1914] 
BURT—THELEPHORACEZ OF NORTH AMERICA. I 189 
Europe. In the later pages names of the many botanists who 
have participated in this work by the contribution of speci- 
mens from their respective regions are given in connection 
with the specimens. I feel my obligation to each of these cor- 
respondents. 
Having become thoroughly familiar with the species of a 
family of fungi, one then faces the task of deciding under what 
genera they shall be grouped in order that others may more 
easily recognize them. Our studies in systematie botany and 
the aecumulations of plants in herbaria are primarily for the 
purpose of enabling those who wish to obtain information about 
any particular plant, however obscure, to determine its name 
accurately and so be in a position to get at the world’s literature 
and knowledge concerning that species; and also to enable 
botanists so to entitle and index their researches that the 
results will be more available to the world at large. Stability 
in the nomenclature of plants is therefore important, and revo- 
lutionary changes in generic conceptions should not be lightly 
and frequently made. Whenever one proposes new genera to 
supersede a well-established genus which has satisfactorily 
embraced the related species of the world, the burden of proof 
should be on the one who makes the change to demonstrate 
that the advantages from the innovation will more than com- 
pensate for the confusion which would result as well as for the 
loss of knowledge indexed under the superseded name. 
Many new genera of fungi have been proposed during recent 
years. These have frequently come from students with a 
limited knowledge of the species of the world. It is not sur- 
prising that a botanist working on the few species of a limited 
region should be led to the establishment of new genera on the 
basis of what seem to be sharp differences in his species or groups 
of species. When, however, his knowledge encompasses just 
as definitely the structure of the many species of some large 
portion of the world, his perspective changes, and he may now 
find that the species which he formerly regarded as generically 
distinct are so closely connected by intermediate species that 
the contemplated generic separation would be unnatural and a 
hindrance to botanical progress. It is fundamental that genera 
be so sharply defined that any accurate observer who will make 
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