THE SUMMITS 163 



showed 84 rings of annual growth, which could not be counted 

 without the aid of a lens. The accompanying table prepared 

 from observations on the trees of the sub-alpine forest, shows 

 similar conditions, although in neither of these eases were the 

 conditions less than of average advantage, and might have been 

 even better than the usual sites occupied by trees. It will be 

 observed that it required 60 years for the Engelmann spruce 

 to reach a diameter of SV-; inches, 80 years for the pine to reach 

 4% inches, and 108 years for the fir to attain 41^4 inches in diam- 

 eter. These may be taken as typical figures for most situations 

 in the sub-alpine zone. The altitude in all these cases was about 

 6,200 feet. The first case cited was in the Swan Range east of 

 Bigfork, the figures in the table are from observations made near 

 Swift-Current Pass in Glacier National Park. 



The shi-ubs most common in the sub-alpine forest are : 

 Salix Barclayi Memiesia ferruginea 



" vestita Ledum glandulosum 



" glaucops Kalniia polifolia 



Alnus incanu Phyllodoce enipetriformis 



Kibes lacustre Cassiope Mertensiaita 



Sorhus scopulina Vaccinium erythrococcum 



Crataegus rivularis " scoparium 



Pachysfima Myrsiniies " oreophilum 



Of these Salix Barclayi forms dense thickets three or four 

 feet in height here and there in basins at the heads of streams 

 in Glacier Park and elsewhere. In the openings in such forma- 

 tion Ealmia microphylla occurs along with Sphagnum and grasses 

 and sedges. 



The other species of willow are plentiful but are not massed 

 and are only locally conspicuous. Ahnis i'nca)ia, however, forms 

 pure, dense and matted covering on some of the slopes of the 

 Arctic drainage, and in places elsewhere is prominent in the 

 forest undergrowth. The most characteristic of the high moun- 

 tain shrubs are some of the heaths and huckleberries, Ledum, 

 Cassiope and Pltyllodoce are especially conspicuous in many 

 places, and Vaccinium erythrococcum and V. oreophilum, low 

 and slender, are frequent in forests or open parks. Most of the 

 others named have an altitudinal range more or less extensive 

 and are found in the forests of the white pine and hemlock 



