PIPER FLORA OF THE STATE OF WASHINGTON, 



53 



Parrya mcnzicHiL 

 Pentstenivn attciiuatiis. 

 Pentxtemoii phictoniui. 

 Pentstemon rich a nisonii. 

 Pentstemon triph yUiis. 

 Phaca atTccta. 

 Phaca conjuncta. 

 Phaca spuldingii. 

 Physaria gcyeri. 



Platyspenii iini scapigcniiii. 

 Polygon Kin polygaloides. 

 Ranunculus tritcriiatus. 

 Silcne spaldingii. 

 Sphaeralcea longiscpala. 

 Tri folium doiiglasii. 

 Trilliuni pctiolatuvi. 

 Viola trincrvata. 



COMPARISON OF THE HUMID AND ARID TRANSITION FLORAS. 



As before stated, the Cascade Mountains form a sharp and efficient 

 barrier betAveen the areas of the Transition zone. The Humid Transi- 

 tion does not cease abruptly with the crest of the Cascade Mountains, 

 but many species descend for some distance on the eastern slope, at 

 lower altitudes becoming mixed indiscriminately with Arid Transi- 

 tion plants. 



In the moisture portions of the western slopes of the Bitterroots 

 and in the Blue Momitains the climatic conditions approach those of 

 western AVashington. It is therefore not surprising- that in the 

 moister portions of the yellow pine subarea in western Idaho a great 

 many of the Humid Transition plants of western Washington reap- 

 pear. Indeed at least one-half of the species are thus common, and 

 it is therefore largely an arl)itrary matter to class the one as Humid 

 Transition, the other as Arid. 



The complex nature of the problem is realized, however, when we 

 consider the remaining species. They may be thus grouped : First, 

 those that occur in the Vancouver strip, but not in North Idaho; sec- 

 ond, those that occur in Idaho, but not in the Vancouver strip, and 

 third, those that are abundant in Idaho, but very rare in the latter 

 area. The following tables bring out clearly the relative importance 

 of these elements: 



PLANTS EQUALLY COMMON IN THE HUMID TRANSITION AREA OF THE VANCOUVER 

 STRIP AND THE MOISTER PORTION OF THE YELLOW PINE SUBAREA IN NORTH IDAHO. 



Trees. 



Abies grand is. 

 Acer douglasii. 

 Pvnus contorta. 

 Pinus monticola. 

 Popuhis trichocarpa. 

 Pseudotsugd m ucronata. 



Rhatnnns purshlana. 

 Balix scoulerianu. 

 Tuxus brevifoJia. 

 Thuya plicata. 

 Tsuga mcrtensiana. 



