332 University of California Publications in Zoology [VOL. 16 



perature of this period is 74.8 F. On the basis of temperature it 

 would be necessary to place Walla Walla and the Columbia Basin 

 prairie area about midway in the Upper Austral life-zone (Merriam, 

 1894, p. 236), but the fauna indicates closer affinity to the Transition 

 life-zone. In this matter the fauna is probably a better criterion than 

 the temperature, because the life-zones are founded primarily on 

 faunal relationships. 



The yellow-pine areas of the lower parts of the Blue Mountains in 

 Columbia County make up the timbered division of the Transition 

 life-zone as recognized by Piper (1906, p. 35). 



The part of the Blue Mountain area above the Transition life-zone 

 belongs to the Boreal region of Merriam. Piper (1906, pp. 58, 60, 62) 

 recognizes Canadian, Hudsonian, and Arctic life-zones in the flora of 

 these mountains. In the vertebrate fauna the Arctic life-zone cannot 

 be distinguished and the Canadian and Hudsonian life-zones are very 

 difficult to separate. If the Hudsonian life-zone be recognized as dis- 

 tinct it must be restricted to the summits of the ridges. Here is found 

 the alpine fir (Abies lasiocarpa), a characteristic Hudsonian tree 

 (Piper, 1906, p. 60). The vertebrate species found on these higher 

 ridges, and not reported from lower altitudes, are Zapus princeps ore- 

 gonus, Picoides americanus dorsalis, and Nucifraga columbiana. None 

 of these species can be considered strictly Hudsonian. It seems best 

 to place the part of the Blue Mountain area above the Transition life- 

 zone in a single life-zone, the Boreal. 



COMPARISON OF THE DIFFERENT SYSTEMS OF 

 CONSIDERING DISTRIBUTION 



The facts of animal and plant distribution are very complex and it 

 is convenient to have some system or systems of arranging these facts 

 so that they can be considered in groups rather than as isolated in- 

 stances. Several systems are now in use. Each of these emphasizes 

 different features of the facts of distribution. 



THE ZOOGEOGRAPHICAL SYSTEM 



The system of zoogeography points out the barriers to distribution, 

 and indicates something as to the origin of the faunas of different 

 regions. Because different species of animals are not limited by the 

 same barriers, they do not all fall evenly into zoogeographical divisions. 



