THE LICHENS OF MINNESOTA. 
By Bruce FINnk. 
INTRODUCTION. 
BASIS AND AIMS OF THE PRESENT WORK. 
The author began his investigation of the lichen flora of Minnesota 
during the summer of 1896 and finished the work in the field during 
the summer of 1902. The preparation of the descriptive catalogue 
offered herewith has been in progress since the latter date. During 
the course of the field work seven papers were published in the Min- 
nesota Botanical Studies, which are referred to in the present work 
as the “preliminary reports.’ Their full titles will be found in the 
bibliography at the close of the introduction. 
The data of distribution as given in the preliminary reports could 
not be incorporated in full in the catalogue, but in case of species 
known only from one, two, or three places the specific localities are 
cited. Local students are referred to the reports mentioned for more 
complete information. To these reports also, the reader must be 
referred for matter relating to geographical and ecological distribution 
until it becomes possible to publish the fuller data on these subjects 
already brought together. 
The aim in the catalogue has been to furnish descriptions and keys 
adapted to the use not only of specialists but also of younger students. 
To this end it has been the endeavor to avoid technicality so far as is 
consistent with clear presentation. 
One of the faults of existing descriptions of lichens is their failure 
to give measurements of the size of thalli. Such measurements can 
only be approximate, often including neither the smallest nor the larg- 
est specimens that actually occur; but even so it is believed that they 
will greatly aid in the determination of the species, and they are 
accordingly here supplied. Another error on the part of some authors, 
found especially in brief descriptions, consists in the arbitrary defini- 
tion of characters, leading the student to expect a constancy as to 
size, form, and color which does not exist in lichens. The attempt 
has been made in the present descriptions to state these variations as 
accurately as possible. While the catalogue treats of the lichens of 
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