PROTEINS 



281 



-r-am 



FIG. 



of & 



251. Section from a cotyledon 

 ghowing a few cellg . - ? intercellu . 



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 



the Legumes are especially 



rich in protein, ranging from 



about 14 percent in some dl~ 



Lentils to as much as 60 per- 'Oi 



cent in some Beans. Also 



the hay of Legumes contains 



considerable protein. In 



vegetables the protein ranges lar S p ace ' ; a m, 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. 252. Cross section through grain of (Fig. 252.) 



wheat (Triticum vulgare); p, pericarp; t, testa; Proteins are extreme- 



al, aleurone layer containing numerous protein 



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 C239H3 86 O 7 8N58S 2 . They 



differ from carbohydrates in containing nitrogen, usually 



