August 25, 1992

ONE of the most distinctive features of tropical forests is the vines that festoon trees in great tangles or run from branch to branch in a network of aerial highways for the creatures of the forest canopy. This intriguing family of plants plays a vital role in the life of the forest and is a cornucopia of unusual chemicals, yet remains largely a mystery to biologists. One reason for the neglect, perhaps, is that many vines flower only in the inaccessible high canopy. Yet their importance was spotted long ago by Charles Darwin, who published a treatise entitled "Movements and Habits of Climbing Plants" in 1875. To maintain their upwardly mobile life styles, vines have adopted special searching and climbing behaviors. They have radically altered their internal anatomies and devised powerful chemical defenses, which have provided humans with everything from latex to birth-control drugs. In the first comprehensive work on vines since Darwin's essay, researchers have recently published their latest findings in "The Biology of Vines" (Cambridge University Press). "It's hard not to be fascinated with these plants once you see them," said Dr. Francis Putz, a forest ecologist at the University of Florida and a co-editor of the new volume. "It's becoming apparent that depending upon other plants for support has important consequences that are felt in every aspect of the vines' lives, from rooting patterns to chemistry, even their flowering and fruiting cycles. As plants, in some ways they are really odd, since they even have real behaviors." Noel Holbrook, a graduate student in ecology at Stanford University, said vines zipped along as though they had "been liberated in a sense, just crawling around, free from the cares of having to support themselves. But there are difficulties in being a vine; it's not a perfect life style." The life of these so-called structural parasites demands an endless search for trees on which they can slither toward the bright light above the canopy. Unlike self-supporting plants, which can send their shoots and leaves directly up to the sun, vines must find help in trying to escape the shadowy forest floor. Scientists have found that vines send out exploratory shoots that trace circles in the air as they search sightlessly for something to climb. "The tip will grow in a way that moves it, even in completely still air, in a wide circle sometimes a yard and a half in diameter in an hour," Dr. Putz said. Researchers have recently reported that plants can even sense the presence of a nearby support. When a vine's exploratory groping brings it near a tree, even though it has yet to make contact, it begins to extend farther in the tree's direction. Scientists suggest that vines may be able to "smell" their prey, detecting chemicals that are given off by useful supports like trees. But just finding a tree is no promise of making it to the sunlight. Not every vine can climb every tree, and not every tree is the towering redwood a vine might prefer to ascend. Vines that use tendrils to climb can only ascend plants with branches small enough for them to grasp. On the other hand, vines that twine around stems, and can circle the entire trunk, can grip even the slippery, smooth trunks of small saplings and trees. Other vines mount with curved hooks or even touch-sensitive leaves that wrap the necks of their leaf clusters around branches and twigs. If a snared tree turns out to be too short for a vine to reach the sunlit forest canopy, the vine will search for others, often lassoing a whole series of progressively taller trees in its steady ascent skyward. Although vines may drape half the trees in a rain forest, most never find a ticket up and out of the forest shadows. When researchers placed artificial trellises on the forest floor, eager vines raced up their newly found supports. Dr. Putz said that as many as a quarter of the seedlings on the floor of a tropical forest could be vine seedlings that had not yet found supports. Some tropical plants manage to shake off vine attacks by giving refuge to swarms of ants that drag away the soft tendrils of intruding vines. If plants are not able to fend off the vines, they become weighed down and debilitated. When one enveloped tree falls, it will often drag down all the others snared in the vine's far-flung tentacles. Reaching the Top When a vine reaches the forest canopy, it crowns its efforts with a burst of light-catching leaves. A vine two inches in diameter will sprout as many leaves as a tree a foot across. To supply the leaves with water, according to Ms. Holbrook, the vines have wider water-carrying tubes than other plants. Some vines are thought to have life spans of hundreds of years, so they must also be prepared to survive the demise of their hosts. In most plants, stiff water-conducting tubes are bundled together toward the center of the stem, with softer tissues encircling the entire package. In vines, the different tissues are dispersed, enabling the vines to withstand extensive twisting and crushing because their stiff tubes are well padded by the softer tissues that surround them. "We could twist some vines several full rotations before they stopped transporting water," Ms. Holbrook said, "whereas a tree would stop after a quarter of a turn." Observations of small-scale disasters in the forest bear this out. According to Dr. Putz, 1 to 2 percent of the trees in a tropical forest die each year, and many topple over. While only some of the trees sprout again from the broken stem, virtually all the vines sprout. Startlingly rapid growers, vines can move along at a clip of half a foot a day. Some grow as thick as a man's thigh and as long as two redwoods placed end to end. Poised to invade any open space and choke off cleared areas, vines are a major pest confronting forest managers. "In these immense vine tangles, you'll see them smothering bushes, shrubs, seedlings, whatever is there," Ms. Holbrook said. "They're incredible opportunists." Dr. Putz said that particularly large tangles, like the vine forests in Borneo, could span acre after acre. Vines can be a serious obstacle even for those who simply want to get past them. "In some spots, like the sunny sides of rivers, the perfect conditions for climbing plants, there are often curtains of vines that essentially close the forest on its edge, draping down like a green curtain and making entry into the forest somewhat challenging, with several meters of vines to chop through," Dr. Putz said. Food and Medicine Although vines pose a threat to trees, they are also a precious source of food, transport and medication. According to Oliver Phillips, a graduate student in ethnobotany at Washington University in St. Louis, yams and sweet potatoes harvested from vines are two of the major foods that feed people in the tropics. A whole range of other food-producing vines are found throughout the world, including melons, cucumbers and squashes. Vines provide nectar to birds and insects, and their fruits are one of the most important food sources for primates in the American tropics. While Tarzan may have been the only human to get extensive use out of vines for transportation, these bushropes serve as public transit for many other animals, from howler monkeys to ants, that prefer to traverse the forest canopy without setting their feet on the ground. "Without vines, trees a few yards apart would be isolated. As it is, with so many vines around, there are plenty of pathways for animals," Ms. Holbrook said. "It's a highway network up in the forest canopy." Rattans, the climbing palms that provide the raw material for patio furniture and handicrafts sold around the world, have become the most important nontimber forest product in Asia. Mr. Phillips said this multibillion-dollar industry was still largely based on the harvesting of wild vines from the rain forests of Malaysia, Indonesia and the Philippines. Perhaps the most intriguing uses of vines are medicinal. Early studies have suggested that vines as a group may be the best source of drugs in the plant world. Curare, a drug used in surgery, and diosgenin, a steroid used in oral contraceptives, were first discovered in tropical vines. People living in rain forests derive from vines a variety of substances, like poison for darts, ant-bite and snakebite remedies, and drugs to treat diarrhea, conjunctivitis and syphilis. For many Indian peoples in the Amazon basin, vines are a source of hallucinogenic drugs, like a drink called ayahuasca, which is made from the bark of a tropical vine. The importance of these vines in Indian religion can be seen by an extensive field knowledge of these hallucinogen-carrying vines, as well as by the prominence of drug-induced visions in Indian art. As indigenous peoples adopt more modern life styles, they may be losing the knowledge of how to identify vines and pick out the useful ones. Ethnobotanists say that scientists need to make quick use of that source of information because vines can be difficult to classify. "Often all you can see of a canopy vine is a long, thin stem that disappears up into the trees," Mr. Phillips said. "The fact that their leaves and flowers are often in the canopy makes them hard to identify from the ground, and the knowledge about which kind of vine is poisonous and which is medicinal is often the first to go when indigenous peoples lose their traditions." Dr. Putz said: "Whatever science may have to say about them, maybe more than anything, these plants are really gorgeous. They make the exotic atmosphere in movies and novels about the jungle, bushropes hanging everywhere. Even though I've worked on vines for a lot of years, I'm still stunned by the beauty of their form."

Declaring that the nation "cannot afford to waste the talent of one single worker," President Bush said today that he would ask Congress next year to approve a major expansion of Federal job training programs that would provide about $10 billion in additional money over five years. The proposal would provide vouchers that could be used to pay tuition at trade schools, colleges and community colleges for unemployed adults and some others in danger of losing their jobs. The plan is clearly a response to accusations in the political campaign that Mr. Bush has been insensitive to the American work force.

In an unusual show of common cause, five competing diet companies joined forces yesterday to petition the Federal Trade Commission to establish industrywide standards and regulations for fair advertising. They say they want all competitors in the field to operate under uniform and fair rules. But their critics contend that they are trying to stall the commission's enforcement of such regulations.

The 40 miles along Route 1 stretching south from Miami to Florida City were transformed today from comfortable suburban sprawl to a trail of devastation. A drive that would normally take less than an hour was a daylong obstacle course of downed trees, limp power lines, wrecked vehicles and ambling bands of looters. By morning light, it was clear that Miami and points north had been spared the worst of Hurricane Andrew. The greatest damage was in the southern stretch of Dade County and was shared by migrant workers, retirees, struggling young families and the rich.

EVEN as it closes the books on its disappointing Fifth Generation computer project, the Japanese Government is embarking on a new 10-year quest to develop extremely fast computers that can mimic the human brain, understand speech and interpret facial expressions and gestures. When it was started a decade ago, the Fifth Generation Project set off fears around the world, which proved to be unfounded, that Japan would take over the computer industry. The new effort, known as the Real-World Computing Program, is raising some suspicions that Japan is trying to tap into advanced American technology, but for the most part it is eliciting more puzzlement than fear.

U.S. Warns Iran on Iraq The U.S. has told Iran not to exploit a Western plan that would protect Shiites in southern Iraq from Iraqi air strikes, officials said. Page A11. Swindling Fellow Immigrants Using new foreign-language TV shows, newspapers and the Yellow Pages, unscrupulous immigrants prey on fellow newcomers. Page B1. Dollar Keeps Losing Value The dollar fell further, putting pressure on Germany's central bank to lower interest rates. Page D1.

A special congressional panel issued a long-awaited report today accusing President Fernando Collor de Mello of accepting millions of dollars in illegal payments and benefits from business interests and said there was sufficient evidence to begin impeachment proceedings against him. The 200-page report, produced after three months of investigation, deepened the political crisis for the 43-year-old Mr. Collor, who in 1990 became Brazil's first popularly elected president in 30 years after waging a campaign against government corruption.

THE large upstate New York hospital was desperate for help. Flies appearing from seemingly nowhere had invaded the surgical suites, dropping onto patients and operating-room personnel in the midst of surgery. With the hospital unable to stem the invasion, the whole surgical staff walked out in disgust and patients in need of operations had to be transferred elsewhere. The administrator put in an emergency call to Dr. Edgar Raffensperger, a professor emeritus at Cornell University with an unusual specialty. Dr. Raffensperger is an insect sleuth, a cultural entomologist who is an expert on the role that insects, spiders and other arthropods play in people's lives, like it or not. The hospital, needless to say, did not like the flies and asked Dr. Raffensperger to figure out where they were coming from and how to get rid of them -- fast.

The dollar plunged another 2 percent against the German mark today, pushing it to a new low of 1.4015 at the close of trading in New York, even as central banks tried to support the dollar by buying dollars and selling marks. As the mark continued its rise, pressures mounted both domestically and internationally on the Bundesbank, Germany's central bank, to lower short-term interest rates. The Bundesbank raised its discount rate to 8.75 percent last month, while the Federal Reserve Board cut its discount rate to 3 percent in early July.

Trans World Airlines said yesterday that it had reached agreements in principle that could soon transform the privately owned carrier into an employee-owned airline. Plagued by mounting debt and a weak national economy, T.W.A. has faced the perception that it could soon go the way of the defunct carriers Pan American and Eastern. If the agreement is approved by all the interested parties, it will give a new lease on life to T.W.A., which has been losing almost $1 million a day in recent weeks.

In the search for ways to slow the surge in national medical spending, policy makers and economists are paying growing attention to this prosperous industrial city of 232,000 in upstate New York. Health-care experts say Rochester is one of the few American cities that have systems that work. Although medical costs have also been rising rapidly here in recent years, they are still at least 25 percent lower per capita than national levels. And in Rochester, only 6 percent of the population does not have insurance, according to a survey by Louis Harris & Associates, far below the 14 percent national rate.

In another gesture to improve the climate of the Middle East peace talks, Prime Minister Yitzhak Rabin revoked expulsion orders today against 11 Palestinians who were accused of inciting terrorism in Israeli-occupied territories. The action, which overturns orders issued last January by the previous, right-wing Government, came a day after Mr. Rabin announced the release of 800 Arab prisoners and a loosening of some restrictions on Palestinians in the West Bank and Gaza Strip.