280 



LEA\^S 



am 



The vegetable proteins are of many kinds and they vary greatly 

 in physical and chemical properties. They occur as crystals, 



granules, or in solution 

 in the vacuoles of the 

 protoplasm, or in inti- 

 mate association with 

 the protoplasm. They 

 are present to some ex- 

 tent in all plant cells, 

 l)ut are more prominent 

 as storage products in 

 seeds, where they are 

 usually associated with 

 starch and fats. Some- 

 times, as in the aleurone 



Fig. 251. -Cross section through grain of ^^^^"^ .^^ }^^ «^^^^1«' 

 wheat (Triticum vulgar e); p, pericarp; <, testa; there IS little else but 

 a/, aleurone layer containing numerous protein proteins. {I^W- 251.) 



grains; n, nucleus; am, starch grains. Enlarged The Leo^umes store COn- 

 240 times. After Strasburger. siderabTe quantities of 



proteins, and for this reason some of them, especially the Beans 

 and Peas, are very desirable 

 for food. {Fig. 252.) 



Proteins differ chiefly from 

 the carbohydrates and fats 

 in that they contain nitro- 

 gen. They are known as 

 nitrogenous foods. In 

 addition to nitrogen thej- 

 usually contain sulphur and 

 sometimes phosphorus; but 

 nitrogen is the chief mineral 

 constituent. The proteins 

 are extremely complex, as the 

 formnlf, P TT M O d TiG. 252. — Section from a cotyledon 



lOrmUla '--720Aln34iN.ii8U94Sk55 r r) u • e 11 • • a. ii i 



• r ofaPea, showmgafewcells; r.mtercellular 



lor one oi tnem inaicates. space; am, starch grains; al, aleurone 

 The steps in the process grains; n, nucleus. Enlarged 240 times. 

 by which the photosynthetic ^^^*«^ Strasburger. 

 sugar and the mineral elements are formed into proteins are not well 

 known; but it seems clear that the elements of the sugar are first 



