14 PROXIMATE CONSTITUENTS OF PLANTS 



CHAPTER II 

 Proximate Constituents of Plants 



The proximate constituents of plants, or the actual organic com- 

 pounds existing in plants, are practically infinite in number, 

 although only a few individual members are of sufficient import- 

 ance to deserve especial attention. It is usual to divide the 

 proximate constituents into two main divisions, nitrogenous and 

 non-nitrogenous, according as nitrogen is present or not. 



The carbohydrates constitute the most important group of non- 

 nitrogenous constituents, while the. proteins or albuminoids^ which 

 are almost invariably present in smaller amount than the carbo- 

 hydrates, are the most important of the nitrogenous. 



{a) Proteins. 



Many different complex bodies differing only slightly in 

 chemical composition containing carbon, oxygen, hydrogen, 

 nitrogen, and sometimes sulphur and phosphorus, are classed 

 under the one head of proteins or albuminoids, and are found 

 in varying amounts in different plants, e.g.^ legumin or vegetable 

 casein in members of the Leguminosae, and gluten in the wheat 

 grain (the latter containing the largest amount of albuminoids of 

 any of the cereals). 



S. Preparation of Gluten from Wheat. 



About 50 grams of wheat flour are made into a stiff 

 dough by the addition of sufficient water, and the mass 

 allowed to stand for fifteen minutes or so, in order to 

 allow of the production of gluten from the other 

 proteins by the action of a ferment present. The 

 dough is then placed in a cloth and well kneaded, while 

 a stream of water is allowed to run on to it in order 

 to carry away the starch. After a few minutes the 

 mass may be removed from the cloth, and kneaded 

 directly with the hands in the stream of water until all 

 starch is removed, as shown by the absence of any 



