TEE ORGANISM 53 



hydrogen atoms of hydrocarbons by atoms or 

 groups of atoms (radicals) of other elements. As a 

 convenient theory, then, all organic compounds are 

 regarded as derivations of hydrocarbons. 



The ideas of structure (pattern of combination) 

 and of substitution (the disappearance of elements 

 and the appearance of other elements or groups of 

 elements) are the simple basic concepts of organic 

 chemistry concerning the formation of the many 

 thousands of complex organic compounds. 



A highly important group of organic substances 

 are the carbohydrates, (l) sugars, (2) starches and 

 celluloses, compounds of carbon, hydrogen, and 

 oxygen. The molecular formula is known for prac- 

 tically all the sugars. The structure of the molecule 

 of the starches and of the celluloses is unknown. 

 The chemical constitution of sugars and starches and 

 the formation of these carbohydrates in the living 

 plant, of course, are two very different things; the 

 process, which can take place only with the aid of 

 sunlight, involving the living plant, the soil, and the 

 air (carbon dioxide, and nitrogen, since it has been 

 proved that many, if not all, green plants are able 

 to fix atmospheric nitrogen). (Moore, Webster, 

 Mameli and PoUaci.^) 



* See Carleton Ellis and Alfred A. Wells, The Chemical Action of Ultraviolet 

 Rays, 233. 



