230 BOTANICAL GAZETTE [APRIL 
trees, though larger than most of the conifers of the eastern states, 
are small compared with the vigorous trees found in the hemlock- 
arborvitae-Douglas spruce forests west 6f the Cascade Mountains. 
It is in this region of greater rainfall and warmer winter months that 
Douglas spruce makes its best growth. With its great power of adapt- 
ing itself to adverse conditions, it has spread through all the Rocky 
Mountain region as far south as Mexico. While Douglas spruce 
can adapt itself to varying conditions of moisture, it is very intoler- 
ant of shade, in this respect being like western larch, and even requir- 
ing slightly more open places in the forest to gain a foothold. Thus 
the tree will be reproduced only in open places in the forest. 
The distribution of bull pine in Flathead valley is more limited 
than that of either Douglas spruce or western larch. It occurs in 
open park-like growths on the borders of the prairie formation, with 
patches of the prairie between (fig. 18). In the forest formations 
in the vicinity of Nigger Prairie there is a close stand of this species 
(jig. 14). Indeed so thick are the trees in certain situations that 
there is not sufficient light under them for the reproduction of either 
Douglas spruce or western larch, though young trees of Engelmann 
spruce and lowland fir can endure the shade. Isolated groups of 
bull pine are scattered through Swan valley, usually along streams 
where abundant light can reach them, and in pebbly soils, where 
other trees have difficulty in maintaining a stand, bull pine is found. 
Wherever a single tree is found surrounded by other trees it usually 
overtops them, showing that it probably started before they were 
present, for it is exceedingly intolerant of shade; it must have open 
places in which to pass its young stages, and this perhaps accounts 
for its scarcity in the mesophytic area in deep rich soils. Where 
found in Swan valley, it is a very healthy tree and very likely would 
do well in pure stands there if given a chance. In other words, bull 
pine does not grow in the dry soils on the border of the prairie because 
it prefers the moisture conditions found there, for it does better in 
the soils where there is more moisture; it is almost entirely forced 
out of the latter soils in the struggle for existence with the more suc- 
cessful trees. It undoubtedly demands a greater amount of heat 
than the other species, with the possible exception of lowland fir, 
for its altitudinal range is more limited. The highest point at which 
it was observed on the surrounding mountains was 1375*- 
