to the Rocky Mountains. 249 



tosis; germinibus sessilibus ; squamis acuminatis; stigmatibus 

 sessilibus, sub-bilobis. 



Hab. On the western rivers, to the Rocky Mountains; 

 common. 



Obs. A shrub with smooth fuscous branches. Leaves 3-6 

 inches long, subfalcate, scarcely two lines broad. Probably 

 a new species, but nearly allied to Salix Humboldtiana of 

 Willdenow. 



424. Populus tremuloides, Michx. arb. iii. p. 285. t. 8. 

 f. 1. On the upper part of the Arkansa, and about the base 

 of the Rocky Mountains. 



425. P. angustifolia, foliis ovato-lanceolatis, attenuatis, 

 basi acutis, glabris, crenato-serratis; ramulis teretibus, glabris. 



P. angustifolia, James in Long's Ex. i. p. 497. Narrow- 

 leaved Cotton-wood of Lewis and Clarke. 



Hab. Sources of the Platte. 



Obs. This species is found intermixed with the common 

 cotton-wood, which it resembles in size and habit, but its trunk 

 is smoother, and its branches more slender and flexile. 



42G. P. angulata, Willd. sp. pi. iv. p. 805. Purshfl. ii. 

 p. G19. On all the western rivers to the Mountains. 



CONIFERS. 



427. Pinus resinosa, L. Pursh. ji. ii. p. 642. On the 

 Rocky Mountains. 



428. P. flexilis, James in Long's Ex. ii. pp. 27. and 35. 

 On the Rocky Mountains, extending from their base to the 

 region of perpetual frost. 



Obs. Leaves in fives, short and rather rigid ; sheaths 

 short and lacerate. Strobile erect ; scales large, unarmed, 

 (something like those of P. rigida,) exuding much resin. 

 Branches leafy, chiefly at the extremity, remarkable for their 



