INTROGRESSION IN IRIS 7 



tern of relationship between these two species, however, has 

 been greatly changed by human occupation. The delta re- 

 gion was settled mainly by the French, and for more than a 

 century little French farms have lined the rivers and bayous. 

 Property lines run straight back at right angles to the rivers. 

 Each family's holding is long and narrow, so that all through 

 the countryside the houses are close together. There has 

 been Uttle large-scale farming. The whole covering of nat- 

 ural vegetation has not been wiped clear as in much of the 

 cotton belt. The average family has cleared some lands for 

 fields, left others in pasture, and has kept a good deal of 

 w^oodland from which small amounts of cordwood and timber 

 are cut from time to time. ^ -~ ~ 



This outline of the two species and the environment in 

 w^hich they meet presents the two fundamentals of the Fulva- 

 HGC interaction on the Mississippi Delta: (1) The two 

 strikingly different but interfertile species, (2) largely kept 

 apart by dissimilar natural environments, progressively al- 

 tered in part by thousands of small farmers, no two of whom 

 treated their small holdings in exactly the same fashion but 

 few of whom obliterated entirely the natural vegetation. By 

 the early 1900's observant local naturalists were beginning 

 to comment on the results. From New Orleans southward, 

 in many a small community there would be cow pastures 

 brilliant with many-colored irises, white, yellow, wine-col- 

 ored, red, and blue, many of them so attractive that they 

 were moved into nearby gardens. Eventually, Dr. John K. 

 Small, of the New York Botanical Garden, called them to 

 the attention of botanists and iris gardeners, illustrating 

 them in full color and describing them as species new to sci- 

 ence (1927; Small and Alexander, 1931). From the first, 

 both among botanists and iris gardeners, there w^ere those 

 w^ho suggested that the w^hole complex was of hybrid origin, 

 and eventually Viosca's careful ecological survey of the prob- 

 lem convinced all but a few. Foster came to the same con- 

 clusions independently on taxonomic and cytological evi- 

 dence, and Riley's investigations confirmed and extended 



