dide of zinc, it is rendered quite
transparent, and the young spore sacs colored a beautiful blue, so
that they are readily distinguishable.

[Illustration: FIG. 43.--_A_, a small cup fungus (_Ascobolus_), x 5.
_B_, young spore fruit, x 300. _ar._ archicarp. _C_, an older one,
x 150. _ar._ archicarp. _sp._ young spore sacs. _D_, section through a
full-grown spore fruit (partly diagrammatic), x 25. _sp._ spore sacs.
_E_, development of spore sacs and spores: i-iii, x 300; iv, x 150.
_F_, ripe spores. _G_, a sterile filament (paraphysis), x 300. _H_,
large scarlet cup fungus (_Peziza_), natural size.]

The development of the spore sacs may be traced by carefully
crushing the young spore fruits in water. The young spore sacs
(Fig. 43, _E_ i) are colorless, with granular protoplasm, in which a
nucleus can often be easily seen. The nucleus subsequently divides
repeatedly, until there are eight nuclei, about which the protoplasm
collects to form as many oval masses, each of which develops a wall
and becomes a spore (Figs. ii-iv). These are imbedded in protoplasm,
which is at first granular, but afterwards becomes almost
transparent. As the spores ripen, the wall acquires a beautiful
violet-purple color, changing later to a dark purple-brown, and
marked with irregular longitudinal ridges (Fig. 43, _F_). The
full-grown spore sacs (Fig. 43, _E_, _W_) are oblong in shape, and
attached by a short stalk. The sterile filaments between them often
become curiously enlarged at the end (_G_). As the spore fruit
ripens, it opens at the top, and spreads out so as to expose the
spore sacs as they discharge their contents (Fig. 43, _D_).

Of the larger cup fungi, those belonging to the genus _Peziza_
(Fig. 43, _H_) are common, growing on bits of rotten wood on the
ground in woods. They are sometimes bright scarlet or orange-red, and
very showy. Another curious form is the morel (_Morchella_), common in
the spring in dry woods. It is stalked like a mushroom, but the
surface of the conical cap is honeycombed with shallow depressions,
lined with the spore sacs.

ORDER _Lichenes_.

Under the name of lichens are comprised a large number of fungi,
differing a good deal in structure, but most of them not unlike the
cup fungi. They are, with few exceptions, parasitic upon various forms
of algae, with which they are so intimately associated as to form
apparently a single plant. They grow everywhere on expo