176 ON FALLOWING. 



that vegetable matter can be placed in ; or the 

 best adapted as food for plants ; and particularly 

 of those which are desired to be prolific in fruits, 

 seeds, bulbs, and tubers. And as to such an ex- 

 posure to the atmosphere, producing either nitre 

 or ammonia ; it certainly cannot be likely, that 

 lands submitted to common cultivation, can be 

 sufficiently pregnant with animal and vegetable 

 matter to produce either ; but if it does so, nitre 

 is the most probable ; and this is constituted 

 to be the most profitable ; for nitre being com- 

 posed of oxygene and nitrogene, it contains one 

 of the vital principles of plants, and of which 

 they cannot take up too much, as they possess 

 the power of expelling any superfluous quantity. 

 But ammonia contains nothing that a plant can 

 need, it being composed of hydrogene ; and ni- 

 trogene. By a due supply of water, plants ob- 

 tain a due supply of hydrogene ; and nitrogene 

 is worse than useless, as it produces disease j and 

 indeed, the wise providence of nature seems here 

 distinctly displayed, by making ammoniacal gas 

 so much lighter than the atmospheric air, that it 

 may as speedily fly off as it is formed. 



But whether the additional fertility obtained 

 by fallowing, can be equal to that produced by 

 other operations, is another question ; and is> 

 indeed, one more of expediency than of scientific 



