16 FOREST DISTKIBUTIOX 



paeity of the species, including not only the amount of seed and 

 the frequency of seed years, but the comparative ages at which 

 seeds are produced, their viability, their mode of dissemination 

 and germination and the time involved, the requisite conditions 

 of successful pollination, etc. In addition to these factors must 

 be considered the matters of specific protoplasmic functions, 

 such as resistance, or susceptibility, to the attacks of destructive 

 insects, or fungi, the range of adaptability in relation X« climate 

 and soil. Only by an appreciation of the value of these and 

 other factors can the relative importance of a species in any 

 given area be fully understood. Furthermore, it would seem 

 that no estimate of the influence of these causes is adequate 

 which does not take some account of the time during which the 

 various influential factors have been operative. 



The immensity of the task involved in the thorough study 

 of the vegetation of an area becomes the more apparent when 

 we reflect that native vegetation is dynamic, not static, and 

 that the changing quality of the soil through long periods of 

 time is attended by conspicuous changes in the plant covering. 

 Our knowledge of the ecology of a region or locality must in the 

 end be a product of our knowledge of the separate units (species) 

 of that area. It seems, therefore, important that the study of 

 plant geography, or ecologj% be approached primarily from the 

 standpoint of the species and merely incidentally from that of 

 the physical conditions. 



It is the aim of this paper to present an introduction to the 

 subject of forest distribution in a portion of the northern Rocky 

 ^lountains, with a few tentative conchisiims. and to point the 

 way to a more thorough study, the results of which should be 

 of importance, both in their scientific and their economic as- 

 pects. 



Up to the present time, the flora of ilontana has been 

 studied chiefly from the standpoint of the systematist. ilore 

 than a century of botanical exploration, from the time of Lewis 

 and Clark to the present day, has made known to us the prin- 

 cipal components of its flora. The first collection within the 

 region was that of ^leriwether Lewis in 18()6. who traversed the 

 northern part of the State from Lolo Pass in the Bitter Root 

 Range through the Hellirate and Blackfoot countrj' via Sun 



