MUSHROOM.

=Value of Form and Characters.=--The different kinds of mushrooms vary
in form. Some are quite strikingly different from others, so that no one
would have difficulty in recognizing the difference in shape. For
example, an umbrella-shaped mushroom like the one shown in Fig. 1 or 81
is easily distinguished from a shelving one like that in Fig. 9 or 188.
But in many cases different species vary only slightly in form, so that
it becomes a more or less difficult matter to distinguish them.

In those plants (for the mushroom is a plant) where the different kinds
are nearly alike in form, there are other characters than mere general
form which enable one to tell them apart. These, it is true, require
close observation on our part, as well as some experience in judging of
the value of such characters; the same habit of observation and
discrimination we apply to everyday affairs and to all departments of
knowledge. But so few people give their attention to the discrimination
of these plants that few know the value of their characters, or can even
recognize them.

It is by a study of these especial characters of form peculiar to the
mushrooms that one acquires the power of discrimination among the
different kinds. For this reason one should become familiar with the
parts of the mushroom, as well as those characters and markings peculiar
to them which have been found to stamp them specifically.

=Parts of the Mushroom.=--To serve as a means of comparison, the common
pasture mushroom, or cultivated form (_Agaricus campestris_), is first
described. Figure 1 illustrates well the principal parts of the plant;
the cap, the radiating plates or gills on the under side, the stem, and
the collar or ring around its upper end.

=The Cap.=--The cap (technically the _pileus_) is the expanded part of
the mushroom. It is quite thick, and fleshy in consistency, more or less
rounded or convex on the upper side, and usually white in color. It is
from 1--2 cm. thick at the center and 5--10 cm. in diameter. The surface
is generally smooth, but sometimes it is torn up more or less into
triangular scales. When these scales are prominent they are often of a
dark color. This gives quite a different aspect to the plant, and has
led to the enumeration of several varieties, or may be species, among
forms accredited by some to the one species.

=The Gills.=--On the under side of the pileus are radiating plates, the
gills, or _lamellae_ (s