306 BIOCHEMICAL SYSTEMATICS 



stances may appear in hybrids. The substance need not be previously 

 unknown to be phylogenetically new in the sense impHed above. In 

 many cases, of course, the distinction between atavistic and non- 

 atavistic hybrid characters will be difficult. 



It is equally correct to expect hybrids to contain, frequently, 

 constituents peculiar to one or the other parent and in fact to approxi- 

 mate the sum of the two parental complements. Vickery and Olson 

 (1956), who examined the carotenoid and flavonoid pigments of a 

 number of Mimulus species and their hybrids, produced data which 

 indicate that the pigment complement of the hybrid, insofar as could 

 be determined, was in each case the sum of the two parental comple- 

 ments. This was true in several different inter-specific crosses. No 

 "hybrid" substances were reported, however. Henke (1960) found that 

 hybrids of Vitex species contained the flavonoids of both parents, 

 generally in larger quantity, though no new hybrid substances 

 appeared. 



A similar case in which the phenolic components of hybrids 

 of apple X pear represented clearly the sum of the parental compo- 

 nents is that of WiUiams (1955). Apple leaves contain the gluco- 

 side phloridzen as the principal phenolic constituent, along with 

 some of the aglycone phloretin, a quercetin glycoside, and traces of 

 chlorogenic acid and epicatechin. Pear leaves contain chlorogenic and 

 isochlorogenic acids plus arbutin as the chief phenohcs, with smaller 

 amounts of catechin, epicatechin, flavonol glycosides, and hydro- 

 quinone, the aglycone of arbutin. Phloridzin is apparently quite specific 

 for species of apple while arbutin is found in all pear species. Phlo- 

 ridzin is absent from pear species, and arbutin does not occur in 

 apple species. 



Among the hybrids the leaves contained phloridzin, arbutin, 

 chlorogenic and isochlorogenic acids in large amounts together with 

 lesser quantities of phloretin, epicatechin, and flavonol glycosides. 

 None of the hybrids were without the typical phenolics of either 

 parental species. According to the author. 



This apparently simple addition of the parental phenolic pattern in 

 the hybrids contrasts with the dominant recessive relationships found 

 with the anthocyanin coloring matter of flowers in intraspecific crosses. 



No reference is cited for the final statement, but it is prob- 

 ably an oversimplification of the situation, since among various plants 

 in which the inheritance of anthocyanins has been studied sometimes 

 epistasis is apparent and sometimes several pigments, each governed 

 by a single gene, may coexist. In any event the metabolism of one 

 particular class of phenolics (namely, anthocyanins) is more directly 

 interrelated than that of a series of classes of phenolics such as rep- 



