192 



the 9 western species, three, starred in the following list, are 

 practically confined to the sand region. 



Atherpogon curtipendulus Polytcenia Nuttallii 



*Talinum rugospermum Nabalus asper 



*Erysimum arkansanum Ratibida pinnata 



Ribes missouriense * Artemisia <-<tu<h<t<i 

 Petalostemon candidus 



A comparison of the vegetation of the Illinois River valley 

 sand region with that of the dunes along Lake Michigan is of 

 interest on account of the short distance between the two re- 

 gions. Excepting the temperature, the difference in the eco- 

 logical conditions is scarcely sufficient to cause a wide varia- 

 tion in the floras. The dunes of Lake Michigan, however, are 

 essentially a beach formation, and the vegetation as described 

 by Cowles ( '99 ) shows but slight relationships with the western 

 prairies. On the beach proper only eight species occur which 

 are common to the two dune areas, and three of these, Artemi- 

 sia caudata, Calamovllfa longifolia, and Lithospermum Gmelini, 

 are western in their range. The flora of the shifting dunes 

 shows scarcely more similarity. In the established dunes the 

 resemblances are stronger. Six species of the basswood dunes 

 and nearly all those of the oak dunes are found also in the 

 inland region, and (Jovvles's list includes Quercus velutina, Wins 

 aromcttica, ( ' r<i<-<-n virginiana, ( 'yperus Schweinitzii, Opuntia humi- 

 fusa, Oenothera rhombipetala, Monarda punctata, and other spe- 

 cies abundant on the sand along the Illinois River. In both 

 localities these plants belong principally to the derived element; 

 and as the adjacent forests are of the same type in both regions 

 it is to be expected that the same species would be able to 

 adapt themselves to the sand. It is in the endemic element 

 that the greatest contrast lies. The dunes of Lake Michigan 

 have no Cristatella, Eragrostis trichodes, Bouteloua, Ambrosia 

 psilostachya, Froelichia, Euphorbia Geyeri, Callirrhoe, or Chry- 

 sopsis, all characteristic of the inland region; while the latter 

 lacks Cakile americana, Corispermum hyssopifolium^ Euphorbia 

 polygonifolia, Lathyrus maritimus, Ammophila arenaria, and 



