280 



LEAVES 



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, 

 but 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 la ^ er f ,. ^ e T Cereals > 

 wheat (Triticum vulgare)', p, pericarp; t, testa; there 1S llttle else but 

 al, aleurone layer containing numerous protein proteins. (Fig. 251.) 

 grains ;n, nucleus; am, starch grains. Enlarged The Legumes store con- 

 240 times. After Strasburger. siderable 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 they 

 usually contain sulphur and 

 sometimes phosphorus; but 

 nitrogen is the chief mineral 

 constituent. The proteins 



are extremely complex, as the 



f 1 P TT 1M C\ Q ^ IG * 252. Section from a cotyledon 



^720lii34iN 2i8<J24805 of a p eaj showing a f ew ceUg . ^ intercellular 



for one of them indicates. spa ce; am, starch grains; al, aleurone 

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

 by which the photosynthetic After 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 



