THE BIO-CHEMISTRY OF ANIMALS AND PLANTS 68i 



demned to inactivity at the low temperatures of 4-15° of the 

 northern seas, and thus the nitrogenous materials are left 

 available for plant and subsequently for fish life.^ 



We are now able to finish the picture of the nitrogen cycle 

 in Nature, and the following schematic drawing is left to speak 

 for itself: 



|5fAWA7-f/?[ ^ . •• 



The Synthesis of Protein in Plants 



Moulds. — The statements that some fungi {Aspergillus and 

 Penicillium varieties) are able to fix atmospheric nitrogen like 

 certain bacteria have so far not been sufficiently established. 

 Moulds and yeasts, however, are able to satisfy their nitrogen 

 want by making use of ammonia salts and nitrates. For yeasts, 

 nitrates are less suitable than for moulds. It has further been 

 shown that the latter synthesise their protein material still 

 better if simple amino acids are offered to them. For one of 

 the commonest moulds, Aspergillus, it was demonstrated by 



' For a detailed account of these and similar problems, see J. Johnstone, 

 Science Progress, vol. ii. 1907, 191. 



