THE ORGANIC MATTER OF THE SOIL 129 



the products built up are more complex than the original 

 tissue. Most of this decay and simplification is due to 

 that great group of organisms so universally present in 

 soil, called bacteria. Some of these are putrefactive in 

 their action, while others deal to a large extent with the 

 products of the decomposition. All, however, exert a 

 general simplifying influence. The action of such or- 

 ganisms may be direct, but is more likely to be enzymotic 

 in its nature, and may take place either within or outside 

 of the cell. A cycle is therefore set up, in which the higher 

 plants and animals are occupied in building up, while 

 bacteria are tearing down and reducing the residue of 

 plant action to simple forms, such as can be ultimately 

 utilized again in plant nutrition. The great importance 

 of bacteria is thus evident, and the encouragement of 

 their growth and function is clearly a part of good soil 

 management. 



When the complex molecules that make up plant 

 tissue break down, they split along definite lines of cleav- 

 age, depending on the structure of the original molecule. 

 These bodies, which are usually simpler in nature than 

 those from which they have sprung, are called cleavage 

 products, and without a doubt they are the primary 

 products of the first step in organic decay. These com- 

 pounds are subject to still further change, and because 

 of the great number of agencies at work the secondary 

 products that result may be simpler or more complex, 

 according to conditions. Bacteria have a tendency, 

 while tearing down organic matter, to construct certain 

 built-up products which present a very complicated 

 molecule until they are in turn degraded. The secondary 

 products therefore vary widely because of differences in 

 temperature, moisture, aeration, and other conditions. 



