d, consisting generally of large cushion-shaped
masses covered without by a white foam-like crust; within, composed of
numerous tubular sporangia, developed from a common hypothallus,
irregularly branched, contorted and more or less confluent; the peridial
wall thin, delicate, frosted with stellate lime-crystals, which mark in
section the boundaries of the several sporangia; capillitium of delicate
threads, generally only slightly branched, terminating in the sporangial
wall, marked with occasional swellings or thickenings.

By the descriptions offered by most authors, and especially by
Rostafinski's figures (_Mon._, Pl. ix.), a pronounced columella is
called for in the structure of _Spumaria_. The individual sporangia rise
from a common hypothallus, and occasionally portions of this run up and
give to a sporangium the appearance of being stipitate. Sometimes also
this upper extension of the hypothalline protoplasm passes beyond or
behind the base of the sporangium or between two or more, and is more or
less embraced by these in their confluent flexures. This, it seems,
suggested Rostafinski's elaborate diagram, Fig. 158; at least, none
other form of columella is shown by American materials at hand.

1. MUCILAGO SPONGIOSA (_Leyss._) _Morgan._

PLATE VII, Figs. 6, 6 _a_, 6 _b_.

1783. _Mucor spongiosus_ Leysser, _Fl. Hal._, p. 305.
1791. _Reticularia alba_ Bull., _C. Fl. France_, p. 92.
1791. _Spumaria mucilago_ Pers., Gmel., _Syst. Nat._, II., 1466.
1805. _Spumaria alba_ (Bull.) DC., _Fl. Fr._, II., p. 261.
1897. _Mucilago spongiosa_ (Leyss.) Morg., _Bot. Gaz._, XXIV., p. 56.

Aethalium white or cream-colored, of variable size and shape,
half-an-inch to three inches in length and half as thick, the component
sporangia resting upon a common hypothallus and protected by a more or
less deciduous calcareous porous cortex; peridial walls thin, and where
exposed iridescent, generally whitened by a thin coating of lime
crystals; capillitium scanty, of simple, mostly dark-colored, slightly
anastomosing threads; columella indefinite or none; hypothallus white,
spongy; spore-mass black, spores violaceous, exceedingly rough, large,
12-15 mu.

Very common in all the eastern United States and the Mississippi valley,
south to Texas. The plasmodium is dull white, of the consistence of
cream, and is often met with in quantity on beds of decaying leaves in
the woods. In fruiting the plasmodium ascends preferably livin