8 HOW CROPS GROW. 



attempted to touch, much less cover, all this ground, but 

 some account will be given of certain subjects whose un- 

 derstanding will be of the most direct service to the agri- 

 culturist. The Theory of Agriculture, as founded on 

 chemical, physical and physiological science, in so far as 

 it relates to the Chemical Composition, the Structure and 

 the Life of the Plant, is the topic of this volume. 



Some preliminary propositions and definitions may be 

 serviceable to the reader. 



Science deals with Matter and Force. 



Matter is that which has weight and bulk. 



Force is the cause of changes in matter it is appre- 

 ciable only by its effects upon matter. 



Force resides in and is inseparable from matter. 



Force manifests itself in motion and change. 



All matter is perpetually animated by force is there- 

 fore never at rest. What we call rest in matter is simply 

 motion too fine for our perceptions. 



The different kinds of matter known to science have 

 been resolved into some seventy chemical elements or sim- 

 ple substances. 



The elements of chemistry are forms of matter which 

 have thus far resisted all attempts at their simplification 

 or decomposition. 



In ordinary life we commonly encounter but twelve 

 kinds of matter in their elementary state, viz. : 



Oxygen, Carbon, Mercury, Tin, 



Nitrogen, Iron, Copper, Silver, 



Sulphur, Zinc, Lead, Gold. 



The numberless other substances with which we are 

 familiar, are mostly compounds of the above, or of twelve 

 other elements, viz.: 



Hydrogen, Silicon, Calcium, Manganese, 



Phosphorus, Potassium, Magnesium, Chromium, 

 Chlorine, Sodium, Aluminum, Nickel. 



