e inner is simpler and comparatively thin. The whiteness of the
outer peridium is however, easily displaced. The colony may not show it
at all, in which case the peridia remaining give to the fructification
entire a pale lead color, very characteristic. The disposition of the
lime in the capillitium is also notably variable. Specimens occur which
in so far realize Rostafinski's _Crateriachea_; that is, the lime is
massed as a snow-white pseudo-columella in the centre of each
sporangium. In such cases the lime of the outer peridium is scant or
limited in amount, never forming the calcareous cap shown in Fig. 1. The
size of the spores is also variable. Rostafinski gives 12.5-14.2 mu; not
infrequently a single spore reaches 16 mu, a very unusual range of
variation.

The species is not common in the upper Mississippi valley, but can be
obtained in quantity where once it appears, as the plasmodia are
profuse.

Ohio, Carolinas, Tennessee, Iowa, South Dakota, Kansas. Especially to be
looked for on the bark of fallen stems of _Populus_ and _Negundo_.

Brazil, India, Japan.

_Physarum lividum_ Rost., _Mon._, p. 95, is but a less calcareous form
of this, as is evident even by the author's description. Professor
Morgan thought _P. lividum_ a phase of _P. griseum_ Lk. Link, however,
reckons _P. griseum_ the same as _P. cinereum_. Link, _Diss._, I., p.
27.

37. PHYSARUM LEUCOPUS _Link._

PLATE IX., Figs. 7, 7 _a_, 7 _b_.

1809. _Physarum leucopus_ Link, _Diss._, I, p. 27.

Sporangia gregarious, stipitate, globose snow-white, with a didymium
like covering of calcareous particles; stipe white, not long, conical or
tapering rapidly upward, slightly sulcate, brittle, from an evanescent
hypothallus; columella none or small; capillitium, consisting of rather
long hyaline threads, connecting the usual calcareous nodes, which are
large, angular, snow-white; spore-mass black; spores by transmitted
light, violet-brown, distinctly warted, about 10 mu.

The snow-white, nearly smooth stem, the small sporangium (1/2 mm.)
covered with loose calcareous granules, distinguish this rare species.
It looks like a small _Didymium squamulosum_. Fries called it _D.
leucopus_, _Syst. Myc._, III., p. 121.

Rare. Iowa, Ohio, Maine; Portugal.

38. PHYSARUM COMPRESSUM _Alb. & Schw._

PLATE XVIII., Fig. 14, and PLATE XIX., Fig. 12 and Fig. 4.

1805. _Physarum compressum_ Alb. & Schw., _Fung. Lus._, p. 97.
1875. _Physarum nefroideum_