PIPER—FLORA OF THE STATE OF WASHINGTON. 71 
the adjoining Bitterroots reach the Blues excepting the higher alpine 
Larix Tyallii and the giant cedar (Thuja plicata). 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, Pentstemon pinetorum, Coptis occidentalis, and Asaruni 
caudatum. 
The explanation of this peculiar interrelation in the floras of these 
distant mountains is probably to be sought in two facts. First, these 
mountain regions are alike in being composed wholly or largely of 
vranite rocks; second, the intervening portion of the Cascades 1s 
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 
surrounding 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 
chows 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 whith are common to the Rocky 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 
