PIPER FLORA OF THE STATE OF WASHINGTON. 71 



the adjoining Bitterroots reach the Blues excepting the higher alpine 

 Larix lyallii and the giant cedar {Thuja pUcata). The absence 

 of the last tree is the more marked as it is common throughout the 

 Bitterroots, even on most of the outlying peaks. 



Some few other plants common in the Bitterroots are likewise 

 absent from the Blues. Among them are Frasera fastigiata^ Mitella 

 stauropetala^ Fentstemon pinetoruni^ Coptis occidentalism and Asarum 

 Cauda turn. 



The explanation of this peculiar interrelation in the floras of these 

 distant mountains is 23robably to be sought in two facts. First, these 

 mountain regions are alike in being composed wholly or largely of 

 granite rocks; second, the intervening portion of the Cascades is 

 wholly made up of volcanic rocks. 



THE BLUE MOUNTAINS. 



The greater part of this range lies within the State of Oregon. 

 Its central portion, known as the Powder River Mountains, consists 

 of granitic peaks which rise to an altitude of 2,400 to 2,700 meters 

 (7,000 to 9,000 feet). Surrounding this granite center are lower 

 mountains composed wholly of basalt. Such is the case with the 

 portion which extends into Washington. 



Occupying as they do a nearly central position in the Columbia Ba- 

 sin, quite widely separated from the Cascade Mountains to the west- ' 

 ward and the scattered mountains southward, while almost contig- 

 uous to the outlying ranges of the Bitterroots to the east, peculiar- 

 ities in the constitution of the flora of these mountains would be ex- 

 pected. That such is the case was recognized by their earliest ex- 

 plorer, Douglas, who made no less than three trips into this rather 

 unique region. 



The general facies of the flora is that of all the other mountains 

 i-airrounding the Columbia basin. The great majority of the plants 

 are identical with those of the eastern slope of the Cascade Mountains 

 and scarcely a smaller proportion with those of the adjacent moun- 

 tains in Idaho. 



An analysis of the remaining portion of the Blue Mountains flora 

 shows that it consists of several elements of diverse origin which 

 combine to make it peculiar. These elements are, first, those species 

 that are known to occur only in the Blue Mountains; second, those 

 species which are common to the Kocky Mountains but which do not 

 reach the Cascades, and third, those species which are also of more or - 

 less local distribution in the Cascade Mountains. 



The plants known to be limited in distribution to the Blue Moun- 

 tains are neither numerous nor strikingly different from their nearest 

 relatives. In themselves they indicate scarcely more than that their 



