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 Berberis repens 1% 
Amelanchier cusickit 1 Clematis ligusticifolia 2 
69 
