189 



Helianthus strumosus L. 

 Coreopsis palmata Nutt. 

 Achillea Millefolium L. 

 Arte ml. si a caudata Michx. 

 Mesadenia atrvplicifolia (L. ) Raf. 



Phytogeographical Relationships of the Flora. 



A casual inspection of the preceding list of* species, 188 in 

 number, will show the presence in the sand vegetation of nu- 

 merous plants of western distribution. Some of these occur in 

 Illinois only in the sand regions, so far as known, and others 

 are of limited range in various parts of the state. In order to 

 stud} 7 more carefully this western relationship the flora has been 

 divided into two groups, including, first, those species living 

 in the prairie formation, and, second, those found only in the 

 black-jack forest. It is believed that this separation will dis- 

 tinguish the older and more primitive flora, inhabiting the old- 

 er plant-formation, from the younger and more recent flora, 

 occupying the younger formation, and doubtless derived to a 

 large extent from the vegetation of the surrounding woodlands 

 and prairies. It has been mentioned that nearly all the species 

 of the sand prairie grow also in the black-jack, and that their 

 presence there is probably due frequently to persistence through 

 the changed ecological conditions. It is also evident that mauy 

 of the more recent species have penetrated into the bunch- 

 grass prairies and are now mingled with the endemic element 

 there. A third and minor group of five species has not been 

 included in this division, since its members occur only on the 

 front of dunes which have invaded natural groves on the Miami 

 loam, and are undoubtedly derived directly from the vegetation 

 of that soil. These are Clematis Simsii, Euphorbia heterophylla , 

 Sicyos angulatus, Solatium nigrum, and Urticastrum divaricatum. 



The vegetation of Illinois, with the possible exception of 

 the extreme southern part, has been developed since the close 

 of the glacial period. Postglacial migration into the state has 



light green, short- petioled leaves which are nearly erect in a basal cluster, while in 

 Eelianth us illin oensis they are darker green, more or less spreading and scattered on 

 the stem.— Ohio Naturalist, Vol. V. (1904), p. 214. 



