PIPER FLORA OF THE STATE OF WASHINGTON. 



51 



cially sticky laurel {Ceanothus velutinus) and thimbleberry {Ruhus 

 parviforus), form dense thickets. 



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

 abundant 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 

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

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

 ]Vk>untains have a flora very similar to that of the Cascade Mountains, 

 it is not surprising that the higher and moister 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 of 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 Basin. 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 grandiflora. 

 Agoseris retrorsa. 

 Alopecurus californicus. 

 Amsinckia intermedia. 

 Aradis suhvillosa. 

 Arenaria pusilla. 

 Valandrinia menziesli. 

 Valochortus macrocarpus. 

 Ceanothus prostratus. 

 Vlarkia rhomboidea. 

 Cuscuta californica. 

 Deschampsia calycina. 

 Elatine californica. 

 Eriogomim sphaerocephalum. 

 Eryngium articulatum. 

 Festuca confusa. 



Festuca pacifica, 

 Frasera nitida. 

 Gilia harknessii. 

 Lagophylla ramosissima. 

 Lepidiuni nitidum. 

 Linum digynum. 

 Lomatium piperi. 

 Melica fugax. 

 Merathrepta californica. 

 Microseris nutans. 

 Mimulus pulsiferae. 

 Orthocarpus hispidus. 

 Orthocarpus tenuifolius. 

 Pectocarya penicillata. 

 Pectocarya pusilla. 

 Plagiobothrys tenelliis. 



