PLIED TO CERTAIN STRUCTURAL CHARACTERS OF
MUSHROOMS.

By H. HASSELBRING.

In fungi, as in higher plants, each organ or part of the plant is
subject to a great number of variations which appeal to the eye of the
student, and by which he recognizes relationship among the various
individuals, species, and genera of this group. For the purpose of
systematic studies of mushrooms or even for the recognition of a few
species, it is of primary importance to be acquainted with terms used in
describing different types of variation. Only a few of the more
important terms, such as are employed in this book, together with
diagrams illustrating typical cases to which they are applied, will be
given here.

=The pileus.=--The _pileus_ or _cap_ is the first part of a mushroom
which attracts the attention of the collector. It is the fleshy fruit
body of the plant. This, like all other parts of the mushroom, is made
up, not of cellular tissue as we find it in flowering plants, but of
numerous interwoven threads, called _hyphae_, which constitute the flesh
or _trama_ of the pileus. Ordinarily, the filamentous structure of the
flesh is very obvious when a thin section of the cap is examined under
the microscope, but in certain genera, as _Russula_ and _Lactarius_,
many branches of the _hyphae_ become greatly enlarged, forming little
vesicles or bladders. These vesicles lie in groups all through the flesh
of the pileus, sometimes forming the greater part of its substance. The
filamentous _hyphae_ pass around and through these groups, filling up the
interstices. In cross section this tissue resembles parenchyma, and
appears as if it were made up of rounded cells. Such a trama is said to
be _vesiculose_ to distinguish it from the ordinary or _floccose_ trama.
The threads on the outer surface of the pileus constitute the cortex or
cuticle. They are thick walled and often contain coloring matter which
gives the plants their characteristic color. In many species their walls
become gelatinized, covering the outside of the pileus with a viscid,
slimy, or glutinous layer, often called _pellicle_. In other instances
the corticle layer ceases to grow with the pileus. It is then torn and
split by the continued expanding of the rest of the plant, and remains
on the surface in the form of hairs, fibers, scales, etc.

[Illustration: FIGURE 239. Portion of vesiculose trama in the pileus of
a Russula.]

[Illustration: FIGURE 240. Portion of a flocco