P. plumbeum Fr. belongs here. It has similar spores, the only difference is a less calcareous peridium and more scattered habit of fructification with more nearly regular, depressed-globose sporangia.

P. cinereum Pers. as cited by Link, op. cit., is apparently a badhamia, may be P. vernum, while P. griseum is probably the present species.

14. Physarum virescens Ditmar.

[Plate VIII.], Figs. 7, 7 a, 7 b.

Sporangia sessile, crowded or heaped in small bunches, a dozen or more sporangia in one pile, spherical, ovoid or elongate, yellow or greenish yellow; peridium thin, fragile; capillitium delicate, with rather small, irregular, yellowish, calcareous nodes; columella none; spores bright violet, minutely roughened, 7–9 µ.

This species occurs more commonly on moss-tufts, with which it is frequently con-colorless, or escaped on dead leaves, etc. The peridium is flecked with calcareous scales or grains stained yellow or green, and to these the whole fruit owes its peculiar color. The color and aggregate, heaped sporangia are distinctive macroscopic characters.

In the Monograph, p. 113, Rostafinski adopted properly Ditmar's name for this species. Upon later consideration, in the Appendix, p. 8, he changed the name, writing P. ditmari, on the ground that virescens was descriptive of a character to which the species in question occasionally refuses to conform. Most authors since Rostafinski have simply accepted his suggestion, so that the species is often entered P. ditmari Rost. P. virescens is certainly to be preferred. N. A. F., 2692.

Canada, New England, New York, Pennsylvania, Ohio, Iowa, Black Hills, South Dakota.

15. Physarum rubiginosum Fries.