

THE SYLVA OF MONTANA. : 7 409 
tinguishable when leafless by its yellow twigs. I doubt 
whether P. monilifera grows so far north in the mountains. 
AsPEN (P. tremuloides). The aspen occurs at intervals 
throughout the mountains, usually about gravelly ponds, but 
is not common. 
Twisrep Prive (Pinus contorta). I first met with this 
pine at the east base of Mullan's Pass, where a single tree 
of unusual size seemed to me at first distinct from this spe- 
cies. It was two feet in diameter, and fully sixty in height, 
the branches erowded with cones of all ages, but west of the 
pass I found the more usual form abundant, which indicated 
this to be only a luxuriant specimen. It is the most preva- 
lent tree of the higher Rocky Mountains, as far down the 
west slope as Deer Lodge prairie. It then becomes rare in 
the valley until reaching the crossing of the Bitterroot, when 
it again becomes abundant, forming groves by itself on poor 
sandy or gravelly soil exactly as on the coast. Towards the 
rainy summit of the Cœur d’Alefie Mountains, however, it 
is searcer, being the seventh in abundance of the trees; it is 
still rarer on the west slope, but at the Mission rather com- 
mon, though not observed much farther west. Its growth 
seems like that of most other trees more dependent on a cer- 
tain degree of moisture than on temperature. 
Piron Prive CP. rigida). This eastern species is common 
9n the eastern spurs of the Rocky Mountains, in the upper 
"Bad Lands" of the Missouri, from Milk to Judith river, 
and on the “Black Hills” near Fort Laramie, but I did not 
find it west of the Rocky Mountains or of Fort Benton. 
Yzrrow Prine (Pinus ponderosa). The Yellow Pine is 
the prevailing species in most parts of the Rocky Mountains 
traversed, though much less common than others in the 
Cœur d'Aleie Range. It presents the same appearance from 
the east base of the Rocky to that of the Cascade Moun- 
tains, being unmistakable as far as it can be seen. On the 
Hell Gate I saw the largest, some fully four feet in diame- 
. ter, and it grows in the driest sandy soil, where no other 
=~ AMER. NATURALIST, VOL. III. 52 
