Sporangia simple and subglobose, or plasmodiocarp, rarely combined into an Æthalium. Wall of the sporangium a thin membrane with an outer layer composed of minute stellate crystals, or of minute roundish granules of lime; these either lie singly upon the surface, or are compacted into a crustaceous coat. Stipe present or often wanting; the columella usually conspicuous and well-developed. Capillitium consisting of very slender, often sinuous threads, which extend from the base of the sporangium or from the columella to the walls, either simple or outwardly branching a few times at a sharp angle, combined into a loose irregular net by a few transverse branchlets, which are situated chiefly at the extremities. Spores globose, violaceous.

This order is readily distinguished from the PhysaraceÆ by the absence of lime from the threads of the capillitium.

Table of Genera of DidymiaceÆ.

a. The lime on the wall of the sporangium in the form of minute stellate crystals.

• 1. Didymium. Sporangium simple, subglobose and stipitate, the base commonly umbilicate, or sometimes sessile and plasmodiocarp.
• 2. Spumaria. Æthalium composed of numerous elongated irregularly-branched sporangia, closely compacted together and confluent.

b. The lime on the wall of the sporangium consisting of minute roundish granules.

• 3. Diderma. Wall of the sporangium with the outer calcareous layer usually compacted into a smooth continuous crust.
• 4. Lepidoderma. Wall of the sporangium with an outer layer of large scales, consisting of bicarbonate of lime.

I. DIDYMIUM, Schrad. Sporangium simple, subglobose and stipitate, the base commonly umbilicate, or sometimes sessile and plasmodiocarp; the wall a thin membrane with an outer layer of minute stellate crystals of lime. Stipe present or sometimes wanting; the columella mostly conspicuous, sometimes thin or obsolete. Capillitium of very slender threads, straight or often sinuous, stretching from the columella to the wall of the sporangium, simple or outwardly sparingly branched at a sharp angle. Spores globose, violaceous.

Didymium, together with Spumaria, is to be distinguished from all other genera of the Myxomycetes by the covering of stellate crystals, like hoar-frost, upon the outer surface of the sporangium.

§1. Cionium. Columella prominent, subcentral, globose, obovoid, or turbinate; the threads of the capillitium radiating in all directions to the wall of the sporangium.

A. Sporangium stipitate.

1. Didymium squamulosum, A. & S. Sporangium variable in form and size, small and globose, or large and much depressed, the base usually umbilicate, stipitate, or sometimes sessile, and even plasmodiocarp; the wall very thin and pellucid, with a thin, gray-white layer of stellate crystals of lime, breaking up into subpersistent scales. Stipe short, erect, snow-white, longitudinally furrowed or plicate; the columella central, snow-white, various in shape, globose, obovoid, turbinate, and stipitate or sessile. Capillitium of numerous colorless threads, radiating from the columella and separating outwardly into several branches. Spores globose, very minutely warted, dark violaceous, 8–10 mic. in diameter.

Growing on old wood, leaves, herbaceous stems, etc. Sporangium .4-.6-.8 mm. in diameter, the stipe scarcely longer than the diameter, often much shorter or nearly wanting.

2. Didymium proximum, B. & C. Sporangium globose or depressed-globose, the base more or less umbilicate, stipitate; the wall very thin and pellucid, with a loose white covering of stellate crystals of lime, the upper part breaking up and falling away. Stipe long, erect, tapering upward, yellow-brown to reddish-brown, expanding at the base into a small hypothallus; the columella central, white, turbinate, or discoid turbinate. Capillitium of slender, colorless threads, radiating from the columella, branching and often anastomosing. Spores globose, even, pale violaceous, 8–10 mic. in diameter. Plate XII, Fig. 37.

Growing on old leaves, sticks, culms, etc. Sporangium .4-.6 mm. in diameter, the stipe two or three times the diameter.

3. Didymium eximium, Peck. Sporangium depressed-globose, the base umbilicate, sometimes very much depressed and also umbilicate above, stipitate; the wall pale ocher or pale yellow, with a thin layer of minute white crystals of lime, the upper part gradually breaking away. Stipe long, erect, tapering upward, pale yellow-brown, darker below, expanding into a small brown hypothallus; the columella central, large, discoid, or sometimes rough and irregular, pale ochre or yellowish. Capillitium of much-branched colorless threads, radiating upward and downward from the columella. Spores globose, very minutely warted, dark violaceous, 9–11 mic. in diameter. Plate XII, Fig. 38.

Growing on old leaves, sticks, etc. Sporangium .5-.6 mm. in diameter, the stipe about twice the diameter.

4. Didymium microcarpum, Fr. Sporangium small, globose, the base slightly umbilicate, stipitate; the wall a dark-colored membrane, covered with abundant snow-white crystals of lime. Stipe long, slender, erect, delicately striate, yellow-brown to blackish in color, expanded at the base into a small hypothallus; the columella small, globose, sessile or substipitate, pale yellow-brown. Capillitium of pale brown threads, somewhat branched and forming a loose net. Spores globose, very minutely warted, violaceous, 6–7 mic. in diameter.

Growing on old wood, leaves, mosses, etc. Sporangium .4-.5 mm. in diameter, the stipe two or three times as long. The species is more particularly distinguished by its small spores.

5. Didymium minus, Lister. Sporangium depressed-globose, the base umbilicate, stipitate, rarely sessile and plasmodiocarp; the wall a dark-colored membrane with a thin layer of stellate crystals of lime, breaking up gradually and falling away. Stipe erect or sometimes bent at the apex, variable in length, rarely wanting, from pale brown to blackish in color, rising from a small hypothallus; the columella reaching the center, brown or blackish, rough, convex, subglobose or pulvinate, substipitate. Capillitium of slender colorless threads, radiating from the columella and more or less branched outwardly. Spores globose, very minutely warted, violaceous, 8–10 mic. in diameter. Plate XII, Fig. 39.

Growing in vast abundance in Spring on old leaves, bark, wood, etc. Sporangium .4-.6 mm. in diameter, the stipe scarcely longer but usually shorter than the diameter of the sporangium rarely absent. It is considered by Lister to be a variety of D. farinaceum; it differs from this species in its smaller and less-depressed sporangium and in its smaller nearly smooth spores.

B. Sporangia sessile.

6. Didymium effusum, Link. Sporangia gregarious or scattered, sessile on a flattened base, convex above, various in shape, subrotund or by confluence effused and venosely creeping; the wall very thin and pellucid, invested with a thin flocculose layer of minute crystals of lime. The columella hemispheric, rugulose, usually snow-white. Capillitium of very slender colorless threads, furnished with numerous minute protuberances, much branched and combined into a dense net. Spores globose, very minutely warted, dark violaceous, 10–11 mic. in diameter.

Growing on old leaves, wood, etc. Sporangium about .5 mm. in diameter or thickness, sometimes confluent and more or less elongated as a plasmodiocarp. This species is reported from the United States, but I have seen no specimens.

7. Didymium physaroides, Pers. Sporangia roundish or hemispheric, more or less irregular and deformed, sessile or with a very short stipe, and closely crowded together upon a strongly-developed common hypothallus; the wall a dark colored membrane, with a thin layer of stellate crystals of lime. The columella large and thick, divided into cells which are filled with irregular lumps of lime, common to all the sporangia. Capillitium of stout threads, usually simple, only rarely branched, furnished with numerous fusiform swellings. Spores globose, minutely warted, dark violaceous, 12–14 mic. in diameter.

Growing on old wood, bark, moss, etc. Reported from Carolina by Curtis. It is said superficially to resemble somewhat Physarum didermoides.

§2. Placentia. Columella basal, much depressed, very thin or quite obsolete, connate with the base of the sporangium; the threads of the capillitium ascending to the wall of the sporangium.

A. Sporangium stipitate.

8. Didymium farinaceum, Schrad. Sporangium hemispherical, more or less depressed, the base profoundly umbilicate; the wall firm, rugulose, dark-colored and nearly opaque, with a mealy coat of stellate crystals of lime, rupturing irregularly. Stipe variable in length, rigid, erect, black or sometimes rusty-brown, arising from a small hypothallus; the columella broad, hemispherical or pulvinate, black, the lower side connate with the wall of the sporangium. Capillitium of dark-colored sinuous threads, simple or scarcely branched. Spores globose, dark violaceous, minutely warted, 10–13 mic. in diameter. Plate XII, Fig. 40.

Growing on old wood, leaves, mosses, etc. Sporangium .6-.9 mm. in diameter, the stipe about as long as the diameter of the sporangium or sometimes much longer, usually, however, much shorter than the diameter and almost concealed within the umbilicus. My specimens are from Pennsylvania and Alabama. It is readily distinguished from Didymium minus by the much larger and more distinctly warted spores.

9. Didymium clavus, A. & S. Sporangium pileate, very much depressed, convex above and concave below, stipitate; the wall a dark-colored membrane, thickly covered with minute white crystals of lime, except the brown concavity underneath, the upper part breaking away, the lower persistent. Stipe short, erect, rugulose, brown or blackish, expanding at the base into a small hypothallus; the columella reduced to a thin layer of minute brown scales upon the base of the sporangium. Capillitium of simple or sparingly-branched threads, colorless at the extremities and dark-colored between. Spores globose, even, violaceous, 6–8 mic. in diameter.

Growing on old leaves, sticks, herbaceous stems, etc. The sporangium .6-.8 mm. in diameter, the stipe about the same length. Fries considered this to be a mere variety of D. farinaceum, but it is readily distinguished by its very small spores.

B. Sporangia sessile.

10. Didymium serpula, Fr. Plasmodium yellow. Plasmodiocarp much depressed, subrotund or usually more or less elongated, bent, flexuous and reticulate; the wall dark-colored, with a thin layer of stellate crystals of lime. Columella entirely wanting. Capillitium of very slender threads, extending from base to upper surface, much branched, the branches combined into a dense network; to these threads adhere numerous roundish vesicles, composed of a brownish membrane, inclosing a yellow coloring matter, the vesicles 30–50 mic. in diameter. Spores globose, very minutely warted, violaceous, 7–8 mic. in diameter.

Growing on old leaves, bark, etc. The plasmodiocarp .6-.8 mm. in thickness and extending from one to several millimeters in length. This species is reported from the United States by Massee. It ought to be readily recognized by its yellow plasmodium and the peculiar vesicles adherent to the capillitium.

11. Didymium anellus, Morgan, n. sp. Plasmodiocarp in small rings or links, then confluent and elongated, irregularly connected together, bent and flexuous, resting on a thin venulose hypothallus; the wall firm, dark-colored, with a thin layer of stellate crystals of lime, irregularly ruptured. Columella merely a thin layer of brown scales. Capillitium of slender dark-colored threads, which extend from base to wall, more or less branched, and combined into a loose net. Spores globose, very minutely warted, violaceous, 8–9 mic. in diameter. Plate XII, Fig. 41.

Growing on old leaves in woods in Spring. Plasmodiocarp in rings .3-.5 mm. in diameter, or often more or less elongated into links and chains, which are bent and flexed in quite an irregular manner, the thread or vein composing them about .2 mm. in thickness. A more minute species than Didymium serpula, without characteristic thickenings upon the threads of the capillitium, and wanting the peculiar large cells of this species.

II. SPUMARIA, Pers. Æthalium composed of numerous elongated, irregularly-branched sporangia, more or less closely compacted together and confluent, seated upon a well-developed common hypothallus; the walls of the sporangia a thin membrane with an outer layer of minute, stellate crystals of lime. Each sporangium traversed by a central subcylindric hollow columella, which extends also to the branches, but does not reach to their apices. Capillitium of slender threads, more or less branched, and combined into a network. Spores globose, violaceous.

Spumaria is essentially related to Didymium by the crystals of lime upon the walls of the sporangia. Rostafinski's figure 158 can only be regarded as ideal or diagrammatic. I am disposed to question the existence of the central columella altogether; if it does exist, it must be extremely defective.

1. Spumaria alba, Bull. Plasmodium white, amplectant. Æthalium variable in form and size, resting upon a white, membranaceous hypothallus, and usually covered by a white, friable, common cortex composed of minute crystals of lime. The component sporangia elongated, irregular, more or less branched, the branches rude, deformed, compressed, laterally confluent, obtuse or pointed at the apex; the walls of the sporangia thin and delicate, rugulose, pellucid, with a tinge of violet, iridescent when divested of the crystals of lime. Capillitium of slender threads, more or less branched and combined into a net; the threads dark colored, with pellucid extremities, and furnished with occasional rings or roundish swellings throughout their length. Spores globose, densely spinulose, dark violaceous, 10–14 mic. in diameter. Plate XII, Fig. 43.

Climbing up and surrounding the stems of small shrubs, herbaceous plants, culms of grasses, etc., especially those of living plants, rarely effused upon old wood, bark, leaves, etc. The Æthalium from two or three to several centimeters in length, and with a radial thickness of two or three to several millimeters. The following forms or varieties have been distinguished as species at different times:

Var. 1. DIDYMIUM. Sporangia irregular, simple or lobed and branched, lifted up on narrow, flat extensions of the hypothallus, as if furnished with short white stipes; the common cortex wanting. This is Didymium spumarioides, Fr.; it is probably a dwarf form of the next variety. Plate XII, Fig. 42.

Var. 2. CORNUTA. Æthalium large and rugged in outline, cinerous from the scanty cortex; the sporangia loosely compacted, the branches running out into numerous free-pointed extremities. Capillitium of rather thick threads, forming a dense net, with broad expansions at the angles. Spores 11–14 mic. in diameter. This is Spumaria cornuta, Schum. It is evidently the form so elaborately figured by Rostafinski, and which Fries says abounds in Northern Europe.

Var. 3. MUCILAGO. Æthalium large, even and uniform in outline, covered by a thick, white, common cortex; the sporangia laterally confluent and densely compacted together throughout. Capillitium of rather slender threads, forming a loose net, scarcely expanded at the angles. Spores 10–13 mic. in diameter. This is Spumaria mucilago, Nees, as figured by Greville in the Scottish Cryptogamic Flora. The capillitium is figured by McBride in The Myxomycetes of Iowa. This is the only form I have met with in this country.

III. DIDERMA, Pers. Sporangia subglobose and stipitate or more often sessile, sometimes plasmodiocarp; the wall a thin membrane, with an outer layer composed of minute roundish granules of lime, which are usually compacted into a smooth continuous crust. Stipe present or mostly absent; the columella usually well developed. Capillitium of very slender threads, stretching from the columella to the wall of the sporangium, more or less branched, and combined into a loose net by short lateral branchlets. Spores globose, violaceous.

This genus is easily recognized by the smooth crustaceous layer of lime on the outer surface of the sporangium; in many cases this easily shells off or breaks away. Such a coating occurs in a few species of Physarum, but here the vesicles of lime attached to the threads distinguish them. This is Chondrioderma of Rostafinski's monograph; the reason for coining a new name and entirely discarding the old one is not apparent.

§1. Leangium. Sporangium usually stipitate; the wall at maturity separating from the inner mass of spores and capillitium and splitting in a stellate manner, the segments becoming reflexed.

1. Diderma radiatum, Linn. Sporangium depressed-globose, the base flattened or umbilicate, stipitate or nearly sessile; the wall smooth, whitish or pale brown, splitting from the apex downward into a few reflexed irregular segments. Stipe short, thick, erect, tapering downward, standing on a thin membranaceous hypothallus; the columella large, convex, globose or obovoid, roughened. Capillitium of slender dark-colored threads, radiating from the columella, simple or branching outwardly. Spores globose, minutely warted, dark violaceous, 8–10 mic. in diameter.

Growing on old bark and wood. Sporangium .8–1.2 mm. in diameter, the stipe shorter than the diameter, sometimes nearly obsolete. Apparently rare in this country.

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, Massee, 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, Massee 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 shelling 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."—Massee.

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. Æthalium 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.

The Journal of the Cin. Soc. Natural History
Vol. XVI. Plate XII.