IOWA ACADEMY OF SCIENCES. 
27 
must confine our attention to his work upon the lichens. 
In this field his activity continued to the time of his death, 
and collections were determined by him, not only from all 
portions of the Western Hemisphere, but also from the 
Eastern Hemisphere and from the islands of the sea. How 
much labor and self-sacrifice is involved in such a task will 
be appreciated by those who have attempted a similar one 
even though upon a smaller' scale, in some field of 
taxonomic study. This work brought Tuckerman a knowl- 
edge of lichen species possessed by very few even of the 
European lichenists, and culminated in his two great con- 
tributions to North American lichenology, the “Genera 
Licherium” in 1872 and the “Synopsis”, the first volume of 
which appeared in 1882 and the second in 1888. Of these 
two great works, we may venture a few words. The author 
was conservative in his view of genera and species and 
seemed to have followed Fries very largely in his classifi- 
cation of the American lichens. His views as to system of 
classification and as to generic and specific limitations can 
scarcely be expected to endure in all particulars. Yet his 
conservatism was by no means a fault, and has no doubt 
greatly aided in the study of our lichens. Plainly it was 
not possible for one man to do so much of the great con- 
structive work in American lichenology and at the same 
time be given to hair-splitting discriminations as to generic 
and specific limitations. Tuckerman was to lichenology 
what Gray was to the study of our seed-plants, and we can 
not pay too high a tribute to the labors of these two men. 
Tuckerman’s contributions to North American lichen- 
ology consist of 48 titles, but the number by no means 
measures the amount of work involved, for he aided others 
continually and much of his labor received no public rec- 
ognition. Conservative as he was, his new species and 
varieties number some 365, about 250 of these being found 
on the North American continent, some 60 of the re- 
mainder on the island of Cuba, and nearly an equal number 
from various parts of the world and not to be regarded as 
North American. Including the Cuban lichens named by 
Tuckerman, the number of species and varieties described 
