UNDRAINED SWAMPS. 263 



evidence of its escape. The farmer should be well acquainted 

 with this gas; it is his wealth. And here, often and to a 

 great extent, is the leakage of the farm. 



Manures are valuable mainly for the amount of ammonia* 

 they will produce. This gas, it is believed, always readies tlie 

 plant through its roots. It is composed of nitrogen and hydro- 

 gen gases. Hydrogen, it is believed, is never deficient. Nitro- 

 gen is often wanting in the soil. It is of the utmost importance 

 in the growth of all vegetables. The principal source of supply 

 is from ammonia. Altliough the air is composed of about four- 

 fifths of pure nitrogen, it is believed that plants obtain only a 

 small amount from this source. 



Almost every farm in New England has within easy reach 

 deposits of vegetable matter called muck swamps. These de- 

 posits are as securely locked up by their dead and stagnant 

 waters as if hermetically sealed. "We have seen that a fertile 

 soil contains five per cent. — sometimes a little more, often less 

 — of vegetable matter. But in the muck swamp it lias been 

 proved that the deposit, after being thoroughly drained, contains 

 sixty per cent., often, of dried vegetable matter, which only 

 needs aeration to become an active manure, having all the 

 elements of the most fertile and virgin soil. 



The ploughing into the soil of green crops is another source 

 of manurial supply. Red clover is among the best for this pur- 

 pose. This plant, having a tap-root, draws its nourishment 

 largely from the subsoil, bringing up to the surface mineral 

 matter, the nature and importance of which will be subsequently 

 considered. The mechanical effect of the green crop thus 

 ploughed in is to hold the soil in lightness, and, by its decay, 

 producing heat at the same time that it affords the best and 

 most ready nourishment to the growing crop. Worn soils may 

 be greatly amended in this way. 



The limits of this article will not admit of a very extended 

 notice of the mineral substances necessary to fertility. Neither 

 will it be necessary, in view of the fact that many of them are 

 fully supplied in the mineral portion of the earth, which con- 

 stitutes more than nine-tenths of the whole cultivated soil. 



The ashes of plants after combustion, often not more than 

 one-fiftieth part of their dry weight, is the mineral portion of 

 plants. As small as tliis proportion is, plants will not grow 



