204 BOTANICAL GAZETTE [MARCH 
hold in the spruce association, where it is found on the ridges and 
hillocks, and it forms an important element in the neighboring 
forests. There are extensive areas in Swan valley where this is 
decidedly the predominating species, and on the west slope of the 
Mission Range in some places there are almost pure stands. It 
extends out into the prairie regions along the river courses and on 
protected slopes. It does not grow in as dry soils as Douglas spruce 
and bull pine, and hence is more restricted in its distribution in 
regions where the rainfall is slight. The young trees, unlike those 
of silver pine and lowland fir, cannot endure shade. In no instance 
was a seedling observed growing in the shade of a forest. Other 
things being equal, it does best in broad open places, although it 
can do fairly well in slight openings where the sunlight enters at 
least during the middle of the day. The western larch then does not 
tolerate shade and cannot reproduce itself unless an opening be 
made first in the forest. This may be done in the mature primeval 
forest by the dropping out of old trees, but more frequently accidents 
such as fires and winds bring about open places suitable for its repro- 
duction, provided of course seed-bearing trees are left to stock the 
soil with seeds. In contrast with silver pine and lowland fir, it may 
_be called a fire-resisting tree. Its thick bark enables it to withstand 
fires that would kill silver pine and lowland fir, old trees often being 
found still living in the midst of burned areas. Sometimes isolated 
trees stand towering over the young lodgepole pine growth that has 
come in after fires (fig. 12), and the only young trees competing with 
lodgepole pines are western larch. 
Observations on the rooting habits of trees are in any case difficult 
to obtain, unless windfalls are frequent. Many trees of weste™ 
larch were found standing in windfalls where silver pine, lowland 
fir, and Engelmann spruce had been blown over. From this on¢ 
would judge that its roots penetrate much deeper than the roots of 
these trees; indeed this may be one of the reasons why western larch 
is able to exist in drier areas than can some other trees, for 4 deep 
root system will enable it to reach nearer to the underground water 
level or at least below the superficial dry surface layers where 4 tree 
with shallow roots could not get sufficient moisture. 
Since Douglas spruce is a successful tree in the regions bordering 
