The vegetative mycelium, usually inconspicuous, is formed in water on a variety of plant and animal parts. The aerial mycelium is lacking as a rule; it is formed in certain species and then much as in Streptomyces. Reproduction is by spores formed in sporangia, the spores in Actmoplanes possessing fiagella and being motile, and those in Streptosporangium pos- sessing no flagella and being non -motile; conidia are formed in many species. Culturable on a variety of artificial media and then resembling, in vegetative characters, certain spe- cies of Nocardia, Micromonospora or Streptomyces. Widely distributed in soil and fresh water. Key to the genera of family Actinoplanaceae. I. Aerial mycelium usually not formed; coiled conidiophores lacking; sporangiospores motile. Genus I. Actinoplanes, p. 826. II. Aerial mycelium abundant ; coiled conidiophores as well as sporangia are formed in some species; sporangiospores non-motile. Genus II. Streptosporangium, p. 828. Genus I. Actinoplanes Couch, 1950. (Couch, Jour. Elisha Mitchell Scientific Society, 66, 1950, 87; also see ibid., 71, 1955, 148; Myceliochytrium fulgens Johanson, in part, Torreya, 45, 1945, 104.) Ac.ti.no.pla'nes. Gr. noun actis, actinis a ray, beam; Gr. noun planes a wanderer; M.L. noun Actinoplanes literally, a ray wanderer; intended to signify an actinomj^cete with swimming spores. On sterilized leaves in water, a very inconspicuous mycelium which branches throughout the leaf tissue is formed, the external hyphae being scattered or in tufts on the leaf sur- face and forming a fringe around the edge of the leaf; aerial mycelium is lacking or spar- ingly formed as a rule. The mycelium is usually pinkish to reddish, sometimes hyaline, on leaves, frequently decolorizing the green leaf and giving it a pinkish or reddish color. Hy- phae are slightly to considerably branched, irregularly coiled, twisted or straight, spar- ingly septate and 0.2 to 2.6 microns in diameter. Sporangia of varied sizes and shapes are usually abundant on leaves and are formed only when the leaf is at or close to the surface of the water, i.e., they are formed typically only in air; owing to refraction, they appear black under the low power of the microscope. The spores are in coils, nearly straight chains or are irregularly arranged in the sporangia; they are 1.0 to 1.5 microns in diameter, globose or subglobose, usually slightly angular, possess one to several shiny bodies and several polar flagella and are motile. Germination is by a minute germ tube which branches to form a mycelium. Sporangial wall evanescent or persistent. Usually not acid-fast. Gram- positive. Gelatin is liquefied. On various nutrient agars a brilliantly colored, toughish to pasty growth is usually formed; surface very variable; growth smooth and even with the agar or elevated, bumpy, convoluted, ridged, folded, cracked, etc.; usually moist and shiny, rarely pulverulent. The hyphae are of two or more distinct forms, the submerged and the surface hyphae, the latter usually more or less vertical, in some species forming a compact "palisade." Sporangia are abundant on some agars and are usually formed at the surface. Conidia formed by some species. On certain agars, the mycelium of some species . breaks up, when crushed, into irregular pieces of hyphae, rods and coccoid bodies. Some iso- lates produce a distinctive pleasant or slightly unpleasant odor, while others are odorless. Aerobic. Saprophytic in a variety of soils and in fresh water; world-wide in distribution.* The above description is based not only on the type species, Actinoplanes philippinensis, but also on over a hundred and twenty isolates representing a number of species groups. The genus is readily distinguished horn Streptosporangium. On leaves the latter produces a conspicuous aerial mycelium which resembles that produced by most species of Strep-
- For methods of collection and isolation, see Couch, Trans. New York Acad. Sci., Ser.
II, 16, 1954, 315.
