76 PLANT PHYSIOLOGY 



Animals fix the nitrogen, resulting from the complete disinte- 

 gration of proteins, in the form of urea and excrete it from their 

 bodies as unnecessary refuse. It is of no use to the animal 

 organism, which cannot bring about the reverse synthesis of 

 amino acids and proteins from ammonia and nonnitrogenous 

 substances. Plants on the contrary, having high synthetic 

 capacity, fix ammonia in the form of asparagine, which remains 

 unaltered in the plant and then serves as the foundation material 

 for further synthesis, splitting off ammonia when needed. 

 Asparagine is the initial product of the synthesis that always 

 accompanies the hydrolysis of protein substances at germination. 

 Germination is really a double process, consisting in the breaking 

 down of stored substances and in their resynthesis into material 

 to be used for the newly developing parts of the young plant. 

 In discussing the transformations of carbohydrates during 

 germination, it has already been noted that the breaking down 

 of starch and other polysaccharides into the simple sugars is 

 followed by the synthesis of cellulose, which serves for the build- 

 ing of membranes of the new cells. The same is true of proteins. 

 The reserve proteins are hydrolyzed, while the crystalline prod- 

 ucts of their disintegration, the amino acids, appear. These in 

 turn give rise to ammonia. This stage, however, is followed by 

 synthetic processes. Ammonia changes into asparagine, which, 

 together with nonnitrogenous substances, forms new protein 

 compounds, the living compounds of the protoplasm of the 

 new cells. 



The protein substances entering into the composition of the 

 nucleus and the cytoplasm differ quite radically from the reserve 

 proteins of the seed. Most of them belong to the complex 

 proteins. The most studied of these are the nucleoproteins, 

 which evidently form the main part of the chromatin of the 

 nucleus. Nucleoproteins are very complex compounds. The 

 pepsin of the gastric juice removes the protein group from these 

 compounds, leaving the indigestible nuclein. By further 

 hydrolysis, the nuclein can be broken down by splitting off 

 another protein group and leaving only nucleic acid, which 

 has nothing in common with proteins. Finally by still more 

 thorough hydrolysis, the nucleic acid itself can be broken down 

 into phosphoric acid, a carbohydrate group, and pyrimidine and 

 purine bases. 



