PLANT GROWTH. 431 



and some ship-loads of that material had found their way to 

 the London market. In citing these instances, I need not 

 state that neither Licbig nor any other well informed stu- 

 dent of the agricultural practice in previous ages denied the 

 high appreciation of wood ashes, bones, gypsum, lime, marl, 

 and other mineral substances, besides the various kinds of 

 animal manures, in the farm management of earlier times. 

 Modern rational agriculture does not rest its claim of prog- 

 ress on the mere introduction of any particular new mode 

 of operation. For to try to maintain a remunerative fer- 

 tility of the soil under cultivation by fallow and the rotation 

 of crops, or to enrich one portion of the farm lands at the 

 expense of another one by retaining a certain proportion of 

 meadows and pastures to secure manure for the grain- 

 bearing lands ; or to enrich the surface soil at the expense of 

 the subsoil by raising deep-rooting plants, as root crops, or 

 leguminous crops, as clover, etc., for fodder and manure ; 

 or to improve the natural productiveness of the lands by 

 deep ploughing, or by drainage, or by irrigation, are all 

 modes of farm practice known, more or less, for hundreds 

 of years. Our real progress in this direction consists 

 mainly in the discovery of the principles which control the 

 successful application of these practices in the management 

 of farms. 



Rational modern agriculture recognizes as the foundation 

 of a successful farming, the necessity of a strict restitution 

 to the soil, in an available form, of those substances which 

 the crops have abstracted, and it promises to that class of 

 farmers who strive to comply with that requirement in the 

 most economical way, the best chances of a continued finan- 

 cial success. 



From a similar standpoint the earlier practice of using the 

 above-named mineral substances and others in the farm 

 management has to be judged as compared with their appli- 

 cation at the present time. 



As long as the composition of the air and the water was 

 butlittlo understood, and that of the soil practically unknown, 

 no correct idea could be formed concerning their mutual 

 relations, and still less regarding their connection with the 

 life and the growth of plants. 



