STUDIES OF TROPICAL AMERICAN FERNS—NO. 4. 
By Wiiuam R. Maxon. 
INTRODUCTION. 
The present paper, like the preceding ones of this series,’ includes 
brief discussions of several genera or smaller groups of species which 
have been the subject of great confusion, but which it is now possible 
to treat with some degree of assurance. Similar conditions prevail- 
ing in very many, if not in most, genera of tropical American ferns | 
lead to the conclusion that effort in this field should at present be 
directed more to the systematizing of work already done than to the 
description of new forms. The preservation of most of the older type 
specimens in European herbaria affords to European students a dis- 
tinct advantage which is, perhaps, not fully realized. At any rate 
very little monographic or even synoptical work upon the part of 
European fern students has recently found its way into print, a note- 
worthy exception being the conscientious and elaborate work of 
Christensen in the difficult genus Dryopteris. 
Indeed, the method of treatment adopted by Christensen, involving 
a critical review of actual type specimens, supplemented by a study 
of the vast aggregate of additional material which it is now possible 
to bring together from the larger herbaria, may well serve as a model. 
Studies like this are urgently required in Adiantum, Pteris, Blechnum, 
certain groups of Asplenium and Athyrium, Hypolepis, Denn- 
stedtia, Lindsaya, and Polystichum—to mention a few of the more 
conspicuous examples. Many of the species of these genera are 
without doubt correctly understood by fern students generally; but 
it is equally true that a large proportion of the less well known species 
have been repeatedly published as new, partly from ignorance or dis- 
regard of results obtained by others, and partly from failure to inter- 
pret successfully the faulty diagnoses of others, especially the early 
writers. The necessity of studying and restudying the constantly 
increasing number of scattered desvriptions imposes a heavy burden 
1 Contr. U.S. Nat. Herb. 10: 473-508. pls. 55, 56. March 30,1908. Ibid. 13: 1-43. 
pls. 1-9. June 30, 1909. Ibid. 16: 25-62. pls. 18-84. June 19, 1912. 
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