30 SCIENCE AND SOIL 



of hydrogen and oxygen, enters the leaf through the stem, having 

 passed from the soil into the plant through the roots. 



As the carbon dioxid and water come together within the leaf, a 

 chemical reaction occurs which may be illustrated by the following 

 equation: 



HJ_ fV_i_'o r* C} TT r'o _i_ r\ 

 a \J T \J \_y=vj = jnoV^V-' T v 



The dotted line shows how the bonds are broken. The two atoms 

 of oxygen that are set free immediately join hands to form a mole- 

 cule of oxygen (O 2 ), which passes from the leaf into the outer air. 

 The two hydrogen atoms (H 2 = ) attach themselves to the group, 

 =CO, forming the compound, H 2 CO, which may also be written 

 CH 2 O, to show its hydrate character, and which might be called 

 monose, but is commonly known as formic aldehyde. This reac- 

 tion occurs only in the light and only in the presence of active 

 living chlorophyll (the green coloring matter of leaves). In other 

 words, this compound is formed under the influence of life, and 

 by it we enter a new field known as organic chemistry. 



Organic matter. Organic matter consists of compounds formed 

 by life processes, compounds that are, or have been, living 

 matter; whereas, inorganic matter consists of rocks, minerals, and 

 metals, of salts, liquids, and gases, whose origin has no necessary 

 connection with any living substance. Organic matter consists 

 of carbon compounds, 1 such as hydrocarbons (containing only 

 hydrogen and carbon), fats (containing much carbon and hydrogen 

 with little oxygen), carbohydrates (containing carbon with hy- 

 drogen and oxygen in proportion to form water as the name in- 

 dicates), and proteids, which contain not only carbon, hydrogen, 

 and oxygen, but also nitrogen, and sometimes phosphorus and 

 sulfur. These are the great groups of organic compounds compos- 

 ing plants and animals. The carbohydrates are the most abundant 

 in plants, while the proteids, although a necessary part of plants, 

 are the most abundant compounds in animals. 



Aldehydes and carbohydrates. Formic aldehyde is only one of 

 many aldehydes, which constitute a large class or series of organic 

 compounds. The aldehydes are extremely active substances and 



1 Many of the simpler carbon compounds can be made artificially. 



