SECTION IV. THE NITROGEN COMPOUNDS 

 IN PLANTS 



As the study of the animal proteins already forms the 

 chief subject matter of one of the other books of this series 

 (Bennett), it will only be necessary to indicate in this section 

 some of the differences occurring between the vegetable 

 proteins and the animal proteins, and to give details of 

 nitrogenous bodies other than proteins. 



The Cereal Proteins. In the eighteenth century a 

 considerable amount of work was done in examining the 

 protein matter in wheat. In 1747 Beccari examined wheat 

 flour, and concluded that wheat gluten resembled animal 

 matter. The process chiefly used in that day was destructive 

 distillation. Kessel Myer, in 1759, determined the action 

 of various sulphates upon wheat gluten, and in 1773 Rouelle 

 showed that the wheat gluten was also present in various 

 other plants. Parmentier showed that wheat gluten was 

 insoluble in mineral acids, but soluble in vinegar, and that 

 there was some relationship between ther^colour of flour and 

 its gluten content. In the nineteenth century the solubility 

 of wheat gluten in alcohol was also considered, and the 

 elementary position of the proteins began to be accurately 

 studied. Destructive distillation at this period seems to have 

 been the method of the investigators. 



The chief protein in wheat grain is now called glutenin, 

 and the next most important gliadin. These are contained 

 in slightly greater quantities in spring wheat than in winter 

 wheat, but this variation is very likely due to the longer 

 period during which winter wheat grows. Reserve seed 

 proteins are usually more stable towards reagents than the 

 proteins which form part of the living substances of the 



