PIPER—FLORA OF THE STATE OF WASHINGTON. 69 
Rainiera stricta, Solidago caurina. 
Rudbeckia alpicola, Sphaeralcea longisepala. 
Sazxifraga apetala, Spiraea cinerascens, 
Senecio elmeri, Valeriana columbiana, 
This extremely restricted range of so considerable a number of 
species in a mountain chain which would seem to offer no barrier to 
their extension southward is perhaps due primarily to the fact that 
the greater portion of the Cascade system from Mount Rainier south- 
ward is volcanic. Indeed, the eruption of the igneous rocks not only 
may have brought about the isolation of the plants above mentioned, 
but, through their preference for granitic soils, may have kept them 
from spreading southward. This idea further obtains support in the 
fact that there are some striking similarities between the flora of the 
Mount Stuart region and that of the Klamath region in southwestern 
Oregon, which is also largely granitic in character. 
This is exemplified by a number of species which do not occur in 
the intermediate region. Among them are— 
Arabis suffrutescens. Hoorebekia greenei. 
Bikukulla uniflora. Kelloggia galioides, 
Campanula scabrella. Ledum glandulosum. 
Chaenactis nevadensis. 
To these should perhaps be added Cacaliopsis nardosmia glabrata 
and (. nardosmia, Luina hypoleuca, and L. hypoleuca californica. 
Facts to be adduced hereafter in connection with the make-up 
of the flora of the Blue Mountains emphasize still more the above 
conclusions. 
While a great portion of the plants of the Cascade and the Blue 
mountains are identical, there are nevertheless many species whose 
occurrence in the former mountains is so local that their recurrence 
in the latter furnishes some strikingly peculiar facts. As before 
stated, the central and southern portions of the Cascade system are 
composed of recent voleanic rocks, while the northern portion and 
the Siskiyou and other mountains of the Klamath region con- 
tiguous to the southern end of the Cascades are made up of older 
rocks, largely granite. This difference in geological structure seems 
to be directly associated with the distribution of certain plants 
here discussed. The facts of the distribution are, first, that there 
are species in common between the northern Cascades and the 
Klamath region which are absent in the intermediate portion of the 
Cascades; second, that certain species occur only in the Blues and 
the Klamath region or the northern Sierras; third, that others occur 
only in the northern Cascades and the Blues; and finally some 
species occur in all three regions, but not elsewhere. 
