(U MYl'TlAX AGRICULTURE. 



particular carbonic acid, give the soil water a very much 

 increased power of dissolving mineral matter. 



The bacteria found in the soil are not all working for 

 the benefit of the crop. The "Denitrifying" bacteria 

 reduce nitric acid and set free nitrogen gas, and in this 

 way cause a loss of valuable material. Fortunately, the 

 bad micro-organisms are only active in soils which are in 

 a poor physical state. They thrive best in badly aerated, 

 ill-drained soils and, unless under exceptional circum- 

 stances, they probably do very little harm. 



In nature, a comparatively small proportion of the 

 total nitrogen is found in a combined state and, as plants 

 generally cannot use nitrogen gas as a food, it follows that 

 the fixation of this gas to form compounds is essential 

 for the cultivation of crops. The combined nitrogen 

 found in coal, in tafla, and in soil, has almost entirely been 

 fixed through the action of life. Certain lowly organised 

 plants, and one of the bacteria in particular, have the 

 power to take nitrogen gas from the atmosphere and unite 

 it with other bodies in the form of organic matter. Hence, 

 this micro-organism which can take nitrogen gas and 

 change it into compounds available for feeding the higher 

 plants is of the greatest importance in agriculture. These 

 nitrogen -fixing bacteria live either in the soil or inside the 

 roots of certain of the higher plants. When living in the 

 soil, the activity of these bacteria is evidently much less 

 than when they are living in the tissues of the plant root. 

 Whether they exist in the ro3t however or in the soil, 

 they are always collecting and enriching the soil with a 

 most valuable plant food. The only plants which have 



