INTRODUCTION xi 



are much alike, in many cases the word Plain also includes the Sonoran portion 

 of the plains, the so-called Staked Plains. Tables showing the approximate 

 altitudes occupied by the different zones in southern Colorado and southern 

 Montana, and in Alberta at the crossing of the Canadian Pacific Railroad, and 

 also the approximate latitudes at which they meet the plains, lowlands, or level 

 basins are shown below. 



The western side of the mountains is warmer than the eastern. It is also 

 dryer, except in the northern part, where the moisture conditions are reversed. 

 The lower zones, therefore, extend further north on the west side. 



Colorado Montana Alberta 



Alpine (Alp.) 3500-^300 m. 2700-3500 m. 2100-3500 m. 



Subalpine (Subalp.) 3000-3500 m. 2500-2700 m. 1800-2100 m. 



Montane (Mont.) 2500-3000 m. 1800-2500 m. 1200-1800 m. 



Submontane (Submont.) . . . 1800-2500 m. 1500-1800 m. Plain 



Upper Sonoran (Son.) 1350-1800 m. Plain 



This table may be given also in the English measures: 



Alpine... . 11,500-14,400 ft. 9,000-12,000 ft. 7,000-12,000 ft. 



Subalpine 10,000-11,500 ft. 8,000- 9,000 ft. 6,000- 7,000 ft. 



Montane 8,000-10,000 ft. 6,000- 8,000 ft. 4,000- 6,000 ft. 



Submontane 6,000- 8,000 ft. 5,000- 6,000 ft. Plain 



Upper Sonoran 4,500- 6,000 ft. Plain 



The different zones meet the lowlands, plains or level basins at approximately 

 the following latitudes: 



East side West side 



Alpine-arctic . . . 69-90 69-90 



Subalpine 55-69 55-69 



Montane 48-55 50-55 



Submontane 38 30'-48 42-50 



Upper Sonoran 35-38 30' 35-42 



TIME OF FLOWERING 



At the end of the specific description is given the month of flowering. The 

 symbols used are: Ja, F, Mr, Ap, My, Je, Jl, Au, S, O, N, D. 



