The Botanist and the Rain Forest : ONE RIVER: Explorations and Discoveries in the Amazon Rain Forest by Wade Davis; Simon & Schuster $27.50, 537 pages

The rapid destruction of great parts of the Amazon rain forest has become a matter of great concern to the world. This book explains why.

Not explicitly. It mostly tells the story of botanist Richard Evans Schultes.

He is, Wade Davis writes, “the greatest ethnobotanist of all, a man whose own expeditions . . . earned him a place in the pantheon along with Charles Darwin, Alfred Russel Wallace, Henry Bates, and his own hero, the indefatigable English botanist and explorer Richard Spruce.”

With that single-minded devotion that geniuses possess, Schultes, now 81, explored for plants, almost continuously in the field, from 1936 to 1953. First he identified ololiuqui, the long-lost Aztec hallucinogen, and collected the first specimens of the sacred mushroom of Mexico, teonanacatl.

Then in 1941, Davis writes, Schultes “disappeared into the Northwest Amazon of Colombia.”

“Twelve years later he returned from South America,” Davis says, “having gone places no outsider had ever been, mapping uncharted rivers and living among two dozen Indian tribes while collecting some 20,000 botanical specimens, including 300 species new to science.

“The world’s leading authority on plant hallucinogens and the medicinal plants of the Amazon, he was for his students a living link to the great natural historians of the 19th century and to a distant era when the tropical rain forests stood immense, inviolable, a mantle of green stretching across entire continents.”

A generation later the author, who has a PhD in ethnobotany, and his older friend and colleague, the late Timothy Plowman, both students of Schultes’ at Harvard, traveled in roughly the same places, living with various Amazonian tribes and looking for the origins of coca, the plant from which cocaine is derived.

Ethnobotany is the science of peoples’ plant lore. The Amazon teems with species of plants, and the indigenous tribes of the Amazon and elsewhere in the continent possess knowledge that has already contributed greatly to the health and healing of mankind: quinine, for instance, for malaria.

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The implicit message of this book is: Destroy the great mass of diverse life that is the rain forest, and you put the future of life at risk.

Davis’ tale shifts back and forth between Schultes’ travels and the later expeditions of Davis and Plowman. Though the transitions between the two are not always smooth, the contrasts between the earlier and the later journeys tell the tale of the growing “development” of the Amazon. There is less forest, but more drilling for oil.

Not all the trips in this book are by canoe or on foot or in tiny airplanes. Schultes experimented with the hallucinogens the many shamans found for him. Chiefly through his efforts, Harvard in the early ‘50s became the leading center for hallucinogenic research.

Davis details what Schultes said of his many psychedelic experiences, the swirling colors, purples deeper than deep, fantastical transports into realms unimagined, and so forth, but the descriptions are oddly unconvincing. Much more authentic-sounding are the accompanying racking vomiting and violent headaches that you would readily trade for the worst hangover you ever had.

Davis and Plowman partook too and once nearly died of a jungle drug.

If Davis makes no judgments on these experiments, he has definite views on coca. Not coca as it is when turned into the strong addictive drug cocaine, but coca as it has been used for millenniums by Indians of the Andes and its Amazonian slopes.

American-inspired efforts to stop the growing of coca, he believes, will never succeed. Coca leaves, he argues, are not a drug “but a food and mild stimulant essential to the adaptation of the Andean people.” “In the Andes to use coca is to be Runakuna, of the people. Take away access to coca, and you destroy the spirit of the people.”