2 Southern Gardener^ s Practical Manual 



grated the rock, forming small rock particles, which we 

 call soil. The carbonic acid and oxygen of the air further 

 acted upon these rock particles and still further disinte- 

 grated them. Rain-water, flowing over the surfaces 

 of the rock, gradually moved these particles to lower 

 elevations until there accumulated sufficient inorganic 

 material to constitute what we term soil. The organic 

 constituents, however, being absent, economic plants 

 could not be grown. 



Another agency participated in remedying this defect. 

 There are primitive plants, known as lichens, which grow 

 upon the surface of rocks. These catch and hold rain in 

 their season of growth. This water freezes and lifts the 

 little plants from their moorings, and, torn asunder from 

 the rocks, they are washed down to form a nucleus of 

 organic matter in the soil below. These primitive plants 

 evidently have the power of collecting nitrogen from the 

 air, thus contributing this most important volatile ele- 

 ment to the newly formed soil; and, the nitrogen com- 

 bining with the mineral constituents derived from the dis 

 integrated rock, the growth of a higher order of plant 

 life is rendered possible. Bacteria are now supposed to 

 have had an active agency in the formation of soil. 



THE SAME AGENCIES STILL ACTIVE 



Few gardeners realize the extent to which all of these 

 natural agencies, — mechanical, chemical, and bacterio- 

 logical, — are collaborators with them in their efforts to 

 improve their soils and increase their crops. 



By fall plowing, the gardener utilizes the work of 



