3. DIDYMIUM WILCZEKII _Meylan_.

1908. _Didymium wilczekii_ Meyl., _Bull. Soc. Vaud. Sci. Nat._, XLIV., p. 290.

1911. _Didymium wilczekii_ Meyl., List., _Mycetozoa, 2nd ed._, p. 134.

Plasmodiocarpous, dehiscing irregularly, columella scant; capillitium abundant, the threads brown, anastomosing, forming an elastic net; spores purple-brown, minutely spinulose, 10-12 .

Resembling plasmodiocarpous forms of _D. squamulosum_, a montane var.; small and delicate, our specimen about 16 6 mm. Evidently not common; collected but once by Professor Bethel at an alt.i.tude of 11,000 feet, Rocky Mountains of Colorado.

Reported in Switzerland and Sweden.

In certain Swiss gatherings made in 1913 Miss Lister finds capillitial threads with _spiral_ taeniae as in _Trichia_! (_Jour. of Bot._, Apr.

1914.) The threads in our specimen are roughened, somewhat as in _D.

squamulosum_, though less strongly; the spores are nearly smooth, fuliginous at first, paler and violaceous when saturate.

4. DIDYMIUM FULVUM _Sturgis._

1917. _Didymium fulvum_ Sturgis, _Mycologia_, IX., p. 37.

Sporangia gregarious, sessile, elongate or forming curved plasmodiocarps, sometimes confluent, rarely sub-globose, concave beneath, pale-raw-umber in color, 0.5-0.8 mm. in diameter, occasionally seated on a concolorous, membranous, lime-encrusted hypothallus which may form pseudo-stalks; sporangium wall membranous, stained with yellow blotches, thickly sprinkled with cl.u.s.ters of large acicular crystals of pale-yellowish lime; columella very much flattened or obsolete; capillitium an abundant network of delicate, almost straight or flexuose, pale-purple or nearly hyaline threads, frequently with dark, calyciform thickenings as in _Mucilago_, and occasionally showing fusiform, crystalline blisters; spores dark-purplish-brown, coa.r.s.ely tuberculate, the tubercles usually arranged in curved lines, paler and smoother on one side, 12.5 to 14.5 . Colorado.

5. DIDYMIUM CRUSTACEUM _Fr._

1829. _Didymium crustaceum_ Fr., _Syst. Myc._, III., p. 124.

Sporangia closely aggregated, globose, or by compression deformed, sessile, snow-white, by virtue of the remarkably developed covering of calcareous crystals by which each sporangium is surrounded as if to form a crust, the peridium membranous, colorless, usually shrunken above and depressed; columella pale, small, or obsolete; hypothallus scant or vanishing; capillitium of rather stout violaceous threads seldom branched except at the tips, where they are pale and often bifid, or more than once dichotomously divided; spores strongly warted, globose, violet-brown, 10-13 .

This species has in some ways all the outward seeming of a diderma, but cannot be referred to that genus because of the crystalline character of its crust. This is a very marked structure; loosely built up of very large crystals, it is necessarily extremely frail, nevertheless persists, arching over at a considerable distance above the peridium proper. Sometimes, however, caducous, evanescent.

The sporangia are said to be sometimes stipitate. This feature does not appear in any of the material before us. Lister in _Mycetozoa_ Pl. XL., _c._ draws the capillitium much more delicate than it appears in our specimens. The hypothallus is sometimes noticeable under some of the sporangia where closely crowded, but is not a constant feature.

Rostafinski (by typographical error?) confused in the _Monograph_, pp.

164, 165, this species with Persoon's _Physarum confluens_. In the _Appendix_ he subst.i.tutes the Friesian nomenclature. Persoon's description of his species is insufficient, and throws no light on the problem whatever.

Rare. Iowa; Black Hills, South Dakota. Reported common in Europe.

Canada; Vancouver Island to the St. Lawrence.

6. DIDYMIUM SQUAMULOSUM (_Alb. & Schw._) _Fries._

1805. _Diderma squamulosum_ Alb. & Schw., _Consp. Fung._, p. 88.

1816. _Didymium effusum_ Link, _Diss._, II., p. 42.

1829. _Didymium squamulosum_ (Alb. & Schw.), Fries, _Syst. Myc._, III., p. 118.

1875. _Didymium effusum_ (Link) Rost., _Mon._, p. 163.

1894. _Didymium effusum_ (Link) List., _Mycetozoa_, p. 99.

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 .

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. f.u.c.kelianum 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 coa.r.s.er 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 columellae in such cases confluent, the stipes distinct. Furthermore, the largest spores reach the limit of 12.5 , and perhaps the larger number range from 10-12.5 , 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 , 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._

1794. _Physarum melanospermum_ Pers., _Rom. N. Mag. Bot._, p. 89.

1797. _Didymium farinaceum_ Schrader, _Nov. Gen. Pl._, p. 26, t. 5, Fig. 6.

Sporangia gregarious, hemispheric, depressed, umbilicate below, stipitate or sessile; the peridium firm, dull brown in color, frosted with minute crystals of lime, breaking irregularly; stipe, when present, short, stout, dull black, opaque, arising from a broad base or hypothallus; columella large, prominent; dark-colored, rough above, concave below; capillitium of more or less sinuous, usually dark-colored threads, sparingly branched, and often with calyciform thickenings; spore-ma.s.s black, spores by transmitted light pale, purplish-gray, spinulose or rough, 10-12 .

A well-marked and common species, distinguished by its depressed sporangium and dark-colored, opaque stipe. The latter is usually very short, almost completely concealed in the concavity of the umbilicate sporangium. The columella is dark-colored, forming the floor of the peridial cavity.

Persoon first named this species as here. Later on, _Uster's Ann._, XV., 6, he subst.i.tuted _villosum_ as a more appropriate specific name.

Schrader rejects both names given by Persoon as unsuitable, and suggests _farinaceum_. Schrad., _op. cit._, p. 27.

New England, Ohio, Missouri, Alabama, Iowa, Nebraska; Europe; probably cosmopolitan.

8. DIDYMIUM MINUS _Lister._

PLATE X., Figs. 4, 4 _a_, 4 _b_.

1892. _Didymium farinaceum_ Schr., var. _minus_, List., _Mycetozoa_, p. 97.

1896. _Didymium minus_ List., Morg., _Jour. Cin. Soc._, p. 61.

1899. _Didymium minus_ List., Macbr., _N. A. S._, p. 89.

Sporangia gregarious, depressed-globose, umbilicate below, whitish or gray, small, about mm., stipitate; stipe erect, rather slender, black, faintly striate, about equal to the sporangium in the horizontal diameter; columella distinct, dark brown, globose or depressed-globose, attaining in some cases the centre, rough; capillitium delicate, almost colorless, radiating, spa.r.s.ely branched; spores in ma.s.s dark brown, by transmitted light violet-tinted, minutely roughened, 8-10 .

Probably more common than the preceding, and generally mistaken for it.

Distinguished by its smaller size, longer and more slender stem, and general trim, well-differentiated appearance. Certainly very near the preceding, of which Mr. Lister regards it as merely a variety. Professor Morgan thought it in this country the more common form.

New York, Ohio, Iowa; reported from Europe, Africa, South America.

9. DIDYMIUM CLAVUS (_Alb. & Schw._) _Rabenhorst._

1805. _Physarum clavus_ Alb. & Schw., _Consp. Fung._, p. 96.

1829. _Didymium melanopus_ Fries, _Syst. Myc._, III., p. 114.

1844. _Didymium clavus_ (Alb. & Schw.) Rabh., _Ger. Cr. Fl._, No. 2282.