usually as anastomosing branches from a
well-developed columella, which in a single
genus contains lime; sporangia otherwise
non-calcareous II. STEMONITALES

SERIES B

3. Capillitium none, or very imperfectly developed; spores of some
shade of brown, rarely purplish III. CRIBRARIALES

4. Capillitium the inwardly produced irregular extremities of plates
or tubules, which by their interweaving outwardly make up the
aethalial wall; spores pale, ashen IV. LYCOGALALES

5. Capillitium made up of more or less distinctly sculptured threads,
parietal or free, simple, branched, or reticulate; spores
commonly yellow V. TRICHIALES

This sequence is meant to convey the idea that the presence of lime is
indicative of differentiation less complete. That the plasmodium should
at the outset eliminate, by refusing the unnecessary lime, is indicative
of higher rank than that the lime should be carried until the last and
then be crystallized out, or excreted by simple desiccation. The
circumstance that the excreted lime may sometimes serve a protective
purpose in the fruit, does not vitiate the general principle. In Series
B the differentiation reaches a climax in the sculptured capillitium of
the trichias.

ORDER I

=PHYSARALES=

Spores violaceous-black. The capillitium usually delicate and
thread-like; peridium and capillitium, one or other or both, more or
less extensively surcharged with lime. Peridium simple or double.
Fructification various.

This order is recognizable by several characteristics, but is especially
marked by the peculiar calcareous deposits which affect the capillitium
or peridium, now one, now the other, more often both.

As here defined, the order Physarales includes two distinct families; of
the one _Physarum_, of the other _Didymium_, is type.

=Key to the Families of the Order Physarales=

_A._ Fructification often calcareous throughout;
capillitium intricate _Physaraceae_

_B._ Calcareous deposits, when present, affecting the
peridium only, or sometimes the stipe, in the
typical genus plainly crystalline; capillitium
simple
_Didymiaceae_

A. PHYSARACEAE

=Key to the Genera of the Physaraceae=

_