INTRODUCTION 



The group of plants which is the subject of this treatise comprises those Rosaceous 

 genera that usually have several free dry achenes, and styles that are articulated to the 

 ovary and mostly dehiscent. In other words, the tribe Potentilleae is taken in a narrower 

 sense than usual, and is about equivalent to the third division of the Potentilleae of 

 Bentham & Hooker's Genera Plantarum, or to Rosoideae — Potentilleae — Potentillinae of 

 Engler & Prantl's Natuerlichen Pflanzenfamilien. 



The monograph here presented is the result of a study, not only of herbarium ma- 

 terial, but also of living plants in the field. I have collected about half the North 

 American species of Potentilla, Argentina, Fragaria and Drymocallis, besides the Amer- 

 ican monotypes of Sibbaldia, Comariom, Comocarpa and Ghamaerhodos. The study of 

 Horkelia, Gomarella and Stellariopsis, all of which belong to the Pacific slope, has natur- 

 ally been confined mostly to herbarium specimens. The study comprised most of the 

 more important collections of this country, as those of Columbia University, the United 

 States National Herbarium, Harvard University, Missouri Botanical Garden, University 

 of Minnesota, California Academ}'' of Sciences, Geological Survey of Canada, Iowa Agri- 

 cultural College (including the Parry Collection), Lafayette College, New York Bo- 

 tanical Garden, College of Pharmacy of New York City, and the University of Ne- 

 braska. 



I hereby extend my thanks to the directors and curators of these institutions, as 

 well as to the following persons who have kindly loaned me their private collections or 

 sent specimens : S. B. Parish, San Bernardino, Cal. ; Thomas Howell, Clackamas, Ore. ; 

 C. F. Baker, Auburn, Ala. ; Professor Aven Nelson, University of Wyoming ; Geo. E. 

 Osterhout, New Windsor, Colo. ; O. A. Farwell, Detroit, Mich., and others. 



To enumerate all the books referred to would be useless, as references are given 

 under each species. They include practically all general systematic works as well as 

 all books and other publications referring particularly to American botany. It has, 

 however, been thought unnecessary to include purely local floras or mere catalogues of 

 plants, but wherever a description or some interesting data regarding distribution, 

 habitat, or other important information are found, such references are given. Wherever 

 it has been possible, the references have been verified. Where I have not had access to 

 the works cited, the citation is followed by an asterisk. Specimens cited but not seen 

 by me are indicated in the same way. 



