PREFACE 



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After more than twenty-five years of study of the flora of the Rocky 

 Mountain region, and seventeen years after the first description was drawn 

 for the book, this manual is now presented to the pubUc. Its history, pur- 

 pose and scope are given in the introduction, with certain necessary explana- 

 tions regarding the general features of the book. 



Thanks are due to the custodians of many herbaria for the privilege of 

 studying collections and types, and for the loan of specimens; these herbaria 

 are enumerated in my introduction. The author wishes to thank all his 

 associates at the New York Botanical Garden, especially Dr. X. L. Britton, 

 Director-in-Chief, for encouragement and help in his work; Dr. J. K. Small, 

 for help in critical cases and in certain groups, as for instance Polygonaceae 

 and Saxifragaceae, and in the original draft of the key to the families; 

 and Dr. J. H. Barnhart, for help in questions of nomenclature and literature. 

 In drawing the generic descriptions, the author has frequently consulted 

 Dr. Small's Flora of the Southeastern" United States. Dr. Barnhart 

 has contributed also the list of authors, including their full names and yei 

 of births and deaths wherever it has been possible. 



Thanks are also due to Mr, K. K. Mackenzie, who contributed the manu- 

 script of Carex; to Professor E. Brainerd, who prepared that of Viola; and 

 to Mr. W. W. Eggleston, who revised that of Crataegus, 



As most manuals of phaenerogamic botany also contain the ferns and 

 their allies, an account of the fern-worts by Miss Margaret Slosson has been 

 appended. The families Isoetaceae, Equisetaceae and Selaginellaceae 

 were left by her until the last. She did some preliminary work on Selagin- 

 ella, but before the work was finished she left the Xew York Botanical Gar- 

 den temporarily, and the completion of the fernworts fell upon the author, 

 who feels that the treatment of the three families is not adequate, as the 

 manuscript was prepared hurriedly while the book was going through the 

 press. 



The author is indebted especially to the following botanists, who have 

 kindly corrected the statements of the ranges of all of the species and fur- 

 nished additions to the list of species known to occur in their respective 

 states and provinces: Mr. J. M. Macoun, western Canadian provinces; 

 Professor J. E. Kirkwood, Montana; Mr. J Francis Macbride, Idaho; Pro- 

 fessor A. 0. Garrett, Utah; and Mr. George E. Osterhout, Colorado. Thanks 

 are also due to the following persons who have gratuitously helped in read- 

 ing the proofs: Professor A. 0. Garrett, Mr. G. E. Osterhout, Miss K. D. 

 Kimball, and Mr. A. E. Urban, now manager of The Hershey Press, who 

 kindly continued proofreading even after he left his old concern. The help 

 of Mr. Urban, who is an amateur botanist as well, has been especially valu- 



able. 



P. A. Rydberg. 



The New York Botanical Garden, November, 1917. 



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