NOMENCLATURE AND CLASSIFICATIONS. l6l 



A separation into two genera does not appear to be desirable at the present time. 

 No such difference exists inside this genus as there is between the genus Microspira, 

 which only exceptionally has more than one flagellum on the pole, and the genus 

 Spirillum, which has many polar flagella. Between the one-flagellate and many- 

 flagellate forms there are all sorts of transitions in the genus Pseudomonas. Possibly 

 the boundary between Pseudomonas and Microspira is artificial. Slight crooking of 

 the rods, especially in stained preparations, has been observed in many species of 

 Pseudomonas, and it is not always possible to decide whether a one-flagellate form 

 belongs to this genus or to Microspira. Ordinarily, a decision may be reached by 

 observing the shape of the threads or chains, those of Pseudomonas never being 

 twisted into the form of a screw. 



3. Family SPIRILLACEAE (Screwbacteria) . 



Cells spirally wound or representing a portion of the turn of a spiral, in which 

 latter case the entire spiral is visible only when several cells remain united. Endo- 

 spore formation established for some species, but rare. Apparently, in some of the 

 larger species resting forms are also produced by the breaking up of the rods into 

 short segments which envelop themselves in a gelatinous membrane. Usually motile. 

 Division only in one direction of space perpendicular to the long axis. 



Spirosoma Migula. 



Cells generally rather large, spirally bent, rigid, and without organs of motion. 

 Cells single, free, or united into small gelatinous families. 



(1) Subgenus EUSPIROSOMA : Cells single or united into a spirally twisted thread. 

 Free, that is, not inclosed in any gelatinous envelope. 



(2) Subgenus MYCONOSTOC: Cells single or united into spiral threads, which are 

 surrounded by a roundish general envelope. 



Microspira Schroter. 



Cells bent like a comma or sausage, rigid, single or several united, in which latter 

 case screws or S-shaped figures are produced. Motile by means of i wavy-bent polar 

 flagellum (rarely 2 or 3 flagella). The flagellum is usually not much longer than the 

 cell. Endospore formation has thus far not been demonstrated. Many authors do 

 not distinguish between this genus and the next. 



Spirillum Ehrenberg. 



Cells rigid, rods of various thicknesses, length, and pitch of the spiral, forming 

 either long screws or only portions of a turn. Cells motile by means of a tuft of polar 

 flagella (5 to 20), which are mostly half circular, rarely wavy-bent. These flagella 

 occur on one or both poles. Their number varies greatly and is difficult to determine, 

 since in stained preparations several are often united into a common strand. Endo- 

 spore formation has been observed in some species. There are many undescribed species. 



Spirochaeta Ehrenberg. 



Cells thin, mostly quite long, motile and flexible, winding snake-like, but also 

 moving in the manner of a screw. Organs of motion unknown. Endospore forma- 

 tion not observed. 



Nearly related to the Algal genus Spirulina, but colorless and not segmented into 

 single cells. 



4. Family CHLAMYDOBACTERIACEAE. 



Cells cylindric, united into threads which are surrounded by a sheath. Repro- 

 duction by means of motile or non-motile conidia which arise directly from the vege- 

 tative cells, and without passing through any resting stage grow into new threads. 



