Manures and Commercial Fertilizers 111 



teriods or forms similar to bacteria. But scientists have 

 now agreed that they are true bacteria, and that they pre- 

 sent merely an added form to the many already recog- 

 nized. They are parasitic on the roots of the legumes; 

 having no green matter in them they cannot get material 

 for growth from the air as green plants do, and hence are 

 obliged to live on what green plants have obtained. But 

 though these minute plants draw their sustenance from 

 the clover or other leguminous plants, their parasitism is 

 not harmful, since they are the means of enabhng the 

 legumes to get the nitrogen in a combined form which 

 they cannot use as a gas. I have said that the process by 

 which they get the nitrogen into combination is still a 

 matter of study and investigation. The most plausible 

 theory is that these plants are of a nature similar to the 

 yeast plants that cause fermentation in the liquids con- 

 taining sugar, and that they are really nitric foments 

 which oxidize or bring into chemical combination the free 

 nitrogen of the air with oxygen. Now, when an element 

 is combined with oxygen the result is the formation of 

 an acid, and when nitrogen is oxidized the result is nitric 

 acid. When nitric acid is formed in the soil it does not 

 remain an acid, because the soil contains lime, potash, 

 and other things of an alkaHne nature that are bases for 

 the nitric acid, and at once a neutral salt or nitrate is 

 formed, which is at once taken up by the roots of the 

 clover or other legumes and formed into organic nitro- 

 gen, which will be finally carried through the nitrifying 

 process in the soil when the clover decays, so that the fol- 

 lowing crop gets the benefit of it. We have seen that all 

 green plants use nitrogen from the soil only after it has 



