144 Report on Tbials of Plows. 



some lime salt, a new compound is formed, in which the soda is 

 I'eplaced by lime; in the same way the lime may be supplanted 

 by magnesia, and the latter by potash. 



It is very instructive to observe that these successive replace- 

 ments take place in a regular and unvarying order, which Prof. 

 Way has determined as follows: Soda, lime, magnesia, potash, 

 ammonia. 



Thus, in the double silicate of alumina and soda, the soda may 

 be replaced by lime, the lime by magnesia, the magnesia by 

 potash, and the potash by ammonia; but this cannot take place in 

 the reverse order. Ammonia will dispossess any of the articles 

 which precede it on the list; but none of these, either singly or 

 in combination, has the power to dispossess ammonia. The value 

 of these double silicates is in the order in which they are placed 

 above. The double silicate of soda is less valuable than the 

 double silicate of lime; the double silicate of lime is less valu- 

 able than the double silicate of magnesia; the double silicate of 

 magnesia is less valuable than the double silicate of potash, and 

 the latter is less valuable than the double silicate of ammonia.' 

 Thus we see the admirable provision of Divine Providence, that 

 the more valuable compound shall alwaj's have the power of dis- 

 placing the less valuable, while the inferior is restrained by 

 impassible barriers from supplanting the superior compound. 



When we learn that the formation and the transformation of 

 these double silicates from a lower degree into a higher one is 

 g]-eatly promoted by a porous condition of the soil, we see an 

 additional reason for the thorough pulverization of the soil by 

 the plow. 



The distance to which the roots of a plant will extend when 

 there is no physical obstruction to their progress through the soil 

 is far greater than is usually supposed by those who have not 

 actually witnessed their extension. We have seen the roots of 

 Indian corn extending seven feet downward; the roots of lucerne 

 will penetrate fifteen feet: onions will run downward three feet 

 where the physical condition of the soil favors the extension of 

 their range. It is obvious that, as the nutritive matters in the 

 soil cannot travel to the root, the latter must therefore go to the 

 former; and the fjirther the root extends, the greater the amount 

 of food which the plant can obtain, and the greater must be its 

 growth and nutritive capacity. The roots of plants always develop 

 themselves in the direction of least resistance. If the roots of 



