ORGANIC SUBSTANCES AS PLANT FOOD 229 



crystalline products of their hydrolysis, the amino acids, appear. 

 These in turn give rise to ammonia. This stage, however, is fol- 

 lowed by synthetic processes. Ammonia changes into asparagine, 

 which, together with non-nitrogenous substances, forms new 

 protein compounds, thus making 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. Many of them belong to the complex pro- 

 teins. 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 pro- 

 teins. Finally, by still more thorough hydrolysis, the nucleic 

 acid itself can be broken down to phosphoric acid, a carbohydrate 

 group, and pyrimidine and purine bases. 



Purine and pyrimidine are heterocyclic compounds. Nucleic 

 acid contains two purine derivatives, adenine and guanine, and 

 two pyramidine derivatives, cytosine and thymine. All of these 

 being substances of a basic character, they therefore will combine 

 readily with phosphoric acid. The carbohydrate group is a rem- 

 nant of glucose. Plant nucleoproteids contain uracil instead of the 

 thymin of animal proteins, the pentose ribose, C5H10O5 and 

 ^-xylose, C5H10O5. In the breaking down of nucleoproteins in the 

 animal organism the derivatives of purine most often give uric 

 acid. 



The proteins of the protoplasm have been studied very little. 

 In protoplasm, glucoproteins are often found — complex proteins 

 which split off the carbohydrate group on hydrolysis. Fungi 

 are especially rich in glucoproteins. Protoplasm contains also 

 special phosphorus-containing proteins, which do not belong to the 

 nucleoproteins and are called plastins. Many authors, including Le- 

 peschkin, suppose that the proteins of protoplasm, though of a very 

 complex structure, are chemically bound still further with lipoids 

 forming molecular complexes of an enormous size and capable of the 

 most varied biochemical reactions. It was at one time supposed 

 that "living" proteins of the plasma differ from " non-living" ones 

 in that nitrogen is found in them not in the form of the amino 



