ing. _lamella_). These in shape resemble somewhat
a knife blade. They are very thin and delicate. When young they are pink
in color, but in age change to a dark purple brown, or nearly black
color, due to the immense number of spores that are borne on their
surfaces. The gills do not quite reach the stem, but are rounded at this
end and so curve up to the cap. The triangular spaces between the longer
ones are occupied by successively shorter gills, so that the combined
surface of all the gills is very great.

[Illustration: FIGURE. 1.--Agaricus campestris. View of under side
showing stem, annulus, gills, and margin of pileus. (Natural size.)]

=The Stem or Stipe.=--The stem in this plant, as in many other kinds, is
attached to the pileus in the center. The purpose of the stem seems
quite surely to be that of lifting the cap and the gills up above the
ground, so that the spores can float in the currents of air and be
readily scattered. The stem varies in length from 2--10 cm. and is about
1--1-1/2 cm. in diameter. It is cylindrical in form, and even, quite
firm and compact, though sometimes there is a central core where the
threads are looser. The stem is also white and fleshy, and is usually
smooth.

=The Ring.=--There is usually present in the mature plant of _Agaricus
campestris_ a thin collar (_annulus_) or ring around the upper end of
the stem. It is not a movable ring, but is joined to the stem. It is
very delicate, easily rubbed off, or may be even washed off during
rains.

=Parts Present in Other Mushrooms--The Volva.=--Some other mushrooms,
like the _deadly Amanita_ (_Amanita phalloides_) and other species of
the genus _Amanita_, have, in addition to the cap, gills, stem, and
ring, a more or less well formed cup-like structure attached to the
lower end of the stem, and from which the stem appears to spring. (Figs.
55, 72, etc.) This is the _volva_, sometimes popularly called the "death
cup," or "poison cup." This structure is a very important one to
observe, though its presence by no means indicates in all cases that the
plant is poisonous. It will be described more in detail in treating of
the genus _Amanita_, where the illustrations should also be consulted.

[Illustration: FIGURE 2.--Agaricus campestris. "Buttons" just appearing
through the sod. Some spawn at the left lower corner. Soil removed from
the front. (Natural size.)]

=Presence or Absence of Ring or Volva.=--Of the mushrooms which have
stems