PIPER FLORA OF THE STATE OF WASHINGTON. 57 



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 occupy in the coastal area. Among the exam- 

 ples may be cited the following: 



Popidus trichocarjxi. 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 : 



DelphiniiDii })icnziesH. Rhatmnis piirshiana. 



GeraniuDi. caroUnianum. , Schizonotus discolor. 

 Heuchera cylhidrica. Speciilaria pcrfoliata. 



Loinatiiuii midicanlc. 



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, typically Canadian on the west slopes of the Cascades, 

 are just as typically Arid Transition in the Bitterroots. Vaccimmi 

 tiicwrophyllum 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. hracteosa 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 applies to : 



Ahies lasiocarpa. Priitstemo7i proceruf<. 



Alt! us shiuata. Polygonmn histortoides. 



Gatiltheria ovatifolia. Saiissurea americana. 



Hemieva ranunvulifolia. Stcnanthimn occidentale. 



HydrophyUum albifruns. ThaUctrum occidentale. 



Pentstcmon confertiis. Trautvetteria grandis. ■ 



