PROTEINS 



281 



Proteins.— Proteins are mostly storage forms of food and usually 

 most abundant in seeds, although they are present in all parts of 

 plants. In the kernels of 

 cereals, close to 12 percent 

 of the dry weight is protein. 

 In straw it commonly ranges 

 from 4 to 7 percent and from 

 5 to 8 percent in hay and 

 green fodder. The seeds of J^ 

 the Legumes are especially Q^-i 

 rich in protein, ranging from 

 about 14 percent in some 

 Lentils to as much as 60 per- 

 cent in some Beans. Also 

 the hay of Legumes contains 

 considerable protein. In Fi«- 251 -Section from a cotyledon 

 , ,1 ,, ^ . or a Pea, snowmg a iewcelJs;i, mtercellu- 



vegetables the protem ranges j^^ space; am, starch grains; al, aleurone 

 from about 2 percent in grains; n, nucleus. Enlarged 240 times. 

 Sweet Potatoes to 26 percent After Hayden. 



in Cucumbers. In all fruits there is some protein and sometimes 

 as much as 36 percent in Pumpkins. 



Some of the proteins 

 are in solution in the 

 cell sap, but mostly 

 they are in the form of 

 granules or crystals dis- 

 tributed through the 

 cell among starch grains 

 and other cell con- 

 stituents. (Fig. 251.) 

 Sometimes as in the 

 aleurone layer of cere- 

 als, the cells are filled 

 with protein granules. 

 Fig. 262. — Cross section through grain of {Fig. 262.) 

 wheat {Triticum vulgare); p, pericarp; i, testa; p + ■ + 



al, aleurone layer containing numerous protein -rrotems are extreme- 

 grains; n, nucleus; am, starch grains. Enlarged ly complex substances. 

 240 times. After Hayden. The formula given for 



the protein in the white of an egg is C239H386078NsgS2. They 

 differ from carbohydrates in containing nitrogen, usually 



-«w 



