Urnula craterium. (Schw.) Fr.
Figure 438.—Urnula 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.