Soon Nick and I see scores of mushrooms, set in ragged half-circles, with broad tops that look like cooling milky coffees inexplicably placed among dead leaves. They’re cloud caps, a common species here, and considered toxic. We leave them and walk on. A little while later, Nick spots a yellowish gleam in the long grass. This is more interesting. He crouches beside it, and frowning, pushes a thumb and index finger underneath the specimen and gently pulls it free of moss and grass. ‘‘Tricholoma,’’ he says. ‘‘Tricho­loma sulphureum.’’ Mycologists generally use scientific names to describe fungi, as their common names vary widely. The mushroom he holds is sometimes called the sulfur knight, or the gas agaric. He offers it to me to smell, and an unpleasantly sulfurous tang makes me wrinkle my nose. He puts it in the basket.

I am not very good at identifying fungi, but I am getting better. Over the years I have not only learned to identify a few species by looking at them or smelling them, or seeing what color their cut surfaces turn; I have also become intrigued by the curious place they occupy in our imaginations. We have been foraging and eating mushrooms for millenniums, and they still have the power to disturb us, to conjure the deepest human mysteries of sex and death. Nineteenth-century sensibilities were horrified by the common stinkhorn, a fetid fly-attracting species that bursts out of a membranous egg into a shape perfectly described by its scientific name, Phallus impudicus. In her later years, Charles Darwin’s daughter Henrietta went into the woods to collect stinkhorns for the express purpose of bringing them back to be ‘‘burned in the deepest secrecy of the drawing-room fire, with the door locked; because of the morals of the maids,’’ according to a memoir by her niece. Our continuing pieties about sex are reflected in the way some modern field guides describe the distinctive odor of mushrooms like Inocybes as ‘‘unmentionable’’ or ‘‘disgusting’’ rather than the more accurate ‘‘spermatic.’’

The unpredictable flowering of beautiful alien forms from rotting wood, dung or leaf litter in a forest moving toward winter is a strong and strange conjuration of life-in-death — in Baltic mythology, mushrooms were thought to be the fingers of the god of the dead bursting through the ground to feed the poor. But mushrooms have a more direct relationship to mortality. Many of them, of course, are deadly. You might survive if you eat a destroying angel or death cap, but you’ll probably need a liver transplant. And the particular toxicity of fungi is as mysterious as the forms they take. A mushroom can contain more than one kind of toxin, and the toxicity can change according to whether it has been cooked, how it has been cooked, whether it has been eaten with alcohol or fermented before ingestion.