156 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 



New Mexico: San Juan Valley; Santa Fe; Zuni; Mogollon Mountains; Burro 

 Mountains; Black Range; Deming; Socorro; Mesilla Valley; above Tularosa. Along 

 the larger streams, in the Lower and Upper Sonoran zones. 



The common "valley cotton wood," as it is called by those who are acquainted with 

 the "mountain cottonwood," is perhaps the best known tree of the State. It is doubt- 

 less the most common shade tree of New Mexico, being used almost everywhere. It 

 is very common along the broad flood plains of the Rio Grande and the San Juan, 

 where it forms "bosques" of considerable extent. Besides its use as firewood and for 

 fence posts, straight trunks are used by the Mexicans for the "vigas" or rafters of their 

 houses. When stripped of their bark, the trees do not decay rapidly. 



3. Populus acuminata Rydb. Bull. Torrey Club 20: 50. 1893. 

 Type locality: Carter Canyon, Scotts Bluff County, Nebraska. 

 Range: Montana to New Mexico. 



New Mexico: Carrizo Mountains; Farmington; near Alma; mountains west of San 

 Antonio; Cliff; Fort Bayard; Dog Spring; Kingston; Deming. Canyons and river 

 valleys, in the Upper Sonoran Zone. 



This species grows in situations similar to those in which P. uislizeni is found, 

 besides extending farther up into the mountains. At Deming and Silver City it is 

 used as a shade tree along with the valley cottonwood and is probably equally valu- 

 able for that purpose. 



4. Populus angustifolia James in Long, Exped. 1: 497. 1823. 



Mountain cottonwood. 



Type locality: Rocky Mountains. 



Range: British America to Nebraska, Utah, and New Mexico. 



New Mexico: Common in all the mountain ranges from the Black Range, Organ 

 Mountains, and White Mountains northward. Canyons and along streams, in the 

 Transition and Upper Sonoran zones. 



The mountain cottonwood or "narrow-leaved cottonwood " grows naturally in the 

 mountains along streams, sometimes attaining a great size. It is also common along 

 the valley of the San Juan in San Juan County. It is a rapid grower like its con- 

 geners, and is worthy of much more extensive use than has so far been accorded it. 



2. SALIX L. Willow. 



Shrubs or small trees, from a few centimeters to several meters high; leaves from 

 narrowly linear to short-elliptic or obovate; flowers in aments, appearing before or 

 with the leaves; perianth a single scale; stamens few; pistil single, with a gland at 

 the base of the ovary, the stigma short; fruit a capsule, containing numerous very small 

 hairy seeds. 



The plants of this genus occur at all levels in the State, but are always found where 

 the ground water is abundant and near the surface during the growing season. 



KEY TO THE SPECIES. 



Leaves usually only about 3 times as long as broad, elliptic-oval 

 to obovate, never narrowly lanceolate or linear; capsules 

 hairy (except in S. monticola). 

 Styles obsolete, or less than 0.5 mm. long. 



Alpine plants less than 10 cm. high 1 . S. saximontana. 



Small trees or shrubs, much more than 10 cm. high, at 

 middle elevations in the mountains. 

 Aments slender, lax; scales pale; stigmas very short; 



leaves elliptic-lanceolate, acute 2. S. bebbiana. 



