98 



INTROGRESSIVE HYBRIDIZATION 



polate character by character from HGC to the hybrid to 

 the other putative species. It would have had to have been 

 an iris with very narrow, red petals, strongly exserted sta- 

 mens, a yellow tube, no crest, and small stylar appendages. 

 Such a species having been predicted, if we can find exactly 

 such a one in this same area, its very existence will constitute 



R 



RV 



to 

 a> 



c: 

 ■o 



(U 



on 



BV 



VB 



Fulva 

 plotted from Riley's data 



7 8 



Petal size - 



10 



n 



Fig. 23. Within lower-right-hand box are the symbols used in all the 

 pictoriahzed scatter diagrams of Figs. 20 to 23. Upper left: 23 plants of 

 Iris fulva, plotted from Riley's data. Note the exact correspondence 



with the predictions of Fig. 21. 



strong evidence for the suspected hybridization. Our hypo- 

 thetical introgressant, of course, proved to be Fulva. The 

 diagram of its population plotted from Riley's data (Fig. 

 23) agrees exactly with our extrapolations. A series of such 

 predictions successfully made forms almost indisputable 

 evidence for the validity of the method of extrapolated cor- 

 relates and confirms the hypothesis of introgression. 



The ease of extrapolation will vary with the number of 

 easily measured differences separating the species under ob- 



