134 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM, 
upon the student who is desirous of avoiding the publication of “new” 
species which will ultimately be relegated to synonymy. Relief will 
be found only in the manner mentioned—by the publication of 
synopses of the genera, with full synonymy. 
The much larger task of preparing an authoritative treatment of 
the Pteridophyta as a whole would at the present time be beset with 
difficulties of many sorts; in part those inherent in any full treatment 
of so large and difficult a group, in part others of the kind encoun- 
tered in many groups of lower cryptogams especially, in which there 
has been not only a lack of stability in the generic concept, but also 
no general agreement upon a method of selecting the generic type. 
Many of the genera present other and grave difficulties which need 
not here be enumerated. In the endeavor to order the species by 
genera according to their affinities it will often be necessary to disre- 
gard differences of venation and the presence, absence, or modifica- 
tion of special structures like the indusia, which, though formerly 
regarded as all-important, are now frequently found to be charac- 
- teristic of species only or of minor groups of species, and on the other 
hand to lay greater stress upon habital characters, these, though less 
tangible, serving to indicate far more accurately the probable lines of 
descent. The recognition of genera upon this basis will necessitate 
a wide comparison of specimens from regions now isolated, and will, 
unfortunately, afford fewer absolute superficial criteria to the maker 
of the generic keys. But this inconvenience carries small weight 
against the more natural arrangement which will certainly result, 
involving also a possible reduction in the number of genera. 
Inability or lack of opportunity to deal with the subject in a large 
way should not, in any case, serve to delay critical studies of the 
smaller groups, whose limits and principal characters can be clearly 
indicated. Studies of the latter sort may often be carried to com- 
pletion merely as phases of the larger work and will prove useful not 
only in themselves but also in their bearing upon the study of related 
groups of Pteridophyta. Considering the great amount of explora- 
tion carried on in the past it is only natural that so much attention 
should have been given purely to the description of new species; but 
this pioneer work having in great measure been accomplished, it may 
reasonably be expected that, with the benefit of modern systematic 
methods now generally employed, a more serious attempt will be 
made in the immediate future to definitely systematize the knowledge 
which we now have. 
ASPLENIUM TRICHOMANES AND ITS AMERICAN ALLIES. 
The writer’s especial interest in the group of Asplenium trichomanes 
dates from 1900, when he described Asplenium vespertinum from 
specimens collected in San Diego County, California. This well- 
