ON the side of a hill near a waterfall, Paul Martin Brown lies on his back, half inside a cave, shining a flashlight into a rocky grotto. One by one, students climb up the slope to peer into the darkness. The flashlight beam reveals a small growing thing. It is the rare Filmy Fern.
``Looks like the fuzz on a tennis ball,'' says one student.
``It's only a single cell thick,'' says botanist Brown. ``It looks like moss on a rock, but you can just barely see the stem - as thin as a thread,'' he says.
This fern is spread on the feet of bats: They take it by accident to caves, there to be found by intrepid plant hunters like Mr. Brown.
Brown's lectures, part of the New England Wild Flower Society's annual program, often include field trips like this one to Everett, Mass.
Brown has a passionate interest in the world of nature, a genius for observation, and a flair for clearly (and often beautifully) describing his observations and discoveries.
He can identify most if not all of the approximately 3,000 species of plants that grow in New England except, he says, ``for some of the sedges and rushes.'' He has also ``botanized'' in Venezuela, West Germany, Canada, and Israel.
``Paul Brown seems to have an affinity for uncommon plants,'' says Al Bussewitz, an educator, naturalist, and past president of the Thoreau Society. ``Paul is a real detective where endangered plants are concerned,'' he continues. ``If you want to know where rare and unusual plants may be found, he knows the exact spots.''
``I'm only happy when I'm working with plants, more so the wild plants,'' says Brown. ``I've always wanted to find and observe them as they grow naturally.''
Growing up in Foxboro, Mass., Brown looked for plants while other kids played baseball. Once at an outing at Wallum Lake in the state forest on the Massachusetts-Rhode Island border, he found Pink Buttons, identifying it from his ``Gray's Manual of Botany.'' Much later, an adult botanist wrote up the ``rediscovery'' of the flower.
Brown didn't know it was lost, for he was only 12.
More recently, Brown found a dwarf witch hazel in Connecticut, a mutant and not a new species. He watched it for some time before taking cuttings to Harvard University's Arnold Arboretum, where it was grafted to standard witch hazel. The new form will be small and good for gardens, he hopes, but it will take a few years of growing. If successful, a scientific name pending publication might well include the name of the finder: Hamamelis virginiana forma pumila P.M. Brown.
Brown is a fearless, indomitable proponent of saving endangered plants.
``A dozen or more plants have disappeared from New England in the past 25 years, most the result of building developments, factories, malls, and highways,'' Brown says.
He constantly reminds students not to pick wild plants, and to question the background of nurseries that sell wild plants to be sure they haven't been taken from the wild indiscriminately.
Students in Brown's classes saw breathtaking drifts of graceful pink flowers - Plymouth Gentian and Rose Coreopsis - on the sandy shore surrounding Mary Dunn Pond in Barnstable, Mass.
But when Brown returned that afternoon, flowers had been destroyed, and the area was muddy and rutted from four-wheel-drive vehicles, despite signs prohibiting vehicle access. Luxury homes are slated to be built on one side of the pond.
``In this rich, glacial kettle-hole, there are 17 rare endangered plants and several endangered butterflies and dragonflies,'' Brown says.
Among the botanical rarities here was the Common Pipewort, which looks like a tiny geodesic globe on a spiky stem. This plant literally goes up and down with the water level. The stem gets twice as tall when the water rises, with the head above water. It shrinks when water recedes.
One of Brown's first encounters with endangered plants occurred when he was young. Hazel Bourne, a childhood neighbor, had one of the best wildflower gardens around. He was forbidden to go in her yard, but one day he couldn't resist picking a few yellow lady-slippers for his mother's birthday.
His mother was pleased but made him take them back and confess. Mrs. Bourne then explained why he should not disturb lady-slippers and gave him other flowers instead. ``It was an important event for me,'' Brown explains.
``If she had been angry, it might have changed my attitude, but instead it only furthered my interest in rare and endangered plants,'' he says.
Nature lovers know that the pink lady-slipper is a common orchid. Few, however, know there are some 50 species of wild orchid growing in the Northeast.
Of this elite group, the rarest is the Small Whorled Pogonia. There are 49 sites where it is found in North America, ``including eight small populations along the Spaulding Turnpike in New Hampshire and a few in short distance of Route 128 in Massachusetts,'' Brown says.
The spectacular Orange-fringed Orchis is one of the most highly sought-after wild orchids and is rapidly disappearing in New England.
It was a rare treat for a Brown-led field trip to see a New England field with about 2,500 blooms of this rare, exotic plant in a natural (and protected) setting in south-central Connecticut. Rare here, it is also found in some parts of southern United States and in the Carolinas.
Armed with cameras, binoculars, and magnifying glasses, today's naturalists capture their prize on film. That which is rare and choice in New England, of course, may be common in the Carolinas and vice versa.
Brown's stories of finding plants in hard-to-get-to places, from mountains to deserted islands to marshy bogs, are endless. He adds points of interest that help students identify habitats and the plants on his enormous collection of about 40,000 plant slides.
Brown tells of a week-long trip on an island in Lake Superior where there was only a small cabin and a lighthouse. The island was being sold, and a nature conservancy wanted Brown to make a survey of the plant life. He was set down alone by seaplane, and the very first day he was thrilled to find a whole field of rare Moonwort. There were thousands - and here he was all alone and nobody to tell of his wonderful find.
But Brown's unique plant information is not limited to difficult, out-of-the-way spots.
``Fringed gentian is a lovely blue plant, and there are three miles of it on the right-hand side of the Massachusetts Turnpike going west, between exits 3 and 2,'' he says.
``Road crews mow it, but the gentian grows low, and it's like a blue carpet in September and October. Watch for it.''
Most of Paul Martin Brown's lectures are in collaboration with Harvard University's Arnold Arboretum (Jamaica Plain, Mass.), the Massachusetts Horticulture Society (Boston), and the New England Wild Flower Society (Framingham, Mass.).