196 



UNIVERSITY OF COLORADO STUDIES 



8. Populus angustifolia James. Narrowleaf Cottonwood 



Rydberg, Flora Colo. 91; Coulter, Manual 339; Sargent, Manual Trees of 



N. A. 159; Nelson, Key to Rocky Mountain Flora 15. 



Leaf-blades narrowly lanceolate, some 

 times broader; varying from acute to obtuse 

 at apex; diflfering greatly in shape even on 

 the same twig (see accompanying figures); 

 finely toothed all around; usually not more 

 than 2 cm. (f in.) broad, but sometimes twice 

 as broad. Leaf-stalks channeled above, 

 short, generally less than one-third the length 

 of the blade. 



A rather small, spreading tree, with pale 

 gray twigs, except the youngest, which are 

 yellow-brown. Bark not thick, divided near 

 the base by shallow 

 fissures into broad 

 flat ridges. Wood 

 soft, compact, close 

 grained; specific 

 gravity 0.3912, the 

 heart -wood brown 



and sap-wood nearly white. Used for fuel. 



River bottoms and canyons from North Dakota to the 



Pacific coast and south in the mountain ranges from Canada 



to New Mexico. This is one of the commonest cottonwoods 



in northern Colorado where it is found on river banks of 



the plains regions and extending well up in the canyons. 



Distinguished from other species by the very short leaf- 

 stalks. 



9. Populus acuminata Rydb. Lanceleaf Cottonwood ] 



Rydberg, Flora Colo. 91; Sargent, Manual Trees of 

 N. A. 160; Nelson, Key to Rocky Mountain Flora 1$. 



Leaf-blades ovate or broadly lanceolate, variable as to 

 shape and size, crenately serrate, averaging about 4 cm. 

 (if in.) broad. Leaf-stalks slender, about half or two- pig ^ x i 



thirds as long as the blades. 



A rather small tree with compact, round-topped crown, branchlets roughened, 

 the larger branchlets whitish or gray. Wood light, soft, of little value except for 

 fuel. 



