and branches of _Vaccinium_. It seems to
affect the heather of Europe, moorland, etc. I have also specimens from
the herbarium of the lamented Dr. Rex. These are more plasmodiocarpous,
but open beautifully by a median fissure as in _Physarum sinuosum_
Bull. In no American gathering that I have examined does the capillitium
show calcareous thickenings as described by the British text.

4. DIDERMA GLOBOSUM _Persoon._

PLATE VII., Figs. 5, 5 _a_.

1794. _Diderma globosum_ Pers., _Roem. N. Mag. Bot._, I., p. 89.
1875. _Chondrioderma globosum_ (Pers.) Rost., _Mon._, p. 180.

Sporangia more or less closely gregarious, sessile, globose or by mutual
pressure prismatic or polyhedral, white, the outer wall smooth,
polished, crustaceous, fragile, far remote from the inner, which is
thin, smooth, or rugulose, iridescent blue; hypothallus usually
pronounced and spreading beyond the sporangia, sometimes scanty or
lacking, columella variable, sometimes very small, inconspicuous,
sometimes large, globose, ellipsoidal, even pedicellate; capillitium
abundant, brown or purplish brown, branching and occasionally
anastomosing to form a loosely constructed superficial net; spores
globose, delicately spinulose, 8 mu.

This species seems rare in this country. We have specimens from Iowa. It
is distinguished by small spores and generally snow-white color.
Lister has thrown doubt upon Rostafinski's definition of this
form--_Mycetozoa_, p. 78. Almost everything distributed in the United
States under this name belongs in the next species. Reported also from
Ohio,--_Morgan._ Washington. But:--it should be found in Europe, where
first described!

There are two ways to meet the difficulty. In the first place it seems
probable that a small-spored form really hides somewhere in Europe. The
difference between the _Monograph_ measurement and the size admitted for
_D. crustaceum_ Pk., evidently considered by Mr. Lister as type and so
used in his illustration, Pl. 85, is too great to be esteemed merely an
error. That added .3 (Rost.) indicates caution, the average of several
measurements. Our _D. globosum_ may represent what the _Monograph_
describes.[32] In the second place we may as American students mistake
larger and more globular forms of something else, of _D. spumarioides_
Fr., whose spores are but little larger; or of _D. effusum_ (Schw.)
Morg., where the flattened plasmodiocarps anon splatter out to globose
drops of polished whitenes