a to Nebraska, and
Washington and south to Nicaragua.

This species is so common that its plasmodium and fructification may be
easily observed. Professor Morton E. Peck, who has been for years a
close observer of the vegetative phases of our Iowa species, says of _P.
polycephalum_: "In one instance I observed a plasmodium for twelve
successive days on the surface of a decaying stump. During this period
it crept all around the stump and from top to bottom several times. At
one time the color was bright yellow; at another, greenish yellow; and
once, shortly before fruiting, it became clear bright green. A heavy
rain fell upon the plasmodium but it appeared to sustain little injury
and ultimately developed normal sporangia."

55. PHYSARUM NUTANS _Pers._

1791. _Sphaerocarpus albus_ Bull., _Champ._, p. 137, t. 407, III.,
and t. 470, I, A-L.
1791. _Stemonitis alba_ (Bull.), Gmel., _Syst. Nat._, p. 1469 (?).
1795. _Physarum nutans_ Pers., _Ust. Ann. Bot._, XV., p. 6.
1803. _Trichia cernua Schum., Enum. Pl, Saell._, II., p. 241.
1829. _Physarum cernuum_ (Schum.) in part, Fr., _Syst. Myc._, III.,
pp. 130, 147.
1848. _Tilmadoche cernua_ (Schum.) Fr., _Summ. Veg. Sc._, p. 454.
1873. _Tilmadoche nutans_ (Pers.) Rost., _Versuch_, p. 10.
1899. _Tilmadoche alba_ (Bull.) Macbr., _N. A. S._, p. 58.
1911. _Physarum nutans_ Pers., List., _Mycet., 2nd ed._, p. 67,
in part.

Sporangia gregarious, depressed-spherical, stipitate, umbilicate, gray
or white, thin-walled, nodding; stipe long, tapering upward, brown or
black below, ashen white above, lightly striate, graceful; capillitium
abundant, threads delicate, intricately combined in loose persistent
network with occasional minute, rounded, or elongate calcareous nodules;
spores minutely roughened, globose, about 10 mu.

The nodding, lenticular, umbilicate sporangium, barely attached to the
apiculate stipe, is sufficient to distinguish this elegant little
species, recognized and quite aptly characterized by mycologists for
more than one hundred years. As _Sphaerocarpus albus_ Bulliard first
prescribed the limits by which the species is at present bounded. The
description by Fries (_Syst. Myc.,_, III., 128) is especially graphic;
"Peridium very thin, in form quite constantly lenticular, umbilicate at
base, at first smooth then uneven, generally laciniate-dehiscent, the
segments persistent at least at base."

The stipe is usually