Wisilizenus ' Cottonwood 



173 



The tree is much planted along roads and streets in the West, and grows 

 rapidly. Its wood is light brown, weak and soft, with a specific gravity of about 

 0.39, and is of little value. The species has often been regarded as a variety of 

 the Balsam poplar and is said to hybridize with it where the two grow together. 



8. TWEED Y'S COTTONWOOD — Populus Tweedyi Britten, new species 



Tweedy's cottonwood is known only from 

 river-bottoms in southern Wyoming. 



The young twigs are brownish, somewhat 

 angled, smooth, becoming orange, and finally 

 nearly white. The mature leaves are smooth, 

 thin, firm in texture, broadly ovate or some 

 of them nearly orbicular, very finely toothed, 

 pointed or blunt, rather dark green on the 

 upper side, paler green on the lower, distinctly 

 heart-shaped at the base, or some of them 

 roimded, 3 to 7 cm. long, 2.5 to 4 cm. wide; 

 the stout leaf-stalks are about one fourth as 

 long as the blades. The fruiting pistillate cat- 

 kins are rather dense, 6 cm. long or less; the 

 capsules are ovoid, finely and densely papillose, 

 4 mm. long, their stalks only i mm. long. 



The type specimen was collected by Mr. 

 Frank Tweedy of the United States Geologi- 

 cal Survey, at Encampment, Carbon county, 

 Wyoming, June 20, 1901 (no. 4567). 



Fig. 129. — Tweedy's Cottonwood. 



9. WISLIZENUS' COTTONWOOD— Populus Wislizeni (S.Watson) Sargent 



Populus Fremontii Wislizeni S. Watson 



This poplar inhabits the banks of rivers and streams from southern Colorado 

 to western Texas, New Mexico, and adjacent Mexico, perhaps extending into 

 southeastern Utah. It becomes at least 15 meters high, the lower branches spread- 

 ing. 



The young shoots are brownish, smooth, becoming orange and finally gray. 

 The buds are ovoid, pointed, brown, shining, and about 1.5 cm. long, their scales 

 a little hairy. The leaves are broadly triangular, often longer than wide, firm in 

 texture, coarsely and irregularly bluntly toothed, except near the tip, sharp-pointed, 

 smooth, light green on both sides, 5 to 10 cm. long, nearly truncate or somewhat 

 kidney-shaped at the base, finely netted-veined ; their stalks are flattened sideways 

 and about as long as the blades; the stipules are ovate, thin, and pointed. The 



