139 



CHAPTER V. 



ORGANIC MATTER — THE NATURE AND COMPOSITION OF 

 VEGETABLE SUBSTANCES. 



315. We have now very briefly described most of 

 those substances which are of importance in studying 

 vegetable chemistry. Before explaining the action 

 which they have on the growth of plants, it will be 

 proper to go a little more into detail respecting the 

 nature of organic matter ; that is to say, the various 

 compound substances which constitute the bodies of 

 animals and plants. 



316. Most of the substances hitherto described, 

 such as water, ammonia, carbonic acid, common salt, 

 &c., consist wholly of two elements, and are therefore 

 sometimes called binary compounds. On the contrary, 

 all animal and vegetable substances consist of three 

 or four elements, and are consequently termed ter- 

 nary or quaternary compounds. It has been already 

 stated that plants and animals are composed of carbon, 

 oxygen, hydrogen, and nitrogen (92). It is very 

 important to understand clearly the nature of the 

 compounds formed by these elements. 



317. When we endeavor to analyze a plant, that 



