xiv CONTENTS. 



The yield of the soil is regulated by that inorganic plant 

 constituent which is present in smallest proportion. The 

 Minimum Theory applied to phosphoric acid. The stores 

 of phosphoric acid available. Guano. Animal refuse. 

 Bones. Coprolites. A conservancy department for the 

 animal kingdom necessary. The assimilation by the 

 plant of its inorganic parts. Endosmose. The transfor- 

 mation of the sap in the leaves. Prince Salm Horstmar's 

 experiments proving the relative necessity of each of the 

 mineral plant constituents. The absence of a single one 

 in the soil affects the whole organism of the plant. The 

 division of plants into groups according to their principal 

 inorganic constituents. The different kinds of soils best 

 suited for the different kinds of plants 51 



CHAPTEE IV. 



THE SOIL AND ITS FUNCTIONS. 



The soil is the supplier of the inorganic constituents of plants. 

 The condition in which these inorganic substances must 

 be present. Their mere presence does not prove the fertility 

 of a soil. The fallacy of judging by a chemical analysis 

 of the capabilities of a soil. Tables to "measure" the 

 fertility of a soil. The injury done to scientific agriculture 

 by hasty conclusions drawn from imperfect experiments. 

 The constituent parts of the soil are in their original form 

 insoluble in water. The action of moisture, heat, and 

 atmospheric air renders them soluble. The peculiar 

 absorptive power of the soil to abstract the elements of 

 inorganic plant-food from their solutions. The capillary 

 absorbing power of the soil. Its bearing upon vegetable 

 life. The physical force of attraction of the soil is stronger 

 than the solvent power of water ; but yields when " Endos- 

 mose" comes into play. To judge of the capabilities of a 

 soil, it is necessary to distinguish between the assimilable 

 and unassimilable portion of inorganic plant constituents 

 present in it. 



