38 MYCOLOGY 



Crenothrix. — The cells are arranged in unbranched threads attached 

 at one end and enlarging toward the distal extremity. Filaments 

 covered by a rather thick sheath. The reproductive cells are non- 

 motile conidia, which on discharge immediately germinate. Crenothrix 

 polyspora in springs and water pipes, where it forms attached slimy 

 growths. The sheaths in iron waters are impregnated with iron 

 oxidhydrate. 



Phragniidiothrix. — Cylindric cells with delicate, scarcely visible 

 sheath. The cells of the filament are at first in one plane which later 

 divide in three directions to form clumps or packets of cells. Later 

 the single cells round off and become free. Ph. nrnltiseptata with fila- 

 ments 3 to 12/X broad and looyu long attached to the bodies of crustaceae. 



Cladothrix {SphceroHlus in part). — The fixed and often tufted 

 filaments form delicate sheaths. The cells are cylindric and by inter- 

 calary growth may break laterally through the sheath to form false 

 dichotomous branches. Reproduction is accomplished by motile 

 swarm spores (gonidia) which bear a tuft of flagella a little to one side 

 of a pole. Cladothrix dichotoma occurs frequently in stagnant water, 

 attached and forming furry growths. The following species occur in 

 the soil: C. rufula, C. profundus, C. intestinalis, C. fungiformis, while 

 C. intrica has been isolated from sea water and sea mud. 



Family 5. Thiobacteriace^ (Beggiatoace.e). — Cells with sul- 

 phur inclusions, unpigmented, or colored rose, red or violet by bacterio- 

 purpurin; never green. The plants are generally filamentous with 

 division transverse to the long axis. 



Thiothrix. — Unequally thick attached filaments encased in a 

 delicate, scarcely visible sheath. Rod-shaped conidia are formed at 

 the ends of the threads. Th. nivea is found in sulphur springs and in 

 stagnant water. 



Beggiatoa. — Sheathless, free-filamentous bacteria, motile by means 

 of an undulating membrane. Cells with included sulphur granules. 

 Spore formation unknown. B. alba is found in dirty water, drain 

 water from sugar factories and attached to decayed plants in sulphur 

 springs. B. mirabilis forms white growths on dead marine algae. 



The colored sulphur bacteria, sometimes placed in the family 

 Rhodobacteriace^, belong here. They have rose, red or violet cell 

 contents due to the presence of bacteriopurpurin (see ante). The im- 



