2 INTROGRESSn^ HYBRIDIZATION 



interpretation presented below is as valid an explanation as 

 one may ordinarily hope to find for complex natural phe- 

 nomena. It has been studied taxonomically by Foster (1937), 

 cytologically by Randolph (1934), genetically by Riley (1938, 

 1939a, 19396), and ecologically by Viosca (1935). The evi- 

 dence from Reed's experimental genetical analysis (1931) 

 of a closely related cross has been confirmed by numerous 

 horticulturists who have repeated the hybridization of the 

 species from the Delta for garden purposes. Anderson has 

 investigated the problem in both the field and the breeding 

 plot. Riley, Foster, Viosca, and Anderson are in virtual 

 agreement concerning the following account, though they 

 have worked at different institutions and employed differing 

 techniques. 



The two species concerned, Iris fulva and 7m hexagona 

 var. giganti'Caerulea,'^ are strikingly different. In appraising 

 the results of any hybridization, the problem is usually 

 simplified if there are such conspicuous, manifold, clear-cut 

 differences between the hj'bridizing entities as those which 

 distinguish Fulva from HGC. The outstanding differences 

 between these two species are presented in tabular form in 

 Table 1, and a few details are illustrated in Plate 1. For 

 those who have never seen these two irises, it is difficult to 

 overemphasize how strikingly they differ. Though they cross 

 easily and the hybrids have a considerable measure of 

 fertility, they do not seem to be closely related. HGC is 

 certainly more closely allied to Iris hexagona of the eastern 

 seaboard and to Iris hrevicaulis of the northern Mississippi 

 Valley than to Fulva, from which it differs conspicuously in 

 color, color pattern, size, habit, and ecological preferences. 

 Fulva has smallish flowers of the color of old red brick; 

 those of HGC are large with a brilliant pattern of dark blue, 

 light blue, and white, set off by a signal patch of bright yel- 

 low. Its relatively few flowers are held crisply erect, whereas 



* Since these names are cumbersome and no generally accepted com- 

 mon names are available, they will be shortened to 'Tulva" and "HGC" 

 in the following discussion. 



