AGRICULTURAL 

 BACTERIOLOGY 



CHAPTER I 

 THE ROLE OF MICROORGANISMS 



Animate nature is commonly divided into two great 

 groups: the plants and the animals. It is possible, how- 

 ever, to make the division of life along other lines than 

 form and function. Every living form must have building 

 material; the various chemical elements that are essential 

 for its structure must be available in fitting combinations. 

 Every living form must also have energy ; for work is being 

 done by even the simplest forms of life, and without energy 

 no work is possible. The sole source of energy for our 

 world is the sun. The energy is transmitted in some inex- 

 plicable way through the space that separates the earth 

 from the sun. 



One group of living organisms is able to receive directly 

 this radiant energy, and to use it in the work of growth and 

 development. This power is limited to those forms that are 

 provided with the compound known as Morophyl, the sub- 

 stance that gives to the higher plants their green color. 

 They obtain their building materials from the soil, the 

 water, and the air, in compounds that contain but little or 

 no energy. They combine these simple compounds into 

 complex forms that contain a great store of energy. Thus 

 the plant uses as food carbon-dioxide, water, oxygen, ni- 



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