380 METASPERMAE OF THE MINNESOTA VALLEY. 
Many other titles might be added to this list, but those cited 
will put any student into contact with the general literature. 
Most of these works do not devote themselves solely to the 
subject in the caption, but all serve to illuminate it more or 
less. Works of purely historical value, such as those of Brong- 
niart, Amici, R. Brown, Schacht, Radikofer, Karsten, et al., 
have not been cited, for it is not my intention to give in this 
place a complete bibliography of the subject, but only to cite 
enough works to enable readers to come in contact with the 
original sources. ; 
Statistical discussions. The chapters following the list 
take up in order certain statistical investigations based 
upon facts collated in the list itself, No complete sta- 
tistical investigation can be made of even this limited area, the 
Minnesota valley, in the present advancement of our know- 
ledge. There are, however, data enough at hand to determine 
certain characters of our flora. It is believed that the points 
of view from which the statistics are gathered, and the prin- 
ciples underlying their tabulation, enable one to present some 
facts less barren and meaningless than those commonly put 
forward in such chapters. By keeping steadily in view the 
facts discussed above, in relation to the difference between 
natural and artificial districts, and with a constant compre- 
hension of the indubitable fact that one can not consider even 
a natural district apart from surrounding districts, the writer 
has attempted to penetrate to some of the inner facts which 
become accessible in such a labor as has been undertaken. It 
is believed that the characters of the Minnesota valley flora thus 
determined throw some unexpected light upon the general con- 
ditions of plant distribution in this central region of the conti- 
nent. And while some of the conclusions may seem simple to 
trained geographical botanists, it must be recalled by them 
that this work is not primarily addressed to any coterie of 
savants in some special line of science, but to the general pub- 
lic of Minnesota, under whose ultimate sanction, and by whose 
open-minded comprehension of the value of scientific knowledge 
in all departments of human activity, this Geological and Na- 
tural History Survey has been established, developed and 
directed. 
