Relation of Bacteria to Fertility. 177 



4000 pounds of limestone per acre increased the number 

 of bacteria from 440,000 per gram to 6,600,000 in a 

 period of seven weeks. 



It will be seen that whatever makes the soil a better 

 home for our cultivated plants, increases the number of 

 bacteria in it. The question at once comes to mind: Is 

 the increased fertility as shown by the larger crop, the 

 cause of the growth of the microscopic plants, or is. the 

 rapid growth of the bacteria the cause of greater fertility, 

 and hence the larger crop of corn or oats, etc. results ? As 

 will be seen, the latter is the true statement. Without 

 great bacterial activity in the soil, large crops cannot be 

 grown. 



Higher forms of life in the soil. Bacteria are not 

 the only forms of life that live in the soil and exert an 

 effect on its properties. In acid soils, molds may grow 

 luxuriantly. The soil also contains various kinds of tiny 

 green plants found so abundantly in water, the green 

 algae. Still larger forms of life are of great importance, 

 such as the common angle worm, that, by its formation 

 of burrows, brings the lower layers of the soil to the sur- 

 face, and thus in the course of a few years, turns the 

 soil over as completely as does the farmer's plow. The 

 burrows allow the air to penetrate into the soil. The 

 land under permanent grass is thus aerated and culti- 

 vated by these animal forms. These and all other low 

 animal forms live on organic matter ; they help to decom- 

 pose it, and are in turn decomposed by bacteria. Sta- 

 tistics that have been collected indicate that each acre 

 of land supports as much life, measured in pounds, in the 

 shape of low animal forms, as the farmer keeps in the 

 form of domestic animals. 



The soil is. thus, not a dead and inert mass, but some- 



