100 Agricultural Chemistry. 



tent in fixed proportion of the simpler nitrogenous bodies known 

 as amino-acids. Asparagin, which is a derivative of an amino- 

 aeid, occurs in freshly sprouted asparagus, peas and beans. It 

 is produced from seed proteins by enzyme action and is, in part, 

 eventually fitted into the proteins of the seedling. 

 Plant proteins may be classified briefly as follows : 



1. Albumins: Soluble in pure cold water; coagulated by 

 boiling ; occur in seeds only in small amounts. 



2. Globulins: Insoluble in water; soluble in salt solutions; 

 separate out on diluting or saturating the solution. Most com- 

 mon and abundant of plant proteins. Occur in largest amount 

 in the seeds of leguminous plants. Certain globulins appear to 

 be characteristic of the seed in which they are found, as with 

 avenalin of the oat, maysine of corn, and hordein of barley. 

 Edestin, the globulin of the hemp seed, however, occurs in sev- 

 eral grains. 



3. Alcohol' soluble proteins: (Prolamins). Nearly or wholly 

 insoluble in water; soluble in alcohol of from 70 to 90 per cent 

 strength. They have been found only in the seeds of cereal 

 plants. 



4. Glutelins: Not dissolved by water, salt solutions, or al- 

 cohol; may be extracted by treating the residue of seeds from 

 which the other proteins have been removed, with dilute alkaline 

 solutions. Isolated and purified with much difficulty. The only 

 well defined glutelins are glutenin of the seed of wheat and orys- 

 enin of the seed of the rice. 



5. Conjugated (compound) proteins: These proteins have 

 been modified by combining with other compounds. They in- 

 clude nucleo-proteins, in which a large proportion of protein is 

 combined with a small amount of nucleic acid. Phosphorus is 

 present in these compounds, being contributed by the nucleic 

 acid. Conjugated proteins of other types occur in the animal 

 kingdom, but the exact nature of other preparations than nucleo- 

 proteins from plants, assigned to this group of compounds, has 

 not been clearly established. Such knowledge as we possess in- 



