able variation in the diameter of the indi- vidual trichomes, the base measuring 1.5 to 5.0 microns and the swollen tip measur- ing 6.0 to 9.0 microns. Each trichome is sur- rounded b}' a colorless sheath which later may become rust-colored and heavily en- crusted, especially at the base, with deposi- tions of ferric hydroxide and, to a lesser e.xtent, manganese oxides. The ensheathed trichomes may reach a diameter of 12 mi- srons or more. Cells within the trichomes are usually about 1.5 times as long as they are wide and are more or less rectangular in shape. During reproduction the cells divide by longitudinal and transverse fission into non- motile conidia of two types: microconidia, which are 1 to 2 microns in diameter, and macroconidia, which measure about 5 microns in diameter; intermediate forms may also occur. When the tip of the sheath ruptures, the conidia are extruded; these may attach themselves to some object and grow into trichomes, or they may germinate upon the exterior of the sheath from which they were liberated, giving rise to new tri- chomes attached to the surface of the older one, thus simulating false branching. The conidia often form a zoogloeal mass, but only in the presence of dissolved iron. In addition to the above-mentioned types of reproductive cells, Cohn (ibid., 120) ob- served a third structure which he condi- tionall}'^ alluded to as a spore. These cells originate from the swollen terminal cell which is usually ellipsoidal in shape and sometimes as much as seven times as long as it is wide (3.67 by 26.25 microns). The protoplasm of this terminal cell becomes finely granular and eventually emerges from the sheath. From these cells, short, color- less Oscillaria-like trichomes are produced which contain no more than eight cylindri- cal cells measuring 5 to 6 by 10 to 12 microns. The trichomes have a characteristic, slow, gliding motion and are surrounded by a fine, transparent membrane, but no sheath. Subsequent authors, when describing this species, have usually failed to mention this third type of reproductive cell observed by Cohn. Cultivation: Has not been grown on artificial media in pure culture. Grows readily in water containing organic matter regardless of the iron content of the water. Related species: Cholodny believed Clonothrix fusca to be identical with Creno- thrix polyspora. However, Clonothrix ftisca shows genuine false branching and produces conidia by fission in only one plane so that the trichomes taper toward the tip instead of expanding (see Kolk, Amer. Jour. Bot., 25, 1938, 11, for a differentiation of these two species). Comments: Zopf (Entwicklungsgesch. Unters. (i. Crenoihrix polyspora, die Ursache der Berliner Wasserkalamitat. Berlin, 1879, 2) regards Leptothrix kuehniana Rabenhorst as identical with Crenothrix polyspora Cohn, and there seems to be much evidence in favor of considering the tw-o species as identical. If Cohn's organism proves to be identical with Rabenhorst's, then the spe- cific epithet kuehniana has priority over polyspora; however, until the relationship of the two organisms has been clarified, the name Crenothrix polyspora is retained here. Source: This organism is wide-spread in water pipes, drain pipes and springs w^here the water contains iron. It frequently fills pipes under such circumstances and causes a real nuisance. Found by Cohn in samples of water from springs in the neighborhood of Breslau, Germany. Habitat: Found in stagnant or running waters containing organic matter and iron salts. Harmless, but frequently becomes bothersome in w^ater pipes and city water supplies; grows as thick, brownish masses.
Genus II. Phragmidiothrix Engler, 1883.
(Vierter Ber. d. Commission z. wissensch. Unters. d. deutsch. Meere in Kiel fiir 1877 bis 1881, I Abt., 1883, 187.)
Phrag.mi'di.o.thrix. Gr. noun phragma fence; Gr. noun eidus form, shape; Gr. noun thrix, trichis hair; M.L. fem.n. Phragmidiothrix fence-like hair.
Trichomes are articulated, unbranched and attached, the free ends being swollen. Sur-
