62 Irrigation and Drainage 



occupied with corn roots that not a cube of earth one inch on a 

 side existed in the three feet of depth which was not penetrated 

 by more than one fiber of threadlike size. In many parts of 

 the soil the roots were much closer together than this. 



At the distance apart of planting in the field from which these 

 roots were taken, there were, in the surface three feet, 40% cubic 

 feet of soil available for each four stalks, so that by multiplying 

 the 1,723 cubic inches in one cubic foot by 40%, the number of 

 cubic feet of soil occupied, we get a total of 69,696 cubic inches. 

 If, then, each cubic inch of this soil contained not less than one 

 linear inch of thread-like root, their aggregate length could not 

 be less than one-twelfth of 69,696, or 5,808 feet, which is 1.1 

 miles. But this extent of root-surface does not even express the 

 amount of that to which the root -hairs, which are the real absorb- 

 ing surfaces, are attached ; and hence we must understand that 

 the actual area of surface of root-hairs for a full-grown hill of 

 corn is very much greater than would be indicated by the figures 

 given above. 



Let the reader bear in mind that the corn roots here under 

 consideration grew in the field under perfectly natural conditions, 

 and that the cage of wire shown in the engraving was simply 

 slipped over the block of soil which contained the roots there 

 shown, after the corn had reached that stage of maturity. 

 It should also be understood that the four stalks of corn which 

 absorbed from the soil the 150.6 pounds of water in 13 days did 

 it at the stage of growth represented by the oldest plants in 

 Fig. 11 ; and further, that these were only good average plants, 

 such as would make a yield of 4.5 tons of dry matter per acre. 



It may be difficult for some persons to realize how it is 

 possible for the delicate roots of plants to force their way 

 through the soil to depths such as are indicated by the engrav- 

 ings above, especially when the subsoil is a stiff, heavy clay, as 

 it \vas in this case. Nature's method of overcoming the diffi- 

 culty, however, is simple enough when we come to understand it, 

 and it is as effective as it is simple. 



The first fact which we need to understand when we wish to 

 learn how a root advances through the soil, is that the soil grains 



