368 THE BEGOLITH 



an agriculturist, the amount of surface exposed to the solvent 

 action of roots and percolating waters. Indeed, it has been 

 estimated that the total surface areas of the grains in a cubic 

 foot of soil amounts, on the average, to 50,000 square feet. 

 The amount is of course greater in a fine than a coarse soil, but 

 in any case sufficiently large to enable us to understand how, 

 under the ordinary conditions of cultivation, all the materials 

 essential to plant growth may in a brief time be removed, unless 

 renewed by artificial fertilizers. 



Further than this, the amount of space between the grains 

 is of very great importance in determining the circulation of 

 water in the soil, and its capacity for retaining the right propor- 

 tion essential to plant growth as noted later. 



The experimental work of late years goes to show that fertil- 

 ity is dependent upon these physical properties perhaps even 

 more than upon chemical composition. If the structure, i, e., 

 the manner of arrangement of the soil particles, is such as to be 

 most favorable to root action and conservation of moisture, there 

 are few soils but may be made fertile by proper treatment, even 

 cannot the desired physical properties be imparted by artificial 

 means. A soil which contains too large a proportion of fine 

 clay matter may hold so large a proportion of moisture as to 

 be quite unsuited for cultivation when saturated, and become 

 equally unfitted by induration when dry. A light, porous, 

 sandy soil on the other hand, though fertile during seasons of 

 abundant precipitation, parts with its moisture so readily as to 

 be quite barren in seasons of drought. Porosity and capillarity, 

 two properties dependent wholly on the size and shape of the 

 soil particles, are therefore very essential items in this consid- 

 eration. Moisture precipitated in the form of rain soaks into 

 the ground or flows off upon the surface in varying proportions, 

 according to local conditions, an open porous soil naturally 

 absorbing more rapidly than one that is close and compact.^ 



When, after the rain ceases, evaporation sets in from the 

 surface, the water which has soaked into the ground is brought 

 back again in part, by capillarity, though a part escapes through 

 leaching downward beyond the reach of capillarity, ultimately 



^The relative '^run off" of water to rainfall in the humid east has been 

 calculated as from 25% to 40% j in the Cordilleran region 20% to 

 25% and in the arid region as from 0° to 20%. Of the total rainfall from 

 50% to 100% is controlled by the belt of weathering. (Van Hise.) 



