MANAGEMENT OF THE SOIL 33 



cultivator be passed over the land, stirring the soil to 

 the depth of a few inches, the soil particles will be 

 torn apart so that this capillary pumping system 

 is broken u]) and the dried particle can no longer 

 reach down and help itself from the moisture film of 

 its neighbor. The result is that the surface soil that 

 has been stirred dries out very quickly, but this 

 layer of loose dry soil acts as what is called a " dust 

 mulch " and protects the lower undisturbed portion 

 from drying, in just the same way that a mulch of 

 straw or of coarse manure would effect the same 

 object. The growth of our crops depends almost en- 

 tirely on this film of moisture that is retained by the 

 soil particles. The root hairs which develop in 

 such immense numbers near the tips of tlie youngest 

 rootlets appress themselves close to the soil particles 

 and are able to absorb moisture from this film to- 

 gether with the small amount of soluble material 

 which it has taken up from the soil. It is in this 

 way, and in this way only, that plants are able to 

 supply themselves with the necessary mineral food 

 elements, and with the excessively important ni- 

 trates, and it is from these films only tliat the neces- 

 sary moisture is obtained to maintain the turgidity 

 of the cells, supply tlie large amount lost by trans- 

 piration, and provide for all the manifold activities of 

 life. If the soil contains too much water, so that the 

 spaces between the particles are filled with it instead 

 of with air, these absorptive root hairs perish for 

 want of oxygen. If the films lose too much water 

 from surface evaporation, the root hairs can no 

 longer absorb it in sufficient quantities, and growth 



