a branched and anastomosing in all directions, forming
an intricate network, closely packed together and inseparable. The
surface of the aethalium is often covered by a continuous layer of some
excreted substance, which is called the _common cortex_.

The wall of the sporangium, typically, is a thin, firm membrane,
colorless and pellucid, or colored in various shades of violet, brown,
yellow, etc.; it is sometimes extremely delicate, as in Lamproderma, or
is scarcely evident, as in Stemonitis; in other instances it is
thickened by deposits on the inner surface, as in Tubulina, or by
incrustations on the outer surface, as in Chondrioderma. The stipes are
tubes usually with a thick wall, which is often wrinkled and folded
lengthwise, and is confluent above with the wall of the sporangium; in
some cases the stipe also enters the sporangium, and is more or less
prolonged within it as a _columella_. The stipe commonly expands at the
base into a membrane, which fastens it to the substratum, and is called
the _hypothallus_; when all the stipes of the same group of sporangia
stand upon a single continuous membrane, it is called a _common
hypothallus_.

In the simplest forms, the cavity of the sporangium is filled
exclusively with the numerous spores; but in most all of the genera,
tubules or threads of different forms occur among the spores and
constitute the _capillitium_. The capillitium first makes its appearance
in Reticularia, in which upon the inner surface of the walls of the
sporangia there are abundant fibrous thickenings; next in Cribraria it
is spread over the inner surface of the wall, and is early separated
from it; here, also, it first assumes a more definite form and
arrangement; in Physarum it is in connection with the wall of the
sporangium only by its extremities while it traverses the interior with
a complicated network; in Stemonitis and its allies the capillitium
originates wholly from the columella; in most species of Arcyria it
issues from the interior of the stipe. The capillitium in Trichia
consists of numerous slender threads which are _free_, that is, are not
attached in any way; they are usually simple and pointed at each
extremity; the surface of these threads exhibits beautiful spiral
markings.

ORDER I. LICEACEAE.

Sporangia always sessile, simple and regular or plasmodiocarp, sometimes
united into an aethalium. The wall a thin, firm, persistent membrane,
often granulose-thickened, us