l is torn away from the margin of the cap, and remains
for a time like a collar around the stem. Fragments of the veil often
remain attached to the margin of the pileus, and the collar adherent
to the stem falls back, and thenceforth is known as the _annulus_ or
ring. We have in this stage the fully-developed hymenophore,--the stem
with its ring, supporting an expanded cap or pileus, with gills on the
under surface bearing the hymenium.[B] A longitudinal section cut
through the pileus and down the stem, gives the best notion of the
arrangement of the parts, and their relation to the whole. By this
means it will be seen that the pileus is continuous with the stem,
that the substance of the pileus descends into the gills, and that
relatively the substance of the stem is more fibrous than that of the
pileus. In the common mushroom the ring is very distinct surrounding
the stem, a little above the middle, like a collar. In some Agarics
the ring is very fugacious, or absent altogether. The form of the
gills, their mode of attachment to the stem, their colour, and more
especially the colour of the spores, are all very important features
to be attended to in the discrimination of species, since they vary in
different species. The whole substance of the Agaric is cellular. A
longitudinal slice from the stem will exhibit under the microscope
delicate tubular cells, the general direction of which is lengthwise,
with lateral branches, the whole interlacing so intimately that it is
difficult to trace any individual thread very far in its course. It
will be evident that the structure is less compact as it approaches
the centre of the stem, which in many species is hollow. The
_hymenium_ is the spore-bearing surface, which is exposed or naked,
and spread over the gills. These plates are covered on all sides with
a delicate membrane, upon which the reproductive organs are developed.
If it were possible to remove this membrane in one entire piece and
spread it out flat, it would cover an immense surface, as compared
with the size of the pileus, for it is plaited or folded like a lady's
fan over the whole of the gill-plates, or lamellae, of the fungus.[C]
If the stem of a mushroom be cut off close to the gills, and the cap
laid upon a sheet of paper, with the gills downwards, and left there
for a few hours, when removed a number of dark radiating lines will be
deposited upon the paper, each line corresponding with the interstices
between