Plasmodiocarp an elongated, irregularly limited, close-meshed net, closely applied to the substratum, the wall thin, transversely rugulose, and roughened, dull orange-yellow, splashed here and there with scarlet, anon entirely red, within marked by transverse calcareous ridges, supporting in part the calcareous system of the capillitium; capillitium of delicate, rigid, reticulating yellow tubules or threads with numerous free, uncinate or sickle-shaped branchlets, and large, irregular, calcareous plates, more or less transverse to the axis of the sporangium, attached to the peridial walls, as if to form septa, ordinary calcareous nodules few; spore-ma.s.s jet-black, spores, by transmitted light, violaceous, minutely roughened, 9-10 .

A very rare species, as it appears, easily recognized by the Coddington even, much more by the microscopic characters quoted; probably often overlooked by the collector, as to the naked eye it presents the appearance of some imperfectly developed, dried-up plasmodium. Very unlike _Physarum serpula_ Morgan, not infrequently offered by collectors as _Cienkowskia_. It is _Diderma reticulatum_ of Fries, who, strangely enough, thought it might be a plasmodial phase of _Diderma_ (i. e.

_Leocarpus_) _fragile_ (_Syst. Myc._, III., p. 102).

Eastern United States, Europe, Java, Ceylon, California. See under _L.

fragilis_, next following.

=7. Leocarpus= (_Link_) _Rost._

1809. _Leocarpus_ Link, _Diss._, I., p. 25.

Sporangia sessile, or short stipitate; peridial wall double, the outer thick, dest.i.tute of lime, polished, shining within and without, the inner very delicate, enclosing the capillitium and spores; capillitium of two, more or less, distinct systems, the one a delicate network of hyaline, limeless threads, the other calcareous throughout, or nearly so, the meshes large and the threads or tubules broad; columella none, although a pseudo-columella may sometimes be detected.

This genus was by Link established on characters purely external.

Rostafinski supplemented Link's definition by calling attention to the peculiar character of the capillitium and to microscopic characters in general. The outer peridium is thick and strong, unlike the ordinary structure in _Physarum_. Some physarums, however, have a very similar outer wall; _P. brunneolum_, for instance; compare the peridium of _P.

citrinellum_. In dehiscence and structure there is also some resemblance to some species of _Diderma_, and by Persoon and Fries the common species was so referred, but the capillitium is again definitive.

A critical study of all these things really begins with Rostafinski's microscope. Under his definition of the present genus _P. squamulosum_ Wingate and _P. albescens_ Ell. might well be entered here. Such course at present would but increase confusion, and until by future research the ontogeny of all these, and so their relationship, shall be more exactly known, the genus may be left with its historic species,--montotypic.

LEOCARPUS FRAGILIS (_d.i.c.kson_) _Rost._

PLATE VIII., Figs. 3, 3 _a_, 3 _b_.

1785. _Lycoperdon fragile_ d.i.c.kson, _Fasc. Pl. Crypt. Brit._, I., p. 25.

1795. _Diderma vernicosum_ Persoon, _Ust. Ann. Bot._, XV., p. 34.

1809. _Leocarpus vernicosum_ Link, _Diss._, I., p. 25.

1875. _Leocarpus fragilis_ (d.i.c.ks.) Rost., _Mon._, p. 132.

Sporangia gregarious or cl.u.s.tered, sessile or stipitate, obovoid, rusty or spadiceous-yellow, shining; peridium opening at maturity in somewhat stellate fashion; stipe filiform, white or yellow, weak and short; spores dull black, spinulose, 12-14 .

A common species, distributed through all the world, Iowa to Tasmania.

Recognizable at sight by the form and color of the sporangia. In shape and posture these resemble the eggs of certain insects, and, occurring upon dead leaves, generally where these have drifted against a rotten log, they might perchance be mistaken for such structures. With no other slime-moulds are they likely to be confused. The outer peridium opens irregularly, or more rarely stellately. At centre of the capillitium is a calcareous core. The plasmodium is yellowish white, spread in rich and beautiful reticulations. _N. A. F._, 1123.

A plasmodiform gathering of this species which will be mistaken for an entirely different thing, is yellow, sessile, and has _adherent_ spores; looks like a badhamia, but is after all a leocarpus and probably belongs here. The spores are irregularly cl.u.s.tered and the badhamioid section of the capillitium seems now dominant.

California.

B. DIDYMIACEae

=Key to the Genera of the Didymiaceae=

1. Fructification aethalioid 1. _Mucilago_

2. Fructification plasmodiocarpous, or forming more often distinct sporangia.

_a._ Calcareous deposits crystalline, stellate 2. _Didymium_

_b._ Calcareous deposits amorphous, peridium double 3. _Diderma_

_c._ Calcareous deposits in form of scattered scales 4. _Lepidoderma_

_d._ Peridium double, the outer gelatinous 5. _Colloderma_

=1. Mucilago= (_Mich._) _Adans._

1729. _Mucilago_ Micheli, _Nov. Pl. Gen._, in part.

1763. _Mucilago_ (Mich.) Adanson, _Fam. des Pl._, II., p. 7.

1791. _Spumaria_ Pers. in Gmelin, _Syst. Nat._, II., p. 1466.

Fructification aethalioid, consisting generally of large cushion-shaped ma.s.ses covered without by a white foam-like crust; within, composed of numerous tubular sporangia, developed from a common hypothallus, irregularly branched, contorted and more or less confluent; the peridial wall thin, delicate, frosted with stellate lime-crystals, which mark in section the boundaries of the several sporangia; capillitium of delicate threads, generally only slightly branched, terminating in the sporangial wall, marked with occasional swellings or thickenings.

By the descriptions offered by most authors, and especially by Rostafinski's figures (_Mon._, Pl. ix.), a p.r.o.nounced columella is called for in the structure of _Spumaria_. The individual sporangia rise from a common hypothallus, and occasionally portions of this run up and give to a sporangium the appearance of being stipitate. Sometimes also this upper extension of the hypothalline protoplasm pa.s.ses beyond or behind the base of the sporangium or between two or more, and is more or less embraced by these in their confluent flexures. This, it seems, suggested Rostafinski's elaborate diagram, Fig. 158; at least, none other form of columella is shown by American materials at hand.

1. MUCILAGO SPONGIOSA (_Leyss._) _Morgan._

PLATE VII, Figs. 6, 6 _a_, 6 _b_.

1783. _Mucor spongiosus_ Leysser, _Fl. Hal._, p. 305.

1791. _Reticularia alba_ Bull., _C. Fl. France_, p. 92.

1791. _Spumaria mucilago_ Pers., Gmel., _Syst. Nat._, II., 1466.

1805. _Spumaria alba_ (Bull.) DC., _Fl. Fr._, II., p. 261.

1897. _Mucilago spongiosa_ (Leyss.) Morg., _Bot. Gaz._, XXIV., p. 56.

aethalium white or cream-colored, of variable size and shape, half-an-inch to three inches in length and half as thick, the component sporangia resting upon a common hypothallus and protected by a more or less deciduous calcareous porous cortex; peridial walls thin, and where exposed iridescent, generally whitened by a thin coating of lime crystals; capillitium scanty, of simple, mostly dark-colored, slightly anastomosing threads; columella indefinite or none; hypothallus white, spongy; spore-ma.s.s black, spores violaceous, exceedingly rough, large, 12-15 .

Very common in all the eastern United States and the Mississippi valley, south to Texas. The plasmodium is dull white, of the consistence of cream, and is often met with in quant.i.ty on beds of decaying leaves in the woods. In fruiting the plasmodium ascends preferably living stems of small bushes, herbaceous plants, or gra.s.ses, and forms the aethalium around the stem some distance above the ground. The cortex varies in amount, is also deciduous, so that weathered or imperfectly developed forms probably represent the var. _S. cornuta_ Schum.

Two varieties of this species are recognized; the one from Bolivia, var.

_dictyospora_ described by Mr. R. E. Fries (_Arkiv. for Botanik_ Bd. 1, p. 66) differs from the type chiefly in its finer capillitial threads its darker spores with longer spines and fine reticulate sculpture; the other from Colorado, var. _solida_ described by Professor Sturgis differs, as the name implies, princ.i.p.ally in its greater compactness and slightly smaller calcareous crystals; a desert phase.

=2. Didymium= (_Schrad._) _Fr._

1797. _Didymium_ Schrad., _Nov. Gen. Plant._, p. 20, in part.

1829. _Didymium_ (Schrad.) Fr., _Syst. Myc._, III., p. 113.

1875. _Didymium_ (Schrad.) DeBy., Rost., _Versuch_, p. 13.

Sporangia distinct, stipitate, sessile or even plasmodiocarpous, never aethalioid; the peridium thin, irregular in dehiscence, covered with a more or less dense coating of calcareous crystals; columella more frequently present; capillitium of delicate threads, simple or sparingly branched, extending from the columella to the peridial wall.

The genus _Didymium_, as set up by Schrader _l. c._, included a number of species now a.s.signed to _Diderma_, _Lepidoderma_ or _Lamproderma_.

Fries set out the didermas; DeBary and Rostafinski completed the revision by setting out the remaining alien forms.

The genus is among Myxomycetes instantly recognized by the peculiar form of its calcareous deposits, stellate crystals coating, or merely frosting, usually distinct sporangia.