CAUSES OF FERTILITY. 223 



99.70 100.60 100.2] 



Inspection of these soils will show the cause of the different 

 degrees of fertility. The soil A, which was the poorest, con- 

 tains of soluble vegetable matter, 2.50 per cent. The soil B, 

 next in fertility, contains 1.60 per cent., most of the soluble 

 matter having been removed by the agency of the ashes, with 

 the crop ; while the soil C, in the highest state of fertility, 

 contains 4.60 per cent, of soluble vegetable matter. This 

 alone is sufficient to account for their difference. In fact, in 

 all other respects, they are all nearly alike. Now this soluble 

 vegetable matter, is composed of humic and crenic acids, or 

 their salts, the very substances which it is generally be- 

 lieved are the nutritious portions of the soil. On Liebig's 

 theory, such a result is perfectly inexplicable. 



A third example is of two soils analyzed by Prof. Hitchcock, 

 according to Dr. Dana's rules ; one. A, from Lazelle county, 

 Illinois, and never cultivated, and the other, B, from Sciota 

 Valley, Ohio, and cultivated 14 years without manure. 



106.1 105.3 



Both of these soils are of the first quality. The quantity of 

 soluble geine is large, and also the amount of salts. But the 

 difference between that which has been cultivatefl, and that 

 which has not, developes one of the most important facts in 



