INTRODUCTION. 3 
the early colonial days. These fall into three classes,’ political, 
geometrical and natural, with reference to the areas of which 
they treat. To political areas 590 titles are referred, upon 
examination of the whole list; to geometrical, 142 titles and to 
natural areas only 59 titles. The more popular methods do 
not, however, afford so good a field for scientific grouping of 
facts nor do they permit, without a most tedious and pains- 
taking tabulation and criticism, any particularly useful gener- 
alisations which might be based upon the facts when properly 
arranged. For there is, apparently no very close connection 
between those conditions which govern the boundary-lines of a 
political district and the distribution of plants within those 
boundaries. The boundaries of Minnesota are certainly not 
accidental, but have been fixed through the interaction of a 
complicated series of causes and events, many of them too 
subtile and elusive to permit of classification. Just as certainly 
the kinds of plants in Minnesota, their relative abundance or 
scarcity. their positions in forest, lake or meadow, their general 
or local distribution are determined by a similarly complicated 
and interlocking series of causes and events, many of which will 
also, it is probable, be found to be too difficult and hidden for 
successful analysis. In the effort to unravel somewhat of the 
problems suggested, it is necessary that attention should not 
be diverted to something quite extraneous or superficial and, 
therefore, just as we should not attempt to interpret the laws 
governing the action of a constitutional convention, by periodic 
examinations of a mercury-barometer, no more should we 
attempt to investigate the laws of plant-distribution in Minne- 
sota by adhering to the artificial lines which separate it from 
adjacent commonwealths or divide it into counties, towns or 
sections. 
The Minnesota valley as a natural area. When one endeav- 
ors to divide the state of Minnesota into natural regions for the 
purpose of prosecuting a botanical survey, the river-valleys at 
once present themselves as suitable areas. As is well-known 
Minnesota lies squarely at the crest of the North American 
continent. Its altitude above the sea is less than that of other 
places which might be named; but notwithstanding this it is 
within its borders that the three great river systems of the 
continent find their head-waters. Flowing northward is the 
Red river, the principal tributary to Hudson Bay; flowing 
eastward is the St. Lawrence, the principal tributary to the 
Atlantic, and flowing southward is the Mississippi, the great 
