DR. SCHLEIDEN'S THEOKV OF AGEICULTURE. 153 



and ulmic acid, especially in a moist state, neutralize twenty or 

 thirty times their volume of carbonic acid or ammonia. 



It appears then from the tables above mentioned that pure 

 quartz sand has the smallest, lime and gypsum a medium, clay 

 and humus the highest power of absorbing carbonic acid and 

 ammonia from the atmosphere, on which alone the proportionate 

 fertility of these soils depends. 



d. The moisture of the ground is however the medium of 

 these powers. Dew and rain will not by themselves supply the 

 demands of vegetation, and therefore the soil must have the 

 power of absorbing steam from the atmosphere. And tins power 

 is in exact accordance with what has just been mentioned with 

 respect to carbonic acid and ammonia. And to this must be 

 added that property of retaining water when absorbed, as well 

 as of absorption. 



B. The chemical peculiarities of the soil form the second liead 

 under this division. Soil which is capable of producing plants 

 in luxuriance must contain the necessary chemical constituents. 

 It is not immaterial in what combination these exist in the soil, 

 which must also contain many constituents which are not neces- 

 sary for nutrition, but whose presence and quantity affect the 

 physical qualities of the soil, which are themselves of great 

 moment. 



a. Insoluble combinations are of course useless to plants, 

 however rich they may be in the requisite materials. On the 

 other hand, analyses which regard merely wliat is held in solution, 

 inasmuch as a greater portion is carried off by drainage, are, in 

 great measure, useless. The most important constituents of the 

 soil are those which are gradually rendered soluble by the decom- 

 posing influence of water containing carbonic acid and ammonia, 

 and partly also by the oxygen of the atmosphere. Silicates, rich 

 in alkalies, answer these conditions. The most favourable com- 

 binations are those in which the requisite inorganic matters are 

 contained in organic substances, w hicli protect them from imme- 

 diate solution, and still, in consequence of their constant decom- 

 position, part with them as the exigencies of the plants require. 



Almost all important inorganic matters are destructive or 

 injurious to plants when concentrated, and therefore they must 

 be carried by the water away from the influence of evaporation, 

 which might concentrate them too much, or at least they should 

 be in such chemical relation to water, that it can contain only a 

 certain quantity, and therefore on evaporation parts with the 

 superfluous quantity in an insoluble state. Plants are not 

 capable of selecting their food. The chemical constituents must, 

 therefore, exist in the proper proportion. In uncultivated soils, 

 where the proportions necessary to a particular plant do not 



