58 LAW OF ISOMORPHISM. 



orphism exists, so long may potash, soda, magnesia, 

 that is, ashes, supply the place of lime. 



97. Isomorphous substitutions in plants, relate on- 

 ly to the vegetable or organic acids. The mineral 

 or inorganic acids, exist already saturated in the soil, 

 as sulphates, phosphates, or muriates. 



98. In consequence of the law of isomorphism, 

 the oxygen in the bases of organic acid salts is a 

 constant quantity, although ashes of the same plant 

 may, by analysis, show a great diversity of compo-, 

 sition ; this can arise only from the fact, that the or- 

 ganic acids exist, probably in a definite proportion, 

 in each family of plants. The acids are formed by 

 the essential vital functions of the plant. To the 

 perfection of this process, the silicates and salts of 

 the soil, are not less necessary, than is life to the 

 vegetable ; but though one element may be substi- 

 tuted for another, yet no one element may supply 

 the place of all others. This is a problem yet to be 

 solved. Nor may any possible mixture of mere sili- 

 cates and salts, give fertility to a barren soil. Fer- 

 tility depends on the presence in soil, of matter, 

 which has already formed a part of a living structure, 

 or the organic elements of soil. 



99. The inorganic are simple combinations ; the 

 organic simple in number, but wonderfully complex 



