218 BOTANICAL GAZETTE [MARCH 
apart in the growth of their roots. However, on the rocks there is 
never more than a scattered growth of trees. Where the soil is less 
shallow, more trees are present and a more closed stand is developed. 
In the ravines and other situations where a deep soil has accumu- 
lated, a heavy growth often occurs; especially is this true in the 
protected ravines and on the sheltered slopes. Along the front of 
Flathead Lake there is a series of ridges which has an open growth 
of Douglas spruce and bull pine on the side facing the lake; and 
protected from winds, the slopes on the east side of these ridges and 
the valley between them and the higher ridges to the east have in 
addition western larch, which in places is the dominant tree. Again, 
where the surface of this valley is not far above water level, Engel- 
mann spruce and its associates are found, though these places are 
infrequent. In many protected areas on the west side of the Mission 
Range western larch is present, though as contrasted with the eastern 
slope the exposed western face of the mountains is not so favorable 
a habitat for the mesophytic trees. 
The temperature conditions on top of these mountains and at the 
foot are not known. No doubt the climate is considerably cooler 
at an altitude of 1372™, the highest point of the range in the plot, 
than it is at 8g90™, the level of the lake. However, this difference 15 
not enough to exclude the lowland species and introduce those found 
on the higher Swan Mountains to the east. The presence of a large 
body of water like Flathead Lake no doubt influences the tempera 
ture conditions along its shores, for early fall frosts are less frequent 
here than at a short distance inland. Whether or not this affects 
the forest growth is not known. 
[To be concluded.]} 
