craterium. Two-thirds natural size.]

Urnula means burned; craterium means a small crater; hence the
translation is a burned-out crater, which will appear to the student as
a very appropriate name. It is a very common and conspicuous
Ascomycetous, or cup fungus, growing in clusters on rotten sticks that
lie in moist places. When the plants first appear they are small, black
stems with scarcely any evidence of a cup. In a short time the end of
the stem shows evidence of enlargement, showing lines of separation on
the top. It soon opens and we have the cup as you see it in Figure 438.
The hymenium, or spore bearing surface, is the interior wall of the cup.
The cup is lined inside with a palisade of long cylindrical sacs, each
containing eight spores with a small amount of liquid. These sacs are at
right angles to the inner surface, and are provided with lids similar to
that of a coffee-pot; at maturity the lid is forced open and the spores
are shot out of these sacs, and, by jarring the fungus when it is ready
to make the discharge, they can be seen as a little cloud an inch or two
above the cup. Place a small slip of glass over the cup and you will see
spores in groups of eight in very small drops of liquid on the glass.
This species appears in April and May, and is certainly a very
interesting plant. It is called by some Peziza craterium, Schw.

_Helotium. Fr._

Disc always open, at first punctiform, then dilated, convex or concave,
naked. Excipulum waxy, free, marginate, externally naked.

_Helotium citrinum. Fr._

LEMON-COLORED HELOTIUM.

[Illustration: Figure 439.--Helotium citrinum. Disc-fungus, yellow
growing on rotten logs. Slightly magnified.]

This is a beautiful little Disc-fungus, yellow, growing upon rotten logs
in damp woods. They often grow in dense clusters; a beautiful
lemon-yellow, the head being plane or concave, with a short, thick,
paler stem, forming an inverted cone. Asci elongated, narrowly
cylindrical, attenuated at the base into a long, slender, crooked
pedicel, 8-spored.

Sporidia oblong, elliptical, with two or three minute nuclei.

This is quite a common plant in our woods during wet weather or in damp
places, growing upon old logs and stumps, in woods, in the fall. Figure
439 will give an idea of their appearance when in dense clusters. The
plants photographed by Dr. Kellerman.

_Helotium lutescens. Fr._

YELLOWISH HELOTIUM.

Lutescens means yellowish. The plants are smal