d large, irregular,
calcareous plates, more or less transverse to the axis of the
sporangium, attached to the peridial walls, as if to form septa,
ordinary calcareous nodules few; spore-mass jet-black, spores, by
transmitted light, violaceous, minutely roughened, 9-10 mu.

A very rare species, as it appears, easily recognized by the Coddington
even, much more by the microscopic characters quoted; probably often
overlooked by the collector, as to the naked eye it presents the
appearance of some imperfectly developed, dried-up plasmodium. Very
unlike _Physarum serpula_ Morgan, not infrequently offered by collectors
as _Cienkowskia_. It is _Diderma reticulatum_ of Fries, who, strangely
enough, thought it might be a plasmodial phase of _Diderma_ (i. e.
_Leocarpus_) _fragile_ (_Syst. Myc._, III., p. 102).

Eastern United States, Europe, Java, Ceylon, California. See under _L.
fragilis_, next following.

=7. Leocarpus= (_Link_) _Rost._

1809. _Leocarpus_ Link, _Diss._, I., p. 25.

Sporangia sessile, or short stipitate; peridial wall double, the outer
thick, destitute of lime, polished, shining within and without, the
inner very delicate, enclosing the capillitium and spores; capillitium
of two, more or less, distinct systems, the one a delicate network of
hyaline, limeless threads, the other calcareous throughout, or nearly
so, the meshes large and the threads or tubules broad; columella none,
although a pseudo-columella may sometimes be detected.

This genus was by Link established on characters purely external.
Rostafinski supplemented Link's definition by calling attention to the
peculiar character of the capillitium and to microscopic characters in
general. The outer peridium is thick and strong, unlike the ordinary
structure in _Physarum_. Some physarums, however, have a very similar
outer wall; _P. brunneolum_, for instance; compare the peridium of _P.
citrinellum_. In dehiscence and structure there is also some resemblance
to some species of _Diderma_, and by Persoon and Fries the common
species was so referred, but the capillitium is again definitive.

A critical study of all these things really begins with Rostafinski's
microscope. Under his definition of the present genus _P. squamulosum_
Wingate and _P. albescens_ Ell. might well be entered here. Such course
at present would but increase confusion, and until by future research
the ontogeny of all these, and so their relationship, shall be
more exactly