82 GENERAL SYSTEMATIC BACTERIOLOGY 



B. Usually a number of spores develop within a swollen cell. 



Genus 4. Metabacierium 



Key to the subgenera of Bacillus 



A. Spore not barrel-shaped in longitudinal section and not star-shaped in cross 



section. 



I. Motile by means of peritrichous flagella. 



Subgenus 1. Eu-Bacillus 

 II. Non-motile Subgenus 2. Bacteridium 



B. Spore barrel-shaped in longitudinal section, longitudinal striations evident. 



Subgenus 3. Astasia 



Key to the subtribes of the Bacterieae 



A. Cells usually fusiform Subtribe I. Fusiforminae 



B. Cells not fusiform. 



I. Requiring serum or hemoglobin for development. Obligate parasites. 

 Gram-negative. Non-motile. 



Subtribe II. Hemophilinae 

 II. Not requiring serum, or at least hemoglobin, for development. Gram- 

 negative or positive. Motile or non-motile. 



a. Obligate aerobes, securing growth energy by oxidation, etc. 



Subtribe III. Rhizobiinae 



b. Not obligate aerobes, not securing growth energy by oxidation of 



carbonaceous compounds. 



Subtribe IV. Bacteriinae 



Key to the Genera of Fusiforminae 



One genus only Fusiformis. 



Key to the Genera of Hemophilinae 



A. Requiring serum for growth. Cells almost ultra-microscopic. Stain best by 



Giemsa. Involution forms characteristic. 



Genus 1. Asterococcus 



B. Requiring hemoglobin for growth. Stain readily with ordinary aniline dyes. 



Involution forms infrequent Genus 2. Hemophilus 



Key to the genera of Rhizobiinae 



A. Not fixing atmospheric nitrogen; securing growth energy usually by the oxida- 



tion of ethyl alcohol to acetic acid.. Genus 1. Mycoderma 



B. Capable of fixing appreciable amounts of atmospheric nitrogen. Grow well 



on nitrogen-free media. 



a. Small motile rods, with abundant involution forms, frequently living in 



root nodules of the higher plants (legumes). 



Genus 2. Rhizobium 



b. Not symbiotic. Cells larger, plump, almost spherical in some cases. 



Genus 3. Azotobacter 



