BIOCHEMICAL STUDIES OF HYBRIDS 317 



exceptional (Fig. 15-2, a-h). In Texas, for example, complex hybridiza- 

 tion involving four species occurs. One population including all four 

 species and all six of the possible different hybrid types has been 

 located, and in various other locations hybrids between any two of the 

 four species occur. Of the Baptisia species illustrated in Fig. 15-2 the 

 following natural hybrid combinations have been definitely established 

 through combined chromatographic and morphological analyses: 

 a X b, a X c, a X eL, b X c, b X eL, c X eL, e X g, e X f, f X g, f X h, 



and g X h. 



Alston and Turner (1962) executed a combined chromato- 

 gi-aphic and morphological analysis of a comphcated population, near 

 Beaumont, Texas, composed of Baptisia leucophaea, B. sphaerocarpa, 

 B. leucantha, and several different types of "hybrids." Hybrids of B. 

 sphaerocarpa x B. leucantha were previously reported from the 

 same area (Larisey, 1940), but no hybrids of B. leucophaea X B. 

 leucantha were known. 



In the population described above the presence of three 

 species comphcated the situation sufficiently to make the population 

 difficult to study effectively by even a painstaking morphological 

 examination. Putative hybrids of B. leucophaea x B. leucantha were 

 rare and highly conjectural, and the question was raised as to whether 

 there was any gene exchange between the two species, perhaps with B. 

 sphaerocarpa acting as a bridge for such gene exchange, since its flower- 

 ing period is intermediate. Related questions of preferential hybridiza- 

 tion, degree of fertihty of particular Fi types, backcrossing patterns, 

 and so on, are all relevant to an understanding of the evolutionary 

 past and future of the population, but the question raised above can- 

 not be answered precisely in this instance through morphology (and 

 not at all by chromosomal studies since n = 9 in all species concerned, 

 and meiosis in the putative hybrids appears to be normal). 



Alston and Turner selected about fifty plants, mostly hybrid 

 types taken from a population which consisted of the three parental 

 species about equally represented, and about 5 per cent hybrids or 

 their derivatives. A morphological tri-hybrid index utilizing twenty 

 characters was designed, based on examination of individuals from 

 pure populations of each of the three species. As illustrated in Table 

 15-2 each plant keys out to a percentage representation of each of the 

 three species. For example, a hybrid of A x B backcrossed to C would 

 key out, presumably, to about 25 per cent A: 25 per cent B: 50 per 

 cent C. It is obvious from the table that complex hybridization in- 

 volving all three species in interaction was inferred from application 

 of the morphological criteria. 



Chromatographic evidence was acquired as follows. After a 



