Sub-class 2. DICOTYLEDONES. 

 Order 19. SALICALES. 



Family 35. SALICACEAE Lindl. Willow Family. 



Bracts incised; disk cup-shaped; stamens usually lo or more; stigmata elongated 

 and expanded; winter buds with several scales. i. Populus. 



Bracts entire; disk reduced to i or more small glands; stamens less than lo, 

 usually 2 ; stigmas short, not expanded ; winter-buds with one scale each. 



2. Salix. 



I. POPULUS L. Poplar, Cottonwood, Aspen. 



Petioles strongly flattened laterally. 



Leaf-blades suborbicular. acute or very short acuminate. i. P. tremidoides. 



Leaf-blades broadly deltoid or cordate, abruptly long acuminate. 



Teeth of the leaves few, less than lo on each side; cup of the pistillate 

 flowers 6-8 mm. broad ; pedicels equalling or exceeding the capsule. 



2. P. Wisliseni. 

 Teeth of the leaves many, more than lo on each side; cup of the pistillate 



flowers less than 6 mm. broad ; pedicels shorter than the capsule. 



3. P. occidentalis. 

 Petioles terete or nearly so. 



Petioles half as long as the blade or longer ; blades ovate or rhombic, abruptly 

 long-acuminate. 4- P- acuminata. 



Petioles about one-third as long as the blades or less : blades lanceolate, not 

 abruptly acuminate. 5- P- attgusiifolia. 



1. Populus tremuloides Michx. In open woods and on mountain sides from 

 Newf. to Alaska, Tenn. and Nev. — Alt. 6000-10.000 ft. — Near Georgetown; 

 Cheyenne Caiion; dry rocks, Cheyenne Mountain; Minnehaha; chaparral- 

 covered hills southeast of Ouray; South Park; near Pagosa Peak; South 

 Cheyenne Cafion; Colorado Springs; Ojo; foot-hills, Larimer Co.; Chicken 

 Creek, West La Plata Mountains; Rist Canon; Fort Collins; Redstone; 

 Howe's Gulch. 



2. Populus Wislizeni (S. Wats.) Sarg. In caiions and on river banks from 

 Tex. to Colo, and Ariz. — Alt. 4000-9000 ft.— River bottoms, Arboles; Grand 

 Junction ; plains, Colorado Springs. 



3. Populus occidentalis (Rydb.) Britton. (P. deltoides occidentalis Rydb. ; 

 P. angulata Port. & Coult. ; not Ait.) In river valleys and hillsides from 

 Sask. to Mont., Kans. and Ariz. — Alt. 4000-7000 ft. — Plains near Denver; 

 Walsenburg; Palisade; near Boulder; Lyons; Fort Collins; along the Arkan- 

 sas River, Lamar; Eldora to Baltimore. 



4. Populus acuminata Rydb. On river bottoms and in cafions from the 

 Black Hills of S. D. to Ida., N. M. and Nev.— Alt. 4000-6000 ft.— Fort Col- 

 lins; Walsenburg; Denver; Hardin's ranch; Redstone. 



5. Populus angustifolia James. In cations and along streams from N. D. 

 to Wash., N. M. and' Calif.— Alt. 6000-11,000 ft.— Pike's Peak; Upper Platte; 

 plains near Denver; South Cheyenne Canon, Colorado Springs; Gunnison; 



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