a dreamscape, a deliberate arrangement of living things that makes one forget about time and engages all the senses without demanding logic. It is the outer life meant to reverberate in the inner life, which is what it evidently does for Raven.

This oldest botanical garden west of the Mississippi opened to the public in 1859, the same year Origin of Species was published, and was the inspiration of an Englishman, Henry Shaw. In 1819, at 18, Shaw arrived in the river town of St. Louis and took half a day's horseback ride westward until he came to a piece of ground that his imagination claimed. When he became rich 20 years later, he bought the property and turned it into a horticultural display that today, thanks largely to Raven's benign manifest destiny, covers 79 acres and extends its research work over much of the globe.

Raven has a very green thumb. Under him the garden has recently acquired a multimillion-dollar research center from Monsanto, and he is looking toward a $146 million Donald Danforth Plant Center, named for the former president of Ralston Purina. The garden advertises almost as many names of donors as of plants. The library contains 122,000 volumes. Tropicos, a botanical database, attracts thousands of hits a month. When Raven first came to the garden in 1971, he had 85 employees and a budget of $650,000. Today there are 354 people on staff, and the budget is $20 million.

Among the garden's components are an azalea-rhododendron garden that explodes with color--red, pink, yellow and white in April; Linnean House, one of the last buildings constructed by Shaw, where camellias bloom in late winter; a bulb garden (tulips, hyacinths, narcissuses); a scented garden (geraniums and lamb's ears); two rose gardens; a garden for irises and day lilies; a garden for aquatic plants; a Japanese garden; an English garden. The most visually impressive structure is the Climatron, a geodesic greenhouse dome a la R. Buckminster Fuller that rises 70 ft. at the center and measures 175 ft. in diameter at the base. It covers half an acre but appears much larger--a whole tropical rain forest under glass.

Raven and I walk around it beneath a vast green umbrella that looks more lush than a real rain forest. There are a droning of bugs and a loud rush of falling water. We make our way among a density of exotic plants, an endangered Hawaiian plant called alula, a cacao tree, conifers and vines that trap insects. A banyan tree towers on its stilts. A red-and-black bird flits in the branches. "That's something I haven't seen before," says Raven, noting the pale lavender of a particular iris. He stares at the flower with innocent interest. "Stay here long enough," he says, "and you appreciate what Darwin meant when he wrote in praise of differences." A sign at the exit exhorts visitors to save the rain forest "before it is too late." On the way out I am stopped by an orchid whose rose-colored leaves alternate with gold. The leaves are shaped like fragments of bells.

The admiration of the garden's appearance Raven leaves to me and other tourists; he acknowledges that the plants and flowers are lovely, but his attentions go elsewhere. Before he became an eco-administrator and a biopolitician, Raven was a pure and first-rate scientist--still is--and he views science--process--as the garden's most important exhibit. Apart from his grander design of using the place as a reminder that the world calls out to be preserved, his mission is to make the garden the largest plant-research center in the world. Current projects, which are huge, include volumes on the flora of North America and China.