WOOTON AND STANDLEY—FLORA OF NEW MEXICO. 155 
1. POPULUS L. Corronwoop. 
Trees with rough light-colored bark and scaly resinous buds; leaves usually long- 
petioled, somewhat coriaceous, with prominent veins; flowers in pendulous aments, 
appearing before the leaves; seeds with a conspicuous white coma (the ‘‘cotton”). 
This is the genus containing the common cottonwoods of the State and the less well 
known aspen or ‘‘quaking asp” of the higher mountains. They are all rather short- 
lived trees and grow in stations where the soil is at least moderately wet, preferring 
the broad river valleys, where one species (P. wisiizent) is almost the only tree, or 
locations besides mountain streams or springs. The aspen is a characteristic plant 
of the Canadian Zone. Three of the species here mentioned are used more or less 
extensively and effectively as shade trees, and might well be used a great deal more. 
The wood of all species is light and spongy and not valuable for posts or firewood, 
although frequently used for these purposes for lack of something better. 
The silver-leaf poplar (Populus alba), the Lombardy poplar (P. italica), and the 
Carolina poplar (P. deltoides) are cultivated in many localities in the State, and prove 
very satisfactory, though short-lived, shade trees. Doctor Britton states that P. mezi- 
cana 8. Wats. occurs in New Mexico, but we have seen no material like the Mexican 
plant. . 
KEY TO THE SPECIES. 
Petioles flattened laterally; leaves broad, deltoid to rotund. 
Leaves broadly ovate to rotund, abruptly short-acuminate, 3 to 
5 cm. long and broad, paler beneath; small tree of the 
high mountains. ..............-----------+----2--------- 1. P. aurea, 
Leaves broadly deltoid, acuminate, 5 to 8 cm. long and 6 to 
10 cm. broad, of the same color on both surfaces; large 
tree of the lower valleys...................-.-.---+---- 2. P. wislizeni. 
Petioles terete, or channeled on the upper surface; leaves narrower, 
ovate to narrowly lanceolate. 
Leaves ovate to ovate-lanceolate, 6 to 10 cm. long, 3 to 5 cm. 
broad, rather coarsely crenate, both surfaces of the same 
6) 0) 3. P. acuminata. 
Leaves broadly to narrowly lanceolate, 7 to 15 cm. long and 2 
to4cm. wide, finely serrate with blunt teeth, much paler 
beneath.........0..- eee eee eee eee eee eee eee e eens 4. P.angustifolia 
1. Populus aurea Tidestrom, Amer. Mid. Nat. 2: 35. 1911. QUAKING ASPEN, 
Populus tremuloides aurea Daniels, Univ. Mo. Stud. Sci. 2?: 98. 1911. 
TYPE LOcALITy: Vicinity of Mount Carbon, Colorado. 
Rance: New Mexico and Arizona to British America. 
New Mexico: Common in all the higher mountain ranges. Canadian Zone. 
The aspen is a slender, white-barked tree found along streams and on cool slopes 
of the mountains, or in shaded canyons, associated with firs and spruces, occasionally 
forming pure forests covering small areas. It is the first tree to take possession of 
burned areas, cgmpletely covering them before the conifers establish themselves. In 
pure stands the trees are usually very close together, and, the trees being short-lived, 
such forests soon become a dense tangle of fallen timber. The foliage is thin and 
scanty, and notwithstanding the number of trees their shade is never dense. 
2. Populus wislizeni (S. Wats.) Sarg. Man. Trees N. Amer. 165. 1905. 
VALLEY COTTONWOOD. 
Populus fremontit wislizent 8. Wats. Amer. Journ. Sci. TIT. 15: 3. 1878. 
Type Locauity: ‘‘From 8. California to the Rio Grande.”’ 
RanGeE: Colorado to western Texas and northern Mexico. 
