4 INTROGRESSIVE HYBRIDIZATION 



those of Fulva droop as if half wilted, one above the other, 

 from successive internodes. Examination of the flowers re- 

 veals that Fulva has a red pigment over a yellow ground 

 color; HGC, a blue pigment on a white ground. 



When HGC and Fulva are hybridized, the most conspic- 

 uous results are due to the recombinations of these two 

 ground colors (and their various intermediates) with the 

 two sap colors (and their intermediates) . Although such hy- 

 brids have never been subjected to detailed genetic analysis, 

 the cross has been repeatedly made for garden purposes by 

 various hybridizers. The Bulletin of the American Iris So- 

 ciety from 1930 to 1945 contains frequent reference to these 

 and similar hybrids, occasionally with full descriptions of 

 some of the segregates. Reed, however, has given a fairly 

 detailed report (1931) on experimental hybrids between Iris 

 hrevicaulis and Fulva. Since /. brevicaulis is closely related 

 to HGC (differing from it mainly in its low zigzag stem), 

 Reed's results can be applied directly to the analysis of nat- 

 ural hybridization between Fulva and HGC, the more readily 

 since they agree with those obtained by practical breeders. 



As Reed's experimental results indicate (see in particular 

 his colored Plate 1), bizarre recombinations are formed in 

 the second generation and in backcrosses when the pigment 

 genes segregate more or less independently of the ground- 

 color genes. The differences between red pigment vs. blue 

 and white ground color vs. yellow each seem to be multi- 

 factorial, so that for the first we get a w^hole series from blue 

 to purple to red, and for the second a similar transition from 

 white to ivory to light yellow to bright yellow. In the second 

 generation we may get a blue pigment more or less like that 

 of HGC on top of a yellow ground color; the result will be a 

 flower with soft tones of ashy gray. At the other extreme we 

 may get the red of Fulva over the white ground color of HGC, 

 resulting in a delicate rose pink. HGC, furthermore, varies 

 from plant to plant in the strength of its blue pigment, some 

 plants being practically albinos. If this extreme is carried 



