136 Report ox Trials of Plows. 



Let us first endeavor to underwtimd how the ploAv makes land 

 more fertile. To accomplish this we must know what fertility is, 

 and what causes it. 



All plants whatever have their origin in a minute germ whose 

 weight is exceedingly small compared with the weight of the 

 fully developed plant. The germ has no creative power what- 

 ever; it can only assimilate other matter with its own substance, 

 and the whole of the extra weight of the mature plant consists 

 of foreign matter which, by a curious but not unintelligible 

 chemistry, the germ has assimilated with its own tissues and made 

 a part of its own substance. 



The substances thus assimilated are numerous, varying in differ- 

 ent plants, but all derived originally from the rains and dews, 

 from the atmosphere and the soil. 



The compounds derived from air and water are called organic; 

 those derived from the soil are called inorganic. Gum, sugar, 

 and woody fibre are examples of the former; lime, potash, iron 

 and saline matters are examples of the latter. 



The amount of inorganic matter in plants varies from one to 

 twelve per cent of their whole weight, according to their differ- 

 ent natures; 100 pounds of wheat contains 1.18 pounds of ash 

 or inorganic matter; 100 pounds of rye contains 1.04 pounds; 100 

 pounds of barley contains 2.35 pounds; 100 pounds of oats con- 

 tains 2.58 pounds; 100 pounds of wheat straw contains 3.51 

 pounds of ash; 100 pounds of rye straw contains 2.79 pounds; 

 100 pounds of barley straw contains 5.24 pounds; 100 pounds 

 of oat straw contains 5.74 pounds. 



If we have an acre of hmd which yields us 1,500 pounds of 

 wheat and 2,000 pounds of straw, it has taken from the soil about 

 eighty-eight pounds of mineral matter. 



An acre of land which bears a crop of oats, consisting of one 

 ton of straw and forty bushels of grain, will abstract one hundred 

 and fifty-six pounds of mineral matter from the soil. 



The mineral matter absorbed by growing plants does not exist 

 in the soil in unlimited quantities, but in definite quantities that 

 can be exactly ascertained if we resort to the proper methods of 

 inquiry. When we have ascertained the absolute amount of 

 mineral matters required by plants in the soil, if we divide the 

 whole number of pounds of these matters in an acre of soil by 

 eighty-eight, we shall know the exact numlier of crops of wheat 

 that can be taken from an acre; and if we divide it by one hundred 



