Although Rostafinski's description of this species is accurate and marks exactly a Tilmadoche and is very different from his description of Physarum polymorphum, nevertheless it is probable that both descriptions have reference to the same thing. All specimens on which both species were based were American; P. polymorphum, North American. But the only North American form to which reference can be made is that by Schweinitz called P. polycephalum and, fortunately, sufficiently described. Furthermore, Rostafinski, under T. gyrocephala, himself affirms the probable identity of Montagne's Didymium gyrocephalum with the Schweinitzian species, and uses Montagne's specific name provisionally. For these reasons it seems proper to write the species as above.

Widely distributed and common, from Maine and Canada 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.

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 µ.

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 white above, fuscous below, at the apex almost evanescent; hence the cernuous sporangia. The same character is less strikingly manifest in the species next following.

The plasmodium is bright yellow, sometimes greenish. Brought in from the field and maturing under a bell-jar, the color changes to a watery white just before the sporangia rise in fruit. P. album Fuckel, Rhen. Fl., No. 1469, 1865, is believed to be P. cinereum (Batsch) Pers.

Persoon changed Bulliard's specific name in this case to furnish one himself, more descriptive as he thought and distinctive. His success in this attempt must be esteemed but partial since all the related forms, immediately listed, nod as well. Bulliard's name as applied by Persoon is therefore to be preferred. But the transfer from Tilmadoche to Physarum loses for us one step in the ladder of priority. P. album (Bull.) may not enter here, since Fries has given us one species under that title. So Persoon comes next on the list, all the world now nodding approbation, let us hope!