one pair of gills. These lines are made up of spores which
have fallen from the hymenium, and, if placed under the microscope,
their character will at once be made evident. If a fragment of the
hymenium be also submitted to a similar examination, it will be found
that the whole surface is studded with spores. The first peculiarity
which will be observed is, that these spores are almost uniformly in
groups of four together. The next feature to be observed is, that each
spore is borne upon a slender stalk or sterigma, and that four of
these sterigmata proceed from the apex of a thicker projection, from
the hymenium, called a _basidium_, each basidium being the supporter
of four sterigmata, and each sterigma of a spore.[D] A closer
examination of the hymenium will reveal the fact that the basidia are
accompanied by other bodies, often larger, but without sterigmata or
spores; these have been termed _cystidia_, and their structure and
functions have been the subject of much controversy.[E] Both kinds of
bodies are produced on the hymenium of most, if not all, the
Agaricini.

[Illustration: FIG. 2.--Section of Common Mushroom.]

[Illustration: FIG. 3.--_a._ Sterile cells. _b._ Basidia. _c._ Cystidium.
From _Gomphidius_ (de Seynes).]

The basidia are usually expanded upwards, so as to have more or less
of a clavate form, surmounted by four slender points, or tubular
processes, each supporting a spore; the contents of these cells are
granular, mixed apparently with oleaginous particles, which
communicate through the slender tubes of the spicules with the
interior of the spores. Corda states that, although only one spore is
produced at a time on each sporophore, when this falls away others are
produced in succession for a limited period. As the spores approach
maturity, the connection between their contents and the contents of
the basidia diminishes and ultimately ceases. When the basidium which
bears mature spores is still well charged with granular matter, it may
be presumed that the production of a second or third series of spores
is quite possible. Basidia exhausted entirely of their contents, and
which have become quite hyaline, may often be observed.

The cystidia are usually larger than the basidia, varying in size and
form in different species. They present the appearance of large
sterile cells, attenuated upwards, sometimes into a slender neck.
Corda was of opinion that these were male organs, and gave them the
n