204 BACTERIA AND SOIL FERTILITY 



groups become disproportionately prominent, while others are al- 

 most entirely suppressed. 



^'(2) The rapid increase in the numbers of the bacteria is fol- 

 lowed by a more intense transformation of plant- food substances. 

 Decomposition and fixation processes result in an accumulation of 

 readily available nitrogen compounds utilized by the crops. 

 Hence, the action of carbon bisulfid is in the nature of nitrogen 

 action. 



^'(3) The initial suppression of the nitrifying species becomes 

 of advantage in that the nitrogen compounds, simplified by other 

 species are prevented from being rapidly changed into nitrates and 

 being leached out of the soil. 



^'(4) The more or less permanent suppression of the denitri- 

 fying organisms must be regarded as an additional factor favor- 

 ins: plant erowth. 



^■k iLducdon of ,h. poison in.o ,he soil a, fcs. ded™«s 

 its bacterial flora, but with the disappearance of the injurious 

 carbon bisulfid vapors it also encourages a vigorous and long-con- 

 tinued increase of the organisms, resulting in an increase of the 

 store of more readily available nitrogen. It is still to be deter- 

 mined whether this increase is largely due to the fixation of at- 

 mospheric nitrogen or to the unlocking of the vast store of com- 

 bined nitrogen in the soil. It is most probable, however, that even 

 though one of these processes predominates the other is surely 

 more'extensive than it would be in normal soil. The nitrogen 

 thus secured is not at once made accessible to the higher plants but 

 is at first laid fast in the bacterial bodies. This assumption would 

 best explain the fact that plants growing upon a soil treated with 

 carbon bisulfid show retarded growth, even some time after the 

 application of the latter, and the explanation hitherto accepted 

 that the injury results from the direct action of the poison seems 

 hardly reasonable after our discovery that the most intense bac- 

 terial activities are asserting themselves just at this time. The 

 nitrogen fixed in the bacterial bodies is gradually rendered soluble 

 by decomposition processes, and thereby made accessible to nitrifi- 

 cation and the higher plants. Hence, when the carbon bisulfid is 



