PIPER FLORA OF THE STATE OF WASHINGTON. 



51 



ciallv sticky laurel {Cea/iof/ti(s reli/tlnifs) and thiiubk4)erry {Ruhus 

 /><fri'ifforus) , form dense thickets. 



Such Arid Transition forests, in which the red fir becomes the most 

 abvmdant tree, resemble very closely the Humid Transition forests 

 of western Washington. Indeed, they are intermediate in character 

 between the two. merging at lower altitudes into the ordinary yellow 

 ])ine forests, and at higher altitudes into the Canadian or white pine 

 zone. Inasmuch as the Canadian and higher zones in the liitterroot 

 Mountains have a flora very similar to that of the Cascade Mountains, 

 it is not surprising that the higher and molster portion of the Arid 

 Transition shows a like similarity. 



ORIGIN OF THE ARID TRANSITION FLORA. 



The Arid Transition flora, like the Upper Sonoran, is clearly made 

 up for the most part of three sets of species. These may be denomi- 

 nated the Californian element, consisting qf plants which have 

 migrated from California; the Rocky ^Mountain element, species 

 whose distribution is easterly and southerly from the region here 

 considered; and the Columbian element, those species which are con- 

 fined to the Columbia Basin and have in all probability originated 

 there. 



THE CALIFORNIA ELEMENT. 



This consists of species which range from California through the 

 low passes in the Klamath region into the Columbia Basiw. A large 

 number of the species range also into the Willamette Valley on the 

 west side of the Cascade Mountains, most of these also reaching the 

 gravelly prairies of western Washington. These species have been 

 discussed in connection with the Humid Transition area. The fol- 

 lowing list is composed of species confined to the Arid Transition area 

 east of the Cascade Mountains : 



Agoseris grandlflora. 

 Agoseris retrorsa. 

 AJopecurus californicus. 

 Amsinckia intcrm edia. 

 Aral)is subviUosa. 

 Arenaria pusilla. 

 Calandrinia nienzirsii. 

 Calochortus macrocarpus. 

 Veanothus prostmtus. 

 Clarkia rliomboidca. 

 Cuscutw californica. 

 Deschampsia calycina. 

 Elatine caUforjiica. 

 Lriogojium sphaerocephalum . 

 Eryngium articulatuni. 

 Festuca confusa. 



Fcstiica pacifica. 

 Frasera nitida. 

 Gilia harkricssii. 

 Lagophylla rainosis^aima. 

 Lcpidiiini ii it id Hill. 

 Lin urn digyniun. 

 Loviatiinn pipcri. 

 Melica fiiga.r. 

 Mera tli rcpta califoni ica. 

 Microscris )i utaus. 

 Mini uiiis puUifcrac. 

 Orthocarpiis hispid iifi. 

 Orthocarpiis ten uifoliiis. 

 Pectoearya penicillata. 

 Pectocarya pusilla. 

 Plagiobothrys tenellus. 



