STANDLEY — TREES AND SHRUBS OF MEXICO. 159 



5. Populus wislizeni^ (S. Wats.) Sarg. Man. Trees N. Amer. 165. 1905. 

 Populus frcmotitu ■wislizeni S. Wats. Amer. Journ. 8ci. III. 15: 3. 1878. 

 Along streams at low altitudes, northern Chihuahua and Sonora. Western 



Texas to Colorado. 



Often 15 meters high, with a very thick trunk and large crown ; bark pale 

 gray, fissured ; leaves 5 to 10 cm. long ; wood soft, brownish, its specific gravity 

 about 0.46. Commonly known as " dlamo " ; " giierigo " (Chihuahua). 



In the Rio Grande Valley the wood is much used for firewood, fence posts, 

 and rnfters of houses. It is not very good for fuel, since it burns almost like 

 paper. The fallen leaves are eaten By cattle. This Cottonwood is the most 

 common shade tree of New Mexico. It was reported from Mexico by Hemsley 

 as Populus balsamifera L., a species of more eastern and northern distribution. 



6. Populus dimorpha T. S. Brandeg. Zoe 5: 197. 1905. 



Along arroyos and streams at low altitudes, Sonora and Sinaloa ; type fi"om 

 Culiacan. 



A large tree, often planted in parks; remarkable for the dimorphism of its 

 leavas, those on the older branches ovate-deltoid, very long-acuminate, those 

 on young shoots linear-lanceolate to ovate-lanceolate. 



7. Populus arizonica Sarg. Bot. Gaz. 57: 210. 1919. 

 Populus arizonica jonesii Sarg. Bot. Gaz. 57: 211. 1919. 



Baja California to Chihuahua, Tamaulipas, and Puebla, chiefly in river bot- 

 toms ; Chiapas (?). Southern California to New Mexico; type from Arizona. 



Large tree, sometimes 25 meters high, with a trunk diameter of 1.5 meters; 

 crown rounded, with spreading branches ; bark light gray, ridged, or on young 

 trees smooth. Generally known as "alamo," bv:t also as " chopo " (Chihuahua, 

 San Luis Potosi) and " olmo " (Tamaulipas). 



The wood is used for fuel, carts and cart wheels, fence posts, water troughs, 

 etc. P. arizonica' jonesii (type from Valley of Palms, Baja California), to 

 which most of the Mexican material belongs, is a form with longer pubescence 

 than the type. 



8. Populus mexicana Wesm. in DC. Prodr. 16^: 328. 1864. 



Type collected between Tamptco, Tamaulipas, and Real del Monte, Hidalgo. 



Leaves broadly ovate, 4.5 to 7 cm. long, long-petiolate, abruptly long-acumi- 

 nate at the apex. 



The writer has seen no material agreeing satisfactorily with the type collec- 

 tion. 



9. Populus fremontii S. Wats. Proc. Amer. Acad. 10: 350. 1875. 



Baja California; Sonora (?). California and Nevada; type from Deer Creek, 

 California. 



Large tree, sometimes 35 meters high, with a trunk 2 meters in diameter, the 

 branches spreading and drooping; bark light gray and smooth on young trees, 

 brown and ridged in old trees ; wood soft, light brown, weak, its specific gravity 

 about 0.48. "Alamo" (Baja California). 



^The species was named for Adolf Wislizenus (1810-1889), who came to the 

 United States from Germany in 1835. He was one of the first of United States 

 botanists to visit Mexico, having gone, by way of the Santa Fe trail, to Chi- 

 huahua in 1846. He obtained in that State a large collection of plants, which 

 were reported upon by Dr. George Engelmann in a book published by Wislizenus 

 detailing his travels. 



