oides_.

Sec.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.

_B. Sporangia sessile._

10. DIDYMIUM SERPULA, Fr. Plasmodium yellow. Plasmodiocarp much
depressed, subrotund or usually more or less elongated, bent, flexuous
and reticulate; the wall dark-colored, with a thin layer of stellate
crystals of lime. Columella entirely wanting. Capillitium of very
s