6. Didymium squamulosum (Alb. & Schw.) Fries.

Sporangia, in typical forms, gregarious, globose or depressed-globose, gray or snow-white, stipitate; the peridium a thin iridescent membrane covered more or less richly with minute crystals of lime; the stipe when present, snow-white, fluted or channelled, stout, even; columella white, conspicuous; hypothallus usually small or obsolete; capillitium of delicate branching threads, usually colorless or pallid, sometimes with conspicuous calyciform thickenings; spores violaceous, minutely warted or spinulose, 8–10 µ.

This, one of the most beautiful species in the whole series, is remarkable for the variations which it presents in the fruiting phase. These range all the way from the simplest and plainest kind of a plasmodiocarp with only the most delicate frosting of calcareous crystals up through more or less confluent sessile sporangia to well-defined elegantly stipitate, globose fruits, where the lime is sometimes so abundant as to form deciduous flaky scales. The hypothallus, sometimes entirely wanting, is anon well developed, even continuous, venulose, from stipe to stipe. The capillitium varies much in abundance as in color; when scanty, it is colorless and in every way more delicate, when abundant, darker in color and sometimes with stronger thickenings.

D. fuckelianum Rost., as shown in N. A. F., 2090, and in some private collections, seems to be a rather stout phase of the present species; the stipe is more abundantly and deeply plicate, is sometimes tinged with brown, and the capillitium is darker colored and coarser than in what is here regarded as the type of the species; but withal the specimens certainly fail to meet the requirements of Rostafinski's elaborate description and figure, Mon., p. 161 and Fig. 154.

D. effusum Link, probably stands for a sessile form of this species, but Link's brief description (1816) is antedated by the much better one of Albertini and Schweinitz, l. c.

Generally distributed throughout the wooded regions of North America, from New England to Nicaragua, and from Canada to California. Not uncommon about stable-manure heaps, in flower beds, and on richly manured lands. July, August.

Nicaragua specimens not only show a continuous vein-like hypothallus, but have the peridia often confluent, the columellæ in such cases confluent, the stipes distinct. Furthermore, the largest spores reach the limit of 12.5 µ, and perhaps the larger number range from 10–12.5 µ, and all are very rough. This corresponds with D. macrospermum Rost., which is distinguished, says the author (Mon., p. 162, opis), "chiefly by the large and strongly spinulose spores." However, the same sporangium in our Central American specimens yield spores 9.5–12.5 µ, a remarkable range. So that D. macrospermum on this side the ocean, at least, cannot be distinguished from D. squamulosum, as far as spores are concerned. A similar remark may be made relative to the form of the columella which Rostafinski, in his figures especially, would make diagnostic. The columella in the sporangia with largest and roughest spores is that of a perfectly normal D. squamulosum.

7. Didymium melanospermum (Pers.) Macbr.

[Plate VII.], Figs. 3, 3 a.