6 Theory of Agriculture. [Jan., 



its qnantity is less ; still, compounding the whole together, it 

 is vastly greater. It can hardly be said that in this state, and 

 in this condition of things, it is absolutely essential to life. Its 

 relations to life are certainly different, and its functions are of 

 a different kind. Oxygen, for example, stands in such a rela- 

 tion to the function of respiration, a function never absent in 

 any living thing, that life is at a stand, when it is interrupted. 

 We cannot say this of carbon, or any other solid. In this mat- 

 ter, v/e do not mean to be understood that there are not mutual 

 relations and mutual dependencies, and hence in many instan- 

 ces it would be improper to speak of one element as possessing 

 an importance greater than another. 



The atmosphere, as is well known, is the great source of 

 oxygen. It constitutes four-fifths of its material. Water is the 

 great reservoir of hydrogen, where it is found in the proportion 

 of 15 to 85. 



Sulphur, phosphorus, lime, magnesia, iron, silex, and alu- 

 mine, compounded with oxygen, are often elements essential to 

 the perfect constitution of organized matter. It is unnecessary 

 to speak of the distinctive properties of these substances — these 

 may be known by reference to any elementary work on che- 

 mistry. Constituted as soil now is, every element which we 

 have named is foimd in it. Carbon, in combination with oxy- 

 gen, exists as an acid in combination with the alkalies and al- 

 kaline earths. It is also found dissolved in rain water, in the 

 soil, and forms the base of all vegetable products, under what- 

 ever name they are known, as humus, humic acid, crenic and 

 apocrenic acids, peat and muck. As carbon forms so large a 

 proportion of vegetable matter, the source from which it is de- 

 rived by the growing plant, has been the subject of much 

 speculation. A contrariety of opinion is known to exist. 



The source of carbon, according to a distinguished che- 

 mist, is the atmosphere ; and as the vegetable tissues are com- 

 posed of a very great per centage of this substance, it is main- 

 tained that the only adequate quantity can be found in the 

 atmosphere which the leaves of plants can abstract, and which 



