252 THE FARMER OF TO-MORROW 



However, the statement that all soils are 

 equally fertile must be qualified by the addi- 

 tional statement only in so far as the pres- 

 ence of minerals affects fertility. 



The opponents of the new hypothesis have, 

 in many instances, seized upon the general 

 statement without regard to its qualifying 

 clause and held it up to ridicule. The cham- 

 pions of the new hypothesis do not deny that 

 soils vary in fertility. But they assume that 

 the factor of mineral plant food is practically 

 fixed and can be ignored in exploring the 

 problem of why some soils are fertile and 

 others are not. They occupy the role of phy- 

 sicians diagnosing the ailments of sick plants. 

 If the plants have proper food they should 

 not starve. Yet some plants do starve. It 

 is found they have the proper food, there- 

 fore the physicians can ignore the food supply 

 as a factor. They must look for something 

 beyond that to explain the ailment. That is 

 exactly what they are doing in explaining 

 the ailments of plants and soils, as we shall 

 see in the next chapter. 



The "exhaustion" of the soil has been a 

 subject of vital concern since historic times. 



