36 THE PEINCIPLES OF 



grounds abound in organic matter, and they abound in 

 nitrogen. One is the index of the other. Organic matter is 

 also a source of carbonic acid gas. As a source of this ferti- 

 lizing gas in the soil, it becomes with the aid of moisture a 

 , digester of mineral matter which otherwise would be much 

 slower in being liberated. Besides, carbonic acid gas is a 

 plant-food in itself. It is taken up by the roots, and elabor- 

 ated in the tissues of the plant, the carbon being retained 

 and the oxygen being given off by chemical decomposition. 

 Organic matter also contains mineral matter. Straw and 

 haulm and roots of plants cannot be produced without mineral 

 matter, and it is evident that the mineral matter is in pre- 

 cisely the state in which it can be taken up by plants as it 

 is liberated through decay. That organic matter contains 

 mineral matter is a fact which might readily be overlooked. 



Organic matter is in a constant state of change oxidation 

 and decay ; and in that decay not only is nitrogen liberated 

 but salts are also liberated, so that there are important 

 chemical changes going forward which help us to understand 

 the great value of organic matter. Experiments have shown 

 that the most recently added vegetable matter is more 

 valuable than the older stocks of similar material which 

 abound in all fertile soils. Nitrification is principally carried 

 on upon the roots, leaves, haulm, farm-yard manure, and other 

 remnants of plant life belonging to the last crop or the most 

 recent dressings. Previous accumulations, owing to their 

 becoming more permanent or fixed in character, are com- 

 paratively inert, and although they are sources of nitrogen, 

 they cannot be compared in this respect to substance in a 

 rapid state of decay such as those above mentioned. 



With reference to the points that appeal directly to the 

 farmer's instincts, we have in organic matter a wonderful 

 improver of the texture of soils. The organic matter confers 

 upon the soil softness, mellowness, and the power of retaining 



