PREFACE 



IN 1885 the Manual of the Botany of the Rocky Mountain Region 

 was published. It was based upon general explorations of the 

 region concerned, and was confessedly tentative. During the 

 last twenty-four years, general explorations of the vascular flora 

 have merged into more or less intensive studies, and the manual 

 long ago became inadequate. 



It was the original purpose to revise it as frequently as new 

 material justified, but the author's time and attention became 

 absorbed in other kinds of botanical work, so that no revision has 

 appeared. As the book continued to be in demand, it seemed 

 necessary, in justice to its users, to bring it up to date. This work 

 has been undertaken by Professor Aven Nelson of the University 

 of Wyoming (Laramie), whose great familiarity with the flora of 

 the Rocky Mountain region suggested his fitness for the task. 



Professor Nelson has completely rewritten the book, and in 

 such a way that it is as far from being a compilation as so general 

 a manual can be. He has checked up the descriptions by an 

 examination of the plants and by his extensive field experience. 

 Descriptions and keys have been tested repeatedly, and are 

 believed to be workable. 



The manual is intended to represent current knowledge in 

 reference to the flora for the benefit of the ordinary user of a 

 manual. The professional taxonomist will not find in it all of the 

 subdivisions of genera and species that he might wish, but it is 

 thought that this will make it more serviceable to the general 

 user, and that it presents an adequate account of the flora from 

 the more conservative viewpoint. 



The sequence of families is that known as Engler's, which is in 

 general use by botanists; and the nomenclature, so far as practi- 

 cable, is that adopted by the Vienna Congress. Names following 

 the descriptions, but without citation or parenthesis, are those 

 of the old manual, which have been changed. Names with cita- 

 tion and parenthesis represent what are regarded as synonyms. 

 When new combinations have been found necessary, the discarded 



