STRUCTURAL CHARACTERISTICS OF THE AGARICINI.

By far the greater number of the Agaricini have both cap and stem. The
form of the cap, as well as that of the stem, varies somewhat in the
different genera and species. Those which are terrestrial in habit are
generally of an umbrella-like shape, while those which grow upon trees
and decayed tree-stumps are apt to be one-sided or semi-spherical.

In many of the parasitical mushrooms the stem is absent. Where the stem
is present it is either an interrupted continuation of the hymenophore
or fleshy substance of the cap, or else is supported separately as a
pillar on which the cap rests, a more or less distinct line of
demarcation showing where the fibers terminate. Sometimes it is quite
easily detached from the cap socket, as in the Lepiota procerus. It may
be hollow or stuffed, solid or fibrillose. It varies in length and
thickness. In some species it is smooth and polished, in others rough
and hairy, reticulated, etc., sometimes tapering, sometimes distinctly
bulbous at the base.

The spores of the species differ in color and are usually globular or
oblong in shape. All of these characteristics assist in determining the
species.

MUSHROOM GILLS.

Mushroom gills, or lamellae, anatomically considered, are composed,
first, of a central portion, a prolongation of the hymenophore or flesh
of the cap, more or less dense, sometimes so thin as to be scarcely
perceptible; second, the hymenium or spore-bearing membrane covering the
surfaces of this prolonged hymenophore. They are vertical, simple,
equal, respectively, or more frequently alternating with shorter gills.
They are often evanescent and putrescent, sometimes liquefying
altogether. Their color is usually different from the upper surface of
the cap, not always similar to that of the spores borne upon them, at
least in youth; with age, however, they usually assume the color of the
mature spore. The change of color of the gills according to the age of
the plant is very important in the study of the Agaricini; it accounts
for the white gills of certain species in youth, the pink in maturity,
and the brown when aged.

The end of the gill nearest the stalk of the plant is termed the
posterior extremity; the opposite end, the anterior extremity. In most
of the Agaricini the gills are unequal. Some extend from the margin to
about half the space between it and the stem; others are still shorter.

THE VOLVA.