This section is from the book "Studies of American Fungi: Mushrooms, Edible, Poisonous, Etc.", by George Francis Atkinson. Also available from Amazon: Studies of American Fungi: Mushrooms, Edible, Poisonous, Etc..
Hymenomycetes, the subdivision of the Basidiomycetes in which the fruiting surface is exposed before the spores are ripe.
Hymenophore, the portion of the fruit body which bears the hymenium.
Hypha (pl. hyphae), a single mycelium thread.
Imbricate, overlapping like the shingles on a roof.
Involute, folded or rolled inward.
Mycelium, the vegetative or growing portion of the mushrooms, and other fungi, made up of several or many threads.
Pectinate, like the teeth of a comb.
Peridium, the wall of the puff-balls, etc.
Pileus (pl. pilei), the cap of the mushroom.
Plicate, plaited, or folded like a fan.
Punctate, with minute points.
Pulverulent, with a minute powdery substance.
Resupinate, spread over the matrix, the fruiting surface external and the pileus next the wood.
Revolute, rolled backward.
Rugulose, with minute wrinkles.
Saprophytic, growing on dead organic matter.
Sessile, where the pileus is attached directly to the matrix without any stem.
Sinuate, said of the gills when they are notched at their junction with the stem.
Stipe, the stem.
Squamulose, with minute scales.
Squarrose, with prominent reflexed scales.
Tomentose, with a dense, matted, hairy or woolly surface.
Trama, the interior portion of the gills or pileus.
Umbo, with a prominent boss or elevation, in the center of the pileus.
Umbilicate, with a minute abrupt depression in the center of the cap.
Veil, a layer of threads extending from the margin of the cap to the stem (partial veil or marginal veil). A universal veil envelops the entire plant. Veins, elevated lines or folds running over the surface of the lamella? in some species, and often connected so as to form reticulations. Ventricose, enlarged or broadened at the middle, bellied.
Vesiculose, full of small rounded vesicles, as the trama of the pileus of a Russula. Volva, a wrapper or envelope, which in the young stage completely surrounds the plant, same as universal veil. At maturity of the plant it may be left in the form of a cup at the base of the stem, or broken up into fragments and distributed over the cap and base of the stem.