228 TEXTBOOK OF PLANT PHYSIOLOGY 



ammonium chloride was observed. This is formed from the 

 ammonium absorbed from the nutrient solution. 



Prianishnikov has expressed it figuratively by saying that 

 ammonia must be recognized as the alpha and omega of the trans- 

 formation of protein substances in plants. It splits off from amino 

 acids, appearing as the final end product of protein decomposition. 

 Similarly, it is the initial substance from which asparagine is pro- 

 duced and from which the synthesis of nitrogenous compounds in 

 plants begins. In some plants rich in proteins but poor in non- 

 nitrogenous substances, especially the fungi, instead of asparagine, 

 urea is the intermediate product of protein exchange, so that 

 in this respect they are still closer to the animal organism than higher 

 plants. 



Large quantities of urea are accumulated in the fruiting bodies 

 of Lycoperdon, in which it constitutes 10 per cent or more of the 

 total dry weight. In plants whose cell sap is very rich in organic 

 acids, the ammonium salts of these acids are accumulated instead 

 of asparagine. 



This analogy between asparagine and urea emphasizes a very 

 important physiological difference between animals and plants. 

 Animals fix ammonia, resulting from the complete disintegration 

 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 pro- 

 teins from ammonia and non-nitrogenous substances. Plants on 

 the contrary, having high synthetic capacity, fix ammonia in the 

 form of asparagine, which remains unaltered in the body of the 

 plant and then serves as the foundation material for further syn- 

 theses, splitting off ammonia when needed. 



72. Proteins of the Protoplasm and the Nucleus. Synthesis 

 of Protein Substances in Plants.— Asparagine is the initial product 

 of the synthesis which always accompanies the hydrolysis of protein 

 substances at germination. Germination is really a double process, 

 consisting of the breaking down of stored substances and of their 

 resynthesis into material to be used for the newly developing parts 

 of the young plant. Thus, in the transformation of carbohydrates 

 at germination the breaking down of starch and other polysac- 

 charides into the simple sugars is followed by the synthesis of cellu- 

 lose, which serves for the building of membranes of the new cells. 

 The same is true of proteins. They are hydrolyzed, while the 



