THE AMERICAN FERNS OF THE GROUP OF 



DRYOPTBRIS OPPOSITA CONTAINED IN 



THE U. S. NATIONAL MUSEUM 



By carl CHRISTENSEN, Copenhagen 



In a paper entitled "Revision of the American species of Dryop- 

 teris of the group of D. opposita,"^ I presented recently a review 

 of the American species of Dryopteris having free, simple veins and 

 the bipinnate lamina narrowed downwards. There were mentioned 

 in some detail 82 species, of which I had seen original specimens, 

 or, in some few cases, specimens which could be regarded as typical. 

 Those species of which I had seen no specimens were omitted, as I 

 found it impossible to form an exact idea of these from descriptions 

 alone. Mr. William R. Maxon, Assistant Curator in the U. S. 

 National Museum, offered, however, to send me typical material of 

 some of the species described by Jenman, and at the same time 

 suggested that I examine critically the whole collection of this group 

 in the U. S. National Herbarium, consisting largely of specimens 

 gathered in Central America and the West Indies in recent years 

 by several collectors. Inasmuch as many of the species included in 

 my "Revision" had been treated on the basis of a few specimens, or 

 even of a single specimen, I was anxious to study this material, but 

 for different reasons, partly on account of Mr. Maxon's absence in 

 the field, it did not reach me before my paper was in press. Upon 

 his request I then undertook to work out a separate paper, dealing 

 only with these specimens. Later on, Mr. Maxon sent me a large 

 number of specimens from the John Donnell Smith Herbarium, a 

 collection extraordinarily rich in Central American forms, presented 

 by Captain Smith to the Smithsonian Institution, and now a part 

 of the U. S. National Herbarium. I have thus had in these two lots 

 about 425 specimens, representing practically all the material of this 

 group in the National Herbarium, and in the following paper all 

 of these which I could determine with accuracy are enumerated by 

 locality, collector, and collector's number, with the exception only 

 of the identical numbers enumerated from other herbaria previously, 

 in my "Revision," these being omitted. 



' Kgl. Danske Vidensk. Selsk. Skrifter, 7 Raekke, Naturvidensk. og Math. 

 Afd. 4:247-336 1907. 



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