BIOCHEMICAL STUDIES OF HYBRIDS 305 



series of alleles occurs, when complementary factors are involved 

 or when a complex of other factors influences the ability of another 

 factor to express itself phenotypically (as perhaps is the case in some 

 penetrance effects), all of the phenomena cited above by Reichert will 

 not only be possible, they will be inevitable. There is no reason either 

 to expect the principles to apply only to intraspecific hybrids. Later 

 in this section more will be said about the appearance of traits in hy- 

 brids not present in either parent. Such traits have been observed 

 repeatedly, if sporadically, and, theoretically, inter-specific comple- 

 mentary genetic effects for both morphological and biochemical 

 characters are anticipated. 



Such complementary effects may not always represent the 

 formation of a new biochemical component. For example, Bopp (1958) 

 found that in reciprocal hybrids of Streptocarpus wendlandii X S. 

 vandeleum flower color changed from blue-violet to red during de- 

 velopment although the change did not occur in the parents. Bopp 

 considered that the color change took place as the pigment, malvi- 

 din glucoside, was adsorbed onto a polysaccharide present in the hy- 

 brid. Since pH changes also affect anthocyanin coloration significantly, 

 pH differences in cell sap of hybrids could, through modifying the 

 visible flower color, suggest falsely the existence of a different pig- 

 ment. There are known cases of single dominant genes affecting the 

 pH of cell sap. 



Earlier, it was noted that Birdsong et al. had suggested the 

 possibility of complementary action in inter-specific crosses of cana- 

 vanineless genera of legumes to produce a hybrid which could syn- 

 thesize canavanine. In view of this it is interesting to see the full rec- 

 ognition of this type of phenomenon as well as other related ones as 

 early as 1919 in the writings of Reichert. 



A recent example of the appearance of a "new" substance in 

 hybrids is that reported in Collinsia (Garber, 1958). Specific sub- 

 stances were noted in the amphidiploid, C. concolor X C sparsiflora, 

 which could not be detected in either parental species. The author 

 pointed out that the different genetic background and modifier com- 

 plex in the amphidiploid compared with either of the parental species 

 permitted consideration of such a possibility. Rensch (1959) has dis- 

 cussed cases, involving hybrids of canaries and serins, goldfinches, 

 linnets, and greenfinches wherein colors appeared which were absent 

 from either parent. The colorations, however, were typical of a group 

 of related species and are interpreted by Rensch as atavisms. Although 

 some such phenomena are truly atavistic in that the parents have de- 

 veloped independently metabolic blocks at different points in a 

 sequence of steps, it is also possible that phylogenetically "new" sub- 



