INTRODUCTION 9 



The plant products thus obtained are rarely fit for 

 immediate use and have to undergo fuither manipulations. 

 vSometimes crops are fed to cows which give milk which 



Gbaph. 



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



Below Mean "o. Above Mean %. 



•15 



II 



o 5 oJp O 1 k 



-10 -0 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" (Grifl&n) (1802-12). 



Liebig, " Chemie fiir Agricultur u. Physiologie " (Vieweg) (about 1840). 



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

 Bachelier) (about 1850). 



Collins and Hall, "The Inter-relationships between the Constituent? 

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



