HOW THE PLANT GROWS 7 



11. Nitrogenous compounds. We have learned how in the life-holding 

 protoplasm of the green parts of plants, especially their leaves, tlie 

 carbohydrates and fats are formed from the elements of carbon dioxid 

 and water by the energy of the sun. To these life centers, with their 

 green coloring matter, holding sugar and starch, the sap brings nitrates 

 and other mineral salts gathered by the roots from the soil. Thru the 

 union of the elements of the nitrates and other salts with those of the 

 starches and sugars, there is formed a new group of complex compounds 

 called crude proteins, which, in addition to carbon, hydrogen, and oxy- 

 gen, found in the carbohydrates, contain nitrogen, sulfur, and sometimes 

 phosphorus. These nitrogenous compounds are the most complex of all 

 plant substances. For example, the following are given as the probable 

 molecular composition of legumin, a protein found in the seed of the 

 field pea, and hordein, found in the barley grain : 



Legumin C 718 H 1158 238 N 214 S 2 

 Hordein C 675 H 1014 194 N 181 S 4 



On account of this great complexity and also because of the great 

 number of different nitrogenous compounds found in plants, these com- 

 pounds are the most difficult of all plant substances to study and classify. 

 For years able chemists have been attacking these intricate problems 

 with great energy and patience. But even yet, altho much valuable in- 

 formation has been gained, our knowledge of the differences in the com- 

 position of the various nitrogenous compounds and their relative feeding 

 values is limited. For this reason, in discussions of feeding stuffs and 

 of the nutrition of animals these compounds are grouped under the 

 general classes of crude protein, proteins, and amids. 



Crude protein is the term employed to designate all the nitrogenous 

 compounds of the plant. The chemist finds that about 16 per ct. of the 

 plant proteins is nitrogen. Accordingly, he multiplies the nitrogen 

 found in a given plant substance by 6.25 (100-^-16=6.25) and calls the 

 product crude protein. Crude protein embraces two great groups of 

 nitrogenous plant compounds proteins and amids. 



Proteins are the more complex and highly organized forms of crude 

 protein. They are not always soluble and therefore in many cases not 

 transportable in the juices of the plant. The proteins form the basis 

 of the living protoplasm of all plants and animals, and so are essential 

 to all life. 



Amids are the more simple compounds included in the crude protein. 

 They may be termed the building stones of the proteins, for from them 

 the plant constructs the more complex proteins, and on decomposition 

 the proteins are again broken down into these more simple bodies. These 

 compounds are the portable nitrogenous building compounds of the 

 plant, for they are soluble in its juices and hence may be conveyed 

 wherever needed thruout the plant structure. Commonly included under 



