242 
O. A. STEVENS 
2. Bailey, V. Life zones and crop zones of New Mexico. North American Fauna no. 
35, U. S. Dept. Agric, 1913. 
3. Bergman, H. F. Flora of North Dakota. Bien. Rept. Dir. Agric. Coll. Surv» North 
Dakota (1911-1912) 6: 151-372. 1918. 
4. Coulter, J. M., and Nelson, A. New manual of botany of the central Rocky Moun- 
tains. New York, 1909. 
5. Gary, M. A biological survey of Colorado. North American Fauna no. 33. U. S. 
Dept. Agric, 191 1. 
6. . Life zone investigations in Wyoming. North American Fauna no. 42. U. S. 
Dept. Agric, 1917. 
7. Leonard, A. G. The surface features of North Dakota and their origin. Quart. 
Journ. Univ. N. D. 9: 209-219, and map. 1919. 
8. Lunell, J. Enumerantur plantae Dakotae Septentrionalis vasculares. Amer. Mid. 
Nat. 4, 5. 1915-1918. 
9. Merriam, C. H. Life zones and crop zones in the United States. U. S. Dept. Agric. 
Biol. Surv. Bull. 10. 1898. 
0. Robinson, B. L., and Fernald, M. L. Gray's new manual of botany. 7th ed. New 
York, 1908. 
1. Rydberg, P. A. Flora of the Rocky Mountains and adjacent plains. New York, 1917. 
2. Upham, "W. Geographic limits of species of plants in the basin of the Red River of 
the North. Proc Bost. Nat. Hist. Soc. (1890) 25: 140-172. 1891. 
3. Wheeler, W. A. Contributions to the flora of the Red River valley in Minnesota, 
Minn. Bot. Studies 2: 569-600. 1901. 
4. Willard, D. E. Story of the prairies. Chicago, 1902. 
5. Wooton, E. O., and Standley, P. C. Flora of New Mexico. Contr. U. S. Nat. Herb. 
19. 1915. 
