198 BOTANICAL GAZETTE [MARCH 
and bull pine forests and the prairie to a low ridge near the Flathead 
River, where it issues in the form of springs, making conditions 
favorable for an Engelmann spruce formation. Thus a bit of forest 
is projected, as it were, into the prairie formation. Where the water 
level comes nearer the surface the meadow already mentioned is 
associated with the forest. 
Another meso-hydrophytic forest in which the spruce is almost 
entirely wanting needs to be mentioned. Around the head of Flat- 
head Lake, including the delta at the mouth of the river (figs. 1 and 4), 
and extending up the river from its mouth, is a region that is annually 
submerged." This region is occupied by a dense growth of willows, 
cottonwoods, birch, aspen, and other trees. On each side of the 
mouth of the river are long, low peninsulas of sand, the ends of 
which are entirely barren of vegetation. These are above water 
only a short time during the growing season, and this fact no doubt 
prevents plants from getting a start. A short distance back from 
the end of the delta on a little higher land is Salix fluviatilis, in some 
places so thick as to be almost impenetrable. Underground stems 
are sent out from this center, and thus new territory is gradually 
conquered, so that as fast as the delta is built out it is occupied by 
this pioneer willow, which prepares the way for changes that make 
it possible for higher forms to exist. When the water is high its 
contact with the willows causes a deposit of fine silt, so that the delta 
is gradually built higher and higher, making conditions favorable 
for the growth of such plants as the red dogwood, other species of 
willow, narrow-leaved cottonwood, paper birch, aspen, choke cherry, 
two species of hawthorn, and service berry. 
Around the head of the lake there is a low terrace which is also 
submerged in the spring and early summer months. Instead of 
Salix fluviatilis there is a thicket of other willows; and on the lake 
side of this there are a few scattered specimens of S. fluviatilis and a 
amygdaloides. On the land side of the willow thicket are the birch, 
sive floods do great damage to the country lying at the head of the lake. Since nearly 
= oe in the valley have their sources in the mountains to the east, the pooner 
tion of this region would greatly increase these spring floods and greater damage woul 
be the result. 
a 
