a. The walls of
the sporangia when fully matured generally break into several petal-like
segments which finally become reflexed. The description given by
Berkeley is entirely insufficient.

In an earlier edition this species was entered as _P. obrusseum_
following the Polish text. Miss Lister who has the type of _Didymium
obrusseum_ at hand considers it as representing a phase of _Physarum
polycephalum_ Schw. _D. tenerrimum_ Berk. & Curt. is judged the same.
_P. tenerum_ Rex is, in any event, certain, and the combination is
adopted.

Rare:--Pennsylvania, Ohio, Louisiana, Texas, Iowa, Portugal, Japan.

51. PHYSARUM FLAVICOMUM _Berk._

PLATE XV., Figs. 3, 3 _a_.

1845. _Physarum flavicomum_ Berk., _Hook. Jour. Bot._, IV., p. 66.
1873. _Physarum cupripes_, Berk. & Rav., _Grev._, II., p. 65.
1875. _Physarum berkeleyi_ Rost., _Mon._, p. 105.
1894. _Physarum berkeleyi_ Rost., List., _Mycetozoa_, p. 57.
1899. _Physarum flavicomum_ Berk., Macbr., _N. A. S._, p. 53.
1911. _Physarum flavicomum_ Berk., List., _Mycetozoa, 2nd ed._, p. 58.

Sporangia gregarious, small, spherical, at first fuliginous throughout,
stipitate; the peridium thin, destitute of lime, iridescent, breaking up
and deciduous in patches, except at the base; stipe twice the diameter
of the peridium, brown, fluted, not hollow, tapering upward from a small
but distinct, radiant hypothallus; columella none; capillitium dense,
persistent, the nodes frequently calcareous, elongate and vertical,
especially below, yellow; spore-mass brown; spores by transmitted light,
bright violaceous-brown, slightly papillose, 9-10 mu.

This species is instantly distinguishable from all cognate forms by its
peculiar sooty color. Not less is the species structurally marked by its
capillitium. The latter below is exactly as in the species of
_Tilmadoche_. Indeed, the present species unites characters supposed to
distinguish _Physarum_ from _Tilmadoche_, and would so far justify those
authors who bring all the species of both genera together under one
generic name. In any case the species is by its capillitium entirely
distinct from _P. galbeum_, as well as by the structure of the stipe and
the peridial surface. The plasmodium, at first watery, emerges from
decayed elm logs and soon takes on a peculiar greenish tint preserved
somewhat in the mature fruit.

Rostafinski, _Monograph_, pp. 105, 106, rejects Berkeley's specific
name, _flavicomum_, because it refers to