2 INTRODUCTION. 



Sir Humphry Davy very justly observes, " It 

 is scarcely possible to enter upon any investiga- 

 tion in agriculture without finding it connected, 

 more or less, with doctrines or elucidations de- 

 rived from chemistry." And a chemical examin- 

 ation, shows, that the earth is but little con- 

 cerned in vegetation, otherwise than as a me- 

 dium or vehicle, bed or couch, in and on which, 

 the most important operations of nature are 

 conducted and performed. 



We are commonly led to consider vegetables 

 as the chief produce of the earth ; but vegetables 

 and animals are so completely dependent upon 

 each other, that before we can affect in any de- 

 gree the produce of the one, we must comprehend 

 the influence they have each on the other. From 

 a great similarity to themselves in nature, man- 

 kind were very early enabled to form a clear com- 

 prehension of the general functions of animals, 

 in regard to their food, and as they are influenced 

 by climate ; also, of the difference in the sexes, 

 and the natural result of their intercourse : but it 

 was not understood until a much later period, 

 that the general functions of vegetables are in 

 every respect similar to those of animals, and 

 that the operations of nature regarding both, 

 are regulated by much the same laws j this, how- 

 ever, is now clearly demonstrated. 



