COASTAL FLORA OF THE GREAT LAKES 83 



ocean; it is covered with a dry short grass," while the higher knobs, 

 now concealed by the forest, rose from the midst of the prairie and 

 were visible thirty miles. A little later we find farmers near St. Louis 

 complaining that the rapid growth of trees had seriously restricted 

 the natural pastures. 55 The Mississippi and Illinois rivers at that 

 time ,had long strips of prairie in their floodplains, which are now 

 completely forested, except where under cultivation. The dune region 

 at the head of Lake Michigan, which is now well forested with oak, was 

 then "treeless, except for a few stunted pines." Forested areas in 

 Indiana were developed, within the memory of men now living, from 

 barrens over which a man on horseback had been visible for six miles 

 (personal communication from Mr. C. C. Deam). The rapid develop- 

 ment of forests on the sand dunes of the Illinois River has been noted 

 elsewhere. 56 



This great forest advance of the nineteenth century proceeded by 

 ordinary successional processes and affected hundreds of square miles. 

 It ceased only with the complete occupation of the prairie land for agri- 

 culture. Since then, that is, during the last 50 years, forest succession 

 has been limited to sand dunes, roadsides, and railway lines. Every 

 roadside in the Middle West is a potential forest and would speedily 

 become so in fact except for constant effort in keeping the thickets and 

 young trees cut down. 



Coastal Flora of the Great Lakes. — The extensive sandy beaches 

 of the Great Lakes are characterized by a number of species which do 

 not occur or are rare elsewhere in the Middle West. The geographical 

 origin of many of these species is indicated by their distribution else- 

 where or by the range of their nearest relatives. Thus 7ns lacustris 

 is closely related to Iris cristata,; Solidago Houglitonii to S. Biddellii 

 and S. ohioensis, and both were probably derived by immigration from 

 the south, accompanied by specific evolution. Cirsium Pitcheri may 

 have a similar origin. Corispermum hyssopifolium, for similar reasons, 

 appears to have entered the region from the west. Besides these, there 

 is a considerable group of species which are distributed along the 

 northern shores of the Atlantic, sometimes in Europe as well as Amer- 

 ica, are not ordinarily found inland, but appear along the shore of 

 the Great Lakes. This group includes Ammophila arenaria, Elymus 

 arenarius, J uncus ba^ticus, Halerpestes Cymbalaria, Cakile edentula, 

 Prunus pumila, Lathyrus maritimus, Chamaesyce polygonifolia, Hud- 



65 Peck, J. M. A gazetteer of Illinois. Philadelphia, 1837. 



ee Gleason, H. A. The vegetation of the inland sand deposits of Illinois. Bull. 

 Illinois State Lab. Nat. Hist. 9: 21-174. 1910. 



