THE ORGANIC MATTER OF THE SOIL 101 



mineral matter or so-called ash exists as a part of the com- 

 pounds listed under these headings. The carbohydrates, hav- 

 ing the general formula of Cx(H20)n include such compounds 

 as starch, cellulose, dextrose, glucose, cane sugar, and the like. 

 The fats and oils may be represented in plants by such glycer- 

 ides as butyrin, stearin, olein, palmitin, while many acids of 

 an organic nature exist especially in fruits and vegetables. 



¥m. 20. — ^Diagram showing the general composition of green plant tissue. 

 The nitrogen which is generally less than .5 per cent, is included 

 with the ash in the above diagram. (After Stoddard.) 



Of the five groups, however, the nitrogenous compounds are 

 probably the most complicated as they carry not only carbon, 

 hydrogen, oxygen, and nitrogen, but also mineral elements 

 such as sulfur, phosphorus, calcium and iron. They are com- 

 pounds of high molecular weight and many are of unknown 



IV. Organic acids and their salts — Citric acid, malic acid, tannic acid, 

 tartaric acid, and the like. 



v. Mtrogenous compounds — ^Nitrates, ammonia, amides, amino-acids, 

 alkaloids, and proteins. 



