140 ON THE PRINCIPLES OF 



are the means by which the mineral elements contained in 

 the soil are resolved into a state adapted for being- assimi- 

 lated by the plants; this is generally effected by the appli- 

 cation of slacked lime. They consequently exercise on the 

 vital process of the plants not a mere stimulus like the 

 spices, but are consumed for the development of the leaves, 

 seeds, roots, etc.; they becom.e constituent parts of them, 

 as can be shown with certainty by chemical analyses. 



The success which has followed the application of these 

 substances to the fields, has explained, in a most striking- 

 manner, the origin of the carbon and nitrogen in the 

 plants. 



In the marl, in the bone earth, in the gypsum, in the 

 nitrate of soda, no carbon is provided to the fields ; and yet, 

 in many cases, the same produce, in some even a higher one 

 was obtained, than by the application of a manure contain- 

 ing carbon and nitrogen. As the soil after the crop does 

 not contain less carbonaceous or nitrogenous substances, it 

 is evident that these products which had been obtained 

 without any carbonic or azotic manures, must have got the 

 carbon and nitrogen of their leaves, roots, and stalks from 

 the atmosphere ; it follows, therefore, that the productive- 

 ness of the fields cannot be in proportion with a supply of 

 carbonaceous and azotic substances, but that the fertility 

 depends only on the supply of those ingredients which 

 should be provided by the soil. 



The soil does not only serve the purpose of fixing the 

 plants and their roots; it participates in vegetable life 

 through the absorption of certain of its elements. If these 

 elements are present in sufficient quantity, and in appropriate 

 proportions, the soil contains the conditions which render 

 the plant capable of absorbing carbonic acid and ammonia 

 from the air, which is an inexhaustible storehouse for them, 

 and renders their elements capable of being assimilated by 

 their organism. 



The agTiculturist must, therefore, confine himself to giving* 

 to the field the composition necessary to the development of 

 the plants which he intends to grow ; it must be his principal 

 task to supply and restore all the elements required in the soil, 

 and not only one, as is so frequently done ; the ingredients 

 of the air, carbonic acid and ammonia, the plants can, in 

 most cases, procure without man's interference: he must 

 take care to give to his field that physical condition which 

 renders possible and increases the assimilation of these in- 



