I9I91 



VESTAL— PHYTOGEOGRAPHY OF COLORADO 



173 



determinative influence upon the vegetation; this can be done in 

 only the barest manner in this section, but these relations are again 

 brought out in the part on geographic relations of the vegetation. 



Temperature conditions of the different parts of the region may 

 be summarized as follows: The foothills have a lower mean tem- 

 perature and shorter period without frost than either plains or 

 mountain-front. Certain of the foothills vegetation-types and 



TABLE II 



Temperature data 



Area 



Foothills (4) 



Northern (2) 



Southern (2) 



Mountain-front (5, excl. 

 Divide) 



Northern (i, Boulder).. . . 



Divide (2) 



Southern (4) 



Plains near mountains (5) . . 



Northern (3) 



Southern (2) 



Dry plains (5) 



Northern (2) 



Southern (3) 



"Northern area" (8) 



"Southern area" (11) 



Average mean 

 temperature ° F. 



43 



42 

 44 



50 



50 

 46 



50 

 47 



47 

 48 

 50 



48 



51 

 45 

 49 



Maximum 

 temperature 



100 



98 

 100 



104 



97 



99 



104 



105 



ros 

 103 

 106 

 103 

 106 

 105 

 106 



Minimum 

 temperature 



Average number 



of days in 

 growing season 



36 



-32 

 -36 



■30 



-20 



■33 

 ■30 

 •38 

 -38 

 ■32 

 -45 

 ■45 

 -32 

 -45 

 36 



99 



95 

 104 



154 



164 

 122 



151 

 138 



134 

 143 

 151 

 145 

 156 

 131 

 142 



The number of stations for each area is given in parentheses. The mountain-front does not include 

 the two stations of the Platte-.^rkansas divide, which is so much more elevated than other parts of the 

 mountain-front as to be much cooler. The "northern and southern areas" are respectively the northern 

 and southern parts of the region, each extending over foothills, mountain-front, and plains. 



many of the pfant species are characteristic of northeastern and 

 northwestern coniferous forest regions, are in fact southern exten- 

 sions of them. The boreal character is much more evident in the 

 higher mountains than in the foothills. 



The mountain-front has the longest frostless season, the highest 

 mean temperature, the mildest winters, and the least range in 

 temperature extremes. Mountain-front localities are mostly 

 comparatively sheltered; temperature inversion is common. 

 Early spring plants flower several weeks earlier at the mountain- 

 front than in either plains or foothills; at Boulder in spring the 



