324 BIOCHEMICAL SYSTEMATICS 



suggests that simple hybridization predominates in the population. 

 The chromatographic data thus leads to conclusions quite different 

 than expected from the previously analyzed exomorphic features. The 

 most important difference was the fact that the biochemical data did 

 not suggest any mixing of B. leucophaea and B. leucantha genomes. 



It should be noted that the species under consideration appear 

 to be mostly cross-fertilized, but if perchance the Fi hybrids are self- 

 fertile, the major concentration of points on the plot would be more 

 diffuse, and perhaps no secondary concentrations would be noted. It 

 is obvious that the relative sizes of the various concentrations of points 

 provide a quantitative index of hybridization patterns. At the risk of 

 over-extending the hypothetical possibilities of a relatively untested 

 system, it is nevertheless theoretically vahd that such a system could 

 provide insight into the mode of inheritance of the compounds under 

 consideration, and also, if individuals around the periphery of an 

 area of hybridization were examined, biochemical evidence of 

 introgression. 



Generalizations which can be stated with assurance concern- 

 ing Baptisia hybrids so far examined are the following: 



(1) There is a tendency for some reduction in the amounts of 

 many compounds present in the hybrids so that often 

 some minor components tend to drop out. 



(2) Although the hybrid tends to inherit the parental com- 

 pounds additively, there are often some major spots 

 missing. 



(3) Some substances are present which, on the basis of the 

 facts available, must be regarded as organ-specific in the 

 hybrid only. 



Substances of group 3, above, are not sporadic and capricious among 

 the hybrids but are regularly observed. 



The case of hybridization between B. leucophaea and B. leu- 

 cantha is quite interesting. As noted above, no evidence of gene 

 exchange between the two species in the tri-hybrid population was 

 obtained, at least on the basis of the biochemical criteria. Mixed 

 populations of B. leucophaea and B. leucantha have been examined 

 without detection of any obvious Fi plants, although introgression is 

 suggested by the morphology of some of the individual plants. How- 

 ever, on the basis of biochemical evidence and the absence of any 

 really intermediate morphological type, it is doubtful that the sug- 

 gested introgression is real. Several unequivocal hybrids, probably Fi 

 between B. leucophaea and B. leucantha have now been discovered and 

 vahdated chromatographically (Fig. 15-3), but it is evident that exten- 

 sive hybridization between B. leucophaea and B. leucantha does not 



