CLASSIFICATION OF THE BACTERIA 33 



roots of leguminous plants. By use of the energy secured 

 from the oxidation of carbon compounds, usually sugars, 

 they are capable of fixing atmospheric nitrogen. The 

 species found generally upon the roots of leguminous plants 

 is Rhizobium leguminosarum. ^ 



It is capable of fixing atmospheric nitrogen when grown 

 in the laboratory in solutions containing carbohydrates. 



II. Family Bacillaceae 



The organisms belonging to this group are always rod- 

 shaped, all produce endospores, and the flagella when pres- 

 ent are peritrichous. For the most part they are able to 

 decompose complex organic compounds, and are active in 

 producing decay in nature. Two genera are included in 

 this family ; the genus Bacillus, including those forms which 

 require free oxygen for their development; and Clostri- 

 dium, including those forms which do not grow in the 

 presence of free oxygen. 



Bacillus. — The organisms belonging to this genus are all 



8 



Fig. 12. — Bacillus. A. Motile species. 1. Vegetative cells. 2. 

 Sporulating cells. 3. Free spores. B. Nonmotile species. 1. 

 Vegetative cells in capsules. 2. Left. Noncapsulated vege- 

 tative cells. Right. Sporulating cells. 3. Free spores. 



rod-shaped, sometimes occurring in chains. Under the 

 right conditions these bacteria are among the most active 



1 Many other names have been applied to this organism. It is 

 frequently discussed in literature as the Bacillus radicicola. 



