ILLUSTRATIONS {Continued) 



Figure Page 



27. South exposure in upper Bitter Eoot Mountains 13S 



28. Yellow pine on Wildhorse Island in Flathead Lake 140 



29. In the valley of the Swan River.... 142 



30. In the Priest River Valley in northern Idaho 144 



31. Larch and pine on the east shore of Flathead Lake 



Frontispiece 



32 A mountain valley in the upper Bitter Root 146 



33. Distribution of larch along snow drifts 148 



24. A north mountain slope near Missoula... 150 



35. Encrusting lichen vegetation on the talus 152 



36. A ''slide-rock" slope in the upper Bitter Root 154 



37. Pure stand of Engelmann spruce in Avalanche Basin.... 156 

 3S. Western slope of the 3Iission Range overlooking Flat- 

 head Lake... — — .. 15S 



39. A burn being reoecupied by lodgepole pine — — . 160 



40. Lodgepole forest at top of Continental Divide.. 162 



41. Summit of the Bitter Root Mountains 164 



42. A typical sub-alpine park in the Swan Range in July.... 166 



43. At an altitude of 6200 feet in the Swan Range 16S 



44. A cirque lake in the Swan Range 170 



45. Section of stem of small fir showing rate of growth 172 



