Part 16

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.