2. DIDERMA FLORIFORME, Bull. Sporangium globose or obovoid, stipitate, growing closely crowded together on a thin brown membranaceous hypothallus; the wall smooth, varying in color from whitish or yellowish to bright brown, splitting into irregular segments, which become reflexed and revolute. Stipe long, erect, white or yellowish to brown; the columella elongated, obovoid to clavate, roughened, colored as the stipe. Capillitium of dark-colored threads, radiating from the columella and sparingly branched. Spores globose, with minute scattered warts, dark violaceous, 9-11 mic. in diameter. Plate XII, Fig. 44.

Growing on old wood of oak, hickory, etc., late in Autumn. Sporangium .7-1.0 mm. in diameter before dehiscence, the stipe usually longer than the sporangium. The color of stipe, columella and sporangium varies from white through yellowish to brown; the spores are quite peculiar by reason of their prominent scattered warts. I do not think _Chondrioderma Lyallii_, Ma.s.see, can be maintained as a separate species.

--2. STROMNIDIUM. Sporangia growing closely crowded together upon a thick highly-developed calcareous common hypothallus, either seated upon it or partially imbedded in its substance; the wall rupturing irregularly.

3. DIDERMA SPUMARIOIDES, Fr. Sporangia rather small, irregularly subglobose, sessile, seated close together on a strongly-developed whitish or yellowish common hypothallus; the wall white, rugulose, covered by a dense farinaceous layer of lime. Columella convex, roughened, white or yellowish, sometimes scarcely developed. Capillitium rather scanty, of slender colorless threads, sparingly branched, ascending from the columella. Spores globose, minutely warted, violaceous, 8-10 mic. in diameter.

Growing on old leaves, bark, moss, etc. Sporangia .4-.6 mm. in diameter, irregular and rugulose. On account of the pulverulent coat of lime on the sporangium, Ma.s.see refers the species back to Didymium, where it was placed by Fries.

4. DIDERMA STROMATEUM, Link. Sporangia large, subglobose, depressed, irregular and angular from mutual pressure, closely crowded together on a thick yellowish or pinkish common hypothallus; the wall smooth and even, grayish-white or cinereous, with a thin closely connate outer layer of minute granules of lime. Columella considerably elevated or much depressed, convex, subglobose or quite irregular, white or colored, as the hypothallus, especially at the base. Capillitium of abundant colored threads, more or less branched and combined into a loose net.

Spores globose, minutely warted, violaceous, 8-10 mic. in diameter.

Growing on Hickory bark. The sporangia .5-.8 mm. in diameter, the surface smooth. Rostafinski, in his Monograph, places this species as a variety of _D. spumarioides_, but in the Appendix it is separated as a species. The sporangia are quite different from those of _D.

spumarioides_, but I can see no difference in the spores.

5. DIDERMA GLOBOSUM, Pers. Sporangia subglobose, more or less irregular from mutual pressure, closely crowded together on a thick, white hypothallus, seated upon it or usually sunk into its substance at the base; the wall with a white, smooth, and polished crustaceous outer layer of lime, distinct and separable from the inner membrane, easily breaking into fragments, and falling away: the inner membrane very thin, rugulose, cinereous with granules of lime or free from them and iridescent. Columella white, small, irregular, subglobose or ellipsoidal, rarely wanting. Capillitium of slender, dark colored threads, more or less branched and combined into a loose net. Spores globose, very minutely warted, violaceous, 8-10 mic. in diameter.

Growing on old leaves. Sporangia .5-.8 mm. in diameter, the surface smooth and polished.

6. DIDERMA CRUSTACEUM, Peck. Sporangia subglobose, irregular from mutual pressure, closely crowded together on a thick, yellowish-white common hypothallus, and at the base confluent with its substance; the wall with a creamy white, smooth, crustaceous outer layer of lime, distinct and separable from the inner membrane, and easily breaking up and falling away; the inner membrane very thin, rugulose, cinereous and iridescent.

Columella whitish or cream colored, small, irregular, subglobose or ellipsoidal, often wanting. Capillitium of slender, uneven, dark colored threads, branched and combined into a loose net. Spores globose, minutely warted, violet-black, opaque, 12-15 mic. in diameter. Plate XII, Fig. 45.

Growing on old leaves, sticks, etc. A common species in this country.

Sporangia .7-1.0 mm. in diameter, the surface even but finely pulverulent rather than polished. _Chondrioderma affine_, Rost., is said to be the same species. It is readily distinguished from _D. globosum_, by the much larger spores.

--3. ASTROTIUM. Sporangia gregarious, scattered, or sometimes crowded and confluent, often much depressed, sessile, rarely stipitate; the hypothallus none or very scanty.

7. DIDERMA MICHELII, Lib. Sporangia orbicular, very much depressed, often umbilicate above and concave underneath, stipitate or sessile, gregarious, with the margins of the sporangia sometimes confluent. The wall with a white crustaceous layer of lime, which soon ruptures around the edges, allowing the upper part to break in pieces and fall away; the inner membrane cinereous, rupturing irregularly. Stipe short, stout, erect, arising from a small, circular hypothallus, whitish or alutaceous, longitudinally rugulose, expanding at the apex, the wrinkles running out as veins on the under side of the sporangium; the columella much flattened, lenticular or discoid, alutaceous or pinkish.

Capillitium of very slender, colorless threads, simple or forking a time or two, and connected by short branchlets at the extremities. Spores globose, even, violaceous, 7-9 mic. in diameter.

Growing on sticks, leaves, herbaceous stems, etc. Sporangium .8-1.2 mm.

in diameter, the stipe shorter than the diameter, sometimes very short or quite obsolete.

8. DIDERMA TESTACEUM, Schr. Sporangia circular or oval, much depressed, sessile, without any hypothallus, gregarious, irregularly scattered, sometimes close and even confluent. The outer calcareous layer of the wall thick, smooth, crustaceous, separate and distinct from the inner membrane, white or pinkish-white to rose-red in color, gradually breaking up in pieces and falling away; the inner membrane thin, pellucid, cinereous from the adherent granules of lime, irregularly dehiscent from the apex downward. Columella hemispheric or depressed, granulose-roughened, white, pinkish, or fleshy-red. Capillitium of very slender, nearly colorless threads, more or less branched. Spores globose, very minutely warted, 8-10 mic. in diameter.

Growing on old leaves, wood, mosses, etc. Very common in this country.

Sporangium .6-1.0 mm. in diameter, sometimes a little irregular, especially the form growing on mosses, and occasionally confluent.

9. DIDERMA CINEREUM, Morgan, n. sp. Sporangia subglobose, more or less irregular, somewhat depressed, sessile, usually close or crowded, sometimes confluent; the hypothallus a thin membrane, pellucid or with occasional patches of lime granules, sometimes not apparent. The wall very thin, even or rugulose, cinereous, the thin membrane covered by a single layer of closely-adherent granules of lime, rupturing irregularly. Columella white, hemispheric or depressed and irregular, the surface granulose. Capillitium of very slender, colored threads, the extremities pellucid, more or less branched. Spores globose, minutely warted, violaceous, 9-11 mic. in diameter. Plate XII, Fig. 46.

Growing on old wood, leaves, etc. The sporangium .3-.5 mm. in diameter, thin and smooth or rugulose. The species superficially greatly resembles _Physarum cinereum_.

10. DIDERMA DIFFORME, Pers. Plasmodiocarp roundish, oblong, or more or less elongated and flexuous, scattered or seriately disposed; the hypothallus a thin brownish membrane, or commonly not apparent. The outer calcareous layer of the wall snow-white, thin, smooth, distinct from the inner membrane, breaking into pieces and falling away; the inner membrane thin, opaque and bluish or pellucid and iridescent.

Columella reduced to a thin layer of scales and granules upon the brownish basal membrane. Capillitium scanty, consisting of short nearly colorless threads, which are simple, or fork a time or two. Spores globose, even, dark violaceous, 10-13 mic. in diameter.

Growing on bark, leaves, twigs, herbaceous stems, etc. Plasmodiocarp .3-.5 mm. in thickness and variable in length, sometimes elongated several millimeters.

11. DIDERMA RETICULATUM, Rost. Plasmodiocarp very much depressed, roundish, oblong, much elongated and flexuous, closely crowded together and confluent; the hypothallus a thin white granulose layer of lime, scarcely broader than the plasmodiocarp. The outer calcareous layer of the wall white, distinct, very fragile and easily sh.e.l.ling off; the inner membrane much shrunken and withdrawn from the outer coat, rugulose, cinereous, with a dense closely-adherent layer of granules of lime. The columella a thin alutaceous, granulose-roughened layer, extending along the base of the plasmodiocarp. Capillitium of threads short and very slender, colorless, somewhat branched. Spores globose, even, pale violaceous, 6-8 mic. in diameter. Plate XII, Fig. 47.

Growing on old wood, leaves, twigs, etc. Plasmodiocarp .5-.8 mm. in width, much flattened and usually closely crowded. The rough calcareous base of the plasmodiocarp might be considered as either all columella or all hypothallus, with the upper surface leather-colored. I am indebted to Arthur Lister, of London, for the determination of my specimens.

12. DIDERMA EFFUSUM, Schw. Plasmodiocarp very much flattened, longitudinally creeping and reticulate or altogether widely effused; hypothallus none. The wall very thin, smooth, white or cinereous, the thin membrane covered by a single layer of closely-adherent granules of lime, rupturing irregularly. The columella reduced to a thin alutaceous layer of granules of lime, forming the base of the plasmodiocarp.

Capillitium of short colorless threads, extending from base to wall, the extremities branched and connected together. Spores globose, even, pale violaceous, 8-10 mic. in diameter. Plate XII, Fig. 48.

Growing on old leaves. The plasmodiocarp forms very much flattened irregular patches from a few to several millimeters in length or extent.

I am indebted to Dr. Geo. A. Rex, of Philadelphia, for the identification of my specimens, with those in the herbarium of Schweinitz, under the name of _Physarum effusum_.

IV. LEPIDODERMA, DeB. Sporangium stipitate or sessile, sometimes plasmodiocarp; the wall a thin, firm, colorless membrane, with an outer layer of large scales consisting of bicarbonate of lime, the scales either lying upon the wall or inclosed in lenticular cavities of the membrane. Stipe present or absent; the columella usually conspicuous.

Capillitium of very slender threads, simple or outwardly branching at a sharp angle, connected at the extremities. Spores globose, violaceous.

"In the present genus the carbonate of lime is present in the form of very minute amorphous lumps until near to maturity, when it is dissolved and reappears as bicarbonate of lime deposited in comparatively large flakes."--_Ma.s.see._

1. LEPIDODERMA TIGRINUM, Schr. Sporangium large, much depressed, hemispheric or lenticular, the base umbilicate, stipitate; the wall a firm, dark colored membrane, variegated with large and small irregular shining scales, greenish-yellow or straw color, rupturing irregularly.

Stipe stout, thick, erect, rugulose, ochraceous or ferruginous, variable in length, expanding at the base into a thin hypothallus; the columella brown, convex or hemispheric. Capillitium of slender, dark colored threads, simple or sparingly branched, radiating from the columella to the wall. Spores globose, minutely warted, dark violaceous, 10-13 mic.

in diameter.

Growing on old wood, moss, etc. Sporangium 1-1.5 mm. in diameter, the stipe 1 mm. or less in length. This appears to be the only species of the genus thus far discovered in this country.

EXPLANATION OF PLATE XII.

Fig. 37.--Didymium proximum, B. & C. _a._ Sporangium and stipe 33.

_b._ Section through the columella.

Fig. 38.--Didymium eximium, Peck. _a._ Showing the rough columella of one form. _b._ Section through the discoid columella of the very much depressed form. Magnified by 33.

Fig. 39.--Didymium minus, Lister. _a._ Sporangium and stipe 33. _b._ _c._ _d._ Sections through the columella showing different forms.

Fig. 40.--Didymium farinaceum, Schr. Section through the columella.

After Rostafinski.

Fig. 41.--Didymium anellus, Morgan, _a._ Growing upon a leaf 3. _b._ Plasmodiocarp 17.

Fig. 42.--Spumaria alba, Bull. Var. 1. didymium, sporangia 3. Drawn from a foreign specimen.

Fig. 43.--Spumaria alba, Bull. _a._ aethalium natural size. _b._ Capillitium and spores as seen by a magnifying power of 500 diameters.

Fig. 44.--Diderma floriforme, Bull. Stipe and columella 20.

Fig. 45.--Diderma crustaceum, Peck. _a._ Sporangia crowded on the thick hypothallus, natural size. _b._ Sporangia 11. _c._ Section through outer coat, inner membrane, and columella.

Fig. 46.--Diderma cinereum, Morgan, _a._ Sporangia growing on a leaf 3. _b._ Sporangia 23. _c._ Section through the wall and columella.

Fig. 47.--Diderma reticulatum, Rost. Plasmodiocarp growing on leaf 3.

Fig. 48.--Diderma effusum, Schw. Plasmodiocarp effused on a leaf 3.

[Ill.u.s.tration: The Journal of the Cin. Soc. Natural History.