CHAPTER XXVI 

 Bacteria and Plant Food 



It has been shown in an earlier chapter that the micro- 

 scopic forms of Ufe called microbes or bacteria often cause 

 serious losses on account of the blights and rots that they 

 induce in plants. Such bacteria are true parasites, develop- 

 ing within the tissues of living plants and causing injury 

 and death. It is well known that vast numbers of bacteria 

 are similarly parasitic upon animal life, causing many of 

 the most fatal diseases in man and the lower animals. 

 Most of these forms of germ life must, of course, be 

 reckoned among the farmer's foes. 



The Nitrifying Bacteria 



There are many other bacteria, however, that may well 

 claim to be friendly to the farmer, for they serve an im- 

 portant purpose in furnishing food to his crops. One 

 group of these is present in vast numbers in fertile . soils 

 where they help to form the nitrates which are very im- 

 portant in supplying food to plants. The plant or animal 

 materials added to the soil for fertilizing purposes con- 

 tain nitrogen in combination with various other elements. 

 Consequently most of the nitrogen in the soil exists in the 

 form of these organic compounds — that is, compounds 

 made by organized or living things. In order that the 

 nitrogen in these organic compounds may be utilized by 

 growing plants, it must be recombined to form nitrates — 



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