308 MISCELLANEOUS FARM SUBJECTS 



stable body of the soil. The fluid part is a solution consisting of 

 water carrying mineral and organic matter ; it forms the circulatory 

 medium of soil and plants. The gaseous part consists of air (nitro- 

 gen and oxygen) mixed with aqueous vapor, carbon dioxide, hydro- 

 gen dioxide, etc. ; it permeates the body of the soil, moving with 

 the movement of the circulatory fluid, changes in temperature and 

 barometric pressure, etc. The three parts are conveniently known 

 as soil body, soil fluid, and soil gas. 



The soil of a country forms a unit or entity hardly less com- 

 plete and distinct than the flora or the fauna. It differs from these 

 in that it is suborganic rather than definitely organized, and in 

 that it commonly contains a larger proportion of mineral matter; 

 yet it resembles them in that it has' its own modes of action and 

 self-perpetuation, and in that it functions in accordance with its 

 own special properties. Its internal action or functioning goes for- 

 ward chiefly through the agency of its fluid and gaseous parts. In 

 the absence of its circulatory medium it soon becomes inert or dead, 

 losing its suborganic character; in the presence of soil fluid it is 

 constantly vitalized. 



We include in the soil all the material to the depth to which 

 plant roots are able to distribute themselves. It therefore includes 

 a wide range of material in depth and character. It may be deep 

 or shallow, coarse or fine, loose or compact, light or dark, wet or 

 dry. It is all soil because it is a medium for the growth of some 

 kind of plant. In general, the soil may be divided into two classes 

 of material: The particles of mineral and fragments of rock, and 

 bits of organic matter of both plant and animal origin that have 

 become more or less decomposed. 



Practically all soils result from disintegrating rocks (muck 

 and peat may perhaps be excepted). While the processes of dis- 

 integration are going on, vegetable matter is gradually accumulat- 

 ing in the decomposed materials, and as a final result there is 

 formed the soil which is so familiar to us all. 



Among the physical agencies which combine to effect the de- 

 composition of the rocks may be mentioned heat and cold, water 

 and wind, as well as the action of plants and animals. Chemical 

 changes are also constantly taking olace which aid very materially 

 in breaking up the rocks. The oxidation of iron pyrites and the 

 solution of limestone by carbonated waters are examples of these. 



If, then, soil results from disintegrated rocks, it must partake 

 of the nature of the underlying rock, unless some outside agency 

 such as moving ice has disturbed the surface since the decompo- 

 sition took place. However, on account- of the long period during 

 which the soil has been subjected to leaching, it will have lost much 

 of some of the mineral compounds that existed in the parent rock. 



It is apparent, then, that all the mineral elements that enter 

 into a plant's composition must have come originally from the 

 rocks. When the plant or animal ceases to exist as such and de- 

 cays, then these elements are returned to the earth to be again taken 

 up probably by other plants, or they may dissolve in the ground 



