INTRODUCTION 9 



The plant products thus obtained are rarely fit for 

 immediate use and have to undergo fuither manipulations. 

 Sometimes crops are fed to cows which give milk which 



GRAPH. 



Correlation between the Hay Crop and MgO% = x or MnO% = o 

 Below Mean %. Above Mean %. 



a 



> *05 



o S . 05 



I s 



w 



p * 



I %MnO l -5 



is turned into cheese, or other products. There is therefore 

 hardly any ultimate limit to the subject of plant products, 

 and sooner or later they all appear in some other volume 

 of this series. 



REFERENCES TO INTRODUCTION 



Daubeny, " Roman Husbandry" (Oxford) (from Columella and Virgil). 



Davy, "Agricultural Chemistry" (Griffin) (1802-12). 



Liebig, "Chemie fur Agricultur u. Physiologic " (Vieweg) (about 1840). 



Boussingault, "Agronomic, Chimie Agricole et Physiologic" (Mallet- 

 Bachelier) (about 1850). 



Collins and Hall, "The Inter-relationships between the Constituents 

 of Basic Slag," Journ. Soc. Chem. Ind., May, 1915, p. 526. 



