CASCO, Maine -- Mushroom hunter Sam Ristich shouts ''Hallelujah!" or ''Holy cow!" as he tramps through the Maine woods finding uncommon beauty in fungi, lichen, and slime mold.
On a recent outing to Mayberry Hill Preserve, Ristich led a group of 29 amateur mycologists on one of his walks, teaching by the Socratic method -- ''What's on this log?" ''What's this fuzz?" ''Who knows the genus?" -- and inspecting particularly interesting finds with a magnifying glass.
At 89, Ristich, his limbs gnarled like an old apple tree, needs oversize eyeglasses, hearing aids in both ears, and a back support belt. But his knowledge is encyclopedic and his enthusiasm ageless.
While mushroom walks have become popular among epicures, true fungiphiles like Ristich look for all species, not just edibles, and ooh and aah over minutiae and strange growths on rotting wood that look nothing like a typical capped mushroom. To them, a mushroom foray is a hunt for treasures with Latin names like Leucocoprinus luteus (yellow parasol), Suillus americanus (white pine bolete), and Trametes versicolor (turkey tail).
''I'm not out only for a mushroom walk, I'm out for a walk of wonderment," said Ristich, who has a doctorate in entomology from Cornell University. ''I look at everything. You must look above, and below, and on all sides."
In New England, wild mushroom collecting begins in May with short-lived morels like Morchella esculenta (yellow morel) and Morchella elata (black morel), prized as delicacies. But the peak season traditionally runs mid-July through October for most of the approximately 2,000 species cataloged in the area. The best time to go is four to 10 days after significant rain.
In Maine, Ristich said, picking has been erratic this season due to lengthy dry spells.
While it's impossible to know how many hunters gather mushrooms in the woods, either singularly or in groups, a spokesman at the Northeast Mycological Federation Inc., an organization consisting of 18 clubs that have sprouted up from Canada to Pennsylvania, said affiliated groups average 140 members.
Portobello, shiitake, and other cultivated varieties found in restaurants and on grocery store shelves have whetted consumers' appetites, collectors say, though less than a quarter of a typical harvest on leisurely walks like the one led by Ristich is edible.
''My primary interest is in finding stuff I can put in the pan," said 69-year-old Anne Rugh of Portland, a Persian rug dealer along for the outing, ''but I can't help being drawn into the rest of it."
Affectionately nicknamed the ''Mushroom Guru" (or sometimes the ''Guru of Sligo Road," after the street on which he lives), Ristich has achieved ''mycogod status" among an elite subgroup of hard-core mushroom aficionados.
''If you're walking with him and there isn't anything conspicuous in front of you, he'll see a log. Then he'll show you five mushrooms on the log you hadn't noticed," said Gary Lincoff, 62, of New York, author of ''National Audubon Society Field Guide to North American Mushrooms" and a friend of Ristich for more than 30 years. ''He's the greatest -- has always been and will always be."
Indeed, Ristich is such a legend among mushroom fanciers throughout North America that he has had a local nature trail, a regional mushroom foray, and even a mushroom species named in his honor.
He offers monthly nature hikes, April-November, along the half-mile Sam Ristich Nature Trail off Route 9, not far from the ramshackle, white clapboard farmhouse on 26 wooded acres along the Royal River in North Yarmouth that he shares with his wife of 59 years, Ruth, 91.
In 1981, Ristich retired from his job as a pesticide research scientist and the couple relocated from Ithaca, N.Y. They have five children, six grandchildren, a newborn great-granddaughter, and a house crammed with hundreds of dried fungi specimens and thousands of pinned insects inside boxes.
Ristich hopes to attend the 12th Annual Samuel Ristich Foray, sponsored by the Northeast Mycological Federation, next Sept. 1-4 at St. Anthony's Hermitage of Lake Bouchette in northern Quebec province. The foraging expedition usually draws 225.
It was while mushroom-hunting in Windham in 1983 that Ristich discovered the mushroom eventually named Amanita ristichii by hobbyist Rodham E. Tulloss, one of Ristich's former students at the New York Botanical Garden, where he taught special courses in winter botany and the natural history of galls and fungi. The mostly white, inedible mushroom typically has strikingly orange-white or pink gills and fruits in July and August.
Asked how it feels to have a namesake fungus, Ristich quipped: ''Why not? Carry a halo if you can!"
Accompanying Ristich on the field trip to Mayberry Hill was a bit like going back to school -- in a classroom as big as all outdoors.
''Whooooeeee! Oh! Look at this!" Ristich exclaimed about a branch covered with several species of fungi. ''Oh! This is great in the sunlight! Take a look at this and tell me what you see."
Participants, carrying garden baskets and hods, hiked the trail through mixed hardwood and pine, struggling to keep up with Ristich's curiosity and incessant quizzing and to pronounce and spell the scientific nomenclature.
Sometimes, beauty didn't need a name.
''That's a beautiful fungus there! Look!" shouted Lawrence Leonard, 76, a semiretired orthopedic surgeon in Falmouth, as he pointed to the specimen. ''Now, isn't that a gorgeous fungus?"
Finds of the day included the crusty, uncommon Xylobolus frustulatus, a fungus that resembles cracked plaster, found on a big oak stick, and Arcyria nutans, a yellow ochre slime mold less than a half-inch tall that is spongy and fingerlike.
''My father is an incredible nerd," said daughter Jodee Ristich, 50, a nursing assistant who lives next door to her parents, ''but he has an amazing sense of humor. Sometimes, people think he's brilliant, but he studies every day of his life. . . . He works at being who he is."
Another daughter, Ruthie Ristich of Somerville, Mass., a jazz musician, recalled distressing Ristich on a recent trip home when she wiped a windowpane and washed a couple of common houseflies down the kitchen sink.
''Two hours later, my father's in the kitchen and I hear, 'Ohhh noo! My fly! I'll never find another fly like that! It had been parasitized by this fungi; the spores were the white things.' "
''Who knew?" said Ristich, 51. ''I felt bad. To me, it looked like a dead fly. To him, it was this amazing testimony to the cycle of life."
After the Mayberry Hill hunt, the odd-shaped, fleshy spoils were laid out on folding tables for everyone to observe. Participants sat on blankets in a meadow, ate brown-bag lunches, and tried to identify their bounty by consulting one another and poring over thick, dog-eared books like Lincoff's guide, as well as ''Mushrooms of Northeast North America" by George Barron (Lone Pine) and ''Mushrooms Demystified" by David Arora (Ten Speed). No indices seemed as complete, however, as the one in Ristich's mind.
One of the founders of the Maine Mycological Association, Ristich shares his observations in a quirky, folksy column dubbed simply Sam's Corner in the group's newsletter, Mainely Mushrooms. In 2002, the best of those columns from 1986 to 2000 were compiled and edited into a book, ''Sam's Corner: The Public Journal of a Mushroom Guru" (V.F. Thomas).
''Sam is like a tenured professor of mycology," said Paul Currier of Portland, 50, a software troubleshooter who has a biology degree. ''This is one of the most interesting things I've ever done."
Ristich charmed the group not only with his esoteric appreciation for the finer points of mushroom identification, but by occasionally launching into an impromptu lecture on some arcane aspect of natural history, like the difference between solid and empty galls or how an egg-laying midge results in a puffball.
In addition to studying and eating them, collectors sometimes use mushrooms like Cortinarius semisanguineus (red-gilled cort), a cinnamon-colored brown spore mushroom, to make vibrant dyes, or bracket fungi like Ganoderma applanatum (artist's conk) as miniature canvasses for etchings. ''Spore art" is created by cutting off the cap of a mature mushroom and laying the gills down on a white piece of paper so the spores spill out in beautiful, random patterns, then applying a fixative.
Currier's friend, Sandy Swatsky of Industry, began a search three years ago for a mushroom used in a distinctive soup her Polish aunts used to make for Christmas Eve.
''It's this particular kind of mushroom -- and I have yet to find it -- but that's what started me on this mission," said Swatsky, 51, a microbiologist. ''You never know what you're going to find out there in the woods."
Wild mushrooms can be classified as edible or poisonous -- or even deadly -- but are generally considered inedible if edibility is uncertain. Less than 15 percent of all wild mushrooms in New England are poisonous if ingested, Ristich said, and handling them is not dangerous. Eating a bad mushroom typically causes gastrointestinal upset, including severe vomiting and diarrhea. Deadly varieties attack kidney and liver cells.
A volunteer consultant to the Northern New England Poison Center based at Maine Medical Center in Portland, Ristich is tapped for his expertise in cases of suspected mushroom poisoning. Last year, he fielded 25 calls.
''Fortunately, you become ill with most of these quickly, and you hope you were dead for four hours, and then you recover," Ristich said.
Sometimes, local people drop in for an opinion. Recently, Ristich advised a woman that what she thought was an edible Cantharellus cinnabarinus (cinnabar chanterelle) growing in her backyard was actually a deadly poisonous Omphalotus olearius (jack-o'-lantern). Both are yellowish-orange.
When a courier needs to deliver a suspected mushroom for analysis, Ristich hangs out his shingle: a cardboard sign with a hand-drawn mushroom and the words ''Mushroom Guru" in black marker propped against a stool at the end of his driveway.
Even after a lifetime, though, he still struggles to explain his fungal obsession.
''There are no answers to 'why' questions. At least not a logical answer to 'why' questions," said Ristich, who clearly has been asked numerous times about his love of these misshapen life forms. ''I've always wrestled with people on the God concept. From whence. Whither. And why.
''My own comment to all of this," he said, ''is, you can't answer the 'whys,' you have to appreciate the magnitude of the universe. Twenty billion light-years big! Light travels at 186,000 miles per second. How much more wonderment do you need? Why worry about God?"
Contact Stacey Chase, a freelance writer in Maine, at email@example.com.