hen Mark Plotkin first landed at the edge of the rain forest of southwest Suriname, north of Brazil, his pilot gave him this advice: ''Stay away from the women. If you do not, the men will come after you, and all their arrows have poison tips. Have a good trip, and I'll see you in two months.''
The plane flew away, leaving the 27-year-old Tufts Ph.D. candidate surrounded by Tirio Indians, clad in red breechcloths and harpy eagle feathers and bristling with poisoned arrows.
The Tirio called the pale-skinned student from Boston ''pananakiri'' - ''the alien.'' But his mission was even stranger: He had come to apprentice himself to a witch doctor.
It was 1982, and he was one of the first of a new generation of scientists in a field that most people had never heard of: ethnobotany, combining anthropology
with botany to study how people use plants as medicines.
Today, ethnobotany is no longer obscure, thanks in no small part to Plotkin, now 43.
''More than anyone, he's popularized ethnobotany, and the importance of oral natural history of indigenous people,'' said Michael Goulding, a University of Florida expert on Amazon fishes.
In fact, some researchers privately grouse that science shouldn't be popularized Indiana Jones-style, and object to Plotkin's showmanship. ''It takes courage to do that, especially as a scientist,'' said Goulding. ''He's going to take some heat for that, like Carl Sagan'' (who was repeatedly voted down for membership in the National Academy of Sciences amid criticism of his efforts to popularize science). ''But his work has been really important.''
Plotkin's 1993 book, ''Tales of a Shaman's Apprentice,'' has gone through 15 printings. His first book for children, ''The Shaman's Apprentice,'' co-authored and illustrated by Lynne Cherry, was published in April and is being hailed by reviewers as the best book on the rainforest for children.
On Friday, Plotkin returns to Boston, where his exotic career began, for the opening at the Museum of Science of a large-format Omnimax film featuring his quest for herbal medicines. Nominated for an Academy Award, the 45-minute film ''Amazon'' has drawn record crowds at the American Museum of Natural History in New York and large-screen theaters from Munich to Taipei.
''Mark has done more than anybody else to get this message across to audiences that might not intrinsically care about rain forests and indigenous cultures,'' said crop ecologist Gary Nabhan, director of science at the Arizona Sonora Desert Museum. ''He can make that connection - a living bridge between modern science and indigenous science.''
Until a decade or so ago, ''indigenous science'' was dismissed as mumbo-jumbo. But as Plotkin points out, ''the line between magic and medicine can be very thin.'' Studies of plant chemistry show not only that many herbal cures do work, but also why: Particularly in the buggy tropics, plants have evolved a chemical warfare arsenal against leaf-munching insects. Those chemicals can profoundly affect the human body as well, with effects ranging from the kick of caffeine to the lethal toxicity of strychnine, from the addictive compounds in heroin to the painkiller in codeine.
Amazonian herbalists have known this for centuries. In the foreword to Plotkin's first book, Richard Evans Schultes, the Harvard professor emeritus who is credited with founding ethnobotany as a science, wrote that one of Plotkin's ''outstanding qualities'' was ''his conviction that among the Indians, he is the student and they are the teachers.''
Plotkin, in turn, says he learned this conviction from Schultes - the man Plotkin calls ''The Great White Witch-Doctor,'' and the first shaman to whom he apprenticed himself.
As a young college dropout working as a curatorial assistant at Harvard's Museum of Comparative Zoology, Plotkin signed up to take a night course with Schultes. A slide from the first lecture changed Plotkin's life.
''These are Yukuna Indians doing the sacred Kaiyahree dance under the influence of a hallucinogenic potion,'' the tall, white-haired Schultes narrated, projecting an image of three men wearing bark masks and grass skirts. ''The one on the left has a Harvard degree. Next slide, please.''
From the moment he saw his mentor in the photo, says Plotkin, he knew what he wanted to do. But becoming an ethnobotanist meant much more than learning plant chemistry in the classrooms of Harvard, Yale, and Tufts. At times, Plotkin discovered, his work demanded that he pick squiggling worm larvae out of bubbling pots and eat boiled rats with the whiskers still on. He's participated in tribal festivals and ceremonies, festooned himself with macaw feathers and anteater claws, and let himself be painted with dark blue ink for festivals (ink that, he discovered on his way back to the States, does not readily wash off.)
Sometimes he has been welcomed more warmly than he expected. When he first introduced himself to a shaman of a tribe of Yanomamo Indians on the Brazil-Venezuela border, the witch doctor smiled, took down a long bamboo tube from the rafters of his roundhouse, inserted the end into Plotkin's right nostril and exhaled forcefully. The researcher spent the rest of the day wildly hallucinating with his new-found Yanomamo friends.
''You come to build up a relationship based on trust, friendship and even love,'' said Plotkin, ''before they'll open up to you and teach you the secrets of the forest.''
Over the last 50 years, those secrets have yielded a number of drugs now used in Western medicine. The most effective chemotherapy drugs for childhood leukemia, vincristine and vinblastine, are based on the rosy periwinkle, which Malagasy healers used to treat diabetes. Epibetadine, an experimental new painkiller, is made from the toxic secretions of a rainforest frog. A compound extracted from the Amazon's dragon's blood tree became the basis of the experimental herpes drug Virend, which is featured in the film.
But as some 90 other ethnobotanical research projects vie to extract new medicines from the tropics, Plotkin is focused on preserving vanishing tribal knowledge and lands. By some estimates, a patch of rain forest nearly the size of the Boston Common is destroyed every 90 seconds; 10 percent of the world's plant species may be extinct by the millennium. No fewer than 90 tribes in Brazil alone have also gone extinct in this century.
''Every time one of these medicine men dies, it is as if a library has burned down,'' Plotkin said. ''In fact, it's worse than that, because this is knowledge that is recorded nowhere else. When these men die, this knowledge is lost forever.''
In an interview, he recalled that he saw this firsthand among the Tirio, who taught him herbal cures for eye ailments, colds and sore throats, and deep fungal infections of the skin. By the time he left, they no longer called him ''pananakiri'' but ''jaco'' - brother.
But when he returned to the village in 1994 after an absence of several years, Plotkin was dismayed to find that missionaries had convinced the Tirio that their medicine was inferior.
Plotkin found his Tirio friend Amasina red-eyed with conjunctivitis. Plotkin was traveling with a Mexican doctor, a fellow ethnobotanist. The physician had run out of antibiotic cream, but he had recognized an herb growing on the airstrip: in Mexico, it is called golondrina, and local healers use it to cure conjunctivitis.
The doctor squeezed some of the sap into Amasina's eye. Plotkin asked his friend if he knew the plant.
''Yes,'' said the Tirio. ''And did you once have a medicinal use for it?'' Plotkin asked. ''Sure,'' he replied. ''We used to use it to treat red-eye.''
Incidents like these ignited the Shaman's Apprentice program. Begun in 1987 when Plotkin was chief ethnobotanist for World Wildlife Fund, the program provides young men and women in forest societies with the funds they need to make it their jobs to learn from traditional healers. Funded in part by proceeds from Plotkin's first book, the program currently supports apprentices in Costa Rica, Colombia, and Suriname. Guaymi Indians walked dozens of miles from Panama through the jungle to see for themselves how the program was working in Costa Rica - and decided to begin a similar program of their own.
To augment those efforts, Plotkin in 1995 founded the Ethnobiology and Conservation Team. Its officers and consultants, who draw little salary and no benefits, work in the villages and outlying jungles with their indigenous colleagues, training apprentice shamans and lobbying to protect forest dwellers' traditional lands from timbermen, miners, ranchers and farmers. The point, says Plotkin, is to ''marry the ancient wisdom of the shamans to 21st century technology to reinvent the conservation agenda.''
Shamans from different tribes also learn much from one another, like Western scientists at scientific meetings. In July, the Ethnobiology and Conservation Team facilitated a meeting of six shamans and 12 apprentices from the Ingano and Correguaje tribes in Colombia.
The value of such cross-cultural exchange forms the storyline for the film ''Amazon.'' At the same time that Plotkin sets out for the Amazon, the film portrays a tribal shaman from the Andean highlands of Bolivia setting off downriver on a similar quest. (The Bolivian shaman is played by a Bolivian musician; Plotkin explained the tribe couldn't spare its shaman for the six months it took to shoot the film.)
''Traditionally, people are considered the conservation problem,'' said Plotkin. ''People kill animals. People destroy habitat. But the beauty of ethnobotany is it shows that people are not only a threat to the forest, but people, and particularly so-called primitive people, are going to provide us with many of the answers.''
Sy Montgomery is an author and naturalist who lives in New Hampshire.
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Mark Plotkin will read from his new book at the Boston Museum of Science Friday, Sept. 25, at 3 p.m. at the opening of the film ''Amazon.'' The reading is free. ''Amazon'' will be shown at 2, 4, 6, 8, and 10 p.m. Friday, and thereafter at various times m. daily through December. Call 617-723-2500. Tickets are $7.50, $5.50 for children and seniors.
You can visit Ethnobiology and Conservation Team's Web site at http://ethnobotany.org
