PHYSICAL INTER-RELATIONS IN SOILS 57 



surface to their burrows, great quantities of fragments of 

 organic (chiefly vegetable) material, the greater part of 

 which remains there to become a part of the soil and per- 

 form important functions in developing desirable physical 

 conditions. There -thus arise various cycles of activities, 

 all of which result in the mellowing, deepening, and per- 

 fecting of the soils. 



82. Food-preparers. At the same time there gradu- 

 ally come in and develop such vegetable forms as the nitri- 

 fiers and nitrogen fixers, and other food-preparers. In 

 the absence of air they cannot exsist ; at low temperatures, 

 they work not at all or only feebly. With the mellowing 

 of the soil, opportunity is afforded for the distributing and 

 multiplying of their colonies. With the more complete 

 access of air and increasing temperature, and with the 

 gradual accumulation of organic matter from the decom- 

 position of roots or from the improved condition of the 

 organic matter which may already be present, the activi- 

 ties and products of the nitrifiers and free nitrogen fixers 

 are greatly increased. Moreover, those processes, whether 

 physical, chemical, or biological, by which the mineral 

 foods are prepared, are greatly favored by these same 

 conditions. 



83. The final results. Under adverse conditions 

 evil results seem to be cumulative, and usually really are 

 so. It is equally true that if the removal of undesirable 

 ground water is supplemented with rational practice, the 

 beneficial results are cumulative. As the changes above 

 described take place, every other desirable physical con- 

 dition is favored. Optimum temperature, optimum ven- 

 tilation, optimum capillarity are all approached, and all 

 mutually cooperate as is always the case when condi- 

 tions are correct or favorable. 



