274 



BULLETIN UNIVERSITY OF MONTANA 



form almost pure forests. Near the top of the two mountains under dis- 

 cussion, the exposed places have only the two alpine trees, the white- 

 bark pine and the alpine fir. In basins on the east side, however, the con- 

 ■ditions are different. Here the snow lies longer. The white-bark pine 

 is infrequent here, but the alpine fir does better than on the exposed 

 ridges. In the basins there are three distinct plant associations. On the 

 steep slopes where the weathering processes are frequently adding new 

 rock material, (Plate XL VII) the conditions are too strenuous for the 

 existence of any plants. As soon as one of these talus slopes becomes 

 stable enough, then plants begin to get a foothold, and finally trees may 



Fig it. Portion of an alpine meadow, yotjo ft. altitude, Swan range, 

 August, 190,3. Photo, by M.J. E. 



appear. In places where the snow lies the year around, there is no 

 vegetable life except the simple one-celled plant known as the "red snow." 

 Bordering on these snow banks are the so-called alpine meadows. (Fig. 

 31.) They usually follow up the retreating snow and sometimes dog 

 tooth violets, spring beauties, and anemones come up through the snow 

 itself. Thus one can see these forms just appearing on the border of 

 the snow field. At a little distance they are in full bloom, further away 

 where the snow has disappeared earlier they have produced seeds, and 

 still further from the snow they have finished their growth and have 

 died down to the ground. It is usually in the latter places that one 

 finds groups of trees, (Plate XLVII) nearly all alpine fir, for they appear 

 where the snow first melts. Thus there is a relation between the plant 

 societies found in these regions, and the time snow lies on the ground. 



