CELIA THAXTER (1835-1894) planted flowers for pleasure and wrote poetry and prose for posterity. No one reads Thaxter any more, but the flowers have made her immortal.

Thaxter's wild and wonderful flower garden on Maine's rockbound and windswept Isles of Shoals inspired hundreds of the finest works of Childe Hassam (1859-1935), her friend and America's leading impressionist painter. She and her flowers can be seen in living color in an elegant and elegiac new exhibition at the National Museum of American Art.

Hassam was drawn to the artist's colony that Thaxter created on the island where she'd grown up in the glow of the lighthouse her father tended. Hassam built a studio near her celebrated cottage salon, which one friend recalled as so filled with flowers "it was like living inside a rainbow," and continued to paint there for a dozen summers after she died.

A tireless and effective promoter of the art of her friends as well as her own, Thaxter won Hassam's collaboration in illustrating several of her books. She also persuaded him to drop his first name, Frederick, and use the middle name that gives a touch of the exotic to this solid American boy.

When after her death Thaxter's neglected garden became overgrown, Hassam's viewpoint shifted toward the island's barren granite headlands and glacier-scoured slopes, and his attachment to the place was so strong that he kept coming back even after her cottage, his studio and the island's popular resort hotel were destroyed by fire in 1914. If the earlier works were brilliant, some of the later ones are among his most luminous and powerful.

The island inspired over 400 drawings, watercolors and oil paintings, amounting to perhaps a tenth of Hassam's prodigious output ("Think," one early critic said, "of the appalling number of Hassam pictures there will be in the world by the time the man is seventy years old.")

The setting also inspired a number of his negligible nudes-by-the-sea. Hassam often essayed classical studies, but neither mastered the human figure nor ever figured out how to fit his awkward figurines into a landscape. (Co-curator David Park Curry's comment on Hassam's numberless nudes is "Alas.")

But the glories of the gardenscapes, rockscapes and seascapes in the show more than expiate such sins. Hassam bristled at being called "the American Monet," but it's a fair description if not carried too far. The young Hassam studied in Paris, which he called "a huge Coney Island, noisy and dirty," and plainly was influenced by Monet, but there's nothing derivative about his work.

Exhibit designer Georgina Reed has somehow managed to turn the cavernous exhibition space into an echo of Thaxter's garden, complete with twining vines, beds of dried flowers and a cosy reading nook well furnished with appropriate titles. The moment in time that the setting evokes is the morning after first frost, before the warming sun reveals the frozen blossoms to be dead.

Reed had to hand-tint the flowers to match the hues of the paintings, which is not a failing of art but of nature. "Many of Thaxter's friends commented," Curry says, "that when they trasplanted flowers she gave them to their mainland gardens, they never again were so vivid as when they blossomed by the sea."

Thaxter's garden was far-famed, and if you were not artistically talented, the way to win her friendship was to bring her a sack of potting soil. Her garden plan defied the formal conventions of the time, being not just informal but antiformal. Poppies popped up everywhere, and the grounds were a riot of asters, nasturtiums, sweetpeas, marigolds, morning-glory, columbine and scores of others. She purposely planted too much, too early and too late.

Her garden has been partly recreated in recent years by the marine scientists who now maintain a research station on the Isles of Shoals. But of course, because Thaxter also cultivated Childe Hassam, her garden never had died.

CHILDE HASSAM: An Island Garden Revisited -- Through Jan. 6 at the National Museum of American Art, Eighth and G streets NW. Open 10 to 5:30 daily. Metro: Gallery Place.