1890. _Physarum tenerum_ Rex., _Proc. Phil. Acad._, p. 192. 1894. _Physarum polymorphum_ Rost. var. _obrusseum_, Lister, _Mycet._, p. 48. 1899. _Physarum obrusseum_ (Berk. & C.) Rost., Macbr., _N. A. S._, p. 52. 1911. _Physarum tenerum_ Rex., List., _Mycetozoa, 2nd ed._, p. 52. The peridium thin, membranaceous, thickly studded with circular, flattened, yellow granules of lime; stipe long, slender, subulate, opaque, pale brown, striate and black below, pale yellow above; columella none; capillitium yellow or white, delicate, forming a loosely but regularly meshed network with numerous small round or rounded granules at the intersections; spores dark brown, delicately warted, 7-8 mu. This delicate physarum, very fragile and evanescent, seems to be distinct, by reason of its characteristic rounded lime granules, from any similar, stipitate species. It varies a little according to locality. Ohio specimens are a little larger and have thicker and more calcareous stipes than is usual in those from Philadelphia. The walls of the sporangia when fully matured generally break into several petal-like segments which finally become reflexed. The description given by Berkeley is entirely insufficient. In an earlier edition this species was entered as _P. obrusseum_ following the Polish text. Miss Lister who has the type of _Didymium obrusseum_ at hand considers it as representing a phase of _Physarum polycephalum_ Schw. _D. tenerrimum_ Berk. & Curt. is judged the same. _P. tenerum_ Rex is, in any event, certain, and the combination is adopted. Rare:--Pennsylvania, Ohio, Louisiana, Texas, Iowa, Portugal, Japan. 51. PHYSARUM FLAVICOMUM _Berk._ PLATE XV., Figs. 3, 3 _a_. 1845. _Physarum flavicomum_ Berk., _Hook. Jour. Bot._, IV., p. 66. 1873. _Physarum cupripes_, Berk. & Rav., _Grev._, II., p. 65. 1875. _Physarum berkeleyi_ Rost., _Mon._, p. 105. 1894. _Physarum berkeleyi_ Rost., List., _Mycetozoa_, p. 57. 1899. _Physarum flavicomum_ Berk., Macbr., _N. A. S._, p. 53. 1911. _Physarum flavicomum_ Berk., List., _Mycetozoa, 2nd ed._, p. 58. Sporangia gregarious, small, spherical, at first fuliginous throughout, stipitate; the peridium thin, destitute of lime, iridescent, breaking up and deciduous in patches, except at the base; stipe twice the diameter of the peridium, brown, fluted, not hollow, tapering upward from a small but distinct, radiant hypothallus; columella none; capillitium dense, persistent, the nodes frequently calcareous, elongate and vertical, especially below, yellow; spore-mass brown; spores by transmitted light, bright violaceous-brown, slightly papillose, 9-10 mu.