olbitius, etc. The edge of the gills is acute in Agaricus,
Marasmius, etc., but obtuse and vein-like in Cantharellus,
longitudinally channelled in Trogia, and splitting in Schyzophyllum."

In the Polyporei, pore-bearing mushrooms, the gills are replaced by
tubes or pores. The tubes are little cylinders, long or short, pressed
one against another, forming by their union a layer on the under surface
of the cap, and the sporiferous membrane or hymenium lines their inner
walls. Their upper end is always closed, while the lower extremity is
open to permit the outward passage of the spores. The tubes are
generally joined together and are not easily disunited. They are free,
_i. e._, separable, in the sole genus _Fistulina_. As regards their
attachment to the cap, the tubes may be firmly adherent as in the genus
Polyporus or easily detached in a single mass as in Boletus, the fleshy
form of the order Polyporei. They frequently leave a circular space of
greater or less dimensions around the stem, or they adhere to or are
prolonged upon it in such a manner that the orifices rise in tiers one
above another. The color of the tubes, although not offering as
characteristic varieties as that of the gills, changes nevertheless
according to species and according to the age of the plant. The tubes
may sometimes be of a different color from their orifices, as in
_Boletus luridus_. In some of the Boleti the color of the flesh is
changed on exposure to the air and the tubes often assume the same
tints. The tubes, generally called pores, are sometimes closely adherent
to the substance of the cap, which is often hard, corky, or coriaceous,
as seen in most of the _Polyporei_.

In the Hydnei, spine-bearing mushrooms, the hymenium is seen covering
the spines or needle-like processes which take the place of gills in
this order, and which project from the under surface of the cap. These
spines may be divided or entire, simple or ramified, and are formed of
the substance of the cap. In the early stages of development they appear
like small projecting points or papillae, those on the margin of the cap
and at the apex of the stem being always less developed, frequently
remaining in this rudimentary state. They are rounded in the species
Hydnum imbricatum, sometimes compressed in Hydnum repandum, sometimes
terminating in hairs or filaments, as in Hydnum barba Jovis, or very
much divided, as in Hydnum fimbriatum.

In the Clavarei, the whole plant co