346 BOTANICAL GAZETTE [November 



suga habitat. One other set of observations was made at the bottom of 

 Boulder Canon at 3:40 p.m. on August 29 at an approximate 

 altitude of 2250"^. Here Picea Engelmanni is common and the 

 physical factors typical of the cool, moist portions of the habitat 

 of this formation. The results obtained at this latter point are as 

 follows \ ' 



Temperatures 



ii?5 14*^ 17° i8?7 



Water content 



11.25*™ 22.5— II. 25*^" 



135 . 7 per cent. 5,8 per cent. 



(7) THE PICEA ENGELMANNI-ABIES LASIOCARPA FORMATION 



{figs. 4,10, II) 



This formation occupies chiefly the canons and to a lesser extent 

 the ridges of the mountains from 2850"^ to timber-line, in the latter 

 situation mingling with the Apinus formation. The two characteristic 

 species are of comparatively equal abundance, although the firs are 

 more numerous above 3000"^ and do not extend much below 2400 

 while the spruces are more abundant below 3000^ and pass down, as 

 already noted, to 1950"^. 



Where the forest is virgin it forms a dense growth, excluding 

 practically all forms except Vaccinium micro phyllum and a few mosses 

 and lichens. Along the wet stream banks through the forest, however, 

 we find the brookside formation of the Hudsonian zone characterized 

 by Caltha leptosepala^ Mertensia ciliatay and Senecio triangularis, 

 while occasional invaders from adjoining open slopes occur in the 

 more open parts of the formation. Of these must be noted especially 

 Erigeron salsuginosus and Pedicularis racemosa. It is doubtful 

 whether the latter form is to be considered as an invader or not. It is 

 more common in open timber than in clearings, but does not occur 

 in the dense forest. 



The results obtained from obser\^ations in the Apinus flexilis 

 formation are representative of the drier part of the habitat of this 



formation. In addition to these re<^nhQ arp fhoQe obtained at two 



m 



points 



The first of these, which I shall 



design 



