CLASSIFICATION OF BACTERIA 3 1 



of these useful organisms in the soil is stimulated by aeration, by some 

 organic material, by proper soil drainage, by the application of lime 

 which overcomes soil acidity. The farmer becomes independent of 

 the ordinary nitrogenous fertilizers, which are expensive, by plowing 

 under the leguminous crops, which on decay yield up to the soil the 

 nitrogenous substance largely accumulated by bacterial action where 

 it is available to that large class of nitrogen-consuming plants such as 

 the grasses, weeds, root crops, fruit crops and the like, which are de- 

 pendent on the soil nitrates for their nitrogen. The leguminous plants 

 as nitrogen-storing plants should, in an up-to-date rotation, be 

 alternated with the nitrogen-consuming crops. 





C' '"b-^y 



Fig. io. — Left, branching forms of bacteria from clover tubercle (X2000); 

 right, rod forms from fenugreek tubercle ( X 2000). {After Moore, Geo. T., Yearbook 

 U. S. Dept. Agric, 1902, pi. xxxix.) 



Metatrophic Bacteria. — The metatrophic bacteria include the zymo- 

 genic, saprogenic and saprophile bacteria, which cannot live unless 

 they have organic substances at their disposal, both nitrogenous and 

 carbonaceous. They flourish where organic substances and foodstuffs 

 are exposed to decay in impure water and in the waste from animal 

 bodies. Many of them produce profound fermentative changes 

 (zymogenic bacteria) in bodies. Others cause putrefaction and decay 

 (saprogenic bacteria), while others develop in media which have been 

 decomposed by saprogenic species and as saprophile organisms break 

 these substances up into simpler chemical form. 



