Cornus canadensis, Trientalis americana, Streptopus roseus, S. 

 ample xifolius, Vaccinium canadense, Clintonia borealis, Lyco- 

 p odium lucidulum, Phegopteris polypodioides, P. Dryopteris, 

 Lister a cor data, Moneses grandiflora, Goody era tesselata, and an 

 abundance of Monotropa uniftora and M. Hypopitys, giving 

 these woods a very mesophytic aspect. 



This mesophytic forest covers the Great basin, South basin, 

 the Northwest basin, most of the outer slopes and ridges, and 

 extends far out into the lowlands about the mountain. Ascend- 

 ing the basins, the trees gradually become smaller until at the 

 base of the last long precipitous ascent, the walls proper of the 

 basins, there is an apparent tree line which skirts the base ; espe- 

 cially is this noticeable in the Great basin. (Fig. 5). This 

 "timber-line," so called, is more apparent than real and has its 

 only delimitation in large trees. The walls of these basins are 

 much subjected to slides of rock and gravel, and snow in spring, 

 which rush down the slopes and strike at the base with tre- 

 mendous force. In this plunge these avalanches sweep all 

 before them being checked only by the larger trees at the base. 

 The multitudinous repetition of these slides has thus formed a 

 line of trees which represent not a climatic but an avalanche tim- 

 ber-line. Trees soon appear on these slides and within a few 

 years they become reforested. The birch, Betula papyrifera 

 c or di folia, is the most abundant on the slope trees. It seems, on 

 account of its flexibility, particularly adapted to this precarious 

 slope life. This very property of bending without breaking 

 doubtless explains its predominance as a slope form. Mixed 

 with it is the alder, Alnus viridis, and frequent spruce and 

 fir. These trees form a continuous forest growth with the 

 mesophytic forest of the lowlands and, gradually diminishing in 

 size, extend up to the "tableland" and "saddle," there joining the 

 Krummholz and reaching far up toward the summit. Most of 

 the spurs, notably the Northern ridge, are also covered by this 

 forest. Where slides are rare the composition is largely spruce 

 and fir and would never suggest a timber-line, for the decrease 

 in size is gradual. This same apparent "timber-line" exists upon 

 the western and southwestern slopes. Harshburger 1 states that 

 this timber-line is here at 3,700 feet and so maps it in a very dia- 



37 



