E.

_a. The lime on the wall of the sporangium in the form of minute
stellate crystals._

1. DIDYMIUM. Sporangium simple, subglobose and stipitate, the base
commonly umbilicate, or sometimes sessile and plasmodiocarp.

2. SPUMARIA. AEthalium composed of numerous elongated
irregularly-branched sporangia, closely compacted together and
confluent.

_b. The lime on the wall of the sporangium consisting of minute roundish
granules._

3. DIDERMA. Wall of the sporangium with the outer calcareous layer
usually compacted into a smooth continuous crust.

4. LEPIDODERMA. Wall of the sporangium with an outer layer of large
scales, consisting of bicarbonate of lime.

I. DIDYMIUM, Schrad. Sporangium simple, subglobose and stipitate, the
base commonly umbilicate, or sometimes sessile and plasmodiocarp; the
wall a thin membrane with an outer layer of minute stellate crystals of
lime. Stipe present or sometimes wanting; the columella mostly
conspicuous, sometimes thin or obsolete. Capillitium of very slender
threads, straight or often sinuous, stretching from the columella to the
wall of the sporangium, simple or outwardly sparingly branched at a
sharp angle. Spores globose, violaceous.

Didymium, together with Spumaria, is to be distinguished from all other
genera of the Myxomycetes by the covering of stellate crystals, like
hoar-frost, upon the outer surface of the sporangium.

Sec.1. CIONIUM. Columella prominent, subcentral, globose, obovoid, or
turbinate; the threads of the capillitium radiating in all directions to
the wall of the sporangium.

_A. Sporangium stipitate._

1. DIDYMIUM SQUAMULOSUM, A. & S. Sporangium variable in form and size,
small and globose, or large and much depressed, the base usually
umbilicate, stipitate, or sometimes sessile, and even plasmodiocarp; the
wall very thin and pellucid, with a thin, gray-white layer of stellate
crystals of lime, breaking up into subpersistent scales. Stipe short,
erect, snow-white, longitudinally furrowed or plicate; the columella
central, snow-white, various in shape, globose, obovoid, turbinate, and
stipitate or sessile. Capillitium of numerous colorless threads,
radiating from the columella and separating outwardly into several
branches. Spores globose, very minutely warted, dark violaceous, 8-10
mic. in diameter.

Growing on old wood, leaves, herbaceous stems, etc. Sporangium .4-.6-.8
mm. in diameter, the stipe scarcely longer than the diameter, often much
s