332 BIOCHEMICAL SYSTEMATICS 



related not to any inherent major theoretical barriers, but rather to 

 practical difficulties. Technical advances in the development of equip- 

 ment are quite rapid at present. The area in which the most progress 

 may be expected using gas chromatographic techniques includes the 

 essential oils. Techniques for treating this class of compounds are 

 highly refined. 



Physiological or chemical races 



Chemical variation in both populations and individuals is a 

 problem that is often considered to be of major significance— perhaps 

 sufficient to impair seriously the general effectiveness of the bio- 

 chemical approaches to systematics. Anyone slightly familiar with 

 populations of wild flowers will perhaps recall seeing considerable 

 variation in the flower color of certain species. (Horticultural color 

 varieties are often truly remarkable, but these usually result from the 

 careful preservation and propagation of many individual color 

 mutants.) A population of spiderwort {Tradescantla) , for example, 

 may have dark purple, light purple, dark blue, light blue, pale pink, 

 deep pink and white individuals, not as rare "mutants," but in large 

 numbers, and other similar examples may be recalled. Such chemical 

 variation, which is overt in the flower color pigments, is obviously to 

 be encountered among other types of substances. However, only a 

 small fraction of the compounds useful in biochemical systematics are 

 amenable to analysis by visual inspection. In fact, some substances 

 are so refractory that large numbers of individual plants may be re- 

 quired in order to get a sufficiently large sample of the compound. 



It is well known that secondary substances are likely to vary 

 in different populations, or even within individuals, of the same popu- 

 lation, from year to year. The question of whether the variation is 

 genetical or environmental in origin is not always easily answered 

 though it is pertinent to biochemical systematics. 



The occurrence of physiological races involving many classes 

 of compounds has already been noted, and only a few additional 

 examples need be cited here. Penfold and Morrison (1927) found 

 significant differences in the piperitone content of the oil from dif- 

 ferent populations of Eucalyptus dives, and even earlier Armstrong, 

 et al. (1913) had described populations of Lotus corniculatus differing 

 markedly in their cyanogen content, Tetenyi (1958) noted that in- 

 dividuals of Cinnamomum camphora sub-species formosana exist in 

 at least six chemical forms; they include as major constituents 

 borneol, camphor, cineole, linalool, safrol, and sesquiterpene. 



