ALLIED AND MISCELLANEOUS PRODUCTS 185 



As waste products the purine bases seem to answer the require- 

 ments better than the others. Uric acid which is found in the 

 urine of animals has the formula: 



HN— C=0 



H 



/ 

 OC C— N 



\c=o 



HN— C— N 



\ 

 H 



It is thus seen to be a purine base, showing that there is more 

 than a superficial resemblance between urine and tea. The 

 uric acid is known to be an excretory product, and it is only- 

 reasonable to suppose that the similar compounds in plants 

 play an analogous role. Plants have no method of active ex- 

 cretion for eliminating nitrogen wastes, and these purine bases 

 may in certain cases meet this metabolic demand, the nitrogen 

 being stored in an insoluble manner which cannot harm the 

 plant. 



Weevers (1930), however, holds that these purine bases, or 

 xanthene derivatives as they are frequently called, function in 

 much the same way as asparagine (see preceding chapter), i. e., 

 they are formed from the breaking down of proteins and are then 

 used again to make new proteins. They are thus both " waste" 

 and "feed" material, depending upon the phase emphasized. 

 Weevers bases this theory largely on the fact that in plants rich 

 in these products, e. g., tea, coffee, cocoa, herba mata, etc., when 

 branches or leaves die, the xanthene derivatives are not permitted 

 to fall off with the dead organs but are transformed and sent back 

 into the trunk or other active, living parts of the plant. As we 

 have seen, plants are very saving of their nitrogen, and this theory 

 deserves serious attention. Theron and Cutler (1924) believe the 

 alkaloids play a somewhat similar role when present and cite a 

 similar group of facts to prove their point. 



All of the plant bases may be of some survival value in pro- 

 tecting plants against the attacks of animals and fungi and many 

 of them, e. g., the decomposition products of the glucosides, have 

 an antiseptic property. 



