FLORA OF THE GREEN RIVER GROUP. 157 



Salix media, Heer. 

 "U.S. Geol. Kep.," vii, p. 168, |>1. xxii, fig. 3. 



Salix angusta, Al. Br. 



Ibid., p. 168, pi. xxii, fige. 4, 5. 



Salix elougata, O. Web. 



Iliid., p. 169, pi. xxii, figs. 6,7. 



POPTJLUS, Linn. 

 Ihid., vii, p. 169. 



Populus Heerii, Sap. 



Plate XXX, Fige. 1-8; XXXI, Fig. 11. 



Sap., "fit.," i, p. 87, pi. vii, fig. 3. 



Leaves long-petioled, ovate, long-lanceolate, acuminate, obtusely serrate; pri- 

 mary nerves thick ; lower secondary nerves at a more acute angle of divergence and 

 ascending higher along the borders, the others curving in passing to the borders and 

 reticulate in following them. 



The leaves are extremely variable in size, some, as shown in fig. 5, being 

 20 to 30 centimeters long and 10 to 12 centimeters broad below the middle; 

 others, as in tig. 2, scarcely 5 centimeters long and 2 broad ; others still, 

 as in tig. 11 of pi. xxxi, being narrow comparatively to their length, 10 

 centimeters long, 2 centimeters broad, thus resembling leaves of willows. 

 That all these leaves represent the same species is evident enough. 

 Besides the essential characters in common, they have the same some- 

 what thick consistence, and are all colored reddish-yellow even upon shales 

 where all the fragments of other plants are colored black. 



Saporta, who has described a fruit of Populus found upon the same 

 slate as his leaf, compares it to that of P. Euphratica, Oliv., and the leaves 

 to P. laurifolia, Ledeb. We have still living in the Rocky Mountains of 

 Colorado and Utah a species, P. angustifolia, James, considered by some 

 authors as a variety of P. balsamifera, Linn., which represents the fossil 

 species in the different forms and size of its leaves. Those of the living 

 species vary from 5 to 24 centimeters long and 2 to 10 centimeters broad, 

 being either attenuated or broadly cordate at base, according to their width. 



Hah. — Florissant. Found in all the collections. 



