The following additional introduced weeds now frequently appear in the 

 prairie region, more especially where the surface has been disturbed, as 

 along roadsides; and they are not infrequent on the drier sandy beaches. 

 The weeds restricted to gardens and farms are not here included. 



Several native species, such as SoUdago rigida, Iva xant Mi folia, etc., have 

 also become troublesome weeds. 



Prairie 



Asparagus officinalis L, 



Anthemis cotula L. 



Brassica nigra (L.) Koch. 



Brassica arvensis (L.) Ktze. 



Bromus ciliatus L, 



Bromus secalinus L. 



Capsella bursa-pastoris (L.) Medic. 



Camelina sativa (L.) Crantz. 



Chenopodium album L. 



Chenopodium botrys L. 



Chenopodium murale L. 



Cirsium arvense (L.) Scop. 



Echinoehloa crusgalli (L.) Beauv. 



Lactuca scariola L. 



Lactuca scariola var. integrata Grren. 



& Godr. 

 Linaria vulgaris Hill. 

 Linum usitatissimum L. 

 Melilotus alba Desv. 



weeds 



Melilotus officinalis (L.) Lam. 

 Martynia louisiana Mill. 

 Polygonum erectum E. 

 Polygonum persicaria L. 

 Polygonum aviculare L. 

 Polygonum aviculare var. littorale 



(Link.) Koch. 

 Pastinaca sativa L, 

 Phleum pratense L. 

 Sisymbrium officinale (L.) Scop. 

 Sisymbrium altissimum L. 

 Setaria glauca (L.) Beauv. 

 Setaria viridis (L.) Beauv, 

 Setaria vertieillata (L.) Beauv. 

 Silene noctiflora L. 

 Taraxacum erythrospermum Andrz. 

 Taraxacum officinale Weber. 

 Trifolium pratense L. 

 Tanacetum vulgare L. 



The Border Areas 



The numerous detached groves and the forest fringes border- 

 ing the lakes and streams which everywhere break the monotony 

 of the prairie, present an exceptional opportunity for the study 

 of the belts that mark the transition from forest to prairie. 



The deep woods, such as those near Elm Crest, in the big loop 

 of the Little Sioux, at Arnold's Park, on the east shores of East 

 Okoboji lake, at the Inn, at Center lake, and in the Hottes lake 

 region, are truly mesophytic; the prairies which occupy the 

 greater part of the land area are just as truly xerophytic; and 

 between them, and forming a transition from one to the other, is 

 a belt in which, on account of the blending of physical condi- 

 tions, there is a mixture of the two floras. This belt is variable 

 in width. Where the topography changes very abruptly this 

 transition belt is narrow, as at Twin Mounds, and at other points; 

 but where the change is gradual as on the west side of Elm Crest 

 forest, and at other points, the belt is broader and less definite. 



38 



