X INTRODUCTION 



Measurements 



The measurements have been given in metric system, now used by most of 

 the scientific bureaus of the United States and universities and colleges of the 

 country. In the old English system, formerly used in descriptive iDotahy, the 

 inch was divided into twelve lines. A ruler with this division is hard to find 

 now-a-days, while metric rulers can be had nearly everywhere. For those who 

 are more accustomed to the English measurements a table is given on page xii, 

 with equivalents near enough for all practical purposes. 



Habitat and Distribution 



Near the end of each sj)ecific description is given the usual habitat of the plant 

 and its geographic distribution. In order to save space the latter is given in 

 abbreviation. Usually four states or provinces, or less, are mentioned; if the 

 distribution is irregular, sometimes more than four. The expression: Man. — 

 Kans. — Utah — Alta. would mean that the area in which the plant grows naturally 

 extends frorii Manitoba to Kansas, Utah, and Alberta. If a state or province 

 is placed within parenthesis with a question mark preceding, as for instance 

 (? Colo.), it means that the plant has been reported from said state, but that the 

 author has not verified the assertion and doubts its correctness. Isolated or 

 exotic distribution is set off from the general endemic one by a semicolon; and 

 immigrants are distinguished as adventive (adv.), i. e., not fully established, or 

 fully naturalized (nat.), or escaped from cultivation. The abbreviations used 

 are included in the table on page xii. 



Altitudes and Life Zones 



In the original draft, altitudinal distribution was stated. In an area which 

 extends in latitude 18 degrees, or approximately 1250 miles, however, a statement 

 of the altitudes does not mean very much, as a plant which has its best develop- 

 ment in Colorado at 3000 meters (10,000 feet) does not reach half that altitude 

 in the Canadian Rockies. Instead of the altitude in meters or feet, the zonal 

 distiibution is therefore given. The following life zones have been accepted in 

 this work: 



Alpine Zone (Alp.), the region above timberline. 



Subalpine Zone (Subalp.), or Spruce Belt. 



Montane Zone (Mont.), or Pine Belt. 



Submontane Zone (Siibmont.), or Foothills, or in the south the Chaparral Belt. 



Sonoran, or rather Upper Sonoran, Zone (Son.), or Piiion-Cedar Belt and the 

 Upper Desert. 



Lower Sonoran Zone (L. Son.) or Lower Desert, limited with the manual 

 area to the Colorado River Canon and Virgin River Valley in Utah. 



As the first four of these zonal names apply only to a mountain region, they 

 could not be used for the part of the area occupied by the plains, especially east 

 thereof. The same life zone that occupies the high mountains in temperate 

 latitudes will occupy the lowlands nearer the poles, and these zones there become 

 Arctic, Subarctic, Boreal, and Subhoreal. The Montane and Subalpine Zone 

 reach the lowlands or plains in Alberta and hence also meet the western exten- 

 sion of the Boreal and Subarctic Zones of the east. This merging takes place, 

 however, mostly north of latitude 55°, as the grass-covered plains push across the 

 northern branch of Saskatchewan River; it is practically only along the lower 

 part of said river that the Boreal and Subarctic flora enters the area of this work. 

 The hardwood forests of the subboreal zone does not reach the Rockies; only a 

 small element represents it in the foothills of the Black Hills, South Dakota, and 

 exceedingly few of its plants reach eastern Saskatchewan. The zone is repre- 

 sented on the plains by grasslands and as these are so different from both the 

 foothills of the Rockies and the eastern subboreal hardwood forest, it has seemed 

 better to designate them with a different name, and the word Plain represents 

 the grass-covered portion of the Subboreal Zone. The plains south of the divide 

 between the Arkansas and Platte rivers belong in reality to the Sonoran Zone, 

 but as the transition is so gradual and the general characters of the two divisions 



