334 BIOCHEMICAL SYSTEMATICS 



three groups: (1) those with allyl isothiocyanate only; (2) those with 

 3-butenyl ( = crotonyl) isothiocyanate only; (3) those with a mixture of 

 the two mustard oils. Seeds from China, Japan, Nepal, and Eastern 

 Europe were of type 1 (except for three out of forty-nine samples with 

 traces of component 2). Seeds from India and Pakistan were either 2 or 

 3. Twenty-six samples from North America and Western Europe had 

 contents compatible with their described origins. The authors con- 

 sidered that perhaps Brassica juncea had arisen independently 

 through hybridization between B. nigra (which forms allyl isothio- 

 cyanate) and B. campestris (which forms 3-butanyl isothiocyanate). 

 The widespread existence of chemical races renders such an hypothesis 

 of limited value unless supported by other data. 



With respect to alkaloids, Marion (1945) confirmed a report 

 of the presence of the alkaloids, nicotine and sedamine, in Sedum 

 acre; however Beyerman and Muller (1955) could not detect these 

 two alkaloids in a European population. Instead, they found another 

 alkaloid, sedridin. The latter results were confirmed independently 

 by Schopf and Unger (1956) who studied a population of Sedum acre 

 near Darmstadt, Germany. There is no need to cite other examples 

 of a similar nature. To borrow a phrase from Brachet (1960), who 

 applied it to the mitochondrion: there is one thing we know about 

 chemical variation, it exists. In fact, serious proposals have been 

 made to establish formal nomenclature for chemical races, and the 

 question has been discussed in a symposium (Dillemann, 1960; 

 Jaminet, 1960). 



Since the existence of a considerable amount of variation in 

 the chemistry of a species is established, the next question involves 

 the extent of variation. Does chemical variation undermine the 

 effectiveness of biochemical systematics? For every species which ex- 

 hibits variation in flower color, there are numerous species whose 

 flower color is distinctive, even diagnostic (except for the true 

 mutant). The distinctive blue of Commelina flowers is contrasted 

 with the color varieties in its close relative, Tradescantia. Distinctive 

 colors, tastes, and odors, and the mere existence of drug plants should 

 remind us that it is better not to become overly concerned about the 

 problem of variation. Even so, chemical variation may be excessive. 

 The variation found in the alkaloids of individual plants from various 

 populations of Baptisia levcophaea (Chapter 9) is matched by the 

 variation found in different plants within a single population. Some of 

 the leaf coumarins are also quite variable in amounts in B. leucophaea. 

 Yet, a larger number of other leaf substances including, probably, 

 flavonoids are relatively constant and some are diagnostic for the 

 species. No generalization can account adequately for the infinite 



