260 Broadhurst: Struthiopteris in North America 



Other possible divisions of this large genus, based upon cha- 

 racters offered by the sterile fronds, the indusium, and the spo- 

 rangia and spores, have been considered by the writer and found 

 unsatisfactory for the following reasons: (i) The variations in the 

 sterile leaves in proportion, cutting, and texture depend greatly 

 upon the age of the leaf and of the plant; (2) in the fertile leaves 

 the indusium remains entire in the pinnatifid species, and though 

 it usually becomes lacerate or fimbriate in the pinnate species, these 

 show all degrees of laceration; (3) a careful microscopic study 

 of the spores and sporangia, which Fee apparently considered 

 important, reveals no constant differences in the North American 

 species. 



The greatest variation is undoubtedly in the habit, for the 

 North American species include: (1) Tree-climbing forms with 

 pendent leaves, (2) terrestrial, cespitose forms, (3) terrestrial, 

 inclined or erect forms with stems 5-45 cm. long, and (4) sub- 

 arboreous forms with stems at least 20 cm. high and 12 cm. thick. 

 These differences we are at present unable to correlate with any 

 other character. The habits of some species are not definitely 

 known, because collectors have so often brought back incomplete 

 specimens without field notes; mention of the habit is rarely 

 included in the original description; and further, even American 

 writers have confused our own species with the descriptions of 

 African and other foreign ones and attributed to them characters 

 they never possess. In making the key for this genus, habit has 

 therefore been almost ignored; the key is strictly artificial and 

 based mainly upon the frond characters rather than upon those 

 of the whole plant. 



The following key and descriptions have been based chiefly 

 upon the specimens in the herbaria of the New York Botanical 

 Garden and the United States National Museum. Begun under 

 the direction of Professor Lucien M. Underwood, this paper has 

 been completed with assistance from Mr. William R. Maxon 

 and Dr. Ralph C. Benedict. Dr. H. Christ and Dr. B. P. G. 

 Hochreutiner also kindly sent tracings or material from their 

 herbaria. Access was freely given to the herbaria at Geneva and 

 Kew. 



