RELATIONSHIPS OF THE METASPERMIC 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 qnestions: How 
did the present plant inhabitants 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 press 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 flux and modifi- 
cation. This shifting about of plants is recognised at once in 
those cases where the agency of man has intervened. The 
