INTRODUCTION 21 



having; been made in the Blackfoot Valley from the days of Lewis 

 and Clark to the present time, and probably the upper valleys 

 of the South and Middle Forks of the Flathead have never been 

 visited by a, botanist. The latter represents an area some 200 

 square miles in extent and part of it is isolated, wild and in- 

 accessible. The Yellowstone Valley and the upper branches of 

 the Missouri, especially the Gallatin Valley, the upper valley of 

 the Clark's Fork reaching to Deer Lodge with its principal 

 tributaries the Bitter Root and the Flathead and the regions 

 surveyed by Williams and Jones above mentioned constitute the 

 areas which have received most attention, yet even these, em- 

 bracing as they do hundreds of square miles, are yet imperfectly 

 known. The higher mountain ranges, especially the heights of 

 the Bitter Root Mountains which form a natural barrier to the 

 eastward migration of Pacific species, still furnish important 

 fields for investigation. 



Systematic collections and description represent the most of 

 the work on the Montana flora and almost nothing has been 

 done on the phytogeographical and ecological aspects of the 

 vegetation of the region. A series of brief contributions by 

 Rydberg (53-55), Whitford's (73) study of the Forests of the 

 Flathead Valley, and the work by Leiberg (29-32) above referred 

 to represent about all of the literature on this phase of the 

 plant life of the Northern Rockies. Nothing has yet appeared 

 which attempts to relate the vegetation of the area within the 

 present boundary of Montana to the topographic and climatic 

 influences which have had so large a part in determining its 

 quantity and quality. 



The area considered within the scope of this paper comprises 

 a wide belt across the northern Rocky Mountains mostly in 

 Montana. That portion of Idaho, adjoining on the west will 

 also be considered as floristically belonging to this region and 

 as possessing certain points of special interest in this connection. 

 The whole area covered by this paper covers about 175,000 

 square miles. It is unequally divided between prairie and forest, 

 the latter covering about 75,000 square miles. The prairies dif- 

 fer in their composition and topography arid while representing 

 the typical condition in the eastern part of the State, they are 

 broken here and there by forest islands of greater or less extent, 



