INTROGRESSION IN IRIS 11 



signed values to the seven morphological characters re- 

 corded in Table 1 and set the scores in such a way that re- 

 semblance to HGC was always high in value and resemblance 

 to Fulva low in value. This procedure produced an index 

 running from to 17. The calculated index values for the 

 ten representative plants are shown in Table 1. In his Fig. 3 

 the combined scores for all the plants of each colony were 

 shown graphically. The plants of Fulva have uniformly low 

 values; those of HGC are uniformly high. Colony H-2 is 

 much like HGC but has a slight trend in the direction of 

 Fulva. Colony H-1, on the other hand, is in general a mix- 

 ture of everything from intermediates to plants closely re- 

 sembling HGC. 



The presentation of Table 1 and Plate 1 completes the de- 

 scription of hybridization between Fulva and HGC. In 

 succeeding chapters we shall discuss the ways in which the 

 results of interspecific hybridization are controlled by the 

 d^Tiamics of the environment, by the dynamics of the germ- 

 plasm, and by the interactions of these forces in. actual 

 populations. We shall continue to refer to this example. It 

 has been well documented by Viosca and by Riley (in ad- 

 dition to the papers cited above, there are others on pollen 

 fertility and on developmental rates) . It serves the better as 

 illustrative material because it demonstrates features that 

 we shall notice again and again when other examples of hy- 

 bridization are described in detail: (1) the relation between 

 the effects of hybridization and man's disturbance of the 

 habitat, (2) the differences between various hybrid popula- 

 tions made between the same species and in the same region, 

 (3) the predominance of mongrels of partially hybrid an- 

 cestry which closely resemble one of the participating species. 



