Mar., 1921] MCNAIR — A STUDY OF RHUS DIVERSILOBA I33 
in southern California at an altitude of 4,500 feet. The lowest and highest 
regions of California are therefore free from poison oak. 
From rainfall data compiled by the United States Government the plant 
requires an annual rainfall of at least ten inches. 
Geographical Distribution of Rhus diver siloha {Poison Oak) According to Literature aud 
Correspondence 
Date Author Location 
1 83 1 Douglas Common on the outskirts of woods in dry soils in northwest 
America. Plentiful at Fort Vancouver. 
1832 Hooker and Arnott . .San Francisco and Monterey Bay. 
1845 Lindley and Lyon . . .Common everywhere in California. An inhabitant of Santa 
Catalina Island. 
1855 Newberry Common throughout northern California; more rare in the 
Klamath Basin. 
1856 Torrey Plains and mountains near San Gabriel; Martinez. 
1876 Brewer and Watson From southern California to British Columbia; in California 
most abundant in the Coast Range. 
1878 Wheeler Common on the Pacific Coast. 
1886 Greene On the north side of Santa Cruz Island. 
1886 Lyon An inhabitant of Santa Catalina Island. 
1889 Brandegee In Lower California, very abundant about El Rosario. 
1890 Brandegee Common on San Miguel, Santa Rosa, Santa Cruz, and Santa 
Catalina Island. 
1893 Coville Found at several points on rocky hillsides in the foothill belt 
of the western slopes of the Sierra Nevada. 
1894 Greene Copious in the Coast Range hills, preferring cool northward 
slopes and the banks of streams; absent from the more ele- 
vated portions of the Sierra. 
1895 Gray Common throughout California, north to the borders of 
Washington. 
1897 Jepson Fort Bragg to Sherwood Valley in redwood belt. 
1898 Howell In forests and rocky hillsides, British Columbia to California. 
1898 Jepson Mitchell Canyon, Mount Diablo. 
1899 Jepson Crane Creek and Rosewood, Stiver's ranch. 
1900 Jepson Cedar Creek. 
1901 Jepson Smith Mountains, Palomar, 6,000 feet. 
1901 Jepson Kaweah Range, north slopes and moist places. 
1901 Jepson St. Helena, climbing redwood. 
1901 Jepson Pine Canyon, Mt. Diablo, shrubs 6 feet high. 
1902 Chestnut Common in valleys and on hillsides everywhere throughout 
Mendocino County. 
1902 Jepson Givin Mine, Calaveras County, 1,100 feet altitude. Shrubs 
12 and 13 feet high. 
Schoolhouse Creek, Ft. Bragg, Cahto. 
Redstone Park. 
Hawley School, Willits. Fort Seward, Ranch Ridge, Hum- 
boldt County, 3,000 feet. Abundant. 
Idolwild (near Camp Grant), Humboldt County. Climbs 
up redwood trunks 90-100 feet. 
Hawkins Bar (Dyer's ranch). 
Usal to Cottonaby Creek. 
