| I. | Spread over the surface of lamellæ or gills. | Agaricaceæ. |
| II. | Lining the interior of tubes or pores. | Polyporaceæ. |
| III. | Clothing the surface of spines or protuberances of various forms. | Hydnaceæ. |
b. HYMENIUM EVEN.
| IV. | Horizontal and mostly on the under surface. | Thelephoraceæ. |
| V. | Vertical and produced all over the surface. | Clavariaceæ. |
| VI. | Superior, gelatinous fungi. | Tremellaceæ. |
FAMILY I.—AGARICACEÆ.
In the Agaricaceæ the hymenium is spread over lamellæ or gills which radiate from a center or stem. The gills are composed of a double membrane, and are simple or branched.
The parts of an Agaric may all be present as in Amanitæ, or severally absent in other genera. When the young fungus is entirely enclosed in a wrapper or case, this case is called the universal veil. When this veil is ruptured by the growth of the stem, that part which remains attached to the base is called the volva. The membrane reaching from the stem to the margin of the cap is the partial veil; when it ruptures by the expansion of the cap and all or a portion adheres to and about the stem it forms the annulus or ring. In some species one or both veils may be present, or one or both may be absent.
The stem is central when supporting the cap at its center; excentric when at one side of the center; lateral when it supports the cap from the side. If the stem is absent, the cap is said to be sessile; if the cap is horizontal and supported by a broad base it is dimidiate; if attached to its place of growth by its back it is resupinate.
Genera are largely distinguished by the manner in which the gills are attached to the stem. These distinguishing attachments are shown in the plates illustrating genera and in Plate [IV]. Gill-shapes.
For convenience Agaricaceæ is divided by the color of the spores into five series: white, pink, brown, purple, black. The last two, owing to the similarity of hue, are by some writers (preferably) included in the black-spored series. Spore color is a valuable assistant in determining species.