128 UNDERDRAINIXG AND DEEP TILLAGE. 



and thus change the nature of the dead subsoil to the quality or 

 nearly the quality of the upper soil. All disintegration and pul- 

 verization of rocks is caused by the combined action of air and water. 

 By these two fluids, the rocks of former geologic periods have been 

 changed to fragments and dust. And this, together ^Yith the depos- 

 its of leaves and other decaying organic substances, forms our soil. 

 The comminuting process is still going on wherever air and water 

 can have access, thus forming finer and consequently richer soil. 

 Without air this action ceases, and soils to which air and water can 

 obtain no access remain unchanged. Air alone cannot perform the 

 work ; and water unaided is inadequate to the task. Therefore 

 soil, which is saturated with water and consequently contains no 

 air, must remain in the same undivided state ; while in soil well 

 underdrained the water does not fill all the little crevices between 

 the particles of earth, but air is allowed to come in and act. Then 

 the work commences. The larger particles become finer, and the 

 smaller ones finer still. Thus the soil is deepened by the work, 

 more soil is rendered fit for use. But this change is not rapid ; on 

 the contrary, it is very gradual in its operation, and the benefit aris- 

 ing from it is a constantly increasing one. Seeds germinate more 

 readily and grow more luxuriantly than in soil where the particles 

 are crude and coarse. And, since draining aids in deepening the 

 soil, roots will descend farther and take better hold on the ground 

 and grow more vigorously and luxuriantly. A portion of the farm- 

 er's crops consists of plants whose roots are ultimately used for food 

 for other plants, as clover. These, in order to grow and develope 

 fully, need depth of soil. It is hardly credible how deeply roots will 

 go in quest of food in some soils. Mangold wurzel and white tur- 

 nips have grown three and one half feet long, and parsnips have 

 been grown in some instances to the surprising depth of thirteen 

 feet. The roots of lucerne have been traced to even a greater depth. 

 Not only do roots need depth of soil, but they require more than 

 this, they need a porous soil. All roots require air. This they 

 cannot have when water excludes it from the soil as we have just 

 seen; but free access of air is permitted by draining. Thus they 

 get air which they need as much as they need water, since plants 

 arc not like fishes, fitted to exist under water. In fact, the aquatic 

 flowering plants are confined to a few genera like pond weed and its 



