1006 COMPREHENSIVE KEY 



Note: The unequal length of the flagella suggests that this may be an algal 

 or protozoan cell. 

 Not as above 12 



12. Rods arranged at random in zoogloea; encrusted with iron. . . . Sideromonas p. 222 



(Including Siderocapsa major) 

 Cells arranged in pairs or chains in capsules Ferribacterium p. 221 



13. Cells in mass appear green to greenish yellow; contain a photosynthetic pigment which 



is not bacteriochlorophyll or chlorophyll "a" but which may be chlorobium chloro- 

 phyll; individual cells usually colorless; grow anaerobically when exposed to light, 

 oxidizing sulfide to sulfur, which is deposited outside the cell; no growth aerobically 



14 



Not as above 18 



14. Cells found adherent to the surface of other organisms, apparently living in symbiosis 



with them 15 



Note: The taxonomic significance of these groups is doubtful, but until they 

 are isolated from the supposed symbiont and studied separately, they must 

 be treated in this fashion. 

 Cells free-living 17 



15. Green cells attached to the surface of a protozoan Chlorobacteriuni p. 65 



Green cells attached to bacteria 16 



16. Aggregates small, barrel-shaped, activeh' motile, consisting of a central, polar-flagel- 



late, rod-shaped cell covered with the green organisms; green cells 0.5 to 1.0 by 1.0 

 to 2.5 microns, usually 8 to 16 surrounding the central cell; aggregates measure 



2.5 to 5.0 by 7 to 12 microns Chlorochromatium p. 65 



Aggregates large, long and cylindrical; non-motile; consist of green cells, 0.5 to 1.0 by 

 2.0 to 4.0 microns, lying on the surface of a slime capsule which covers the inner 

 cylindrical cell. They are themselves covered by a layer of slime. Aggregates measure 

 7.0 to 8.0 microns wide by up to 50 microns long Cylindrogloea p. 66 



17. Encapsulated cells forming characteristic aggregates consisting of net-like structures, 



irregular three-dimensional masses or two-dimensional masses in which cells lie in 



parallel strands Pelodictyon p. 63 



Cells may produce slime but usually remain dispersed; in young healthy cultures, small 

 ovoid rods, 0.7 to 0.9 by 1.5 microns, forming chains; at pH 7.5 to 8.0, involution forms 

 such as cork-screw type rods and cocci are characteristic. . . .Chlorobium p. 62 



18. Cell masses are various shades of red or purple 19 



Not as above 20 



19. Cells contain bacteriochlorophyll and carotenoid pigments; capable of growth anaero- 



bically when exposed to light; proceed to Section J p. 1031 



Not as above 20 



20. Cells motile only by a gliding movement on solid surfaces or along each other; single 



cells non-motile when free in solution. Motility can be observed at the glass- 

 water interface on a slide or on the surface of agar plates where cells move singly or 

 in groups, frequently leaving a trail of slime behind. Cells are flexible, the extent of 



the flexibility being dependent on length and turgidity (see note below) 21 



Note: This subdivision is represented by two main groups: In one the cells 

 are usually less than 10 microns long, frequently only 2.0 to 5.0 microns; Gram- 

 negative; in wet preparations fi.xed with osmic acid, they may appear as blunt- 

 ended rods; in stained preparations subjected to heat fixation, they are fre- 

 quently curved, S-shaped, bent or spirilliform. In the other, the cells are 

 usually longer than 10 microns and may form articulated chains. 



There are, however, much shorter representatives of this subdivision which, 

 because of their shortness, are more rigid and resemble ordinary bacteria in 

 many respects except for their gliding movement and lack of flagella. Species 



