PURINE BASES 377 



tween this substance and the other purine bases, the assump- 

 tion does not seem unwarranted that the purine bases in the 

 plant are also waste products (see below). In this connection, 

 it is interesting to find that the presence of urea, in very 

 small amounts, has been observed by Fosse * in the higher 

 plants. 



In the fruit bodies of Lycoperdon and other higher Fungi, 

 urea, either free or loosely combined, accumulates especially 

 under conditions of growth involving a large supply of nitro- 

 gen.f Similarly, moulds, Aspergillus, for example, and bacteria 

 Bacillus tumescens, for instance, grown in culture media rich 

 in nitrogen, especially in the form of peptone or arginine, 

 produce considerable quantities of urea.J 



The identification of individual members of the purine bases 

 is not very easy, although the recognition of a purine base as 

 such is rendered simple by the so-called murexide test which 

 is given by practically all the members of this group of com- 

 pounds. 



The test consists in evaporating the substance (uric acid 

 or caffeine may be used) in a porcelain basin with dilute nitric 

 acid over a water bath. A yellowish residue remains which 

 on the addition of ammonia or by exposure to ammonia vapour 

 turns pink ; potash changes the colour to purple. 



The identification of caffeine in plants has been the subject 

 of numerous researches || ; it is precipitated by several alka- 

 loidal reagents from solutions containing concentrated hydro- 

 chloric acid, but not from neutral solutions ; these precipitates 

 are, however, not characteristic. Behrens ^ has described 

 methods of identifying this substance with the help of mercuric 

 chloride and of silver nitrate and nitric acid. The method is 

 as follows : — 



* Fosse : " Compt. rend.," 1912, 155, 851 ; 1913, 156, 567. 938 ; 157, 

 948 ; 1914, 158, 1374 ; 159, 253 ; " Ann. Chim.," 1916, [ix], 6, 13, 155. 

 See also Fosse : " L'Uree," Paris, 1928. 



t Ivanoff : " Biochera. Zeit.," 1923, 135, i ; 136, i, 9 ; 143, 62. 



X Ibid., 1925, 162, 425 ; 1926, 175, 181. See also Bokorny : id., 1922, 



I32» 197- 



II Clautriau : " Nature et Signification des Alcaloides vegetaux," 



Brussels, 1900. 



^ Behrens : " Anleitungen z. mikrochemischen Analyse d. wichtigsten 

 organ. Verbindungen," 1897, IV., 14. 



