Southeastern Washington and Adjacent Idaho. 69 



may be even more abrupt, a linear distance of one or two meters 

 giving the necessary differences in soil depth. Consequently the 

 zones are narrower, but no less distinct. 



The uneven disintegration of canyon walls and scab-land and 

 rocky butte ledges and the differences they offer in slope and 

 exposure and in depth and moisture of soils furnish so many 

 habitat conditions that perhaps two-thirds of the total flora find 

 here more or less congenial homes. In the crevices of a lichen- 

 covered rock and separated only a few inches from the lowly 

 inhabitants of the former may thrive a shrubby member of a far 

 more advanced community. An analysis of the habitat shows 

 each is growing in its proper place, the crustose lichen on the bare 

 rock, the shrub in a small area of rich, well moistened soil. 



Striking differences are offered by habitats on sheltered and 

 protected slopes. Near Pullman, during the summer of 1913, 

 a station was maintained on a south slope in the Agropyron 

 community and a second in a rather open growth of low shrubs on 

 the opposite slope about half-way between the rock ledge and the 

 flood-plain thicket. Not only was the evaporating power of the 

 air found to be twice as great in the former situation, but the soil 

 moisture was only about half as great throughout the growing 

 season. Temperature differences were also striking. The soil 

 between the bunches of Agropyron frequently gave noonday 

 temperatures of 90 to 100 F., as compared with 70 F. at the 

 opposite station. 



These illustrations of diverse habitat conditions will make plain 

 the fact that in addition to the plants already mentioned as 

 belonging to the Agropyron or Poa-Polygonum communities, 

 many others occur. 



Characteristic shrubs and lianas found either as crevice plants 

 on rocky talus slopes or forming thickets about springy places 

 are enumerated in the following lists : the numerals indicate their 

 relative importance. In the drier regions the shrubs are notably 

 fewer. 



Amelanchier florida 2 Berberls repens I 



Amelanchier cusickii I Clematis ligusticifolia 2 



