Party sounds float up from a swimming pool in Washington, D.C. Twenty children shout and splash, toss balls, and snack on sandwiches, cookies, chips, and sodas. The guest of honor is nine-year-old Audra Shapiro, who has just finished two years of chemotherapy and whose leukemia is in complete remission. Her recovery from this cancer depended on a plant that originated halfway around the world.

Until the early 1960s Audra's disease would have meant sure death. Now the long-term survival rate for childhood leukemia is above 90 percent, thanks in part to vincristine, a chemotherapeutic drug made from the Madagascar rosy periwinkle. Vinblastine, another drug made from the same plant, helps cure most cases of Hodgkin's disease.

Plants like the periwinkle have contributed