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."