282 LEAVES 



sulphur and sometimes phosphorus. They are known as nitro- 

 genous substances. 



In the formation of proteins apparently the elements of sugar 

 are first combined with nitrogen to form amino-compounds. The 

 amino-compounds then combine in proper portions with sulphur 

 and sometimes phosphorus taken into the combination to form 

 proteins. The amino-compounds, chiefly amino acids, are nearly 

 always present in plants. Asparagin, (C 4 H 8 O 3 N 2 ), especially 

 abundant in garden Asparagus, is one of the most common amino- 

 compounds occurring in plants, but a number of others, such as 

 arginin, tyrosin, leucin, and tryptophane, are often present in 

 considerable quantities, especially in germinating seeds and seed- 

 lings. When proteins are decomposed by enzymes or other agents, 

 simpler proteins and amino-compounds are produced, and in 

 these soluble forms proteins are transported in both plant and 

 animal bodies. 



Most of the proteins formed in plants are included in the gen- 

 eral classes albumins, globulins, glutelins, gliadins, and nucleo- 

 proteins. The albumins, the proteins present in the white of an 

 egg, are represented in Peas by legumelin and in wheat and other 

 cereals by leucosin. The globulins are common in the Legumes, 

 legumin being a common one. Kidney Beans contain 20 percent, 

 Peas 10 percent, and Lentils about 13 percent of globulins. In 

 all seeds, except cereals, globulins are probably the most abundant 

 of the reserve proteins. The glutelins are represented by the 

 glutenin of Wheat and the oryzenin of Rice. Gliadins are com- 

 mon in the cereals, the gliadins and glutelins constituting gluten 

 which is responsible for the sticky character of dough. The 

 nucleo-proteins occur chiefly in cell nuclei, being an important 

 constituent of chromatin. 



The plant proteins are fundamently the source of all proteins. 

 Animal cells can make other proteins from plant proteins, but 

 they must first have the plant proteins to furnish the constituents. 

 As food for animals, proteins are especially necessary since they 

 furnish the material for repairing and building up tissues. They 

 are most needed by young growing animals. As a source of energy 

 they are equal to the carbohydrates, each gram furnishing about 

 4 calories of energy. In determining rations for animals no con- 

 stituent of feeds receives more attention than the proteins. The 

 constituents of the broken down plant proteins are the sources of 



