168 PLANT PHYSIOLOGY 



Simple Proteins.— The simple proteins yield only amino acids 

 when hydrolyzed. The albumins are soluble in water and dilute 

 salt solutions and are coagulated by heat. They are widely dis- 

 tributed in plants and animals. Egg albumin is the most familiar 

 animal albumin, while among the plant albumins are leucosin 

 (wheat, rye, and barley), legumelin (legume seeds), and ricin 

 (castor beans). 



Globulins are insoluble in water, soluble in dilute salt solutions, 

 and are coagulated by heat. The vegetable globulins form the 

 major portion of the protein of most seeds except the cereals and 

 are among the most common protein reserves. Among the com- 

 mon globulins are legumin (beans and peas), amandin (seeds of 

 almonds, peaches, and plums), acerin (maple), and edestin (hemp). 

 Fibrinogen from the blood is a familiar animal globulin. 



Glutelins are insoluble in water and dilute salt solutions but are 

 soluble in dilute acids and alkalies. They are not coagulated by 

 heat. No animal glutelins have thus far been isolated and only 

 a few from plants. These are in the cereals,— glutenin (wheat) 

 and oryzenin (rice). 



Prolamins or gliadins are insoluble in water and salt solutions 

 but are soluble in dilute acids and alkalies as well as in 80% 

 alcohol. This solubility in alcohol is their outstanding charac- 

 teristic. Thus far they have been found only in the plant kingdom 

 and there only in the cereals. Among the better known prolamins 

 are gliadin (wheat and rye), hordein (barley), and zein (corn). 

 Gliadin has the peculiar property of combining with water to 

 form a sticky paste which holds the particles of glutenin together; 

 the two, glutenin and gliadin, form gluten, which gives the sticky 

 and elastic properties to dough made from wheat flour. 



The histories, which are soluble in water, insoluble in am- 

 monia, and are not coagulated by heat, have not yet been found in 



plants. 



The protamines are the simplest proteins known. They are 

 soluble in water and ammonia and are not coagulated by heat. 

 They are related to the histones but are simpler. None have 

 been found in plants although there is evidence that they may 

 occur in pollen. In fish sperm, several protamines have been 



found. 



The albuminoids are insoluble in water, salt solutions, acid, or 

 alkalies. They have not been found in plants but include such 



