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plant food. Those soils derived from the green sandstone, trap- 

 rocks, lavas and millstone grits are generally considered the most 

 fertile. It is, then, quite evident that the phosphoric acid and potash 

 is inert to plant life until they are freed from their silicates by some 

 decomposing agency. 



The organic matter is derived from the dead vegetables and 

 animals that lived on the land. The most of our knowledge 

 of how plants absorb the organic matter they contain has been 

 obtained within the last fifty years. The carbon is generally con- 

 sidered to be absorbed from the soil and from the atmosphere. 

 The manner in which the plant absorbs its nitrogen has in the last 

 half century given rise to a good many theories and occasioned no 

 small amount of contention between scientists until twenty years 

 ago, when a solution of the problem was given by the discovery 

 in 1877 of the two eminent French chemists, Schloesing and 

 Miint/, that soils were teeming with micro-organisms, or bacteria, 

 converting ammonia salts and nitrogenous matter into nitrates, in 

 which state the plants absorb their nitrogen. This has been inves- 

 tigated by a great many chemists, but the investigations of the two 

 English chemists, R. Warington and Prof. P. Frankland, fully 

 explained the real action that takes place in the soil. They found 

 that there are two different bacteria at work in the soil in the 

 process of converting the nitrogen into nitrates. The one converts 

 the ammonia salts and nitrogenous matter into nitrites, and the 

 other converts the nitrites into nitrates, in which state the plants 

 absorb the most of their nitrogen. In the case of the leguminous 

 plants they have a power of absorbing nitrogen from the atmos- 

 phere which is not possessed by other plants. This po\ver of 

 absorbing nitrogen direct from the atmosphere is obtained through 

 the agency of another micro-organism ; but the manner of their 

 actions on the leguminous plants is at present not known. 



This process of converting nitrogen into nitrates is called nitri- 

 fication, and is of the utmost importance to tanners. Kvery farmer 

 should know the conditions under which nitrification takes place. 

 There is still another micro-organism which, under certain conditions, 

 acts the very reverse of nitrification, and causes a loss of nitrogen. 



R. Warington gives the following conditions for nitrification 

 to take place : First, in moist soil ; second, when the soil is 

 sufficiently porous to admit air ; third, the process is most active in 

 summer, and ceases at the free/ing point of water ; fourth, gypsum, 

 carbonate of lime, potash ;nd soda compounds promote nitrification ; 

 fifth, the nitrifying bacterium cannot liv in presence of light; 

 sixth, the bacterium of nitrification can only live at certain depths in 

 the soil, it is not geuerallv found in the subso 1. He found no 

 nitrification gf>iut> <>u at a depth of seven feet ; >e\eutli, ammonia 

 is always one of the products formed when clung is decomposed. 

 The bacterium is supposed to be capable of converting this 

 ammonia into nitric acid. 





