282 GENERAL SYSTEMATIC BACTERIOLOGY 



from the sheath and grow into threads. Reproduction by spores, which are 

 formed in the sheath by further subdivision of the joint-cells. The spores either 

 grow directly into threads, or form by continued subdivision gelatinous colonies 

 of roundish cells, which afterwards produce threads. 



Other writers who recognized the genus were Van Tieghem (1884), 

 Zopf (1885), Fliigge (1886), Schroeter (1886, p. 172), Hansgirg (1888, 

 p. 230),Trevisan (1889, p. 10), De Toni and Trevisan (1889) and Hueppe 

 (1885, 1891). Hansgirg (1891, p. 313) discussed the synonomy of the 

 genus, and included within it the genus Phragmidiothrix Engler. He 

 divided the genus into two sections, as follows: 



Section 1. Phragmidiothrix (Engler) nob. Plantae marinae. 1. Crenothrix- 

 foetida (Fior.-Mazz.) nob. (C. marina Hansg.) cum aliis synonymis. Section 

 2. Eucrenothrix nob. Plantae aquae dulcis. 2. Crenothrix Kuhniana (Rbh.) 

 Ciard. (C polyspora Cohn) cum synonymis. 



Ludwig (1892), Hueppe (1895, p. 38), Migula (1895, p. 40, 1897, 

 p. 47, 1900, p. 1033, 1904, p. 145), Fischer (1897, p. 32, 1903, p. 61), 

 Chester (1897, p. 64, 1901, p. 372), Schmidt and Weis (1902, p. 380) 

 A. J. Smith (1902, p. 272), Kendall (1902), Erwin F. Smith (1905, p. 

 162), ElUs (1909, p. 9), Orla-Jensen (1909, p. 334), Molisch (1910), 

 Frost (1911, p. 59) and Heim (1911, p. 254) have all described this 

 genus 



Migula (1894, p. 238) says: 



Zellen zu unverzweigten Faden vereinigt, mit anfang nur nach einer Richtung 

 vor sich gehender Teilung. Spater teilen sich die Zellen nach alien drei Rich- 

 tungen des Raumes, die Teilungsprodukte runden sich ab und werden zu Fort- 

 pflanzungszellen. 



The later diagnosis of the genus by Migula gives the modern con- 

 ception of the genus: 



Cells united into unbranched filaments, attached, and gradually enlarging 

 toward the free end, i.e., with a distinction between base and apex. Sheath rather 

 thick. In iron waters the old and empty sheaths are permeated with iron oxid 

 hydrate. Cells cylindric or flat discoidal. Multiplication by non-motile (mostly 

 roundish) conidia, which arise from the vegetative cells by division and rounding 

 off. For this purpose the cell of the thicker threads divide in three directions of 

 space, those of the thinner threads only perpendicularly to the long axis of the 

 thread. The conidia are discharged and germinate immediately, often on the 

 sheath of the mother thread. 



Molisch (1910, p. 16) used practically the same description. He 

 discusses Crenothrix polyspora Cohn at length. He states that there 



