17 



plants in this area are rare or have been exterminated by cultivation. The 

 area, however, contains some extinct lake areas and springy places which 

 accounts for the many lake area plants in it. 



Illinoia/n Drift Area 



This area lies south of the Tipton Till Plain, north of the glacial bound- 

 ary, and east of the Lower Wabash Valley area. It is divided into an 

 eastern and a western lobe. The topography varies from level areas to 

 deeply cut ravines. The flora of the two parts has several species not in 

 common. The Appalachian flora has entered in a small degree the eastern 

 part while the southwestern flora has entered the western part. In Clark, 

 Jefferson, Jennings, and Ripley Counties are level, poorly drained areas 

 with an acid soil that are locally known as "flats." These may be divided 

 into high and low "flats." The principal tree species of the "high flats" 

 are beech, sweet gum, tulip, and black gum. Often a depression a foot in 

 depth will result in a "low flat" wooded with swamp chestnut oak, swamp 

 white oak, pin oak, southern red oak, and red maple. Sometimes the low- 

 est places will consist of a pure stand of pin oak. All of the species named 

 will not be found in the same "flat" but usually two or three of them will 

 be the dominant species. The western part has some low areas but these 

 are usually wooded with pin oak and shingle oak, associated with hickory. 

 In the western lobe are sand dunes that have a peculiar flora. Such a sand 

 area forms the terrace of the Wabash River from north of Terre Haute 

 southward to Posey County. In Knox County in places its width increases 

 to more than a mile. On this sandy terrace are found plants not found 

 elsewhere in Indiana which have their mass distribution in the Lower 

 Mississippi Valley. East of the North fork of White River in the north- 

 western part of Daviess County are many low dunes upon which, and in 

 the low places between them, occur several Coastal Plain plants. Among 

 those that are restricted to this area are Gymnopogon ambiguus and Gaura 

 filipes. 



Prairie Area 



This area is small and the boundary very irregular. The many small 

 prairies and "oak openings" that occur throughout the lake and Tipton Till 

 Plain areas are not included in this area. Our distribution maps may show 

 a prairie species fairly well distributed over the whole of northern Indiana 

 which does not mean that the whole area is an uninterrupted prairie. 

 There was probably not a county in the lake and Tipton Till Plain areas 

 that did not have one or more areas of an acre or more in prairie. The 

 tension zone between the prairie and the forest is one of the most interest- 

 ing studies in plant geography. The whole area is now devoted to agri- 

 culture and since no one made a record of its plant life before cultivation, 

 our knowledge of it must now be gleaned from the few plants that have 

 survived along railroads and roadsides and in cemeteries and waste places. 

 Every year our roadsides are mowed and the rights of way of railroads 

 are mowed and usually burned, so that the extermination of our native 

 prairie plants will soon be complete. 



