magnified. 579. Piece
of thallus of a Sticta, with section, showing the immersed apothecia;
the small openings of these dot the surface. 580. Cladonia coccinea; the
fructification is in the scarlet knobs, which surround the cups.]

516. =Fungi.= For this immense and greatly diversified class, it must
here suffice to indicate the parts of a Mushroom, a Sphaeria, and of one
or two common Moulds. The true vegetation of common Fungi consists of
slender cells which form what is called a _Mycelium_. These filamentous
cells lengthen and branch, growing by the absorption through their
whole surface of the decaying, or organizable, or living matter which
they feed upon. In a Mushroom (Agaricus), a knobby mass is at length
formed, which develops into a stout stalk (_Stipe_), bearing the cap
(_Pileus_): the under side of the cap is covered by the _Hymenium_, in
this genus consisting of radiating plates, the gills or _Lamellae_; and
these bear the powdery spores in immense numbers. Under the microscope,
the gills are found to be studded with projecting cells, each of which,
at the top, produces four stalked spores. These form the powder which
collects on a sheet of paper upon which a mature Mushroom is allowed to
rest for a day or two. (Fig. 581-586.)

517. The esculent Morel, also Sphaeria (Fig. 585, 586), and many other
Fungi bear their spores in sacs (asci) exactly in the manner of Lichens
(515).

[Illustration: Fig. 581. Agaricus campestris, the common edible
Mushroom. 582. Section of cap and stalk. 583. Minute portion of a
section of a gill, showing some spore-bearing cells, much magnified.
584. One of these, with its four spores, more magnified.]

[Illustration: Fig. 585. Sphaeria rosella. 586. Two of the asci and
contained double spores, quite like those of a Lichen; much magnified.]

518. Of the Moulds, one of the commoner is the Bread-Mould (Fig. 587).
In fruiting it sends up a slender stalk, which bears a globular sac;
this bursts at maturity and discharges innumerable spores. The blue
Cheese-Mould (Fig. 588) bears a cluster of branches at top, each of
which is a row of naked spores, like a string of beads, all breaking
apart at maturity. Botrytis (Fig. 589), the fruiting stalk of which
branches, and each branch is tipped with a spore, is one of the many
moulds which live and feed upon the juices of other plants or of
animals, and are often very destructive. The extremely numerous kinds of
smut, rust, mildew, the fe