THE CHEMISTRY OF COFFEE 165 



NH CO 



CO C NH 



^CO 

 NH C NH 



This acid does not occur in plants ; yet its formula shows such a 

 close relationship to other purine bases as to indicate that the forma- 

 tion of purine bases in plants may, as in animals, be waste products 

 of metabolism. In fact, Foss, in Compt. Rend. 155 (1912) 851 and 

 156 (1913) 567, has observed urea traces in higher plants. It is, 

 however, questionable whether or not they are a physiological pro- 

 duct of the cell. 



The function of alkaloids in plants is difficult to explain. It has 

 been suggested that they are nutritive materials utilized in vegetable 

 metabolism, and that they are protective materials against animal 

 attack. It seems more probable that they are end-products of nitrog- 

 enous metabolism, which are rendered harmless to plants by con- 

 version into alkaloids and merely happen to be stored up because of 

 the inability of the plant to rid itself of them. Caffeine does not 

 seem to be so intimately related to protein metabolism as are the 

 other purine bases. Nevertheless, the purine bases, which are a part 

 of the nucleic acids, form the major proportion of the nucleus which 

 is the center of all cell-division. Thus it seems plausible that these 

 purine bases play an essential part in the growth of both plants and 

 animals. 



The purine bases to which the coffee alkaloid caifeine belongs, in- 

 clude caffeine which is found in Thea sinensis L. leaves; in Cola 

 acuminata Schott & Endl. fruit; in Ilex paraguariensis St, Hil. 

 leaves (mate) ; in Paullinia Cupana H.B.K. fruit (guarana) ; and 

 in Cojfea arabica L. seeds, which are of special interest in this treatise. 

 The purine alkaloids also include theobromine which is present in the 

 fruit of Theobroma cacao L. ; theophylline in the leaves of Thea 

 sinensis L. ; xanthine in the leaves of Thea sinensis L. ; in the root 

 sap of Beta vulgaris L., and in a number of sprouting seedlings; 

 hypoxanthine in the seeds of Piper nigrum L. ; inosine, a pentoside of 

 hypoxanthine, which is found in yeast and beet root; guanine, found 



