PIPER—FLORA OF THE STATE OF WASHINGTON. a7 
seems to be by far the more likely one. First, because these rare 
species show none of the aggressiveness to be expected in recent intro- 
ductions that have found a congenial environment; second, because 
this hypothesis fits in with the explanation that these species were 
forced southward in the glacial period, and under the changed condi- 
tions following have lingered in regions to which they are not well 
adapted. 
One other fact indicates also that many species have had to adjust 
themselves to a changed environment, and as this has been done with- 
out morphological change, the readjustment must have been recent. 
In endeavoring to fix the zonal limits of plants which occur on both 
sides of the Cascade Mountains, the curious fact becomes evident 
that many species have a lower zonal range in the interior region 
than that which they oceupy in the coastal area. Among the exam- 
ples may be cited the following: 
Populus trichocarpa, a Humid Transition or even Canadian spe- 
cies in western Washington, is more abundant east of the Cascades 
as an Upper Sonoran than as an Arid Transition plant. Other spe- 
cies of which the same statement holds true are: 
Delphinium menziesti. Rhamnus purshiana, 
Geranium carolinianum. Sehizonotus discolor. 
Heuchera cylindriea, Specularia perfoliata. 
Lomatium nudicaule. 
It may be argued that the Humid Transition character of these 
plants is not altogether demonstrated in their zonal range in western 
Washington where no lower zone occurs. But nearly all of the above 
species in their range southward confine themselves strictly to the 
Transition Area. 
Some species, tvpically Canadian on the west slopes of the Caseades, 
are just as typically Arid Transition in the Bitterroots. Vaccinum 
macrophyllum is perhaps the most conspicuous example of this, but it 
is also illustrated in less degree by Pterospora andromedea and 
Cornus canadensis, 
Pedicularis racemosa and P. bracteosa in the Cascades and Olympics 
are Hudsonian species, extending more or less into the Arctic above 
or the Canadian below. On the west slope of the Bitterroots they 
occur in undoubted Arid Transition, ranging also into the Canadian. 
This same statement also apples to: 
Abies lasiocarpa. Pentstemon procerus. 
Alnus sinuata. Polygonum bistortoides. 
Gaultheria ovatifolia. Saussurea americana. 
Hemieva ranunculifolia, Stenanthium occidentale. 
Hydrophyllum albifrons. Thalictrum occidentale. 
Pentstemon confertus. Trautvetteria grandis. 
