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AMERICAN JOURNAL OF BOTANY 
[Vol. 8 
of the flowers of both plants will permit the reader to decide whether or not 
there is sufficient difference to constitute a separation into species. 
Fig. 2. Tracings of mature leaves of Rhus diversiloba (Reduced 6^ X). 
Geographical Distribution of R. diversiloba 
The distribution of poison oak includes Lower California north of latitude 
29° (Brandegee, 6), Santa Barbara and Santa Catalina Islands (Brandegee, 
7), California, Oregon, Washington, Vancouver Island, and British Colum- 
bia. The region inhabited by the plant has been approximately defined by 
citations from botanical literature, sources of herbarium specimens, and 
places where birds were found that had poison oak seeds in their stomachs. 
From these data, the territory inhabited by poison oak embraces the Sonoran 
and lower transition life zones, and excludes the desert and central valley 
regions of California together with the upper transition and boreal zones. 
The inhabited area has an altitude varying from sea level to 6,000 feet 
above sea level. Hall's (24) observations in the Yosemite Valley make it an 
inhabitant of the Hetch Hetchy and the low foothills with a maximum alti- 
tude of about 4,000 feet. In southern California he noticed it in the San 
Jacinto Mountains along the North Fork of the San Jacinto river at an 
altitude of approximately 3,000 feet. I have found it in Cold Water 
Canyon on the southwest side of Mt. San Antonio in the San Gabriel Range 
