INTRODUCTION 5 



with the sun's energy. All energy utilized by plants or animals 

 thus comes directly or indirectly from the sun. 



We have used the term ''organic" in connection with the com- 

 pounds formed in plants. It was believed in the beginning of the 

 1 9th century that organic bodies, such as starch, sugar, urea, etc., 

 differed greatly in chemical nature from inorganic bodies, and 

 could only be formed under the influence of mysterious life- 

 forces. But in 1820 Wohler prepared a product of animal life 

 found in the urine, called urea, from a purely inorganic body, am- 

 monium cyanate. The supposed barrier between organic and in- 

 organic substances was thus broken down; great numbers of 

 organic compounds have since, been prepared, some of which 

 occur in nature, and the chemist now hardly places bounds to the 

 possibilities of organic synthesis in the laboratory. It is well 

 known that organic and inorganic bodies obey the same laws, 

 though on account of the size and complexity of the subject, 

 organic chemistry is still treated separately. 



As far as agricultural chemistry is concerned, there is a wide 

 difference between organic and inorganic bodies. Organic com- 

 pounds may serve as food for animals, but inorganic do not. On 

 the other hand, inorganic bodies serve as food for plants ; but to 

 only a very limited extent, if at all, do plants make use of organic 

 bodies. With the aid of light, plants build up organic bodies 

 which possess chemical energy, from inorganic bodies which do 

 not possess chemical energy. For the student of agriculture, 

 organic compounds are compounds of carbon which possess 

 chemical energy, and they are usually the products of plants or 

 animals. 



Conditions of Plant Life. The conditions necessary for the 

 production of organic matter by green plants may be summed up 

 briefly as follows: 



(1) Light. 



(2) Favorable Temperature. 

 ' (3) Water. 



(4) Certain elements in certain forms of combination. 

 If any of these conditions are unfavorafre, the plant will suffer 



