MISCELLANEOUS COMPOUNDS 



287 



Papaveraceae and two other small families (Tovariaceae and Bret- 

 schneideraceae) comprise the order Rhoeodales. The Papaveraceae, 

 so far not known to produce isothiocyanates, is a major alkaloid pro- 

 ducer, but alkaloids are not known from the isothiocyanate-producing 

 families of the Rhoeodales. Such examples of mutual exclusion, 

 together with the sporadic appearance in other widely separated 

 families of isothiocyanates identical with those of the Cruciferae 

 should be observed. Taxonomic speculations based solely on similar 

 correlations involving other groups of compounds need to be stated 

 conservatively. An interesting example of such parallelisms is the 

 occurrence of both isothiocyanates and the rare fatty acid, erucic 

 acid, in the families Cruciferae and Tropaeolaceae. There is no 

 obvious relationship between the two types of compounds, and the 

 families concerned bear no obvious relationship to each other. 



There is little doubt, however, of the taxonomic significance 

 of mustard oils within the family Cruciferae. Practically all members 

 of this family so far investigated have proven to contain isothiocya- 

 nates, and even more remarkable is the variety of different types of 

 isothiocyanates which occur in the family. Most of the series illustrated 

 in Table 14-3 are represented in one or another species of Cruciferae. 

 Kjaer (1960) may be consulted for a comprehensive account of the 



