This extremely delicate and beautiful form is certainly not to be referred to Tilmadoche alba (Bull.) Fr. Fries, who seems to have known of P. compressum A. & S. and refers it to P. nutans Pers., op. cit., p. 130, annotates the present species: "Species especially remarkable in the stipe, in the internal structure, and in its whole habit, nor is there any other with which it may be compared. Peridium thin, not uniform, presently breaking up into laciniate scales; at first yellow, then bluish-ashen; when empty, white. The form inconstant, globose, depressed, but never umbilicate at the base." If we may judge by what Fries says on the subject, he certainly distinguished clearly between this species and T. alba (Bull.), to say nothing of the stouter, larger, in every way coarser forms called by Rostafinski P. nefroideum, P. compressum, P. lividum, etc.

The shadowy little species has had an eventful history, dipping in and out of our story in most uncertain fashion. Beginning with Fries, as noted, it received confirmation at the hands of DeBary, and by Rostafinski was given priority over a long list of synonyms, and figured. The earlier English authors follow Rostafinski, but for Lister in the Mycetozoa, p. 51, the species becomes a synonym of T. alba as P. nutans, the description appropriately enlarged to receive it. Meantime American students generally confused it with the tilmadoches on the one hand and P. nefroideum R. (supposed) on the other. In 1897, Robt. Fries in Sver. Myxom. Flora, brings the species again to view as co-partner with P. nutans and in the Mycetozoa, 2nd ed., p. 67, it appears as sub-species to the same.

The resemblance to P. album or P. nutans, is chiefly as intimated, a matter of definition; real differences are found in the irregular capillitium, fitting a globose sporange, in the character of the stipe and the consequent pose. See under P. nutans and P. notabile.

34. Physarum nodulosum Cke. & Balf.

Sporangia gregarious; minute, globose, bluish-white, the sporangial wall thin and more or less encrusted with lime, breaking up irregularly, stipitate; stipe slender, longer than the sporangium, attenuate upward or even, bright brown, rugose, expanded above into a shallow cup-like base for the sporangium; columella none; capillitium with lime-knots more or less abundant, white, often uniting, badhamioid; spore-mass black; spores by transmitted light, pale lilac-brown, almost smooth, 10–12 µ.

Pennsylvania, Ohio, Iowa; Canada.

One of the smallest species of the genus, by its proportionally long stipe and small round sporangium reminding one somewhat of P. globuliferum; much smaller, however, and in every way different. The generic characters are mixed, and the species has been accordingly variously referred. The lower part of the peridium is sometimes persistent after the dehiscence, and so far reminds of Craterium. But this character is not constant, and even at best the persisting part is very small, not greater than in P. melleum, for example. On the other hand, the capillitium in some sporangia is strongly calcareous, reminds of Badhamia, but in most sporangia the Physarum characters are sufficiently clear.

In the Kew Herbarium, it is said, are two American specimens under one label, "Didymium pusillum." One specimen is a didymium indeed, but, as it appears, D. proximum Berk., already described. The other is a physarum. It is proposed in Mycetozoa, 2nd ed., to use the combination thus set free, as if applied by the original author to the second specimen, not didymium, and to make the new combination date from 1873 and so take precedence of the binomial applied in 1881 by Cooke and Balfour here retained by the law of priority.

35. Physarum maculatum Macbr.