200 BOTANICAL GAZETTE [MARCH 
raphy brought the surface of the soil near the underground water 
level, and along streams. However, trees in these situations seldom 
reach large dimensions. 
The Engelmann spruce can tolerate shade fairly well; in this 
respect it is different from western larch and Douglas spruce and 
is classed with silver pine and lowland fir. The fact that it can endure 
shade probably accounts for the presence of its seedlings in the forests 
that occupy the drier areas in the plot, for the forest canopy in these 
situations brings about a local climate that makes it possible for trees 
to exist that could not otherwise do so. The Engelmann spruce has 
the power of germinating in the open if there is sufficient soil mois- 
ture, and like the other shade-enduring species it does better in these 
situations than in the shade. 
It will be seen from the foregoing that outside the semi-hydrophytic 
conditions Engelmann spruce does not flourish in the plot under 
discussion, being confined to the level stretches of land bordering 
on the meadows and open bodies of water. There is little doubt 
that as the waters of the former Swan Lake withdrew, meadows first 
occupied these areas and then were replaced by spruce stands. Just 
as the meadow conditions may be considered the first stage in the 
development toward the climax forest of the region, so the spruce 
forest may be considered the second stage. As the channel of Swan 
River is cut deeper the water level of the valley will be lowered, thus 
bringing about a condition favorable to the development of other 
types of forest which will replace the spruce association. 
In the above account the distribution of the Engelmann spruce }§ 
discussed only in the area mapped. In the mountains bordering 
the area on the east it shows a wide altitudinal range, but is always 
associated with good moisture conditions, for it is found best devel- 
oped in the damp cafions and on damp slopes where it is invariably 
associated with Abies lasiocarpa. In the high basins it does not do 
so well as the fir, but in the lower valleys it flourishes where the alpine 
fir does not. 
THE WESTERN LARCH-DOUGLAS SPRUCE FORMATIONS (MESOPHYTIC)- 
In the discussion of the Engelmann spruce formation it was shown 
that on its borders and on the dry hummocks in stands of this tree 
other trees obtained a foothold. Just as there is a gradation from 
