SUMMARYTwoArchangiumisolates,A. primigeniumandA. gephyra, were secured from soil and elm tree bark. Pure cultures were established and maintained on a variety of media. Agar plates containing rabbit dung and rabbit dung decoction agar proved most useful. The cultures were incubated at 22–26 C.Vegetative rods ofA. gephyraaveraged 10.5×0.6μ, whileA. primigeniumaveraged 7×1.2μ. Cells were needle-like, tapering slightly to blunt, rounded ends. Characteristic gliding and oscillating movements were observed for both species.Colonial morphology was similar for both species. A flat, thin sheet of cells with a microscopically irregular periphery was typical. The texture of the colonial mass varied in consistency.Fructification was observed in liquid and on solid media. In a liquid medium, atypical, star-like clusters culminated in a solid mass of shortened rods. On solid media, circular and wave-like masses of cells joined to form a mound of cells which matured into the typical, tubular, fruiting body mass.Fruiting bodies from soil or bark averaged 1 mm2or smaller in size. When grown in pure culture, fruiting bodies coalesced to cover areas of over 20 mm2. Fruiting bodies were usually enveloped in a slime layer. Encysted rods ofA. primigeniumaveraged 4.5×0.9μin size andA. gephyra2.5×1.4μ.Germination of fruiting bodies followed either of two patterns both resulting in normal, migrating colonies. Activated rods either pulsed forth from a germinating fruiting body or projected perpendicularly from the surface of the entire fruiting body as quills on a porcupine.Carotene as a component ofArchangiumpigmentation was ascertained by using conc. H2SO4. Loss of pigmentation by a fruiting body indicated loss of viability. Standard nuclear stains produced dense areas within vegetative cells and granulations. Granulations also occurred when5%methylene blue was employed. All rods were gram-negative and non-acid fast.