80 A Study of the Vegetation of 
Creek, at a distance of 12 miles from any contiguous body of 
timber. However, this is a phase of the problem which I found 
little time to study. 
The yellow pine consocies forms the transition zone from 
prairie or shrub to other types of woodland. In the mountains 
it occupies exposed south or southwest slopes or only the tops of 
these if the lower slopes are sheltered. Not infrequently it is 
accompanied by Douglas fir. 
On the exposed buttes only scattered trees may occur among 
the shrubs on north slopes. In other cases well developed for- 
ests may be found. On higher buttes, the rocky tops, ravines, 
and sheltered bases may be clothed with a pine forest, while large 
stumps, or isolated pines towering above the Douglas fir and tam- 
arack now in possession of the moist, sheltered slopes, tell the 
story of a former occupation by a pine forest. Thus all stages 
of development are strikingly shown on these butte ramparts of 
the forest frontiers. Often on wind-swept ridges a sheltering 
spur permits the growth of pines, while a slight descent from a 
pine-clad ridge may reveal an entire change in tree dominants, 
the Douglas fir and tamarack replacing the pine. 
As already indicated, the pines have worked their way down 
the Palouse River and along Rock Lake. In the shallow canyons 
they are practically confined to the sheltered canyon sides. Doug- 
las fir and Larix accompany them in the deeper canyons of the 
Palouse River, but I have found only the former with the pine 
about Rock Lake. Opulaster pauciflorus invariably accompanies 
these forest outposts and its. distribution is undoubtedly due to 
chipmunks and squirrels, which are likewise ever present in pine 
woods. Numerous plants, which otherwise are found only in the 
mountains also occur in these pine-clad canyons. Among others 
Aconitum columbianum, Actaea spicata arguta, Thermopsis mon- 
tana, and Veratrum viride may be mentioned. In fact, the study 
of plant populations upon wooded buttes isolated by a distance 
of from only a few to several miles from the forests proper is 
fascinating and instructive, but one into which we can not well 
enter here. 
The xerophytic conditions under which the pines grow about 
80 
