CONSTITUENTS OF PLANTS 



359 



the plant. Amides are also formed from proteids by the action 

 of acids, or the digestive juices of animals, or by other agencies. 



The most important amido compounds are leucin, tyrosin, 

 phenyl-amido-proponic acid, asparagin, and glutamin. Of these 

 asparagin is relatively the most common and most abundant. It 

 has the formula C 2 H )5 (NH 2 ) (CONH 2 ) (COOH). Leucin, 

 tyrosin, and phenyl-amido-propionic acid are amido-acids ; that is 

 to say, they are acids in which the amido group NH 2 has 'replaced 

 an atom of non-acid hydrogen. Thus leucin, C 5 H 10 (NH 2 )CO 2 H, 

 is derived from capronic acid, C^H^COaH, by replacing an atom 

 of hydrogen by NH 2 . 



Determination of Proteids and Amides. An accurate method 

 for this determination is much to be desired. The usual method 

 consists in boiling the substance with water and precipitating the 

 proteids with copper hydroxide. The nitrogen in the precipitate 

 multiplied by 6.25 is supposed to give the proteids. The differ- 

 ence between the precipitated nitrogen and the total nitrogen, is 

 the amide nitrogen. 



PROTEIDS AND AMIDES IN PLANTS. 1 (IN DRY MATTER.) 



The preceding table shows that the protein of seeds consists' 

 mostly of proteids, but a considerable part of the protein of hays 

 and fodders may consist of non-proteid materials. The per- 

 centage of nitrogen in the amido compounds we have mentioned, 

 is given in the following table : 



1 Bulletin 172, North Carolina Exp. Sta. 



