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..
The gills or lamellce are thin blades on the under side of the pileus, radiating from the stem to the margin. When the pileus is cut in halves the general outline of the gills may be observed. In outline they may be broad, narrow, lanceolate, triangular, etc. In respect to their ends they are attenuate when gradually narrowed to a sharp point, acute when they end in a sharp angle, and obtuse when the ends are rounded. Again, the gills are arcuate when they arch from the stem to the edge of the pileus, and ventricose when they are bellied out vertically toward the earth.
Mycena galericulata, pileus conic to campanulate, gills decurrent by a tooth, stem fistulose.
The terms given above are often used in descriptive works, but the most important feature to be noted in the section of the plant is the relation of the gills to the stem. This relation is represented by several distinct types which are sometimes used to limit genera or sub-genera, since the mode of attachment is usually constant in all species of a group. The principal relations of the gills to the stem are described as follows: Adnate when they reach the stem and are set squarely against it (Fig. 247); decurrent when they run down the stem (Fig. 244); sinuate or emarginate when they have a notch or vertical curve at the posterior end (Fig. 246); and free when they are rounded off without reaching the stem (Fig. 243). In all cases when the lamellae reach the stem and are only attached by the upper angle they are said to be adnexed. This term is often used in combination with others, as sinuate-adnexed (Fig. 248, small figure), or ascending adnexed (Fig. 248, larger plant). Sometimes the lamellae are adnate, adnexed, etc., and have a slight decurrent process or tooth as in Mycena galericulata (Fig. 245). In many plants the gills separate very readily from the stem when the plants are handled. Sometimes merely the expansion of the pileus tears them away, so that it is necessary to use great caution, and often to examine plants in different stages of development to determine the real condition of the lamella'.
Tricholoma, gills sinuate, stipe solid.
Panaeolus papilionaceus, gills adnate.
Left-hand small plant, Hygrophorus, gills sinuate, adnexed. Right-hand plant Panaeolus retirugis, gills ascending adnexed; veil appendiculate.
In certain genera the gills have special characteristics which may be noted here. Usually the edge of the lamellae is acute or sharp like the blade of a knife, but in Cantharellus and Trogia the edges are very blunt or obtuse. In extreme forms the lamelke are reduced to mere veins or ridges. Again, the edge is generally entire, i. e., not noticeably toothed, but in Lentinus it is often toothed or cut in various ways. In some other plants the edges are serrulate, crenulate, etc. In Schizophvllum alneum, a small whitish plant very common on dead sticks, the gills are split lengthwise along the edge with the halves revolute, i. e., rolled back. In Coprinus the gills and often a large part of the pileus melt at maturity into a dark, inky fluid. The hymenium. -
The term hymenium is applied to the spore-bearing tissue of many fungi. In the Agaricaceae the hymenium covers the entire surface of the gills and usually the portion of the pileus between the gills. It originates in the following manner : the threads forming the trama of the gills grow out from the lower side of the pileus and perpendicular to its under surface. As growth advances many branches of the threads turn outward toward either surface of the gill and finally terminate in club-shaped cells. These cells, therefore, lie side by side, perpendicular to the surface, forming a pavement, as it were, over the entire surface of the gills. Some of them put out four little prongs, on each of which a spore is borne, while others simply remain as sterile cells (Figs. 249, 250). The spore-bearing cells are basidia; the others are called paraphyses. They resemble each other very much, except that the basidia bear four sterigmata and a spore on each. In a few species the number of sterigmata is reduced to two and in some low forms the number is variable. The layer just beneath the basidia is usually more or less modified, being often composed of small cells different from the rest of the trama. This is called the sub-hymenial layer or sub-hymenium (Fig. 250).
Section of portion of gill of Marasmius cohaerens. t. trama of gill; sh, subhymenium; h, hymenium layer. The long, dark cells are brown cystidia, termed spicules by some to distinguish them from the colorless cystidia. The long cells bearing the oval spores are the basidia.
Inocybe repanda (Bull.) Bres. (= Ento-loma repandum Bull.), t, trama of pileus; sh, subhymenium; h, the hymenial layer; the long cells with a drop of moisture at the ends are cystidia (sing. cystidium).
Other cells called cystidia occur in the hymenia of various species distributed through nearly all the genera of the agarics. Cystidia are large, usually inflated, cells which project above the rest of the hymenium (Fig. 250). They originate either like the basidia, from the sub-hymenial cells (Fig. 250), or from special hyphae deeper down in the trama of the gill (Fig. 249). They are scattered over the entire surface of the hymenium, but become more numerous on the edge of the lamellae. Their number is much smaller than that of the basidia, but in some species where they are colored they may greatly change the appearance of the gills. Cystidia often secrete moisture which collects in drops at their tips, a phenomenon common to all free fungous cells.