64 H. A. GLEASON VEGETATIONAL HISTORY OF MIDDLE WEST 



selections from a western or southwestern flora, not found elsewhere 

 in the state, such as Geoprumnon mexicanum and Megapterium mis- 

 souriense, but it must be noted that these are much fewer than the 

 southern element, and also much fewer than species of the same western 

 element in western Illinois. 



Some of the most noteworthy mesophytic trees are nearly or quite 

 absent from the same region, such as Fagus grandifolia, Cynoxylon 

 floridum, Liriodendron Tulipifera, and Magnolia acuminata, although 

 some of them extend much farther north in almost the same longitude 

 and all of them, crossing Illinois at its southern end, extend westward 

 as far as the Ozark mountains. 



The Ozarkian flora at the present time barely reaches Illinois. A 

 few species occur on the rocky hills of the Ozark uplift, such as Soli- 

 dago Drummondii and Solidago Radula; Trillium viride occurs north- 

 east of St. Louis, but in general the flora is poorly developed east of 

 the Mississippi, although strongly marked only a few miles west of 

 it. Even such a mobile species as Yemonia Baldwini, common in 

 the vicinity of St. Louis, is scarcely known on the Illinois side. There 

 is no evidence as to the date when this flora appeared in Illinois, and 

 no reason to believe that it ever extended farther east or took a more 

 prominent part in the plant life of the region. 



In western Illinois, beyond the Wisconsin drift, north of the low 

 range of hills which divided the Illinoian till into two portions (see 

 Leverett's map 30 ), and mostly west of the Illinois river, there are a 

 number of intensely xerophytic western species, such as Bouteloua 

 hirsuta, Bouteloua oligostachya, Schedonnardus paniculatus, Opuntia 

 fmgilisj Mentzelia oligospermia, Lesquerella argentea, and Cristatella 

 Jamesii. They are not merely xerophytes, but are limited to peculiar 

 and extreme habitats. They have not been reported east of the ter- 

 minal moraine, even from similar habitats on the sand dunes of Lake 

 Michigan. Schedonnardus paniculatus, with a single station in Illi- 

 nois, and Cristatella Jamesii, with two known stations in Illinois and 

 one in eastern Iowa, present excellent examples of discontinuous dis- 

 tribution, since their nearest, stations to the west are 300 to 500 miles 

 away. Such distances are much beyond the normal range of their 

 migration and these eastern stations must be regarded as the relics 

 of a former nearly continuous range across eastern Nebraska and 

 Iowa. This in turn implies a climate some time in the past much 

 drier than at present. There are also in this part of the state a few 

 xerophytic southern plants, such as Quercus marylandica and Croton- 

 opsis elliptica, but their successional relations indicate a later arrival 

 in the region. 



