RELATIONSHIPS OF THE METASPERMK^ FLORA 

 OF THE MINNESOTA VALLEY. 



Statement of the problems. As has been explained above, 



the evidence is conclusive that within times geologically 

 recent the valley of the Minnesota was encroached upon by a 

 continental glacier which doubtless destroyed all the metasper- 

 mic plants that hai previously established themselves within 

 the borders of the basin. To-day, as indicated in the list pre- 

 ceding, 1,174 species and varieties of metaspermic plants are 

 known to exist where previously there were none. This im- 

 pressive fact at once suggests a multitude of questions: How 

 did the present plant inhabitajits enter the Minnesota valley? 

 In what order did they enter? Which are the old settlers and 

 which the comparatively recent immigrants? What relation 

 does this modern plant- population bear to the more ancient one 

 which was overwhelmed by the glacial detritus piled 250 feet 

 thick over the old level of the country? How is it that some 

 kinds of plants are established more abundantly than others? 

 What has determined the various habitats of the different 

 species? Why are the individuals more numerous in some 

 species than in others? How long did the immigration take? 

 Along what routes did the incoming plants travel? What rela- 

 tion does the present metaspermic flora bear to those of ad- 

 jacent or more distant regions? Under what laws did the 

 repopulation of the valley progress? Does this immigration 

 still continue? What is the trend of evidence derived from the 

 present and from the past concerning the future movements of 

 plant-population in the valley of the Minnesota? These are 

 but illustrative of the problems that j^ress for solution when 

 the plants of any natural region are given systematic study. 

 To answer some of them is the purpose of these pages. 



The dynamic inter-relations of plants. It is necessary first 

 of all to call attention to a fact well known but not universally 

 apprehended. The plant-population of the globe is nowhere 

 in a static condition but is always undergoing llux and modifi- 

 cation. This shifting about of plants is recognised at once in 

 those cases where the agency of man has intervened. The 



