PREFACE. 



The First Part of the following Lectures was addressed 

 to a Society* of practical agriculturists, most of whom pos- 

 sessed no knowledge whatever of scientific Chemistry or Ge- 

 ology. They commence, therefore, with the discussion of 

 those elementary principles which are necessary to a proper 

 understanding of each branch of the subject. Every thing 

 in such Lectures, which is not — or may not be — easily un- 

 derstood by those to whom they are addressed, is worse than 

 useless. It has been my wish, therefore, to employ no scien- 

 tific terms, and to refei to no philosophical principles, which 

 1 have not previously explained. 



To many who may take up the latter portions cf the work, 

 some points may appear obscure or difficult to be fully un- 

 derstood ; such persons will, I hope, do me the justice to be- 

 gin at the beginning, and to blame the Author only when that 

 which is necessary to the understanding of the later is not 

 to be found in the earlier Lectures. 



For the sake of clearness, I have, in the following pages, 

 divided the subject into four Parts — the study of each pre- 

 ceding Part preparing the way for a complete understanding 

 of those which follow. Thus, Part I. is devoted to the or- 

 ganic elements and parts of plants, the nature and sources 

 of these elements, and to an explanation of the mode in which 

 they become converted into the substance of plants ; — Part 

 II., to the iiiorganic elements of plants, comprehending the 

 study of the soils from which these elements are derived, and 



 The Durham County Agricultural Society, and the Members of the Dur- 

 ham Farmers' Club. 



290S-I7 . • 



