38 BIOLOGY AND TECHNIQUE 



Genus III. Spirillum. — Cells rigid, with polar tufts of five to twenty 

 flagella usually curved in semicircular or flatly undulating curves. 



Genus IV. Spirochcete.— Cells sinously flexible. Organs of locomo- 

 tion unknown, perhaps a marginal undulating membrane. 



Family IV. Chlamydobacteriace^. — Forms of very varying stages 

 of evolution, but all distinguished by a rigid sheath (HuUe) or 

 covering, which surrounds the cells. The cells are united in 

 branched or unbranched threads. 



Genus I. Streptothrix.— Cells united in simple, unbranched threads. 

 Division in one direction of space only. Reproduction by non- 

 motile conidia. 



Genus II. Cladothrix. — Cells united or pseudodichotomously branch- 

 ing threads. Division in one direction of space only. Vegeta- 

 tive multiplication by separation of entire branches. Repro- 

 duction by swarming forms with polar flagella. 



Genus III. Crenothrix. — Cells united in unbranched threads, at 

 ■ first with division in one direction of space only. Later the cells 

 divide in all three directions of space. The daughter cells ,be- 

 come rounded and develop into reproductive cells. 



Genus IV. Phragmidiothrix. — Cells at first united in unbranched 

 threads, dividing in three directions of space, thus forming a 

 rope of cells. Later some of the cells may penetrate through the 

 delicate sheath, and thus give rise to branches. 



Genus V. Thiothrix. — Unbranched, non-motile threads, inclosed 

 in fine sheaths. Division of cells in one direction only. Cells 

 contain sulphur granules. 



Family V. Beggiatoace,e. — Cells united in sheathless threads. 

 Division in one direction of space only. Motility by undulating 

 membrane as in Oscillaria. 

 Genus Beggiatoa. — Cells with sulphur granules. 



It will be seen in reviewing the classification just given that the sub- 

 divisions are based upon questions of form, motility, and situation of 

 flagella. While these characteristics, so far as we know, are constant, 

 there are, nevertheless, many instances in which types entirely similar 

 in these respects must be differentiated. This can be done only by care- 

 ful study of staining reactions, finer structure, cultural characteristics, 

 and biological activities. 



