NITROGEN SUPPLY 85 



particular salt, but to the acidity which develops as the nitro- 

 gen is assimilated. 



Terroine, Wurmser and Montane * studied Aspergillus 

 niger and found that the nitrogen content of the mycelium 

 decreases to a steady value which is unaffected by large 

 variations in the amount of ammonium sulphate in the culture 

 medium. If the ammonium salt be replaced by sodium nitrate 

 or by urea, the nitrogen content is unaffected, but its substi- 

 tution by peptone lowers it slightly, while guanidine lowers it 

 much. A considerable increase in the carbohydrate content, 

 glucose or sucrose, of the culture medium causes an increase in 

 the nitrogen content of young cultures but has the reverse 

 effect on old cultures. The substitution of glucose by ara- 

 binose or by xylose has no effect, but galactose effects an ap- 

 preciable decrease in the nitrogen content. These authors 

 consider that the nitrogen metabolism of Aspergillus is similar 

 to that of higher animals. 



For ordinary green plants the supply of nitrogen is found 

 in the simple nitrogen-containing salts of the soil water. Thus 

 the fertility of the soil, not only with respect to nitrates but 

 also in regard to other substances, f is an important factor, 

 conditioning the amount of protein found in the plant. In 

 addition to nitrates, some plants can make use of ammonium 

 salts. Hutchinson and Miller % found this to be true in 

 conditions of culture which precluded the presence of nitrates 

 in the soil. In this respect, however, all plants do not be- 

 have alike ; whilst some will grow equally well whether 

 supplied with nitrates or ammonium salts, others flourish 

 best when supplied with the former, and others seemingly 

 prefer ?.mmonium salts to begin with and then nitrates. 



Mention has just been made of the importance of soil sub- 

 stances other than nitrates in the protein synthesis of plants : 

 potassium may be taken in illustration. Species of bacteria 

 grown in the dark in culture media containing the requisite 



♦Terroine, Wurmser and Montane: "Bull. Soc. chim. biol.," 1922, 4, 



623. 



t Whitson and Stoddart : " Ann. Rep. Wisconsin Exp. Sta., 1904, 



193- 



J Hutchinson and Miller: " Journ. Agric. Sci.," 1909. 3, 179- 



