266 LABORATORY EXERCISES IN BACTERIOLOGY. 



IV. Family: Mycobacteriaceae (cells straight, short or long, cylindric, clavate, 



cuneate in form ; at times showing a true branching, or as long, branched 

 mycelial filaments; no sheath; without endospores, but with formation 

 of gonidia-like bodies due to transverse segmentation of cells). 



(a) Genus: Mycobacterium (cells commonly short, cylindric rods, sometimes 



bent and irregularly swollen, clavate or cuneate; may show Y-shaped 

 forms or longer filaments with true branchings; may produce short 

 coccoid elements which are perhaps gonidia). 



(b) Genus: Streptothrix (cells commonly long-branched filaments; produce 

 gonidia-like bodies; form aerial hyphae in cultures, causing resemblance 

 to moulds). 



V. Family: Chlamidobacteriaceae (filaments composed of rod-shaped cells, 



and surrounded by a distinct sheath ; cell division transverse or in three 

 directions, resulting in formation of gonidia-like bodies which may or 

 may not be motile). 



(a) Genus: Leptothrix (filaments unbranched; division transverse). 



(b) Genus: Phragmidiothrix (filaments unbranched; divisions in three direc- 

 tions; sheath scarcely visible). 



(c) Genus: Crenothrix (filaments unbranched; division in three directions; 

 sheath distinct). 



(d) Genus: Cladothrix (filaments show false branching). 



(B) Suborder: THIOBACTERIACE^ (cells show presence of colored granules, or 

 sometimes diffuse coloring, red or violet). 



I. Family: Beggiatoaceae (filamentous; with or without sheath; motile or non- 



motile ; sulphur granules in cell contents ; gonidia formation not known) . 



(a) Genus: Beggiatoa (filaments motile by means of undulating membrane; 



segmentation not apparent except when stained with iodine; colorless 

 or faintly reddish-violet). 



(b) Genus: Thiothrix (filaments non-motile; surrounded by delicate sheath; 



sulphur granules in cell contents; at ends of filaments rod-shaped gonidia ; 

 filaments unequal in diameter). 



II. Family: Rhodobacteriaceae (cells irregular, globular, oval, cylindric, non- 



filamentous ; contents show the presence of sulphur granules or bacterio- 

 purpurin, red or violet). 



(A) Subfamily: THIOCAPSACE^ (cells divide in three planes). 



(a) Genus: Thiocystis. 



(b) Genus: Thiocapsa. 



(c) Genus: Thiosarcina. 



(B) Subfamily: LAMPROCYSTACE;^ (cells divide in three planes, then in two). 



(a) Genus: Lamprocystis. 



(C) Subfamily: THIOPEDACE^E (cells divide in two planes). 



(a) Genus: Thiopedia. 



(D) Subfamily: AMEBOBACTERIACE^ (cells divide in one plane). 



(a) Genus: Amebabacter. 



(b) Genus: Thiothece. 



(c) Genus: Thiodictyon. 



(d) Genus: T hi o poly coccus. 



