CHAPTER IX 

 THE GERM LIFE OF THE SOIL 



Thus far we have been engaged in considering soil as 

 lifeless material, on which plants are to be grown, but which 

 in itself is inert and inanimate. Such a conception of soil 

 is inadequate, for there is to be found in all arable land a 

 vast number of forms of microscopic life that really consti- 

 tute a part of the soil itself. From the standpoint of crop 

 production they are of great importance, as we probably 

 should not be able to maintain soil fertility without them. 



Under germ life ; as used in this chapter, are included 

 bacteria, fungi, alga?, and some of the molds, but we shall in 

 the main, dispense with these distinctions and use the term 

 " germs " or " microorganisms " to cover all or any of them. 

 In spite of what has just been said about the importance of 

 germs in plant production, there are many that are injurious 

 to plants both directly in the causation of disease, or indi- 

 rectly by contributing to processes in soils that are detri- 

 mental to the conditions favorable to plant growth. In dis- 

 cussing the subject it will be convenient to take up first 

 the soil germs that are directly injurious to plants. After 

 that the subject will be discussed according to the processes 

 in the soil with which microorganisms are concerned. 



154. Microorganisms injurious to crops. — The soil germs 

 that injure crops do so by attacking the roots. Those that 

 attack other parts of plants may live in the soil during their 

 spore stage but they are not strictly microorganisms of the 

 soil. Some of the more common diseases produced by soil 



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