6 KNOWLEDGE KEQUIRED BY THE 



permit, to show how much we have as yet attained, how our 

 methods of experimental procedure may be improved and made 

 more reliable, and what new inquiries may be entered upon, 

 in the hope of solving the numerous agricultural problems 

 which lie still unexplained before us. 



The progress of scientific agriculture cannot fail to be 

 greatly promoted by an extension of the habit of cautious 

 experimenting, and the multiplication of results in which con- 

 fidence can be placed. But many persons, capable of benefiting 

 the art of culture in this way, are unaware of the points which 

 chiefly require to be investigated, and in what way the investi- 

 gation is to be commenced ; while others are now groping in 

 the dark, uncertain, and therefore unsuccessful, in their experi- 

 ments. Many also, who have hitherto felt no interest in such 

 pursuits, require only to have their objects clearly set before 

 them to become warmly and zealously devoted to them. These 

 have served as additional inducements to me in preparing the 

 following pages. 



2. Knowledge which ought to be possessed by the suggester and 

 performer of agricultural experiments. 



The suggester of experiments in scientific and practical 

 agriculture ought to be guided by a knowledge, in so far as it 

 is understood, 



1. Of the various substances of which plants consist, or 

 which they require to promote their growth, and of the most 

 important chemical properties, mutual relations, and chemical 

 combinations of these substances. 



2. Of the functions performed by these substances in the 

 soil and in the plant at different seasons, and at different periods 

 of the plant's growth. 



3. Of the forms of chemical combination in which these 

 substances usually exist in the soil, enter into the roots, circu- 

 late in the sap, and fix themselves in the solid part of the plant. 



4. Of the general chemical composition of soils, of their 

 local origin and natural differences, and of the local sources of 

 supply (if any) of those substances which plants especially 

 require, in the district where the experiments are to be made. 



