*(; 



i64 COFFEE 



It is noteworthy that plant alkaloids seem to occur only in certain 

 families of the vegetable kingdom. Although alkaloids occur in many 

 other families in addition to the list given below, one finds them most 

 frequently in dicotyledonous phanerogamous plants, less frequently in 

 monocotyledons, and least frequently in cryptogams. 



Families Rich in Families Poor in Families Inter- 



Alkaloids Alkaloids mediate 



Ranunculaceae Gramineae Compositae 



Papaveraceae Orchidaceae 



Fumariaceae Rosaceae 



Leguminosae Labiatae 



Apocynaceae 



Solanaceae 



Rubiaceae 



It has been found not only that alkaloids are present mainly in few 

 families but also that the alkaloids in any one family and especially 

 in any particular genus are, as a rule, closely related. The purine 

 group of alkaloids, however, to which caffeine belongs, are contrary 



j "f to this generalization, as they are closely related and occur in sev- 



j[s eral families. 



'Jj The origin of alkaloids in plants is a debatable question. Pictet 



If states that they are produced in two successive stages: (i) Decompo- 



.4 sition of complex nitrogenous substances (ex. Protein or Chlorophyll) 



j" to simple basic substances. (2) Combination of these simple basic 



substances with compounds present in the plant, which results in 

 the formation of the complex alkaloid molecules. Thus Drs. Haas 

 and Hill ^ have stated, "The processes of metabolism within the 

 plant would therefore be strictly analogous to those taking place in the 

 animal body, in which waste products, such as phenol, glycerine, 

 etc., are coupled up with other substances such as sulphuric or benzoic 

 acid, before being eliminated." A well-known product of the metab- 

 olism occurring in animals is uric acid which is recognized systemat- 

 ically as 2 : 6 : 8 trioxypurine and may be represented by the constitu- 

 tional formula: 



^ Haas & Hill Chem. PI. Prod. ed. 3, i (1921) 271. 



