Chapter 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.