Introduction. 



The present work is the first part of a monographical review of the genus 

 of ferns, Drgopteris, and it deals with the tropical American species having the 

 lamina from subentire to bipinnatifidly cut. This delimitation is, of course, artificial, 

 as the degree of cutting is of no greater value as systematic character, but it is chosen 

 from practical reasons. 



In earlier papers I have published a review of the species belonging to the 

 two subgenera Lastrea and Stigmatopteris '). Since the publication of these papers 

 I have received for determination or examination a large number of specimens of 

 species belonging to the two subgenera mentioned; several of these species were 

 previously unknown to me, and some others were found to be undescribed. I 

 have now, therefore, not a few additions to my earlier papers, and as my former 

 keys consequently now are uncomplete, I give in the present work new keys to 

 all known species of the two subgenera. In this work 280 species are dealt with; 

 about 100 of these were treated in detail in my earlier papers. 



The systematic grouping of the 280 species into 10 subgenera is entirely new 

 and it is, as to several points, very different from all older classifications. I dare 

 maintain, however, that my classification is the most natural that has been pro- 

 posed. It is based on a minute examination of not lesser than about 10,000 spe- 

 cimens belonging to about 500 species. Further, the study of that enormous ma- 

 terial has enabled me to unravel the real relationship of several critical forms and 

 to get an idea of the value as species of nearly all described "species". Not a few 

 of these were described from very imperfect specimens, and many of them were 

 described in such a way, that it is impossible from the descriptions alone to see, 

 what the form in question may be. If I should, therefore, make myself any hope 

 of clearing the synonymies of several species, it would be necessary to have for 

 examination type-specimens, or, at least authentical specimens of as far as pos- 

 sible all species described. By the kindness of the curators of several collections 

 I have succeeded in obtaining for study original specimens of all described species 

 some few excepted. These original specimens are to be found in various museums 

 and private collections, as follows : 



') 1. Revision of tlie American Species of Drgopteris of ttie group of D. opposita. Kgl. Danske 



Vid. Sclslv. Skr. VII, 4. 1907. A supplement hereto is 



2. Tlie American Ferns of tlie group of Drt/opteris opposita contained in the U. S. National Mu- 



seum. — Smithsonian Miscell. Collections (quarterly issue) 52: 3(j5 — 396. 1909. 



3. On Stigmatopteris, a new genus of ferns, with a review of its species. — Bot. Tidsskrift 29: 



291-304. 1909. 



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