A rather crude, primitive representative of this beautiful genus. The inner peridium seems to be lacking,--a comfort to Rostafinski! Rare. Our best specimens are from New Jersey, by courtesy of Dr. C. L. Shear. These went to fruit on leaves 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.
1794. _Diderma globosum_ Pers., _Röm. 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 µ.
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 whiteness, and whose spores are 8 µ. But even here the chances of error are small. In the species last named the columella or sporangial base is alutaceous, not white; in Fries' species, while the columella if present may be white, the peridial walls are different, difficult to distinguish.