2. Thioploca ingrica Wislouch, 1912. (Ber. d. deut. bot. Ges., 30, 1912, 470.) in'gri.ca. M.L. adj. ingricus pertaining to Ingria; named after Ingria, an ancient district of Leningrad, Russia. Individual trichomes, 2.0 to 4.5 microns in diameter, occur in a mucilaginous sheath up to 80.0 microns in diameter. The number of trichomes embedded in one sheath is variable. The trichomes are segmented, each segment measuring 1.5 to 8.0 microns in length. Source: Identified from various localities in Central Europe. Habitat: Found in fresh-water and ma- rine mud containing hydrogen sulfide. 3. Thioploca minima Koppe, 1923. (Arch. f. Hydrobiol., 14, 1923, 630.) mi'ni.ma. L. sup. adj. minimus least, smallest. Individual trichomes, 0.8 to 1.5 microns in diameter, occur in a common, mucilagi- nous sheath up to 30.0 microns in diameter. The number of trichomes embedded in one sheath is variable. Segmentation is gen- erally observable only after removal of the sulfur droplets; the segments are 1 to 2 mi- crons long. Source: Identified from various localities in Central Europe. Habitat : Found in fresh-water and marine mud containing hydrogen sulfide. 4. Thioploca mixta Koppe, 1923. (Arch. f. Hydrobiol., U, 1923, 630.) mix'ta. L. part. adj. mixtus mixed. Individual trichomes of two clearly differ- ent sizes, the one 6 to 8 microns and the other about 1 micron in diameter, occur in a common, mucilaginous sheath usually about 50 microns thick. The number of tri- chomes embedded in one sheath is variable. The wider trichomes are clearly segmented, the segments measuring 5 to 8 microns in length; in the narrower trichomes, segmen- tation is visible only after removal of the sulfur droplets, each segment measuring 1 to 2 microns in length. Source: Identified only from Lake Con- stance. Habitat: Found in fresh-water mud con- taining hydrogen sulfide. Genus IV. Thiothrix Winogradsky , 1888. (Beitr. z. Morph. u. Physiol, d. Bakt., I, Schwefelbacterien, Leipzig, 1888, 39.) Thi'o.thrix. Gr. nounthium sulfur; Gr. noun thrix hair; M.L. fem.n. Thiothrix sulfur hair. Cells occur in non-motile, segmented trichomes which are differentiated into base and tip and surrounded by a delicate sheath. Trichomes grow attached at the base to solid ob- jects by means of gelatinous hold-fasts. Reproduction is by transverse fission of the seg- ments and by rod-shaped, so-called conidia which probably are the apical segments which become free. Temporarily, the conidia show creeping motility, become attached to solid objects and develop into new trichomes. The following key to the species of the genus Thiothrix is based upon the diameters of the trichomes and their habitats, the only criteria used by previous authors for the differ- entiation of the seven recognized species. The validity of these distinguishing characteristics is, however, doubtful because their constancy has not been sufficiently established; so far the morphology of the species in Thiothrix has not been studied in pure cultures. The type species is Thiothrix nivea (Rabenhorst) Winogradsky. Key to the species of genus Thiothrix. From fresh-water environments. A. Diameter of trichomes is greater than 0.5 micron. 1. Diameter of trichomes about 2.0 (1.4 to 3.0) microns. 1. Thiothrix nivea. 2. Diameter of trichomes about 1.0 micron. 2. Thiothrix tenuis.
