6 MANURES FOR FRUIT TREES 



important facts that " a rational system of agri- 

 culture cannot be formed without the application 

 of scientific principles ; for such a system must be 

 based on an exact acquaintance with the means of 

 nutrition of plants, and with the influence of soils 

 and action of manures upon them. This know- 

 ledge we must seek from chemistry, which teaches 

 the mode of investigating the composition and of 

 studying the characters of the different substances 

 from which plants derive their nourishment." 



Liebig gave the death-blow to the humus theory 

 of plant-nutrition, and he showed experimentally 

 the value of his mineral theory. He proved that 

 the ash ingredients of a plant were essential for its 

 proper growth ; and that a soil's fertility depended, 

 largely, upon its mineral constituents. 



Liebig fully established the laws which govern a 

 proper system of husbandry (see chapter iii.) ; and 

 these laws form the basis of modern scientific 

 agriculture and horticulture. 



Since the year 1840, modern agricultural 

 chemistry has been developed by an enormous 

 number of workers in all parts of the world — 

 among these may be mentioned : Lawes, Gilbert, 

 Warington, Ville, Berthelot, Hellriegel, Wilfarth, 

 Deherain, Wolff, Wagner, Schioesing, Beyerinck, 

 Mtlntz, Frankland, Winogradsky, Voelcker, and 



