CLASSIFICATION OF BACTERIA 29 



gradsky has shown that the process is assisted by the iron bacteria 

 and the ferric hydroxide is deposited as a tube about such organisms 

 as Leptothrix ochracea. These tubes, or sheaths, are deposited later 

 as bog iron ore. 



The nitrifying bacteria are found in the soils of our gardens, fields 

 and meadows and in virgin soil derived from places the world over. 

 Winogradsky has discovered that the conversion of ammonia into 

 nitric acid takes place in two steps and that bacteria are effective in 

 both of these operations. One set of bacteria belonging to the genera 

 Nitrosococcus and Nitrosomonas oxidize the 

 ammonia to nitrous acid, or its nitrite, and the 

 conversion of this nitrous acid (nitrite) to nitric 

 acid, or its nitrate, is accomplished by Nitro- 

 bader. Nitrosococcus is a non-motile spheric 

 cell, 3^t in diameter, found in soil from South 

 America and Australia, while Nitrosomonas 

 europcea found in all soils from Europe, Africa 

 and Japan is a short ellipsoidal motile iorm 0.9 

 to iju wide and 1.2 to i.8/x long with a short 

 cilium. Nitrosomonas javanensis from Java is 

 almost spheric, 0.5 to 0.6/^, with a cilium 30/x 

 long, which is the longest known among bac- 

 teria. Nitrobacter are minute non-motile rods 



/ . , \ rr.1 • r ii. Fig. 8. — Roots of soy 



(o.5M X 0.25M). These organisms are of the i,ean. Glycine his pida, with 

 greatest importance in putting the nitrogen of tubercles. (After Conn, 



,1 •!•- r !•! uuuji Agricultural Bacteriology, 



the sou mto a form which can be absorbed by p g^ ) 

 the roots of the cultivated plants. 



The bacteria which produce the nodules (Fig. 8) on the roots of 

 leguminous plants are probably the same the world over and to them 

 Beyerinck has given the name of Bacillus radicicola, while Frank called 

 them Rhizobium leguminosarum (Fig. 10). When the seeds of clover, or 

 some other leguminous species are planted, and soon after the primary 

 root appears with its root hairs. Bacillus radicicola, attracted chemo- 

 tactically to the fine root hairs, penetrates the walls of these root hairs 

 by ferment action. So many bacilli enter the root hair cells that they 

 form slimy cords, almost hyphae-like, as they move into the middle 

 cortex cells of the root. Here in the cortex cells, the microorganisms 

 form nests or pockets, that are filled with the nodule-producing bacteria 



