6. Didymium effusum, Link. Sporangia gregarious or scattered, sessile on a flattened base, convex above, various in shape, subrotund or by confluence effused and venosely creeping; the wall very thin and pellucid, invested with a thin flocculose layer of minute crystals of lime. The columella hemispheric, rugulose, usually snow-white. Capillitium of very slender colorless threads, furnished with numerous minute protuberances, much branched and combined into a dense net. Spores globose, very minutely warted, dark violaceous, 10–11 mic. in diameter.
Growing on old leaves, wood, etc. Sporangium about .5 mm. in diameter or thickness, sometimes confluent and more or less elongated as a plasmodiocarp. This species is reported from the United States, but I have seen no specimens.
7. Didymium physaroides, Pers. Sporangia roundish or hemispheric, more or less irregular and deformed, sessile or with a very short stipe, and closely crowded together upon a strongly-developed common hypothallus; the wall a dark colored membrane, with a thin layer of stellate crystals of lime. The columella large and thick, divided into cells which are filled with irregular lumps of lime, common to all the sporangia. Capillitium of stout threads, usually simple, only rarely branched, furnished with numerous fusiform swellings. Spores globose, minutely warted, dark violaceous, 12–14 mic. in diameter.
Growing on old wood, bark, moss, etc. Reported from Carolina by Curtis. It is said superficially to resemble somewhat Physarum didermoides.
§2. Placentia. Columella basal, much depressed, very thin or quite obsolete, connate with the base of the sporangium; the threads of the capillitium ascending to the wall of the sporangium.
A. Sporangium stipitate.
8. Didymium farinaceum, Schrad. Sporangium hemispherical, more or less depressed, the base profoundly umbilicate; the wall firm, rugulose, dark-colored and nearly opaque, with a mealy coat of stellate crystals of lime, rupturing irregularly. Stipe variable in length, rigid, erect, black or sometimes rusty-brown, arising from a small hypothallus; the columella broad, hemispherical or pulvinate, black, the lower side connate with the wall of the sporangium. Capillitium of dark-colored sinuous threads, simple or scarcely branched. Spores globose, dark violaceous, minutely warted, 10–13 mic. in diameter. [Plate XII, Fig. 40.]
Growing on old wood, leaves, mosses, etc. Sporangium .6-.9 mm. in diameter, the stipe about as long as the diameter of the sporangium or sometimes much longer, usually, however, much shorter than the diameter and almost concealed within the umbilicus. My specimens are from Pennsylvania and Alabama. It is readily distinguished from Didymium minus by the much larger and more distinctly warted spores.
9. Didymium clavus, A. & S. Sporangium pileate, very much depressed, convex above and concave below, stipitate; the wall a dark-colored membrane, thickly covered with minute white crystals of lime, except the brown concavity underneath, the upper part breaking away, the lower persistent. Stipe short, erect, rugulose, brown or blackish, expanding at the base into a small hypothallus; the columella reduced to a thin layer of minute brown scales upon the base of the sporangium. Capillitium of simple or sparingly-branched threads, colorless at the extremities and dark-colored between. Spores globose, even, violaceous, 6–8 mic. in diameter.
Growing on old leaves, sticks, herbaceous stems, etc. The sporangium .6-.8 mm. in diameter, the stipe about the same length. Fries considered this to be a mere variety of D. farinaceum, but it is readily distinguished by its very small spores.