THE SUMMITS 169 



of Missoula. at 3,300 feet opens from the 20th to 30th of April 

 and gradually unfolds at successively higher altitudes on north 

 slopes until in about five weeks, the same phase of development 

 nrny he found at 5,300. Under such conditions spring, summer 

 and autumn are telescoped into one brief period and the flowers 

 of these seasons at lower altitudes are mingled in one brilliant 

 assemblage, during the few weeks of vegetative activity. So short 

 is the growing season that the plants can scarcely await the 

 removal of the snow and ice. In one year on the 22nd of July 

 in a mountain park at an altitude of about 6,500 feet the writer 

 observed this luxuriance of vegetation where the blades of 

 Erythronium grandiflonim, Jiun-oldcs glabratum and other 

 plants were forcing their way through sheets of ice an inch or 

 more in thickness. The edges of old snowdrifts condensing into 

 a solid fringe of ice of varying thickness were closely surrounded 

 by the vigorous shoots of numerous plants several inches in 

 height. Some had perforated the ice and others under the thicker 

 parts had pushed upward into it and w r hen the cakes of ice were 

 overturned their bottoms were marked by deep pits plainly evi- 

 dent. 



Local differences are thus evident in the length of season 

 and the conditions of development in small areas side by side. 

 This must have its influence upon forest development as well as 

 upon herbaceous vegetation. The earlier an area is cleared of 

 its snow the longer its growing season. The occupation by forest 

 trees of slight elevations above the general surface in protected 

 coves where the snow usually accumulates may be susceptible of 

 this explanation for from such the snow must sooner dis- 

 appear, while in the alternate depressions it may not entirely 

 melt during the Avhole summer. The advantages of a relatively 

 long growing season may thus account for the establishment of 

 forest species w 7 here otherwise it w r ould be impossible. 



SUMMARY. 



1. The area here under discussion covers the State of Mon- 

 tana and neighboring parts of Idaho. Approximately one-half 

 of the total area may be said to be forested, but some of the 



