82 



FIG CULTURE 



cay. Every animal directly affects the physical 

 condition of the soil by manurial returns, while all 

 subterranean pests, such as ants, "crawfish," beav- 

 ers, squirrels, gophers and moles are man's good 

 friends in preparing the earth for his use, and en- 

 richment, by their natural methods of tillage. 



The creation of mineral plant food is largely a 

 question of surface exposure to soil water; the 

 ability of plants to avail of it is another matter. 

 The quantity of mineral food in any soil depends 

 mainly upon how fine the particles are divided and 

 how well water can percolate through it around 

 each particle. A single boulder has comparatively 

 little surface; cut into quadrants the exterior is 

 more than doubled ; divide each quadrant into four 

 more parts and the exposure is doubled again ; con- 

 tinue this division until each cubic inch of rock 

 has a billion soil particles and the surface is 

 infinitely increased. If percolating water can 

 surround each particle its opportunity to ab- 

 sorb potash and phosphorus is immeasurably 

 greater than when unable to penetrate the single 

 rock. We think of glass as a most insoluble 

 substance, but if a tumbler be reduced to an 

 impalpable powder and soaked in rainwater the 

 solution will have three per cent potash and 

 phosphorus. "We must conclude, therefore, that 

 the mineral food stored in all ordinary soils is 

 adequate for plants an indefinite period of time. We 

 can also infer that indiscriminate additions of min- 



