our most common form. Found in fall on dead twigs, leaves, etc.
Recognized by its rather large, white, depressed or flattened sporangia
tending to form reticulations, and hence suggesting the name. The lines
of fruiting tend to follow the venation of the supporting leaf; where
the sporangium is round, the columella is a distinct rounded or
cake-like body; where the fruit is venulose, the columella is less
distinct.

By these rounded forms we pass easily, as by a gate, to _D.
hemisphericum_, which, when wholly sessile, differs still in greater
diameter of the sporangia and in having somewhat larger spores. Usually
in such case the compared colony will show somewhere a very short and
stout but very real stipe supporting the discoid fruit.

Rostafinski divided the genus _Chondrioderma_, i. e. _Diderma_, into
three sections:--

_Monoderma_ to include those species in which the calcareous crust is
less distinct or connate with the true peridium.

_Diderma_, in which the two structures were plainly separate.

_Leangium_, used as in the present work. In his first section
Rostafinski placed _C. reticulatum_ and _C. michelii_; in the second,
_C. difforme_ and _C. calcareum_.

Lister has examined Rostafinski's type of _C. reticulatum_ and declares
that it has the usual didermic characters. Hence there is no doubt that
our small-spored American specimens are covered by Rostafinski's
description, No. 72. On the other hand, Lister makes _C. difforme_
(Pers.) Rost. a _Didymium_, by its crystalline coat. That species
therefore is removed from consideration in this connection. _C.
calcareum_ remains as applicable to American forms having the spores
10-12 mu, but according to the author of the species the capillitium is
abundant and definitive. Unhappily the type of _C. calcareum_ is lost
(Lister, _Mon._, p. 95), so that there is no other means of verification
than the description and Rostafinski's figure. Under these circumstances
we consider the name _calcareum_ inapplicable to any American forms we
have so far seen. See next species. As to the American species which
have been distributed as _C. calcareum_ (Lk.) Rost., they are, so far as
seen, referable to _D. reticulatum_ (Rost.), Morg. Here also belongs No.
1217, Ellis, _N. A. F._

New York, Pennsylvania, Ohio, Iowa, Nebraska. Probably to be found
throughout the eastern United States.

2. DIDERMA SPUMARIOIDES _Fries_.

1829. _Diderma spumarioides_ Fries, _Syst. Myc.