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.]