CLASSIFICATION OF BACTERIA 31 



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

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

 ivhich overcomes soil acidity. The farmer becomes independent of 

 :he ordinary nitrogenous fertilizers, which are expensive, by plowing 

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

 litrogenous substance largely accumulated by bacterial action where 

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

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

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

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

 ilternated with the nitrogen-consuming crops. 



Fig. 10. — ^Left, branching forms of bacteria from clover tubercle ( X2000) ; 

 ight, rod forms from fenugreek tubercle ( X2000). (After Moore, Geo. T., Yearbook 

 7. S. Depl. Agric, 1902, pi. xxxix.) 



Metatrophic Bacteria. — ^The metatrophic bacteria include the zymo- 

 ;enic, saprogenic and saprophile bacteria, which cannot hve unless 

 hey have organic substances at their disposal, both nitrogenous and 

 arbonaceous. They flourish where organic substances and foodstuffs 

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

 odies. 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 

 ecomposed by saprogenic species and as saprophile organisms break 

 liese substances up into simpler chemical form. 



