SUMMARY1. Tetracladium Marchalianum De Wild, has been discovered on dead and decaying leaves of Isoetes lacustris growing in the greenhouse tanks at Columbia University.2. It is without question a fungus which grows readily on ordinary culture media and produces well developed mycelial colonies.3. The conidia are essentially three- to four-pointed, brush-like, flat, hyaline, multicellular, 22 μ to 75 μ in length, filled with refractive globules at maturity, and belong in the Staurosporeae division of the family Mucedinaceae.4. The mycelium is hyaline, septate, highly branched, rich in refractive globules at maturity, and varies from 2 to 10 μ in diameter, depending somewhat on age and degree of anastomosis.5. Tetradadium Marchalianum is doubtless an aquatic Saprophyte of wide occurrence. No evidence of parasitism has yet been observed on Isoetes lacustris, and it appears to develop only in dead and decaying tissues.6. This fungus, in the author's opinion, is identical with Ce-rasterias raphidioides Reinsch (1888) var. incrassatum and inacquale, and consequently the name T. Marchalianum should supersede it, since it is confused with the algal genus bearing the same name.
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John S. Karling (1935) studied this question.